Cyrille Chazallon

Georg Koval

Saïda Mouhoubi

Hossein Nowamooz

Ioana Maria Arsenie

Andrea Themeli

Kai Li

Xiaofeng Gao

Peng Jing, Quoc

Tuan Trinh

Saeid Nikoosokhan

Anicet Dansou

Laura Gaillard

Guixian Liu

Ba Xuan Nam Ho

Danh Le

Hossein Assadollahi

Fujiao Tang

Jochen K Ärcher

Hartmut Herb

Manuel Niever

Sonja Cypra

Elke H Äußler

Tim Reuber

Jan Wachsmann

Kai W Ächter

Kevin M Üller

Daisy Wiede

Jan Schulte

Thank

Keywords: Grille en fibre de verre, renforcements, cisaillement, fatigue, module de rigidité, deflexions - Flexible pavements, glass fibre grids, reinforcement, shear strength, fatigue life, stiffness modulus, deflections -

Cette thèse traite de l'effet des grilles en fibre de verre, utilisées pour renforcer les structures routières, sur la liaison entre deux couches d'enrobés bitumineux, la durée de vie en fatigue et le module de rigidité des éprouvettes cylindriques renforcées, ainsi que sur les déflexions mesurées sur une section de route renforcée in situ.

Des essais de cisaillement (LEUTNER) ainsi que de module et de fatigue (ITT) ont été conduit sur des éprouvettes renforcées et non renforcées en utilisant différentes grilles, différentes emulsion ainsi que différentes quantités d'emulsion. Pour ces essais, une surface de test a été construite in-situ, de laquelle les éprouvettes ont été extraites.

Une section de route in-situ a également été construite, renforcée avec 3 différentes grilles et avec deux sections de références. Les deflexions de la chaussée ont été déterminées avant et après les travaux. Une modélisation de la strucutre a été faites basée sur les résultats des mesures de déflexion.

was the indirect tensile test, during which a cylindrical asphalt specimen is submitted to sinusoidal a cyclic compressive stress on its vertical diametric plane, causing the rupture of the specimen through splitting along the centre in vertical direction.

Regarding the bonding, it was shown that the tests without reinforcement grid reached more important shear strength, that higher application rates resulted in higher shear strengths for the reinforced specimens and that larger strand sections of the grids led to greater shear resistances. Regarding the stiffness modulus, it was shown that the specimens reinforced with grid 5 gave constantly higher results for temperatures from -20 • C to +30 • C compared to unreinforced specimens. It was also observed that the influence of the interface at low temperature caused strongly weakened stiffness modulus compared to uni-layered specimens. Regarding the fatigue life, it was shown that reinforced specimens were able to achieve a longer life cycle compared to unreinforced specimens, but that the difference depends from the test temperature, being more constant for 10 • C than for 20 • C. Deflections were measured on a French road with a traffic of 300 trucks per day before and after maintenance works, implying the construction of a new AC 10 surface course on the old road structure. Parts of the road were reinforced with different glass fibre grids and overbuilt with 4 cm of the new surface layer, two unreinforced reference sections were built with 6 cm of the new surface layer. Deflections measured after the maintenance work showed an improvement of the deflections on all parts of the roads. Special distinctions of a section, showing that its characteristics (e.g. reinforcement) brought especially good or bad improvements in comparison to the deflections measured on the old structure, could

Experimental and analytical study of the reinforcement of pavements by glass fibre grids I not be observed.

The deflection results as well as the known characteristics of the layers of the structure were used to model the structure. It was shown that the structures modelled with BISAR gave results near to the actual measured deflections for the unreinforced parts, but that the results calculated on the reinforced parts were higher than the actually measured values. This led to the assumption that the grids had an positive effect on the deflections.

Résumé

Cette thèse traite de l'effet des grilles en fibre de verre, utilisées pour renforcer les structures routières, sur la liaison entre deux couches d'enrobés bitumineux, la durée de vie en fatigue et le module de rigidité des éprouvettes cylindriques renforcées, ainsi que sur les déflexions mesurée sur une section de route renforcée in situ.

L'étude de la liaison entre les couches, de la durée de vie en fatigue et du module de rigidité a été effectuée en laboratoire. Les éprouvettes utilisées pour cela ont été extraites d'une surface d'essai extérieure à deux couches, consistant en une couche inférieure AC 16 avec un bitume 25/55-55 RC et une couche supérieure AC 11 avec le même bitume, représentant deux structures plutôt typique en Allemagne. Au total, 24 interfaces différentes ont été construites, en utilisant deux émulsions différentes, trois à quatre taux d'application d'émulsion différents, 4 grilles (1, 5, W, N) et des sections de référence. La détermination de la résistance au cisaillement a été effectuée sur toutes les variantes avec le test Leutner, un test de cisaillement destructif impliquant le cisaillement d'une couche de l'échantillon avec un taux de déplacement constant de 50 mm/min tandis que l'autre Experimental and analytical study of the reinforcement of pavements by glass fibre grids III couche est maintenue. La détermination de la durée de vie en fatigue et du module de rigidité a été faite uniquement sur les éprouvettes renforcées avec la grille 1 et 5 et le taux d'émulsion le plus élevé ainsi que sur les sections de référence non renforcées également avec le taux d'émulsion le plus élevé. Le test utilisé pour la mesure de la fatigue et de la rigidité a été l'essai en traction indirecte, au cours duquel un échantillon cylindrique est soumis à une contrainte de compression cyclique sinusoïdale sur son plan diamétral vertical, ce qui provoque la rupture des éprouvettes par le biais du milieu dans la direction verticale.

En ce qui concerne le collage, il a été démontré que les essais sans grille de renforcement ont atteint des valeurs de résistance au cisaillement plus importantes, que les taux d'application plus élevés entraînent une résistance au cisaillement plus élevée pour les éprouvettes renforcées et que les grilles ayant des fils avec une section plus hautes peuvent atteindre de plus grandes résistances au cisaillement. En ce qui concerne le module de rigidité, il a été démontré que les éprouvettes renforcées avec la grille 5 donnaient des résultats plus élevés pour des températures de -20 • C à + 30 • C que les éprouvettes non renforcées. Il a également été observé qu'à basse température, l'influence de l'interface provoque un module de rigidité fortement affaiblie par rapport aux éprouvettes homogènes.

En ce qui concerne la durée de vie en fatigue, il a été démontré que les éprouvettes renforcées atteignaient une durée de vie plus longue que les éprouvettes non renforcées, mais que la différence dépend également de la température d'essai, étant plus constante pour Quelques parties de la route ont été renforcées avec différentes grilles en fibre de verre sur lesquelles 4 cm de nouvelle couche de surface ont été posée, deux sections de référence non renforcées ont été construites avec 6 cm de nouvelle couche de surface. Les déflexions mesurées après les travaux de maintenance ont montré une amélioration des déflexions sur toutes les parties de la route. La distinction particulière d'une section, montrant que ses caractéristiques (par exemple, le renforcement) aient apporté une amélioration particulièrement bonne ou mauvaise par rapport aux déflexions mesurée sur l'ancienne structure, n'a pas pu être observée.

Les résultats des déflexions ainsi que les caractéristiques connues des couches de la structure ont été utilisés pour modéliser la structure. Il a été montré que la structure modélisée avec BISAR donnait des résultats proches des déflexions mesurées en temps réel sur les sections non renforcées, mais que les résultats calculés sur les parties renforcée étaient supérieurs aux valeurs réellement mesurées. Il en a été conclu que les grilles devaient avoir un effet positif sur les déflexions.

Mots-clés: Grille en fibre de verre, renforcements, cisaillement, fatigue, module de rigidité, deflexions

XIV

General Introduction

Keeping in mind sustainable development, the building and maintenance of road pavements should take into account the fact that in time some raw materials such as oil by-products are going to be more difficult to find and to extract. In view of the existing road network in Europe, maintenance is becoming a major issue. The ageing road network requires developping affordable ecological solutions to allow a partial, total or graduate rehabilitation of the road.

Grids, especially glass fibre grids, represent an effective and economic solution to reinforce the asphalt structure, increasing its lifetime and slowing down crack propagation.

Grids can be installed in new roads or in existing ones. Grids are used as reinforcement to enhance the existing road properties against traction and their resistance to cracking.

Yet, using grids means inserting an additional layer between the two asphalt layers. This additional layer may have a strong impact on the bonding between the two asphalt layers and may lead to a loss of adhesion.

A feeble bonding may lead to a bad transmission of traffic-induced stresses and strains through the layers as each layer must be considered independently instead of having all layers working as a whole. Consequently tensions can occur in the lower parts and compression in the upper parts of every layer.

The subject of this thesis is to study the positive impact of the glass fibre grids on the reinforcement of asphalt structures, the containment of reflective cracks and the increase of the road lifetime, as well as negative impacts of the grids on the bonding between road layers, which may reduce the life time of asphalt structures.

For this investigation, this study is built on five different pillars:

1. A general introduction, explaining the general behaviour of roads and road materials under traffic loads, climate changes and passing time, as well as possible rehabilitation methods for aged pavements 2. A literature review about effects and impacts of glass fibre grids inserted into asphalt structures in order to reinforce them. The review looks at laboratory tests as well as in-situ observations.

Three different laboratory tests carried out during this study:

(a) On the bonding between two aspahlt layer, with and without glass fibre grids at their interface. In this part of the study, the effect of different grids as well as different emulsions and different emulsion application rates is observed. Each layer has its own function, enabling the structure to reduce the stresses and strains induced by traffic loads and movements.

Basically road structure differentiates between rigid and flexible types. Rigid pavements are generally built using Portland cement as a hydraulically binding agent. This agent enables them to withstand tensions through the strong bonds between particles. The advantages of this pavement type are its stiffness, tensile strength, fatigue resistance and its good resistance to permanent deformation. The strong vulnerability of hydraulically bound materials to temperature change can easily create cracks on its surface and obliges the adding of joints in the concrete.

With 90 % of bitumen bound paved highways [ THO 14], this pavement type constitutes the most used form of road structures. Bitumen is a highly viscous liquid or semi-solid form obtained from petroleum. Unlike hydraulic binders, bitumen enables deformations in the structure without breaking the bond between the particles and can afterward find back to its original form, enabling self-healing properties of the bitumen. The advantage of bitumen bound pavements are their stiffness, their resistance to deformation under repeated load and their main insensitivity against temperature changes [THO 14] . Bitumen mixed with aggregates is named asphalt concrete. In this study, the pavement type considered and used is asphalt concrete.

I.1.1 Asphalt concrete

Asphalt concrete is a composite material consisting of bitumen or bituminous binders and aggregates. This mixture can be technically made or found in nature (for example Trinidad asphalt). When technically made, it is important to mix the components in a water free environment with mixing temperature in the range of 150 • C, depending on the bitumen used for the mixture [LAV 03].

I.1.1.1 Bitumen

Bitumen is a dark, heavy-transient complex mixture of different organic substances [STR 09], which is extracted during the reconditioning of different crude oils. Bitumen consists largely of hydrocarbons with small amounts of sulphur, oxygen and nitrogen and traces of Experimental and analytical study of the reinforcement of pavements by glass fibre grids halogens, phosphor, and metals. Bitumen has a colloidal structure where the asphaltene particles are dispersed in the maltene matrix. This colloidal structure gives the bitumen its characteristics such as its temperature dependency and its bond. The elastoviscous properties and the degree of hardness depend on the crude oil used. Bitumen can be modified with polymers such as elastomers and thermoplastics.

I.1.1.2 Aggregates

Aggregates used for asphalt concrete are classified in three groups, depending on their size:

• Coarse aggregate, going from a minimum diameter of 2 mm to a maximal diameter of 45 mm

• Fine aggregates, going from a minimum diameter of 0.063 mm to a maximal diameter of 2 mm.

• Filler, aggregates with a diameter smaller than 0.063 mm.

The shape of the particles is important for the resistance against deformation. An angular shape will lead to a greater resistance.

In order to ensure a water free environment during the mixing with bitumen, the aggregates are preheated in a dryer. The task of the wearing course is to enable a safe trafficability of the road. For this, the wearing course has to:

• Ensure a good friction between the surface and the tyres Experimental and analytical study of the reinforcement of pavements by glass fibre grids

• Seal the surface against water ingress through the prevention of cracking • Have a cross slope important enough to discharge water

• Have a stiffness high enough to prevent the creation of rutting. Some of these points, however, request opposite measures: the prevention of cracks requires flexible and elastic pavement, which however is unfavorable for the prevention of rutting. Finding the appropriate mixture for the wearing course is, therefore, an important task during the road design.

The binder course is used for strongly trafficked pavements and ensures the transmission of the stresses created by traffic loads and movements from the wearing course to the lower base courses. Furthermore, the binder course shall correct unevennesses and irregularities of the base course.

The base course is mainly responsible for the strength of the structure. Its most important task is the absorption of vertical and horizontal stresses caused by traffic. The base course can be divided into different layers, which can be bound hydraulically or by the bitumen or consisting of unbound materials. Layers of unbound materials would be positioned at the bottom of the base course. They can favour the draining or rerouting of water through the course and so be a protection against freezing. In unbounded courses, compressive forces are absorbed through the contacts between the particles. However the absence of cohesion between the particles prevent a good absorption of tensile stresses.

In bitumen bounded base course, the existing cohesion between the particles due to the bitumen as well as the indentation between the particles are responsible for the stability and deformation resistance.

The subbase course is a compacted unbound granular layer whose upper surface serves as plateform for the superstructure. The subbase can help reducing traffic stresses as well as work as a drainage layer. A particular sustainable subbase course can enable a thinner superstructure.

The subgrade is the lowest part of the structure. Usually it is only made of compacted soils. In cases of a soil with low bearing capacity, an exchange or a treatment with lime, cement or other hydraulic binders may be necessary.

I.1.2.2 Interlayer bonding

The bonding between two layers is of crucial importance for the transmission of strains and stresses through the structure and so for the apparent stiffness of the road. The following three major factors constitute the bonding between two layers (see also figure I.1.2):

Experimental and analytical study of the reinforcement of pavements by glass fibre grids A) Indentation Indentation describes the interlocking between grains of the upper and lower layers.

The indentation between the layers is created during the compaction of the layers when the aggregates of the upper layer are pressed in the depressions and voids of the lower layer

B) Adhesion

Adhesion depends on the binder type and content of the layers as well as on the emulsion or tack coat used between the layers. Adhesion is particularly important at lower temperature.Its importance decreases at higher temperatures, as the bitumen To ensure a good bonding, different measures can be taken.

The most common form is to use tack coats such as bitumen emulsions on the interlayer, which provides for a better adhesion in addition to the existing indentation. Yet too much tack coat or emulsion can lead to the formation of slip planes on the interface, which can hinder the proper functioning of the indentation.

Bonding can also be improved by milling the lower courses to enhance the indentation or the construction of the layers in hot-on-hot manner, using the compact asphalt method.

I.1.3 Damage mechanisms on road structures

The most important causes of damage to road structures are: The roads most subject to deformation are the ones with frequent, slow driving or standing heavy traffic as for example the heavy traffic lane of a motorway, the bus lane or parking places for trucks.

The use of certain materials can prevent or retard rutting, for example crushed aggregates, harder binder and polymer modified bitumen. A small bitumen content in the upper layer can also have a positive effect.

The flowing of the materials can also cause deformations due to horizontal movements.

Damages caused this way can be observed as slippages at stop lines of junctions, as a result of decelerations.

Cracks are the direct results of traffic caused tensile strains which exceed the tensile strength of the structure. This may be due to a wrongly designed road structure having to bear heavy loads or a great repetition of load passages.

Therefore the most important and decisive factors for the design of a road structure are: Cracks induced by traffic passages will mostly appear in or beneath the wheel path and have a longitudinal form with many junctions. In cases of too thin asphalt layers or too soft foundations, the cracks will appear as so called crocodile or alligator cracks.

Cracks appearing in the wheel path are mostly caused by the tension at the bottom of the pavement structure and are cracks that evolve from bottom to the top. The surface directly under the wheel path is subject to compression. Cracks appearing beneath the wheel path are cracks starting from the surface and working their way down.

The distribution of compressions and tensions due to traffic load on a road structure is sketched in figure I.1.5. When the temperature drops, the material shrinks. This results in tensions which lead to stresses in the structure. The lack of relaxation ability caused through the non-effective viscous properties of the bitumen at cold temperature induces a slow reduction of these stresses. Tensions and stresses appearing this way are called cryogenic.

When traffic load is applied to the structure, these two types of stress combine to generate cracks appearing as transversal cracks across the full width of the pavement. To prevent such damages, the use of softer or modified bitumen can be useful.

At low temperatures the frost impermeability of the unbound granular layers under the pavement structure is crucial. Otherwise, the capillary action of the granular base course will lead to an increase of water directly under the pavement structure. The result Experimental and analytical study of the reinforcement of pavements by glass fibre grids can be deformations of the upper structure due to the formation of ice packs under it.

Warm temperature can have a negative influence on the deformation properties of bitumen, as described before.

I.1.3.3 Time

Ageing means principally the oxidation of bitumen. This oxidation takes place between polar molecules within the bitumen and free oxygen of the air. It leads in additional crosslinking between the molecules and so to a higher stiffness and an increase in viscosity of the bitumen.

The ageing process can be split into two different time frames. The first one is a shortterm frame taking place during the mixing, transportation, installation and compaction of the asphalt and before it is exposed to the traffic. In this first time frame, the bitumen is exposed to high temperatures from blending with the rock aggregates in the asphalt mixing equipment to the completion of the asphalt layers.

The second one is long-term ageing during which the bitumen is exposed to the air on the surface and through the voids inside the structure.

Aged bitumen are accountable for a faster formation of cracks under fatigue loading, as well as a weaker adherence between grains and bitumen. This may result in pull-outs at the surface, affect the adhesion between two layers and weaken the interlayer bonding.

I.1.4 Road maintenance methods

Road maintenance can be differentiate between 1. Superficial repairs 2. Rehabilitation work

Renewal of one or more layer

This section only deals with maintenance works carried out on bituminous layers and specifically excludes processing on concrete roads.

I.1.4.1 Superficial repairs

Superficial repairs on asphalt roads are performed in order to maintain acute road safety through minor and preferably fast repairs.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids Gritting Gritting describes the procedure of spraying emulsion and approximately 3 mm size particles on a road. This surface treatment is used to improve the grip between the tyres and the road and can be used to eliminate crocodile cracks and the loss of material.

Use of bituminous sludge's and pore filling mixtures Bituminous sludge's are products made of bituminous emulsions, filler, additives and water and are used against the loss of material as a result of abrasion.

Asphalt patching and emergency pothole repairs

In these cases, the affected surface is cut out of the road and backfilled with suitable material. This method can be used for surfaces with an excessive accumulation of binder, surfaces showing a loss of granular materials and around potholes. The most effective way to seal a crack is to cut it with a saw first, in order to ensure a good infiltration of the sealing material in the crack. The sealing can be done by hand or using a pump unit. Hot in situ recycling This methods consists in the repaving of asphalt layers with the already existing materials. For this, the apshalt layer is warmed up, then loosened and then compacted again. In some cases, the existing material is mixed with another, new material during the loosening step. The working procedure is shown in figure I.1.9. After renewal works, the new surface shows no damages it had before. The quality of the new surface is at it's highest.

I.1.4.4 Alternative maintenance methods: Use of interlayers

The use of interlayer system as increased in the last few decades, as interlayer systems have been showed able to delay crack initiation and propagation through an asphalt structure, even though their mechanical behaviour is mostly not fully understand. In his book 'Principles of Pavemant Engineering' [THO 14], Nick Thom lists the five following interlayer options:

• A geogrid or strong geotextile, prviding actual enhanced strength • A standard geotextile, acting as a separation layer Experimental and analytical study of the reinforcement of pavements by glass fibre grids

• A high durability asphalt layer

• A granular interlayer

• An open-graded asphalt layer Speaking of geogrids and strong geotextiles, he explains that they can slow down the rate of crack propagation almost by a factor 4. Particularly in the case of thin overlays, most geotextiles are capable of providing a significant degree of reinforcement.

One type of geogrid is the glass fibre grids, a composite material made of glass fibre surrounded by a resin. Glass fibre grids can be installed between a cracked asphalt or concrete structure and a new surface layer. Their purpose is to stop the propagation of the crack through the new layer thus increasing the lifetime of the new pavement.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

I.2 Glass fibre grids

Glass fibre grids are composite materials. A composite material is a material consisting of at least two materials, a reinforcement and a matrix, connected in a non-miscible manner and having properties and performances different of the individual component.

I.2.1 Reinforcement

The reinforcement ensures the mechanical strength and the rigidity of the composite material through a strong atomic bond. Typical reinforcements are different types of fibres as for example:

• Glass fibre, with a high resistance against traction and a relatively low density.

• Carbon fibres, with a low density hence a reduced weight and high tensile strengths, which enable their use for example in wind turbines and aerospace market.

• Organic fibres, with mostly a rather low elasticity modulus but sometimes with a very high melting temperature, enabling their use for protective clothing against fire.

They are also found in rubber and in pressurized structures.

Fibre reinforcements offer often greater strength and stiffness than the original materials in a compact form. This is mainly due to the difference in size between the fibres and the compact shape, as larger volumes will rather show weak or weakened links. It can also be observed that the size of a defect in a smaller volume can not be as great as in a larger volume.

The reinforcement used in the grids of this study is glass fibre. Glass fibre is an inorganic material whose strength is derived from strong covalent bonds between silica and oxygen. Different types of glass can be used as reinforcing fibres:

• Type E (abbreviation for 'electric'): This type is most often used because of its good value for money, its relatively high Young modulus its good tensile strength.

• Type S (abbreviation for 'strength') & R (abbreviation for 'resistance'). These types have a high young modulus and are mostly used for high performance structures.

• Type C (abbreviation for 'corrosion'): This type has a good resistance to corrosion in acid environments, but has a rather low resistance to traction.

• Type D (abbreviation for 'dielectric')

The glass used in the grids studied in this report is of type E. Some of the properties of glass fibres of this type are shown in table I.2.1:

Experimental and analytical study of the reinforcement of pavements by glass fibre grids To manufacture the fibres, the silica is mixed with other components in order to reduce the melting temperature of the mixture to about 1200 • C. The liquid glass is then poured into a die with several hundred holes with a diameter of 1 to 2 mm. The filaments exiting this die are then wound rapidly, allowing to stretch them to reduce their section to a diameter of 5 to 15 µm. This rapid change in diameter causes a massive movement in the material from the core to the surface, which helps to remove most of the faults.

I.2.2 Matrix

The matrix plays two key roles: First as a binder between the various components of the material, ensuring the transmission and the distribution of the stresses acting on the material to the reinforcement, secondly as a protection for the reinforcements against possible external aggressions as moisture and to a certain extent against abrasion.

II.1.1.1 Laboratory tests

In their study of 2014, Nejad et al [NEJ 14] investigated the effect of several geosynthetics on the crack propagation by building a multi-layered slab made of an artificially cracked lower layer (made with a fibre saw), an asphalt overlayer with a thickness varying between 50 mm, 75 mm and 100 mm and a geosynthetic positioned between the two layers.

The geosynthetics used in this study were different geocomposites, polypropylene nonwoven geotextiles and polyethene non-woven geotextiles.

The slab was loaded under cyclic condition through a circular plate positioned on the top of the slab, above the crack, with a maximum load of 6.79 kN at 10 Hz and with a rest A slab consisting of two 50 mm thick asphalt layers and an interlayer was subjected to cycling loading through a beam load on the top of the structure, while the lower asphalt layer was cut in order to simulate a 40 mm high crack.

The asphalt layers used in this study were made of an AC16 surf mix with a 60/70 bitumen. The interlayer used were polyester geogrids with and without non-woven geotextiles with non-woven and with un-woven polypropylene fibres and a SAMI. The emulsion used as tack coat was a C69B3, the residual binder content used to coat the interlayer was modified to observe its influence on the durability of the structures.

The test was conducted at 20 • C with a frequency of 10 Hz. The loading range went from a maximum load of 19 kN to a minimum load of 3 kN. The failure criterium was chosen as to be the breach of the crack through the surface course.

Zamora-Barraza et al. showed that all anti reflecting cracking systems performed better than the reference system. The most effective interlayer was the geogrid systems, which withstand three to six times more cycles than the reference specimens. It was also observed that geogrids with higher modulus showed better performances and that an increasing geogrid stiffness provided higher resistance to deformations.

Regarding the tack coat content, Zamora-Barraza et al. observed that for structures with polyester geogrids and without reinforcements an optimum content of residual binder could be determined. For contents higher than the determined optimum, the specimens showed lower durabilities. On the other hand, polypropylene geotextiles showed no optimum binder content, but a low influence regarding the tack coat application rate.

Zamora-Barraza et al. reminded that crack propagation is closely related to deformations.

This could be seen as reflective cracks could reach the surface of reinforced specimens whereas the geosynthetic materials inside the structure remained unbroken.

Romeo et al [ROM 14

] observed the mechanical response of flexible pavements reinforced with fibre glass. To do so, they built multi-layered slabs and beams consisting of a 20 mm thick asphalt lower layer, a glass fibre grid at the interlayer and a 40 mm asphalt

Experimental and analytical study of the reinforcement of pavements by glass fibre grids wearing course. The reinforced pavements were subjected then to a static three point bending test.

The nominal maximum aggregate size of the asphalt mixture was 12.5 mm. The bitumen used had a penetration grade of 68-28. The three fibre glass grids used had different mechanical and geometrical properties.

The static three point bending test performed in the study was conducted at a constant application speed of 0.084 mm/s and at a test temperature of 20 • C. The stresses and strains were measured during the test and strain maps of the specimens were drawn.

It was observed that the failure load reached by reinforced specimens was significantly higher than the failure load reached by unreinforced specimens. The use of reinforcements resulted in a strength increase of about 50 %, showing that the reinforcement was able to improve the resistance of the specimens.

The strain maps showed that for reinforced specimens, the strains were mainly concentrated at the bottom layer, showing that the reinforcements acted like a barrier to the crack, as represented in figure II.1.2. the reinforcing material has a stiffness higher than the asphalt mixture and when the reinforcing material has sufficient cross sectional area to strengthen the overlay. The pavement was loaded with 1 million cycles at 65 kN and 200 000 cycles at 70 kN.

During the tests, the crack propagation on the two sections was monitored and given as a percentage of the ratio between the length of pavement with cracks and the initial length.

After 600 000 cycles, the first cracks were observed on the unreinforced section. After 1.2 million cycles, the extent of cracking on the unreinforced sections reached 70 %, while the reinforced sections showed no cracks at all.

Deflection measurement made with a Benkelman beam at different numbers of load cycles showed no significant differences in deflection between the reinforced and unreinforced sections.

Another part of their study consisted in regarding the reinforcement of a cracked structure achieved through various maintenance methods. For this purpose, Nguyen et al.

built three types of new overlays on an old structure consisting of an unbound granular layer, an 80 mm thick, cracked binder course and a 60 mm cracked bituminous course, which had been milled before the installation of the new sections.

The first of these three sections consisted in adding a 40 mm thick surface course to the old

Experimental and analytical study of the reinforcement of pavements by glass fibre grids structure. The second structure consisted in placing a glass fibre grid on the interlayer on which a 25 mm thick surface layer was built. The third sections consisted in adding of a 25 mm thick surface layer to the old structure. Both unreinforced sections were coated with a residual binder application rate of 300 g/m 2 , the reinforced section with an application rate of 500 g/m 2 .

Here again, the crack propagation was monitored. The first cracks appeared after 430 000 loads on the third section (25 mm overlayer, without reinforcement). After 530 000 loads, cracks appeared in the second section (25 mm overlayer, with reinforcement), followed by the first section after 600 000 loads.

