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International audience; This study compares the (nitrogen oxides) NOx photocatalytic degradation performance of the commercial bare semiconductors, titanium dioxide (TiO2 P25) and zinc oxide (ZnO), with that of the homemade gold (Au)-decorated semiconductors, Au/TiO2 and Au/ZnO (1 wt% Au). A plasmonic absorption band was observed at 550 nm for Au/TiO2 and around 700 nm for Au/ZnO. Aqueous dispersions based on these oxides were sprayed on mortar surfaces. The results revealed that Au/ZnO had a high NO degradation capability, comparable to that of TiO2 P25, and the best selectivity towards the formation of nitrates instead of NO2. The Au decoration clearly improved the photocatalytic response of ZnO, notably by avoiding the production of NO2. This positive effect was attributed to the better charge carrier separation and higher OH• production induced by the presence of Au. To the best of our knowledge, this was the first study on Au/ZnO used for NO photocatalytic degradation.

The aim of this work was to benchmark several binders by testing their capacity to resist external sulfate attack (ESA) under similar experimental conditions. Concrete samples were fabricated from seven different binders: two Portland cements, one blast furnace slag Portland cement, one super sulfated ground granulated blast furnace slag cement, one sodium carbonate alkali-activated slag cement, one metakaolin geopolymer and one calcium sulfoaluminate-belite cement. Mechanical strength measurements were used to characterize the concretes in the hardened state. Resistance to ESA was studied by measuring the longitudinal expansion of concretes submerged in a sulfate solution. In order to better understand the behavior of the binders in ESA, this study was completed by microstructural and mineralogical analyses carried out before and after attack by using Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM/EDS), X-ray diffraction and thermodynamic calculations. It was found that ordinary Portland cement had high expansions (> 0.1%) due to the formation of excess ettringite caused by the reaction between aluminates and sulfates. Portland cement without C3A presented lower expansions but gypsum was found to be responsible for cracking at later ages. Alternative binders had low expansions, in the range of 0.01–0.03%, explained by the absence of C3A and portlandite, in addition to the formation of ettringite during hydration (case of ettringite binders) and the absence of calcium (case of the geopolymer-based metakaolin).

Spreader Stoker thermal power plants are initially used to burn bagasse during the sugarcane harvest, but also coal when the season is over. The drawback is that, compared to standard pulverized coal fly ashes, the coal fly ashes resulting from this process contain many more unburned particles. Therefore, Spreader Stoker Coal Fly Ash (SSCFA) is sent to landfill despite its potential for valorisation in construction. The main objective of this work was to evaluate the potential of laboratory manufactured composite cements incorporating SSCFA by using a variety of manufacturing methods, such as co-grinding/separate grinding of the components, and grinding of laboratory cements to equivalent global fineness. The behaviour in the fresh, hardening and hardened states was investigated to bring out the influence of Blaine specific surface and type of addition in different combinations of composite cements. Despite the high carbon content of the coal fly ash studied, the mechanical behaviour of SSCFA-cements was better than that of cement with the local pozzolan, which is the reference in Reunion Island. In addition, the use of slag and the pozzolan/SSCFA association in composite cements showed good results. An artificial neural network approach was employed to predict compressive strength in mortars with parameters such as amounts of clinker, gypsum, pozzolana, SSCFA and slag, and the Blaine specific surface. The results also enabled compressive strength response curves to be developed for mixes according to the amount of clinker in the cements.

