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International audience; This paper studies the behavior of four different calcined clay-based geopolymers under sulfuric acid attack and gives insights into their degradation mechanisms. Pastes were cast using metakaolin and meta-illite and were activated by two different alkaline solutions. Mineralogical and microscopic characterizations were performed on pastes before and after attack. Results indicated that all pastes were affected by low leaching of alkali cations, and thus by a linkage disequilibrium of the geopolymer network. Meta-illite based geopolymers, which had not been addressed in the literature until now, hold promise for improving the durability of materials in aggressive environments.

International audience; The biodeterioration of cement-based materials in sewer environments occurs because of the production of sulfuric acid from the biochemical oxidation of H2S by sulfur-oxidizing bacteria (SOB). In the perspective of determining the possible reaction pathways for the sulfur cycle in such conditions, hydrated ce-mentitious binders were exposed to an accelerated laboratory test (BAC test) to reproduce a biochemical attack similar to the one occurring in the sewer networks. Tetrathionate was used as a reduced sulfur source to naturally develop sulfur-oxidizing activities on the surfaces of materials.The transformation of tetrathionate was investigated on materials made from different binders: Portland cement, calcium aluminate cement, calcium sulfoaluminate cement and alkali-activated slag. The pH and the concentration of the different sulfur species were monitored in the leached solutions during 3 months of exposure. The results showed that the formation of different polythionates was independent of the nature of the material. The main parameter controlling the phenomena was the evolution of the pH of the leached solutions. Moreover, tetrathionate disproportionation was detected with the formation of more reduced forms of sulfur compounds (pentathionate, hexathionate and elemental sulfur) along with thiosulfate and sulfate. The experimental findings allowed numerical models to be developed to estimate the amount of sulfur compounds as a function of the pH evolution. In addition, biomass samples were collected from the exposed surface and from the deteriorated layers to identifythe microbial populations. No clear influence of the cementitious materials on the selected populations was detected, confirming the previous results concerning the impact of the materials on the selected reaction pathways for tetrathionate transformation.

Materials and structures 55(3), 92 (2022). doi:10.1617/s11527-022-01928-6 special issue: "RILEM TC-267 TRM: Development and validation of tests for measuring the reactivity of supplementary cementitious materials", Published by Springer, Dordrecht

International audience; In situ X-ray Micro-Tomography (XMT) analyses with a pixel size of 0.325 µm were conducted on slag-based blended cements containing 75% of Ground-Granulated Blast-Furnace Slags (GGBS) and 25% of Ordinary Portland Cement (OPC), with or without CaCl2 acceleration. Results show the identification of the main cementitious phases and the need to perform data repeatability tests in order to allow their quantification. Investigation of the early hydration during the first 31 h of hydration by image subtraction showed (i) the dissolution of OPC/GGBS, (ii) the precipitation of hydrates including C-S-H, (iii) the accelerating effect of CaCl2, and (iv) phase-identification based on their specific grey level.

Materials and structures = Matériaux et constructions 55(5), 142 (2022). doi:10.1617/s11527-022-01947-3 special issue: "RILEM TC-267 TRM: Development and Validation of Tests for Measuring the Reactivity of Supplementary Cementitious Materials", Published by Springer Netherlands, Dordrecht

Various durability tests require a drying step to remove free water without altering the chemistry or microstructure of the materials. However, little is known about the effects of drying on alkali-activated materials (AAMs). This study focusses on the drying stage to assess the behaviour of four alkali-activated binders compared with conventional binders: a metakaolin-based geopolymer, ground granulated blast-furnace slag (GGBS) activated by sodium silicate or by sodium carbonate, and a mixture of metakaolin-GGBS activated by sodium silicate. After a 28-day autogenous cure, mortar and paste samples were dried at temperatures ranging between 20 °C and 125 °C. Micro-structural damage was observed in metakaolin-based AAMs dried at temperatures above 40 °C, but occurred only between 40 and 60 °C for GGBS-based AAMs. SEM observations and MIP porosimetry coupled with mineralogical analyses, allowed AAMs drying mechanisms to be better understood, and recommendations to be made for the preconditioning of these materials.

International audience; Anaerobic digestion allows renewable energy to be produced through the degradation of bio-waste. The process, which is of economic and ecological interest, is implemented industrially in concrete digesters. Bio-waste is a complex medium with a composition that can vary in time and space. It contains several chemical compounds, including volatile fatty acids, ammonium, and CO2, which are aggressive towards concrete and compromise its durability. The individual effects of the different compounds on concrete are significantly different. To move toward a better design of concrete intended for the building of biogas digesters, this paper aims to understand the mechanisms and intensity of alteration associated with the different components of biowaste and their contribution to the total deterioration. Ordinary Portland cement pastes were immersed for 16 weeks in six synthetic solutions made of the three metabolites, taken alone or in mixes. The mass variations of the specimens, the pH, and the concentration of the chemical elements in solution were monitored over time. The microstructural, chemical and mineralogical changes of the samples were analysed by scanning electron microscopy, electron probe micro-analysis and X-Ray diffraction analyses and showed phenomena of dissolution, leaching and carbonation. The results show that the acetic acid solution was the most aggressive, in accordance with its pH value, and had a predominant effect in mixed solutions, whereas sodium bicarbonate solution induced carbonation and showed a protective effect. Interestingly, despite its reputed high aggressiveness, ammonium nitrate did not have a major impact in mixed solutions.

International audience; Cements with high substitution rates of ground granulated blast furnace slags (GGBS) have the potential to significantly lower CO 2 emissions of concrete, but their early age strength is often below those of traditional OPC cements. One way of mitigating this drawback is to use accelerating admixtures. In this study, the effect of CaCl 2 additions on the hydration of blended cements was investigated by measuring compressive strength, porosity, heat release and propagation of ultrasound in blends containing 70 wt.% of GGBS. The onset of formation of aluminate phases was monitored using in-situ XRD. The effect of CaCl 2 on slag hydration was isolated by replacing GGBS by an inert quartz filler. Results showed that compressive strength values at one, two and seven days were increased by 50% by the CaCl 2 addition. The increases in compressive strength corresponded to a reduction in pore space. GGBS hydration contributed to the heat development, structuration and compressive strength of the blended cements from 15 hours. The addition of CaCl 2 led to an earlier onset of the GGBS reaction, at around 10 hours, and increased the rate of GGBS hydration during the first seven days. The time of onset of the GGBS contribution was also the moment when AFm precipitation started. In CaCl 2-containing blends, Cl was incorporated in AFm.

