Jin Bo Su

Olivier Cazorla

Stéphane Blot

Nicolas Blanchard-Gutton

Younss Ait Mou

Inès Barthélémy

Lucien Sambin

Carolina Carlos Sampedrano

Bradykinin restores left ventricular function, sarcomeric protein phosphorylation, and e/nNOS levels in

Methods

Echocardiography examinations

Conventional echocardiography and 2D color tissue Doppler imaging (TDI) were performed by the examiners blinded to the animals' study group as previously described. [START_REF] Chetboul | Tissue Doppler assessment of diastolic and systolic alterations of radial and longitudinal left ventricular motions in Golden Retrievers during the preclinical phase of cardiomyopathy associated with muscular dystrophy[END_REF] Before thoracotomy, 2-3 weeks after surgical intervention as well as after 2 and 4 weeks of infusion, conscious dogs gently restrained in standing position and monitored with a continuous EKG were examined with a Vivid 7 ultrasound unit equipped with 5-7.5 and 2-5MHz phased-array transducers (GE, Waukesha, WI). Left ventricular (LV) diameter, LV free wall and interventricular septal wall thicknesses were measured at end-diastolic and endsystolic points in accordance with the recommendations of the American Society of Echocardiography. [START_REF] Sahn | Recommendations regarding quantitation in M-mode echocardiography: results of a survey of echocardiographic measurements[END_REF] LV fractional shortening (%) was calculated as (LV end-diastolic diameter-LV end-systolic diameter) / LV end-diastolic diameter x 100%. Pulsed-wave Doppler variables including early (E) and late (A) diastolic mitral inflow velocities were assessed from the left parasternal 4-chamber view and the mitral E/A ratio was calculated.

For 2D color TDI examinations, real-time color Doppler was superimposed on the gray scale with a high frame rate (> 150 frames/sec). Doppler receive gain was adjusted to maintain optimal coloring of the myocardium, and Doppler velocity range was set as low as possible to avoid aliasing. All digital images were analyzed using specific software (Echo Pac 5.4, GE, Waukesha, WI). A 2 x 2 mm sample was used and a tissue velocity profile displayed in each sample location. Myocardial velocities resulting from the radial LV free wall motion were measured using the right parasternal ventricular short-axis view and measurements were made between the 2 papillary muscles in subendocardial and subepicardial segments of the LV free wall. For each myocardial velocity, the mean value was calculated based on the measurements of 3 consecutive cardiac cycles on the same frame. Radial endo-epicardial systolic myocardial velocity gradients (defined as the difference between systolic subendocardial and subepicardial velocities) were then calculated. Heart rate was also calculated by EKG monitoring during each radial TDI examination by averaging the same 3 cardiac cycles used for the velocity measurements.

Myocyte preparation and single cell experiments

Immediately after euthanasia, LV myocardial samples were placed in an ice-cold modified-Tyrode's solution containing (in mM): NaCl 140, KCl 4.8, NaHCO 3 2.5, NaH 2 PO 4 1.6, MgSO 4 5.0, HEPES 12, glucose 12.5, pH 7.4, adjusted with NaOH. Several subendocardial and subepicardial strips (8 mm long, 2 mm wide, and 1 mm thick) were dissected from the same heart. Muscle strips were either frozen in liquid nitrogen for biochemistry or prepared for mechanical experiments as previously described. [START_REF] Cazorla | Transmural stretchdependent regulation of contractile properties in rat heart and its alteration after myocardial infarction[END_REF] For micromechanical experiments, muscle strips were permeabilized 10 min at 4°C in relaxing solution containing 1% Triton X-100 and protease inhibitors (0.5 mM PMSF, 0.04 mM leupeptin, and 0.01 mM E64). Strips were then placed in fresh ice-cold relaxing solution and mechanically disrupted at 11,000 rpm for 2-3 s (Polytron PT45-80 with a PTA 10TS shaft, KINEMATICA AG, Switzerland), resulting in a suspension of small clumps of myocyte-sized preparations and cell fragments. The homogenized tissue was centrifuged (100 g, 1 min at 4°C). The pellet containing the myocytes was permeabilized in 0.3% Triton X-100 solution for 6 min to remove remaining sarcolemma membranes and then was extensively washed in relaxing solution. Cells were kept on ice and used within the day. Relaxing and activating buffers contained (in mM): phosphocreatine 12, imidazole 30, free Mg 2+ 1, EGTA 10, Na 2 ATP 3.3, and dithiothreitol 0.3 with pCa 9.0 (relaxing solution) and pCa 4.5 (maximal activating solution), pH 7.1 adjusted with acetic acid (osmolarity 280 mOsm). Potassium acetate was added to adjust ionic strength to 180 mM. The skinned myocyte was attached at either end to a piezoresistive strain gauge (model AE 801, SensoNor a.s., Horten, Norway; 500 Hz unloaded resonant frequency) and a stepper motor driven micromanipulator (MP-285, Sutter Instrument Company, Novato, CA) with thin needles and optical glue (NOA 63, Norland Products, North Brunswick, NJ) that was polymerized by UV illumination for 2 min. The sarcomere length was determined online throughout the experiment (Ionoptix system). Force was normalized by the cross-sectional area measured from the imaged cross-section as described elsewhere. [START_REF] Cazorla | Differential expression of cardiac titin isoforms and modulation of cellular stiffness[END_REF] Force-pCa relationships were established at two sarcomere lengths of 1.9 and 2.3 μm. Active tensions at submaximal activations were normalized to maximal isometric tension (obtained at pCa 5) at the same sarcomere length. The relation between force and pCa was fitted to the following equation: force=[Ca 2+ ] nH /(K+[Ca 2+ ] nH ), where nH is the Hill coefficient and pCa 50 , pCa for half-maximal activation equals -(log K)/nH.