International audience; Excavation operations during construction produce millions of tons of soil sometimes with high leachable molybdenum (Mo) contents, that can lead to risks for both human health and the environment. It is therefore necessary to immobilize the Mo in excavated soils to reduce pollution and lower the costs of soil disposal. This paper studies the immobilization of Mo by three cementitious binders. To this end, one Ordinary Portland cement (OPC), one binder composed of 90% ground granulated blast furnace slag (GGBS) and 10% OPC, and one supersulfated GGBS binder were spiked with sodium molybdate at six different Mo concentrations from 0.005 wt% to 10 wt% before curing. In addition, to gain mechanistic insights, the capacity of synthetic calcium silicate hydrates (C-S-H) to immobilize Mo was studied. This study was completed by thermodynamic modeling to predict the immobilization of Mo at low Mo concentrations (95%) by the coprecipitation of powellite. Thermodynamic modeling was in good agreement with measured values when the equilibrium constant of powellite was modified to LogK = −7.2. This suggested that powellite is less stable in cementitious environments than would be expected from thermodynamic databases. Moreover, modeling showed that, for a solution at equilibrium with portlandite or C-S-H, the Mo concentration is limited to 1.7 mg/L by powellite precipitation. In contrast, for a solution saturated with respect to ettringite, the threshold concentration for powellite precipitation is 6.5 mg/L.

International audience

“Almost real-life” experiments of abatement of a pollutant, actually nitrogen monoxide, were carried out in a 10-m3 chamber, the walls of which were covered with plasterboard samples, themselves coated with a photocatalytic dispersion. The experimental protocol consisted in first injecting NO polluted air into the chamber to a certain level, then maintaining a steady level of pollution by tuning the flow rate to balance the leaks and, finally, illuminating the chamber. In a first stage of analysis, a three-flow (injection, leakage and renewal flows) model was used in order to characterize the leakage flow rate. This model was based on the difference of NO concentration between the interior and the exterior rather than on a pressure difference. A two-parameter empirical law was specially formulated for this purpose. In a second stage, the photocatalytic phenomenon was described by a four-flow model completing the previous one, the fourth flow being associated with the photocatalytic oxidation of NO. This flow was described by a rate law derived from the Langmuir-Hinshelwood (L-H) law, which was generalized to the experimental chamber. The parameters K (adsorption constant) and k (abatement kinetics constant) of the rate law were identified using a standardized lab-scale reactor. The equations, integrated by finite differences, fitted the experimental results correctly. The “diffusive zone thickness” was introduced as the thickness of the air layer potentially concerned by the photocatalysis and was quantified. This first attempt to model photocatalysis on a large scale was promising. However, further research work is needed to enable the model to take more parameters into account.

International audience; itanium metal is widely used in the aeronautical sector for its specific properties and corrosion resistance. The design of titanium workpieces is based on chemical milling: a fast, precise, low cost technique popular in the aerospace industry. Material is removed from selected areas of a part by immersing it in a strong chemical reagent. This process produces shallow cavities on plates and sheets or removes shallow layers of materials from large aircraft components to optimize the strength/weight ratio. However, it leads to large volumes of wasted acid baths, which are harmful to the environment and have to be sent to an approved waste facility. The objective of this paper is to highlight a cleaner production process based on the circular economy concept, i.e. reduce, reuse and recycle to limit environmental pollution and operating costs. Waste from chemical milling baths used in the design of titanium parts was recovered with the aim of synthesizing titanium dioxide and using it for air depollution applications. The waste consisted of hexafluorotitanate compounds. Various processing techniques to synthesize titanium dioxide from hexafluorotitanate compounds were tested and resulted in powders having different physicochemical characteristics. The synthesis parameters studied were the nature of the decomplexing agent, the dehydration temperature and the heating period. Photocatalytic coatings were then formulated on the basis of the synthesized powders. They were applied to a mortar surface to evaluate their efficiency to degrade nitric oxide under two UV lighting intensities, 5 and 20 W/m2. Depending on the synthesis process conditions, the concentration and crystal form of titanium dioxide particles varied, leading to more or less efficient photocatalytic coatings. The proportions of anatase and rutile phases in the synthesized powders were between 3 and 13%, and 5 and 30%, respectively. Concerning the particle size distribution, the variations observed were dependent on the D-values. D10% was quite similar for all powders. However, D50% and D90% differed by a factor of two for some powders, notably because of the presence of impurities or remaining decomplexing agent particles. NO degradation varied depending on the photocatalytic dispersions and could reach 7% under an irradiation of 20 W/m2. This article highlights the possible valorization of a massive industrial waste for specific applications provided that the conditions of processing techniques are optimized.