International audience; Concrete structures of anaerobic digestion plants face chemically aggressive conditions due to the contact with the complex liquid fraction of the fermenting biowaste. This paper aims to determine the biogeochemical dynamic interaction phenomena at play between the biowaste and cementitious matrices at the local scale, and to identify durable binders in such environments. Binder materials likely to show increased durability – slag and calcium aluminate cement, and a metakaolin-based alkali-activated geopolymer – and a reference Portland cement were inserted into sealed bioeactors during 5 cycles (245 days) of broken maize anaerobic digestion. Cementitious pastes suffered chemical and mineralogical alteration related mainly to carbonation and leaching. However, they had no negative impact on the bioprocess in terms of pH, metabolic evolution of volatile fatty acids and NH4+, planktonic microbial community composition or CH4 production. In all reactors, the microbial community was able to perform the anaerobic digestion successfully. The MKAA was only slightly altered in its outermost layer. Its presence in the biowaste induced lower NH4+ concentrations, a slightly higher pH and a marked shift in the microbial community, but CH4 total production was not affected. Substantial enrichment of acid forming bacteria, especially members of the genus Clostridium, was observed in the biofilm formed on all materials.Keywords: Anaerobic digestion, cementitious materials, geopolymer, durability, biodeterioration, biofilm

International audience; Ground granulated blast furnace slags (GGBS) are glassy by-products from iron production that are commonly used as supplementary cementitious materials in blended cements. The glass structure of seven industrial GGBS was investigated by Raman and Nuclear Magnetic Resonance spectroscopies. The complex composition of the slags induced multiple analytical challenges. Under usual continuous excitation, the Raman signal was masked by strong luminescence, so that analysis was carried out on a time-resolved Raman (TRR) device. TRR allowed to eliminate luminescence and resulted in exploitable spectra that showed variations in line with theoretical NBO/T values. The analysis of 27 Al and 29 Si NMR spectra was complicated by the presence of paramagnetic nuclei and the wide variety of environments. Nevertheless, 27 Al NMR showed that Al was present as a network former, mainly in 4-fold coordination and careful analyses of 29 Si NMR spectra allowed the comparison of glass network polymerization of industrial GGBS in line with the theoretical NBO/T based on their composition.

International audience; The biodeterioration of cementitious materials in sewer networks has become a major economic, ecological, and public health issue. Establishing a suitable standardized test is essential if sustainable construction materials are to be developed and qualified for sewerage environments. Since purely chemical tests are proven to not be representative of the actual deterioration phenomena in real sewer conditions, a biological test–named the Biogenic Acid Concrete (BAC) test–was devel- oped at the University of Toulouse to reproduce the biological reactions involved in the process of concrete biodeterioration in sewers. The test consists in trickling a solution containing a safe reduced sulfur source onto the surface of cementitious substrates previously covered with a high diversity microbial consortium. In these conditions, a sulfur-oxidizing metabolism naturally develops in the biofilm and leads to the production of biogenic sulfuric acid on the surface of the material. The representativeness of the test in terms of deterioration mechanisms has been validated in previous studies. A wide range of cementitious materials have been exposed to the biodeterioration test during half a decade. On the basis of this large database and the expertise gained, the purpose of this paper is (i) to propose a simple and robust performance criterion for the test (standardized leached calcium as a function of sulfate produced by the biofilm), and (ii) to demonstrate the repeatability, reproducibility, and discriminability of the test method. In only a 3-month period, the test was able to highlight the differences in the performances of common cement-based materials (CEM I, CEM III, and CEM V) and special calcium aluminate cement (CAC) binders with different nature of aggregates (natural silica and synthetic calcium aluminate). The proposed performance indicator (relative standardized leached calcium) allowed the materials to be classified according to their resistance to biogenic acid attack in sewer conditions. The repeatability of the test was confirmed using three different specimens of the same material within the same experiment and the reproducibility of the results was demonstrated by standardizing the results using a reference material from 5 different test campaigns. Furthermore, developing post-testing processing and calculation methods constituted a first step toward a standardized test protocol.Keywords

Alkali-activated materials (AAM) are now seriously considered by the cement industry as an economical alternative to Portland cement, especially for its low CO2 footprint. However, their durability still remain to be assessed in more details. The aim of this study is to focus on the sample preconditioning conditions required for testing, especially the drying stage involved in most of the current tests. Four alkali-activated binders were studied: a geopolymer (Na-silicate activated metakaolin), a Na-carbonate activated slag (GGBS), a Na-silicate activated slag and a Na-silicate activated mixture of 50% metakaolin with 50% GGBS. After an endogenous cure of 28 days at 20°C, mortar specimens were dried at different temperatures (from 20°C to 125°C) until mass stabilization. Drying kinetics and released water contents were evaluated, as well as physical, mechanical and mineralogical analyses at the end of drying. Optimal drying temperature for each alkali-activated binder was determined by coupling mechanical strength measurements and mercury intrusion porosimetry. This study revealed that an inappropriate drying temperature could modify the porosity of some classes of AAM, and reduced the compressive strength by up to 30 to 40%. Antagonistic behaviors were observed in the four alkali-activated materials studied, therefore one should be careful about selecting preconditioning protocols for assessing the properties and the durability of these binders.

International audience; Ground granulated blast furnace slags (GGBS) are glasses (>99%) of the CaO-Al 2 O 3-SiO 2 compositional system and are widely used as supplementary cementitious materials. Differences in reactivity of GGBS were screened by modifying the content of 11 minor elements (namely Ba, Ce, Cs, Cr, Mn, P, Sn, Sr, Ti, V, Zr). SEM observations showed that most elements entered the silicate glass matrix, only Sn was reduced to its metallic form and P accumulated in minor minerals. Mortar strength tests showed that 2d-compressive strength was reduced by > 50% for a TiO 2 content of 2.5 wt.% in the slag. At 28 days the loss in compressive strength was still > 40%. Calorimetric tests on other element additions showed that network modifiers (Ba, Cs and Sr) and GGBS reactivity are positively correlated, whereas Ce, Cr, V and Zr significantly decreased reactivity. It is shown that these effects can be well estimated by the weighted field strength of the added element.

International audience; Permittivity is a widespread property used to estimate the water content in concrete. To improve the reverse conversion from permittivity measurements to moisture content, we suggest the building of an electromagnetic model of concrete. In this paper, such a model is developed for the case of cement pastes. It relies on electromagnetic homogenization schemes which require an information about the permittivity of the predominant species in the material. Estimating those properties over the frequency range [200 MHz; 1 GHz] was achieved by synthesizing model cementitious binders (C-S-H and portlandite mixtures), by characterizing their macroscopic permittivity with an open-ended coaxial probe and by identifying their intrinsic permittivity with a specific homogenization procedure combining effective medium equations. The identified values are used as inputs for a homogenization procedure estimating the water content in cement pastes. For a wide range of water content, the simulated and measured real parts of permittivity show a good agreement.

International audience; Ground granulated blast furnace slag (GGBS) is a glassy by-product of pig iron production and is commonly used in concrete industry to replace cement and thereby lower the carbon footprint of the material. Large variations in reactivity exist depending on the GGBS physical and chemical features. Here we investigate the ability of three rapid calorimetric methods to evaluate the reactivity of GGBS. On a set of 16 industrial GGBS, we show that 24 h heat release, using the R3-protocol, correlates well with 2d compressive strength of standard mortars using 75 wt% GGBS. The correlation of R3-test results (R2 = 0.87) is better than for traditional reactivity indices calculated from chemical composition. Furthermore, we present data on the repeatability of the test protocol and show that the R3-protocol is very sensitive to sample fineness. Finally, XRD patterns show that slight differences in phase assemblage exist between the most and least reactive GGBS.

