N Menad

N Kanari

S Guignot

F Diot

L Filippov

F Thomas

J Yvon

MATERIAL AND ENERGY BENEFICIATION OF THE AUTOMOBILE SHREDDER RESIDUES

Keywords: automobile shredder residues, thermal beneficiation, iron oxides reduction

Although vehicles represent a main key of our modern society, they affect our environment via the energy and resource consumption, waste generation during their manufacturing as well as greenhouse gas emissions all along their use. Further, hazardous residues are produced at the end-of-life vehicles "ELV". After collection and dismantling, the remainders of the ELV are directed to shredding operator followed by a series of mechanical and physical separations in order to recover the ferrous and non-ferrous metals. The residue of the shredding process, called automobile shredder residue "ASR" represents about 20-25% of the ELV. The ASR, while toxic enough to be classified as hazardous waste, could be considered as material and energy sources.

The present study deals with the possibility of material and energy beneficiation of the ASR by its use in the metallurgical units. ASR samples from an European automobile shredder company were collected and subjected to the physical separation process followed by a thermodynamic approach and isothermal batch tests to assess the reducing performance and energy capacity of the ASR hydrocarbon matter. Particular attention was devoted to the behavior of several residual and tramp elements (Cl, Pb, Cu, Zn) affecting the metallurgical process and the product quality. Results showed that physical operations (screening, attrition, dry low intensity magnetic separation) lead to a selective extraction of the mineral part of the ASR which can be directed to the blast furnace unit. Direct reduction of hematite by the plastics contained in the ASR was obtained at 1000-1050 °C resulting into multistage steps of Fe 2 O 3 converting into metallic iron. Multi-parametric analysis of the results suggests that the purified ASR can partially substitute raw materials used in pig iron and steel production.

Introduction

Vehicles represent a main key of our modern society and their number in use is increasing from year to year, reaching, in 2010, about one billion cars and light trucks on world's roads [START_REF] Sousanis | World vehicle population tops 1 billion units, Wards Auto[END_REF]. However, vehicles affect the environment through their entire life cycle. This environmental impact relates to the energy and resource consumption, waste generation during their manufacturing as well as greenhouse gas emissions all along their use. Further, hazardous residues are produced at the End-of-Life Vehicles "ELV". 11 million vehicles are annually discarded in the European Union, resulting in about 9 Mt of wastes that have to be disposed of [START_REF] Andersen | Projection of end-of-life vehicles: development of a projection model and estimates for ELVs for 2005-2030[END_REF]. Current European state of practice for spent cars processing falls into a manual depollution followed by the shredding of the cars hulks, which generates 2 to 2.5 million tons of Automotive Shredder Residues (ASR) each year [START_REF] Vermeulen | Automotive shredder residue (ASR): reviewing its production from end-of-life vehicles (ELVs) and its recycling, energy or chemicals valorization[END_REF]. Without further treatments, this residual stream is mainly landfilled or sent to municipal incinerators [START_REF]et du conseil du 18 septembre 2000 relative aux véhicules hors d'usage. J. Officiel des Communautés européennes[END_REF]. European legislation will impose a recycling rate greater than 95% of the car initial weight by 2015, resulting in less than 5% of waste discharge [5]. Although, the ASR is reactive enough to be classified as hazardous waste, it could be considered as a source of energy and reducing agent since it contains more than 70 % in combustible hydrocarbon matter (Figure 1), especially plastics. Note that the shredder companies use, besides ELV, other materials (e.g. plastics from discarded electric and electronic assemblies) in the shredding process leading often to a heterogeneous ASR depending on the input materials. Meeting the legal requirements by addressing the issue of ASR has led to the development of several Post-Shredder industrial lines of treatments [START_REF]et du conseil du 18 septembre 2000 relative aux véhicules hors d'usage. J. Officiel des Communautés européennes[END_REF], in which a fluff fraction is recovered by vacuuming ASR lighter components during shredding. Residual metals and plastic-rich fractions are then extracted from this fluff by means of magnetic, eddy current and sequences of sink-float separations.

Besides being marketed anew, recovered plastics can be valued as a relevant additive to the pulverized coal injected through blast furnace tuyeres [START_REF] Menad | Recycling of auto shredder residue[END_REF]. In addition, considering that iron content in ASR can mount up to 18 (%) wt of the light fraction [START_REF] Jalkanen | On the direct recycling of automotive shredder residue and electronic scrap in metallurgical industry[END_REF], residual mineral fractions might also be used as part of the ore feedstock in metallurgical furnaces, provided further enrichments are performed to curb specific tramp elements. For instance, upon combustion, materials containing chlorine generate gas which is corrosive for the furnace and the dusts removal post-treatments [START_REF]Converting waste plastics into a resourcecompendium of technologies[END_REF]. K 2 O can deposit into coke and sinter porous structures and weakens their Reduction Degradation Index (RDI). Copper is related to surface cracking of steels during hot rolling process. Sb, Sn and As accentuate this negative effect by segregating at grain boundaries during coiling in the hot strip mill, thus reducing the grain cohesion and thereby favoring embrittlement. This segregation is higher in steel containing Ni, Mn and Cr. Lastly, gaseous zinc can condense onto the blast furnaces inner walls, favoring scabs that modify the furnace flow configuration.

Despite such considerations on the chemical composition of plastic and mineral fractions generated from Post-Shredder industrial lines of treatments, few studies consider the design of a separation process which would open the way for a Blast Furnace (BF) injection. The present paper addresses this issue by focusing on 2 plastic fractions and 2 mineral fractions sampled on an industrial Post Shredder line of ASR treatment, so as to dispose of representative composition data. The separation processes associate sieving, gravity separation and low intensity magnetic separation. The separation efficiency is discussed in line with the chemical composition of the various outlets obtained. For the most interesting outlets, their use in a BF is assessed through a mass balance model of the tramp elements inside the furnace, with an attention paid to the effect on the pig iron specifications and the steel quality.

Materials

Four ASR samples were supplied by an European automobile shredder company and two of them, composed essentially of the wasted plastics. They are separated by sink float process and they are classified as Light Fraction "LF" and Dense Fraction "DF". The carbon content of the LF is about 66.8 % whilst that of the DF is 42.1 %. Chlorine is almost concentrated in the DF (6.8 % Cl) indicating the presence of the PVC and of certain rubbers. Tramp elements (Pb, Zn…) as well as calcium are also found mostly in the DF. The other two samples were sampled from successive dry low intensity magnetic separations and called mineral fractions (MF#1 and MF#1). These fractions contain 36.8% and 19.4% of iron oxides respectively. Chlorine is almost the same in both fractions (0.3%). The carbon content of the MF#1 is approximately 8% whilst that of the MF#2 is 10.5%. The tramp elements (Pb, Zn….) as well as CaO and SiO2 are found in both fractions.

Methods

Two PVC samples were used for this investigation of the plastic fractions. The first sample is wasted PVC and it is noted as PVC-1. The second sample is pure chemical grade PVC and is called PVC-2. Iron oxide, subjected to reduction, is high purity hematite (Fe 2 O 3 ). Thermodynamic approach using HSC chemistry was considered for selective removal of tramp elements (Pb, Cu, Zn …) via chloride formation & volatilization and for hematite reduction. Mixtures of ASR and/or PVC samples with hematite were conditioned as pellets by using kaolin clay as useful bonding and plasticizing agent. Obtained pellets were dried in an oven at 70 °C before thermal treatment and different analysis tests. The thermal behaviors of the individual samples and their mixtures were checked in horizontal experimental set-up including a static electrical furnace. Most of the tests were performed under air atmosphere for the treatment of the ASR and PVC alone. The thermal reduction of hematite containing mixtures was performed without gas circulation and/or under a low flow rate of air. Raw samples and solid reaction products were examined by scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD) and infrared (DRIFTS) spectroscopy.

The two mineral fractions MF#1 and MF#2 were subjected to physical separations, where. Sorting operations such as grinding, screening, attrition, and magnetic separation were used in this investigation. Two-stage sieving were performed, first on a rotating, perforated drum loaded with steel bars (cut 2 mm), then manually (cut 100 m) on the -2 mm fraction, resulting in three sub-fractions: -100 m, +100 m and + 2 mm. Dry Low Intensity Magnetic Separation was performed on a two-staged Lenoir Rollmag 500-2 separator. Two separations were successively performed. The first gave two fractions composed of ferromagnetic or weakly magnetic compounds. Each of these fractions was separated again, and the two ferromagnetic parts were mixed together, as well as the two weakly magnetic parts. Attrition was carried out on the materials in pulp (65 (%) wt ) using a Cylab-1 (2125 rpm). 5 cycles of 1 min each were performed. The resulting fractions were dried in an oven (105 °C during 24 h). Using composition data, mass balances were carried out at a blast furnace scale for each tramp element.

Results and discussion

Thermal Behavior of LF and DF Samples in Air Atmosphere

The investigation of reactivity of ASR and PVC samples was performed between 225 °C and 900 °C under air atmosphere. Results are shown in Figure 2 as the evolution of the percent weight loss (%WL) of the samples as a function of the temperature From Figure 2 (a), it can be seen a very rapid weight loss of both plastic fractions (LF and DF) at temperatures lower than 600°C. This is due to the combustion of the organic matter contained. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) reveal the presence of mineral compounds (Si, Ca, Mg, Al…) in the residues obtained at higher temperatures. A rough examination of the % WL curves for PVC samples (Figure . 2-b) suggests that at least two phenomena should be distinguished at temperatures lower and higher than 300 °C. The first phenomenon could be attributed to a complete (PVC-2) or partial (PVC-1) removal of chlorine. The % WL observed at temperatures higher than 300 °C may indicate the reaction of the hydrocarbons with oxygen giving carbon oxides and water vapor as final reaction products. Detailed analysis for de-chlorination of both PVC samples was given early [START_REF] Kanari | Beneficiation of PVC wastes in iron oxide reduction[END_REF] [10]. However, these results suggest a high reactivity of all studied samples at relatively low temperatures.