International audience; Excavation operations during construction produce several tons of soil, which frequently contain high concentrations of sulfates (>0.5 wt%). In accordance with the requirements of the French decree for waste classification for disposal, a soil containing sulfates is classified as “inert and non-hazardous waste” if the leachable sulfate concentration is lower than a mass fraction of 0.1%. To prevent sulfate leaching from excavated soils, solutions for immobilizing sulfates are needed and the associated stabilization mechanisms must be understood. On the other hand, the reuse of soils containing sulfates for civil engineering purposes can lead to significant risks after their treatment with ordinary cementitious binders because of chemical reactions involving sulfates. These reactions can promote the formation of massive ettringite crystals resulting in expansion, cracking and eventually catastrophic damage of materials or structures. For these reasons, the stabilization of soils containing sulfates by adding alternative hydraulic binders is studied in this paper. Several binders were used to treat a sulfate-spiked soil. It was observed that treatment with cementitious binders having high C3A content led to volume expansions greater than 5%, while treatments with binders containing a high fraction of ground granulated blast furnace slag (GGBS) showed volume expansions of less than 5% and about 89% of sulfates were immobilized in the solid matrices. These preliminary results suggest that GGBS binders are effective for the treatment of soils containing sulfates. Moreover, numerical calculations using PHREEQC were compared with experimental results to improve the understanding of sulfate immobilization mechanisms.

Air pollution is a serious public health concern in France and many other countries. Nitrogen oxides (NOx) include nitrogen monoxide (NO) and nitrogen dioxide (NO2). They are mainly outdoor pollutants produced during combustion of fossil fuel. These gases can easily infiltrate buildings and thus increase indoor pollution. The recommended guideline values for NO2 are 200 μg/m3 (short-term exposure) and 40 μg/m3 (long-term exposure). Although no guideline values exist for NO, this gas can be oxidised by atmospheric ozone and thus produce NO2. This paper studies the depollution efficiency of photocatalysis towards indoor NO. Experiments were conducted at real scale, in a 10-m3 experimental chamber developed at the LMDC and used as a reactor. The interior walls of the chamber were equipped with painted plasterboards treated with photocatalytic coating (3 g/m2 of TiO2). Gas was continuously injected into the chamber according to a specific procedure: (1) pollutant injection at high flow rate to reach 200 ppb of NO, (2) pollutant injection at low flow rate in order to keep the NO concentration constant at 200 ± 10 ppb and (3) photocatalysis activation by switching on the light. Typical indoor lighting systems (fluorescent tubes, LED and halogen bulbs) were tested and UV fluorescent tubes were also used to optimise the photocatalytic efficiency. Results showed that NO indoor concentration was reduced by photocatalysis in real-world conditions. Significant NO degradation was obtained under visible light. In addition, using the experimental procedure presented in this paper, a new method for evaluating air depollution efficiency by photocatalysis at real scale is proposed.

This paper deals with the degradation of NO by photocatalytic oxidation using TiO2-based coatings. Tests are conducted at a laboratory scale through an experimental setup inspired from ISO 22197-1 standard. Various parameters are explored to evaluate their influence on photocatalysis efficiency: TiO2 dry matter content applied to the surface, nature of the substrate, and illumination conditions (UV and visible light). This article points out the different behaviors between three kinds of substrates which are common building materials: normalized mortar, denser mortar, and commercial wood. The illumination conditions are of great importance in the photocatalytic process with experiments under UV light showing the best results. However, a significant decrease in NO concentration under visible light is also observed provided that the TiO2 dry matter content on the surface is high enough. The nature of the substrate plays an important role in the photocatalytic activity with rougher substrates being more efficient to degrade NO. However, limiting the roughness of the substrate seems to be of utmost interest to obtain the highest exposed surface area and thus the optimal photocatalytic efficiency. A higher roughness promotes the surface contact between TiO2 and NO but does not necessarily increase the photochemical oxidation.