The test ended after 3.3 millions of loads. At that point, the first and third sections (both without reinforcements) were totally cracked, whereas section 2 showed only 10 % of cracked surface, indicating that under traffic loading, the reinforcement through the grid is mainly activated during crack propagation, and not during the first crack initiation phase.

II.1.2 Ability of geosynthetics to prevent separation

In The specimens were loaded with a constant displacement of 0.85 mm/sec, while the responding force was measured during 5 seconds. The aim was to destroy all specimens.

The tests were carried out at 5 • C and 25 • C.

The force-time graphs obtained showed a steep slope leading to a peak showing the fracturing point of the specimens. The peak is higher and the slope steeper for the specimens without reinforcement.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids For unreinforced specimens, the slope after the peak, representing the loss of resistance after fracture, is also very steep, which is typical for brittle fracture.

The slope of the reinforced specimens after the peak is much flatter, showing a restresistance of the reinforcement even after fracturing of the asphalt materials. This effect is caused by a bridging effect, showing the ability of the geosynthetic to keep the specimen together.

These tests show that an effect of the grid on indirect tensile tests is visible even for small specimens. The layers of the slabs were made with two asphalt mixtures consisting of aggregates with a maximum aggregate size of 10 mm and 14 mm and in both cases an asphalt binder classified as 50/70.

II.1.3 Fatigue life

During the test, loading cycles were repeatedly performed on the beams in a stress controlled mode. The load applied on the beam ranged between 0 kN and 3 kN with a frequency of 1 Hz and a test temperature of 20 • C.

Ferrotti et al. observed that the provided resistance of the reinforced specimens was considerably higher than the resistance provided by the unreinforced specimens. They also showed that a better interlayer shear resistance between the layers of the double-layered slabs, due to the different coating treatments, guaranteed a better resistance performance to repeated loading cycles.

In their study of 2016, Arsenie et al. [ARS 16] tested the fatigue behaviour of glass fibre grid-reinforced asphalt concrete beams using 4 point bending tests (4PB tests) and compared it to the behaviour of unreinforced grids.

To do so, they built three-layered asphalt concrete beams consisting of two 25 mm thick asphalt layers on the sides and a 75 mm thick layer in-between. The asphalt mixture used had a nominal aggregate size of 0/10 mm and a bitumen with a 35/50 penetration grade.

For the reinforced beams, glass fibre grids were installed on both interfaces, using 600 g/m 2 of residual binder as tack coat.

The total dimensions of the beams were 630 mm x 100 mm x 100 mm.

The 4PB tests were performed under sinusoidal alternating loading conditions and were displacement controlled. The force response and the phase angle were measured. Experimental and analytical study of the reinforcement of pavements by glass fibre grids A constant horizontal displacement rate of 2.5 mm/min is applied to the specimens.

The materials used for the tests are the same as before. The samples used for the tests were built under laboratory conditioned and consisted in building cylindrical two-layered asphalt specimens using an asphalt mixture with a nominal maximum aggregate size of 11 mm and a bitumen with a 60 penetration grade. The reinforcement installed in the interlayer were polypropylene non-woven and glass fibres with a tensile strength of 50 kN/mm 2 resp. 100 kN/mm 2 .

The investigation of the shear strength was done with the Leutner test, a monotonic shear testing device described in section III. The two layered specimens used in the tests were made of two asphalt layer [START_REF] Sokolov | Laboruntersuchungen an unterschiedlichen verstärkten Asphaltschichten[END_REF] or of an asphalt layer laid on a concrete superstructure [START_REF] Raab | Interlayer shear performance: Experience with different pavement structures[END_REF]2007). Different

Experimental and analytical study of the reinforcement of pavements by glass fibre grids types of reinforcement were used, as carbon fibre grids, steel grids and glass-non-woven.

No informations were given regarding the application of tack coat.

He observed that reinforcement at the interlayer reduced the interlayer bonding, showing that only one reinforced specimen was able to reach the required shear force of 15 kN whereas all unreinforced specimens were able to exceed it (see figure II.2.2). The slabs constructed in a laboratory were made of two layers of AC 8 and AC 11 with a thickness of 30 mm each. The cores extracted from the in-situ surface were made of a 40 mm thick AC 11 layer on a 65 mm AC 22 layer. Three types of interlayer were installed between the layers: a glass fibre grids installed with a SAMI (A), a polyester grid (B) and a glass and carbon fibre grid (C). The testing device used for the investigation was the

LPDS. The tack coat application rate was not mentioned

The tests of the laboratory cores showed that all specimens were able to exceed a shear strength of 15 kN, while grid B even surpassed the unreinforced specimen.

However, when looking at the in-situ cores, it was observed that, although the ranking of the systems remained similar, the shear strength was weakened. The tests were carried out at 15 • C, the asphalt mixture used for the slab manufacturing was an AC 16 with a binder content of 5 %. Five interlayer options were chosen: a reference interlayer without geosynthetic material, a polyester geogrid with unwoven geotextile material, a polyester geogrid material, a glass fibre geogrid material, and a geotextile material. In order to investigate also the influence of the tack coat, the tack coat application rate was varied.

It was observed that the highest shear resistance was obtained for the reference material, followed by the polyester geomesh. For these options, an optimum amount of residual binder was determined, being of about 0.5 kg/m 2 for the unreinforced structure and of 0.35 kg/m 2 for the polyester geomesh (see figure II.2.4). For the other reinforcements, no optimum binder content was found, which was assumed to be so because the test was less sensitive to binder content. AC 16 layer. The second section was also constructed on an existing surface, on which an AC 8 levelling layer was laid, followed by the application of the grids using two different emulsions with two different application rates each and topped with an AC 16 surface course.

Cores with a diameter of 150 mm were extracted 1 month and 1 year after the construction of the test structures. The interlayer bonding of the cores was tested using the Leutner shear test device.

Plug and de Bondt were able to observe that the shear strength could increase up to 3 times over long time observations. They also observed that a high viscosity emulsion can lead to higher interface shear strength and shear stiffness.

II.3 Conclusion: Literature Review

The literature review showed that glass fibre grids and other geotextiles have proven their positive effect on life prolongation and crack prevention.

But it was also observed that the insertion of a glass fibre grid or other geotextile had mostly a negative impact on the shear resistance of an interlayer.

Yet a debonded interface can shorten the lifetime of bitumen, as a working together of the layer is hindered and with it an effective reduction of the stresses induced by traffic loads.

Therefore, the purpose of the following study is to investigate the effects of the different glass fibre grids on the shear strength, the fatigue life, the stiffness modulus and the in-situ comportment.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

Part III

Laboratory testing III.1 Preparation of specimens for laboratory testing

The laboratory testing shall give us information about the characteristics of asphalt specimens reinforced with different grids. The investigation mainly focuses on:

• Influence of the reinforcement on the shear strength:

These tests are aimed at showing the effects of four different glass fibre grids reinforcements in asphalt specimens submitted to shear strength and compare them to unreinforced specimens, while coated with two different emulsions and with three to four different amount of emulsions. The specimens used for these tests are twolayered cylindrical specimens with a 150 mm diameter and a minimum height of 2

x 40 mm.

• Influence of the reinforcement on the stiffness modulus:

The specimens tested in this tests were two-layered cylindrical specimens (of 100 mm diameter) with and without glass fibre reinforcement, where the interlayer lays perpendicular to the loading direction.

• Influence of the reinforcement on the fatigue life:

The specimens tested in this tests are identical to the ones used for the stiffness modulus.

As the number of specimens required to carry out all tests with a minimum amount of 5 repetitions per shear test, 4 per fatigue and cyclic test was very large, it was decided that the specimens should be extracted from an outdoor test surface, built in in-situ conditions.

III.1.1 Characteristics of the glass fibre grids used on the test surface

The test surface was reinforced with four different grids, whose characteristics are listed in table III.1.1. All grids are from the same manufacturer. The resin of grids 1, 5 and W are the same, whereas the resin of grid N differs slightly, leading to a different form of the strands. The polyester used on grids 1, 5 and N is the same. Grid W is identical to grid 5 but without non-woven, as it was removed from the manufacturing process before the non-woven was glued to it.

A drawing of the grids is shown in figure III.1.1. For asphalt interlayers, the quantity of C40B5-S which is to be used for the bonding is identical to C60B4-S, independent from the amount of residual binder. The use of C40B5-S is not recommended for the use on interlayers with glass fibre grids, yet is not advised against.

Results of initial tests made by the manufacturer of the emulsions are shown in appendix I.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids The different application rate corresponding to each section are listed in table III.1.6. The two lanes differed from each other in the emulsion used for the coating. The upper lane was coated with a C60B4-S, the lower lane with C40B5-S. Information about the emulsions are given in table III.1.2

The right parts of the three lower lanes were planned for the extraction of two-layered cylindrical specimens with a 150 mm diameter for cyclic shear tests. The lower layer was made without a grid, the middle layer with grid 1 and the upper layer with grid 5. The emulsion used for coating was C60B4-S. The cyclic shear test was not carried out during this study.

The left parts were for the extraction of rectangular cores (300 mm x 200 mm), from which

Experimental and analytical study of the reinforcement of pavements by glass fibre grids cylindrical cores of a 100 mm diameter were to be extracted. These cores were planned for fatigue and modulus testing. The grids and emulsion used in this section were identical to the ones used in the right part of the lanes.

III.1.4 Construction of the test surface

Unbound granular base course The test surface was constructed on an unused space on the premises of the company REIF GmbH & Co KG in Rastatt, Germany.

Four dynamic plate load tests were conducted on the existent unbound granular base course, on which the test surface was to be constructed. These tests were performed with a plate of 300 mm diameter and a load of 10 kg. The results of these tests are listed in Coating and application of the different glass fibre grids The coating of the two lower lanes was started on the day of the construction of the binder course. The application of the emulsion was done using a spraying machine. The objective was to spray a quantity of 250 g/m 2 of C60B4-S on the lowest lane and 1000 g/m 2 of C60B4-S on the second lowest lane. However, the application with the spraying machine turned out

Experimental and analytical study of the reinforcement of pavements by glass fibre grids Grid 5 was applied on the second lowest lane before the emulsion broke and pressed on the binder course using brooms.

The coating of the three other lanes took place on June 5th. In order to have a more accurate spreading, the emulsion was applied with painter roller on the middle lane. Grid 1 was applied directly after the spreading of the emulsion and pressed on the binder course using brooms.

For the smaller sections of the upper two lanes, the different amount of emulsion had been weighed and filled in smaller boxes before the construction (emulsion which would remain in the boxes was taken into account in the weighting). In a first step, 2/3rd of the emulsion in the boxes were applied on the respective sections with brushes. The grids were directly applied on the unbroken emulsion. The last third of the emulsion was then spread on the top of the grids and the grids were pressed on the asphalt with brushes.

Upper layer: Surface course The surface course was made June 6th, 2015. As it had rained during the weekend, the surface of the lower layer was cleared of rainwater with compressed air. The characteristics of the surface course are listed in table III.1.5(see also appendix I). Measurements made with the TROXLER 4640-B gave an average compaction of 97.7 %. Extraction of the specimens The extraction of the different specimens started on June, 10th 2015 with the drilling of the cores with 150 mm diameter. 9 cores were drilled in each section of the two upper lanes and 123 cores were extracted from each other lane.

For some cores in the two upper lanes, the drilling broke the bonding between the upper and lower layer, so that the specimens fell apart. This was the case for the following cores:

• Section 4W1: 1 core • Section 6W3: 2 cores Due to this loss, the minimal amount of 5 repetitions for the shear tests could not be met in section 4W3. Here, the missing test was counted with a shear strength of 0 MPa.

The rectangular specimens extracted on the right side of the lower 3 lanes had a width of 20 cm and a length of 30 cm and were cut using a circular saw. The drilling and the resulting loss of specimens gave first impressions about the effects of the glass fibre grids as well as of the emulsion noted. It was noted that the destroyed specimens were all reinforced. It was also noted that most destroyed specimens had been coated with C40B5-S.

Nomenclature The name of each section is based on the applied emulsion (4 for C40B5-S and 6 for C60B4-S) for the first number, the grid (0 = no grid, 1, 5, W and N) for the second number. The third number represents the emulsio application rate from 0 (highest) to 3 (lowest). All sections with the same grid and the same emulsion are summarized in a section group and have an X instead of an application rate number.

For example:

W 1 Emulsion C60B4-S Grid W Application rate 1

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

III.1.5 Characteristics of each section

III.2 Shear tests on reinforced and unreinforced specimens

The shear resistance describes the mechanical resistance of an interface between two layers against stresses acting in the parallel direction. The shear resistance, as well as the shear strength, are used to characterize and quantify the bonding strength between two asphalt layers (see also section I.1.2.2: Interlayer bonding).

Investigation over the interlayer bonding strength can be conducted with different test devices, which can be split into two different groups: destructive tests and nondestructive tests.

The destructive tests can be divided in following subgroups (see also figure III.2.1):

• Torque tests: During this test, both layers are glued to a metal plate. One of them is held while the other is subjected to a twisting load.

• Tensile tests: In this test, one layer is fixed while the other is pulled off in the axial direction. One limitation of this test is its impossibility of measuring any kind of interlocking or friction between the aggregates.

• Wedge splitting tests: This test consists in pushing a wedge in a pre-made notch at the height of the interlayer of the specimen. The test used in this study is the Leutner shear test which is a destructive, monotonic shear test and will be described below.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

III.2.1 Leutner shear test

The Leutner shear test is a destructive monotonic shear test with pure interlayer shearing carried out on cylindrical, two-layered specimens with a diameter of (150 ± 2) mm.

III.2.2 Temperature adjustment

In order to enable the comparison of the shear stress results, the temperatures of the different tests were analytically adjusted to 25 The equation of the regression curves obtained were the followings:

• 600: σ = 10 -0.025 * T +0.740 ; R 2 = 0.81

• 610: σ = 10 -0.033 * T +0.529 ; R 2 = 0.96

• 650: σ = 10 -0.034 * T +0,791 ; R 2 = 0.96

The result of 610 and 650 show very similar slopes of -0.033 respectively -0.034. On the other hand, the unreinforced specimens show a very different slope of -0.025. This shows a greater temperature influence on the shear strength of reinforced specimens, meaning that for lower temperatures, the shear resistance is higher when the interface is reinforced with a grid.

The temperature adjustment was performed on all test results which had not been carried out at 25 • C, using for reinforced specimens the mean value of the 610 and 650 slopes, being a = -0.0335 and for unreinforced the slope value a = -0.025.

The difference between the results before and after the temperature adjustment is shown in figure III.2.4.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

III.2.3 Results after temperature adjustment

The average shear strength of each section, as well as the standard deviation and the coefficient of variation, are listed in table III Experimental and analytical study of the reinforcement of pavements by glass fibre grids It can also be observed that only section 650 can reach values as high as the maximum of the unreinforced sections.

In the following study, the results will be observed under different aspects:

• Influence of the glass fibre grids

• Influence of the emulsion application rate

• Influence of the emulsion type

• Influence of the non-woven

• Influence of the resin respectively the form of the strands

III.2.3.2 Observations made on the interfaces of the specimens after the tests

After the tests, the specimens were broken apart in order to analyse the interface. Observations were made on the state of the interface (evenness, presence of dirt) and on the positioning of the grids and non-woven for reinforced specimens.

A successful shear test is recognizable by the appearance of the interface which should be even and clean as well as by the appearance of the specimens halves, which should show no pressure area on their sides. Examples of the described phenomenon can be found in figure III.2.6. Behaviour of the non-woven In most cases, the non-woven stayed glued on the binder course. 17 specimens (13.7 % of the reinforced specimens) however showed the non-woven torn between the surface and the binder course. An example of a torn non-woven can be seen in figure III.2.7d.

Torn non-woven were found especially on specimens of section 411 (4 of 6 specimens), 4N

(6 of 6 specimens) and 611 (4 of 6 specimens). The sections 413, 451 and 650 showed each 1 specimen with a torn non-woven.

Dirt on the interface Dirt and dust found on the interface of the specimens could come from two possible sources:

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

• Dirt came on the interface during construction, e.g. with construction machines

• Dirt came into the specimen during drilling because of a porous interface.

The spread of dirt in the interface gives indication on its source.

Dirt that was already on the binder course before the surface course was made is positioned on the whole surface while dirt coming from drilling is mainly positioned at the edge of the interface, letting the middle largely dirt-free.

The specimens tested in this study showed only signs of dirt coming from drilling. Some example are shown in figure III.2.8. A degree of dirt-contamination ( • DC )was established, with degree 0: no contamination, degree 1: light contamination, degree 2: medium contamination and degree 3: strong contamination. Intermediate degrees were also possible. It was also observed that 91.6 % of the specimens, in which dirt was found, were reinforced specimens. This amount increased to 100 % when looking only at high dirt-contamination degrees ( • DC ≥ 1.75). When looking at the emulsion application rate, it can be noted that 23.6 % of specimens showing a dirty interface had the application rate 1, 34.7 % the application rate 2 and 41.7 % the application rate 3. When looking only at the higher degrees ( • DC ≥ 1.75), we find 24.5 % of application rate 1, 34.7 % of application rate 2 and 40.8 % of application rate 3.

Keeping in mind that the intrusion of dirt during drilling is mainly due to voids at the interface, we can already conclude that the amounts of voids at the interface is especially high for reinforced specimens coated with emulsion C40B5-S and an application rate 3.

In contrast, high application rate (application rate 0), as well as unreinforced specimens, are not represented or under-represented in the listing.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids The difference in residual binder quantity on the different interfaces becomes visible

Experimental and analytical study of the reinforcement of pavements by glass fibre grids in the loss of evenness for the reinforced specimens, which can be due to the tearing of the non-woven. The difference in application rate was also noticeable by touching of the specimens, as specimens with higher contents of emulsion were still sticky. As no recommendation about the use of C40B5-S is made on the reinforced section, comparison of the shear strength values of the sections coated with C60B4-S was made.

III.2.4 Discussion

The recommended application rates of the sections without grids as well as of the reinforced sections with the grids 1, 5 and W are listed in III.2.5 together with the corresponding shear strength achieved for the residual binder values. The last column shows the loss in shear strength compared to the section without a grid. A loss of at least 60 % can be observed on the reinforced sections compared with the reinforced section.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

Figure III.2.11a shows the influence of residual binder of both emulsions on the bonding

Experimental and analytical study of the reinforcement of pavements by glass fibre grids between two layers without reinforcement. A first glance shows that the behaviour of both emulsions is very similar. For the lowest application rate, the shear strength observed is already above 1.0 MPa, which is mainly due to the interaction between the grains of both layers. By adding residual binder, the bonding strengthens until it reaches a maximum of about 1.4 MPa for application rates of 100 g/m 2 for C40B5-S (section 402) and 150 g/m 2 for C60B4-S (section 602). After these points, the bonding strength drops considerably to values slightly under 0.8 MPa. This effect is mostly explained by the creation of a slip plane caused by a surplus of residual binder, as described by Canestrari et al. [ CAN 13].

This slip plane hinders the interlocking of the grains between the upper and lower layers by creating an interlayer, preventing the bonding of the layers.

However, section 600 with an application rate of 816 g/m 2 reaches an average shear strength of 1.32 MPa, which is almost as high as the peak value of 602. Here it seems that the loss of interlocking is compensated by a stronger adhesion due to the high amount of residual binder between the layers. and 6WX. It can be observed that all three sections show a tendency of 'more is more', meaning that the adding of residual binder improves the shear resistance of these specimens. Only section 652 seems to fall out of the series.

The general tendency for greater shear stress results with greater application rates can also be seen in their linear correlation coefficients, which are of 0.98 for 65X and 6WX, suggesting a nearly perfect linear correlation, and of 0.92 for 61X.

The zoom on all reinforced sections (except section 650) in figure III.2.11c shows the difference between sections coated with C60B4-S and sections coated with C40B5-S. As mentioned before, sections coated with C60B4-S show that the use of more residual binder leads to higher shear resistance values. Sections coated with C40B5-S show, on the contrary no tendency at all.

III.2.4.3 Influence of the emulsion type on the interlayer bonding of reinforced and unreinforced sections

The differences between the emulsions C60B4-S and C40B5-S are listed in III.1.2. The comparison between sections coated with C40B5-S and C60B4-S is based on the use of the same amount of emulsion, which results in different contents of residual binder, as C40B5-S has only 40 % and C60B4-S 60 %.

For the unreinforced specimens (figure III.2.12a), the use of a harder bitumen and the adding of the fluxing agent used in C40B5-S results in very similar shear strengths as well as a similar curve progression compared to the specimens coated with C60B4-S. A shear strength peak is visible for both emulsion types at 100 g/m 2 respectively 150 g/m 2 residual binder. This suggests the creation of a slip plane for both emulsions.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids This similarity in behaviour between both emulsions is not to be found on reinforced sections. As figure III.2.12b shows, the differences in shear strength are relatively high, especially for the higher application rate 1. Analogies in curve progressions, as for unreinforced sections, cannot be found, because, as mentioned before, the C60B4-S coated sections show a rise for more residual binder while the C40B5-S do not.

It can be concluded that the change in emulsion properties, which is interesting for the bonding without grids, is not working on reinforced sections. Here, a softer binder seems to be of greater importance. It can be observed that the strands of grid 1, having a tensile strength twice as high as 5 and N, are nearly twice as wide as the grids 5 and N, without being noticeably higher than the two other grids.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

The comparison of the strands of grids 5 and N shows that the strands of grid N are slightly taller but also slightly thinner than the strands of grid 5, which can lead to a better interlocking with the granular of the upper layer, explaining partly the better results of 4N compared to 452 as discussed before. As the resin used in grids 5 and N is different, it can be assumed that the resin has an impact on the shear strength, firstly as it leads to a different form of the strand, secondly because it can be in some cases self-adhesive. In our study, a self-adhesion was not noticed, however the behaviour of the resin under hot temperatures, as it is the case during construction, was not further investigated.

III.2.4.6 Microscopic examination

The pictures of figure III.2. 16 were made with a 20-times magnification and show about 1 cm of the interface width of 6 observed cores. The upper part of the picture shows the wearing course, the lower part is the binder course. The cores were cut perpendicular to the interlayer in the direction of rolling, the strands coming out of the cores are therefore filling yarns (cmd). As only a few specimen scans were taken, the following pictures can only give a slight overview of the interlayer.

On the picture of the unreinforced specimens (600 and 602) the interface between the wearing course and the binder course is not clearly visible. This similarity in appearance can also be seen in the test results, as both achieve more than 1.1 MPa average shear strengths. No voids are visible in both samples.

The pictures of 610, 611 and 650 show a md-strand running along the interface, picture 651 shows a cmd-strands coming out of the core.

The existence of voids can be seen under the strands of picture 611 and 651. However,

Experimental and analytical study of the reinforcement of pavements by glass fibre grids which fills the voids with binder, leading to a higher binder content at the interface. This residual binder is visible in pictures 650 and 610 as shining black points under the strands.

A high binder content together with no voids at the interface leads to the assumption that in this case, the load is mainly transmitted over the binder, instead of being held by aggregate and binder together.

III.2.4.7 Effect of different bonding conditions on the shear resistance

As observed before, the unreinforced section group 60X shows a peak for an amount of 150 g/m 2 (application rate 2) of residual binder. The negative slope starting after this point is the expected result of the creation of a slip plane as mentioned before, due to the excess of residual binder. This new plane created between the upper and the lower courses of the structure prevents a good interlocking between the granular of the upper and lower courses.

Knowing this, it can be assumed that the positive slope starting again from section 601 (210 g/m 2 of residual binder) and leading to section 600 (816 g/m 2 of residual binder) cannot be due to the interlocking between the aggregates, as it is disturbed through the excess of residual binder. The remaining influencing factor can then only be the adhesion due to the residual binder between the two layers.

The difference between the factor 'interlocking' and the factor 'adhesion' can be seen on the slope between 603 and 602 or 601 and 600. While the first ascension, due to interlocking

Experimental and analytical study of the reinforcement of pavements by glass fibre grids and adhesion, is relatively steep with an average slope of 6.01E-3, the second ascension, where the interlocking is lost and only the adhesion is working, is significantly flatter with an average slope of 9.04E-4.

Based on this result, a comparison was made between the average slopes of the different groups 61X, 65X and 6WX, 603-602 (positive slope before the slip plane appears) and 601-600 (positive slope after the slip plane appears).

The average slopes of each group were calculated using the method of least squares and can be seen in figure III.2.17.

Figure III.2.17: Average slope of each section group

The tendency described before can be observed again on this graph. The group 6WX using grid W, without non-woven, shows the second steepest slope. Here the steep slope can be explained by the non-using of a non-woven, which enables a direct interlocking of the granular. However, as it was observed on the microscope picture, the grids strands are still disturbing the bonding by creating voids under the strands, explaining the difference of slope between the 6WX and 603-602.

Because of this possible interlocking, it can be assumed that with more residual binder a slip plane would appear and cause a fall of the curve as happens on the unreinforced specimens curves.

The groups 61X and 65X show both flatter slopes, having both a non-woven between the strands of their grids. It can be assumed that the interlocking of the aggregates is lightly disturbed by the non-woven so that the main bonding agent is the adhesion through the residual binder. In this case the residual binder fills the voids under the strands of the grids, leading to better shear strength results. It can be observed that a great amount of residual binder as used for section 650, leads to shear strength values equalling the best results of the unreinforced sections.

The representation of the curve as linear to infinity is most likely not correct, it should be assumed that the curves would more likely have a sigmoid form. However, the linearity of the curves is a good approximation for the middle part as represented.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

In conclusion, it can be said that specimens without reinforcement and low residual binder content have an undisturbed interlocking of the grains, while test specimens with reinforcements are bonded together mainly through the residual binder.

This hypothesis is strengthened when looking at the microscope scans (see figure III.2.16),

where the residual binder is visible under the strands of the grids on the pictures of the reinforced specimens, while the residual binder seems to be absorbed in the asphalt around the interface in the pictures of the unreinforced specimens.

The effect of interlocking is visible in the slope of the curves. The steeper the slope, the stronger the interlocking between the grains and on the contrary: the flatter the curve, the stronger the influence of the residual binder on the bonding.

Considering this fact with regard to the temperature dependency of the shear resistance (see section III.2.2, figure III.2.3), it can be observed that the reinforced specimens, in which the residual binder is primarily responsible for the interlayer bonding, are more temperature dependent than the unreinforced specimens, where the interlocking -which is widely temperature independent -has still a role to play. The interface between the layer was treated in 3 different ways:

• Pavement 1: Without treatment (not hot on hot)

• Pavement 2: Pre-coated with a polymer modified emulsion

• Pavement 3: Pre-coated with a conventional cationic emulsion

The shear tests were carried out on 150 mm diameter with a displacement rate of 50 mm/min and at the temperatures 10 The slopes calculated with these results and using equation The specimens (diameter 150 mm) were made in a laboratory and consisted of two asphalt layers with a nominal maximum aggregate size of 11 and a bitumen with penetration grade 60. The three different interlayer options were:

• Tack coat The slope calculated with these results and using equation 1 are:

Tack coat: a = -0.0341 In conclusion, it can be observed that specimens built under the same conditions tend to have greater a-values when a reinforcement is laid on the interface, showing that the influence of the temperature on the shear resistance is higher for specimens with reinforcement than for specimens without reinforcement.

III.2.5 Conclusion about shear tests

28 different sections were built, varying types of grids (with and without non-woven, different resins), types of emulsions and emulsion application rates. The cylindrical cores extracted from the surface were tested with a monotonic shear test. The results are:

• The insertion of glass fibre grids has a negative influence on the bonding, as for the recommended application rates, the shear strength of reinforced specimens reach only about 60 % of the shear strength of unreinforced specimens

• The application rate on reinforced samples has a important effect on the bonding.

For low application rates, no positive influence on the shear stress is visible. However high application rates can lead to shear stresses similar to the ones on unreinforced samples.