The results of the analytical techniques (SEM, XRD, and IR) on treatment products have been at the base of deductions on the thermal behavior of PVC samples. The IR spectra of the PVC-1 Treated at different temperatures are grouped in Figure 3. It can be observed that between 2950 and 2840 cm -1 some signals characteristics of elongation C-H of CH x groups. The intensity of these bands decreases with increasing temperature to 'disappear' for T ≥ 600 ° C. This is consistent with the data given in Figure 2. The presence of carbonates is observed in all the Spectra up to 900 ° C. XRD confirms the presence of calcite in the initial PVC and heat treatment products Figure 3 -IR Spectra after treatment of PVC-1 between 250 and 900 °C.

Reduction of Hematite by PVC and ASR

The following mixtures were tested in view of iron oxide reduction 1. 35% LF + 35% hematite + 30% clay, 2. (35% PVC-1 + 35% hematite + 30% clay, 3. 50% PVC-1 + 50% hematite

The results show that the chlorine was almost removed at about 275°C from PVC, and then, the mixtures were de-chlorinated at 300 °C for 30 minutes. Subsequently, free of chlorine pellets were heated from 600 to 1050 °C for 30 minutes. Several tests were also carried out at 1025 °C with a residence time from 7.5 to 240 minutes. Obtained experimental and analytical results related to the reduction of iron oxides are described below. They are compared with the wellknown Chaudron and Boudouard diagrams drawn in Figure 4. improving the reduction process. 4. The reduction of iron oxides, particularly at high temperatures, is carried out by the CO and H 2 . The carbon monoxide is generated in situ (gasification of carbon by the Boudouard reaction, Figure 4). Hydrogen is also produced during the gasification of carbon by water vapor. The latter comes from the ASR and from the release of structural water from clay during heating. 5. The direct reduction of pellets can be directed using the electric arc furnace for the manufacture of steel.

Considering thermodynamic investigation for a selective extraction of those metals and using an available thermochemical database for the thermodynamic calculation of various Metal-O-Cl systems, a typical example is the predominance area diagram given in Figure 4 for the (Fe, Pb)-O-Cl systems at 500 °C. This diagram clearly shows that lead chloride (PbCl2) is the most stable phase even for a low partial pressure of chlorine and at high partial pressure of oxygen. By analyzing these results, a large zone (greyish zone in Figure 5) of chlorine and oxygen should be chosen in order to transform lead into PbCl2, while hematite remains intact. Similar interpretations are valid for the systems containing zinc and copper. Generally, metal chlorides have lower boiling points compared with their respective sulfides and/or oxides.

As shown in Figure 6, metal chlorides are volatilized at temperatures lower than 1000 °C. This can be suggested that it is possible to achieve a direct reduction of iron oxides into Fe° by ASR and/other plastics and to remove selectively chlorides of tramp elements. The results of size distribution analysis show that most of the materials in MF#1 and MF#2 are located in -2 mm size classes (Figure 7). Fe and Cu in MF#1 are concentrated in coarser size classes, while Fe is homogeneously distributed throughout the classes of MF #2. Thus, a size cut at 2 mm will enable to purify this sample from Cu and to isolate an iron-rich sub-fraction in MF#1.

Figure 7: size distributions and Fe, Cu and Zn repartitions in both mineral fractions Afterwards, a low intensity magnetic separation can be performed to recover magnetic metals. Lastly, considering that some of the smallest materials might be embedded in coarser complex matrixes, the following processes of separation is proposed in this study. This process includes sieving step for separate 4 size fraction of -100µm, -400/100µm, -2/400µm, -8/2µm and 8µm. Manual magnetic separation to recover metallic scrap was applied on the fraction 8mm. The size fractions of -400/100 and -2/400µm were treated by wet low intensity magnetic separation. Gravity separation using jig process was performed on the fraction -8/2mm, the products obtained (light and heavy) were treated by magnetic separation. The size fraction of -100µm was not treated. The products obtained from each operation were analyzed and the results are shown in tables I and II. Using the process given in Figure 8, it is possible to recover about 79% of total iron from the fraction MF#1 with 72.5% of iron content. However the recovery of iron from MF#2 is lesser (62.4%) with 62% of iron content. All tramp elements such as Cu, Zn and Pb are more present in the sterile products with high recoveries. The weight % of -100µm size fraction for both fractions MF# and MF#2 are 2.6% and 5.4% respectively. These fractions contain very low content of iron (14% and 13.3%) and they are not treated in this work. The results of calculations using metallurgical model developed by steelmaking industry in France show that the mineral fraction MF#1 is the closest ore with regards to the iron content. However it is essential to know the nature of the other elements to determine the potential value of this product added to the materials at the agglomeration step before charging into the blast furnaces. Regarding to carbon products, the light plastic fractions (LF) could be more easily valorized in the steel industry, knowing that their major handicap is that they contain volatile carbon while coal or cokes are mainly out of solid carbon. Therefore, valorization channels could focus on:

1. injection into the slag devoted to the electric furnaces to make foam that lead to a better coverage of the electric arc and then improves its thermal performance; 2. addition to the scrap charge to boost the heating of the electric furnace, 3. injection in tuyeres of blast furnaces.

In both the cases (MF#1 and plastic products), it is essential that the process generating these products, used by many shredders, lead to significant tonnages, since the use of coal for foaming is of the order of 5 kg/t of liquid metal for production of electrical steel; what roughly need in France an equivalent of 25 kt of pulverized coal. It must also be considered that the product obtained has a regular composition, what remains to be checked, since the charge of shredders is heterogeneous (ELV, WEEE other equipment). To achieve this goal, it would certainly be needed to go through a stage of homogenization of the products destined to steelmaking industries.

Conclusions

This work had ambition a multi-parametric analysis of the thermodynamic and experimental use of plastics and automotive shredder residues «ASR» as a substitute of energetic material and reducing agent in metallurgy of iron.

Recycling of ASR is performed at least through two stages: treatment / purification by physical methods followed by an injection of those purified ASR in the furnace. However, the physical methods of extraction of tramp elements (Cl, Pb, Zn, Cu) of ASR strongly depend on their dissemination, their liberation degree as well as their adherence to the matrix that surrounds them. In the absence of a final purification by physical methods, the thermal process developed in this study seems to be quite promising for an alternative process and industrial prospects. We deduced from this thermal approach, that the handicap of coexistence of PVC (source of

Figure 1 :

 1 Figure 1: General scheme for the main operations of the ELV.

Figure 2 :

 2 Figure 2: Behavior of ASR (a) and PVC (b) samples in air between 200 and 900°C [10].

Figure 4 :

 4 Figure 4: Equilibrium diagram of some metallic oxides reduction by carbon monoxide.

Figure 5 :

 5 Figure 5: Phase stability diagram of (Fe, Pb)-O-Cl systems at 500 °C

Figure 6 :

 6 Figure 6: Evolution of vapor pressure of several lead (a) and zinc (b) compounds

Figure 8 :

 8 Figure 8: Wet treatment of Mineral fractions (MF#1 and MF#2)

Table I .

 I Results of wet treatment of MF#1

	Products	Wt %	FeOt %	ρFeOt %	Cu %	ρCu %	Zn %	ρZn %	Pb %	ρPb %	Cl %	ρCl %
	Concentrate	36.0 72.5 79.3 0.4 11.6 0.1 22.7 0.1 11.7 0.1 16.6
	Sterile	61.4 10.5 19.6 1.6 87.9 3.6 72.6 4.9 85.5 0.3 81.9
	-100µm	2.6 14.0	1.1	0.2 0.5 0.2 4.67 0.1 2.8 2.5 1.5
	Total	100.0		100.0		100.0		100.0		100.0		100.0
	Reconstituted		32.9		1.2		0.5		0.6		0.2
	Analyzed		36.8		0.94		0.6		0.5		0.3

Table II .

 II Results of wet treatment of MF#2

	Products	Wt %	FeOt %	ρFeOt %	Cu %	ρCu %	Zn %	ρZn %	Pb %	ρPb %	Cl %	ρCl %
	Concentrate	21.4 61.6 62.4 0.3 11.7 0.7 20.8 0.4 16.6 0.1 15.2
	Sterile	73.2 8.7	33.7 0.7 86.4 0.7 71.9 0.5 75.6 0.2 79.5
	-100µm	5.4 13.3	3.9	0.2 1.9 1.0 7.3 0.7 7.8 0.2 5.3
	Total	100.0		100.0		100.0		100.0		100.0		100.0
	Reconstituted		18.8		0.6		0.7		0.5		0.2
	Analysed		19.3		0.5		0.9		0.6		0.3
	Evaluation of the Investigated Samples Quality


Sylvain Guignot
email: s.guignot@brgm.fr

Nour-Eddine Menad

Marc Gamet

Processing automotive shredder fluff for a blast furnace injection

Keywords: automotive shredder residues, fluff, iron recovery, process, blast furnace

Automotive shredder fluff is a by-product vacuumed during the shredding of end-of-life vehicles (ELV) hulks, and further refined in Post-Shredder lines of Treatment (PST). To date in Europe the mineral part exiting the PST is mostly landfilled without regards for its potentially valuable iron content. Yet, iron could be used a use as part of the ore in blast furnaces, provided several issues related to the chemical composition of fluff were solved. Besides increasing iron content, several tramp elements must be curbed below tight specifications to avoid iron spoiling, furnace wall corrosion, and changes in the hydrodynamic profiles during iron reduction.

The present work aims at designing such a fluff sorting process, on the basis of two representative fluff fractions properly sampled on an industrial PST. The size distributions of these fractions and the repartitions of their chemical elements are used to rationalize and compare three different sorting processes which couple sieving, wet attrition, and dry or wet Low Intensity Magnetic Separation. The best process led to an optimized iron recovery of 78.5 % corresponding to an elemental iron content of 51 %, close to the ore grade required in a blast furnace. At the global scale of ELV recycling, these results entail an increase by 4 % of the fluff recycling rate, thus helping to meet the European requirements for 2015.

INTRODUCTION

11 million vehicles are annually discarded in the European Union, resulting in about 9 Mt of wastes that have to be disposed of [START_REF] Andersen | Projection of end-of-life vehicles: development of a projection model and estimates for ELVs for 2005-2030[END_REF]. Current European state of practice for spent cars processing falls into a manual depollution followed by the shredding of the cars hulks [START_REF] Vermeulen | Automotive shredder residue (ASR): reviewing its production from end-of-life vehicles (ELVs) and its recycling, energy or chemicals valorisation[END_REF], which generates 2.0 to 2.5 million tons of Automotive Shredder Residues (ASR) each year.