International audience; Indoor air is contaminated by numerous pollutants, which impact human health, comfort and productivity. These pollutants have various indoor sources such as building materials, furniture, combustion appliances or tobacco smoke. However, the pollution also comes from outside. In urban area, nitrogen oxides (NOx) emitted into the atmosphere can reach alarming levels. These traffic-related pollutants, which seriously impact the global environment and human health, can infiltrate inside buildings. Therefore, limiting the amount of breathable NOx in outdoor and indoor environments is an important priority for the modern society. The photocatalytic process has attracted particular attention in the last two decades and has proved to be efficient to reduce the concentration of NOx. However, further work has to be conducted to assess its efficiency in real indoor environments. The purpose of this paper was to report on the indoor air quality in an open space office in Manchester, UK. Focus was made on nitric oxide (NO) and nitrogen dioxide (NO2). The indoor concentrations of both gases were monitored from 14 January 2019 to 7 April 2019. During this period, a photocatalytic coating was applied to a part of the indoor wall. The influence of this coating on the level of NOx was assessed by comparing the indoor concentrations before and after the application. An attention was paid to the correlation between outdoor and indoor pollution and to the effect of other parameters such as temperature, humidity, pressure and O3 concentration. The results showed that the photocatalytic process led to a decrease in the NOx concentration. The likelihood to find concentrations above 35 ppb for NO and 7.5 ppb for NO2 was clearly reduced after the coating application.

WOS:000373541000027; International audience; Spreader Stoker Coal Fly Ashes (SSCFA) are not considered as standard by-products equivalent to Pulverized Coal Fly Ashes (PCFA) and are currently sent to landfill. From economical and environmental points of view, the landfill of these ashes is a serious concern and an alternative solution consisting in reusing them appears to be essential. For example, they could be incorporated in hydraulic binders for the manufacturing of nonstructural blocks. A previous study showed that SSCFA had interesting pozzolanic properties with specific characteristics approaching those of PCFA and reported encouraging leaching results for blended cements with SSCFA and slag. However, some leachate concentrations were still too high. The aim of this study is to assess the stabilization of SSCFA by using alternative binders (slag, cement, clinker, portlandite) and chemical activators (water glass, calcium sulfate, sodium sulfate, potassium sulfate, calcium chloride), which could be more interesting to activate SSCFA and reduce the leachability of trace elements. Results show that some alternative binders and chemical activators can increase the pozzolanic reactivity of SSCFA and the early strength of SSCFA-based systems. Adding sodium and potassium sulfate to systems composed of SSCFA and portlandite greatly improves the compressive strength value. The value is even increased when a part of portlandite is replaced by cement, clinker or slag. Moreover, the leachability of some trace elements can be reduced. This study points out the fact that alternative solutions to landfill of SSCFA might exist and reminds the need for more research work on waste stabilization. (C) 2016 Elsevier Ltd. All rights reserved.

WOS:000366227100049; International audience; This paper presents a comparison between Si silica fume (a by-product of silicon metal or ferrosilicon alloys) used in civil engineering applications and CaSi silica fume (a by-product of calcium-silicon alloys). Si silica fume has been recognized as being a by-product of more importance to the concrete industry. A lot of studies have looked at its properties and at how it can contribute to the improvements in fresh and hardened concrete. On the contrary, few papers have been published on CaSi silica fume. Chemical, mineralogical and physical characteristics are analyzed here. Rheological and mechanical behaviors of cement pastes and mortars composed of Si and CaSi silica fume are also studied in order to observe the effect of CaSi silica fume as cement replacement. The results show that these two types of silica fume do not affect in the same way the fresh and hardened properties of cementitious materials. Replacing a part of cement by CaSi silica fume does not improve the compressive strength as Si silica fume does but a good rheological behavior is maintained. To complete this work, the alkaline activation of 100%CaSi silica fume mortars is investigated. These preliminary results show that this by-product is worth to be studied and lead us to believe that it could be used in construction materials. (C) 2015 Elsevier Ltd. All rights reserved.