• Important variations can be observed between the different emulsions.

• The use of a non-woven between the strands leads to a loss of interlocking between the layers hence to lower shear stress results. For grids with non-woven, a high application rate is very important.

• The resin with which the glass fibres are coated can have a positive influence on the bonding.

• The form of the strands can lead to a better interlocking between the grid and the upper layer.

• The relation between temperature and shear resistance depends on the acting bonding effects: Interlocking: lower temperature dependency, bonding through residual binder: higher temperature dependency.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

III.3 Stiffness modulus of reinforced and unreinforced specimens

The stiffness modulus is a mechanical value describing the resistance of a body against elastic deformation induced by a force or a moment. The stiffer the material, the greater the effort required to obtain a given deflection.The stiffness depends on the elastic property of the material, but also on its homogeneity.

In road construction, the stiffness modulus is used as a parameter to describe the asphalt materials. With the stiffness modulus of a layer material, it is possible to calculate the deformation and the stresses occurring in a layer when applyig a defined charge.

In The specimens used for the tests are double-layered cores extracted from the test surface described in paragraph III.1, from lane 600 (unreinforced, residual binder application rate:

816g/m 2 ), lane 610 (reinforced with grid 1, residual binder application rate: 600 g/m 2 ) and lane 650 (reinforced with grid 5, residual binder application rate: 1638 g/m 2 ).

In order to test the impact of the grids compared to the unreinforced samples, the specimens had to be extracted from the side. Their extraction was therefore conducted in two steps:

1. Extraction of rectangular slabs from the test surface (dimensions: 20 x 30 x 12 cm) 2. Extraction of cores (diameter 100 mm) from the slabs Thus, it was possible to have the grids positioned where the tension stresses would occur, even if it was not completely possible to extract the specimens in such a way that the grid would be positioned exactly in the center. As the maximal length usable in the testing device was 100 mm, the specimens had to be cut in half after extraction from the slabs. The short length led to a maximal amount of 3 strands in each specimen, as the mesh size of the 2 grids used is 4 x 4 cm 2 .

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

III.3.3 Test implementation

The tests were carried out at four temperatures: -10 • C, 0 • C, +10 • C and 20 • C. At least four samples of each section were tested at each temperature. To ensure a good tempering of the samples, the specimens were laid in a temperature conditioning unit for at least 12 hours before starting the test.

Pre-test Since the test is a non-destructive test, a first specimen was tested in a pre-test for each temperature. This enabled the determination of a suitable loading test to ensure the non-destructivity. During this pre-test, one temperature conditioned specimen of each section was subjected to an increasing maximal loading at 10 Hz, while a minimal compression stress of 0.035 MPa was always kept. After every 100 loading cycles, the maximal The diameter was measured at various points of the specimen. The height of the two layers was only measured on the two front sides of the specimens. Therefore the average diameter of the specimens may vary from the sum of their two layers.

F (t) = A + B * sin(2 * π * f * t + C) (4)
u(t) = a + b * sin(2 * π * f * t + c) (5)
Experimental and analytical study of the reinforcement of pavements by glass fibre grids At first sight, it can be observed that the specimens reinforced with grid 5 (section 650) reach higher stiffness moduli for nearly every test combination except for the test temperature of 20 • C, where section 610 reaches higher values.

The influence of the temperature appears to be less negative on the specimens of section The calculation of the shift factor log(α T ) is based on equation 6. The master curve has the form of a sigmoid curve and can be constructed using a regression function going through the determined data points. The sigmoid function has the form of equation 7. The values corresponding to the curves are listed in table III.3.5.

log(α T ) = E a R ( 1 T - 1 T 0 ) (6)
|E| = y 0 + w 1 + e ( x-x 0 z ) (7)

III.3.5 Test on surface and binder courses: Specimen preparation and test results

In order to compare the results obtained for double-layered specimens with the layer The tests were carried out as described above. The diameter and length of each specimen as well as the achieved stiffness modulus for each frequency and each temperature, are listed in appendix III, table III.3.6 to III.3.9 show the average stiffness modulus for all specimens at one temperature for all frequency as well as the corresponding standard deviation and coefficient of variation. As demonstrated in section III.2.4.8, the influence of temperature on the behaviour of the shear strength depends, inter alia, on whether or not a reinforcement is placed at the interface. This fact is explained by the influence of the residual binder, which is largely responsible for the shear strength in the case of reinforced test specimens. While the bitumen solidifies or liquefies with the temperature, the influence of the interlocking is to a large extent temperature-independent.

Sections 610 and 650 show a strong influence of the residual binder on the bonding of the two layers, as can be seen in section III.2.4.7.

Since 650 has a relatively high shear strength at normal temperatures, the difference between curves 600 and 650 remains essentially constant at all temperatures.

For 610, however, bonding improves massively at lower temperatures compared to its shear strength at 25 • C, which can lead to a displacement reduction within the specimen during the test and thus to higher resulting stiffness modulus.

The higher the temperatures, the more the bonding reduces in all three sections so that the bonding loses in significance. Calculating the shear strength of the three sections at different temperatures according to section III.2.2 results in the following values (table

III.3.11):

Experimental and analytical study of the reinforcement of pavements by glass fibre grids Table III.3.12 lists the slopes of the linear regression curves drawn according to the strain-stress results obtained at each temperature and at 0.1 Hz and 10 Hz frequencies.

It can be observed that for both frequencies the slopes of section 610 are actually the Experimental and analytical study of the reinforcement of pavements by glass fibre grids smallest for the temperatures from -10 • C to 10 • C, being relatively close to the slopes of section 600 at -10 • C. This trends changes at 20 • C, meaning that from -10 • C to 10

• C, for a certain force, the responding deformations within the specimens of section 610 are greater than for 600 and 650.

On the other hand, the 650 curve remains the steepest at temperatures between -10 • C and 10 • C, indicating smaller deformations within the specimens.

Table III.3.12: Slopes of the stress-strain regression curve for every specimen at the four temperatures and two frequencies (10 Hz and 0.1 Hz). The cell colours represents the steepness of the slopes: green: flattest curve, more displacement in the specimen, yellow: middle curve, orange: steepest curve. In addition to the comparisons between sections 600, 610 and 650, these sections are compared with the binder and surface courses (BC and SC) used for the construction of the specimens. It can be observed that for lower temperatures from approximately 0 • C on, the curves of sections 600, 610 and 650 move apart from the curves BC and SC. SC and BC remain relatively close to the curves of CBC and CSC (calibration asphalt, inserted for the sake of comparison). It can be concluded that a strong effect is produced between the two types of test specimens at lower temperatures.

The first question is whether this effect can be attributed to a possible anisotropy in the asphalt, as the test specimens of sections 600, 610 and 650 were taken perpendicularly to the specimens of SC and BC.

In their study of 2016, Hofko et al. [HOF 16] show the effects of asphalt anisotropy and BC increases and does not explain why the curves go apart at temperatures below 0 • C.

The next point to be checked is the influence on the creation of cryogenic stresses at low temperatures. Cryogenic stresses are stresses occurring when low temperatures prevents the asphalt from relieving stresses by modifying its shape.

Transferred to our specimens, it would mean that deformations are strongly inhibited at low temperature in one layered specimen, although they are still possible in double layered specimens, leading to strongly different results in stiffness modulus.

This theory can be examined by looking at the deformation resulting from different stress levels. At low temperatures, these deformations should be greater for two-layered specimens than for uni-layered specimens. For higher temperature (from 0 • C on) the difference due to cryogenic stresses should become smaller.

To investigate this point, the stress-strains curves of the sections 600,610 and 650, defined as two-layered specimens, were opposed to the stress-strains curves of sections SC and BC, defined as uni-layered specimens, for all temperature and at 10 Hz and 0.1 Hz Hz, the slope of the uni-layered curve is clearly steeper than the slope of the two layered specimens. It can be concluded that the deformation achieved for the same stress levels are higher within two-layered specimens. For the mentioned exception of 0 • C, 0.1 Hz, it can be observed that the slopes are nearly equal, even though the slope of the uni-layered specimens is a little steeper than that of the two-layered.

If we observe the difference in percentage between the slopes of uni-and two-layered specimens at each temperature and frequency, as can be seen in figure III.3.16, it can be noticed that the slightest difference is to be found at 0 • C. Below and above this temperature, the differences are more important. The fact that the difference is higher before 0 • C suggest an impact created by the low temperature, which could be due to the difficulty for the asphalt to change its shape at low temperatures.

At higher temperatures, we see quite high differences between the uni-and two-layered specimens, but as the slopes themselves are rather flat, the difference in stiffness modulus, in the end, is manageable, leading to relatively close stiffness modulus curves from 5 • C on (see III.3.11).

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

III.3.7 Conclusion: stiffness modulus

The indirect tensile tests on reinforced and unreinforced specimens give information on the acting of the reinforcement as well as on the acting of the interface inside the specimens.

The comparison of the two-layered specimens 600 and 650, with a rather similar shear strength, show the direct effect of the reinforcement by grid 5 compared to the specimens without grids. This led to a constant difference of approximately 1100 MPa for all temperatures.

The quite different shear resistance at the interlayer of the specimens of section 610 could be seen in the shape of its curve, which was different from the curves 600 and 650. Both courses were parallel on their entire length. The difference in shape showed the influence of the temperature on the displacement happening at the interface.

The comparison of the two-layered specimens with the uni-layered specimens SC and BC also show very different curve shape, especially at temperatures below 0 • C.

The observation of the strain-stress curves of the specimens at temperatures -10 • C, 0 • C, 10 • C and 20 • C and at 0.1 Hz and 10 Hz frequencies showed that, for same stress levels, more deformation took place in two-layered specimens than in uni-layered specimens, leading to different results in stiffness moduli. This difference was smallest at 0 • C, which leads to the assumption that different effects act on the interface of the specimens.

At higher temperatures it can be expected that the bonding between the interfaces becomes poorer, leading to more deformation. At lower temperatures it can be assumed that the differences are the results of cryogenic stresses, which in cases of two-layered specimens can be dissipated along the interface.

A comparison of the uni-layered and two-layered specimens is sadly not possible, as a quantification of the impact of the interface cannot be given. A possibility to investigate this special point could be to test two-layered specimens composed of the same asphalt mix on both sides and to compare with the results of uni-layered specimens made of the same asphalt mix. Such tests could additionally be carried out on two-layered specimens with different bonding characteristics, e.g. with different amount of emulsion or different surface treatments.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

III.4 Fatigue testing of reinforced and unreinforced specimens

The fatigue of a material describes the effect of the repeated loading of a material with a load which, when applied a single time would perhaps cause no damage at all, but after a certain amount of loading can cause the fracturing of the material.

The application of a stress smaller than the rupture stress will lead to a progressive damaging, starting with microscopical damages, obliging a decreasing surface to support a constant stress. The damage due to fatigue will lead to the creation of cracks, which, in a composite material such as asphalt, can cause the loss of bonding between the individual materials being here the aggregate and the binder.

In The fatigue of asphalt materials can be determined with different tests, as described in section III.3. The test chosen for the investigations in this thesis is the indirect tensile

Experimental and analytical study of the reinforcement of pavements by glass fibre grids test (ITT). The description of the indirect tensile test can be found in section III.3.1.

The fatigue life of a specimen depends on various factors, for example, the load, as well as the loading mode, the material properties (Stiffness modulus, Poisson's ratio) and the form of the specimen [ ARS 13].

It is to be noted that this tests adds a creep components, which is not rated in this study.

III.4.1 Specimens used for the fatigue tests

The specimens used for the fatigue tests are two layered, cylindrical specimens with a diameter of 100 mm, as described in section III.3.2.

The grids installed at the interface of the test-specimens were grids 1 and 5 extracted from the sections 610 and 650. The residual binder application rates used for the bonding were 600 g/m 2 and 1636 g/m 2 respectively. The unreinforced specimen was extracted from section 600 and was bonded with a residual binder application rate of 816 g/m 2 . More information about the construction, the materials, the emulsion and the glass fibre grids can be found in section III.1.

III.4.2 Test implementation

The fatigue tests were carried out based on the German directive AL Sp-Asphalt 09

[AL-Sp 09].
The tests were performed at 10 • C and 20 • C, at a frequency of 10 Hz and were load controlled. To ensure a good tempering of the specimens, the specimens were laid in a climatic chamber for at least 12h before the beginning of the tests.

During the test, the cylindrical specimens were repeatedly loaded with cycles of a sinusoidal form, going from a minimum compression stress of 0.035 MPa to a maximum compression stress, chosen so that the failure would occur between 1,000 and 1,000,000 cycles.

Extensometers positioned on each side of the specimen, as shown in figure III.4.2, measured the horizontal displacement during the test.

The failure was defined as the cycle for which the stiffness modulus was only 50 % of the initial stiffness modulus: The stiffness modulus was calculated with equation (2) (see section III.3.3), using the displacements measured by the extensometers and the applied load levels. The fatigue curves of each section and for each temperature were constructed with the various results achieved for different maximum stress levels and their resulting deformations.

F atigue Criterium : E N E init = 0.5 (
For 10 • C, the following stress levels were chosen: For 20 • C, the variation of possible stress levels was limited by the load cell. For small stress levels (under 0.4 MPa), the stress application by the testing device could not be made exactly enough. The fatigue was therefore tested at only two stress levels.

At 20 • C the following stress levels were chosen:

Experimental and analytical study of the reinforcement of pavements by glass fibre grids It can be observed that, for both stress levels 0.4 MPa and 0.8 MPa, the reinforced specimens 610 and 650 achieve more cycles until failure than the unreinforced specimens 600.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

The progression of the determined regression curves is not parallel, showing different influences based on the stress levels of the specimens.

When extended, it can be noted that curves 600 and 650 would meet at a stress level of 0.10 MPa after 2,349,217 cycles, curves 600 and 610 at a stress level of 1.24 MPa after 319 cycles and curves 610 and 650 at a stress level of 1.24 MPa after 3,494 cycles. It can be observed that, unlike for the test-temperature 20 • C, the progression of the determined regression curves is nearly parallel. This can be seen in the very similar slopes of the curves (average: -4.6080, Std. dev.: 0.0711, coefficient of variation: -0.0154). It can also be observed that the axis intercepts of reinforced curves 610 and 650 are equally similar (Average: 9.554, Std. dev.: 0.045, coefficient of variation: 0.005), so that the two curves lie nearly on top of each other.

In contrast, the axis intercept of the unreinforced curve 600 shows a difference of 0.487 compared to the average value of the reinforced section.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

III.4.4 Interpretation

At 20 • C, it is observed that for both stress levels, the number of cycles reached by reinforced samples is always higher than by the unreinforced samples.

The graphical representation shows that the smaller the stress load, the greater the difference to both other curves, showing that the influence of grid 1 at 20 • C becomes particularly important, when small stresses occur, but is less noticeable for higher stress levels.

In contrast, the specimens of 650 show that the higher the stress level, the greater the positive influence of the grid in comparison to the two other groups.

At 10 • C the described behaviours are not shown anymore, as the progression of the three curves is nearly parallel, which leads to the assumption that here again, the temperature influence on the grid impact is great.

When looking at the slopes of the curves at both temperatures, we observe that only section 610 keeps a constant slope of -4.222 at 20 • C and -4.527 at 10 • C, while slopes 600 and 650 vary from -3.553 and -3.307 respectively at 20 • C to -4.637 and -4.660 respectively at 10 • C. Remembering the stiffness modulus testing, it can be noted that the behaviour of sections 600 and 650 keep a constant difference at all temperatures, while the results of section 610 vary compared to the two others.

Keeping this in mind, we can observe a parallelism in behaviour, as at this point again the specimens of section 610 behave differently from the specimens 600 and 650. This would mean that here again, the influence of the shear strength, or of the great amount

Experimental and analytical study of the reinforcement of pavements by glass fibre grids of residual binder at the interface on the fatigue life can be measured.

III.4.5 Observation made on uni-layered and two-layered tested cores

In order to observe the crack propagation during a repeated load test in reinforced and unreinforced specimens, it was decided to film some of the tests.

For good sight conditions and as the horizontal displacement was of secondary importance for these observations, the extensometers were not fixed on the cores.

The tests filmed with a were done with a high-resolution camera, allowing to see the details from crack initiation and propagation until failure occurred.

The cores tested here were two-layered specimens from the section 600, 610 and 650 as used for fatigue and modulus testing as well as uni-layered cores from the surface and binder course of the surface test used during the modulus tests.

The tests were carried out in a stress-controlled way with a constant stress of 0.8 MPa and a sinusoidal loading. In order to protect the test machine, the stopping criteria were set to be a maximum of 7 mm vertical displacement through the pressure cell.

In order to have a better view of the cracks, the specimens were sprayed with white colour, which however still enabled the seeing of aggregates through the colour. The black lines on the 600, 610 and 650 specimens represent the position of the interface. The first observation to be made is the form of the specimens at the end of the tests.

It is clearly visible that the reinforced specimens did not break apart, in contrast to the unreinforced specimens. It can be observed that both glass fibre grids hold the specimens together in absolute contrast to the other specimens.

The second observation is of the crack propagation. When looking at the specimens of 600, 610 and 650 at 50 %, it can be observed that on specimen 600, a crack is in formation on both sides of the interface, while for the cores 610 and 650, the first signs of a crack are to be seen on only one of the two sides (upper side for 610 and lower side for 650).

At 75 %, the cracks on the reinforced specimens are still strongly one-sided, while the two cracks visible on both sides of the interface of specimen 600 have already touched.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids At 20 • C however, the observed parallelism was non-existent and the curves of the reinforced specimens showed a different tendency: Compared to the unreinforced specimens, the specimens of section 650 showed the greatest difference for high-stress levels, but approached the results of 600 for lower stress levels. In contrast, the curve of section 610 showed a steeper slope and improved fatigue life results for low-stress levels.

The picture made during repeated load tests showed the different type of crack propagation, as on two layered, reinforced specimens, the cracks propagated first in one of both layers and crossed the interface only shortly before the end of the test, while the unreinforced specimen showed a crack propagation on both layer sides.

It was also observed that at the end of the test, i.e. after a vertical displacement of 7 mm of the pressure cell, the cores of the unreinforced specimens were falling in two parts, divided through the center, while the cores of the reinforced specimens kept together. As the bitumen 70/100 is rarely used in France, it can be assumed that the bitumen used on the RD4 was either a 50/70 or a 30/45 or a bitumen having a penetration grade in-between. The use of a polymer-modified bitumen is also excluded as it is improbable that such a bitumen was used on a road with such a traffic load.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

IV.1.2.2 Damage types observed on the RD4

The observation of the RD4 showed different damage types:

• Change in road structure

• Longitudinal cracks at the centre line The measurements take place between each double-wheel of the rear axle, which is loaded with a constant load of 13 tonnes. A measuring device consisting of two measuring beams is placed on the surface of the road while the truck is moving. A first deflection measurement is made in an unloaded state (under the truck) and a second measurement

•
Experimental and analytical study of the reinforcement of pavements by glass fibre grids It can be observed that the form of the moving average curves on bank and axis sides is approximately the same, but that the curves of the bank-sides show a more pronounced form and the deflections on the bank sides are much higher than on the axis-side, indicating a more weakened edge of the road, which confirms the visual observation made on the RD4. It can also be seen that after about 2/3rd of the distance, both bank and axis sides show higher deflections. This is especially visible when looking at the moving average curves.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids The average values of the measurements of the bank and axis side in both directions are listed in table IV.1.7 , together with their standard deviations and coefficients of variation.

As an increase in the deflection was observed after about 2/3rd of the distance, it was decided to divide the route into different sections as follows:

• Measurements on axis sides:

IV.1.3 Maintenance works on the RD4

The maintenance works on the RD4 were conducted between the eastern end of the village of Wickerschwihr and the junction of the RD4 with the RD112. The test sections are located in the middle of the route. The works were conducted on two different days:

On the first day, the works were executed from the eastern end of Wickerschwihr to the beginning of the observed section, which is about 300 m later. On the second day, the rest of the road was done, which corresponds to about 1.7 km.

The construction of the observed section took place on October, 30th of 2015.

The maintenance works consisted in adding a new surface layer on the top of the present road. The height of the new surface layer was to vary between 6 cm and 4 cm, corresponding to a BBM and BBTM asphalt layer based on French classification.

The observed section was divided into 5 different sections: two reference sections with 6

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

IV.1 IN SITU OBSERVATIONS: RD4
cm of the new surface course at the beginning and the end of the observed section and 3 reinforced sections in the middle, as shown in figure IV.1.8:

• First section: 'Ref 6 cm' -unreinforced section with 6 cm overlay

• Second section: 'N1' -section reinforced with grid N1 with 4 cm overlay

• Third section: 'N5' -section reinforced with grid N5 with 4 cm overlay

• Fourth section: '5' -section reinforced with grid 5 with 4 cm overlay

• Fifth section: 'Ref 6 cm -2' -unreinforced section with 6 cm overlay The fine content represents 2.6 %, the binder content is 5.4 % with 1 % brought by the recycling materials. The bulk density of the asphalt was 2.429 to/m 3 .

Emulsion The emulsion used for the bonding between the old structure and the new surface layer is C65B4-S with 65 % residual binder. The application rate varied depending on the section of the road. The application rate for every section is shown in figure IV.1.8.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

Glass Fibre Grids The grids used in the section are N1, N5 and 5. Grids N5 and 5 correspond to grids N and 5 applied on the test surface described in section III.1. A description of the grids is given in table IV.1.8 . The construction was done under running traffic conditions, meaning that one lane remained open for traffic while the other was constructed. The construction was started in the morning with the lane towards of Muntzenheim. The lane towards Holtzwihr was constructed in the afternoon.

Before starting the construction, the surface of the old structure was swept with a road sweeper. Afterwards a bitumen sprayer started to spread the emulsion corresponding to the section (figure IV.1.9a). The junction between the road section made the day before and the new section was made by adding a greater amount of emulsion on the junction.

For the section reinforced with grids, the emulsion was always spread only a few meters ahead, so that the grids could be applied on the unbroken emulsion.

The grids were unrolled manually on their full length by pushing the roll with the foot. It was then pressed onto the road surface with the help of brushes until the non-woven was soaked with emulsion.

As the section of grid 5 is partly laid in a curve, the grid had to be cut in smaller parts of about 20 m length each (see figure IV.1.9c).

Grid N5 was laid in two parts: the first one had a length of 80 m, the second one of 50 m.

The overlapping of two grids was done over a length of about 50 cm to 1 m.

The laying of the asphalt layer was started when the installation of the grids was sufficiently advanced so that the laying had not to be interrupted.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids The RD4 was inspected visually a few times between October 2015 and May 2017. The inspection showed no sign of cracks, neither on the reinforced nor on the unreinforced sections. However, other particularities were observed:

• Small pull-outs and small bitumen accumulations As mentioned before, the cores extracted show a structure made of 3 older surface layers, topped with the new surface layer for the cores extracted in May 2017. Under the surface layers is a macadam layer, which can be seen in most cores. A very thin layer is to be found between the macadam and the surface layers, which was probably a surface dressing laid on the macadam.

However, it has to be noted that some of the cores extracted from the second half of the road section were extracted without the macadam layer. This is the case for cores C, 5 and 6. The picture of core B shows the macadam broken apart during drilling.

IV.1.4.3 Height of the different layers of the RD4

The thickness of the different layers was determined in the laboratory of Cerema, Direction territoriale Est and are represented in figure IV.1.17.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids The calculated average thickness of the layers of the old structure, as well as the standard deviation and the coefficient of variation, are listed in table IV.1.9.

The highest coefficient of variation is to be found for the macadam, varying between 30 mm and 100 mm whenever the macadam is present. It can be assumed that in some cases, the macadam broke apart during drilling, leading to smaller layer thickness.

The second highest coefficient of variation was determined for the third surface course of the old structure, as it strongly varies especially between the two travel directions.

The thickness of the new surface layer was between 6 cm and 5.5 cm in the reference sections and 3.5 to 4 cm in the reinforced sections.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids The condition for testing a layer was a minimum thickness of 40 mm. For this reason, the modulus of the small layer 4 was not determined.

The average modulus of each layer together with the standard deviation and the coefficient of variation are listed in table IV.1.10.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids It can be observed that the coefficient of variation of layers NSL and 2 is relatively small with 0.0737 and 0.0880 respectively. Layers 1 and 3, however, show the more important coefficient of variation. It can be concluded that the variation within the layer is quite important.

Normally the stiffness of an asphalt layer depends from: Cores 2 bis, B and H show a medium amount of voids.

Cores C, 5 and 6, both having a low amount of visible voids, are all positioned in the section Ref 6 cm -2. Core D is positioned at the end of section N5, which is the middle section.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

IV.1 IN SITU OBSERVATIONS: RD4

All other cores are positioned in the sections west of section Ref 6 cm -2.

IV.1.4.5 Deflection measurements with Lacroix Deflectograph

In August 2016, deflections were again measured on the RD4, in order to see the effect of the maintenance works. The measurements were now done with a Lacroix Deflectograph, having basically the same working method as the Flash Deflectograph described above but for the measurement speed which is only 3 km/h. The results of the axis side towards Muntzenheim show 3 points which seem to be outliers.

A closer look reveals that these outliers are located at places, where the shear resistance could be weakened: The first point, at a distance of 140 m, is the point where the structure built on October 29th and the structure built on October 30th meet (see figure IV.1.20a).

It can be assumed that the high deflection at this position is related to a bad bonding between the two parts.

The second point at 240 m is at the position where grids N1 and N5 overlap, the third point at 330 m is at the position of the overlapping of the two grids N5. Here it can be assumed that the overlapping caused a particular poor bond between old and new pavement, leading to high deflections at these points.

As a whole, the axis side also shows a slight increase of the deflection on the second half of the route, as was already seen in the measurements of 2015.

The calculation of the average values, the standard deviations and the coefficient of variation will be made again for different parts of the roads. In contrast to the deflection determined in 2015, the axis and bank sides are now also divided in the travel direction, as the direction of Muntzenheim shows an important difference compared to the direction of Holtzwihr. The new section parts are:

•

IV.1.5 Comparison of the deflections measured in 2015 and 2016

The comparison of the deflections is made on the different observed sections of the observed part of the RD4, which are: Experimental and analytical study of the reinforcement of pavements by glass fibre grids We observe that the improvement due to the new surface layer is very different, depending on the direction of travel and on the side measured. The greatest distinction is noticeable between the values of section Ref 6 cm measured on the axis side. Towards Muntzenheim, the improvement due to the new surface layer is very low compared to the other sections. However, towards Holtzwihr we observe the best improvement of all.

•
Another great distinction is visible between the values on the bank side. Here, we see that towards Muntzenheim the greatest improvement made is smaller than the smallest improvement towards Holtzwihr.

A possible explanation for the smaller improvements could be a weaker or stronger bonding between the old surface and the new surface layer.

In the case of section 5 towards Holtzwihr, it should be noted that the deflection results of 2015 showed quite a weak structure. The weaker the structure at the beginning, the bigger the possible improvements after maintenance works.

The bank side showed also quite high deflection results in 2015 in both directions. A better bonding between the new layer and the old surface could have led to a stronger improvement of the deflections compared to the improvement towards Muntzenheim.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

In both cases, the direction of Holtzwihr gives better results than the direction of Muntzenheim. It can also be noted that the new layer towards Muntzenheim was built in the early morning of the 30th of October 2015, while the layer towards Holtzwihr was built in the afternoon of the same day. Knowing this, it could be assumed that the bonding has suffered from the lower temperature in the morning (about 5 • C) compared with the temperatures of the afternoon (> 10 • C).

To investigate this possibility, it was decided to extract again some specimens from the RD4. Some of them were to be used for the determination of the shear resistance between the old structure and the new layer and some for the determination of the modulus of the different courses (especially the new surface layer).