Without further treatments, this residual stream is mainly landfilled [START_REF]A study to examine the benefits of the End of Life Vehicles Directive and the costs and benefits of a revision of the 2015 targets for recycling, re-use and recovery under the ELV Directive -Final report to DG Environment[END_REF], which causes damages to the environment while translating into disposal costs for shredding companies.

European legislation will impose a recycling rate greater than 95% of the car initial weight by 2015, resulting in less than 5% of waste discharge [START_REF]du parlement européen et du conseil du 18 septembre 2000 relative aux véhicules hors d'usage[END_REF]. Meeting the legal requirements by addressing the issue of ASR has led to the development of several Post-Shredder industrial lines of treatments, in which a fluff fraction is recovered by vacuuming ASR lighter components during shredding. Residual plastic-rich fractions are then extracted from this fluff and purified from minerals by means of magnetic, eddy current and sequences of sink-float separations. In the remaining mineral streams, iron content can mount up to 18 (%) wt of the light fraction [START_REF] Jalkanen | On the direct recycling of automotive shredder residue and electronic scrap in metallurgical industry[END_REF][START_REF] Vigano | Material and energy recovery from Automotive Shredder Residue (ASR) via sequential gasification and combustion[END_REF]. Profitable outlets in the iron and steel making industry could be opened up by designing a process which would increase this iron grade while curbing several specific non-ferrous elements detrimental to the furnaces and the surrounding equipment. Among these critical elements, those containing chlorine generate gaseous hydrogen chloride and even dichloride upon combustion [START_REF]Converting waste plastics into a resourcecompendium of technologies[END_REF], corrosive gases for the furnace and the dusts removal post-treatments [START_REF] Mirabile | Thermal valorization of ASR: injection in blast furnace[END_REF]. Potassium oxide K 2 O can deposit into coke and sinter porous structures, and weakens respectively their Coke Strength after Reaction (CSR) and Reduction Degradation Index (RDI). Alkaline species vaporize in high temperature furnace zones and condense onto the colder burden, hence gradually accumulating inside the furnace. Copper is related to surface cracking of steels during hot rolling process. Sb, Sn and As accentuate this negative effect by segregating at grain boundaries during coiling in the hot strip mill, thus reducing the grain cohesion and thereby favoring embrittlement. This segregation is higher in steel containing Ni, Mn and Cr. Lastly, gaseous Zn can condense onto the blast furnaces inner walls, favoring scabs that modify the furnace flow configuration.

On such consideration regarding the chemical composition of fluff fractions, the present work aims at setting a simple and cost-effective separation process to further extract an iron-rich and purified fraction from the residual sorted fluff, so as to enable its injection as part of iron ore in a Blast Furnace (BF). This issue is addressed by considering two mineral fractions sampled on an industrial Post Shredder line of end-of-life vehicles treatment, so as to dispose of representative composition data concerning iron and tramp elements. The process development is rationalized on the basis of a preliminary thorough chemical characterization, and leads to the definition of three sequences of operations, which associate sieving and low intensity magnetic separation performed in a dry or a wet environment. Each process is carried out using the sampled mineral fractions and the experimental iron contents and recoveries are discussed in line with the operations performed.

EXPERIMENTAL PROCEDURE

Material sampling and characterization

Two representative samples of minerals from an automotive shredding company were obtained after a careful sampling according to the standardized methodology described in [START_REF] Pineau | Representativeness of an automobile shredder residue sample for a verification analysis[END_REF].

The fractions are named F#1 and F#2, and correspond respectively to the magnetic outlets of two successive and similar magnetic pulleys. Therefore, F#2 is expected to contain less iron than F#1.

The samples are composed of millimetric particles (up to 20 mm), heterogeneous both in nature and size, and therefore a careful attention must be paid to the representativeness of the stream. This representativeness depends on the mean particle size of the materials and on the amount of the analyzed sample. To lower the sampling mass to reasonable values, the size of the materials must be reduced. In this regard, the initial samples were dried and quartered in 1 kg fractions. The fractions underwent sieving (cut 4 mm) followed by a dry attrition to remove fibers and dusty foams, and a further sieving (cut 400 μm) to recover the -400 μm part. The + 400 μm fraction was grinded using a vibratory disc mill, and sieved again at 400 μm, this process being repeated until all various materials were sized below -400 μm. The grinding of mineral fractions was carried out on a vibratory disc mill Siebtechnik T 1000 equipped with grinding tools made of tungstene carbide. Materials underwent three 5 mincycles of grinding at a speed of 960 rpm. This fraction was quartered to obtain 100 g of materials.

Comprehensive chemical characterization was performed on fractions obtained after a systematic cone and quartering procedure. ICP-AES and atomic absorption analyses were conducted on samples after a caustic fusion (Na 2 O 2 , 450 °C) and an acid digestion (HCl).

Separation operations

Sieving was performed in two or five stages, depending on the process. Two-staged sieving corresponded to size cut at 2 mm and 100 μm. Five-staged sieving included the previous cut plus +400 μm, +8 mm and +20 mm. Obviously, a sieving with the size cut at 100 microns should be conducted in a wet media at an industrial scale. Nonetheless, the justification for this separation step is to assess the content in Fe2O3 in the smallest fraction of the sample. Dry low intensity magnetic separation was performed on a two-staged Lenoir Rollmag 500-2 separator. Two separations were successively performed. The first gave two fractions composed of ferromagnetic or paramagnetic compounds. In the second run, each of these fractions was separated again and the two ferromagnetic parts were mixed together, as well as the two weakly magnetic parts.

Wet low intensity magnetic separation was performed on a SALA separator. The magnet wheel was rotated at approximately 25 -30 rpm. Water used to wash the wheel during the separation.

Attrition was carried out on the materials in pulp (65 % in weight) using a Cylab-1 (2125 rpm). 5 cycles of 1 min each were performed. The resulting fractions were dried in an oven (105 °C during 24 h).

Gravity concentration was obtained on a conventional jig (for size class above 2 mm).

RESULTS AND DISCUSSION

Chemical composition of the initial samples

Table 1 summarizes the content in iron (expressed in Fe 2 O 3 equivalent) and in some elements detrimental to pig iron production. It can be seen that the main major compound in F#1 and F#2 is Fe 2 O 3 , respectively 36.8 % and 19.4 %, which corresponds to iron contents of 25.8 % and 13.5 %. These values are in line with the order of the two magnetic pulleys through which the raw industrial stream passes, but they still remain below the iron ore grade required by a blast furnace, close to 57 %. The remainder consists of combustible carbonaceous materials and Si, Ca and Mg carriers (35 to 46 %). The total carbon content is smaller in F#1 (7.9 %) than in F#2 (10.5 %). Cu is preferentially found in F#1, while F#2 concentrates Zn. Regarding Pb, the difference is too small to draw any conclusions.

Considering these figures, a direct injection in a BF of 20 kg of any of these two fractions per ton of pig iron produced (assuming a 100 % partition towards pig iron rather than slag) would result in exceeding the maximum allowed contents in tramp elements in the pig iron and inside the BF (see Table 2). It should also be mentioned that zinc remains the most problematic element since its maximum allowed content is already reached in industrial BF due to the reuse of convertor dust in the sintering process. Therefore, an enrichment process of these fractions is mandatory.

To design such a process, additional knowledge on the repartition of chemicals in both fractions is required. Fig. 1 and Fig. 2 display the size distributions, along with the repartitions of Fe (expressed in equivalent Fe 2 O 3 ) and two tramp elements (Cu and Zn) in F#1 and F#2. It can be observed that most of the materials are located in -2 mm size classes. In F#1, Fe and Cu concentrate in the coarsest sizes (+2 mm) and Zn shows no significant variation along the distribution. The global Fe 2 O 3 of F#1 is exceeded in materials bigger than 2 mm, since the range of values is 38 to 58 % in size classes +2mm and between 23 and 38 % in size classes -2mm. F#2 displays a steady content of Zn and Fe 2 O 3 along the distribution, while Cu is found in coarse size classes with contents up to 35 000 ppm.

Definition of processes P#1, P#2 and P#3

Following the composition results, a size cut at 2 mm will enable to purify F#2 from Cu, and to isolate an already iron-rich fraction in F#1. Afterwards, a dry low intensity magnetic separation can be performed to recover magnetic carriers. In addition, some of the smallest materials may be embedded in coarser complex matrixes, and therefore a wet attrition, or alternatively, a wet sieving with several more size classes, can be performed to improve their liberation. For operations carried out in water, a loss of iron oxides carriers towards the smallest fractions may happen, therefore, wet low intensity magnetic recovery using SALA equipment can be proposed on the -2 mm fractions. In the case of wet sieving the recovery of the tiny iron oxides particles in the -8 +2 mm fraction can be obtained by gravimetric separation in the form of jigging, with the additional advantage that the dynamic liquid motion can cause a soft liberation of embedded materials. The proportion of magnetic components in the resulting light and heavy fractions is evaluated using a hand magnet, but which could be replaced by an overband device. These considerations result in three processes displayed in Fig. 3. Process 1 (P#1) combines a two-staged dry sieving with cuts at 2 mm an 100 µm, followed by a dry low intensity magnetic separation (LIMS) on the fractions obtained. Process 2 (P#2) starts with a wet attrition on materials in pulp (65 % in weight) followed by oven drying, the resulting dried samples undergo the same operations as in P#1. Cutting at 100 μm allowed evaluating the relevance of a wet attrition to liberate iron compounds. Process 3 (P#3) associates sieving, wet LIMS (on the -2 mm +100 μm) and jigging on the -8 mm.

For each of these processes, the magnetic fractions obtained are gathered in a Concentrate part and the non-magnetic fractions in a Sterile part. Thus, each process leads to a Concentrate, a Sterile and a F-100 μm part.