WOS:000400765900008; International audience; This paper investigates a new test method to assess the photocatalytic activity of plasterboards coated with a TiO2 dispersion under real-world conditions. The degradation of nitrogen oxides NO (x) (NO and NO2) is studied and the photocatalytic efficiency under UV illumination is evaluated in a 10-m(3) room after a constant gas injection. Two ultrafine TiO2 dispersions are used: 0.85% TiO2 and 5% TiO2, and three types of gas are tested: an NO/NO2 mixture (8/8 mol-ppm), NO (45 mol-ppm) and NO2 (45 mol-ppm). The test method presented here is midway between laboratory and real-scale procedures and allows better control of the experimental parameters than a real field experiment. Testing a mixture of NO and NO2 is a way to get closer to real-world conditions as air is polluted by various gases. This study focuses on the degradation of NO and NO2 under UV illumination when two types of TiO2 dispersions are used and highlights the difference in behaviour between these two molecules in terms of photocatalytic degradation. The results show that photocatalytic activity does not appear to be efficient to degrade NO2 molecules. Another mechanism seems to be responsible for the reduction of the concentration of NO2, namely adsorption. Encouraging results are obtained with NO molecules, which can be degraded by photocatalysis. The degradation observed is even greater with the more concentrated TiO2 dispersion.

This paper investigates a new test method to assess the photocatalytic activity of plasterboards coated with a TiO

International audience; We focus in this paper on a potential correlation between yield stress and bleeding. We suggest that the conditions under which a fresh cement paste is able to display a yield stress result from the competition between Brownian motion and colloidal interactions whereas the conditions under which the suspension is stable result from the competition between colloidal interactions and gravity. These competitions highly depend on the solid volume fraction of the system and on the polymer surface coverage. The correlation between yield stress and bleeding is therefore very indirect and difficult to use in practice.

International audience; In this paper, we study the physical mechanisms at the origin of a decrease in viscosity of concentrated cement pastes containing adsorbing polymers. We suggest from our results, similar to other authors, that plasticizers are able to decrease viscous dissipation bymodifying the flocculation state of the system, which, in turn, impacts the way shear localizes. Our experimental results suggest that shear concentrates in fluid layers, the thickness of which scales with the surface-to-surface separating distance between cement grains imposed by the adsorbed polymer conformation. These effects being identical for all polymers, we suggest that the residual difference between polymers in the finalmacroscopic viscosity comes from themore or less pronounced increase in the local viscosity of the interstitial fluid between neighboring particles. This increase could either be correlated to the concentration of non-adsorbed coils in the interstitial fluid or to the local concentration of adsorbed coil side chains.

International audience; Geopolymers are presented in many studies as alternatives to ordinary Portland cement. Previous studies have focused on their chemical and mechanical properties, their microstructures and their potential applications, but very few have focussed on their rheological behaviour. Our work highlights the fundamental differences in the flow properties, which exist between geopolymers made from metakaolin and Ordinary Portland Cement (OPC). We show that colloidal interactions between metakaolin particles are negligible and that hydrodynamic effects control the rheological behaviour. Metakaolin-based geopolymers can then be described as Newtonian fluids with the viscosity controlled mainly by the high viscosity of the suspending alkaline silicate solution and not by the contribution of direct contacts between metakaolin grains. This fundamental difference between geopolymers and OPC implies that developments made in cement technology to improve rheological behaviour such as plasticizers will not be efficient for geopolymers and that new research directions need to be explored.

Self Compacting Concretes (SCC) are characterized by their high fluidity so they can be placed in sections with congested reinforcements and in restricted areas without vibration. Furthermore, SCC cement paste has to be viscous enough to avoid segregation and to maintain the stability of the suspension until the onset of hardening. To fulfil these rheological requirements, mix design engineers combine use of superplasticizers and viscosity agents. The mechanism of action of these chemical admixtures is very sensitive to their adsorption. The blending of these polymers generates a competitive adsorption on surface sites of cement particles, which influences their performances. For a better understanding of competitive adsorption, we measure here both the amount of adsorbed polymers and its consequences on the rheological behaviour of the system in terms of yield stress and plastic viscosity. Our results suggest that the competitive adsorption prevents some of the polymer molecules from adsorbing, thereby moderating the performances of adsorbing polymers and enhancing the effects of polymers potentially in solution on the rheological properties of cement paste.