Western blot analysis

The frozen myocardial tissue was grinded, homogenized and centrifuged (25,000 g, 15 min). The supernatant was used for western blot analysis of nNOS, eNOS, cMyBP-C, phosphorylated cMyBP-C (p-MyBP-C), cardiac TnI, phosphorylated TnI (p-TnI) and two isoforms of VL2 (VLC2, VLC2*) and their phosphorylated forms (p-VLC2, and p-VLC2*).

Protein concentration was determined with the Bio-Rad Protein Assay (Bio-Rad, France).

Equal amounts of extracted proteins were separated on 4-15% SDS-PAGE gels for most proteins studied and transferred to polyvinylidene fluoride membranes using standard technique. After blockade of non-specific epitopes with 5% milk, the blotted membranes were incubated with antibodies against nNOS, eNOS (sc-8309 and sc-654, at a dilution of 1:200 and 1:400, respectively; Santa Cruz Biotechnology, USA), calnexin (rabbit monoclonal antibody, 1:5,000; Sigma-Aldrich, UK), cMyBP-C, phosphor ser 282 -MyBP-C (rabbit, 1:1,000; Alexis, France), TnI and phosphor ser 23/24 TnI (mouse, 1:1,000; Hytest, Finland). Non-phosphorylated and phosphorylated VLC2 isoforms were separated according to their charge on 10% urea gel and revealed after transfer with VLC2 antibody (rabbit, 1:200; Coger SA, France) and calsequestrin (Rabit, ABR). Subsequently, the membranes were incubated with horseradish peroxidase-conjugated anti-rabbit IgG (1:5,000; Dako, France). Specific immunoactive proteins were detected by enhanced chemiluminesence (Biological Industries, Isreal or Amersham Pharmacia, UK). Analysis of images was performed using the ImageJ software (NIH, USA). nNOS and eNOS levels were expressed as a ratio to calnexin and the phosphorylation level of cMyBP-C, TnI and VLC2 isoforms was expressed as a ratio of the phosphorylated form/total form.

Results

We have also measured arterial pressure before and after 4 weeks of placebo or bradykinin infusion using aortic catheter. The data showed that before treatment, mean arterial pressure was significantly lower in GRMD dogs (103±3 mmHg, n=10) than in control dogs (115±2 mmHg, n=8, p<0.01). After 4 weeks of placebo or bradykinin infusion, mean arterial pressure was 114±3, 117±2, 102±7 and 110±3 mmHg, respectively in placebo-treated control, bradykinin-treated control, placebo-treated GRMD and bradykinin-treated GRMD dogs versus 117±4, 114±3, 106±6, and 101±4 mmHg respectively at baseline, indicating no significant change in mean arterial pressure induced by placebo or bradykinin treatment in control and GRMD dogs.

Table 2 .

 2 Baseline echocardiographic data obtained 2-3 weeks after surgical intervention in conscious control and GRMD dogs randomized into placebo or bradykinin group Data are presented as mean±SEM. LV, left ventricular; EDD, end-diastolic diameter; EDFWTh, end-diastolic free wall thickness; FWTh, free wall systolic thickening; EDIVSWTh, end-diastolic interventricular septal wall thickness; IVSWSTh, interventricular septal wall systolic thickening; Vendo, radial systolic velocity in the subendocardial region; Vepi, radial systolic velocity in the subepicardial region; Endo-epi gradient; subendocardialsubepicardial gradient of radial systolic velocity E/A mitral, ratio of early to late diastolic mitral flow velocity.*p<0.05 vs control placebo group and †p<0.05 vs control bradykinin group.

		Control dogs	Control dogs	GRMD dogs	GRMD dogs
		Placebo	Bradykinin	Placebo	Bradykinin
	N	4	4	5	5
	Body weight, kg	26.5±2.6	29.3±3.8	18.8±2.4* †	18.6±2.7* †
	LVEDD, mm	46.1±2.6	46.7±3.6	43.1±4.7	43.2±1.4
	Fractional shortening, %	34.2±1.5	34.6±2.1	27.3±0.8* †	28.1±1.3* †
	LV EDFWTh, mm	9.3±0.2	9.1±0.8	6.9±0.5* †	6.8±0.5* †
	LV FWSTh, mm	5.6±0.3	5.4±0.9	2.9±0.8* †	1.9±1.0* †
	EDIVSWTh, mm	10.4±0.7	10.5±1.2	7.9±1.0* †	8.1±0.4* †
	IVSWSTh, mm	5.0±0.7	5.8±0.6	3.6±1.3* †	3.6±0.9* †
	Vendo, cm/s	6.5±0.8	6.9±1.1	5.8±0.5	5.9±0.4
	Vepi, cm/s	3.6±0.4	3.9±0.7	4.1±0.6	4.5±0.4
	Endo-epi gradient, cm/s	3.0±0.4	3.0±0.3	1.7±0.3* †	1.4±0.1* †
	E/A mitral	2.0±0.4	2.0±0.3	1.7±0.1	1.7±0.3