Results of separations P#1, P#2, P#3

Contents and recoveries in major (Fe 2 O 3 , MgO, CaO) and minor (Cu, Zn, Pb) components are given in Table 3 for F#1 and F#2. The mass of each fraction recovered is also given. Note that in Process #3, the sum of the concentrate, the sterile and the -100 μm fractions does not reach 100 %, due to material losses in the solution streams.

Process #1

From this table, it can be noted that for both fractions, MgO and CaO are almost equally partitioned between Concentrate and Sterile. Specifically in F#1, Pb and Cu have moved to the Sterile fraction while Zn is primarily recovered in Concentrate. The same observations apply in reverse in F#2. In addition, the Concentrate parts of F#1 and F#2 display high recoveries for iron oxides, up to 92.7 % and 76.3 % respectively. However, contents in tramp elements in Concentrate have not been significantly curbed, which rules out an injection in a blast furnace.

Process #2

The following observations can be made. First, none of the tramp elements are preferentially found in the Concentrate fractions. They are rather recovered in Sterile (note the high recovery of copper in F#1, around 83 %) and in -100 microns (see Zn and Pb in F#2). Indeed, a specific feature of the results obtained for Process 2 is a hefty increase of recoveries in the -100 microns fraction. This can be explained by the liberation or even the generation of tiny materials promoted by the wet attrition. Last, iron recoveries in Concentrate are significantly smaller than those in P#1.

Process #3

All tramp elements are predominantly found in the Sterile fractions, see for example Cu (88 %) or CaO (86.4 %) in F#1. In addition, Fe 2 O 3 recovery in Concentrate reaches high contents of 73.1 % and 57.5 % in F#1 and F#2, which, corresponds to about 51 % and 40.1 % in elemental iron. Thus, the iron oxide in high-grade fractions obtained with F#1 is close to the ore quality required in a blast furnace.

Comparison of processes

According to these results, P#1 leads to a very high recovery in Concentrate in both fractions, but with a residual pollution with tramp elements. P#2 leads to iron oxide contents in Concentrate close to those in P#1, but to the detriment of iron recovery. P#3 gives a good

) F#1 F #2 F #1 F #2 F #1 F #2 F #1 F #2 F #1 F #

Fig. 1 -Fig. 2 -Fig. 3 -

 123 Fig. 1 -Content in iron and mass percent of the size distribution (left axis) -Content in Cu and Zn (right axis) in the various size classes of F#1.

Table 1 -

 1 Chemical composition of F#1 and F#2

	FIGURES
	C	Fe 2 O 3	Cl	MgO CaO	Cu	Zn	Pb	SiO 2 Others
	F#1 7.9	36.8	0.3	1.4	11.9	0.9	0.7 0.5	21.5	18.0
	F#2 10.5	19.4	0.3	1.7	14.5	0.5	0.9 0.6	29.8	21.8

Table 3 -

 3 Contents (%) and recovery (ρ) for P#1, P#2, and P#3

		Analyzed	Calculated	Concentrate	Sterile	F-100µm
	Compound	feed	feed	(High Grade Iron)	(Low Grade Iron)	(Low Grade Iron

Acknowledgements

This work was performed in the frame of contract N° ANR-10-ECOT-013. The authors gratefully acknowledge the financial support of the French National Research Agency and other partners of the research project for samples and discussions: ArcelorMittal, LEM (Laboratoire Environnement et Minéralurgie, France) and Recylux. The authors also thank the reviewers for their constructive comments. (P#3) P#3 3

recovery figure associated with high iron content, which may even be close to the iron ore quality required in a BF (F#1). Following these observations, the enrichment process should preferably be carried out in a wet rather than in a dry environment. Wet attrition seemed to enable the liberation of embedded particles of iron and tramp elements, without however providing any enrichment of iron in Concentrate, or of tramp elements in Sterile. These results were rather obtained by performing more size cuts during sieving. Yet, more classification also means more post-sieving separation operations, which evidences a possible optimum in the number of operations balanced by the iron recoveries and purities obtained.

Finally, the similarity for F#1 and F#2 in the Concentrate recoveries for the three processes carried out underlines the robustness of P#3.

Given the recovery figures obtained in P#3, a broad estimation of the proportion of valued materials obtained by Process #3 can be made. According to the end-of-life vehicles recycler involved in the present project, the weight of F#1 accounts for 13 % of the initial fluff. The Concentrate from F#1 after P#3 was carried out represents 35.3 % of F#1. Thus, the process presented herein could enable saving around 0.13 × 0.35 = 4.6 % of materials from landfilling, which contributes to help meeting the European legislation on recycling rate of 95 % by 2015.

CONCLUSIONS

The best process tested in the present study led to an optimized iron recovery of 78.5 % corresponding to an elemental iron content of 51 %, close to the ore grade required in a blast furnace. These results entail an increase by 4 % of the fluff recycling rate, thus helping to meet the European requirements for 2015.


Sylvain Guignot

Kathy Bru

Solène Touzé

Yannick Ménard

ASSESSING A RECLAIMED CONCRETE UP-CYCLING SCHEME THROUGH LIFE-CYCLE ANALYSIS

Keywords: Concrete, aggregate, electro-fragmentation, recycling, life-cycle analysis

The present study evaluates the environmental impacts of a recycling scheme for gravels from building concretes wastes, in which the liberated aggregates are reused in structural concretes while the residual mortar fines are sent to the raw mill of a clinker kiln. The evaluation follows a life-cycle analysis approach performed according to the ISO standard 14040, and whose scope encompasses the production of clinker through a dry kiln technology, the mining processes of the raw materials needed in the kiln, the extraction of round and crushed natural aggregates, and the crushing of concrete wastes using usual jaw crushers or pulsed-power electrical fragmentation. Insofar as possible, the inventory data are collected at the national scale of France and are recovered from the supplier of the fragmentation device, from local quarries and from an estimated mean-technology of clinker production. The choice of the impact assessment indicators is restricted to midpoints according to a problem-oriented methodology, and primarily focuses on a potential reduction in the natural resources depletion and in the CO 2 emissions. The study specifically addresses the influence of (i) the amount of recovered cement paste added to the kiln raw mill, and (ii) the distance of transportation modalities of concrete wastes to the crushing processes and of the recycled aggregates to construction sites. The results establish links between significant environmental gains and the various distances of transportations that intervene in the alternative processing of concrete wastes. These links will be probed more deeply in a future work.

Introduction

The current management policy of reclaimed concrete in France directs 99 % of recycled coarse gravels to low added-value roadway pavement applications. In 2008, 38.2 Mt of wastes were generated by C&D operations, from which 15 Mt of gravels were recovered, a figure that could reach 23 Mt provided the best available techniques for deconstruction and source separation were more widely implemented. On a technical point of view, gravels in reclaimed concretes are recovered through impact and jaw crushing, sieving stages and over-band magnetic separations of scrap metals [START_REF] Chisholm | Best practice guide for the use of RA in new concretes[END_REF]. When replacing part of the natural aggregates in concretes, recycled aggregates (RA) entail: (i) an increased drying shrinkage, (ii) decreased compressive strength, splitting tensile strength and modulus of elasticity, but (iii) no significant variations concerning frost resistance, chloride penetration and rate of carbonation [START_REF] Marinkovic | Comparative environmental assessment of natural and recycled aggregate concrete[END_REF][START_REF] Hansen | Strength of recycled concrete made from crushed concrete coarse aggregate[END_REF]. The loss in compressive strength is ascribed to the weaker adhesion of RA to the surrounding cement matrix in concrete, which is due to higher water absorption of the residual mortar covering the surface of the aggregates [START_REF] Poon | Influence of moisture states of natural and recycled aggregates on the slump and compressive strength of concrete[END_REF]. This absorption can vary between 4 % and 8 % of the aggregate initial mass, while only between 0.8 -3.7 % for NA [START_REF] Hansen | Strength of recycled concrete made from crushed concrete coarse aggregate[END_REF]. Until recently in France, such absorption capacity banned any use of recycled aggregates in concretes [START_REF] Bauchard | Utilisation en technique routière de granulats provenant du concassage de béton de démolition[END_REF].

Over the last three decades, several avenues have been explored to address this absorption issue. The first of them consisted in prewetting the recycled aggregate to the condition termed "water saturated surface dry" before concrete batching, hence preventing the attached mortar from further drawing local water [START_REF] Poon | Influence of moisture states of natural and recycled aggregates on the slump and compressive strength of concrete[END_REF]. However, (i) from a practical point of view, such saturated conditions are difficult to be maintained on a construction site, and (ii) prewetting the aggregates also implies a concomitant increase in cement, to ensure correct compressive strength and drying shrinkage at 28 and 182 days [START_REF] Dosho | Development of a sustainable concrete waste recycling system -application of recycled aggregate concrete produced by aggregate replacing method[END_REF] and maintain a good concrete consistency and workability [START_REF] Cement | Recycled aggregates for reinforced concrete?[END_REF]. The second approach to deal with the residual mortar lie on studies having evidenced a better reliance towards local cracks propagation in concretes made from recycled aggregates, reliance which could be due to local reductions in stiffness promoted by the adhering mortar [START_REF] Kikuchi | Demolition and reuse of concrete and masonry: reuse of demolition waste[END_REF]. The idea is therefore to mitigate the negative effect of RA with natural aggregates, and thus, designing mixed-aggregates concretes. However, the precise quantification of the upper limit for RA addition is still difficult by its dependency to the chemical properties of the RA, to the quality of concretes from which they stem, to the kind of cement used and to the technology of concrete production. A broad common estimate for RA replacement ratio in concrete is about 30 % [START_REF] Corinaldesi | Influence of mineral additions on the performance of 100 % recycled aggregate concrete[END_REF]. Lastly, the third approach to manage cement paste on the RA was to design cleaning process. Several methods have been put forward [START_REF] Dosho | Development of a sustainable concrete waste recycling system -application of recycled aggregate concrete produced by aggregate replacing method[END_REF], among which gravity concentration [START_REF] Abe | Study on production of recycled aggregate by gravity concentration method[END_REF], screw grinding [START_REF] Sakasume | Development for production technique on high quality recyclable aggregate. Part 4. Method of screw grinding[END_REF], and heating and rubbing of concrete [START_REF] Kuroda | A closed-loop concrete on a construction site[END_REF]. Gravity concentration and screw grinding seem to only fit to coarse aggregates (size above 20-25 mm), with low recycling rates, about 20 % and 34-45 % respectively. Crushed concrete comprises 49.1 % of aggregate plus adhered mortar and 43 % of clean aggregates, the remaining part being composed of ceramic, bitumen and other materials [START_REF] Tsujino | Application of conventionally recycled coarse aggregate to concrete structure by surface modification treatment[END_REF]. The use of organic extractants has also been proposed by [START_REF] Etxeberria | Influence of amount of recycled coarse aggregate and production process on properties of recycled aggregate concrete[END_REF], but the environmental gains brought about by the reuse of the aggregates are counterbalanced by the use of organic extractants and the numerous washing steps associated. On these considerations at the present time, a choice seems to be made between (i) producing cement-covered aggregates after a few basic liberation and separation processes, assess their potential use in structural concretes of various grades through standardized indicators related to their physical properties, and determine the extra amount of cement required to maintain comparable concrete properties, (ii) or ridding the aggregates of their mortar layers through more advanced, less environment-friendly separation processes to ensure their use in high-quality concrete.