International audience; The chemical stability and caesium retention properties of a nonstoichiometric compoundK2-xNix/2[NiFe(CN)6].nH2O (KNiFCN) was studied in different pH conditions. Different solutions with controlled pH were prepared. Leaching tests were done with chemical analysis of the solutions. The compound was characterized before and after exposure by chemical analysis, SEM-BSE, X-ray diffraction and infrared spectroscopy. The face-centered cubic (FCC) structure of KNiFCN without caesium was stable even in presence of 1 g/l HNO3 (pH equal 2) or NaOH (pH equal 13). In presence of caesium trapped on KNiFCN structure, it appears that the increase in caesium content change the KNiFCN structure, thus influencing the retention properties in KNiFCN according to the pH of the solution. The KNiFCN structure was decomposed when the NaOH concentration exceeds 1 g/l (pH equal 14), probably due to the hydrolysis of constitutional elements. A selection of cementitious matrix is the proposed to satisfy stability conditions of this compound.

International audience; This study investigates the evolutions of the mineralogy, pore solution and porosity of magnesium potassium phosphate cement pastes (MKPC) over time in neutral and basic environments, media that MKPC pastes might encounter when used as patch repair materials or as stabilization materials for hazardous wastes. Mineralogy evolutions were characterized by X-ray diffraction/Rietveld (XRD) and thermogravimetric analyses (TGA) and completed with scanning electron microscopy (SEM/EDX) microanalyses. Pore solution compositions (ICP-OES, IC) and the porosity of the materials were also analyzed. The results showed an amorphization of MKPC pastes over time that might be related to structural changes for the K-struvite phase. Achieving chemical equilibrium between the cementitious waters and the MKPC pore solution can result in porosity evolutions within the materials. Transport and mechanical changes might be expected, especially for MKPC pastes kept in basic media, since K-struvite [MgKPO4·6H2O], could be partially dissolved, leading to a higher total pore volume.

International audience; La biodégradation des matériaux cimentaires dans les réseaux d'assainissement est une problématique majeure pour des raisons sanitaires et économiques. Cette dégradation est essentiellement due à l'oxydation biochimique des espèces soufrées en sulfate et en acide par des bactéries sulfo-oxydantes colonisant les matériaux cimentaires [1]-[3]. Dans ce contexte, plusieurs études (en laboratoires et en conditions réelles) ont montré une meilleure durabilité des matériaux à base de ciment alumineux face aux attaques biologiques comparée aux matériaux à base de ciment Portland ordinaire dans des conditions d'assainissement [2], [4]-[6]. Différents arguments ont été proposés pour expliquer la meilleure résistance des ciments alumineux ; par exemple (i) l'inhibition de l'activité microbienne par l'aluminium soluble [7], (ii) la formation d'un gel d'hydroxyde d'aluminium (AH3) qui peut agir comme une barrière physique à la diffusion de l'acide vers l'intérieur de la matrice cimentaire [5] et (iii) la meilleure capacité de neutralisation de l'acide (effet tampon) [5]. A travers cette étude, nous posons les premières briques de compréhension des mécanismes d'altération des systèmes se voulant être plus résistants et plus performants contre les attaques biologiques en conditions d'assainissement et dans différentes conditions d'agressivité. Ainsi, nous présentons les résultats issus d'un modèle chimie-transport (1D et 2D) qui a été développé sur le logiciel HYTEC et qui représente une solution d'acide sulfurique s'écoulant à la surface d'un prisme de pâte de ciment. Ces résultats ont montré que la lixiviation du Ca 2+ est contrôlée par les phénomènes de diffusion. De plus, considérant le critère de la zone dégradée (incluant la zone décalcifiée ainsi que les reprécipitations des phases secondaires, le CAC a montré une meilleure performance, comparé au CEM I, à pH 3 tandis qu'il a subi plus de détérioration à pH 1. La précipitation secondaire de l'ettringite a été observée pour les 2 systèmes, aussi bien à pH 1 que pH 3, alors que le gypse n'est observable qu'à pH 1. Cette différence de comportement est principalement liée à la réactivité particulière de l'AH3, relativement stable au pH intermédiaire de 3, se dissolvant à pH 1. Concernant le CEMI, la formation d'une large couche de gypse en surface peut réduire fortement la porosité ainsi que limiter

International audience; In anaerobic digestion plants, biological activities transform biowaste into a renewable energy: the biogas. Thisprocess produces aggressive and complex media in direct contact with the structure. Few studies have focused onthe deterioration of concrete in such environments. In order to support the sustainable development of biogasproduction growing sector, this study intends to provide thorough information on the biowaste chemicalcomposition and on materials biodeterioration mechanisms occurring in biogas plants. Cementitious materialswith various surface compositions (pastes of CEM I, CAC and CEM I treated with oxalic acid) were immersed inthe liquid phase of laboratory bioreactors reproducing anaerobic digestion conditions. Altered depths measurementsin time highlighted the better resistance of the CAC material. The microbial biofilm coverage on thematerial's surface was delayed by the surface pretreatment with oxalic acid and was less dense for the CAC paste.Chemical and mineralogical analyses mainly showed leaching and carbonation phenomena.

Several studies undertaken on the biodeterioration of concrete sewer infrastructures have highlighted the better durability of aluminate-based materials. The bacteriostatic effect of aluminum has been suggested to explain the increase in durability of these materials. However, no clear demonstration of the negative effect of aluminum on cell growth has been yet provided in the literature. In the present study, we sought to investigate the inhibitory potential of dissolved aluminum on nonsterile microbial cultures containing sulfur-oxidizing microorganisms. Both kinetic (maximum specific growth rate) and stoichiometric (oxygen consumption yield) parameters describing cells activity were accurately determined by using respirometry measurements coupled with modeled data obtained from fed-batch cultures run for several days at pH below 4 and with increasing total aluminum (Altot) concentrations from 0 to 100 mM. Short-term inhibition was observed for cells poorly acclimated to high salinity. However, inhibition was significantly attenuated for cells grown on mortar substrate. Moreover, after a rapid adaptation, and for an Altot concentration up to 100 mM, both kinetic and stoichiometric growth parameters remained similar to those obtained in control culture conditions where no aluminum was added. This argued in favor of the impact of ionic strength change on the growth of sulfur-oxidizing microorganism rather than an inhibitory effect of dissolved aluminum. Other assumptions must therefore be put forward in order to explain the better durability of cement containing aluminate-based materials in sewer networks. Among these assumptions, the influence of physical or chemical properties of the material (phase reactivity, porosity, etc.) might be proposed. IMPORTANCE Biodeterioration of cement infrastructures represents 5 to 20% of observed deteriorations within the sewer network. Such biodeterioration events are mainly due to microbial sulfur-oxidizing activity which produces sulfuric acid able to dissolve cementitious material. Calcium aluminate cement materials are more resistant to biodeterioration compared to the commonly used Portland cement. Several theories have been suggested to describe this resistance, and the bacteriostatic effect of aluminum seems to be the most plausible explanation. However, results reported by the several studies on this exact topic are highly controversial. This present study provides a comprehensive analysis of the influence of dissolved aluminum on growth parameters of long-term cultures of sulfur-oxidizing bacterial consortia sampled from different origins. Kinetic and stoichiometric parameters estimated by respirometry measurements and modeling showed that total dissolved-aluminum concentrations up to 100 mM were not inhibitory, but it is more likely that a sudden increase in the ionic strength affects cell growth. Therefore, it appears that the bacteriostatic effect of aluminum on microbial growth cannot explain the better durability of aluminate based cementitious materials.