Pierre Mounanga
email: pierre.mounanga@univ-nantes.fr

- Khalid Cherkaoui
email: khalid.cherkaoui@univ-nantes.fr

Abdelhafid Khelidj
email: abdelhafid.khelidj]@univ-nantes.fr

- Mireille Courtial

-Marie-Noëlle De Noirfontaine
email: marie-noelle.de-noirfontaine]@polytechnique.edudunstet@poly.polytechnique.fr

- Frédéric Dunstetter

Extrudable Reactive Powder Concretes Hydration, shrinkage and transfer properties

Keywords: Béton de poudres réactives, extrusion, hydratation, retrait, durabilité Reactive powder concrete, extrusion, hydration, shrinkage, durability

Le comportement de cinq bétons de poudres réactives (BPR), dont quatre présentent des propriétés d'extrudabilité, a été étudié depuis les premières minutes après leur fabrication jusqu'à plus de 90 jours de maturation. La force d'extrusion, la cinétique d'hydratation, le développement du retrait endogène libre au jeune âge, les propriétés mécaniques et les paramètres de durabilité ont été mesurés. L'analyse des performances a montré l'intérêt d'une substitution partielle de la fumée de silice par du quartz broyé sur les propriétés des BPR. L'analyse coût/performances a mis en évidence que le principal avantage de l'utilisation des BPR réside dans leur potentiel de durabilité, 10 à 100 plus élevé que celui de bétons ordinaires ou à hautes performances, selon la propriété considérée.

ABSTRACT. The behavior of five reactive powder concretes (RPC), with four of them being extrudable, has been studied since the first minutes up to more than 90 days. The extrusion force, hydration rate, free autogenous shrinkage at early age, mechanical properties and durability parameters were measured. The performance analysis showed the benefits of a partial substitution of silica fume with crushed quartz on the RPC properties. The cost/performances analysis highlighted that the main advantage of using RPC lies in their potential of durability, which is 10 to 100 times higher than that of ordinary or highperformance concretes, according to the property considered.

Introduction

Reactive Powder Concretes (RPC) constitute a particular type of cementitious materials developed in the early 1990s [START_REF] Richard | Reactive powder concretes with high ductility and 200-800 MPa compressive strength[END_REF][START_REF] Richard | Composition of reactive powder concretes[END_REF][START_REF] Aïtcin | Cements of yesterday and today: concrete of tomorrow[END_REF] and characterized by ultra-high mechanical performances and very low porosity. After a specific heat treatment, their compressive strength lies between 200 and 800 MPa. RPC are mainly used in civil engineering projects as bridges or airports [START_REF] Aïtcin | Cements of yesterday and today: concrete of tomorrow[END_REF], or as repair materials for concrete structures [START_REF] Denarié | Tailored composite UHPFRC-concrete structures[END_REF][START_REF] Lee | A preliminary study of reactive powder concrete as a new repair material[END_REF]. Also, the low porosity of RPC gives excellent durability and transport properties, suitable for the storage of nuclear waste [START_REF] Matte | Durability of Reactive Powder Composites: Influence of silica fume on the leaching properties of very low water/binder pastes[END_REF]. Their proportioning principles are based on the optimization of the microstructure [START_REF] Bonneau | Characterization of the granular packing and percolation threshold of reactive powder concrete[END_REF], by enhancing the granular packing and minimizing the interparticle porosity. This is obtained by combining fines mineral particles (Portland cement, crushed filler, silica fume, fine sand) in the range of 0.02 to 600 microns, with very low water-to-cement ratio and high amount of high-range water-reducing superplasticizer [START_REF] Richard | Reactive powder concretes with high ductility and 200-800 MPa compressive strength[END_REF].

This cocktail of constituents, with very different physico-chemical properties and particle size distributions, results in a particularly dense skeleton with a wide range of rheological behaviors, from very viscous (Kuder et al., 2007a) to highly flowable [START_REF] Liu | Highly flowable reactive powder mortar as a repair material[END_REF]. Nevertheless, the mix design of RPC remains a complex process because of the sensitivity of the mixture properties to even small changes in the constituent dosages. Another major obstacle to the wide use of these materials is their high cost compared to that of high or very high-performance concretes [START_REF] Blais | Precast, prestressed pedestrian bridge -World's first reactive powder concrete structure[END_REF].

The use of industrial making processes could enable to overcome these issues by ensuring both compliance with the mix design throughout the production chain and high production rates. From this point of view, the extrusion process seems to meet such requirements: it is an advanced processing technique already applied to a wide range of materials (food, polymer, clay and metal). In the field of cement-based materials, extrusion has proved to be an efficient technique, particularly adapted for the production of prefabricated elements with very high mechanical performances [START_REF] Qian | Fiber alignment and property direction dependency of FRC extrudate[END_REF]Kuder et al., 2007b;[START_REF] Perrot | Mortar physical properties evolution in extrusion flow[END_REF].

In this context, the present study is devoted to the development of extrudable RPC (ERPC), especially designed for the manufacture of tubular elements adapted to chemically aggressive environments. To this end, various RPC were prepared with varying dosages of polycarboxylate superplasticizer, silica fume and crushed quartz to obtain extrudable mixtures. Alongside their microstructural analysis by Xray diffraction and scanning electron microscopy [START_REF] Courtial | Microstructure d'un Béton de Poudre Réactive Extrudable[END_REF], the materials were characterized at fresh state (extrudability), at early age (hydration rate and autogenous shrinkage) and at longer term (mechanical strength, porosity and mass transfer parameters). The article proposes a cross-analysis of the ERPC properties measured before extrusion, and a comparative cost/benefits ratio analysis including other types of concretes.