Recently, our team extended the work of [START_REF] Maeda | Research on concrete aggregate collection technology by pulsed power discharge[END_REF] and demonstrated that, by pulsing electrical discharges into concrete blocks, it was possible to separate coarse clean aggregates from a fine fraction having a high grade of a cement paste. Such a fraction could provide substitutes to natural limestone, clay and sand in the raw mill of a clinker kiln, while the aggregates could be up-cycled in high quality structural concretes. Both of these outlets would provide numerous advantages. First, using recycled aggregates could help to meet the forthcoming stringent legislation on the opening of new quarries of natural aggregates. Second, recycling aggregates could also save money by disposing of a cheaper aggregates supply (the pre-tax price of clean recycled aggregates ranges from 15 to 25 euros per m 3 in France [16]), while avoiding paying tipping fees to landfill inert wastes (amounting to 5 euros per metric ton in France). Third, substitutes to raw mill result in reduced consumption of natural calcareous resources, coupled with reduced carbon dioxide emissions stemming from less dissociation of carbonated materials [START_REF] Damtofts | Sustainable development and climate change initiatives[END_REF]. Using recycled aggregates would lessen the environmental burdens of landfilling installations, while reducing the consumption of non-renewable mineral resources. Besides it would offset local shortages of aggregates, thus reducing the need for transportation of aggregates over long distances and the various greenhouse gas emissions associated. Thus, the environmental impacts of this recycling scheme remain to be quantified.

To the best of our knowledge, studies addressing this specific issue are rather scarce. In a LCA study addressing the production of low and high quality concretes, [START_REF] Braunschweig | Recycled concrete: environmentally beneficial over virgin concrete?[END_REF] underlined the significance of even the slight additional amount of cement required by the low quality aggregates (about 5 % according to [START_REF] Marinkovic | Comparative environmental assessment of natural and recycled aggregate concrete[END_REF]), which tended to increase some environmental categories linked to respiratory effect, climate change and energy use. On the contrary, incorporating the aggregates into low quality concretes entailed no increase in cement content, and hence all environmental indicators were reduced. [START_REF] Ishikawa | Issues in LCA in the concrete industry[END_REF] recently reported an evaluation of a recycling scheme in which the aggregates were recovered from a heating and rubbing process and were incorporated to new concretes, while mortar was used either as a soil stabilizer or as a raw material in clinker. As long as mortar was valued, the CO 2 balance became significantly negative (about -217 kg CO2 per ton of concrete block).

Yet, these works seems to miss the fact that using RA in structural concrete rather than in roads implies that the part of gravels diverted from road to construction will have to be made up for by virgin aggregates from quarries. The overall mass balance might be relatively unaffected, but the environmental balance may be changed owing to the differences in the cleaning steps aiming at removing mortar. While part of the reclaimed concrete gravels have to meet harsher technical specifications to be used in structural concrete, the aggregates they replace will follow the reverse pattern and will not require an advanced treatment to be included in road bases. Lastly, as underlined by [START_REF] Marinkovic | Comparative environmental assessment of natural and recycled aggregate concrete[END_REF], the transportation distances of any recycling scheme dealing with heavy materials have to be heeded for, as they can set the borders between environmentally beneficial recycling schemes and the others. Therefore, various scenarios should be built up to examine the sensitivity of the environmental impacts to the transport distances of aggregates and raw materials, as well as to the way they are transported, in different concrete recycling schemes.

The present paper reports an evaluation of the environmental impacts of this alternative management of building concretes, performed according a Life Cycle Analysis methodology. For each operation considered in the processes, inputs and outputs are collected and aggregated to determine their impact on various environmental categories. These inputs/outputs cover consumptions of minerals, water or energy, as well as waste heat, air emissions, water emissions, and solid wastes to the ground. The implementation of LCA comprises four successive steps: the definition of the goal and scope of the study, the inventory of data from the considered processes, the impact assessment of these data, and the interpretation of the results [START_REF]Guidelines for life-cycle assessment: a code of practice[END_REF].

Goal And Scope

Goal

Current practices in concrete recycling consist in largely non-selective crushing and screening processes, which do not allow a straight separation between the clean aggregates and the cement paste. The resulting gravels are thus restricted to low-added value applications mostly in earthworks (excavation filling, roadbeds, or floor foundation). Fragmentation of concrete rubbles by means of pulsed electrical discharges can enhance the aggregate separation from the cement paste in the concrete gravels [START_REF] Lippiat | Investigation of microwave-assisted concrete recycling using single-particle testing[END_REF], thereby broadening their range of use towards structural concretes. As an additional advantage, the hydrated cement paste mixed with sand (also termed Recycled Cement Paste or RCP) contains numerous chemical elements that could advantageously be reused to manufacture new clinkers.

Therefore, incorporating fragmentation in the technological handling of concrete wastes result in defining a new global processing scheme for these wastes, scheme which comprises new outlets for the clean aggregates and the RCP, as well as quantitative modifications in the raw materials production for earthworks, building concrete and clinker production. The objective of the present study is therefore to compare these two processing schemes of concrete wastes according to their respective environmental impacts. The study is thus primarily intended for aggregates suppliers, cement and concrete manufacturers, but can also be of interest to the industry of solid waste management, to several environmental organizations, and to LCA practitioners.

System Boundaries And Functional Unit

A preliminary system would include the emissions and mineral resources and energy consumptions associated with: (i) the production of the raw materials needed in the clinker kiln, and (ii) the usual concrete crushing and the pulsed-power fragmentation processes. For both processing schemes of concrete wastes, and whatever the functional unit consideredprocessing 1 kg of waste building concrete or producing 1 kg of aggregates -a multifunctionality issue occurs due to the fact that the aggregates produced by the two systems have different outlets, either for structural concretes or for road constructions. This multi-functionality is unraveled in accordance to the recommendations of the ISO 14040 standard [START_REF]Life Cycle Assessment. Part I. Principles and Framework[END_REF] by extending the system boundaries to include subsystems fulfilling the functions of (i) producing natural aggregates for concrete production and (ii) producing crushed aggregates for road embankments. In a processing view, the final system is therefore divided into 6 sub-units (Figure 1), and the common function of the two recycling scheme included is "processing 1 kg of waste concrete". Both inputs are concretes pre-sorted from the building rubbles which contain no scrap metal that would come from steel-reinforced structures. The system is not extended beyond aggregates production to concrete manufacturing, since the produced aggregates have the same quality, hence the same use, as natural aggregates. Thus the comparison is drawn between two extreme situations -with a 0 % or a 100 % RA reuse in structural concretes. This deviates only slightly from current practices in France, from which almost 2 Mt in 17 Mt of RA are reused without further treatments. All the processes of production are followed by the cleaning operations needed for the materials to meet the quality standards of their respective function. Second, in line with the recommendations of [START_REF] Tillman | Choice of system boundaries in life cycle assessment[END_REF], the capital goods are included in the present LCA since part of it is intended to compare the production and the operation of alternative equipment (pulsed power fragmentation) with the continued use of existing equipment (concrete crushing). These infrastructure data are fed into the inventory table after being averaged on the totalized "functional unit" outputs of the process on its estimated lifetime. In order to be consistent, infrastructures data are also accounted for in the inventory. Lastly, the LCA involves several transportations of heavy materials, which results in significant emissions to air, and for that reason, transports of the raw materials, of the building concrete wastes, and of the natural and recycled gravels are within the system boundaries.

) ck RCP P p - . ughput of
As a result, the environmental extra-cost ( EEC ) brought by the use of the alternative process of concrete fragmentation will be obtained by applying the following formula:

[ ] [ ] ) 4 ( ) 1 ( . P ) p 1 ( ) 6 ( ) 2 ( ) 5 ( ) 3 ( . p EEC ck RCP - - + - + - = (1)
This data treatment provides a solution for the allocation issue arising from the concomitant production of aggregates and recycled cement paste in the concrete fragmentation process. The environmental burdens are allocated on the basis of the mass repartition of the materials since the hydrated cement paste could not be economically balanced against the aggregates. Lastly, note that this system excludes the landfilling of non-valuable materials stemming from process [START_REF] Bauchard | Utilisation en technique routière de granulats provenant du concassage de béton de démolition[END_REF], and thus minimizes the environmental impact of the usual recycling scheme.

Impact Assessment

The environmental categories considered for the impact assessment depend on the position chosen on the impact pathway of a given substance, they may be chosen at a midpoint or at an endpoint position. As defined in [START_REF] Udo De Haes | Life-cycle impact assessment: striving towards best practice[END_REF] the mid-points indicators concern the human toxicity, the ozone layer depletion, the formation of photooxidant species, the inorganic respiratory effects, the climate change, the aquatic and terrestrial ecotoxicity and eutrophication, the acidification, the abiotic and biotic resources depletion, and the land use. These indicators are further aggregated in indicators accounting for the final environmental impacts, or endpoints, on the human health, the abiotic and biotic natural environment, the abiotic and biotic natural resources and the abiotic and biotic artificial environment. For example, sulphur dioxide causes acid rain (mid-point indicator), and damages both human health and the natural environment (end-point indicators). The farther the indicators are on the impact pathway, the greater the associated uncertainties are. In this study, priority was given to the precision of the results, and therefore the indicator point was put as close as possible to the associated emissions, following a problemoriented, rather a damage-oriented, methodology.