This recommendation is an outcome of the work carried out by a working group within the RILEM Technical Committee 238-SCM “Supplementary Cementitious Materials”. The working group studied the effect of supplementary cementitious materials on the pore solution, the microstructure and the hydration product assemblage of hardened Portland cements blended with common supplementary cementitious materials. The recommendation reflects the results of a round robin test programme on common hydration stoppage methods in 10 participating laboratories. Among four different methods tested, solvent exchange by isopropyl alcohol (isopropanol) gave the best results in terms of preservation of the cement hydrate assemblage and overall reproducibility of the results [1]. The current protocol is developed based on best laboratory practices of the participating laboratories and literature reports [2–4]. The presented hydration stoppage protocol is recommended for the study of Portland cement-based hydrate assemblages by common material characterization techniques such as thermogravimetry and X-ray powder diffraction.

A primary aim of RILEM TC 267-TRM: “Tests for Reactivity of Supplementary Cementitious Materials (SCMs)” is to compare and evaluate the performance of conventional and novel SCM reactivity test methods across a wide range of SCMs. To this purpose, a round robin campaign was organized to investigate 10 different tests for reactivity and 11 SCMs covering the main classes of materials in use, such as granulated blast furnace slag, fly ash, natural pozzolan and calcined clays. The methods were evaluated based on the correlation to the 28 days relative compressive strength of standard mortar bars containing 30% of SCM as cement replacement and the interlaboratory reproducibility of the test results. It was found that only a few test methods showed acceptable correlation to the 28 days relative strength over the whole range of SCMs. The methods that showed the best reproducibility and gave good correlations used the R3 model system of the SCM and Ca(OH)2, supplemented with alkali sulfate/carbonate. The use of this simplified model system isolates the reaction of the SCM and the reactivity can be easily quantified from the heat release or bound water content. Later age (90 days) strength results also correlated well with the results of the IS 1727 (Indian standard) reactivity test, an accelerated strength test using an SCM/Ca(OH)2-based model system. The current standardized tests did not show acceptable correlations across all SCMs, although they performed better when latently hydraulic materials (blast furnace slag) were excluded. However, the Frattini test, Chapelle and modified Chapelle test showed poor interlaboratory reproducibility, demonstrating experimental difficulties. The TC 267-TRM will pursue the development of test protocols based on the R3 model systems. Acceleration and improvement of the reproducibility of the IS 1727 test will be attempted as well. This is a post-peer-review, pre-copyedit version of an article. The final authenticated version is available online at: http://dx.doi.org/10.1617/s11527-018-1269-x

This paper presents novel findings regarding the use of alkali-activated slag for the development of road applications and, more particularly, how the interactions that occur between the binder and the organic matter originally present in the soil can strongly affect its reactivity in the process of stabilization and solidification. The study uses mechanical performances and macroscopic characterization, such as isothermal calorimetry and thermogravimetric analysis of the pure binders as well as of the soil-binder mixes in order to characterize the hydration mechanisms. By analyzing the chemical composition of organic matter extracted with three different alkaline activators, it is shown that both humic and fulvic acids are strong complexing agents, not only of calcium and aluminum ions, as noted in the existing scientific literature, but also of highly soluble silicon. In this study, only sodium hydroxide activated slag was found to be a suitable alkali-activated binder for subbase layer development.

For many microstructural studies it is necessary to “stop” cement hydration—to remove free water. This paper describes the results of a round robin test on the impact of hydration stoppage methods on the composition of hydrated cements. A regular and a fly ash blended Portland cement hydrated for 90 days were selected. Ten laboratories participated in the round robin test. Four common hydration stoppage methods were studied: (1) oven drying at 105 °C, (2) solvent exchange by isopropanol, (3) vacuum drying and (4) freeze drying. After the stoppage of hydration powder samples were studied by thermogravimetry (TG) and X-ray diffraction (XRD). Bound water and Ca(OH)2 content were determined based on the TG data. Portlandite and ettringite content were quantified by Rietveld analysis of the XRD data. The goal was to establish interlaboratory reproducibility and to identify the best available protocols for research and standardization purposes. Based on the results of the round robin test three recommendations are made. (1) Oven drying at 105 °C is not recommended. This dehydrates, alters and decomposes calcium aluminate hydrates significantly more than other methods and often produced carbonation artefacts. (2) Isopropanol exchange is the most appropriate hydration stoppage method for the study of the complete hydrate assemblage of cements, including calcium aluminate hydrates such as ettringite and AFm phases. (3) For quantification of portlandite (Ca(OH)2) all tested hydration stoppage protocols are satisfactory, with the exception of oven drying.

International audience; Biodeterioration of cementitious materials in sewer networks is a major concern for health and economic reasons. Essentially, it is due to the biological oxidation of H2S into H2SO4 leading to a local progressive dissolution of the cementitious matrix and the precipitation of expansive products likely to provoke cracks. However, it is widely known that CAC has a better performance in such environments but the mechanisms are not very well understood. Nevertheless, previous studies focused mainly on measuring the mass loss of the specimens accompanied with little information on the chemical alteration of the cementitious matrix. This study aims to compare the performance of CAC and BFSC mortars in sewer conditions using laboratory test (BAC-test). Leaching kinetics were evaluated by concentrations measurements of cementitious cations in the leached solutions and of sulphate production by the microorganisms. Moreover, SEM observations coupled with EDS analyses allowed the identification of the chemical alteration of the cementitious matrix.

International audience; In biogas structures, concrete faces aggressive media during anaerobic digestion. Biological activities allow the conversion of organic matter into biogas, leading to a medium characterized by a variability of composition in time and space. In order to ensure the sustainability of this expanding industry, solutions for increasing concrete durability are needed. This study aims to analyse the deterioration mechanisms of different binders focusing on the impact of the binder nature on the medium (biochemical composition) during the digestion. Binders with favourable composition to chemically aggressive media were tested: slag cement (CEM III/B), calcium aluminate cement (CAC) and metakaolin-based alkali-activated material (MKAA), and a reference binder: OPC (CEM I). They were exposed to three anaerobic digestion cycles in liquid phase in laboratory bioreactors. The organic acids and ammonium concentrations of the liquid phase were monitored by GC and HPIC. For OPC and slag cement pastes, the chemical and mineralogical changes were characterized by SEM/EDS and XRD. Locally, the presence of binder materials has an impact on the kinetics of the digestion reaction, and therefore on the quantities of gas produced. Ammonium concentrations were above the XA3 class range. Under the conditions explored, biodeterioration mainly led to the carbonation of cement pastes.