Experimental procedures

Materials and mixtures

The ERPC studied were prepared with Portland cement (CEM I 52.5N, produced by Lafarge in Le Havre's plant), silica fume (commercialized by Condensil), crushed quartz powder (Millisil C500, Sibelco), siliceous sand (CV32, Sibelco), superplasticizer, noted SP (Cimfluid 2002, Axim) and water. The cement contained 3.30% of gypsum and its Bogue composition was 67.50% of C 3 S, 10.70% of C 2 S, 2.64% of C 3 A, 12.80% of C 4 AF. The chemical composition of the solid components of ERPC is provided in Table 1. Their density and fineness are given in Table 2. The SP used was a modified-polycarboxylate high-range water-reducing superplasticizer in liquid form with 35% of dry matter. The dosages of SP, indicated in Table 3, correspond to the mass ratio between the SP dry matter and the cement content.

The ERPC were manufactured by mixing the solid compounds with tap water in a 20-L mixer. The water-to-cement (W/C) ratio was equal to 0.16 for all the ERPC. The same mixing procedure, schematized in Figure 1, was rigorously applied for each batch. The total time of mixing was 25 min. The composition of the five ERPC mixtures investigated is given in Table 3.

It is important to note that all the tests presented in the following sections were performed on non-extruded ERPC samples.

Test procedures

In order to control the test conditions, the experimental devices were placed in a temperature-controlled room at 20±1°C.

Extrusion tests

The extrusion tests were carried out with a ram extruder (home-made device) placed on a 50-kN compression test machine. The diameter and the length of the circular die were 1.2 cm and 3 cm, respectively. The experimental system is presented in Figure 2. Before each test, the sample was put under vacuum for 5 minutes, to de-aerate the material without losing significant amounts of water by evaporation. The barrel of the extruder was then completely filled with freshlymixed material.

A pre-compression phase enabled to obtain a similar initial state of the various ERPC before extrusion. Then the extrusion started, and the ram drove down at a selected constant speed. During the test, the force exerted by the piston and its displacement were recorded. Different extrusion rates were applied to measure the effect of this parameter on the extrudability of the RPC.

Hydration rate

Isothermal microcalorimetry (TAM Air apparatus) was used to compare the early-age hydration rate of the different ERPC. For each mix, two samples of about 4 g were taken from the same batch and placed into flasks immediately after mixing. The flasks were then loaded in the apparatus and the heat flow produced by the hydration reactions was recorded during the first six days at 20°C. The average curves from two samples of each mix were used for analysis.

Autogenous strain

Early-age autogenous strains of ERPC in free conditions were measured with a specific experimental system presented in previous articles [START_REF] Bouasker | Free autogenous strain of early-age cement paste: Metrological development and critical analysis[END_REF]Mounanga et al., 2011a). It was a horizontal linear experimental system (Figure 3) inspired by the works of Laplante and Boulay [START_REF] Laplante | Evolution du coefficient de dilatation thermique du béton en fonction de sa maturité aux tout premiers âges[END_REF] and [START_REF] Jensen | A dilatometer for measuring autogenous deformation in hardening Portland cement paste[END_REF]. The fresh material was cast in a molded, tight and very flexible PVC membrane and immersed in a thermostated water bath at 20±1°C. Waterproof contactless sensors were used to measure the longitudinal specimen displacements, which were automatically recorded by a data logging system connected to the sensors. This method made it possible to follow the deformations of the sample from its very early age.

After the gas permeability and porosity tests, each ERPC disc was placed between two chambers containing solutions of NaOH (0.025 mol/L) and KOH (0.083 mol/L). NaCl (0.513 mol/L) was added in the upstream solution and a 12-V potential difference was applied between the two parallel sides of the concrete sample. The chloride concentration in the downstream tank was determined by means of potentiometric titration with a Metrohm SA CH-9101 Herisau automatic titrator, with 0.05 molar silver nitrate (AgNO 3 ) titrant [START_REF] Djerbi | Influence of traversing crack on chloride diffusion into concrete[END_REF].

Results and discussion

Extrudability

The extrusion tests were performed at various ram speeds (10, 20 and 40 mm/min) on the five RPC. Figure 4 presents an extrusion test and the "forcedisplacement" curves obtained on ERPC_1 and ERPC_2. At the die exit of the extrusion system, the self-supporting material left in a continuous manner and without cracks. In addition, the ERPC did not exhibit visible phase migration or separation of phases after extrusion. These observations prove the extrusion capacity of the ERPC. The "force-displacement" curves recorded during the extrusion tests could be segmented into three main parts [START_REF] Aouadja | Contribution à l'étude de simulation du procédé d'extrusion -Mise au point d'un nouvel appareil[END_REF][START_REF] Perrot | Conditions d'extrudabilité des matériaux à base cimentaire[END_REF]):

-The first part of the curves (Zone 1) was relative to a phase of non stationary flow due to the placing and the settling of the material into the barrel. The duration of this phase was particularly influenced by changes in the SP dosage: considering the other mix parameters as constant, we observed that an increase in the dosage of superplasticizer caused an extension of the Zone 1 (Figures 4.A and 4.B).