The results of the shear tests can be seen in section IV.1.5.1, the modulus of the layers are listed in section IV.1.4.4.

IV.1.5.1 Shear resistance between the old structure and the new surface layer

The test used to determine the shear resistance between the new layer and the old surface was the Leutner test, which was already described in this study (see section III.2.1). This test requires cylindrical specimens with at least two layers and a diameter of (150 ± 2) mm.

Unfortunately, the cores extracted from the RD4 only had a diameter of 140 mm to 142 mm, which hinders a comparison of the results achieved here with cores from other projects. Nevertheless, it was decided to test the cores, as a comparison between them was still interesting.

The test procedure remained identical to the normal Leutner test. The test-temperature was 20 • C.

The calculation of the shear strength was done in two different ways:

1. By dividing the determined shear force through the whole surface of the core 2. By dividing the determined shear force through a reduced surface (calcul of the reduced surface see appendix VI)

The cores extracted for this test were taken at locations where a weaken bond was awaited or where the results would be interesting for comparison purposes. shows the location of the extracted specimens.

Cores 1, 6 and 7 were extracted only for modulus-testing (see section IV.1.4.4).

Cores 2 to 5 were extracted from the lane towards Muntzenheim. Core 2 is positioned slightly beneath the place where grid N1 and N5 overlap, core 2 bis is exactly at the overlapping emplacement. Core 3 is at the overlapping of the two N5 grids, core 4 was extracted from section 5, core 5 from section Ref 6 cm -2. Core 8 is at the same height as

Experimental and analytical study of the reinforcement of pavements by glass fibre grids core 2, but on the other lane (direction Holtzwihr).

The cores were always extracted from the middle of one lane. The results of the test for each core are listed in table IV.1.14. Regarding the shear strengh calculated with the reduced surface, the highest shear strength is achieved by core n • 5, which is the only core without grid between the new surface layer and the old structure. This result confirms the investigations made in this study, concluding in the fact that grids can disturb the bonding between two asphalt layers.

The second best result is achieved by core n • 8, which is the only core on the lane towards Muntzenheim. This could confirm the idea that the warmer temperatures in the afternoon had a beneficial effect on the bonding.

The shear strength achieved by core n • 2 bis is unexpectedly high, as it was assumed that the overlapping had a particularly negative effect on the bonding. The result of core n • 2 bis is even slightly higher than the result of core n • 2, which is positioned only one meter beneath core n • 2 bis.

The results of the cores n • 2 bis, 3 and 4 are very similar.

IV.1.6 Deflections measured with the Benkelman Beam

Measurements with the Benkelman beam were made in October 2016.

The Benkelman beam (BB) is a simple deflection test. The Benkelman beam consists of a frame with an arm on a hinge, which is attached to a dial gauge, measuring the displacement of the arm in the vertical direction.

For this measurement, the rear axle of a truck with double-wheels loaded with a specific charge (here 13 tonnes rear axle load) is positioned on the point at which the deflection is sought. The arm is then positioned between the double-wheels of the truck and the value showed by the dial gauge is recorded. The truck moves forward, leading to the discharge of the point. The value showed by the dial gauge is recorded again. The difference between the loaded and unloaded value is the deflection at this position point.

Other variants exist, depending on national standards. One other possibility, for example, is to measure the point in its unloaded form first and then to reverse slowly with the truck so that the arm of the beam is positioned exactly under the double wheel. This variant is interesting regarding the unloaded measurements but its implementation is quite difficult. Compared to each other, it can be observed that the deflections measured on the bank sides are greater than the deflections measured on the axis sides, confirming the observation that the bank side is weaker than the axis side.

On the bank side towards Holtzwihr, we can also observe that the deflections of sections 5 and Ref 6 cm -2 are higher than those of the other three sections, showing again this weakening in the second half of the route. The bank side of the Muntzenheim lane shows higher results for the last two sections but has also higher values for section N1.

The axis sides show more constant deflections. Towards Muntzenheim, the smallest deflections are to be found in section Ref 6 cm, followed by section N5, with a rather high standard deviation value. The other sections show very similar deflections.

Towards Holtzwihr, section N5 shows the lowest average deflection, followed by sections 5 Apart from that, there are similarities:

Both measurement devices show rather low deflections on the axis side on both lanes.

When looking more specifically, it can be noted that for both devices, section Ref 6 cm -2 always shows the highest deflection, followed by section 5 -except for the axis side towards

Holtzwihr measured with the Benkelman beam.

Towards Muntzenheim, both devices show that section Ref 6 cm has the smallest deflections on the axis side.

The bank side of the lane towards Muntzenheim shows higher deflections with both measurement devices.

However the bank side towards Holtzwihr shows much greater results with the Benkelman beam than with the Lacroix deflectograph.

Besides the difference in the measurement method, the differences observed between the two methods can also be the result of different climatic conditions on the days of the measurements, as the measurements with the Lacroix deflectograph were done on the 11th of August at a temperature of about 30 • C while the measurements made with the Benkelman beam were made after the summer, on the 27th of October with a surface temperature being of around 9 • C .

The precipitations in the month before the measurements were in both case of about 50 mm1 . However, it also as to be noted that nearly no rain (4 mm) felt in the week before the Lacroix measurements, while the week before the Benkelman measurement had 31 mm rain.

A softening of the soil under the structure, which could influence the deflections, can, therefore, be considered, explaining the higher values of the bank side, towards Holtzwihr measured in October, compared to the values measured in August.

IV.1.7 Conclusion: Observation of the RD4

A 650 m long part of the RD4 was observed from June 2015 until the end of this thesis.

The road is located near Colmar, between the villages of Holtzwihr and Muntzenheim.

Maintenance works were made on the road in October 2015, consisting in the installation Experimental and analytical study of the reinforcement of pavements by glass fibre grids

The shear test performed on the cores of the RD4 confirmed the results obtained in this study in section III.2.1, showing that a grid at the interface will lower the shear strength of the interlayer. However, a negative influence of an overlapping of two grids on the bonding was not found.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

IV.2 Modelling of the RD4 with the modelling program BISAR

The aim of this chapter is to use the program BISAR to model the structure of the RD4 using the known deflections in the different sections as well as the thicknesses and moduli for each layer of the RD4 to distil the possible effects of the glass fibre grids on the deflections.

As the modulus of the sub-grade under the RD4 is not known and the modulus of the macadam can only be guessed, the first step of the modelling is to determine both moduli using back-calculation based on the known moduli and deflections of the unreinforced sections.

Having all moduli at 15 • C, the model is used for the reinforced sections. The modelled deflections are then be compared to the actual deflections measured with the Lacroix Deflectograph and adjusted to 15 • C.

The structure is changed until the actual and modelled deflections match, thus showing the impact of the glass fibre grids on the structure.

IV.2.1 BISAR: functioning

The program BISAR ('BItumen Structure Analysis in Roads') is a program developed by Shell research in 1970's to calculate stresses, strains and displacements in an elastic multi-layered system. The configurations and material properties required for modelling are [BISAR 98]:

• The system consists of a horizontal layer with uniform thickness resting on a semiinfinite base or half space

• The layers extend infinitely in horizontal directions

• The material of each layer is homogeneous and isotropic

• The materials are elastic and have a linear shear-strain relationship

IV.2.2 Required input for calculation

The input parameters needed for the calculation with BISAR are:

Load:

• One of the following combinations to indicate the vertical normal components of the load:

-Stress and load -Load and radius (used in this study)

Experimental and analytical study of the reinforcement of pavements by glass fibre grids -Stress and radius

• Number of loads

• Position of the load carrying point Layers:

• Number of layers

• Layer thickness (except for the lowest one)

• Elasticity modulus of each layer

• Poisson's ratio of every layer and the soil Others:

• Interface shear spring compliance at each interface (a factor defining the bonding between two layers. In cases of full bonding the factor is zero)

• The coordinates of the positions for which an output is required

IV.2.2.1 Load type

The load used for structure modelling is the load of the double-wheel of the rear axle of the Flash/Lacroix deflectograph used to determine the deflections on the RD4.

As the rear axle was loaded with a total load of 13 tonnes, each double wheel was loaded with 6.5 tonnes, i.e. 3.25 tonnes or 32.5 kN per wheel.

The contact surface of the double wheel on the road is described as a circle with a radius of 0.105 m. The distance between the centre of the circles is defined as 0.315 m.

IV.2.2.2 Poisson's ratio

The Poisson's ratio is a material parameter describing the ratio between transverse contraction strain and axial extension strain in an elastically stretched or compressed sample.

The ratio is mostly written ν and calculated as follows: When the cores were sorted according to the sections from which there were extracted, the following table can be constructed: The corresponding moduli for each section were calculated by taking a modulus of 9181 MPa for layers with a high porosity, 4889 MPa for layers with a low porosity and 7035 MPa for layers with a medium porosity (average of high and low porosity).

ν = - d trans d axial (10)
It results in the following moduli:

• Section Ref 6 cm: 9181 MPa (Std. Dev. 665.4 MPa)

• Section N1: 9181 MPa (Std. Dev. 665.4 MPa)

• Section N5: 7035 MPa (Std. Dev. 1752,1 MPa)

• Section 5: 8466 MPa (Std. Dev. 1239 MPa)

• Section Ref 6 cm -2: 4889 MPa (143 MPa)

Layer 4 The thickness of layer 4 is too small to be tested with the indirect tensile test.

Therefore the thickness of the layer 4 is added to the thickness of the macadam.

Macadam The modulus of the macadam was not determined. Therefore an empirical value had to be taken. It was chosen as 800 MPa.

IV.2.2.5 Layer thickness

The thicknesses taken for modelling are calculated using the thicknesses of the layers of the cores extracted from the respective sections, in both travel direction. This would be:

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

IV.2.3 Output

The program BISAR gives as output the radial, tangential and vertical displacements, stresses and strains at any point in the structure.

The output required in our case is the total vertical displacement on the surface of the structure, in the centre of the double-wheel. The displacement is given in [m] and is then converted in [1/100 mm] in order to be compared to the deflections measured on the RD4.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

IV.2.4 Results of modelling

IV.2.4.1 First step: Determination of the deformation modulus E v 2 of the sub-grade

The first modelling step consists in the determination of the sub-grade modulus using back-calculation.

For this purpose, we used the modulus of the known layers as well as the obtained deflections for each section measured in 2015 (before the works) and changed the modulus of the sub-grade until finding satisfactory values.

The following sub-grade moduli were determined: (table IV.2.3) It can be observed that the differences between the deflections determined with the back-calculated sub-grade moduli and the deflections measured on the RD4 in 2016 are very small.

A calculated p-value of 0.914 shows that the null-hypothesis cannot be rejected, leading to the assumption that no significant difference can be found between the differences determined in 2015 and 2016.

IV.2.4.3 Third step: Calculation of the deflections on reinforced sections and comparison with measured deflections

Now that the moduli of the sub-grade are confirmed, it can be used to model the reinforced structure, in order to see if a difference between calculated and measured deflections exists.

If it exists, it can be assumed that this difference is based on the insertion of the grid in the structure.

The deflections calculated for the 2016-structures are shown in table IV.2.5, together with the measured deflections, the difference and the coefficient of variation between the two values. The coefficient of variation shows important differences between the unreinforced and reinforced sections, as the differences between the measured deflections and the calculated deflections in unreinforced sections is lower than 0.5 [1/100 mm] whereas the differences between the measured deflections and the calculated deflections in reinforced sections are larger than 1 [1/100 mm].

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

The p-value used to compare the differences between the measured and calculated deflections is 0.0015, showing a rejection of the null-hypothesis, suggesting a significant difference between the reinforced and unreinforced values.

We also observe that the differences between the two deflection values on the reinforced sections are positive, showing that the calculated deflections are higher than the measured ones. This means that for the known structure characteristics, the structure should actually achieve higher deflections, and therefore be weaker, as it effectively is.

IV.2.4.4 Fourth step: Comparison of the deflections using best and worst structure characteristics

Up to now the comparison was based only on the average values of the deflection measured on the RD4 as well as on the average thickness and modulus values.

However, we know that variations were observed in all three parameters. In order to include these points in the comparison, the deflections were calculated using the moduli and thicknesses ± their standard deviations and compared to the measured deflections ± their standard deviations on the respective sections. The moduli of the sub-grade and the macadam were kept as given.

The standard deviations of the calculated deflections were then calculated with their average, their worst and their best results. The outcome is shown in figure IV.2.1.

Figure IV.2.1: Comparison of measured and calculated deflections with standard deviation

We observe a difference between the unreinforced sections and the reinforced sections, as the calculated deflections where no grid is placed correspond to the actually measured deflections on the RD4, while the calculated deflections of the reinforced sections show a significant difference to the actually measured deflections.

Therefore it can be assumed that all three glass fibre grids have a positive influence on the deflections. The grid showing the greatest difference is thereby grid 5, followed by grid N1

Experimental and analytical study of the reinforcement of pavements by glass fibre grids Increasing the stiffness of the new surface layer until reaching the actual measured deflection values For this part, the modulus values of all other layers, as well as the thickness of all layers, remain the same, only the modulus of the NSL is modified.

The moduli of the reinforced section, with which the actual measured deflection values are reached, are listed in table IV.2.6. The results show that for section N1, the modulus of the NSL had to be increased by 370 %, for section N5 of 88 % and for section 5 of 505 %. At this point it has to be noted that a modulus of 45 000 MPa is only theoretical and cannot be achieved practically.

Constructing a new upper layer consisting of layers NSL, 1 and glass fibre grids For this part, the thickness of layers NSL and 1 are added in order to model a unique first Compared to the initial thickness of NSL, the new thicknesses are an improvement of 85 % in section N1, 37 % in section N5 and 116 % in section 5.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

IV.2.5 Conclusion of modelling

Using the structure modelling of the RD4, we were able to see the reinforcement impact due to inserted grids, which were not visible by only looking at the deflections measured before and after the maintenance works on the RD4.

It was observed that, for the back-calculated sub-grade modulus, the differences between the calculated deflections and the measured deflections were quite important in the reinforced sections, while the unreinforced sections showed differences of less than 0.5

[1/100 mm]. The greatest difference was found in section 5 (grid with a tensile strength of 50 kN/m), followed by sections N1 (tensile strength of 100 kN/m) and N5 (tensile strength of 50 kN/m).

The structure modelling in order to reach the actual measured deflection values was possible by increasing both the stiffness of the NSL as well as the thickness of the NSL.

The determined modulus values showed that the NSL would have to have a modulus of 35 000 MPa for section N1, 14 000 MPa for section N5 and 45 000 MPa for section 5.

However, a stiffness modulus of more than 20 000 MPa as modulus at 15 • C seems very unlikely.

The description of the impact of the reinforcement as an equivalent to increasing thickness seems more suitable. In this case, it was calculated that the modelled new surface layer would have to be thicker by 85 % forr section N1, by 37 % for section N5 and by 116 % for section 5 in order to achieve the actual measured deflections.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids Part V

General conclusion

Glass fibre grids are composite materials installed in pavements in order to lengthen their lifetime by hindering crack initiation and propagation inside the structure. However, the insertion of glass fibre grids at an interface between two layers is also known to create a weakening of the interlayer bonding, which is a crucial value for the good reduction of traffic induced stresses through the structure.

This study, carried out from 2014 to 2017, dealt on the one hand with the impact of different glass fibre grids, coated with different emulsions and different emulsion application rates on the interlayer bonding strength, and on the other hand with the impact of glass fibre grids as reinforcement in asphalt structures.

The study was divided in 3 experimental parts:

Laboratory tests:

• Investigation of the shear strength

• Investigation of the stiffness modulus and fatigue life using indirect tensile tests

In-situ tests:

• Observation of the RD4 with reinforced and unreinforced road sections Shear test In the first part, shear tests carried out with the Leutner device on double layered cores extracted from an in-situ test surface showed that:

• For recommended emulsion application rates, the specimens reinforced with glass fibre grids achieved low results compared to the unreinforced specimens

• The emulsion application rate had a strong influence on the shear strength, leading to the possibility of equally strong bonds for reinforced specimen and for unreinforced specimens when enough residual binder was added at the interface • The use of a non-woven between the strands of a grid had a negative influence on the bonding

• The form of the grid strands had an influence on the bonding

• The type of emulsion used for coating have a strong influence on the bonding

• The temperature dependence of the shear resistance differs with the acting bonding effects: Interlocking: lower temperature dependency, bonding through residual binder: higher temperature dependency

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

Stiffness modulus

In the second part, the indirect tensile tests on reinforced and unreinforced specimens gave information on the acting of the reinforcement as well as on the acting of the interface inside the specimens.

Using the indirect tensile test to investigate the stiffness modulus of two-layered reinforced and unreinforced specimens, it was observed that, with a similar shear strength, the specimens of sections 600 and 650 showed a constant stiffness modulus difference of about 1100 MPa at all tested temperatures.

Specimens of section 610 on the other hand, having a weakened shear resistance compared to 600 and 650, showed a different curve shape. This differences in shape showed the influence of the temperature on the displacement happening at the interface.

The two-layered specimens were also compared to uni-layered specimens. It was observed that for temperatures under 0 • C, the moduli of the uni-layered specimens were much stiffer than the moduli of the two-layered specimens.

By comparing the strain-stress curves of all the tested specimens at all tested temperatures, it was observed that the interlayer within the two-layered specimens enabled more displacement, and so led to lower stiffness modulus, prohibiting a direct comparison of the two-layered specimens with the uni-layered specimens.

A possibility to investigate this special point could be to test two-layered specimens composed of the same asphalt mix on both sides and to compare it with the results of uni- It was seen that on reinforced specimens, the cracks expanded mainly on one side, while for unreinforced specimens, cracks could be found on both sides of the interface.

It was also observed that even for great vertical deformations, the grids of the reinforced specimens were able to hold the specimens together, while the unreinforced specimens

Experimental and analytical study of the reinforcement of pavements by glass fibre grids were falling in two parts.

In-situ-observations The RD4 is an in-situ test road, on which maintenance works were done in 2015, implying the installation of various grids at the interface between the old, cracked structure and the new surface layer.

Deflection measurements with a Flash deflectograph were made before road maintenance works and with a Lacroix deflectograph as well as with a Benkelman beam after road maintenance works.

The deflection measurements made after the maintenance works showed an improvement in the deflections on all parts of the roads, but a special distinction of a section,

showing that its characteristics (e.g. reinforcement) brought especially good or bad improvements compared to the old structure, could not be observed. It was observed that the effects of the reinforcement due to the inserted grids, which

were not visible on the deflections measured before and after the maintenance works on the RD4, became visible through modelling: For the reinforced sections, the deflections calculated with BISAR were significantly higher than the actual measured deflections on the RD4.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

In order to model the structure so that the same calculated deflections were obtained, the modulus of the new surface layer had to be increased by 370 % for section N1, 88 % for section N5 and 505 % for section 5 or the thickness of the new surface layer had to be increased by 85 % in section N1, 37 % in section N5 and 116 % in section 5.

Perspectives While clearing a few points, the study uncovered a lot of new questions, especially regarding the possibilities of connecting the different investigation points together.

The influence of the interlayer on the stiffness modulus, for example, was clearly visible on the strain-stress curves, showing that it authorized more displacements within the specimen. As the stiffness modulus is crucial for the design of road structures, it would be interesting to be able to model the influence of the interlayer, as to be able to put it apart for tests with reinforcements.

In order to better understand the debonding caused through grids, it would also be very interesting to study the behaviour of specimens under cyclic shearing tests at different temperatures. This way, it would be possible to test the specimens under more in-situ-like conditions.

The observation of the RD4 can also provide the possibility of further investigations regarding long time behaviour of the road.

Shear tests made on cores extracted from the road showed that the unreinforced section achieved the strongest shear resistance when calculated with the reduced surface, while the reinforced sections were weakened. Based on this information, it would be interesting to observe the shear strength behaviours at different time periods of the year, for example during the winter or after the summer. These observations could give an impression of possible de-bonding of the reinforced sections during the winter and possible re-bonding after the summer.

Deflection measurements, which would be done at about the same time than the extraction of the cores for shear tests, could also enable the connection between the bonding between the layers and the measured deflections.

Also, the modelling of the RD4 showed the existing influence of the grids on the deflections of the structure under a certain load. Here, it would be interesting to check how to take into account this influence, e.g. by adding a new layer in-between or by increasing the stiffness of one or more layers which could be affected by glass fibre grids. Des études faites sur les effets positifs des grilles en fibre de verre lors du renforcement des couches, la rétention de la propagation de fissures de réflexion et donc la prolongation de la durée de vie de la route, ainsi que sur les effets négatifs des grilles sur la liaison entre les différentes couches de la route, pouvant conduire à un raccourcissement de la durée de vie, sont les thèmes de cette thèse.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids De plus, il a été noté qu'un non-tissé entre les fils des grilles en fibre de verre, installé pour faciliter l'installation des grilles sur la chaussée, a une influence négative sur le collage et que les grilles ayant des fils avec une section plus hautes peuvent atteindre de plus grandes résistance au cisaillement. Experimental and analytical study of the reinforcement of pavements by glass fibre grids

Détermination du module de rigidité

XLI

Ces valeurs ont ensuite été utilisées pour la modélisation de la structure.

Modélisation BISAR

Le programme BISAR ('BItumen Structure Analysis in Roads') est un programme utilisé pour calculer les contraintes, tension et déformation dans un système élastique et multicouches.

La modélisation de la structure a été faites baser sur les propriétés connues de la RD4, c'est-à-dire :

• Le module de chaque couche sauf du macadam comme déterminer basé sur les essais de module (effectué dans un laboratoire externe)

• Le module du macadam en tant que 800 MPa (valeur empirique)

• Les hauteurs de chaque couche Dans une cinquième étape, les modules et les hauteurs de la nouvelle couche de surface ont été augmenté jusqu'à ce que les résultats mesurés sur la RD4 soit atteint. Regardant le module de la nouvelle couche de surface, il a fallu l'augmenter de 370 % dans la section N1, de 88 % dans la section N5 et de 505 % das la seciton 5 afin d'atteindre les valeurs mesurées. Regardant la hauteur de la couche de surface, il a fallu l'augmenter de 85 % dans la section N1, de 37 % dans la section N5 et de 116 % dans la section 5.

•
Experimental and analytical study of the reinforcement of pavements by glass fibre grids XLIII

Conclusion

Les tests en laboratoire ont montré un affaiblissement de la résistance de cisaillement pour les éprouvettes renforcées, mais également qu'en utilisant assez d'émulsion entre les couches, une résistance aussi bonne que sans grille pouvait être atteinte. Il a également pu être observé que la forme des grilles ainsi que l'utilisation d'un non-tissé avait une influence importante par rapport au cisaillement.

Les tests de module ont montrés une amélioration du module des éprouvettes renforcées par rapport aux éprouvettes non-renforcées quand la résistance aux cisaillement est la même. Il a également été observé que le comportement d'éprouvettes deux-couches est différentes que celui des éprouvettes uni-couches.

Les tests de fatigue ont montrés que l'insertion de grille augmenté la résistance de l'éprouvette.

Il a également été observé que le comportement de rupture des éprouvettes est différentes selon si elles ont une grille ou non.

L'observation de la section de route RD4 entre Holtzwihr est Muntzenheim est la modélisation de cette section avec le programme BISAR ont montré que les déflexions de la route été plus petites sur les sections renforcées que ce qu'elle serait sans grille. Ainsi, il a pu être observé que les grilles ont une influence positive sur la déflexion de la route.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids XLIV

Kewords:

  Flexible pavements, glass fibre grids, reinforcement, shear strength, fatigue life, stiffness modulus, deflections Zusammenfassung Diese Thesis beschäftigt sich mit der Wirkung von Glasfasergittern, die zur Verstärkung von Asphaltbefestigungen für Verkehrsflächen verwendet werden, auf den Verbund zwischen zwei Asphaltschichten, die Ermüdungslebensdauer und den Steifigkeitsmodul von verstärkten zylindrischen Probe-körpern und auf die Auslenkung, die an einem verstärkten in-situ-Straßenabschnitt gemessen werden. Die Untersuchung des Verbundes, der Ermüdungslebensdauer und des Steifigkeitsmoduls erfolgten durch Labortests. Die hierfür verwendeten Proben wurden aus einer zweischichtigen Außen-Testfläche extrahiert, bestehend aus einer unteren AC 16 Schicht mit einem 25/55-55 RC-Bitumen und einer oberen AC 11 Schicht mit dem gleichen Bitumen, zwei durchaus geläufige Deck-und Binderschichten in Deutschland. Insgesamt wurden 24 verschiedene Grenzflächenvarianten, bestehend aus zwei verschiedenen Emulsionen, drei bis vier verschiedenen Emulsionsquantitäten, 4 Glasfasergittern (1, 5, W, N) und Referenzabschnitte hergestellt und untersucht. Die Bestimmung des Verbunds erfolgte bei allen Probevariation mit dem Leutner-Test, einem zerstörenden Schertest, bei der eine Schicht der Probe mit einer konstanten Geschwindigkeit von 50 mm / min abgeschert, während die andere Schicht gehalten wird. Die Bestimmung der Ermüdungslebensdauer und des Steifigkeitsmoduls erfolgte nur auf den mit Gitter 1 und 5 verstärkten Probekörper mit der höchsten Emulsionsmenge sowie auf den unverstärkten Referenzprobekörper, ebenfalls mit der höchsten Emulsionsmenge. Der Test, der für die Ermüdungs-und Steifigkeitsmoduluntersuchung verwendet wurde, war der indirekte Spaltzugschwellversuch, bei dem eine zylindrische Asphaltprobe einer sinusförmigen zyklischen Druckspannung auf ihrer vertikalen diametralen Ebene unterworfen wurde, wodurch der Bruch der Proben durch die Aufspaltung entlang der Mitte in vertikaler Richtung bewirkt wurde. Hinsichtlich des Verbundes wurde gezeigt, dass die Ergebnisse von der Referenzproben höhere Scherfestigkeiten aufwiesen als verstärkte Probekörper, dass höhere Emulsionsmengen zu höheren Scherfestigkeiten bei verstärkten Probekörpern führen und dass die Form der Stränge der Gitter die Scherfestigkeit positiv beeinflussen kann. Hinsichtlich des Steifigkeitsmoduls wurde gezeigt, dass die mit dem Gitter 5 verstärkten Proben bei Temperaturen von -20 • C bis + 30 • C immer höhere Ergebnisse erzielten als die Referenzproben. Es wurde auch beobachtet, dass der Einfluss der Grenzfläche bei niedriger Tem-Experimental and analytical study of the reinforcement of pavements by glass fibre grids II peratur zu einem stark geschwächten Steifigkeitsmodul im Vergleich zu homogenen Proben führte. In Bezug auf die Ermüdungslebensdauer zeigte sich, dass verstärkte Proben einen längeren Lebenszyklus als Referenzproben erreichen konnten, dass aber der Unterschied auch von der Testtemperatur abhängt und für 10 • C konstanter als bei 20 • C war. Die Einsenkungsmessungen wurden auf einer französischen Landstraße mit einem Verkehr von 300 Lkw pro Tag vor und nach einer Erhaltungsmaßenahme gemessen, wobei die Arbeiten den Bau einer neuen AC 10 Asphaltdeckschicht auf dem alten Straßenaufbau als 'Verstärkung im Hocheinbau' bedeutete. Dabei wurden Teile der Straße mit verschiedenen Glasfasergittern verstärkt und mit 4 cm der neuen Deckschicht überbaut, zwei unverstärkte Referenzabschnitte wurden mit 6 cm der neuen Deckschicht gebaut. Die nach der Erhaltungsmaßnahme gemessene Einsenkung zeigte eine Verminderung der Einsenkungen auf allen Teilen der Straßen. Besondere Unterscheidung eines Abschnitts, der zeigt, dass seine Eigenschaften (z. B. Verstärkung) besonders gute oder schlechte Verbesserungen im Vergleich zu den Auslenkungen gemessen an der alten Struktur hervorgebracht haben, konnte nicht beobachtet werden. Die Ergebnisse der Einsenkungsmessungen sowie die bekannten Eigenschaften der Schichten des Aufbaus wurden verwendet, um den Aufbau zu modellieren. Es wurde gezeigt, dass der mit BISAR modellierte Aufbau Ergebnisse in der Nähe der tatsächlichen gemessenen Auslenkungen für die unverstärkten Teile lieferte, aber dass die auf verstärktem Teil berechneten Ergebnisse höher waren als die tatsächlich gemessenen Werte. Dies führte zur Annahme, dass die Gitter einen wichtigen positiven Effekt auf den Auslenkung haben können. Schlüsselworte: Glasffasergitter, Straßenverstärkung, Scherkraft, Ermüdung, Steifigkeitsmodul, Einsenkungsmessung

10 •

 10 C que pour 20 • C. Des déflexions ont été mesurées sur une route française avec un trafic de 300 poids lourds par jour avant et après les travaux d'entretien, impliquant la construction d'une nouvelle couche de surface BBSG TM et M classe 3, 0/10 sur l'ancienne structure routière.