The objective of this thesis is to develop photocatalytic materials to fight against air pollution in conditions approaching those of an indoor environment (50% relative humidity, low UV-A and visible irradiation intensities, small amount of material) and offering an alternative to TiO2, reference product in this field. For this purpose, three semiconducting metal oxides, TiO2, WO3 and ZnO, and the nano-composite ZnWO4/WO3 were synthesized and their photocatalytic activity was evaluated in relation to the degradation of NOx (NO and NO2) on glass and mortar samples at a laboratory reactor scale. The best performing oxides, TiO2 and ZnO, were then decorated with gold (Au) metal nanoparticles in order to improve their photocatalytic activity (separation of photogenerated charges) and their absorption property (plasmon resonance effect), and thus make them active under artificial visible light. The performances of gold-decorated oxides (1% mass), Au/TiO2 and Au/ZnO, and non-decorated oxides, TiO2 and ZnO, were compared on glass and on mortar for NO and NO2 abatement. The results showed the interest of the Au/ZnO material compared to TiO2 with increased degradation performances under NO2 and a higher selectivity under NO. Finally, tests in an experimental chamber of 10 m3, used here as an intermediate scale reactor, have been performed to compare the performances of TiO2 and Au/ZnO under artificial light (UV-A and visible fluorescent tubes) and indirect sunlight (radiation through the glass surface).Our studies have shown that photogenerated charge separation is the predominant effect causing the increase in photocatalytic properties of decorated Au/ZnO under our test conditions. The use of irradiation only in the visible range (400 - 800 nm) of low intensity (6 W/m2) does not activate this photocatalyst significantly. The gold-decorated ZnO oxide, on the other hand, is very effective from very low UV-A irradiations (≤ 0.1 W/m2, 315 - 400 nm), which thus shows the possibility of using the Au/ZnO material indoors under indirect solar irradiation and/or with some indoor illuminants (fluorescent tubes) emitting a minimal fraction of UV-A.; L’objectif de ce travail de thèse est de mettre au point des matériaux photocatalytiques permettant de lutter contre la pollution de l’air dans des conditions se rapprochant de celles d’un environnement intérieur (50% humidité relative, faible intensités d’irradiation UV-A et visible, faible quantité de matériau) et offrant une alternative au TiO2, produit de référence dans ce domaine. Dans ce but, trois oxydes métalliques semi-conducteurs, TiO2, WO3 et ZnO, et le nano-composite ZnWO4/WO3 ont été synthétisés et leur activité photocatalytique a été évaluée par rapport à la dégradation des NOx (NO et NO2) sur des échantillons de verre et mortier à l’échelle d’un réacteur de laboratoire. Les oxydes les plus performants, TiO2 et ZnO, ont été ensuite décorés par des nanoparticules métalliques d’or (Au) afin d’améliorer leur activité photocatalytique (séparation des charges photogénérées) et leur propriété d’absorption (effet de résonance plasmon), et les rendre ainsi actifs sous lumière visible artificielle. Les performances des oxydes décorés par l’or (1% massique), Au/TiO2 et Au/ZnO, et non décorés, TiO2 et ZnO, ont été comparées sur verre et sur mortier pour l’abattement du NO et du NO2. Les résultats ont montré l’intérêt qu’offre le matériau Au/ZnO par rapport au TiO2 avec des performances de dégradation accrues sous NO2 et une sélectivité supérieure sous NO. Enfin, des essais dans une chambre expérimentale de 10 m3, servant ici de réacteur à une échelle intermédiaire, ont été réalisés pour comparer les performances de TiO2 et de Au/ZnO sous lumière artificielle (tubes fluorescents UV-A et visible) et lumière solaire indirecte (rayonnement à travers la surface vitrée).Nos études ont permis de montrer que la séparation des charges photogénérées est l’effet prédominant à l’origine de l’augmentation des propriétés photocatalytiques de l’oxyde décoré Au/ZnO dans nos conditions d’essais. L’utilisation d’une irradiation uniquement dans le domaine visible (400 – 800 nm) de faible intensité (6 W/m2) ne permet pas d’activer ce photocatalyseur de manière significative. L’oxyde ZnO décoré à l’or est en revanche très efficace dès de très faibles irradiations UV-A (≤ 0,1 W/m2, 315 – 400 nm), ce qui montre ainsi la possibilité d’utiliser le matériau Au/ZnO en intérieur sous irradiation solaire indirecte et/ou avec certains illuminants d’intérieur (tubes fluorescents) émettant une fraction minime d’UV-A.