-The second part (Zone 2) corresponded to a zone of steady flow, showing the establishment of a permanent flow of the ERPC for a relatively constant extrusion force. At this moment, the material reached its plasticity threshold [START_REF] Perrot | Conditions d'extrudabilité des matériaux à base cimentaire[END_REF]). The extrusion force, whose intensity corresponded to the horizontal stage of the curves, increased when the ram speed increased and decreased as the dosage of superplasticizer increased, for given dosages in solid constituents, -The third phase (Zone 3) indicated the end of the test. It appeared when the piston approached the entry die. It was characterized by rapid changes in force for a small displacement of the piston. This phase corresponded to the compression of the dead zone of the extruder and the complete emptying of the die. The maximum capacity of the extruder system was then reached and the extrusion was stopped.

During these tests, only RPC_3 appeared as not extrudable because too fluid. Besides, the introduction of crushed quartz, coarser than silica fume, in the mix composition enabled to increase the viscosity of the mixture and to obtain extrudable concretes, even for high dosages of SP (ERPC_4 and ERPC_5). This result shows that the optimization of both dosages of crushed quartz and SP could allow to minimize the force needed for the extrusion of ERPC.

Hydration rate

Figure 5 presents the evolution of the heat flow of hydration monitored by isothermal microcalorimetry. Each curve is characterized by a dormant period with a very low evolution of the heat flow, followed by a peak marking a period of intense chemical activity. This early-age chemical activity of ERPC may be mainly attributed to Portland cement hydration, since it was shown that, at 20°C, the pozzolanic reactions of silica fume remained weak during several days [START_REF] Mansoutre | Quantitative phase analysis of Portland cements from reactive powder concretes by X-ray powder diffraction[END_REF][START_REF] Loukili | Hydration kinetics, change of relative humidity and autogenous shrinkage of ultra-high-strength concrete[END_REF], and even nil for crushed quartz [START_REF] Zanni | Investigation of hydration and pozzolanic reaction in reactive powder concrete (RPC) using 29 Si NMR[END_REF]. The peak of heat flow could therefore be associated with the hydration of C 3 S, the major phase of Portland cement (Taylor 1990;[START_REF] Odler | Hydration, setting and hardening of Portland cement[END_REF]. It occurred at 25.2, 40.7, 59.7, 55.4 and 58.6 h for ERPC_1, ERPC_2, RPC_3, ERPC_4 and ERPC_5 mixtures, respectively. The appearance of this peak was considerably delayed when comparing with the hydration rate of an ordinary Portland cement mortar, whose hydration peak usually developed within the first 12 h of hydration (Mounanga et al., 2011b). This delay was caused by the high dosage of SP in ERPC, which induced an extension of the dormant period of the hydration reactions. This slowing down was particularly high for RPC_3 and also resulted in a significant decrease of the hydration peak intensity, as shown in Figure 5. This secondary effect of SP on cement hydration is well-known and explained by the adsorption of the polymers on cement grains, and also by possible reactions of the Ca 2+ ions with polymer anions [START_REF] Mollah | A review of cementsuperplasticizer interactions and their models[END_REF], which generate a global retardation of hydration.

The presence of crushed quartz enabled to partially limit the retardation effect of SP on hydration rate: indeed, the hydration peak of the ERPC_4-curve developed about 4 h before that of the RPC_3 curve, for identical SP dosage. The peak magnitude was also higher for ERPC_4, as compared with RPC_3, indicating a greater chemical activity at early age. This positive influence of crushed quartz on the advancement of reactions may be caused by an effect of nucleation site on the development of hydrates: Indeed, Cyr et al. [START_REF] Cyr | Efficiency of mineral admixtures in mortars: Quantification of the physical and chemical effects of fine admixtures in relation with compressive strength[END_REF] highlighted that the presence of very fine particles (with specific surface area higher than 100 m 2 /kg) could activate the cement hydration by heterogeneous nucleation. This physical process is related to the nucleation of hydrates on foreign mineral particles and causes an acceleration of the early-age cement hydration and setting.

Several studies have shown that silica fume also has the ability to accelerate early-age cement reactions by nucleation and growth site effect [START_REF] Yi | Hydration reactions in Portland cement-silica fume blends[END_REF][START_REF] Lilkov | Hydration process of cement containing fly ash and silica fume: the first 24 hours[END_REF]Zelić et al., 2000, for example). Some of these studies revealed that this accelerating effect depended on both the initial water content and the dosage of silica fume [START_REF] Langan | Effect of silica fume and fly ash on heat of hydration of Portland cement[END_REF][START_REF] Kadri | Silica fume effect on hydration heat and compressive strength of high-performance concrete[END_REF]. It seems that, for the ERPC investigated and the powder dosage considered here, crushed quartz was more efficient than silica fume in increasing early-age cement hydration rate.