  Experimental and analytical study of the reinforcement of pavements by glass fibre grids IV and 650, with regression curve . . . . . . . . . . . . . . . . . . . . . . . . III.2.4 Difference in average shear strength achieved under laboratory conditions and after temperature adjustment . . . . . . . . . . . . . . . . . . . . . . III.2.5 Average shear strengths against residual binder application rates with standard deviation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.2.6 Interfaces after testing: (a) smooth interface, (b) Pull out on the side, sign of a pressure area next to the actual interface . . . . . . . . . . . . . III.2.7 Position of grids on the interfaces of different specimens: (a): Grid glued on BC (81.5% of the specimens), (b): Grid on both sides (2.4 %), (c) and (d): Grid on surface course (16.1 %) . . . . . . . . . . . . . . . . . . . . . Experimental and analytical study of the reinforcement of pavements by glass fibre grids IX III.2.8 Dirt on the interface of some specimens with respective dirt-contamination degree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.2.9 Interfaces with high (0, left column) and low (3, right column) application rates (left of one picture: SC, right BC). First row: 60X, second row: 61X, third row: 65X . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.2.10 Shear strength against residual binder with standard deviation with markings of reinforced and unreinforced sections . . . . . . . . . . . . . . . . . III.2.11 Shear strength -Residual binder: A: Zoom on unreinforced sections 60X and 40X; B: Zoom on reinforced sections coated with C60B4-S; C: Zoom on reinforced sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.2.12 Shear strength -Residual binder: A: Zoom on unreinforced sections 60X and 40X; B: Zoom on reinforced sections coated with C60B4-S; C: Zoom on reinforced sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.2.13 Influence of the non-woven: Comparison of the results on sections 65X and 6WX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.2.14 Influencing components on the bonding: comparison of grids with resin A (grids 1 and 5) and B (grid N) . . . . . . . . . . . . . . . . . . . . . . . III.2.15 Influencing components on the bonding: comparison of the shape of the strands of grids 1, 5 and N. Left: strands md, Right: strands cmd . . . . III.2.16 Results of the microscopic examination of the interfaces of cores from the sections 600, 602, 610, 611, 650 and 651 with a 20-times magnification . . III.2.17 Average slope of each section group . . . . . . . . . . . . . . . . . . . . . III.2.18 Comparison of calculated parameter a, describing the influence of the temperature on the shear resistance, in ascending order. Shades of green: Interface without reinforcements, shades of red: Interface with different glass fibre grids, shades of grey: Interface with different polypropylene nonwoven and glass fibres . . . . . . . . . . . . . . . . . . . . . . . . . . . III.3.1 Tests described in the european standard 12697:26-2012 for stiffness test on hot mix asphalt [EN12697-26] . . . . . . . . . . . . . . . . . . . . . . . III.3.2 Sketch and principle of the indirect tensile test . . . . . . . . . . . . . . . III.3.3 Specimen preparation for indirect tensile test . . . . . . . . . . . . . . . . III.3.4 (a) Principle of the pre-test and (b) results of the pre-test for section 650 at 0 • C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.3.5 Regression curves: Test at 0 • C, 10 Hz, cycle 98, section 650. (a): Force against time, (b): Displacement against time . . . . . . . . . . . . . . . . III.3.6 (a) and (b) Average stiffness modulus of each step against frequency -(a): Temperatures -10 • C and 10 • C, (b) Temperatures 0 • C and 20 • C . III.3.7 Determination of the master curve by the displacement of the isotherms according to german directive [AL-Sp 09] . . . . . . . . . . . . . . . . . . Experimental and analytical study of the reinforcement of pavements by glass fibre grids X III.3.8 Regression function of the master curve of section 650 with calculated parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.3.9 Stiffness modulus -Temperature for section 600, 610 and 650 . . . . . . . III.3.10 Preparation of cylindrical specimens for stiffness modulus testing of the surface and binder courses of the test surface . . . . . . . . . . . . . . . . III.3.11 Stiffness modulus -Temperature for surface and binder courses (SC and BC), two layered specimens 600, 610 and 650 and for comparison purposes calibrating binder and surface asphalt of RDO 09 (CBC and CSC) . . . . III.3.12 Stress-strain graphs of the test carried out on the specimens of sections 600, 610 and 650 at 10 Hz (upper graphs) and 0.1 Hz (lower graphs) at -10 • C and 0 • C (left graphs) and 10 • C and 20 • C (right graphs) . . . . III.3.13 Extraction of specimens from slabs in the study of Hofko et al. [HOF 16] III.3.14 Stiffness modulus -Temperature: Increased SC and BC values by 23 % due to anisotropy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.3.15 Stress-strain graphs of the test carried out on the specimen of section 600, 610 and 650 (two-layered specimens) and SC and BC (uni-layered specimens) at 10 Hz (upper graphs) and 0.1 Hz (lower graphs) at -10 • C and 0 • C (left graphs) and 10 • C and 20 • C (right graphs) . . . . . . . . III.3.16 Slope difference between uni-layered and two-layered specimens in percentage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.4.1 Typical evolution of the modulus of a asphalt material under repeated loading [ARS 13] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.4.2 Test specimen inserted in the fatigue testing device . . . . . . . . . . . . . III.4.3 Fatigue curves at 20 • C and 10 Hz . . . . . . . . . . . . . . . . . . . . . . III.4.4 Fatigue curves at 10 • C and 10 Hz . . . . . . . . . . . . . . . . . . . . . . III.4.5 Photos of uni-layered and two-layered reinforced and unreinforced specimens during repeated loading test . . . . . . . . . . . . . . . . . . . . . . IV.1.1 (a) Localisation of the RD4 and (b) aerial photograph of the RD4 (Map data c 2017 Google and c 2017 GeoBasis-DE/BKG ( c 2009), Google, Holtzwihr) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV.1.2 Cores, location of the cores and purpose of the cores extracted from the RD4 before road maintenance works . . . . . . . . . . . . . . . . . . . . . IV.1.3 Core of the RD4 with the different layers . . . . . . . . . . . . . . . . . . IV.1.4 Photographs of the RD4 before maintenance and location of the pictures taken (map on the right, second line) . . . . . . . . . . . . . . . . . . . . IV.1.5 Deflectograph Flash and Lacroix: Truck and measuring device [VEC 17] . IV.1.6 Principle of the deflection measurement . . . . . . . . . . . . . . . . . . . IV.1.7 Deflection measured on the RD4 in June 2015 . . . . . . . . . . . . . . . IV.1.8 Five sections and characteristics of each of the observed RD4 . . . . . . . Experimental and analytical study of the reinforcement of pavements by glass fibre grids XI IV.1.9 RD4 maintenance works: Construction steps: (a): Emulsion sprayer at the beginning of the construction works; (b): Difference in emulsion application rate, left: section N1, right: section Ref 6 cm; (c) Application of grid 5 in the curve (d) Finished road . . . . . . . . . . . . . . . . . . . IV.1.10 RD4: Small pull-outs and small bitumen accumulations . . . . . . . . . . IV.1.11 RD4: Medium and big bitumen accumulations . . . . . . . . . . . . . . . IV.1.12 RD4: Crack at the centre line . . . . . . . . . . . . . . . . . . . . . . . . . IV.1.13 RD4: Pull-outs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV.1.14 RD4: Superficial, very straight crack . . . . . . . . . . . . . . . . . . . . . IV.1.15 RD4: Crack between the section built in on 29/10/15 and the section built on 30/10/15 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV.1.16 Cores extracted on the RD4; Cores with a letter as name: Extracted in 2015, Cores with a number: Extracted in 2017 . . . . . . . . . . . . . . . IV.1.17 Thickness of the different layers of the cores extracted from the RD4 . . . IV.1.18 Modulus of the different layers of the RD4 . . . . . . . . . . . . . . . . . . IV.1.19 Layer 3 sorted depending on the visible porosity, with respective modulus IV.1.20 Deflection measured on the RD4 in August 2016 . . . . . . . . . . . . . . IV.1.21 Average deflections of each section measured on the axis side in both directions in 2015 and 2016 with std dev. . . . . . . . . . . . . . . . . . . IV.1.22 Average deflections of each section measured on the bank side in both directions in 2015 and 2016 with std dev. . . . . . . . . . . . . . . . . . . IV.1.23 Difference [%] between the deflections measured in 2015 and 2016 . . . . IV.1.24 Emplacement of the cores extracted for Leutner test on the RD4 . . . . . IV.1.25 Graphical representation of the shear strength achieved by the cores of the RD4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV.1.26 Principle of the Benkelman beam [THO 14] . . . . . . . . . . . . . . . . . IV.1.27 Average deflections of the different sections measured with Benkelman beam (upper graph) and Lacroix deflectograph (lower graph) . . . . . . . IV.2.1 Comparison of measured and calculated deflections with standard deviation133 VI.2.7 Leutner: Calculation of the working surface A . . . . . . . . . . . . . . . XXXI Experimental and analytical study of the reinforcement of pavements by glass fibre grids XII LIST OF TABLES List of TablesI.1.1 Suitability of repair methods for different damage forms [STR 09] . . . . I.2.1 Properties of glass fibres, type E. [RIC 11] . . . . . . . . . . . . . . . . . . I.2.2 Properties of the resin given by the manufacturer . . . . . . . . . . . . . . III.1.1 Characteristics of the glass fibre grids installed on the test surface . . . . III.1.2 Characteristics of the emulsions used on the test surface . . . . . . . . . . III.1.3 Results of dynamic plate load tests on test surface . . . . . . . . . . . . . III.1.4 Characteristics of the lower asphalt layer of the test surface . . . . . . . . III.1.5 Characteristics of the upper asphalt layer of the test surface . . . . . . . . III.1.6 Characteristics of the sections of the test surface . . . . . . . . . . . . . . III.2.1 Shear tests at different temperatures . . . . . . . . . . . . . . . . . . . . . III.2.2 Shear strength results of specimens coated with C60B4-S . . . . . . . . . III.2.3 Shear strength results of specimens coated with C40B5-S . . . . . . . . . III.2.4 Specimens and their respective dirt contamination degree • DC . . . . . . III.2.5 Loss in shear strength due to the insertion of grids in compared withunreinforced specimens . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.2.6 Shear strength results of specimens Canestrari et al. at different temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.2.7 Shear strength results of specimens Vismara et al. at different temperatures III.3.1 Result Moduli at -10 • C, two-layered specimens 600, 610 and 650 . . . . . III.3.2 Result Moduli at 0 • C, two-layered specimens 600, 610 and 650 . . . . . . III.3.3 Result Moduli at 10 • C, two-layered specimens 600, 610 and 650 . . . . . III.3.4 Result Moduli at 20 • C, two-layered specimens 600, 610 and 650 . . . . . III.3.5 Parameters for the creation of the sigmoid curve and stiffness modulus values for different temperatures at 10 Hz -section 600, 610 and 650 . . . III.3.6 Result Moduli at -10 • C, surface and binder courses . . . . . . . . . . . . III.3.7 Result moduli at 0 • C, surface and binder courses . . . . . . . . . . . . . III.3.8 Result moduli at 10 • C, surface and binder courses . . . . . . . . . . . . . III.3.9 Result moduli at 20 • C, surface and binder courses . . . . . . . . . . . . . III.3.10 Parameters for the creation of the sigmoid curve and stiffness modulus values for different temperatures at 10 Hz -surface and binder courses . . III.3.11 Shear strength of sections 600, 610 and 650 at different temperatures . . . III.3.12 Slopes of the stress-strain regression curve for every specimen at the four temperatures and two frequencies (10 Hz and 0.1 Hz). The cell colours represents the steepness of the slopes: green: flattest curve, more displacement in the specimen, yellow: middle curve, orange: steepest curve. Experimental and analytical study of the reinforcement of pavements by glass fibre grids XIII III.3.13 Slope of the stress-strain regression curve of sections 600,610 and 650, summarized as two-layered specimens, and SC and BC, summarized as uni-layered specimens, for all temperatures and two frequencies (10 Hz and 0.1 Hz). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III.4.1 Stress levels chosen for the fatigue tests at 10 • C . . . . . . . . . . . . . . III.4.2 Stress levels chosen for the fatigue tests at 20 • C . . . . . . . . . . . . . . III.4.3 Results of the fatigue tests made at 20 • C . . . . . . . . . . . . . . . . . . III.4.4 Results of the fatigue tests made at 10 • C . . . . . . . . . . . . . . . . . . IV.1.1 Maximum aggregate size and fine content of aggregates of layers 2 and 3 of the RD4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV.1.2 Results of needle penetration test on the bitumen of the 3 asphalt layers of the RD4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV.1.3 Results of Ring and Ball test on the bitumen of the 3 asphalt layers of the RD4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV.1.4 Change of different bitumens characteristics over 15 years . . . . . . . . . IV.1.5 Bitumen values of RD4 before and after the use of an ageing correction factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV.1.6 Void, binder, aggregate and fine contents of the three layers of the core extracted from the RD4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV.1.7 Average values, standard deviations and coefficients of variation of the deflection measured on the RD4 in 2015 . . . . . . . . . . . . . . . . . . . IV.1.8 Characteristics of the glass fibre grids installed on the RD4 . . . . . . . . IV.1.9 Average thickness of the layers of the old structure with standard deviation and coefficient of variation . . . . . . . . . . . . . . . . . . . . . . . . IV.1.10 Average modulus of the layers with standard deviation and coefficient of variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV.1.11 Average values, standard deviations and coefficients of variation of the deflection measured on the RD4 in 2016 . . . . . . . . . . . . . . . . . . . IV.1.12 Comparison of the average deflection of each section measured in 2015 and 2016 on the axis side towards Muntzenheim and Holtzwihr, with standard deviation (Std Dev), coefficient of variation (Coef. of Var.) and the calculation of the difference between the two measurements in [1/100 mm] and [%] of the 2015-values . . . . . . . . . . . . . . . . . . . . . . . . IV.1.13 Comparison of the average deflection of each section measured in 2015 and 2016 on the bank side towards Muntzenheim and Holtzwihr, with standard deviation (Std Dev), coefficient of variation (Coef. of Var.) and the calculation of the difference between the two measurements in [1/100 mm] and [%] of the 2015-values . . . . . . . . . . . . . . . . . . . . . . . . IV.1.14 Shear strength results of the cores extracted from the RD4 . . . . . . . . Experimental and analytical study of the reinforcement of pavements by glass fibre grids

  Experimental and analytical study of the reinforcement of pavements by glass fibre grids (b) On the stiffness modulus of reinforced and unreinforced two-layered specimens, determined with cyclic indirect tensile tests (c) On the fatigue life of reinforced and unreinforced specimens during cyclic indirect tensile tests. 4. Observations made on an in-situ road section before and after maintenance works, during which different grids were installed between the old road structure and the new surface layer. 5. The modelling of the in-situ road section in order to recognize the effect of the glass fibre on the deformations of the road. Experimental and analytical study of the reinforcement of pavements by glass fibre grids Part I Generals I.1 Road pavements: Materials and structures A road usually consists of different layers, bonded to each other to give a complex unit.

I

  .1.2 Road structure I.1.2.1 Different layers of the structure The different layers of a road structure are shown in figure I.1.1.

Figure I.1. 1 :

 1 Figure I.1.1: Example of a typical asphalt pavement structure

  Figure I.1.2: Three factors of bonding: Indentation, adhesion and friction

Figure I.1. 3 :

 3 Figure I.1.3: Modelling of the loss of interlayer bonding in a three layered asphalt structure at two different temperatures [AIF 07]

•

  Traffic: load and movements • Weather and climate change • Time Each of these causes will lead to different sorts of damages which can cause the deterioration of a road. I.1.3.1 Traffic loads and movements Traffic loads have two different effects on the structure: 1. Vertical loads through the weight of the vehicles. Vertical loads are transmitted via the tyres of the vehicles and have therefore shapes similar to an ellipse or a circle. A small car can have a wheel load of 1 kN while the maximum wheel load for a truck in Germany is of 57.5 kN (maximum axle load of 11.5 tonnes) and of 67.5 kN in France (maximum axle load of 13.5 tonnes with double wheels). For moving vehicles, the vertical load operates as a dynamic load. The dynamic load proportion is dependent on different factors such as irregularities of the road surface, speed of the vehicles and vehicle construction (suspension, damping and tyres) [VEL 13]. 2. Horizontal loads through acceleration and deceleration as well as in ascents and curves Experimental and analytical study of the reinforcement of pavements by glass fibre grids I.1 ROAD PAVEMENTS: MATERIALS AND STRUCTURES Damages caused by traffic loads and movements induce principally deformation of the road surface and the formation of cracks. Deformation will appear mostly in form of ruts (see figure I.1.4), describing a longitudinal surface depression of the asphalt in the wheel path. Rutting can have multiple causes, as traffic compaction or displacement of unstable asphalt, base or subgrade consolidation, a low air void design, excessive amounts of asphalt binder, sand, mineral filler or rounded aggregate particles or an insufficient structural strength [LAV 03].The form of the ruts can show the probable cause: ruts with a small radius are mostly caused by a disorder in the bituminous layers, ruts with a larger radius are mostly the result of a disorder in the soil.

Figure I.1. 4 :

 4 Figure I.1.4: Ruts on a road [AP9 15]

1.

  Traffic load and number of passages 2. Stiffness modulus of the layers 3. Thickness of the layers 4. Stiffness of the subgrade soil Experimental and analytical study of the reinforcement of pavements by glass fibre grids

Figure I.1. 5 :

 5 Figure I.1.5: Repartition of stress and strains in a road structure under traffic loading

  Crack sealing The sealing of cracks, open joint and open gaps is done with a bituminous mastic (bitumen and filler) which is poured in the opening, as represented in figure I.1.6.

Figure

  Figure I.1.6: Crack sealing

Figure I.1. 7 :

 7 Figure I.1.7: Reprofiling of a surface with deformation due to rutting

Figure I.1. 8 :

 8 Figure I.1.8: Sketch of the surface dressing [STR 09]

Figure I.1. 9 :

 9 Figure I.1.9: Schematic figure of hot in-situ recycling of asphalt [THO 14]

  period of 50 ms between the loadings. The test device is illustrated in figure II.1.1.

Figure

  Figure II.1.1: Schematic test set-up used by Nejad et al.

Figure II.1. 2 :

 2 Figure II.1.2: Strain maps of [ROM 14]

  Experimental and analytical study of the reinforcement of pavements by glass fibre grids II.1.1.2 Full-scale observations In their study of 2013, Nguyen et al. [NGU 13] showed inter alia the results of their investigation made on the IFSTTAR APT facility, consisting in testing new reinforced pavements in a full-scale test. The IFSTTAR APT facility is a large pavement fatigue carousel in Nantes shown in figure II.1.3.

Figure II.1. 3 :

 3 Figure II.1.3: Pavement fatigue carousel at IFSSTAR in Nantes, France [NGU 13]

Figure II.1. 4 :

 4 Figure II.1.4: Example of a monotonic indirect tensile tests carried out on reinforced and unreinforced specimens of the study of Vismara et al. [VIS 12]

  Arsenie et al. observed that the geogrid was able to increase the fatigue life N f by 50 % based on individual tests to 62 % based on fatigue curves. They also observed that the tensile strains of the reinforced specimens increased by 10.52 % and the fatigue curve slope increased by 11.55 %.II.2 Effect of glass fibre grids on the interlayer bondingIn the same study, Ferrotti et al. [FER 12] conducted ASTRA shear tests on unreinforced and reinforced specimens. The ASTRA device ('Ancona Shear Testing Research and Analysis') is a direct shear box in which the cylindrical, double-layered asphalt specimen is positioned so, that the interlayer is positioned in the unconfined interlayer shear zone (see figure II.2.1).

Figure

  Figure II.2.1: ASTRA device [FER 12]

Ferrotti

  et al. were able to observe that the specimens without the grid offered the highest pure shear resistance values, showing that the presence of a grid generated a reduction in interlayer resistance. As Ferrotti et al. also varied the different coating treatments, they could also observe that some surface coatings were able to maximize the interlayer bonding of reinforced specimens. With this results, Ferrotti et al. were able to confirm other studies showing that the insertion of a geotextile or a grid had a negative influence on the bonding between two layers. Vismara et al. [VIS 12] characterized in 2012 the effect of geosynthetics in Asphalt pavements at different temperatures.

  2.1, at 5 • C and 25 • C. Vismara et al. observed that for both test temperature, the shear strength values of unreinforced specimens were higher than the shear strength values of reinforced specimens. Dietlind Jacobs summarized in his paper of 2010 [JAC 10] the results of some shear tests made in Switzerland on reinforced and unreinforced specimens, using researches done by Sokolov in 2007 [SOK 07], Raab in 2007 [RAAB 07] and Raab and Partl in 2004 [RAAB 04]. The device used in all tests was an LPDS, standing for 'Layer-Parallel Direct Shear', which function is similar to the Leutner test device.

Figure II.2. 2 :

 2 Figure II.2.2: Overview of measured shear forces in different analysis [JAC 10]

  2010, Zamora-Barraza et al. [ZAM 10] investigated new procedures for measuring the adherence between geosynthetic materials and asphalt layers. To do so, they decided to develop a new test, consisting of 3 layered slabs made of the same asphalt mixture.Geotextiles and tack coat were applied on both interlayers between the asphalt layer. The test consisted of applying a load with a deformation rate of 5 mm/min on the middle Experimental and analytical study of the reinforcement of pavements by glass fibre grids layer, while holding the two other layers (see figure II.2.3).

Figure II.2. 3 :

 3 Figure II.2.3: Test device of Zamora-Barraza et al. to investigate the interlayer bonding

Figure II.2. 4 :

 4 Figure II.2.4: Variation of adherence stress for the reference specimens and the reinforced specimens

Figure

  Figure III.1.1: Draft of a grid installed on the test surface

III.1. 3

 3 Dimensions of the test surface The test surface was 22 m large and 5.8 m wide and was divided in 5 different lanes of 1 m each with a border of 40 cm in the breadth and at least 1 m in the length. An outline of the test surface is shown in figure III.1.2.

Figure III.1. 2 :

 2 Figure III.1.2: Outline of the test surface

Figure III.1. 3 :

 3 Figure III.1.3: Construction of lower layer: Finisher on unbound granular base course, test surface, compaction of the surface

Figure

  Figure III.1.4 shows pictures of the test surface after drilling and sawing.

Figure

  Figure III.1.4: Test surface after the extraction of the specimens

•

  Shear test (with or without normal stress): The shear test consists in holding one layer of the specimen while the other layer is loaded with a constant displacement speed until failure occurs. This test can be conducted with a normal stress applied to the specimen, which is more representative of in-situ loads. An example of a device enabling the application of normal stress can be found in [AIF 07].

Figure III.2. 1 :

 1 Figure III.2.1: Destructive tests to investigate the interlayer bonding strength [CAN 13]

  During the test, the binder course of the core is fixed while the wearing course is loaded with a constant shear displacement rate of 50 mm/min until failure occurs. The displacement, shear force and shear stress are measured during the tests. A schematic sketch, as well as a picture of the machine, are displayed in figure III.2.2.

Figure III.2. 2 :

 2 Figure III.2.2: Leutner test: picture and schematic sketch of the machine

Figure

  Figure III.2.4: Difference in average shear strength achieved under laboratory conditions and after temperature adjustment

  The average shear strengths achieved by each section for a given quantity of residual binder are shown in figure III.2.5 (see also appendix II). The orange curves represent the sections coated with C40B5-S and the blue curves the sections coated with C60B4-S.

Figure

  Figure III.2.5: Average shear strengths against residual binder application rates with standard deviation

  Figure III.2.6: Interfaces after testing: (a) smooth interface, (b) Pull out on the side, sign of a pressure area next to the actual interface

  Figure III.2.8: Dirt on the interface of some specimens with respective dirtcontamination degree

Figure

  Figure III.2.9: Interfaces with high (0, left column) and low (3, right column) application rates (left of one picture: SC, right BC). First row: 60X, second row: 61X, third row: 65X

  of the results III.2.4.1 Influence of glass fibre grids on the interlayer bonding In figure III.2.10 the reinforced and unreinforced sections are marked. As mentioned before, it can be seen that no reinforced section (red box) can reach the minimum average values of the unreinforced sections (green box), apart from the strongly overdosed section 650 (1638 g/m 2 of residual binder).

Figure III.2. 10 :

 10 Figure III.2.10: Shear strength against residual binder with standard deviation with markings of reinforced and unreinforced sections

Figure

  Figure III.2.11: Shear strength -Residual binder: A: Zoom on unreinforced sections 60X and 40X; B: Zoom on reinforced sections coated with C60B4-S; C: Zoom on reinforced sections

Figure

  Figure III.2.11b showsthe reinforced sections coated with C60B4-S, being 61X, 65X

Figure

  Figure III.2.12: Shear strength -Residual binder: A: Zoom on unreinforced sections 60X and 40X; B: Zoom on reinforced sections coated with C60B4-S; C: Zoom on reinforced sections

  Figure III.2.13: Influence of the non-woven: Comparison of the results on sections 65X and 6WX

Figure III.2. 14 :

 14 Figure III.2.14: Influencing components on the bonding: comparison of grids with resin A (grids 1 and 5) and B (grid N)

Figure

  Figure III.2.15: Influencing components on the bonding: comparison of the shape of the strands of grids 1, 5 and N. Left: strands md, Right: strands cmd

Figure

  Figure III.2.16: Results of the microscopic examination of the interfaces of cores from the sections 600, 602, 610, 611, 650 and 651 with a 20-times magnification

III. 2

 2 .4.8 Influence of reinforcement at the interface on the shear resistancetemperature behaviour For comparative purposes, the results obtained in this study (see section III.2.2) were compared with the values obtained by Canestrari et al. [CAN 13] and Vismara et al. [VIS 12]. Leutner Test perfomed by Canestrari et al. In their study from 2013, Canestrari et al. [CAN 13] observed the influence of different interface treatments on the shear resistance of double layered specimens. For this purpose, a test surface was constructed consisting of a lower asphalt layer with a nominal maximum aggregate size of 16 mm and a 70/100 bitumen and an upper asphalt layer with a nominal maximum size of 11 and the same bitumen type.

  1 are: Pavement 1: a = -0.021 Pavement 2: a = -0.025 Pavement 3: a = -0.024 It can be observed that first the values of a are relatively close to each other for all 3 pavements, and second that all three values are almost identical to the value of section 600 with a= -0.025. Leutner Tests performed by Vismara et al. Vismara et al. observed in their study of 2012 [VIS 12] the influence of different reinforcements installed on the interface between two asphalt layers on the shear resistance and compared it with an unreinforced specimen variant.