International audience; This paper aims to better understand the mechanisms explaining the superior resistance of calcium aluminate cement (CAC) materials compared to Portland cement (PC) based materials in sewer networks. The bacteriostatic effect of CAC materials on Sulfur Oxidising Bacteria (SOB) is often argued in the literature as a possible mechanism explaining their better resistance. Reactor tests conducted on SOB demonstrated their ability to acclimatise to high aluminium contents. More generally, using a laboratory biodeterioration protocol reproducing aggressive conditions, the nature of the material (CAC or PC with different slag contents) did not significantly affect the SOB selection. Moreover the CAC materials seemed to favour the development of a higher SOB activity (and so acid production) than PC-based systems, leading to more aggressive conditions. Finally, the resistance of CAC materials to biodeterioration appeared to be mainly linked to the intrinsic resistance of phases initially present or precipitated during the deterioration process.

International audience; Up to now few studies concerning the crystallographic features of zirconia materials (HZ) used as refractory material have been performed. The elaboration process through raw material fusion followed by a controlled cooling step lead to a material containing 94 wt.% of dendritic monoclinic zirconia. During cooling, ZrO2 passes through three different structural phase transitions (SPTs), inducing formation of a complex microstructure made of different crystallographic domains called variants. This study focus on formation of these different monoclinic variants in a non-doped zirconia based material and the possibility to reconstruct initial cubic parent crystals formed at high temperature using optical microscopy and Electron Back Scattering Diffraction (EBSD). EBSD experiments allow to identify 24 monoclinic variants issued from tetragonal parent crystal and to highlight the contours of the parent cubic crystal. Then, the microstructure appearing during the first steps of the solidification of the material can be evidenced. © 2012 Elsevier Ltd.

This research investigates the influence of alkali hydroxides on unrestrained volume changes. A detailed multi-method approach is used to characterize the progress of cement hydration, autogenous and drying volume changes (i.e., shrinkage), autogenous RH decrease, compressive strength development, solid and liquid phases and the pore structure. It is noted that under autogenous conditions, alkalis magnify shrinkage; while upon external drying the extent of shrinkage is more similar. This is contrary to expectations which suggest that the reduction in the water activity and the negative pressure developed in the liquid phase, produced by alkali enrichment, should reduce shrinkage. Analysis of the autogenous RH decrease, pore solution chemistry and the mechanical properties indicates that the bulk shrinkage response is linked to multiple parameters including: (1) increased self-desiccation at early ages, (2) a reduction in the strength (and stiffness) of alkali-enriched systems and (3) liquid saturation effects. (C) 2012 Elsevier Ltd. All rights reserved.

International audience; Up to now few studies concerning the crystallographic features of zirconia materials(HZ) used asrefractory material have been performed. The elaboration processthrough rawmaterialfusion followed by a controlled cooling step lead to amaterial containing 94wt.%of dendriticmonoclinic zirconia. During cooling, ZrO2 passesthrough three differentstructural phase transitions(SPTs), inducing formation of a complex microstructure made of different crystallographic domains called variants. Thisstudy focus on formation of these different monoclinic variantsin a non-doped zirconia based material and the possibility to reconstruct initial cubic parent crystals formed at high temperature using optical microscopy and Electron Back Scattering Diffraction (EBSD). EBSD experiments allow to identify 24 monoclinic variantsissued from tetragonal parent crystal and to highlightthe contours ofthe parent cubic crystal.Then,themicrostructure appearing during thefirststeps ofthe solidification ofthematerial can be evidenced.

International audience; New fused cast refractories with a high content of zirconia have been developed to face corrosion in glass furnaces. The controlled cooling process is responsible for thermal gradients. So, thermal mismatches appear between core and edge zones of blocks. Besides, the multiphasic nature of ZrO2 based refractories is associated to thermal mismatches during cooling. Finally, the expansive transformation of ZrO2 can lead to stress generation.This paper is an application of neutron diffraction to study texture generated during the cooling process of zirconia based materials. In fact, it is shown that ZrO2 crystallographic variants have particular crystallographic texture regarding the main direction of the thermal gradient in the block. It was hypothesized that a selection of crystallographic variants could be done depending on the field stress. Tensile-compressive tests at high temperature have been done, to reproduce stress environment during the transformation of zirconia.

International audience; This paper analyses the orientation characteristics of the monoclinic variants inherited in the cubic-tetragonal-monoclinic transformation encountered in the elaboration of zirconia materials through the fusion-solidification process. The possibility of calculating the orientation of the parent cubic crystal from at least two monoclinic variants is also described. Finally this procedure is applied to reconstruct the parent cubic orientation map from the electron backscattered diffraction map of a monoclinic zirconia.

A new line of electrofused refractory materials with a very high content of zirconia (HZ) has been developed to satisfy the needs of new generation manufacturing glass furnaces. Such materials are subjected to severe operating conditions (temperature and corrosion) during their manufacturing and service life. These HZ materials required very high temperature casting and a suitable annealing process to prevent defects and cracks during manufacturing. Therefore, a research program has been launched to build numerical tools able to predict the thermo-mechanical behaviour of these materials during one of the most critical phases of manufacturing: the controlled cooling of the refractory blocks after melting and casting. The efficient development of such a tool requires the knowledge of thermo-mechanical properties of these materials with temperature, in conditions close to that occurring during processing. In the framework of this approach, the present paper deals with the characterization of elastic properties of two HZ materials, using two mechanical testing devices i.e. a pulse echography technique and a tensile test device. An innovative acoustic emission device is also used to help in identification of microdamage occurrence. The goal of this study is to investigate the microstructure organisation of materials at very fine scale (

The basic nature of alkali hydroxides (NaOH, KOH) when added to mixing water, increases the pH in proportion to the level of salt addition. For alite (impure tricalcium silicate; MIII-Ca3SiO5) hydration, this pH increase accelerates the rate of hydration and reduces the duration of the induction, acceleration and deceleration regimes. This study evaluates alite hydration in solutions of varying compositions and alkalinities (0.1 M. 0.2 M and 0.5 M NaOH and KOH) in context of their heat release behavior and analysis of the solid/liquid phases. The modeling platform, mu ic, is used to simulate, describe and discriminate the impact of the pore solution chemistry and reaction product formation parameters on alite hydration (Bishnoi and Scrivener, 2009 [1]). Numerical predictions of the solid and liquid phase compositions and the heat release response show good agreement with experimental determinations. The simulations indicate that the effects up to the end of the induction period follow directly from a change in the pore solution composition under a solution controlled dissolution mechanism. which leads to the faster precipitation of portlandite. The changes in the main heat evolution peak appear to be related to an increase in the nucleation density of C-S-H in alkali hydroxide solutions. Examination under the SEM did not indicate significant difference in C-S-H morphology and composition in the presence of NaOH/KOH. (C) 2012 Elsevier Ltd. All rights reserved.