The environmental impact of a given process can be global or local in scale [START_REF] Huntziger | A life-cycle assessment of Portland cement manufacturing: comparing the traditional process with alternative technologies[END_REF], and the choice is made in the present LCA to assess global effects from local inventory data, as advised by [START_REF] Owens | Life -Cycle Assessment -Constraints on moving from Inventory to Impact Assessment[END_REF].

The study aims at assessing the long-term impacts of an alternative management scheme of concrete wastes on the resource availability, the ecosystem diversity, and the human health. For these reasons, the ReCiPe MidPoint method 1.06, egalitarian version, is chosen for impact assessment [START_REF] Goedkoop | ReCiPe 2008 -a life cycle impact assessment method which comprises harmonized category indicators at the midpoint and the endpoint level[END_REF]. The alternative scheme should enable to reduce the CO 2 emissions, the natural resources consumption, and the energy use. CO 2 affects the human health and the ecosystem integrity through its contribution to the radiative infrared forcing of the atmosphere, therefore, climate change (CC) is a relevant indicator. Less consumption of natural aggregates can be evaluated by the impact category "natural land transformation" (NLT), and conversely, the decrease in the energy use by the category "fossil fuel depletion" (FD). In addition, and owing to the fact that the present processes can be well documented regarding their emission in SOx and NOx, the terrestrial acidity (TA) is also considered, a relevant choice according to a study dealing with the environmental impact of cement production performed by [START_REF] Chen | Environmental impact of cement production: detail of the different processes and cement plant variability evaluation[END_REF]. By contrast, and due to a lack of data, the various indicators related to eutrophication, ecotoxicity, water depletion and particulate matter are discarded from the impact assessment.

The four selected indicators are therefore climate change (CC), natural land transformation (NLT), fossil fuel depletion (FD) and terrestrial acidity (TA).

Data Quality

Given that the present LCA is intended to be used in a decision-making process, the quality of technical data is crucial. A specificity of this work is that it involves the extraction and use of aggregates from earth and from building wastes. Considering that the physical properties of the natural aggregates depend on the geographical situation of the extraction site, and that the extraction process differs with the nature of aggregate, a special attention must be paid in using local rather than global averaged process data. Obviously, a precise description of every quarry procedure cannot be envisaged. But, documenting two extremes extraction process (respectively from an alluvial source or from a solid rock) allows taking into account this situation to some extent. Another consequence is that transportation from a natural mine or from a demolition site to the pulsed power or to the usual crushing process are to be precisely defined, and again, at a regional scale. Data from processes are collected on ongoing industrial processes as far as possible. Lastly, any missing inventory data is supplied by the EcoInvent 7.3.3 database. The Life Cycle Inventory was compiled in the SimaPro software (Pré Consultants), which also performs the impact assessment using a user-selected method of calculus

Choice Of Variables Assessed

The present study aims at catching the influence of the main variables defining a recycling scheme of building concrete gravels based on a straight separation of aggregates and hydrated cement paste. This separation is performed by using specific equipment based on pulsed power fragmentation. Furthermore, the recycling scheme addresses heavy materials (may it be aggregates, raw materials for clinker kiln, or concrete gravels) and consequently, the transport modalities are of uttermost significance in an environmental evaluation. On such consideration, the variables taken into account are listed in Table 1. Their specific values are specified in the following Inventory part.

Life Cycle Inventory (LCI)

Life Cycle Inventory is carried out by considering each process unit as a stand-alone system, for which the surroundings environment acts as a source of all the materials and fuels inputs to the system and as a sink for all outputs from the system. For each unit process described on Figure 1, an inventory table is established and gathers the materials and energy inputs as well as the individual emissions to the air, to natural water and to the ground. To account for the data sensitivity to the location and the geographical scale, data are collected from local quarries operators. Furthermore, data quality was improved by contacting the pulsedpower and the jaw crusher manufacturers. Finally, most of the data are reliable with time since they come from the well-established processes of clinker manufacturing, and rock and concrete crushing.

Pulsed Power Fragmentation Of Concrete

A schematic representation of a reclaimed concrete processing is shown Figure 2, along with the alternative part of process under study in the present work, and composed of the high voltage pulse power fragmentation device marketed by Selfrag (and termed Selfrag in what follows). The materials entering the Selfrag must be below 40 mm in size, and therefore a jaw crushing must be maintained in the global line of process. According to Figure 2, the +40 mm fraction is directed towards an impact crusher to recover materials under 40 mm in size. Thus, the Selfrag can replace the impact crusher according to a scheme highlighted by dotted lines on the figure. Several cycles of Selfrag processing are considered to obtain the maximum amounts of hydrated cement paste on one hand and of clean aggregates on the other hand. Datas concerning the lifespan of the equipment for pulsed-power fragmentation, the chemical composition of its main parts and the total electrical consumption over its lifespan were collected from the industrial manufacturer, and added to the module defining the production of Recycled Aggregates for Concrete RAC (see below in the LCI section). For reasons of confidentiality these data are not disclosed in the present paper, but remain available upon request.

Clinker Manufacturing With And Without Recycled Hydrated Cement Paste Global Process. Clinker is supposed to be produced in a dry process kiln with multistage preheaters and precalciners. Apart from the internal plant transportations, the main CO 2 emissions come from the chemical reactions in the clinker kiln, the fuel combustion during clinker production and the electrical power consumed for raw materials and clinker grinding and milling to the desired sizes. These data fluctuates with time and from one cement plant to another, according to a seven-year monitoring of SOx, NOx, CO 2 and clinker dust emissions performed on six cement plants by [START_REF] Bahr | Experiences of environmental performance evaluation in the cement industry. Data quality of environmental performance indicators as a limiting factor for benchmarking and rating[END_REF]. These fluctuations are related to the process stability and the efficiency of the dust filters used. Consequently, only mean values for the main emissions/consumptions can be used in the inventory, and they are documented from literature data. Estimation Of CO 2 Emissions And Minerals And Energy Consumption At The Kiln Scale. The usual feeding of the kiln is made of limestone, sand, iron ore and clay, which are the main mineral carriers of Ca, Si, Fe and Al. Part of these elements can be supplied by the hydrated cement paste recovered from the alternative concrete fragmentation. The extent of replacement ratio in the raw feed is determined using a calculation method described in a previous communication [START_REF] Guignot | Development of an innovative technique for demolition concrete upcycling: a response to mitigate GHG's emissions and natural resources depletion[END_REF] which extends the pioneering work of [START_REF] Moore | Chemical control of Portland cement clinker[END_REF]. This calculation allows singling out the potential decrease in the CO 2 emissions and in the energy consumption brought by using recycled RCP in raw material. This methodology relates the raw mix composition (proportions of calcite, clay, iron ore and recycled HCP) with the mineralogical composition of the clinker formed (mass proportions of C3S, C2S, C3A and C4AF), through a system of four equations determined by using Bogue equations [START_REF] Bogue | Calculation of the compounds in Portland cement[END_REF] and simple mass balances between the inlet and the outlet of the kiln. [START_REF] Taylor | Cement chemistry[END_REF]). These ratios are allowed to vary within precise ranges to ensure a good clinker workability, which therefore constrains the previous system of four equations. Using a Sequential Quadratic Programing algorithm implemented in Matlab, it is then possible to obtain the acceptable ranges for proportions of calcite, clay, iron ore and RCP in the raw feed. Choosing a definite composition within these ranges enables to perform two calculations: (i) the theoretical enthalpy at 25 °C required for clinker reaction with RCP ( RCP f H Δ

), (ii) and the specific thermic energy consumed, which encompasses the previous enthalpy, the various heat losses around the equipment (conductive and radiative losses), and the heat losses leaving the process through the exhaust fumes, the clinker dusts, and the clinker itself. All these losses are assumed to be not affected by the change in the raw feed, and thus equal to a reference value -estimated to be 1.3 MJ/kg clinker [START_REF] Baudet | Production de CO2 dans l'élaboration des ciments Portland. Bilans et possibilités de réduction des émissions[END_REF]. Thus, by calculating the enthalpy for clinker reaction, the specific energy ( RCP S E ) is obtained by

RCP f RCP S H 3 . 1 E Δ + =
. Knowing the specific thermic energy and the nature of the fuel used, it is possible to calculate the amount of fossil fuel required to fulfill the heat demand of the kiln, and thereby, the amount of SO 2 , NOx and CO 2 released during the combustion. The former value is added to the CO 2 arising from the limestone dissociation, and to the emissions related to the electrical power consumptions in grinding and milling sections to obtain a global value for the CO 2 emissions of the process. Construction Of The Module In Simapro Software. The generic dry process of clinker production is chosen in the Ecoinvent database. The grounding, crushing, milling and mixing of raw materials, as well as the grinding of clinker and the collection of dusts are already allocated. The electricity used for raw meal preparation depends on the hardness of the material and it is assumed that the recycled cement paste displays the same workability as the materials it replaces. Two modules are elaborated from this generic process. The first one corresponds to a reference clinker composed of 57.9 % of C3S, 21.1 % of C2S, 12.6 % of C3A and 8.4 % of C4AF, starting from pure minerals (calcite, kaolinite, silica and goethite). The associated specific thermic energy 0 S E is 3.14 MJ/kg of clinker, which corresponds to a mean value found in dry process kilns operated in France according to [START_REF] Baudet | Production de CO2 dans l'élaboration des ciments Portland. Bilans et possibilités de réduction des émissions[END_REF]. The second module corresponds to a clinker manufactured from recycled cement paste and which meets the same module values as the reference clinker. The solid combustible for both processes is a bituminous coal with a lower heating value of 35.6 MJ/kg and whose elemental composition is 88.5 % of C, 5.0 % of H, 4.5 % of O, 1.0 % of S and 1.0 % of N. The internal plant transportations depend on the internal logistics of each cement plant (spaces allocated to the receipt of raw materials, to the process of production and to the silos containing the manufactured cement), which implies that only a mean value can be chosen. For the sake of simplicity, the Ecoinvent value is chosen. The external transportations are considered to be negligible owing to the fact that cement plants are often located near their respective quarry. Table 4 summarizes the values of the data modified in the Ecoinvent module corresponding to clinker formation. As a preliminary step, two cases are considered, depending whether the LaP, SR and MK mineralogical ratio are chosen to correspond with the values for the reference clinker or with the highest decrease in the CO 2 emissions. [43] -170 [41] 33 -137 30 -127 Fuels kg.km 98 [43] -406 [41] 79 -326 73 -302

The specific heat energies are determined for an output of a 1 kg milled clinker. In the assessment of the global system, they will be weighted by the theoretical clinker mass which can be produced given the extent of substitution of the natural limestone by recycled concrete in the raw material, this extent stemming directly from the respective efficiencies of the recycling technology considered (pulsed power or impact crushing) and processed on a 1 kg input of waste concrete (see the Goal and Scope section).