  Reinforcement A: a = -0.0403 Reinforcement B: a = -0.0548 Comparison of parameter a, describing the influence of the temperature on the shear resistance Figure III.2.18 plots all calculated a-parameters determined with the values of Canestrari et al., Vismara et al. and of this study. The different colours are a reference to the existing interface conditions: green columns indicate an interface without reinforcement, red with glass fibre grids and grey with polypropylene non-woven and glass fibres.

Figure

  Figure III.2.18: Comparison of calculated parameter a, describing the influence of the temperature on the shear resistance, in ascending order. Shades of green: Interface without reinforcements, shades of red: Interface with different glass fibre grids, shades of grey: Interface with different polypropylene nonwoven and glass fibres

  Europe, the European standard EN 12697-26:2012 [EN12697-26] specifies the various methods used to determine the stiffness of asphalt. The tests described in the standard are shown in figure III.3.1. These tests are: • Bending tests: -2PB-TR: Two point bending tests on trapezoidal specimens -2PB-PR: Two point bending tests on prismatic specimens -3PB-PR: Three point bending tests on prismatic specimens -4PB-PR: Four point bending tests on prismatic specimens • Indirect tensile tests: -IT-CY: Indirect tensile tests on cylindrical specimens -CIT-CY: Test with indirect cyclic tensile load of the specimens • Direct uniaxial tests -DTC-CY: Uniaxial tension-compression tests on cylindrical specimens -DT-CY: Direct tensile tests on cylindrical specimens -DT-PR: Direct tensile tests on prismatic specimens Experimental and analytical study of the reinforcement of pavements by glass fibre grids

Figure III.3. 1 :

 1 Figure III.3.1: Tests described in the european standard 12697:26-2012 for stiffness test on hot mix asphalt [EN12697-26]

Figure III.3. 2 :

 2 Figure III.3.2: Sketch and principle of the indirect tensile test

Figure

  Figure III.3.3 pictures the extraction steps as well as the specimen after extraction.

Figure III.3. 3 :

 3 Figure III.3.3: Specimen preparation for indirect tensile test

  compression stress was increased by 0.2 MPa, starting from an initial maximum stress of 0.2 MPa and carried out until reaching maximum horizontal strains of 0.2 . The horizontal deformation of the specimen during the test was measured by two extensometers placed on the lateral surface (see figure III.3.2). The stress was selected in such a way that plastic deformations do not occur in the specimen. The resulting strains should correspond to approximately 0.10 . An example of the 3 cycles of the 3 first steps of the pre-test as well as the result of one pre-test is shown in figure III.3.4.

Figure

  Figure III.3.4: (a) Principle of the pre-test and (b) results of the pre-test for section 650 at 0 • C

WithF

  Figure III.3.5: Regression curves: Test at 0 • C, 10 Hz, cycle 98, section 650. (a): Force against time, (b): Displacement against time

  Figure III.3.6: (a) and (b) Average stiffness modulus of each step against frequency -(a): Temperatures -10 • C and 10 • C, (b) Temperatures 0 • C and 20 • C

Figure III.3. 7 :

 7 Figure III.3.7: Determination of the master curve by the displacement of the isotherms according to german directive [AL-Sp 09]

  With α T : Shift factor E a : activation energy [J/mol] Experimental and analytical study of the reinforcement of pavements by glass fibre grids R: universal gas constant (R=8.314 J/mol) [J/mol] T: Temperature of the wanted stiffness modulus to be calculated (actual temperature) [K] T 0 : Temperature of the master curve. The chosen reference temperature should be 20 • C (293.15 K). [K]

WithE:

  Stiffness modulus [MPa] y 0 : Intersection of the function with the y-axis [Hz] x 0 : Intersection of the function with the x-axis [MPa] x: arbitrary value on the x-axis, log(α T ) [Hz] w: Material parameter [MPa] z: Material parameter [-] The five unknown parameters x 0 , y 0 , w, z and E a are calculated by searching for the minimum residual sum of square with the solver function of Microsoft Excel. The master curve of section 650 with the determined and calculated data points and the values of the different parameters is shown in figure III.3.8.Experimental and analytical study of the reinforcement of pavements by glass fibre grids

Figure

  Figure III.3.8: Regression function of the master curve of section 650 with calculated parameters

Figure III.3. 9 :

 9 Figure III.3.9: Stiffness modulus -Temperature for section 600, 610 and 650

  composing the specimens themselves, indirect tensile tests were carried out on specimens composed of only the surface or binder layer. Unlike the two-layer specimens, the specimens used to determine the stiffness modulus of the surface and binder courses were drilled directly from the test surface. The average diameter of the specimens was 99 mm, their average length was 55 mm. The extraction and cutting steps are shown in figure III.3.10.

Figure III.3. 10 :

 10 Figure III.3.10: Preparation of cylindrical specimens for stiffness modulus testing of the surface and binder courses of the test surface

Figure

  Figure III.3.12: Stress-strain graphs of the test carried out on the specimens of sections 600, 610 and 650 at 10 Hz (upper graphs) and 0.1 Hz (lower graphs) at -10 • C and 0 • C (left graphs) and 10 • C and 20 • C (right graphs)

Figure

  Figure III.3.11 shows the curve of the respective stiffness moduli as a function of the temperature.

  frequencies. The corresponding graphs are shown in figure III.3.15.

Figure III.3. 15 :

 15 Figure III.3.15: Stress-strain graphs of the test carried out on the specimen of section 600, 610 and 650 (two-layered specimens) and SC and BC (uni-layered specimens) at 10 Hz (upper graphs) and 0.1 Hz (lower graphs) at -10 • C and 0 • C (left graphs) and 10 • C and 20 • C (right graphs)

Figure III.3. 16 :

 16 Figure III.3.16: Slope difference between uni-layered and two-layered specimens in percentage

•

  their study of 2004, Di Benedetto et al. [DI BEN 04] divide the fatigue development into three characterizing phases: • Phase I or adaptation phase: A strong loss of stiffness modulus and the creation of micro-cracks due to the repeated loading as well as to thixotropy and material warming. Phase II or quasi-stationary phase: The evolution of the stiffness modulus stays nearly constant, while the cracks spreads and distribute themselves inside the structure • Phase III or failure phase: Phase during which the damage due to cracking accelerates. The micro-cracks become macro-cracks and spread through the structure, leading to failure of the structure. These phases are illustrated in figure III.4.1.

Figure III.4. 1 :

 1 Figure III.4.1: Typical evolution of the modulus of a asphalt material under repeated loading [ARS 13]

  8) With E N : Stiffness modulus at cycle N Experimental and analytical study of the reinforcement of pavements by glass fibre gridsE init : Stiffness modulus measured at the beginning of the test, average of cycles 98 to 102

Figure III.4. 2 :

 2 Figure III.4.2: Test specimen inserted in the fatigue testing device

Figure III.4. 3 :

 3 Figure III.4.3: Fatigue curves at 20 • C and 10 Hz

  The pictures represented in figure III.4.5 (see also appendix IV) show the 5 specimens at 5 different moments of the tests, showing the different advancements, beginning at the first cycle and ending when the maximum 7 mm vertical displacement was reached.

  Figure III.4.5: Photos of uni-layered and two-layered reinforced and unreinforced specimens during repeated loading test

  Experimental and analytical study of the reinforcement of pavements by glass fibre grids Part IV In-situ observations IV.1 In situ observations: RD4 IV.1.1 RD4: Informations and characteristics The in-situ observations were carried out on a 800 m long road section in France, named RD4 ('Route Départementale' n • 4) near the town of Colmar. The purpose was to investigate the impact of the installation of grids on a cracked road section. To do so, the test section was monitored before and after road maintenance works, which took place in October 2015. The section of the RD4 observed in this study is located in the department 'Haut Rhin' in the north east of France, between the villages of Holtzwihr/Wickerschwihr and Muntzenheim in an agricultural region. The road has one lane in each direction and a heavy traffic circulation of 300 a day (total of the two lanes). A map of the location and an aerial photograph of the section are shown in figure IV.1.1.

Figure

  Figure IV.1.1: (a) Localisation of the RD4 and (b) aerial photograph of the RD4 (Map data c 2017 Google and c 2017 GeoBasis-DE/BKG ( c 2009), Google, Holtzwihr)

Figure

  Figure IV.1.2: Cores, location of the cores and purpose of the cores extracted from the RD4 before road maintenance works

  Longitudinal cracks on the right wheel track • Crocodile cracks (especially at the end of the section in direction Muntzenheim, on both lanes) Pictures of the section before road maintenance works can be seen in figure IV.1.4.

Figure

  Figure IV.1.4: Photographs of the RD4 before maintenance and location of the pictures taken (map on the right, second line)

Figure IV.1. 5 :

 5 Figure IV.1.5: Deflectograph Flash and Lacroix: Truck and measuring device [VEC 17]

Figure IV.1. 6 :D 15 : 15 ••

 61515 Figure IV.1.6: Principle of the deflection measurement

  Figure IV.1.7a shows all values measured on both sides of the road and under both double-wheels of the deflectograph (bank and axis).

Figure

  Figure IV.1.7b shows the measurement made under the left double-wheel (axis) and figure IV.1.7c shows the measurements done under the right double-wheel (bank).

  (a)Deflection measured in the direction Holtzwihr and Muntzenheim on axis and bank sides. (b)Deflection measured in the direction Holtzwihr and Muntzheim on axis sides and moving average curves (c)Deflection measured in the direction Holtzwihr and Muntzheim on bank sides and moving average curves

Figure

  Figure IV.1.7: Deflection measured on the RD4 in June 2015

  Part 1: 0 m to 400 m, Part 2: 405 m to 580 m Part 3: 585 m to 650 m • Measurements on bank sides: Part 1: 0 m to 350 m, Part 2: 355 m to 450 m Part 3: 455 m to 650 m

Figure IV.1. 8 :

 8 Figure IV.1.8: Five sections and characteristics of each of the observed RD4

Figure

  Figure IV.1.9: RD4 maintenance works: Construction steps: (a): Emulsion sprayer at the beginning of the construction works; (b): Difference in emulsion application rate, left: section N1, right: section Ref 6 cm; (c) Application of grid 5 in the curve (d) Finished road

First

  Figure IV.1.10: RD4: Small pull-outs and small bitumen accumulations

Figure IV.1. 11 :

 11 Figure IV.1.11: RD4: Medium and big bitumen accumulations

Figure IV.1. 16 :

 16 Figure IV.1.16: Cores extracted on the RD4; Cores with a letter as name: Extracted in 2015, Cores with a number: Extracted in 2017

Figure IV.1. 17 :

 17 Figure IV.1.17: Thickness of the different layers of the cores extracted from the RD4

  IV.1.4.4 Elastic modulus of the different layers of the RD4 The moduli of the different layers were determined with the indirect tensile test in the laboratory of Cerema, Direction territoriale Est and are represented in figure IV.1.18, based on European standard NF EN 12697-26, appendix C [EN12697-26]. The tests were made at 10 Hz and at test temperatures of 10 • C and 15 • C. Based on the standard NF P 98-086 [NF P 98-086], the average of both values was taken as modulus at an equivalent temperature of 15 • C at 10 Hz.

Figure

  Figure IV.1.18: Modulus of the different layers of the RD4

  Experimental and analytical study of the reinforcement of pavements by glass fibre grids • The bitumen • The temperature • The test speed or test frequency • The mixture proportions used As the testing parameters stay the same for all tests and the bitumen as well as the mixture proportions should actually not vary within the layer, it should be assumed that none of these points explain the changes within the layers. When looking in figure IV.1.18, we observe that the changes in layer 1 take place between section Ref 6 cm -2 and the rest of the road: The modulus determined on cores 6 and C (section Ref 6 cm -2) are above 8000 MPa, while the modulus determined on cores 1 and 7 are below 5000 MPa. For layer 3, we observe a change of modulus going along with a change in the material structure of the cores. When looking closely at layer 3 of cores A and 7 (see figure IV.1.19), we observe a strong presence of voids in the layer. On the other hand layer 3 of cores D, 6 and 5 shows no voids.When comparing this fact with the modulus, we observe that cores A and 7 show a layer 3 modulus much higher (> 8000 MPa) than that of cores D, 6 and 5 (4738 MPa -5023 MPa).

Figure

  Figure IV.1.19: Layer 3 sorted depending on the visible porosity, with respective modulus

  The temperature adjustment was done as described before. The graphs representing the deflection on bank and axis sides in both directions, as well as the graphs showing the moving average curves of the axis and bank sides are shown in figure IV.1.20.

  (a)Deflection measured towards Holtzwihr and Muntzenheim on axis and bank sides. (b)Deflection measured towards Holtzwihr and Muntzheim on axis sides and moving average curves (c)Deflection measured towards Holtzwihr and Muntzheim on bank sides and moving average curves

Figure

  Figure IV.1.20: Deflection measured on the RD4 in August 2016

  Part 1: 0 m to 110 m Experimental and analytical study of the reinforcement of pavements by glass fibre grids Part 2: 115 m to 650 m

  Reference 6 cm ('Ref 6 cm'): 0 m to 100 m: 6 cm of new surface layer • Grid N1: 195 m to 225 m: Grid N1 and 4 cm of new surface layer • Grid N5: 245 m to 360 m: Grid N5 and 4 cm of new surface layer • Grid 5: 390 m to 470 m: Grid 5 and 4 cm of new surface layer • Second reference 6 cm ('Ref 6 cm -2'): 510 m -650 m: 6 cm of new surface layer The parts between the sections were cut out so that the influence of overlapping of different grids are not taken into account. For this reason, the outlier at 325 m (section Grid 5) was also removed. The difference between the values of 2015 and 2016 shows the improvement brought by the new surface course. The corresponding graphs are shown in figure IV.1.21 (axis side) and figure IV.1.22 (bank side). The respective average values of each section are listed in tables IV.1.12 (axis side) and IV.1.13 (bank side), together with the standard deviation and the coefficient of variation of each section and the calculated difference between the deflection measured in 2015 and the deflection measured in 2016 on the respective sections, expressed in [1/100 mm] and in percentage of the initial 2015 deflection value.

Figure

  Figure IV.1.21: Average deflections of each section measured on the axis side in both directions in 2015 and 2016 with std dev.

Figure

  Figure IV.1.22: Average deflections of each section measured on the bank side in both directions in 2015 and 2016 with std dev.

Figure

  Figure IV.1.21 shows that on the axis side the distribution form of the deflection is equivalent in 2015 and 2016, with in both cases smaller values for sections Ref 6 cm, N1

Figure

  Figure IV.1.23: Difference [%] between the deflections measured in 2015 and 2016

  Figure IV.1.24

Figure

  Figure IV.1.24: Emplacement of the cores extracted for Leutner test on the RD4

Figure

  Figure IV.1.25 shows the graphical representation of these results.

Figure

  Figure IV.1.25: Graphical representation of the shear strength achieved by the cores of the RD4

Figrue

  Figrue IV.1.26 illustrates the principle of the Benkelman beam.

Figure

  Figure IV.1.26: Principle of the Benkelman beam [THO 14]

Figure

  Figure IV.1.27: Average deflections of the different sections measured with Benkelman beam (upper graph) and Lacroix deflectograph (lower graph)

and

  Ref 6 cm with very similar deflection values and then sections N1 and Ref 6 cm -2. Based on Romero et al. [ROM 94] the comparison of the tendencies of the deflections Experimental and analytical study of the reinforcement of pavements by glass fibre grids measured with the Benkelman beam in October 2016 and the deflections measured with the Lacroix deflectograph in August 2016 should show lower deflections for the measurements done with the Lacroix deflectograph, as the Lacroix deflectograph is a measurement device moving at a constant speed of 5 km/h. Yet the comparison of our values shows that this is only the case for the deflections on the bank sides of the lanes. For the axis side, the deflections measured with the Benkelman beam are smaller than the deflections measured with the Lacroix deflectograph.

  of a new surface layer on the old structure. Some parts of the road were reinforced with different grids, recovered with 4 cm of the new surface layer, the rest of the road was recovered with 6 cm surface layer. As a whole, 5 sections were observed, named 'Ref 6 cm', 'N1', 'N5', '5' and 'Ref 6 cm -2'. Deflections were measured before and after the maintenance works. The measurement before the maintenance works was done with a Flash deflectograph in June 2015. The measurements after the maintenance works were done with a Lacroix deflectograph in August 2016 and a Benkelman beam in October 2016. The visual inspection of the RD4 before the works stated primarily different types of cracks such as cracks at the centerline and crocodile cracks, especially on the bank side of the lanes. The deflection made in June 2015 showed a weakened bank side in both travel directions with average deflections of around 60 [1/100 mm] on the banks side versus 34 [1/100 mm] on the axis sides. It was also observed that the deflections went up on the last third of the observed route, showing a weakened structure on the eastern part of the road.Deflection measured after the maintenance works in August 2016 showed an improvement of the deflections on all parts of the roads. Yet, this improvement was not constant on all parts. The measurements made on the bank side of the lane towards Holtzwihr showed an improvement of 46.1 %, while the measurements on the bank side towards Muntzenheim and the measurements on the axis sides in both directions showed improvements of only 15.7 % to 24.7 %.Any special distinction of a section, showing that its characteristics (e.g. reinforcement) brought especially good or bad improvements compared to the old structure, could not be observed.Deflections measured in October 2016 with the Benkelman beam confirmed the results obtained with the Lacroix deflectograph except for the bank side towards Holtzwihr. The deflections of the bank sides towards Holtzwihr measured with the Lacroix deflectogaph were at a similar height as the deflections on the axis sides. The deflections measured with the Benkelman beam on the bank side towards Holtzwihr were at a similar height as the deflections on the bank side towards Muntzenheim and higher than the deflections measured on the axis sides.

Withν:

  Poisson's ratiotrans : Transverse strain axial : Axial strain Experimental and analytical study of the reinforcement of pavements by glass fibre grids Layer 3 Layer 3 showed variations due to the structure of the layer. Layers showing a high amount of voids also showed a stronger modulus (9181 MPa), while layers with nearly no voids reached feebler moduli (4889 MPa). The moduli of the untested layers were therefore taken depending on their visible amount of voids.

  Fifth step: Modelling the surface course of the reinforced sections in order to achieve the actual measured deflection values Knowing the actual measured deformation, the next step is to determine the effect that the grid has on the stiffness of the surface course. Three methods shall be used: 1. Increasing the stiffness of the new surface layer until reaching the actual measured deflection values 2. Building a new layer out of the NSL and Layer 1, by adding the thickness of both and changing their stiffness until reaching the actual measured deflection values 3. Increasing the thickness of the NSL until reaching the actual measured deflection values.

  layered specimens made of the same asphalt mix. Such tests could additionally be carried out on two-layered specimens with different bonding characteristics, e.g. with different amounts of emulsion or different surface treatments. Fatigue tests Fatigue tests performed with the cyclic indirect tensile test on the same two-layered specimens at 10 • C and 20 • C showed that for both temperatures, the reinforcement had a positive influence on the fatigue life. While for 10 • C, the behaviour of all three sections 600, 610 and 650 was the same, showing very similar fatigue curve slopes, distinguished only by their different axis intercept, the curves at 20 • C were very different. The visual observations made during the tests highlighted the different crack initiation and propagation progress in the reinforced specimens compared to unreinforced specimens.

  The measurements made with the Benkelman beam mainly confirmed the results determined with the Lacroix deflectograph. Shear tests, performed on the cores of the RD4, confirmed the results achieved in this study, showing that a grid at the interface weakens the shear strength of the interlayer.Modelling of the RD4The elastic moduli of the layers of the RD4 were determined by an external laboratory. The values were used for the modelling of the road structure with the program BISAR. The modelling was divided into 5 different steps: 1. Determination of the modulus of the sub-grade under the asphalt structure using the known deflections, measured in 2015 and the modulus of the other layers 2. Confirming the sub-grade modulus by adding the new surface layer and compare the outcoming deflections with the actual deflections measured on the RD4 3. Calculation of the deflections on the reinforced sections 4. Comparing the deflections using best and worst structure characteristics 5. Modelling the surface course of the reinforced sections in order to obtain the actual measured deflection values

  Les grilles, notamment en fibre de verre, constituent une solution performante, et économique pour le renforcement des chaussées bitumineuses, afin d'augmenter leur durée de vie et ralentir la remontée des fissures, tant en chaussées neuves, qu'en renforcement. Les grilles sont utilisées en tant que renfort, pour améliorer les performances en traction, et la résistance à la fissuration. Cependant, l'utilisation de grilles signifie également une couche supplémentaire entre les deux couches en béton bitumineux. Cette couche supplémentaire peut affecter fortement la liaison entre les deux couches en béton bitumineux et conduire à un décollage. Une mauvaise liaison conduit à une mauvaise transmission des forces et des tensions introduites par le trafic à travers les couches, puisque chaque couche fonctionne comme une seule, plutôt qu'ensemble. En conséquence, des tensions peuvent apparaitre dans les parties inférieures et des compressions dans les parties supérieures des couches.

XXXIII 1. 1

 1 Chaussée routière : Matériaux et constructionUne structure routière est généralement composée de plusieurs couches, collées ensemble de façon a créer une unité complexe. Chaque couche a sa propre fonction, permettant à la structure de réduire les tensions et les contraintes induit par le trafic.On différencie essentiellement entre les chaussées souples et rigides, les premières étant généralement construites avec des liants hydrauliques comme le ciment, les deuxièmes avec des liants bitumineux. Dans cette thèse, que les chaussées souples sont étudiées.1.1.1 Chaussée souple en béton bitumineuxLes matériaux utilisés pour la construction de béton bitumineux sont :1. Les granulats2. Le bitumeLes granulats utilisés peuvent être classés en trois groupes, dépendant de leur taille :Gros granulats, allant d'un diamètre de 2 mm à un diamètre maximum de 45 mm, Agrégats fins, d'un diamètre de 0,063 mm à un diamètre de 2 mm, Fines, ou filler, ayant un diamètre inférieur à 0,063 mm.La forme des granulats est importante pour la résistance contre la déformation d'une chaussée. Une forme angulaire apportera de meilleures résistances.Le bitume utilisé est une mixture de différentes substances organiques, extraites pendant le reconditionnement de différents pétroles bruts. Ses propriétés viscoélastiques ainsi que sa dureté dépendes du pétrole utilisé.Le bitume peut être modifié avec des polymères, par exemple des élastomères et des thermoplastiques.1.1.2 Différentes couches de la chausséeUne chaussée est constituée de plusieurs couches, comme représenté dans la figure VII.1.1.

Figure

  Figure VII.1.1: Chaussée constitué de plusieurs couches

Figure••

  Figure VII.1.2: Facteurs de la liaison entre les couches

Figure VII.1. 3 :

 3 Figure VII.1.3: Croquis d'une grille en fibre de verre

Figure VII.3. 4 :

 4 Figure VII.3.4: Croquis de la surface de test

  figure VII.3.6).

Figure

  Figure VII.3.7: Courbe de fatigue à 10 • C (a) et 20 • C (b)

Figure

  Figure VII.4.8: RD4 avec différentes sections

  Figure VII.4.9: Resulats de la modélisation: orange: Valeurs de 2015, bleu: Valeurs de 2016

Table I .

 I 1.1: Suitability of repair methods for different damage forms [STR 09]

					Repair method
	Condition assessment	Cause	Gritting	Use of bituminous sludges	Asphalt patching	Sealing	Roughening	Reprofiling
	Evenness	Deformation	-	-	0	-	-	+
	length profile	Bearing capacity	-	-	-	-	-	-
	Evenness	Deformation	-	-	0	-	-	+
	cross profile	Bearing capacity	-	-	-	-	-	-
	Grip	Binder accumulation	-	-	+	-	+	-
		Polished grain surface	-	-	-	-	+	-
	Crocodile cracks	+	0	-	-	-	-
	Loss of material	+	+ 1	+	-	-	-
	Mends	-	-	+	-	-	-
	Pull-outs	-	-	+	-	-	-
	Single cracks	-	-	-	+	-	-
			+ : suitable; -: limitedly suitable; 0: not suitable
		1 : For the improvement of the condition assessment 'Loss of material
	through abrasion', the process of application of pore filling mixtures is not suitable
	I.1.4.2 Rehabilitation works
	Rehabilitation work consists in construction actions made on the existing road surface. It
	implies surface treatments as surface dressing and the adding of very thin overlays as well
	as hot in-situ recycling.
	Surface dressing Surface dressing consists in spraying bitumen on the road surface,
	on which coarse aggregates are then spread. The aggregates are then pressed by using a
	rubber wheeled roller. The working procedure is outlined in figure I.1.8.
	Experimental and analytical study of the reinforcement of pavements by glass fibre grids

Table I .

 I 2.1: Properties of glass fibres, type E. [RIC 11]

	Density	Young modulus Resistance to traction
			of one fibre
	2.62 g/m 3	73,500 N/mm 2	3450 N/mm 2

Table I

 I

	Part II	.2.2: Properties of the resin given by the manufacturer
	Literature Review
	Resistance to	Young modulus	Elongation at break	Bulk density
	traction 75 N/mm 2 II.1 Effect of glass fibre grids and other geosynthetics on 3200 N/mm 2 1.5 % 1 g/m 3
	fatigue life of the road structure
	II.1.1 Prevention of reflective cracks using geosynthetics
	Reflective cracking describes the propagation of cracks from an old pavement to a new
	overlay. According to Nejad et al. [NEJ 14], this is mainly due to the following three
	types of stresses:
	1. Stress due to cyclic thermal expansion and contraction
	2. Stress caused by thermal gradient variations
	3. Stress due to the loading, which plays the most important part in overlay damage
	Zamora-Barraza et al. [ZAM 11] complete the listing by adding as other reflective
	cracking catalysts differential consolidations and ground contraction. They describe a
	crack as a discontinuity in a structure which reduces the bending strength of the struc-
	ture and creates an area of stress concentration, thus leading to a greater magnitude of
	movements above a crack.

Table III

 III

	Grid Name	Non-woven	Resin	Tensile strength	Mesh size
				kn/m	cm 2
	1	Light polyester fibre	A	100	4 x 4
	5	Light polyester fibre	A	50	4 x 4
	W	-	A	50	4 x 4
	N	Light polyester fibre	B	50	4 x 4

.1.1: Characteristics of the glass fibre grids installed on the test surface

Table III

 III

	Emulsion		C40B5-S C60B4-S
	Content of residual binder	[%]	40	60
	Breaking value		> 180	122
	Penetration grade	[0.1 mm]	100	172
	Softening point ring and ball	[ • C]	46.2	42.8
	Fluxing agent to reduce the viscosity	[%]	2 to 3	< 2

.1.2: Characteristics of the emulsions used on the test surface

table III

 III Lower

			Test 1 Test 2 Test 3 Test 4
	Average sinking of the plate [mm]	0.463	0.400	0.406	0.402
	Evd [MN/m 2 ]		48.6	56.3	55.4	56.0
	Ev2 [MN/m 2 ] ( = Evd * 2)	97.2	112.6	110.8	112.0
			Maximum nominal granular size	[mm]	16
	Bitumen type		25/55-55 RC	Void content	[%]	4.9
	Ring and Ball	[ • C]	63		Bulk density [g/cm 3 ] 2.463
	Penetration grade [0.1 mm]	25 to 55	Height of the layer	[mm]	60

.1.3.

Table III.1.3: Results of dynamic plate load tests on test surface layer -binder course The first layer was made June, 3rd 2015, directly on the unbound granular base course and had the characteristics shown in table III.1.4 (see also appendix I): Table III.1.4: Characteristics of the lower asphalt layer of the test surface Lower layer: AC 16 BS -Asphalt concrete, binder course Compaction was measured on 4 different points with a TROXLER 4640-B. The final compaction values obtained were as follows: 97.3 %, 97.4 %, 97.8 % and 98.3 %. Pictures of the construction of the lower layer are shown in figure III.1.3.