Early-age autogenous shrinkage

Figure 6 shows the results of free linear autogenous shrinkage of ERPC at 20°C. As the deformations were monitored from the very first minutes after mixing, the autogenous strain measured was a combination of chemical shrinkage and selfdesiccation shrinkage. Chemical shrinkage, also called Le Chatelier's contraction, develops before the setting of the matrix: it mainly corresponds to the dissolution of clinker minerals, hydration of anhydrite and precipitation of ettringite (Beltzung et al., 2000), and to the negative balance between the absolute density of hydrates and those of the binder and water [START_REF] Powers | Studies of the physical properties of hardened Portland cement paste[END_REF][START_REF] Mounanga | Predicting Ca(OH) 2 content and chemical shrinkage of hydrating cement pastes using analytical approach[END_REF]. The setting and the progressive water desaturation of the porous network leads to a second type of deformation, called self-desiccation shrinkage. Self-desiccation is directly linked to the initial water content of the cement-based material, a lower water-to-binder ratio giving higher self-desiccation shrinkage [START_REF] Baroghel-Bouny | Autogenous deformations of cement pastes -Part II: W/C effects, micro-macro correlations and threshold values[END_REF]. The transition between chemical shrinkage and self-desiccation shrinkage is generally marked by the flattening of the autogenous shrinkage curve [START_REF] Justnes | Total and external chemical shrinkage of low W/C ratio cement pastes[END_REF].

In our case, considering identical dosages of cement and water and low reactivity of the supplementary cementing materials at early-age, the gap between the autogenous shrinkage curves of the different ERPC may be due to both the varying SP content and the partial substitution of silica fume with crushed quartz. The hydration retardation induced by the SP, highlighted in the previous section, led to a delay of setting and an extension of the deformation phase dominated by chemical shrinkage. The development of the chemical shrinkage of the ERPC was particularly high during the first hours, while the main peak of hydration has not yet

Age (h) ERPC_1 ERPC_4 RPC_3
appeared (Figure 5). This discrepancy between the relatively low heat release of the ERPC and the significant very early-age volume changes was closely related to the dosage in SP of the ERPC: indeed, RPC_3 (SP dosage = 1.8%) exhibited higher autogenous shrinkage values than ERPC_2 (SP dosage = 1.0%), whose autogenous shrinkage was higher than that of ERPC_1 (SP dosage = 0.5%). The flattening of the curves, which indicates the transition from chemical to self-desiccation shrinkage, also appeared later when the SP content increased. All other mix parameters being kept constant, the partial substitution of silica fume with crushed quartz induced a decrease of the autogenous shrinkage of ERPC_4, when compared to that of RPC_3 (Figure 6). This positive effect of crushed quartz on early-age autogenous strain can be linked to its acceleration effect on cement hydration rate (see section 3.2): it may be supposed that the presence of crushed quartz attenuated the SP retardation effect on the setting time of ERPC. Therefore, the material hardened more rapidly and resisted more efficiently to the strain imposed by Le Chatelier's contraction and the water desaturation of the porous network. Crushed quartz probably also led to a better particle packing and, consequently, to a reorganization of the porous network of the cementitious matrix: as the pore distribution is one of the major parameters controlling the evolution of selfdesiccation [START_REF] Jiang | Autogenous relative humidity change and autogenous shrinkage of high-performance cement pastes[END_REF], this effect of crushed quartz on the mitigation of early-age ERPC autogenous shrinkage, should be investigated more deeply. A third complementary explanation to the lower autogenous strain of ERPC_4 was the higher Young's modulus value of this mixture (Table 4): submitted to an identical internal capillary tension, it will shrink less than the other ERPC.

Mechanical and transfer properties

Table 4 provides the 28-day mechanical performances of ERPC, ordinary and high-performance concretes, for comparison. The ERPC compressive strength values were in the same range than those given by Richard and Cheyrezy [START_REF] Richard | Composition of reactive powder concretes[END_REF], for a RPC200 without fibers, cured at 20°C, and more recently by Yazici [START_REF] Yazici | The effect of curing conditions on compressive strength of ultra high strength concrete with high volume mineral admixtures[END_REF].

The increase of SP content resulted in a significant decrease of compressive strength and a simultaneous increase of Young's modulus. Indeed, the addition of SP generates a more homogeneous microstructure, promoting a better distribution of hydrates around the sand grains. This would prevent the phenomena of rigidification and locking created by contacts between solid grains. The SP may also play the role of a lubricant around some solid particles that are not in contact with the hydrates. The effect of SP content was less significant on flexural strength.