Crushing Processes Of Concrete And Natural Gravels

Crushing processes refer to the production of aggregates from natural sources and from concretes for building concretes and for road embankments. LCI For RAC And RGE Processes Of Production. Regarding the crushing of concrete to produce RAC, technical data are not well documented in the literature since the process is barely implemented in the industry. On an energetic point of view, the main difference between the processes of production of RAC and RGE is the replacement of the secondary impact crusher by the high voltage pulsed power device (Figure 1). According to the technical documentation from crusher suppliers, typical jaw and impact crushers need 2 kWh and 1 kWh per metric ton of waste concrete, as opposed to 2.5 kWh/t for the Selfrag. On this basis, the total energetic costs for a RGE and a RAC process of production are respectively 3 and 4.5 kWh/t. Regarding the various emissions and fluid consumptions of the RGE process, Table 5 summarizes inventory data for coarse recycled aggregates obtained from demolished reinforced concrete structure and crushed in a typical mobile plant [START_REF] Marinkovic | Innovative materials and techniques in concrete construction (ACES Workshop)[END_REF]. These data complement the values proposed by the Ecoinvent 7.3.3 database for the module "Gravel crushed at mine", since both processes of production involve heavy crushing steps, which liberate dusts and consume fluids.

Table 5. LCI data for the recovery of recycled aggregates for embankments [36] Consumption The module corresponding to the RAC process is completed with the data supplied by the Selfrag Company, see above the definition of the pulsed-power fragmentation of concrete (Figure 2).

LCI For Natural Crushed Aggregates For Concrete (NAC) And Round Aggregates For Embankments (NAE). As underlined by [START_REF] Van Den Heede | Environmental impact and life cycle assessment (LCA) of traditional and 'green' concretes: Literature review and theoretical calculations[END_REF], three main factors contribute to the environmental load of the processes of natural aggregates recovery: their type, accessibility and regional availability. Accessibility and regional availability impact on the transport of the recovered aggregates to their place of consumption, and have no influence on the extraction process (issues related to transport are dealt with in a following section). By contrast, the impacts are quite different according to the kind of retrieved aggregates, round or crushed. Round aggregates result from the external erosion and the exposure to weather conditions. Except for their excavation, optional transport to a processing plant, washing and grading to meet the requirements of the national standards, neither complex nor energy-costly processes are needed. This is contrasted by the blasting, transportation, crushing/milling, sieving and washing operations performed on crushed aggregates. It is assumed those crushed and round aggregates are respectively dedicated to building concretes and road applications. Precise field data concerning these two schemes of treatment remain scarce; however, a thorough study carried out by [START_REF] Martaud | Evaluation environnementale de la production de granulats naturels en exploitation de carrières[END_REF] earned our attention and will be the main source of information for the present inventory. The study focuses on three sites of aggregate extraction in France, differing either by the physical characteristic of their respective aggregates or by their level of production.

For the sake of simplicity, only data concerning two sites with the same production rate but a different kind of aggregates are used. Both inventories include the production of fixed assets and maintenance vehicles.

Round aggregates are assumed to be excavated from a pit by means of a wheel loader, transported to the processing unit by a conveyor belt and further processed to produce four size fractions, 0/4, 4/6.3, 6.3/10 and 10/14. In 2005 125,000 tons of aggregates have been produced with 13 % of extracted materials being lost during the washing steps or being removed owing to their poor quality. 80 % of the production is used in concrete batching plants or for the production of roof tiles.

Crushed aggregates are supposed to be blasted from rock mass and transported to a crushing and milling unit which falls into three successive parts, composed of a jaw and cone crushers and sieving units. The physical properties of the recovered aggregates are suitable with a use in asphalt concrete. In 2005 180,000 tons of aggregates have been produced with 24 % of extracted materials being non-compliant with a road use according to the French standard NF EN 12620.

The values reported on Table 6 refer to a metric ton of materials produced during the year 2005 in France. Blasting is excluded from this inventory. Toxic gases [38] NO Organics [38] Non-methane VOC g/t 14.42 7.82 POP g/t 2.49 10 -3 1.61 10 -3

Heavy metals [38] Cd g/t 1.94 10 4.85 10 -4 Particles > 30 μm g/t 30.9** [36] 1239** [39] Lastly, in each of these processes the water consumption is missing. The choice of discarding it in an inventory of aggregates extraction may seem irrelevant, particularly since the consumption strongly varies between the two extreme processes. However, choosing one the sparse data available in the literature is equally questionable since the distinction between the water withdrawn from the environment then released on one hand, and the water polluted after washing out clays from the aggregates (spent water) is often not apparent. The volume of spent water also depends on the recirculation system, which is installation-specific. As an example water consumption needed to produce 1 metric ton of aggregates in the UK ranged between 37 and 401 t/t in 2009 [40]. Thus, giving a precise estimation for the water consumption in aggregates production lines seems unrealistic.

Regarding the specific case studied in the present work, the alternative scenario developed for the management of concrete wastes needs extra water not only for the electrical pulsed-power crushing, but also for the extra natural aggregates consumption, meaning that the various water consumptions at every stage of the global process do not balance each other. Neglecting this additional water consumption results in underestimating the depletion in abiotic resources.

Transports

Distances. Table 7 summarizes all the transports heeded in the present study. The values are found in These data represent input variables impacting the environmental balance, and their initial value are found in reports form national statistics offices and from the relevant scientific literature and by a broad estimation considering the cement plant network at a country scale. [44] -170 [41] km

(3) NAE D 2 Natural aggregates Quarry Road Road : 20 [38] -100 [41] km Boat : 100 -150 km (6) NAC D 3 Natural aggregates Quarry Building Road : 40 [41] -59 [43] km Boat : 100 -150 km (2) RAC (5) RGE D 4 Concrete gravels Demolition site WCTU** 20 [41] -100 km

(2) RCP D 5 RCP WCTU Cement plant 150 -200 [46]

Raw materials

The transport distances of raw materials (first line) show a wide range of variations, mirroring two extreme situations for supply of the quarries.

Concrete gravels from demolition sites (RAC and RGE)

The waste concrete treatment unit (WCTU) handles concrete waste through usual crushing or pulsed power/microwave fragmentation: transport distances of concrete gravel are assumed to be equal whatever the treatment applied. The value can be different from zero if WCTU is not located at the demolition site, i.e. if this is not a mobile unit. According to [START_REF] Sayagh | Approche multicritères de l'utilisation de matériaux alternatifs dans les chaussées[END_REF], the distance between road demolition sites to landfilling installations is about 20 km. This value will be assumed to hold for the distance to the non-mobile WCTU.

Aggregates from quarry to road site (NAE and NAC) INSEE (the French National Statistics Office) gives an estimate for the mean transportation distance of raw materials in 2003 of 35 km [START_REF][END_REF]. This distance has been inching up over the last decades, an evolution mainly accounted for by several closings of quarries on environmental grounds and not compensated by the matching openings. For virgin round gravels, [START_REF] Martaud | Evaluation environnementale de la production de granulats naturels en exploitation de carrières[END_REF] states that the distance between the extraction and the production site is less than 2 km, and that the graded aggregates are not sent over distances above 20 km to road construction/resurfacing sites. This figure falls short of the distances -between 75 to 100 km -considered by [START_REF] Sayagh | Approche multicritères de l'utilisation de matériaux alternatifs dans les chaussées[END_REF]. This discrepancy illustrates the need to precise the geographical scope heeded, as [START_REF] Martaud | Evaluation environnementale de la production de granulats naturels en exploitation de carrières[END_REF] refers to one specific quarry while [START_REF] Sayagh | Approche multicritères de l'utilisation de matériaux alternatifs dans les chaussées[END_REF] provide an averaged value. However it is important to stretch that none of this figure is closer to the truth than the other, since both suffers from a lack of representativeness respectively caused by a too small and a too large scale considered. Consequently and for the sake of completeness, both values will be taken into account in the simulation. Regarding natural aggregates supply for structural concretes, [START_REF] Habert | Development of a depletion indicator for natural resources used in concrete[END_REF] gives a precise value of 59 km, valid in the administrative area surrounding Paris.

Aggregates from various origins to road site (RGE)

Recycled aggregates travel 30 km on average to reach the site of road construction, according to the French Union of Carriers and Building Products Industries in a recent publication [45]. No other reliable figure was found in literature concerning local data.

Aggregates from demolition sites to building construction centers (RAC)

The corresponding distances of the aggregates whereabouts remain without a precise value, and therefore will constitute the main variables of the study. Distances considered will be kept above 20 km.