International audience

Anaerobic digestion allows the transformation of organic matter into biogas. In the current context of ecological transition towards renewable energies and the reduction of greenhouse gas emissions, the development of the sector is encouraged in Europe and the sector is growing fast. On an industrial scale, this bioprocess is implemented in concrete structures that are in direct contact with the biowastes being digested and undergo biodeterioration phenomena. Indeed, the liquid medium contains a wide variety of metabolites produced during digestion (volatile fatty acids, NH4+, dissolved CO2) whose concentrations can reach several grams per litre, as well as the microorganisms themselves, colonizing the surface of the concrete in the form of biofilm.This thesis, carried out within the framework of the ANR project BIBENdOM, aimed at (i) analysing the mechanisms of biogeochemical interactions between cementitious materials made from different types of binders, biowaste in digestion, and biofilm in the anaerobic digestion environment and (ii) providing a thorough experimental and numerical understanding of the mechanisms of alteration of cementitious materials in order to tend towards the prediction of the durability of concrete in these complex and variable environments.On one hand, the experimental work was carried out on complete environments in laboratory and highlighted local scale interaction mechanisms between a panel of materials (CEM I, CEM III/B, CAC, alkali-activated metakaolin and alkali-activated slag) and two substrates being digested (cattle manure and maize breakage) allowing to vary the composition and the aggressiveness of the environment toward the materials (during 5 digestion cycles, or about 6 months per experience). The anaerobic digestion process was monitored and analysed in terms of composition of the liquid medium and biogas production, microbial populations and microstructural, chemical and mineralogical modifications of the materials. On the other hand, the individual actions and combined effects of the chemical compounds metabolised during the digestion were finely studied in order to characterise the kinetics and thermodynamic equilibria governing degradation, with a view to proposing a model tending towards the prediction of deterioration in media of varied compositions. For this purpose, aggressive solutions were analysed (cation and anion concentrations) over time and the degradation of cementitious materials was characterised (mass loss, structural, mineralogical and chemical modifications).The work has shown that the presence of materials in the liquid phase only impacts the digestion process in the short term and on a local scale only. The use of substrates of agricultural origin generated environments rich in dissolved CO2 (1000 - 2000 mg.L-1) and favoured the carbonation of the materials, which seems to play a major role in the deterioration mechanisms of Portland based cements, ahead of those of other metabolites (organic acids, ammonium, phosphate salts...). Among the materials used, alkali-activated metakaolin stands out for its very good behaviour and low degradation. It is also the material that has had the greatest impact on digestion, in terms of the composition of the medium (NH4+), digestion kinetics and pH as well as the microbial populations developed. Finally, the experiments carried out on chemical metabolites alone have enabled the development of a thermodynamic model applied to the interactions between cement pastes and aggressive agents, allowing to predict the chemical evolution of the solid phase during degradation and as a function of the metabolite studied.; La méthanisation, ou digestion anaérobie, permet la transformation de la matière organique en biogaz. Dans le contexte actuel de transition écologique vers des énergies renouvelables et de diminution des émissions de gaz à effet de serre, le développement de la filière est plébiscité en Europe et le secteur est en pleine croissance. A l’échelle industrielle, ce bioprocédé est mis en œuvre dans des structures en béton qui sont en contact direct avec les biodéchets en digestion et subissent des phénomènes de biodétérioration. En effet, le milieu liquide contient une grande variété de métabolites produits lors de la digestion (acides gras volatils, NH4+, CO2 dissous) dont les concentrations peuvent atteindre plusieurs grammes par litre, ainsi que les microorganismes eux-mêmes, colonisant la surface du béton sous forme de biofilm.Cette thèse, réalisée dans le cadre du projet ANR BIBENdOM, visait à (i) analyser les mécanismes d’interactions biogéochimiques entre les matériaux cimentaires constitués à partir de différents types de liants, le biodéchet en digestion, et le biofilm dans le milieu de la méthanisation et (ii) apporter une compréhension approfondie expérimentale et numérique des mécanismes d’altération des matériaux cimentaires et cela afin de tendre vers la prédiction de la durabilité du béton dans ces environnements complexes et variables.Le travail expérimental a été mené d’une part sur des milieux complets en laboratoire et a mis en évidence des mécanismes d’interactions à échelle locale entre un panel de matériaux (pâtes à base de CEM I, CEM III/B, CAC, métakaolin alcali-activé et laitier alcali-activé) et deux substrats en digestion (fumier bovin et brisure de maïs) permettant de faire varier la composition et l’agressivité du milieu vis-à-vis des matériaux (durant 5 cycles de digestion, soit environ 6 mois par expérience). Le processus de digestion anaérobie a été suivi et analysé en termes de composition du milieu liquide et production de biogaz, de populations microbiennes et de modifications microstructurales, chimiques et minéralogiques des matériaux. D’autre part, les actions individuelles et effets combinés des composés chimiques métabolisés lors de la digestion ont été finement étudiés afin de caractériser les cinétiques et équilibres thermodynamiques régissant les dégradations, et cela en vue de proposer un modèle tendant vers la prédiction de la détérioration dans des milieux de compositions variées. Pour cela, les solutions agressives ont été analysées (concentrations en cations et anions) au cours du temps et les dégradations des matériaux cimentaires ont été caractérisées (suivi de masse, modifications structurales, minéralogiques et chimiques).Le travail a permis de démontrer que la présence des matériaux en phase liquide n’impacte le processus de digestion que sur le court terme et à l’échelle locale uniquement. L’utilisation des substrats d’origine agricole a engendré des milieux riches en CO2 dissous (1000 – 2000 mg.L-1) et favorisé les phénomènes de carbonatation des matériaux, qui semblent jouer un rôle majeur dans les mécanismes de détérioration des ciments à base de Portland, devant ceux des autres métabolites (acides organiques, ammonium, sels de phosphate…). Parmi les matériaux utilisés, le métakaolin alcali-activé se démarque par son très bon comportement et sa faible dégradation. C’est aussi le matériau ayant eu le plus d’impact sur la digestion, en termes de composition du milieu (NH4+), de cinétiques de digestion et de pH ainsi que de populations microbiennes développées. Enfin, les expériences menées sur les métabolites chimiques seuls ont permis le développement d’un modèle thermodynamique appliqué aux interactions entre les pâtes de ciment et les agents agressifs permettant de prédire l’évolution chimique de la phase solide au cours de la dégradation et en fonction du métabolite étudié.