The partial replacement of silica fume with crushed quartz appeared to significantly improve the mechanical properties of ERPC: it led to an increase of 25% of the compressive strength, 20% of the flexural strength and 16% of the dynamic Young's modulus, for a constant SP content (Table 4). This improvement of mechanical performances could be explained by a better hydration of cement in presence of crushed quartz, as already observed on microcalorimetry curves (Figure 4) and by a better granular packing of the ERPC in presence of crushed quartz, which presents a particle size distribution intermediate between the cement and silica fume used [START_REF] Cherkaoui | Early-age volume changes of extrudable reactive powder concrete[END_REF]. Indeed, the optimization of the particle packing is the main way to obtain denser cement-based matrices and therefore greater mechanical performances [START_REF] Richard | Composition of reactive powder concretes[END_REF][START_REF] Scrivener | Innovation in use and research on cementitious material[END_REF] The water-accessible porosity, the gas permeability and the chloride diffusion coefficient measured on ERPC specimens aged of more than 90 days are presented in Figures 7.a, 7.b and 7.c, respectively, and compared with bibliographical data on ordinary and high-performance concretes [START_REF] Djerbi | Influence de l'endommagement mécanique sur la perméabilité au gaz et sur la diffusion des ions chlore des bétons[END_REF]. Because of the very low porosity of the ERPC, the measurement of their mass transfer properties was not an easy task. The gas permeability of the ERPC_4 and ERPC_5 mixes were too low to be detectable with the Cembureau permeameter. Moreover, the chloride migration test results highlighted the difficulties in saturating the ERPC porosity with conventional procedures (AFPC-AFREM 1997). The possible hydration of anhydrous cement, which is present in large proportion in RPC, and the potential interactions between cement and chlorides further complicated the result analysis. As expected, the water-accessible porosity was very low (Figure 7.a). The values obtained were close to those presented in previous studies: for example, Resplendino and Petitjean indicated water-accessible porosity values of RPC between 1.5 and 5% [START_REF] Resplendino | Ultra-high-performance concrete: First recommendations and examples of application[END_REF]. The absolute differences recorded between the porosity of the five ERPC were not high enough to conclude on a particular effect of SP or crushed quartz content. The gas permeability values of the ERPC_1, ERPC_2 and RPC_3 specimens were 3.75×10 -19 m 2 , 1.62×10 -19 m 2 and 2.56×10 -19 m 2 , respectively. The chloride diffusion coefficients of ERPC lay between 0.88 and 1.38×10 -13 m 2 /s. These results could be compared to those presented by Resplendino and Petitjean, who gave an oxygen permeability value lower than 10 -19 m 2 and a chloride-ion diffusion factor equal to 2×10 -14 m 2 /s for an ultra-high performance concrete [START_REF] Resplendino | Ultra-high-performance concrete: First recommendations and examples of application[END_REF]. Present study

Comparative cost/benefits analysis

The composition of RPC, rich in cement, silica fume and superplasticizer, makes them much more expensive than conventional concretes. Indeed, for the ERPC investigated, the dosages of cement, silica fume and superplasticizer range between 962 and 976 kg/m 3 , 183 and 242 kg/m 3 and 13 and 56 L/m 3 , respectively. The particularly high cost of RPC is one of the main obstacles to a wider use of these concretes, but this aspect is generally not addressed in the articles dealing with RPC. In 1999, Blais and Couture noted that, because of its cost, RPC will not replace conventional concrete where the ordinary concrete can economically meet performance criteria. RPC should rather be seen as a competitor with steel. Blais and Couture also underlined that the cost of RPC dropped one-third between 1997 (the year of the completion of the Sherbrooke pedestrian/bikeway bridge, the world's first major structure to be built with RPC) and 1999. When the Sherbrooke Footbridge was built, the cost of a 200-MPa RPC could be estimated at nearly $ 1,000 US/m 3 [START_REF] Aïtcin | Les bétons à haute performance[END_REF], about 870 €/m 3 . In 2003, Aïtcin indicated that the same RPC could be made for $ 750 US/m 3 (650 €/m 3 ) and in the near future, it should be possible to produce it for $ 600 to $ 650 US/m 3 (520 to 570 €/m 3 ). Aïtcin also analyzed that even at $ 1,000 US/m 3 , that is to say $ 400 US/ton (350 €/ton), for specific applications where durability and compressive strength were key factors, RPC could compete with structure steel that cost $ 1200 to $ 1500 US/t (1,040 to 1,300 €/ton in 2003). Comparison with an ordinary concrete (OC), a high-performance concrete (HPC) [START_REF] Djerbi | Influence de l'endommagement mécanique sur la perméabilité au gaz et sur la diffusion des ions chlore des bétons[END_REF] To complete this analysis, the last part of the article is devoted to an estimation of the cost of the ERPC and a comparison of their cost/benefits ratio with those of an ordinary concrete (OC) and a high-performance concrete (HPC) whose properties were taken from the literature [START_REF] Djerbi | Influence de l'endommagement mécanique sur la perméabilité au gaz et sur la diffusion des ions chlore des bétons[END_REF]. It is worth noting that the approach proposed is only estimative, since the concrete cost and the cost/benefits ratios do not only depend on the cost of the concrete constituents but also on the manufacture process of concrete.

The average costs of each component of concrete are recapitulated in Table 5. The most expensive constituents are the SP and the silica fume. For the latter, the cost is very dependent on the quality and the treatment applied to the material: it can vary from 500 €/ton for the grey silica fume to 2,000 €/ton for the white silica fume. These data were used to estimate the cost of the ERPC investigated. The high dosage of cement, silica fume and SP in ERPC results in a material cost up to 15 times higher than those of the ordinary concrete and high-performance concrete considered (Table 6).

However, the cost per m 3 of ERPC should be analyzed in terms of gain of performances. The performance ratios between each concrete and the ordinary concrete were calculated for the compressive strength R C , the gas permeability K V , the water-accessible porosity n and the chloride diffusion coefficient D e (Table 6). Considering the mechanical properties, the HPC had the best cost/benefits ratio: the ratio between the cost of HPC and OC was about the same that the ratio between their compressive strength. For the ERPC, the cost ratio with OC ranged from 12.7 to 14.7, whereas their mechanical strength was multiplied only by a factor comprised between 3.0 and 3.8. The real benefits of ERPC appeared on their potential of durability: indeed, the performance ratios between ERPC and OC reached 140 for the intrinsic gas permeability, 13 for the water-accessible porosity and 21 for the chloride diffusion coefficient, far from the durability performance ratios between HPC and OC.