Recycled Cement Paste

A detailed mapping of the cement plants in France is available in [START_REF] Lebret | Inventaire des carrières d'approvisionnement des cimenteries en France métropolitaine[END_REF], and enables a broad estimation of the mean cement plant distance in the area surrounding Paris, around 150 km. Various distances, not smaller than this value, will be tested in the study. Mode Of Transportation. Materials are mainly transported by roads with usual 38 t lorries, whereas alternative transports such as inland waterway transport could be used. Road transportation represents 95 % of total weight transported, which is explained by the fact that this mode of transportation fully comply with the constraints facing the building sector, which are (i) short transportation distances, (ii) a seasonal production cycle, (iii) temporary nature of construction site, (iv) small loads transported, and (v) reliable delivery schedules. For such small transportation distances, handling operations in unloading areas are far too significant for rail or waterway transports to compete. In addition railway stations or inland port be located near the quarry or the concrete batching plant are required, and this requirement matter-of-factly increases as natural aggregates are more and more sought in far-away quarries. Still, a closer look at regional specificities in France indicates that in Paris region, waterway is comparable to road in the importation of aggregates (5.3 Mt as against 8.5 Mt in 2002). The Administrative Region which mostly contributes to this importation is the neighbor Haute-Normandie Region (3 Mt), its main inland port being at around 150 km from Paris along the Seine river. Given these considerations, LCA simulations will also include the case of a waterway transportation of aggregates of 150 km. This value will represent the upper bound considered, as the French professional Union in the field gave the estimation of 100 km for a waterway transportation averaged at the national scale.

General Infrastructures

The emissions associated with the electrical consumption are modified in every sub-process of the global system to take into account the specificity of the French production mix of electricity, which strongly differs from the default Swiss one proposed in the Ecoinvent database. The share of electricity produced by nuclear plants is more important in France, and is made up for in the Swiss system by more hydrothermal and conventional thermic source [START_REF]Electricity production and supply statistics[END_REF].

Impact Assessment (IA) and Discussion

The system definition leads to various scenarios depending on the fragmentation technology used, the recycling rate of the cement paste, and the distance of transportation of the various materials involved. In what follows, two recycling rates of the RCP obtained by pulsed electrofragmentation have been considered, along with two distances of transportation for the concrete gravels to the WCTU and the aggregates leaving the WCTU to building construction (D 4 and D 7 ), see Table 7. The other transportation distances are not modified and are respectively D 1 = 41 km for raw materials, D 2 = 20 and D 3 = 40 km for natural aggregates, D 5 = 150 km for RCP, and D 6 = 10 km for concrete gravels (see Table 7). This set of parameters allows evaluating the sensitivity of the results to the location of the WCTU. Values of D 4 and D 7 = 0 would correspond to a WCTU close to the demolition/construction sites, a condition which is not always met in practice owing to the minimal space required for the WCTU operations. Results for the environmental extra-cost brought by the alternative processing of reclaimed concrete are summarized Table 9. All the impacts categories score to negative values, meaning that the proposed alternative processing allows reducing the environmental footprint of concrete wastes. The decrease is impressive concerning the avoided emissions in CO2, about 1 kg saved per kg of concrete wastes handled. The terrestrial acidification shows a constant value, apparently not affected by the various distances of transportation considered. Regarding the natural land transformation and the fossil depletion categories, it can be noted that the gain brought by the alternative processing scheme diminishes when D 4 is increased (except for case 5) or when D 7 is lowered. An important point is that the gain remains positive, whilst RAC is sent over 100 km to building construction sites.

To better understand the global results, the respective costs associated with the production processes (i) of clinker, (ii) of aggregates/gravels for embankments, and (iii) of aggregates for structural concretes are reported on Figure 3. These costs are expressed as differences between the impacts of the various modules presented in Figure 1: (3) - [START_REF] Bauchard | Utilisation en technique routière de granulats provenant du concassage de béton de démolition[END_REF] gives the environmental cost to produce aggregates for embankments in the alternative scenario, (2) -( 6) gives the costs for aggregates for structural concretes and (1) -( 4) the cost for clinker manufacturing. The subtractions are weighted by the mass flows indicated (see Figure 1), to determine their respective significance in the global system. The maximum allowed recycled cement paste in the clinker kiln ( = ck RCP P 0.340). It can be seen from this figure that the production of aggregates for embankments is the main contributor to the decrease in climate change and terrestrial acidification. This is explained by the fact that crushing concrete is more energy-intensive than crushing solid rocks to recover aggregates, and therefore more fuel is consumed, resulting in higher (CO 2 and SOx) emissions.

The gain in natural land transformation is mainly accounted for by the production of aggregates for concrete, which is in agreement with the replacement of natural aggregates by aggregates from concrete. Similarly, the positive cost to produce aggregates for embankments (case 1) comes from the fact that gravels initially obtained from concrete wastes and now diverted to building concretes have to be found in natural quarries. This cost seems to decrease for case 3 and 7, which corresponds to D 4 = 100 km. This is ascribed to the fact that, in ReCiPe Midpoint, an increase in the distance of transportation indirectly results in a higher occupation of natural land by road. Regarding fossil depletion, an important gain seems to accompany the alternative process. This is partly due to the feeding of the clinker kiln with less carbonated materials, requiring less amount of combustible to obtain the free lime. The production of aggregates for concrete depletes more fossil fuel in cases 3, 5 and 7, which is explained by the distances of transportation of gravels to the WCTU or of RAC to building sites. The difference (3) -( 5) reflects the same trend by becoming positive when the distance of transportation of concrete wastes to the crusher is 100 km. These preliminary results establish links between potential environmental gains in an alternative processing of concrete wastes and the various distances of transportations that intervene. Future work will therefore be conducted to investigate these links.

  Figure

Figure 3 .

 3 Figure 3. Costs (in term of environmental impacts) of different processes in the global system described on Figure 1. The numbers on the horizontal axis correspond to the case described inTable 9. The content of RCP in the clinker kiln corresponds to the lowest value for CO2 emission ( = ck RCP P

Table 1 .

 1 Variables considered in the study. *Waste Concrete Treatment Unit

		Variables	Evaluation
	Recycled cement paste (RCP) content in clinker kiln	Chemical analysis of RCP
		Raw materials
		local quarry → clinker plant
		Natural aggregates
	Transportation distances	quarry → road construc on site quarry → building construc on site Concrete gravels WCTU* → road construc on site HCP :	Data from statistics offices and scientific literature
		WCTU → clinker plant
		Recycled aggregates
		WCTU → building construc on site
	Mode of	Hauling
	transportation	Shipping

Table Accordi

 Accordi

	e 2. Schemati summarized in	c representa	tion of a pro	cess for reco overing aggre egates from c concrete. Do otted lines
			correspo ond to the ele ectrical pulse ed fragmenta ation device
	riable param meters of th he pulsed-po ower fragm mentation ar re the numb ber of pulse es and the
	voltage. Ex xperiments	were carrie ed out in o	ur laborator ry on test p pieces of co oncrete to
	ne the value es of these p parameters	to obtain th he greater lib beration rat te of hydrate ed cement
	The characte eristics of t the concrete e specimens s are summ marized in w were cylindr rical, their
	and diamete	r were 40 m mm and 40 m mm respect tively, and t their precise e formulatio on is given
	e 2.
			Tabl le 2. Formula ation of the c concrete spec cimens
	S Shape and d	imension	Cylindric cal, h = 40 m	m, ø = 40 mm m
	C Cement type e	CEM I 52 2.5 N
	M Mass ratio w water/cemen nt 0.6
	M Mass of cem ment	400 kg p per m 3 of con ncrete
	M Mass of aggr regates	1620 kg	per m 3 of co oncrete
	W Water		240 kg/m m 3
	ing to the		chemical a analysis, up	to 32 % i in weight o of the initi	al material	could be
	recovere ed in the -2 2 mm fractio on after 15	pulses of 12 25 kV were e applied. T The process	was run a
	second t time on the		+2 mm frac ction. The c chemical con ntents of Ca aO, SiO 2 , A Al 2 O 3 and Fe e 2 O 3 in the
	two -2m mm fractions s obtained e enable to de etermine the e proportion ns and the ch hemical com mpositions
	of the -2 2mm and th he aggregate es fraction l leaving the p process at th he steady st tate. These v values are

Table 3 ,

 3 and they are used to evaluate the environmental extra-cost, see the Goal and Scope section.

Table 3 .

 3 Steady-state composition of the -2 mm and the aggregate fraction after pulsed-power electrical fragmentation (operating conditions are 125 kV, 15 pulses)

		(%)wt	HCP content (%)wt Aggregates content (%)wt
	-2 mm	47 (= p 1-)	48	52
	Clean aggregates	53 (= p )	10	90

Table 4 .

 4 Data modified in the clinker module from the Ecoinvent database. Data refer to 1 kg of clinker

		Clinker with RCP
	Reference	Case 1 :	Case 2 :
	clinker	Equal	Lowest CO 2
		modules	emissions

Table 6 .

 6 LCI data for the extraction of round and crushed aggregates. *includes fuel burned in building machine and diesel needed for internal transportations. **includes loading and unloading operations

			Round aggregates	Crushed aggregates
			NAE	NAC
	Consumption/emission	Unit	Value	Value

Table 7 .

 7 Transports considered in the present study. *see Figure 2. **Waste Concrete Treatment Unit.

	Module* Name	Material	Starting point	Destination	Values
	(1) (4)	D 1	Raw Materials	Quarry	Cement plant	41

Table 8 .

 8 Variables studied in the present paper.

	Transport	RCP rate
	Recycled aggregates D 7 (RAC)	Concrete gravels D 4 (RAC/RGE)	ck RCP P	Case
	20 km	20 km 100 km	0.340 0.277 0.340 0.277	1 2 3 4
	100 km	20 km 100 km	0.340 0.277 0.340 0.277	5 6 7 8

Table 9 .

 9 Balance of the environmental impacts between the current and the alternative scenario of processing 1 kg of reclaimed concrete

	Case 1 2 3 4 5 6 7 8	Climate change kg CO 2 eq -1.04 -1.02 -1.03 -1.01 -1.05 -1.03 -1.04 -1.02	Terrestrial acidification kg SO 2 eq -1.09.10 -2 -1.08.10 -2 -1.08.10 -2 -1.07.10 -2 -1.09.10 -2 -1.09.10 -2 -1.08.10 -2 -1.08.10 -2	Natural land transformation m 2 -6.37.10 -6 -6.25.10 -6 -2.91.10 -6 -2.79.10 -6 -8.72.10 -6 -1.04.10 -5 -5.52.10 -5 -6.97.10 -6	Fossil depletion kg oil eq -6.74.10 -3 -3.52.10 -3 -3.20.10 -3 -1.32.10 -5 -9.14.10 -3 -7.79.10 -3 -5.60.10 -3 -4.25.10 -3