  Table III.1.5: Characteristics of the upper asphalt layer of the test surface

	Upper layer: AC 11 DS -Asphalt concrete, surface course
			Maximum nominal granular size	[mm]	11
	Bitumen type		25/55-55 A	Void content	[%]	5.59
	Ring and Ball	[ • C]	63	Bulk density [g/cm 3 ] 2.288
	Penetration grade [0.1 mm]	25 to 55	Height of the layer	[mm]	60

  Table III.1.6: Characteristics of the sections of the test surface

	Section	Name			Application	Recommended
	group	of the	Emulsions	Grids	rate, residual application rate
		sections			binder	(residual binder)
					g/m 2	g/m 2
		600		Reference	816
	60X	601	C60B4-S	structure,	210	90-150
		602		no grid	150
		603			90
		610			600
	61X	611	C60B4-S	1	420	600
		612			360
		613			300
		650			1636
	65X	651	C60B4-S	5	360	500
		652			300
		653			240
		6W1			270
	6WX	6W2	C60B4-S	W	210	350
		6W3			150
		401		Reference	140
	40X	402	C40B5-S	structre,	100	80-120
		403		no grid	60
		411			280
	41X	412	C40B5-S	1	240	-
		413			200
		451			240
	45X	452	C40B5-S	5	200	-
		453			180
		4W1			180
	4WX	4W2	C40B5-S	W	140	-
		4W3			100
	4N	4N	C40B5-S	N	200

  Table III.2.1: Shear tests at different temperatures

	Section	Number of tests carried out at different temperatures
		4.5 • C	10 • C	20 • C	30 • C
	600	-	-	4	4
	610	3	-	4	4
	650	-	2	4	4

Figure III.2.3: Shear stress determined at different temperature, for sections 600, 610 and 650, with regression curve

  Table III.2.4: Specimens and their respective dirt contamination degree •

									DC
	•	DC				Specimens
		3	4W3-1
			412-4	412-9	413-1	413-2	413-3	413-7	4W1-4
		2	4W2-4	4W2-7	4W3-2	4W3-7	611-7	612-4	612-5
			613-2	613-5	6W3-1	6W3-4
	1.75	412-8	613-7
	1.5	411-5	411-6	452-7	4W3-6	603-4	612-9
	1.25	453-5	4W1-2	4W1-6	612-2
			403-4	412-3	412-6	451-2	451-5	453-8	4W1-5
		1	4W1-7	4W2-1	611-1	611-2	612-3	612-8	6W2-8
	0.75	4W2-9	653-2
	0.5	413-5	603-3	603-6	613-6	613-9	651-4	652-1
			653-4	6W2-9	6W3-9
	0.25	452-8	453-2	4W1-9	4W2-2	4W2-3	601-6	603-2
			651-7	652-6	653-9	6W1-6	6W2-4	6W2-5

Residual binder quantity Interfaces of section 600 and 603, 610 and 613 and 650 and 653 are shown in III.2.9.

  Table III.2.5: Loss in shear strength due to the insertion of grids in compared with unreinforced specimens

	Grid	Recommended	Shear strength (5	Loss in
		application rate	& W:	comparison to
		(residual binder,	extrapolation)	'no grid'
		C60B4-S)
		[g/m 2 ]	[MPa]	[%]
	No grid (0)	150	1.40	-
	1	600	0.53	62
	5	500	0.46	67
	W	350	0.54	61

One year after the tests, the manufacturer increased the recommended residual binder application rates for the grids used in this study by 100 g/m.

III.2.4.2 Influence of the residual binder application rate on the interlayer bonding of reinforced and unreinforced sections

  Table III.2.6: Shear strength results of specimens Canestrari et al. at different temperatures

		Pavement 1	Pavement 2	Pavement 3
	Temperature [ • C]		Shear stress [MPa]
	10	1.07	2.04	2.22
	20	0.83	1.19	1.34
	25	0.61	0.88	1.02
	30	0.34	0.59	0.75
	40	0.19	0.34	0.36

  The Leutner tests were carried out at 5 • C and 25 • C. The results of the tests are listed in table III.2.7.

	• Reinforcement A: Polypropylene nonwoven and glass fibre with tensile strength of
	50 kN/mm 2
	• Reinforcement B: Polypropylene nonwoven and glass fibre with tensile strength of
	100 kN/mm 2

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

  Table III.2.7: Shear strength results of specimens Vismara et al. at different temperatures

		Tack coat	Reinforcement A Reinforcement B
	Temperature [ • C]		Shear stress [MPa]
	5	5.566	1.932	1.669
	25	1.159	0.302	0.314

  Table III.3.1: Result Moduli at -10 • C, two-layered specimens 600, 610 and 650 Table III.3.2: Result Moduli at 0 • C, two-layered specimens 600, 610 and 650 Table III.3.3: Result Moduli at 10 • C, two-layered specimens 600, 610 and 650

		Temp. : -10 • C Temp. : 10 • C		600 600	610 610	650 650
		Average Average	[ MPa ] [MPa]	17,587 8,131	17,933 7,853	18,875 10,376
	10 Hz 10 Hz	Std. Dev. Std. Dev.	[ MPa ] [MPa]	750 579	2304 327	1649 1528
		Coef of Variation Coef of Variation		0.0348 0.0581	0.1049 40.0360	0.0714 0.1203
		Average Average	[ MPa ] [MPa]	16,586 7,045	16,779 6,732	17,768 8,843
	5 Hz 5 Hz	Std. Dev. Std. Dev.	[ MPa ] [MPa]	780 611	2141 129	1474 1135
		Coef of Variation Coef of Variation		0.0384 0.0708	0.1042 40.0166	0.0677 0.1047
		Average Average	[ MPa ] [MPa]	14,255 4,907	14,716 4,748	15,448 6,554
	1 Hz 1 Hz	Std. Dev. Std. Dev.	[ MPa ] [MPa]	826 475	1998 151	1341 814
		Coef of Variation Coef of Variation		0.0473 0.0791	0.1109 40.0275	0.0709 0.1014
		Average Average	[ MPa ] [MPa]	10,931 2,707	12,163 2,620	12,084 3,821
	0.1 Hz 0.1 Hz	Std. Dev. Std. Dev.	[ MPa ] [MPa]	908 324	2044 116	1190 413
		Coef of Variation Coef of Variation		0.0678 0.0977	0.1372 40.0383	0.0804 0.0882
		Average Average	[ MPa ] [MPa]	17,431 7,836	17,546 7,762	18,633 9,887
	10 Hz 10 Hz	Std. Dev. Std. Dev.	[ MPa ] [MPa]	932 614	2234 200	1758 1292
		Coef of Variation Coef of Variation		0.0436 0.0640	0.1040 40.0223	0.0771 0.1067
	Table III.3.4: Result Moduli at 20 • C, two-layered specimens 600, 610 and 650
		Temp. : 0 • C Temp. : 20 • C		600 600	610 610	650 650
		Average Average	[MPa] [MPa]	14,031 4,248	12,453 6,067	14,401 45,246
	10 Hz 10 Hz	Std. Dev. Std. Dev.	[MPa] [MPa]	1213 384	1597 849	561 543
		Coef of Variation Coef of Variation		0.0706 0.0738	0.1047 40.1212	0.0318 40.0896
		Average Average	[MPa] [MPa]	12,410 3,490	11,187 5,312	13,036 44,305
	5 Hz 5 Hz	Std. Dev. Std. Dev.	[MPa] [MPa]	1278 337	1448 690	692 544
		Coef of Variation Coef of Variation		0.0841 0.0789	0.1057 40.1125	0.0434 40.1095
		Average Average	[MPa] [MPa]	9,965 2,203	8,976 3,468	10,343 42,718
	1 Hz 1 Hz	Std. Dev. Std. Dev.	[MPa] [MPa]	1172 282	1175 453	663 396
		Coef of Variation Coef of Variation		0.0960 0.1045	0.1069 40.1131	0.0523 40.1264
		Average Average	[MPa] [MPa]	6,819 1,106	6,138 1,776	6,934 41,375
	0.1 Hz 0.1 Hz	Std. Dev. Std. Dev.	[MPa] [MPa]	949 139	995 259	583 242
		Coef of Variation Coef of Variation		0.1137 0.1024	0.1323 40.1264	0.0686 40.1526
		Average Average	[MPa] [MPa]	12,855 4,223	11,753 6,256	13,844 45,201
	10 Hz 10 Hz	Std. Dev. Std. Dev.	[MPa] [MPa]	1426 439	1554 629	584 540
		Coef of Variation Coef of Variation		0.0906 0.0849	0.1080 40.0870	0.0345 40.0900
	A graphical representation of the results is shown in figure III.3.6.

  Table III.3.5: Parameters for the creation of the sigmoid curve and stiffness modulus values for different temperatures at 10 Hz -section 600, 610 and 650

		600	610	650
		Parameters of sigmoid function
	x 0	2.13	2.65	1.89
	y 0	5.09	5.09	5.02
	w	18005	21240	19347
	z	1.15	1.56	1.18
	E a	70526	67139	65116
	Temp		Stiffness modulus [MPa]
	-20	17 131	18 027	18 251
	-15	16 525	16 798	17 592
	-10	15 606	15 320	16 645
	-5	14 308	13 643	15 363
	0	12 626	11 856	13 749
	5	10 654	10 062	11 877
	10	8582	8360	9888
	15	6620	6824	7950
	20	4930	5495	6203
	25	3580	4383	4729
	30	2558	3474	3549

  Table III.3.8: Result moduli at 10 • C, surface and binder courses binder and surface courses of the German guideline [RDO 09] are added to the graph. These two curves are shown solely to compare the waveform and the possible stiffness modulus values of the different binder and surface courses (RDO 09 and test surface).

	III.3.6 Interpretation of the result
	Temp. : 10 • C III.3.6.1 Sections 600, 610 and 650		SC	BC
	Average When looking at the curves of 600, 610 and 650 (figure III.3.9), it first becomes apparent [MPa] 8264 11866
	Table III.3.6: Result Moduli at -10 • C, surface and binder courses 10 Hz Std. Dev [MPa] 3241 1334 Coef. of Var. 0.3922 that the two curves 600 and 650 run parallel to one another and maintain a relatively 0.1124 Average [MPa] 7025 9869 5 Hz Std. Dev [MPa] 2939 1874 Table III.3.10: Parameters for the creation of the sigmoid curve and stiffness modulus constant distance of about 1100 MPa, which may be interpreted as a clear indication of values for different temperatures at 10 Hz -surface and binder courses the positive influence of the reinforcement.
	Temp. : -10 • C Average Std. Dev Coef. of Var. Average Std. Dev Coef. of Var. Average Std. Dev Coef. of Var. Coef. of Var. Average Std. Dev Coef. of Var. Curve 610 does not hold to this parallelism. At low temperatures (-20 • C) and high tem-SC BC [MPa] 22961 21807 10 Hz [MPa] 289 2719 0.0126 0.1247 [MPa] 21635 20276 5 Hz [MPa] 255 2732 0.0118 0.1347 [MPa] 18617 17230 1 Hz [MPa] 541 2542 0.0291 0.1475 0.4183 0.1899 [MPa] 5012 7408 1 Hz [MPa] 2176 931 0.4340 Surface Course Binder Course peratures (from 30 • C), grid 1 achieves the highest stiffness modulus, while the results at Parameters of sigmoid function x 0 4.18 9.45 medium temperatures (-10 • C to +10 • C) are the smallest of all three. Here it seems that 0.1257 Average [MPa] 3051 y 0 2109 -6854 the influence of the grid is lost in some ways. 4446 0.1 Hz Std. Dev [MPa] 1451 w 27470 126005 Considering the curves 600 and 650, a further common point can be found: the shear re-557 Coef. of Var. 0.4754 0.1253 Average [MPa] 7574 11298 10 Hz Std. Dev [MPa] 3412 Coef. of Var. 0.4505 -15 25627 25249 0.0795 -20 27391 29509 898 z 1.43 4.01 E a 103246 sistance determined with the Leutner test (see section III.2.3.1) at 25 • C is approximately 74729 Temp Stiffness modulus [MPa] the same for both sections.
		-10	Average	[MPa] 22950	14943 21474	13014
	0.1 Hz	-5	Std. Dev	[MPa] 19409	776 18149	2197
	Coef. of Var. Table III.3.9: Result moduli at 20 • C, surface and binder courses 0.0520 0.1688 0 15429 15231
		5	Average	[MPa] 11649	23011 12678	21038
	10 Hz 10 Hz	Std. Dev Coef. of Var. Temp. : 20 • C 10 Average 15 Std. Dev 20 Coef. of Var. 25	[MPa] 8560 [MPa] 6308 [MPa] 4787 3805	757 0.0329 SC 10449 6374 8504 247 6807 0.0387 5326	2625 0.1248 BC 7067 822 0.1164
	Table III.3.7: Result moduli at 0 • C, surface and binder courses Average [MPa] 5441 5855 30 3184 4032
	5 Hz		Std. Dev	[MPa]	389	645
	10 Hz 1 Hz 5 Hz 0.1 Hz 1 Hz 10 Hz	Temp. : 0 • C Coef. of Var. Average Average Std. Dev Std. Dev Coef. of Var. Coef. of Var. Average Average Std. Dev Std. Dev Coef. of Var. Coef. of Var. Average Average Std. Dev Std. Dev Coef. of Var. Coef. of Var.	[MPa] [MPa] [MPa] [MPa] [MPa] [MPa] [MPa] [MPa] [MPa] [MPa] [MPa] [MPa]	SC 0.0714 16881 3587 1508 256 0.0893 0.0714 13857 1818 251 158 0.0181 0.0867 10790 6032 196 219 0.0182 0.0363	0.1102 BC 3809 14860 452 586 0.1188 0.0395 1891 13024 244 453 0.1290 0.0348 6509 9815 713 626 0.0639 0.1096
			Average	[MPa]	7087	6110
	0.1 Hz		Std. Dev	[MPa]	125	651
	Coef. of Var. The master curves were calculated as described before. The parameters of the regres-0.0176 0.1066
	Average sion curves, as well as the stiffness modulus of the surface and binder courses at 10 Hz, [MPa] 14415 13903
	10 Hz are listed in table III.3.10.	Std. Dev	[MPa]	545	381
			Coef. of Var.		0.0378	0.0274

Figure III.3.11 represents the master curves of the surface and binder course together with the curves of sections 600, 610 and 650. For comparisons purposes, the curves of the calibration Figure III.3.11: Stiffness modulus -Temperature for surface and binder courses (SC and BC), two layered specimens 600, 610 and 650 and for comparison purposes calibrating binder and surface asphalt of RDO 09 (CBC and CSC)

  Table III.3.11: Shear strength of sections 600, 610 and 650 at different temperatures

		600	610	650
	Temperature [ • C]		Shear strength [MPa]
	-20	17.62	15.60	41.30
	-10	9.91	7.29	18.88
	0	5.57	3.41	8.63
	10	3.13	1.60	3.94
	20	1.76	0.75	1.80
	25	1.32	0.51	1.22
	30	0.99	0.35	0.82

To investigate this theory, the stress-strains-graphs of all tests carried out at 10 Hz (1st step of the main test) and 0.1 Hz (4th step of the main test) and for all four temperatures are represented in figure III.3.12.

  determination R 2 of each calculated regression curve are listed in table III.3.13.

	Table III.3.13: Slope of the stress-strain regression curve of sections 600,610 and 650,
	summarized as two-layered specimens, and SC and BC, summarized as uni-layered speci-
	mens, for all temperatures and two frequencies (10 Hz and 0.1 Hz).
		10 Hz		0.1 Hz
		Slope	R 2	Slope	R 2
	Uni-layered, 20 • C	4.24	0.99	1.19	0.99
	Two-layered, 20 • C	2.68	0.98	0.73	0.98
	Uni-layered, 10 • C	6.60	0.97	2.53	0.98
	Two-layered, 10 • C	5.04	0.98	1.72	0.97
	Uni-layered, 0 • C	9.94	0.99	4.13	0.99
	Two-layered, 0 • C	8.37	0.99	4.05	0.99
	Uni-layered, -10 • C	14.46	0.99	8.58	0.98
	Two-layered, -10 • C	11.80	0.99	7.54	0.99

It can be observed that for all temperatures and frequencies, except at 0 • C and 0.1

  Table III.4.1: Stress levels chosen for the fatigue tests at 10 • C

	Stress levels [MPa]	0.4	0.6	0.9	1.0	1.5	1.6
	Section		N • of specimens tested		Total
	600	1	2	1	2	2	1	9
	610	1	2	2	-	3	-	8
	650	1	2	3	-	3	-	9

  Table III.4.2: Stress levels chosen for the fatigue tests at 20 • C The results of the fatigue tests made at 20 • C are listed in table III.4.3. The results are also represented in figure III.4.3, together with the determined regression curves and their equation. Results of the fatigue tests made at 20 • C

	Stress levels [MPa]	0.4	0.6
	Section	N • of specimens tested	Total
	600		3	3	6
	610		3	3	6
	650		3	3	6
	III.4.3 Test results
	III.4.3.1 Fatigue tests at 20 • C
	Table III.4.3: Specimen Max.	Initial	Initial	Failure	Cycle of
	stress σ	strain init	stiffness	stiffness	failure N f
				modulus	modulus
				E init	E f
		[MPa]	[%]	[MPa]	[MPa]
	600A	0.4	0.270	4662.3	2331.1	21197
	600B	0.4	0.272	4639.5	2319.8	24692
	600C	0.4	0.269	4680.9	2340.4	27491
	600E	0.8	0.395	4203.2	2101.6	1591
	600F	0.8	0.343	4837.0	2418.5	1795
	600G	0.8	0.344	4821.3	2410.7	1896
	610A	0.8	0.408	4071.5	2035.7	2299
	610B	0.8	0.287	5794.9	2897.5	2197
	610C	0.8	0.337	4925.6	2462.8	2796
	610D	0.4	0.274	4602.2	2301.1	55100
	610E	0.4	0.247	5106.4	2553.2	41692
	610F	0.4	0.209	6048.5	3024.2	70594
	650A	0.8	0.331	5014.8	2507.4	2697
	650B	0.8	0.353	4705.1	2352.5	3200
	650C	0.8	0.310	5347.5	2673.8	2800
	650D	0.4	0.246	5124.0	2562.0	40995
	650E	0.4	0.268	4703.8	2351.9	30296
	650F	0.4	0.260	4842.2	2421.1	29797

  Table III.4.4: Results of the fatigue tests made at 10 • C

	Specimen	Max.	Initial	Initial	Failure	Cycle of
		stress σ	strain init	stiffness	stiffness	failure N f
				modulus	modulus
				E init	E f
		[MPa]	[%]	[MPa]	[MPa]
	600T	0.4	0.084	7435.7	3717.9	711444
	600V	0.6	0.124	7864.9	3932.4	150539
	600X	0.6	0.130	7472.5	3736.3	136567
	600Q	0.9	0.237	6279.1	3139.6	8093
	600R	1.0	0.172	9639.0	4819.5	19491
	600W	1.0	0.218	7601.9	3800.9	16095
	600M	1.5	0.341	7389.1	3694.5	1591
	600P	1.5	0.457	5511.0	2755.5	995
	600N	1.6	0.390	6883.5	3441.7	998
	610Q	0.4	0.085	7436.5	3718.2	965489
	610U	0.6	0.115	8451.4	4225.7	272817
	610X	0.6	0.141	6901.9	3450.9	293768
	610N	0.9	0.194	7666.3	3833.1	24599
	610P	0.9	0.212	6997.1	3498.5	20298
	610M	1.5	0.323	7776.3	3888.2	2691
	610S	1.5	0.334	7549.2	3774.6	2698
	610T	1.5	0.344	7316.5	3658.3	2495
	650J	0.4	0.065	9734.1	4867.0	928075
	650S	0.6	0.102	9520.2	4760.1	224711
	650R	0.6	0.103	9428.5	4714.3	230788
	650N	0.9	0.172	8680.5	4340.2	33192
	650Q	0.9	0.178	8370.3	4185.1	43597
	650U	0.9	0.201	7383.3	3691.7	25797
	650M	1.5	0.263	9581.0	4790.5	1498
	650P	1.5	0.304	8285.9	4143.0	2194
	650W	1.5	0.328	7681.7	3840.9	2195

Figure III.4.4: Fatigue curves at 10 • C and 10 Hz

  Table IV.1.2: Results of needle penetration test on the bitumen of the 3 asphalt layers of the RD4 The ring and ball tests were performed in accordance with standard DIN EN 1427 [EN 1427]. The results are listed in table IV.1.3. It

				Needle penetration [1/10 mm]
	Layer	Test 1	Test 2	Test 3	Test 4	Test 5	Test 6	Test 7 Average
	1	20.3	20.8	19.1	17.9	21.2	21.0	20.5	20.1
	2	36.9	33.8	24.9	35.0	29.9	30		31.8
	3	17.3	18.5	17.2	19.7	21.8	18	16.2	18.4
	Table IV.1.3: Results of Ring and Ball test on the bitumen of the 3 asphalt layers of
	the RD4
				Softening point [ • C]
		Layer	Test 1	Test 2	Test 3	Test 4	Average
		1	66.6	66.8	66.2	66.5	66.5
		2	59.7	59.5	60.0	60.1	59.8
		3	64.7	64.6	64.7	65.0	64.8
	Table IV.1.4: Change of different bitumens characteristics over 15 years
		Bitumen	∆ RaB [ • C]		∆ Pen [1/10 mm]
		B 80 (70/100)		+ 19.9			-52
		B 65 (50/70)		+ 18.4			-35
		B 45 (30/45)		+ 15.1			-26

is known that no construction works were done on the RD4 in the past few years. It can therefore be assumed that the binder used in the different layers is at least 5 years old, and even 10 to 15 years in the lower layers. As explained in section I.1.3.3, bitumen oxides when it is in contact with air, leading to a stiffer and more brittle bitumen. In order to determine which bitumen was used at the time of the construction, a back-calculation is needed.

Based on the results published in Forschung Straßenbau und Straßenverkehrstechnik, issue 774, [FSS 99], the values of Ring and Ball and Needle Penetration of the bitumen 30/45, 50/70 and 70/100 varies over a time period of 15 years as follows (table IV.1.4):

  Table IV.1.7: Average values, standard deviations and coefficients of variation of the deflection measured on the RD4 in 2015

		Distance	Average	Standard	Coefficient
			deflection	Deviation	of variation
		[m]	[1/100 mm]	[1/100 mm]
		0-400	31.0	4.39	0.142
	M15 Axis	405-580	44.0	9.87	0.224
		585-650	32.4	6.21	0.192
		Total	34.9	8.7	0.2
		0-400	30.2	3.39	0.112
	H15 Axis	405-580	42.1	6.13	0.145
		585-650	36.8	6.42	0.174
		Total	34.0	6.9	0.2
		0-350	62.6	16.50	0.264
	M15 Bank	355-450	83.1	26.66	0.321
		455-650	61.4	23.20	0.378
		Total	65.2	21.9	0.3
		0-350	58.7	15.96	0.272
	H15 Bank	355-450	65.5	12.23	0.187
		455-650	59.5	19.10	0.321
		Total	59.9	16.6	0.3

  Table IV.1.8: Characteristics of the glass fibre grids installed on the RD4

	Grid Name	Non-woven	Resin	Tensile strength	Mesh size
				kN/m	cm 2
	N1	Light polyester fibre	B	100	4 x 4
	N5	Light polyester fibre	B	50	4 x 4
	5	Light polyester fibre	A	50	4 x 4
	IV.1.3.2 Construction steps

  TableIV.1.9: Average thickness of the layers of the old structure with standard deviation and coefficient of variation

	Layer		1	2	3	4	Macadam
			Direction Muntzenheim
	Average	[mm]	51.9	54.2	50.6	13.9	74.3
	Std Dev	[mm]	7.5	5.8	14.8	3.9	30.1
	Coef of Var		0.14	0.11	0.29	0.28	0.40
			Direction Holtzwihr
	Average	[mm]	40.0	56.0	60.0	14.0	73.8
	Std Dev	[mm]	5.5	9.7	16.4	3.7	16.3
	Coef of Var		0.14	0.17	0.27	0.27	0.22
			Both directions
	Average	[mm]	47.6	54.9	53.9	13.9	74.1
	Std Dev	[mm]	9.2	7.7	16.7	4.0	27.2
	Coef of Var		0.19	0.14	0.31	0.29	0.37

Table IV

 IV

		Modulus [MPa]
	Core / Layer	NSL*	1	2	3
	A			7242	9652
	B			6329
	C		8039	6440
	D			7042	4738
	1	7419	4994
	5				5023
	6	8001	8091	5650	4907
	7	6906	4958	6307	8711
	Average	7442	6520	6502	6606
	Std Dev	548.1	1783.6	572.1	2376.3
	Coef. of Var.	0.0737	0.2736	0.0880	0.3597
			*NSL = New Surface Layer

.1.10: Average modulus of the layers with standard deviation and coefficient of variation

  Table IV.1.11: Average values, standard deviations and coefficients of variation of the deflection measured on the RD4 in 2016

		Distance	Average	Standard	Coefficient
			deflection	Deviation	of variation
		[m]	[1/100 mm]	[1/100 mm]
		0-100	22.5	5.5	0.2
		105-170	33.5	18.6	0.6
	M16 Axis	175-500	27.3	8.4	0.3
		505-600	40.7	8.3	0.2
		605-650	29.0	4.2	0.1
		Total	29.1	10.2	0.4
	H16 Axis	Total	25.6	3.3	0.1
		0-100	35.7	9.3	0.3
		105-360	51.1	13.3	0.3
	M16 Bank	365-600	64.2	19.5	0.3
		600-650	27.1	6.8	0.3
		Total	51.7	19.4	0.4
		0-110	41.9 10.9 0.3
	H16 Bank	115-650	30.6	3.8	0.1
		Total	32.3	6.9	0.2

Table IV

 IV

				Axis
				Muntzenheim	Holtzwihr
	Section			2015	2016	2015	2016
		Average	[1/100 mm]	31.3	22.5	31.9	25.1
		Std Dev	[1/100 mm]	5.8	5.5	3.7	3.9
	Ref 6 cm	Coef. of Var.		0.1856	0.2433	0.1152	0.1547
		Difference	[1/100 mm]	8.8		6.8
		Difference	[%]	28.2		21.3
		Average	[1/100 mm]	31.9	24.8	31.0	21.8
		Std Dev	[1/100 mm]	3.7	4.6	2.3	3.6
	N1	Coef. of Var.		0.1172	0.1863	0.0733	0.1659
		Difference	[1/100 mm]	7.1		9.2
		Difference	[%]	22.3		29.8
		Average	[1/100 mm]	29.1	22.5	28.5	24.0
		Std Dev	[1/100 mm]	2.5	3.5	2.5	2.3
	N5	Coef. of Var.		0.0847	0.1566	0.0881	0.0960
		Difference	[1/100 mm]	6.6		4.5
		Difference	[%]	22.6		15.8
		Average	[1/100 mm]	40.9	29.1	36.6	26.4
		Std Dev	[1/100 mm]	13.5	4.6	3.4	2.1
	5	Coef. of Var.		0.3296	0.1580	0.0921	0.0798
		Difference	[1/100 mm]	11.8		10.2
		Difference	[%]	28.8		27.8
		Average	[1/100 mm]	38.9	36.6	41.7	27.8
		Std Dev	[1/100 mm]	9.3	9.3	7.7	2.7
	Ref 6 cm -2	Coef. of Var.		0.2380	0.2531	0.1849	0.0987
		Difference	[1/100 mm]	2.3		13.9
		Difference	[%]	6.0		33.4

.1.12: Comparison of the average deflection of each section measured in 2015 and 2016 on the axis side towards Muntzenheim and Holtzwihr, with standard deviation (Std Dev), coefficient of variation (Coef. of Var.) and the calculation of the difference between the two measurements in [1/100 mm] and [%] of the 2015-values Experimental and analytical study of the reinforcement of pavements by glass fibre grids

Table IV

 IV

				Bank
				Muntzenheim	Holtzwihr
	Section			2015	2016	2015	2016
		Average	[1/100 mm]	52.4	35.7	66.5	43.3
		Std Dev	[1/100 mm]	14.3	9.3	17.4	10.6
	Ref 6 cm	Coef. of Var.		0.2738	0.2590	0.2609	0.2447
		Difference	[1/100 mm]	16.7		23.2
		Difference	[%]	31.8		34.8
		Average	[1/100 mm]	69.3	53.9	58.5	23.0
		Std Dev	[1/100 mm]	12.1	12.7	7.0	4.3
	N1	Coef. of Var.		0.1751	0.2359	0.1201	0.1890
		Difference	[1/100 mm]	15.3		35.5
		Difference	[%]	22.2		60.7
		Average	[1/100 mm]	67.9	54.4	62.0	31.1
		Std Dev	[1/100 mm]	14.1	11.3	10.9	1.9
	N5	Coef. of Var.		0.2080	0.2081	0.1752	0.0623
		Difference	[1/100 mm]	13.5		30.8
		Difference	[%]	19.9		49.8
		Average	[1/100 mm]	83.3	74.4	68.0	31.9
		Std Dev	[1/100 mm]	29.0	25.7	10.8	2.9
	5	Coef. of Var.		0.3479	0.3451	0.1591	0.0918
		Difference	[1/100 mm]	8.9		36.1
		Difference	[%]	10.7		53.1
		Average	[1/100 mm]	60.8	45.7	53.4	32.1
		Std Dev	[1/100 mm]	26.6	19.1	18.2	3.5
	Ref 6 cm -2	Coef. of Var.		0.4379	0.4169	0.3404	0.1080
		Difference	[1/100 mm]	15.1		21.3
		Difference	[%]	24.8		39.8

.1.13: Comparison of the average deflection of each section measured in 2015 and 2016 on the bank side towards Muntzenheim and Holtzwihr, with standard deviation (Std Dev), coefficient of variation (Coef. of Var.) and the calculation of the difference between the two measurements in [1/100 mm] and [%] of the 2015-values

Table IV .