Conclusions

This research work focused on the development and the characterization of the fresh, the early-age and the durability performances of five reactive powder concretes (RPC), prepared with various dosages of superplasticizer and a partial replacement of silica fume with crushed quartz. The analysis of the results highlighted the following key points:

-Among the five RPC manufactured, four of them exhibited properties of extrudability. The extrusion tests, conducted at different ram speeds, gave a homogeneous, continuous and visible crack-free extrudate of these concretes; -The replacement of 25% of silica fume with crushed quartz showed significant positive effects on the hydration rate, the development of earlyage autogenous shrinkage, the 28-day mechanical performances and the long-term mass transfer properties of the extrudable reactive powder concretes (ERPC); -The cost/performances ratio analysis of the ERPC underlined that the major advantage of these concretes lies in their exceptional potential of durability rather than in their mechanical strength, when comparing with conventional and high-performance concretes. This work was conducted to optimize the composition of the ERPC matrix, free of fibers. The study of both the effect of fibers on the behavior of ERPC and the feasibility of extruding tubular pieces will be the next steps of this research work.

Figure 2 .

 2 Figure 2. Extrusion test device

Figure 4 .

 4 Figure 4. Extrusion test results of ERPC_1 (A) and ERPC_2 (B) at three different ram speeds

Figure 5 .

 5 Figure 5. Isothermal calorimetry curves of the ERPC

Figure 6 .

 6 Figure 6. Early-age linear autogenous shrinkage of the ERPC

Figure 7 .

 7 Figure 7. Mass transfer properties of ERPC measured after 90 days of hydration.A: Water-accessible porosity; B: Intrinsic gas permeability; C: Chloride diffusion coefficient. Comparison with an ordinary concrete (OC), a high-performance concrete (HPC)[START_REF] Djerbi | Influence de l'endommagement mécanique sur la perméabilité au gaz et sur la diffusion des ions chlore des bétons[END_REF]

Table 1 .

 1 Chemical composition (mass percentage) of the solid components of ERPC

	Constituents Portland cement	Silica fume	Sand	Crushed quartz
	CaO	64.58	-	< 0.023	< 300 ppm
	SiO 2	21.39	93.50	> 98.7	> 98.9
	Al 2 O 3	3.66		< 0.6	< 8000 ppm
	Fe 2 O 3	4.25		< 0.045	< 800 ppm
	MgO	0.96	6.10	-	-
	K 2 O	0.28		< 0.460	< 6000 ppm
	SO 3	2.63		-	-
	Na 2 O	0.10	0.15	-	-

Table 2 .

 2 Fineness and density of the solid components of ERPC

	Materials	Portlan d cement	Silica fume	Crushed quartz	Sand
	Specific surface area (m 2 /kg)	382	14 000	1030	12.6

End of mixing Addition of water and SP Introduction of solids compounds Figure 1. Mixing procedure of ERPCTable 3 .

 3 Composition of ERPC (mass proportion)

	Mixtures	Portland cement	Sand Silica fume	Crushed quartz	SP*	Water
	ERPC_1	1	1.1	0.25	0	0.5%	0.16
	ERPC_2	1	1.1	0.25	0	1.0%	0.16
	RPC_3	1	1.1	0.25	0	1.8%	0.16
	ERPC_4 ERPC_5	1 1	1.1 1.1	0.25 × 3/4 0.25 × 3/4	0.25 × 1/4 0.25 × 1/4	1.8% 2.0%	0.16 0.16
	*: Superplasticizer

Table 4 .

 4 28-day mechanical properties of ERPC. Comparison with an ordinary concrete (OC) and a high-performance concrete (HPC)

	Concretes	W/C ratio E dyn (GPa)	R C (MPa)	R F (MPa)	References
	OC HPC	0.49 0.38	42.0 46.0	46 83	--	Djerbi 2007
	ERPC_1		54.0	155	19.2
	ERPC_2		59.1	150	18.6
	RPC_3	0.16	60.0	140	18.6
	ERPC_4		69.4	175	22.3
	ERPC_5		65.3	170	20.6

Table 5 .

 5 Average costs of main components of concrete, excluding transport

	Constituents	Cost (€/ton)	References
	Cement	110	(SESSI 2007)
	Silica fume	500 to 2000	Manufacturer's data (2011)
	Crushed quartz	150	Manufacturer's data (2011)
	Fine sand for RPC	80	Manufacturer's data (2011)
	Aggregates	7	(Bodet 2003)
	Superplasticizer (SP)	1640	Manufacturer's data (2011)

Table 6 .

 6 Comparative data of the cost and performances of concretes (the indicated costs are based on the cost of the concrete constituents and do not take into account the cost of manufacturing, transportation, and implementation of concrete)

	Concrete	(€/m 3 )	Estimated cost of ordinary concrete Ratio with the cost	C R	Performance ratios as compared with ordinary concrete (OC) ) OC ) OC ( V K ) OC ( n OC ) ( e D C R ( V K n e D
	OC	52	1		1	1	1	1
	HPC	90	1.7	1.8	3.6	1.3	7.2
	ERPC_1	696	13.4	3.4	60.0	13.4	17.9
	ERPC_2	727	14.0	3.3	138.9	11.6	16.6
	RPC_3	764	14.7	3.0	87.9	10.6	13.6
	ERPC_4	660	12.7	3.8	> 140	6.8	21.3
	ERPC_5	669	12.9	3.7	> 140	9.1	17.4

Acknowledgement

The authors are grateful to Dr. Amor Ben Fraj, for his help in conducting the gas permeability and chloride penetration tests.