Blast furnace slags are a co-product of the metallurgical industry, used in composite cements (CEM II & III) as a partial substitution for Portland clinker and recognized in particular for their advantages in terms of lowering the heat of hydration, increased durability performance and reduced carbon footprint of concrete. Although achieving ultimate mechanical performance comparable to or better than Portland cement (CEM I), binders offering high levels of slag see the development of their mechanical strength greatly slowed down. This phenomenon is explained by a lower reactivity of the slag which requires "activation" conditions to react properly. There are various additives that accelerate the hardening of cements, among which calcium chloride shows the best performance. The effects of calcium chloride are particularly important during the first days of hydration. However, their use is strongly regulated because of the corrosive effect of chlorine on steels of reinforced concrete. The objectives of the thesis are to study the mechanisms of action of calcium chloride on cement-slag binders during the first days of hydration. A panel of experimental techniques has been used to specifically identify the action of chlorides on slag and cement. Coupled results from XRD-NMR SEM experiments show that calcium chloride causes an accelerated precipitation of portlandite and ettringite, resulting from the increase in the reaction rate of clinker. The start of the slag reaction takes place after about 12 hours, and is not impacted by the calcium chloride. On the other hand, the reaction rate of the slag increases in the presence of the accelerator. The rapid, significant and exclusive formation of Friedel salts in the presence of chloride is observed, replacing sulphated and / or carbonated AFm. Increasing the reaction rate of the anhydrous phases results in the precipitation of additional C-S-H. This formation of Friedel salts and C-S-H causes a faster filling of the porosity and the increase of the mechanical performances.; Les laitiers de hauts fourneaux sont un coproduit de l'industrie métallurgique, utilisés dans les ciments composés (CEM II & III) en substitution partielle du clinker portland et reconnus notamment pour leurs avantages en termes d'abaissement de chaleur d'hydratation, d'augmentation des performances de durabilité et de réduction du bilan carbone des bétons. Bien qu'atteignant des performances mécaniques ultimes comparables voire supérieures au ciment portland (CEM I), les liants proposant de forts taux de laitier voient le développement de leur résistance mécanique fortement ralenti. Ce phénomène s'explique par une réactivité plus faible du laitier qui nécessite des conditions "d'activation" pour réagir correctement. Il existe divers additifs ayant pour effet d'accélérer le durcissement des ciments, parmi lesquels le chlorure de calcium montre les meilleures performances. Les effets du chlorure de calcium sont particulièrement importants durant les premiers jours de l'hydratation. Cependant, leur usage est fortement règlementé en raison de l'effet corrosif du chlore sur les aciers du béton armé. Les objectifs de la thèse visent à étudier les mécanismes d'action du chlorure de calcium sur les matrices ciment-laitier durant les premiers jours d'hydratation. Un panel de techniques expérimentales a été utilisé pour identifier spécifiquement l'action des chlorures sur le laitier et le ciment. Des couplages DRX-Analyse d'Images MEB et RMN montrent que le chlorure de calcium entraîne une précipitation accélérée de portlandite et d'ettringite, issus de l'augmentation du taux de réaction du clinker. Le démarrage de la réaction du laitier s'opère après environ 12 heures, et n'est pas impacté par le chlorure de calcium. En revanche, le taux de réaction du laitier augmente en présence de l'accélérateur. On observe la formation rapide, importante et exclusive de Sels de Friedel en présence de chlorure, en remplacement des AFm sulfatés et/ou carbonatés. L'augmentation du taux de réaction des phases anhydres entraîne la précipitation de C-S-H supplémentaire. Cette formation de Sels de Friedel et de C-S-H provoquent un remplissage plus rapide de la porosité et l'augmentation des performances mécaniques.

Ground granulated blast-furnace slags (GGBS) are used in cements in particular because of the overall improvement in the durability of building materials. However, binders with a high content of GGBS have a slower hydration and thus a development of mechanical strength slower than Portland cements (PC). Solutions exist to accelerate the hardening of GGBS-based binders, including the use of chemical activators based on chlorides. The effects of activation on the mechanical strength developments of PC/GGBS blends are discussed in the literature, but the durability of these systems is not very developed. This thesis aims to evaluate the consequences of the use of chlorides activators on the durability of binders containing 50% of GGBS. Firstly, an analysis of the durability indicators shows how the activator modifies the transfer properties of the hardened material as well as the structuring of the porous network. This allows to verify that the activation at early age does not decrease the long-term durability of concretes with GGBS. Then, a study of the corrosion state of steels in these blends is realized to evaluate the impact of chlorides activators, known to initiate corrosion in reinforced concrete. Electrochemical tests coupled with direct observation as well as a microstructural study on how interact chlorides in the cement matrix are carried out. The ability of GGBS-based blends to bind chlorides in hydrates is studied in particular. Finally, the behavior of binded chlorides is analyzed, in the case where the carbonation would destabilize the hydrates. The impact of a possible release of chlorides is evaluated using a coupled model carbonation / chloride diffusion.; Les laitiers de haut-fourneaux (LHF) sont utilisés dans les ciments notamment en raison de l'amélioration globale de la durabilité qu'ils confèrent aux matériaux de construction. Cependant, les liants à forte teneur en laitiers présentent une hydratation plus lente et donc un développement de résistances mécaniques moins rapide que les ciments portland (CP). Des solutions existent pour accélérer le durcissement des liants à base de LHF, notamment l'emploi d'activants chimiques à base de chlorures. Les effets de l'activation des systèmes CP/LHF sur les développements de résistances mécaniques sont abordés dans la littérature, mais leur durabilité est assez peu étudiée. Cette thèse a donc pour but d'évaluer les conséquences de l'utilisation d'activants chlorés sur la durabilité des liants contenant 50% de LHF. D'abord, une analyse des indicateurs de durabilité permet de voir comment l'activant modifie les propriétés de transfert du matériau durci ainsi que sur la structuration du réseau poreux. Cela permet de vérifier que l'activation à jeune âge n'hypothèque pas la durabilité des bétons avec laitier à long terme. Ensuite, une étude de l'état de corrosion des aciers dans ces mélanges est entreprise afin d'évaluer l'impact des activants chlorés, reconnus pour créer de la corrosion dans le béton armé. Des essais électrochimiques couplés à de l'observation directe ainsi qu'une étude microstructurale sur le devenir des chlorures au sein de la matrice cimentaire est effectuée. La faculté des mélanges à base de laitier à fixer les chlorures dans les hydrates est notamment étudiée. Enfin, le comportement des chlorures fixés est analysé, dans le cas où la carbonatation viendrait déstabiliser les hydrates. L'impact d'un relargage éventuel de chlorures est évalué à l'aide d'un modèle couplé carbonatation/diffusion des chlorures.

Ground granulated blast-furnace slags (GGBS) are used in cements in particular because of the overall improvement in the durability of building materials. However, binders with a high content of GGBS have a slower hydration and thus a development of mechanical strength slower than Portland cements (PC). Solutions exist to accelerate the hardening of GGBS-based binders, including the use of chemical activators based on chlorides. The effects of activation on the mechanical strength developments of PC/GGBS blends are discussed in the literature, but the durability of these systems is not very developed. This thesis aims to evaluate the consequences of the use of chlorides activators on the durability of binders containing 50% of GGBS. Firstly, an analysis of the durability indicators shows how the activator modifies the transfer properties of the hardened material as well as the structuring of the porous network. This allows to verify that the activation at early age does not decrease the long-term durability of concretes with GGBS. Then, a study of the corrosion state of steels in these blends is realized to evaluate the impact of chlorides activators, known to initiate corrosion in reinforced concrete. Electrochemical tests coupled with direct observation as well as a microstructural study on how interact chlorides in the cement matrix are carried out. The ability of GGBS-based blends to bind chlorides in hydrates is studied in particular. Finally, the behavior of binded chlorides is analyzed, in the case where the carbonation would destabilize the hydrates. The impact of a possible release of chlorides is evaluated using a coupled model carbonation / chloride diffusion.; Les laitiers de haut-fourneaux (LHF) sont utilisés dans les ciments notamment en raison de l'amélioration globale de la durabilité qu'ils confèrent aux matériaux de construction. Cependant, les liants à forte teneur en laitiers présentent une hydratation plus lente et donc un développement de résistances mécaniques moins rapide que les ciments portland (CP). Des solutions existent pour accélérer le durcissement des liants à base de LHF, notamment l'emploi d'activants chimiques à base de chlorures. Les effets de l'activation des systèmes CP/LHF sur les développements de résistances mécaniques sont abordés dans la littérature, mais leur durabilité est assez peu étudiée. Cette thèse a donc pour but d'évaluer les conséquences de l'utilisation d'activants chlorés sur la durabilité des liants contenant 50% de LHF. D'abord, une analyse des indicateurs de durabilité permet de voir comment l'activant modifie les propriétés de transfert du matériau durci ainsi que sur la structuration du réseau poreux. Cela permet de vérifier que l'activation à jeune âge n'hypothèque pas la durabilité des bétons avec laitier à long terme. Ensuite, une étude de l'état de corrosion des aciers dans ces mélanges est entreprise afin d'évaluer l'impact des activants chlorés, reconnus pour créer de la corrosion dans le béton armé. Des essais électrochimiques couplés à de l'observation directe ainsi qu'une étude microstructurale sur le devenir des chlorures au sein de la matrice cimentaire est effectuée. La faculté des mélanges à base de laitier à fixer les chlorures dans les hydrates est notamment étudiée. Enfin, le comportement des chlorures fixés est analysé, dans le cas où la carbonatation viendrait déstabiliser les hydrates. L'impact d'un relargage éventuel de chlorures est évalué à l'aide d'un modèle couplé carbonatation/diffusion des chlorures.