 IV 1.14: Shear strength results of the cores extracted from the RD4 Calculated using the whole surface, 2 Calculated using a reduced surface

		Core	2	2 bis	3	4	5	8
	Grid at this position		N1	N1 & N5	N5	5	-	N5 or N1
	Diameter	[mm]	141.3	141	141.1	141.1	140.1	142.2
	Displacement	[mm]	1.4	1.4	1.5	1.8	0.8	1
	Shear strength 1	[N/mm 2 ]	0.39	0.47	0.47	0.49	0.52	0.58
	Shear strength 2	[N/mm 2 ]	0.50	0.61	0.60	0.59	0.85	0.80

1 :

Table IV .

 IV 1.15: Average deflections and standard deviations measured with the Benkelman beam on each section

				BB M	BB M	BB H	BB H
				Bank	Axis	Bank	Axis
		Average	[1/100 mm]	45.1	8.3	51.0	15.7
	Ref 6 cm	Std Dev	[1/100 mm]	11.9	3.4	17.5	2.0
		Coef. of Var.		0.3	0.4	0.3	0.1
		Average	[1/100 mm]	79.3	20.2	65.1	18.0
	N1	Std Dev	[1/100 mm]	19.1	3.3	3.6	2.3
		Coef. of Var.		0.2	0.2	0.1	0.1
		Average	[1/100 mm]	59.3	13.6	66.0	9.7
	N5	Std Dev	[1/100 mm]	9.8	7.1	21.1	0.6
		Coef. of Var.		0.2	0.5	0.3	0.1
		Average	[1/100 mm]	74.5	20.3	86.4	11.6
	5	Std Dev	[1/100 mm]	22.9	2.7	23.1	6.7
		Coef. of Var.		0.3	0.1	0.3	0.6
		Average	[1/100 mm]	59.0	23.8	72.7	21.0
	Ref 6 cm -2	Std Dev	[1/100 mm]	11.8	2.6	28.4	1.4
		Coef. of Var.		0.2	0.1	0.4	0.1
	The graphical representation of the average deflection values determined with the
	Benkelman beam as well as, for comparison purposes, the graphical representation of the
	average deflection values determined with the Lacroix deflectograph in 2016 are shown in
	figure IV.1.27.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

  Table IV.2.3: Sub-grade moduli determined using back-calculation with BISAR Experimental and analytical study of the reinforcement of pavements by glass fibre grids

	2015		Ref 6cm	N1	N5	5	Ref 6cm-2
	Modulus Sub-grade	[MPa]	160	190	220	130	125
	Measured deflections	[1/100 mm]	31.6	31.45	28.8	38.75	40.3
	Calculated deflections [1/100 mm]	31.12	31.8	28.97	38.91	40.56
	Difference	[1/100 mm]	-0.48	0.35	0.17	0.16	0.26
	Coef. of Var.		0.011	0.008	0.004	0.003	0.005
	It is observed that the variation of the sub-grade moduli throughout the road section
	is quite important, starting with a modulus corresponding to a gravel sub-grade (150 to
	250 MPa [RDO 09]), but falling to a modulus corresponding to a sub-grade made of a
	sand-gravel mixture after section N5 (100 MPa to 150 MPa [RDO 09]).
	As mentioned in section IV.1.1, the sub-grade is known to be made of a sand, gravel
	and pebble mixture, which corresponds to the calculated values.
	IV.2.4.2 Second step: Confirming the sub-grade modulus
	To confirm the sub-grade moduli determined in the first step, the deflections are calculated
	using the determined sub-grade moduli, but now adding the new surface layer (NSL). This
	new structure is then compared to the deflections measured on the unreinforced sections
	(Ref 6 cm and Ref 6 cm -2) in 2016.
	The results of this comparison can be found in the following table (table IV.2.4):

  Table IV.2.4: Confirmation of the back-calculated sub-grade modulus

	2016		Ref 6cm	Ref 6cm-2
	Modulus Sub-grade	[MPa]	160	125
	Measured deflections	[1/100 mm]	23.8	32.2
	Calculated deflections [1/100 mm]	24.22	32.03
	Difference	[1/100 mm]	0.42	-0.17
	Coef. of Var.		0.012	0.004

Table IV

 IV

	.2.5: Comparison of the deflections measured in 2016 on the RD4 and the
	modelled deflections for the 2016 structure
	2016		Ref 6cm	N1	N5	5	Ref 6cm-2
	Modulus Sub-grade	[MPa]	160	190	220	130	125
	Measured deflections	[1/100 mm]	23.8	23.3	23.25	27.75	32.2
	Calculated deflections [1/100 mm]	24.22	26.57	24.5	32.46	32.03
	Difference	[1/100 mm]	0.42	3.27	1.25	4.71	-0.17
	Coef. of Var.		0.012	0.093	0.037	0.111	0.004

Table IV

 IV

	.2.6: Calculation of an equivalent modulus for layer NSL, in order to reach the
	actual measured deflections on reinforced sections
		N1		N5		5
		D	Mod	D	Mod	D	Mod
		[mm]	[MPa]	[mm]	[MPa]	[mm]	[MPa]
	NSL	40	35000	35	14000	37.5	45000
	1	45	4975.8	46.3	4975.8	49.7	4975.8
	2	48	6502	55	6502	53.7	6502
	3	45	9181	43.8	7035	50	8466
	Macadam	87.5	800	81.2	800	101.7	800
	Sub-grade		190		220		130
	Def calculated	23.27		23.28		27.73
	Def actual	23.3		23.25		27.75

  Experimental and analytical study of the reinforcement of pavements by glass fibre grids layer made of the first two layers and the glass fibre grid in between. The moduli of the newly built layer, with which the actual measured deflection values are reached, are listed in table IV.2.7.Compared to the average modulus of the two upper layer, being of 6209 MPa, it can be noted that the modulus of the new first layer in section N1 had to be increased by 254 %, the modulus of section N5 by 69 % and the modulus of section 5 by 351 %.Increasing the thickness of the new surface layer until reaching the actual measured deflection values For this part, the modulus values of all other layer as well as the thickness of all layers remain the same, only the thickness of the NSL is modified.

	Table IV.2.7: Calculation of an equivalent moduli for a new layer (NSL + 1) in order
	to reach the actual measured deflections on reinforced sections
		N1		N5		5
		D	Mod	D	Mod	D	Mod
		[mm]	[MPa]	[mm]	[MPa]	[mm]	[MPa]
	NSL + 1	85	22000	81.3	10500	87.2	28000
	2	48	6502	55	6502	53.7	6502
	3	45	9181	43.8	7035	50	8466
	Macadam	87.5	800	81.2	800	101.7	800
	Sub-grade		190		220		130
	Def calculated	23.25		23.29		27.71
	Def actual	23.3		23.25		27.75
	The thickness of the reinforced section with which the actual measured deflection values
	are reached are listed in table IV.2.6.
	Table IV.2.8: Calculation of an equivalent thickness for layer NSL, in order to reach the
	actual measured deflections on reinforced sections
		N1		N5		5
		D	Mod	D	Mod	D	Mod
		[mm]	[MPa]	[mm]	[MPa]	[mm]	[MPa]
	NSL	74	7442	48	7442	81	7442
	1	45	4975.8	46.3	4975.8	49.7	4975.8
	2	48	6502	55	6502	53.7	6502
	3	45	9181	43.8	7035	50	8466
	Macadam	87.5	800	81.2	800	101.7	800
	Sub-grade		190		220		130
	Def calculated	23.34		23.28		27.76
	Def actual	23.3		23.25		27.75

  Experimental and analytical study of the reinforcement of pavements by glass fibre grids Table VI.2.10: Result Moduli, 0 • C Table VI.2.11: Result Moduli, +10• C Table VI.2.12: Result Moduli, +20 • C Experimental and analytical study of the reinforcement of pavements by glass fibre gridsTable VI.2.13: Result Moduli at -10 • C, surface and binder courses Experimental and analytical study of the reinforcement of pavements by glass fibre grids XXI Table VI.2.14: Result moduli at 0 • C, surface and binder courses Experimental and analytical study of the reinforcement of pavements by glass fibre grids XXII Table VI.2.15: Result moduli at 10 • C, surface and binder courses Experimental and analytical study of the reinforcement of pavements by glass fibre grids XXIII Table VI.2.16: Result moduli at 20 • C, surface and binder courses La construction et la réparation des infrastructures routières dans une optique de développement durable, se doivent de nos jours d'intégrer les problèmes de rareté future des matières premières tels que les produits dérivés du pétrole. Compte-tenu du patrimoine routier existant, la réparation est un enjeu majeur. Le vieillissement des infrastructures nécessite de développer des solutions abordables de ré-ingénierie écologique, qui vont permettre leur rénovation totale ou partielle, voire graduelle.

	Part VI Appendix III: Stiffness modulus: Test results Part VII
	Two-layered specimens Temp. : 0 • C Specimen number 1 Diameter [mm] 99 Temp. : 20 • C 600 Specimen number 1 2 Diameter [mm] 99 99 Temp. : 0 • C 600 2 99 Specimen number Temp. : 10 • C Specimen number 1 Temp. : 20 • C Specimen number 1 Résumée de la thèse en Francais 610 3 1 2 3 1 98.5 99 98.5 99 98.5 610 3 1 2 3 4 99 98.5 98.5 99 98.5 SC BC 1 2 3 1 SC BC 2 3 1 2 SC BC 2 3 1 2	1 98.5 2	650 2 99 3 98.5 2 3	3 98.5 650	3 99	4 99
	Table VI.2.9: Result Moduli, -10 • C 600 610 2 3 1 2 3 98.5 1 99 98.5 99 98.5 98.5 43.5 51.5 47.5 45 47.5 45 56 46.5 52.5 53.5 51.5 52.5 90 88.5 89 98.5 91 102.5 18,363 16,866 17,533 15,273 19,209 19,316 20,718 17,539 18,367 650 1 2 3 98.5 98.5 98.5 52.5 47.5 48 47 52 50.5 94.5 96.5 98.5 17,587 17,933 18,875 750 2304 1649 0.0348 0.1049 0.0714 17,400 15,844 16,514 14,332 17,695 18,310 19,429 16,617 17,258 16,586 16,779 17,768 780 2141 1474 0.0384 0.1042 0.0677 15,172 13,569 14,024 12,438 15,538 16,172 16,952 14,379 15,012 14,255 14,716 15,448 826 1998 1341 0.0473 0.1109 0.0709 11,975 10,325 10,494 9,819 13,576 13,092 13,393 11,068 11,790 10,931 12,163 12,084 908 2044 1190 0.0678 0.1372 0.0804 18,459 16,642 17,192 14,998 18,471 19,168 20,640 17,366 17,891 17,431 17,546 18,633 932 2234 1758 0.0436 0.1040 0.0771 46.5 44.5 48.5 48 49.5 46.5 45.5 45.5 51.5 52.5 53.5 50 50.5 50 52 53 54 48 90 90.5 89.5 91.5 92.5 99 89 93.5 103.5 12,632 14,670 14,790 10,812 14,001 12,545 14,991 14,337 13,874 14,031 12,453 14,401 1213 1597 561 0.0706 0.1047 0.0318 10,961 13,373 12,897 9,656 12,535 11,369 13,469 13,403 12,238 12,410 11,187 13,036 1278 1448 692 0.0841 0.1057 0.0434 8,658 10,922 10,315 7,819 10,169 8,941 10,538 10,886 9,604 9,965 8,976 10,343 1172 1175 663 0.0960 0.1069 0.0523 5,787 7,655 7,014 5,198 7,180 6,038 6,910 7,529 6,364 6,819 6,138 6,934 949 995 583 0.1137 0.1323 0.0686 11,208 13,660 13,697 10,190 13,298 11,771 14,256 14,101 13,176 12,855 11,753 13,844 1426 1554 584 0.0906 0.1080 0.0345 600 610 650 2 3 1 2 3 4 1 2 51.5 Specimen number Temp. : -10 • C Diameter [mm] Heigth SC [mm] Heigth BC [mm] Length [mm] 10Hz E [MPa] Average [MPa] Std. Dev. [MPa] Coef of Variation 5Hz E [MPa] Average [MPa] Std. Dev. [MPa] Coef of Variation 1Hz E [MPa] Average [MPa] Std. Dev. [MPa] Coef of Variation 0.1Hz E [MPa] Average [MPa] Std. Dev. [MPa] Coef of Variation 10Hz E [MPa] Average [MPa] Std. Dev. [MPa] Coef of Variation Height SC [mm] Height BC [mm] Length [mm] 10Hz E [MPa] Average [MPa] Std. Dev. [MPa] Coef of Variation 5Hz E [MPa] Average [MPa] Std. Dev. [MPa] Coef of Variation 1Hz E [MPa] Average [MPa] Std. Dev. [MPa] Coef of Variation 0.1Hz E [MPa] Average [MPa] Std. Dev. [MPa] Coef of Variation 10Hz E [MPa] Average [MPa] Std. Dev. [MPa] Coef of Variation Temp. : 10 • C Specimen number 1 Height SC [mm] 53.5 48 40 47 46 44.5 44.5 50 Height BC [mm] 47.5 46 50.5 59 52.5 53.5 54.5 54 48.5 54.5 3 45 Length [mm] 90 90 90 95 94.5 103 99.5 88 99 88 10Hz E [MPa] 4,174 3,906 4,663 6,493 6,202 4,836 6,736 4,990 4,607 5,765 Average [MPa] 4,248 6,067 5,246 Std. Dev. [MPa] 384 849 543 Coef of Variation 0.0738 0.1212 0.0896 5Hz E [MPa] 3,304 3,286 3,879 5,682 5,192 4,397 5,976 4,126 3,613 4,743 Average [MPa] 3,490 5,312 4,305 Std. Dev. [MPa] 337 690 544 Coef of Variation 0.0789 0.1125 0.1095 1Hz E [MPa] 2,110 1,979 2,519 3,621 3,384 2,893 3,973 2,587 2,215 3,014 Average [MPa] 2,203 3,468 2,718 Std. Dev. [MPa] 282 453 396 Coef of Variation 0.1045 0.1131 0.1264 0.1Hz E [MPa] 1,069 989 1,259 1,880 1,745 1,434 2,045 1,308 1,062 1,536 Average [MPa] 1,106 1,776 1,375 Std. Dev. [MPa] 139 259 242 Coef of Variation 0.1024 0.1264 0.1526 10Hz E [MPa] 4,123 3,843 4,704 6,781 5,976 5,500 6,766 5,009 4,523 5,612 Average [MPa] 4,223 6,256 5,201 Std. Dev. [MPa] 439 629 540 Coef of Variation 0.0849 0.0870 0.0900 Temp. : -10 • C SC Diameter [mm] 99.1 99 99 99 99 Diameter [mm] 99 99 99 99 99 99 Diameter [mm] 99 99 99 99.1 99 99.2 BC Specimen number 1 2 3 1 2 Length [mm] 56 63.7 63.5 42.5 40.5 Length [mm] 48.2 71 45 47.5 76 43.5 Length [mm] 62.2 51.5 50 57 51 43 Résumée de la thèse 'Experimental and numerical study of 3 Diameter [mm] 99 99 99 99 99 99 Length [mm] 55 65.6 74.5 52.5 49.5 10Hz E [MPa] 15985 18622 16037 14446 Average [MPa] 16881 14860 10Hz E [MPa] 5040 11522 8230 10327 12571 12700 Average [MPa] 8264 11866 10Hz E [MPa] 6199 6656 6267 7313 7739 6150 Average [MPa] 6374 7067 the reinforcement of infrastructure by glass fibre grids' 59 10Hz Std. Dev [MPa] 1508 586 Std. Dev [MPa] 3241 1334 Std. Dev [MPa] 247 822 Étudiante: Loba Sagnol E [MPa] 22913 22699 23271 18976 22049 24397 Average [MPa] 22961 21807 Std. Dev [MPa] 289 Coef. of Var. 0.0893 0.0395 5 Hz E [MPa] 13961 13571 14039 12704 Coef. of Var. 0.3922 0.1124 5 Hz E [MPa] 4026 9900 7149 7706 10873 11026 Coef. of Var. 0.0387 0.1164 5 Hz E [MPa] 5112 5870 5342 5953 6446 5167 Directeur de thèse : Cyrille Chazallon, INSA de Strasbourg, Markus 2719 Coef. of Var. 0.0126 0.1247 5 Hz Average [MPa] 13857 13024 Std. Dev [MPa] 251 453 Average [MPa] 7025 9869 Std. Dev [MPa] 2939 1874 Average [MPa] 5441 5855 Std. Dev [MPa] 389 Stöckner, Hochschule Karlsruhe 645 E [MPa] 21734 21346 21827 17378 20645 22804 Average [MPa] 21635 Coef. of Var. 0.0181 0.0348 Coef. of Var. 0.4183 0.1899 Coef. of Var. 0.0714 0.1102 Début : 01 septembre 2014, soutenance : 15 décembre 2017 20276 Std. Dev [MPa] 255 1 Hz E [MPa] 11001 10613 10755 9372 1 Hz E [MPa] 2752 7092 5191 6336 8013 7875 1 Hz E [MPa] 3326 3838 3596 3958 4168 3301 2732 Coef. of Var. 0.0118 0.1347 1 Hz Average [MPa] 18617 Std. Dev [MPa] 541 Coef. of Var. 0.0291 0.1Hz E [MPa] 14394 Average [MPa] 14943 Std. Dev [MPa] 776 Coef. of Var. 0.0520 10Hz Average [MPa] 23011 21038 Coef. of Var. 0.0378 0.0274 Coef. of Var. 0.4505 0.0795 Coef. of Var. 0.0363 0.1096 E [MPa] 22794 22387 23853 18044 22122 22946 Std. Dev [MPa] 545 381 Std. Dev [MPa] 3412 898 Std. Dev [MPa] 219 713 0.1688 Average [MPa] 14415 13903 Average [MPa] 7574 11298 Average [MPa] 6032 6509 2197 10Hz E [MPa] 15020 13963 14263 13634 10Hz E [MPa] 4122 10945 7654 10307 11527 12058 10Hz E [MPa] 5901 6285 5910 6766 7058 5703 13014 Coef. of Var. 0.0176 0.1066 Coef. of Var. 0.4754 0.1253 Coef. of Var. 0.0867 0.1290 15492 10635 13440 14967 Std. Dev [MPa] 125 651 Std. Dev [MPa] 1451 557 Std. Dev [MPa] 158 244 0.1475 Average [MPa] 7087 6110 Average [MPa] 3051 4446 Average [MPa] 1818 1891 2542 0.1Hz E [MPa] 7183 6946 7132 5650 6571 0.1Hz E [MPa] 1502 4378 3274 3812 4668 4857 0.1Hz E [MPa] 1637 1892 1926 2034 2030 1609 17230 Coef. of Var. 0.0182 0.0639 Coef. of Var. 0.4340 0.1257 Coef. of Var. 0.0714 0.1188 E [MPa] 18628 18071 19153 14491 17687 19513 Average [MPa] 10790 9815 Std. Dev [MPa] 196 626 Average [MPa] 5012 7408 Std. Dev [MPa] 2176 931 Average [MPa] 3587 3809 Std. Dev [MPa] 256 452 1. Introduction	47.5 52.5 90 5,621 4,736 3,055 1,593 5,660
	Diameter [mm] Height SC [mm] Std. Dev [MPa] 99 49	99 49	98.5 46 757	98.5 46	99 44.5	99 49.5 2625 98.5 45.5	98.5 53.5	99 49
	Height BC [mm] Coef. of Var.	49.5	50	53.5 0.0329	53.5	54.5	49 0.1248 54	45.5	49.5
	Length [mm]		89.5	89	102.5	102.5	104	95		99.5	95.5	107.5
	10Hz	E [MPa]	8,800	7,794	7,800	7,748	7,605	7,723	8,334	11,314 11,201	8,612
	Average [MPa]		8,131			7,853				10,376
	Std. Dev. [MPa]		579			327					1528
	Coef of Variation	0.0581			0.0360				0.1203
	5Hz	E [MPa]	7,741	6,600	6,793	6,818	6,772	6,540	6,796	9,434	9,561	7,535
	Average [MPa]		7,045			6,732				8,843
	Std. Dev. [MPa]		611			129					1135
	Coef of Variation	0.0708			0.0166				0.1047
	1Hz	E [MPa]	5,454	4,597	4,669	4,895	4,835	4,556	4,704	7,038	7,010	5,614
	Average [MPa]		4,907			4,748				6,554
	Std. Dev. [MPa]		475			151					814
	Coef of Variation	0.0791			0.0275				0.1014
	0.1Hz	E [MPa]	3,077	2,478	2,564	2,697	2,740	2,537	2,505	4,086	4,031	3,345
	Average [MPa]		2,707			2,620				3,821
	Std. Dev. [MPa]		324			116					413
	Coef of Variation	0.0977			0.0383				0.0882
	10Hz	E [MPa]	8,530	7,364	7,614	7,865	7,823	7,465	7,894	10,632 10,635	8,395
	Average [MPa]		7,836			7,762				9,887
	Std. Dev. [MPa]		614			200					1292
	Coef of Variation	0.0640			0.0223				0.1067

XX

Unilayered specimens

Experimental and analytical study of the reinforcement of pavements by glass fibre grids

http://www.wetteronline.de, Wetterdaten, Rückblick, search of the precipitation on the Basel-Mulhouse Airport, Sept 4th,

2017Experimental and analytical study of the reinforcement of pavements by glass fibre grids

Acknowledgement

on, inter alia, cyclic indirect tensile tests. For these purposes, asphalt slabs consisting of an asphalt with a nominal maximum aggregate size of 22 and a bitumen with penetration grade 50/70 were constructed. Specimens of 100 mm diameter and 60 mm length were extracted in two perpendicular directions (see figure III.3.13). The results checked for are the fatigue and stiffness modulus tests. In their study, the authors were able to find out that the stiffness fatigue performances are highly sensitive to the material anisotropy, noting that the effects of anisotropy tend to increase with the increasing aggregate size of the asphalt.

They observed that the F-Z-Y orientation (left picture of figure III.3.13), which reflects the loading situation on a road, showed 23 % stiffer results and 36% better results in fatigue performance at 20 • C and 10 Hz than the F-X-Y orientation.

The results of this study cannot be transferred one-by-one to this study as the asphalt The layers of core H were cut apart from each other. The bitumen and the aggregates of each layer were extracted with an asphalt analyser using trichloroethylene as dissolvent.

Aggregates The extracted aggregates of layer 2 and 3 were sieved and the maximum aggregate size as well as the fine content were determined. They are listed in table IV.1.1. It is to be noted that these values are purely theoretical and shall give an idea of the possible state of the bitumen in new condition.

Void, binder, aggregate and fine content

The calculation of the void, binder, aggregate and fine contents is based on the values obtained after the extraction procedures.

The different contents are listed in table IV.1.6. Based on the collected values and the national practices, it was assumed that the 3 upper asphalt layers of the RD4 are surface course of the type 'BBSG', standing for 'béton bitumineux semi-grenu' being a rather thick asphalt layer (3 cm to 9 cm) which is often used as a surface or a binder course with nominal maximum aggregate sizes of 0/6, 0/10 or 0/14.

In our case, we assume that the three layers have a nominal maximum aggregate size of 0/10 and a 35/50 or 50/70 bitumen.

The lowest layer is assumed to be a macadam layer. No other characteristics are known.

Experimental and analytical study of the reinforcement of pavements by glass fibre grids Experimental and analytical study of the reinforcement of pavements by glass fibre grids When a material is incompressible, the Poisson's ratio is 0.5.

According to the German Directive RDO Asphalt 09 [RDO 09], the Poisson's ratio for asphalt layers was taken at 0.35 while the Poisson's ratio for the sub-grade was taken at 0.5.

IV.2.2.3 Bonding between layers

BISAR enables the modelling of a non-fully bonded interlayer. To do so, the program proposes the value AK, being the standard shear spring compliance, calculated by means of the following equation:

The value of the relative horizontal displacement and the stress acting at the interface can be taken from the results of the Leutner test with the displacement and stress at fracture.

As the Leutner-tests made on the cores of the RD4 were made under non-standard conditions, these values were not taken into account for the modelling. Therefore the bonding between the Layers was taken as full (AK = 0).

IV.2.2.4 Modulus

The moduli used for modelling the structure of the RD4 are the ones given in section IV.1.10. As the deflection is to be calculated for each section, but we do not have measurements for each section, the moduli have to be assigned appropriately.

Layers NSL and 2 Layers NSL ('New Surface Layer') and 2 showed very little variation along the road. It was therefore decided to take the determined average modulus as reference modulus:

• Layer NSL: 7442 MPa (Std. Dev.: 548.5 MPa)

• Layer 2: 6502 MPa (Std. Dev. 572.1 MPa)

Layer 1 Layer 1 showed strong variations between the determined moduli, depending on the position of the tested layers. It was observed that layers tested in section Ref 6 cm -2 (eastern end of the observed road part) had a stronger modulus than the layers of the other sections. The modulus of layer 1 used for modelling was therefore made dependent on the modelled section:

XXX

Calcul of smaller surfaces for Leutner tests

Normally the shear strength resulting from the Leutner test is calculated by dividing the shear force through the surface of the core, while the surface is calculated by A = π * r 2 .

In our case, the stressed surface is smaller than for normal cores, as the shearing form cannot have continuous contact with the core.

Therefore the working surface was calculated depending on the diameter of the core as well as on the fracture displacement determined during the test. Experimental and analytical study of the reinforcement of pavements by glass fibre grids