Excavation operations produce several tons of soil generally contaminated by the presence of pollutants. Excavated soil is considered as waste and it can be either sent to landfill or destined for reuse depending on the level of pollution. In any case, soil should be properly treated in order to: (i) decrease the release of pollutants into the environment, and (ii) minimize the problems involved in civil engineering applications due to the reactions between cementitious phases and pollutants. In the context of this thesis, we focused on sulfates and molybdenum (Mo). Concerning sulfates, we considered two main issues: (i) external sulfate attack of concrete structures, which are in direct contact with sulfate-rich soil (e.g. dams, foundations), and (ii) the release of sulfates into solution in addition to the swelling and mechanical strength loss in sulfate-rich soil intended for valorization (e.g. reuse in road construction). In the case of Mo, its release into solution is also a serious concern as it can lead to significant risks for the environment. Therefore, in this thesis, we investigated the reaction of concrete in contact with sulfates, and the stabilization of sulfates by using alternative binders for pollution reduction and for reuse of soil. Additionally, we studied the interaction of Mo with alternative binders and their capacity to stabilize Mo. First, we studied the capacity of seven different concretes to resist external sulfate attack under similar experimental conditions. It was found that ordinary Portland cement had high expansions (>0.1%) due to the formation of ettringite in excess caused by the reaction between aluminates and sulfates. Portland cement without C_3A presented lower expansions but gypsum was found to be responsible of cracking at later ages. Meanwhile, alternative binders had low expansions in the range of 0.01-0.03% explained by the absence of C3A and portlandite, in addition to the formation of ettringite during hydration (case of ettringite binders) and the absence of calcium (case of the geopolymer-based metakaolin). Second, we compared the capacity of four different binders to stabilize sulfates in a sulfate-spiked soil. Binders having high C_3A content led to high volume expansions (>5%) caused by the formation of ettringite in excess. These binders also released heavy metals into solution due to their high clinker content. In contrast, binders containing ground granulated blast furnace slag (GGBS) led to low expansions (0,1%) en raison de la formation d'ettringite en excès provoquée par la réaction entre les aluminates et les sulfates. Pour le ciment Portland sans C_3A, des expansions plus faibles ont été mesurées, mais l'apparition de fissures à plus long terme a été attribuée à la formation de gypse. Par ailleurs, les liants alternatifs ont présenté de faibles expansions, de l'ordre de 0,01 à 0,03%, expliquées par l'absence de C_3A et de portlandite, en plus de la formation d'ettringite lors de l'hydratation (cas des liants ettringitiques) et de l'absence de calcium (cas du géopolymère à base de métakaolin). Dans un deuxième temps, nous avons comparé la capacité de quatre liants à stabiliser les sulfates dans des sols sulfatés. Les liants ayant une teneur élevée en C_3A ont entrainé des expansions élevées (>5%) à cause de la formation d'ettringite en excès. Ces liants ont également rélargué des métaux lourds en solution du fait de leur teneur élevée en clinker. En revanche, les liants contenant du laitier ont conduit à de faibles expansions (