Nuclear industry generated waste including radioactive wastes, which have different forms and origins. The wastes produced by reprocessing of nuclear fuel are characterized by important water content, by high pH and temperature sensitivity. The cementation in ettringite systems might be a promising solution to solidify radioactive wastes. Mixtures of Calcium Aluminate Cement (CAC) and calcium sulfate are planned to be used, instead of Ordinary Portland Cement (OPC), to form a significant amount of ettringite able to catch water molecules when forming. Moreover, due to the low pH of CAC-based matrices, the latter have a good compatibility with the compounds used to stabilize active elements. Initially, the stability of the sorbent of cesium used in this study was tested in different pH environments (2 to 14) and temperature. Chemical analysis and different microstructural characterizations like X-ray diffraction, FTIR and SEM-EDS have allowed to set stability limits of ettringite systems. Then microstructural study on binary systems composed by mixture of CAC/calcium sulfate (hemihydrate and/or anhydrite) was realized to characterize ettringite stability during the time of hydration. Low pH properties were checked by chemical pore solutions analysis. However, the heat generated by hydration and the possible formation of expansive systems require an increase of e/s ratio and additional components like Ground Granulated Furnace Slag (GGBS). These two parameters were studied subsequently. Microstructural study of GGBS reactivity and the modification of ettringite assemblage were showed that GGBS act as filler at early time of hydration. To promote the GGBS reactivity at long term of hydration by alkaline and sulfate activation, different nature of calcium sulfate was used. Then the microstructural characteristic of this ternary system in presence of different e/s ratio was studied. Finally, different information on the effect of formulation parameters obtained led to the development of tests on formulations containing an inert simulated waste and enriched in chlorides. Systematic tests of fluidity, mechanical strength and for some expansion and heat generation should identify a series of mixtures adapted to test prototype to industrial scale for cementing wastes.; L'industrie nucléaire est une industrie génératrice de déchets, dont certains sont radioactifs. Ces déchets radioactifs ont des formes et des origines diverses, allant de la paire de gant de manutention faiblement contaminés, à la suspension aqueuse de produits de fissions hautement radioactifs. Dans ce travail, un type de déchet bien particulier a été étudié ; des boues issues de la décontamination d'effluents liquides radioactifs, possédant entre autres les trois particularités suivantes ; * Etre moyennement radioactif, selon les critères de l'ANDRA. * Etre composé d'une forte teneur en eau de constitution (ne pouvant être retirée par simple évaporation) ; * Etre composé d'un sorbant (PPFeNi) dont la stabilité chimique n'est pas assurée pour un pH supérieur à 11. Ces particularités font qu'un enrobage dans une matrice minérale forte consommatrice d'eau, et bas-pH (pH < 11) est envisageable. Le choix c'est alors porté sur le développement d'une matrice ettringitique réalisée à partir d'un mélange de Ciment d'Aluminate de Calcium (CAC) et de sulfate de calcium. Dans un premier temps, la stabilité du sorbant du césium utilisé dans cette étude a été testée dans différents environnements de pH (2 à 14) et de température. Pour cela des analyses chimiques de solution ainsi que des caractérisations du composé par diffraction de rayons X, FTIR et microscopie électronique à balayage-EDS ont permis de fixer les bornes de stabilité que la formulation ettringitique doit avoir. Puis une étude microstructurale (nature et morphologie des produits) de mélanges ettringitiques binaires CAC/sulfate de calcium type hémihydrate et/ou anhydrite a été effectuée afin de caractériser la stabilité de l'ettringite, hydrate fort consommateur d'eau. Les propriétés bas-pH ont été vérifiées notamment par analyse chimique de solutions porales. Certaines limites de ces systèmes concernant le dégagement de chaleur et la possible formation de systèmes expansifs ont été mises en évidence. L'effet de l'augmentation du rapport eau/liant, responsable d'un effet de dilution et permettant de réduire les deux effets précédents, a été également regardé pour ces systèmes binaires. Afin de réduire la chaleur dégagée à court terme tout en permettant le développement de l'hydratation à long terme de systèmes ettringitiques, ces systèmes binaires ont été substitués par des additions minérales à hydraulicité latente type laitier de haut fourneau. Une étude microstructurale de la réactivité du laitier et de la modification de l'assemblage ettringitique a montré une réactivité modérée de ce dernier à jeune âge conformément aux attentes. Pour favoriser sa réactivité à long terme par activation alcaline/sulfatique différentes proportions de sulfate de calcium à dissolution plus lente ont été testés. Les caractéristiques microstructurales de ces systèmes ternaires en présence de différentes teneurs en eau intrinsèquement liée à la nature de type boue du déchet a été étudiée. Enfin, les différentes informations sur l'effet des paramètres de formulation obtenues ont débouché sur la mise en place de tests sur des formulations contenant un déchet simulé inerte et enrichi en chlorures. Des essais systématiques de fluidité, de résistances mécaniques et pour certains d'entre eux d'expansion et de dégagement de chaleur doivent permettre d'identifier une série de mélanges adaptés au test à l'échelle de prototype industriel pour la cimentation de boues.

The biodeterioration of cementitious materials in sewer networks is a major concern for health and economic reasons. Mainly, it is due to the biological oxidation of H2S into H2SO4 leading to a progressive dissolution of the matrix and the precipitation of expansive products likely to provoke cracks. In the literature, it is established that calcium aluminate cement (CAC) has a better resistance in such environments than Portland cement (PC). The better performance of CAC was mainly linked to the high aluminum content of this material and to the physico-chemical properties of the cement matrix (mineralogical phases, porosity, etc.). In addition, recent studies revealed the potential role of iron in the resistance of materials in such environments, however, without clarifying this role.This thesis aimed to (i) study the behavior and the deterioration mechanisms of different low-CO2 cementitious materials (e.g. calcium sulfoaluminate cement (CSA) and alkali-activated slag (AAS)) exposed to a microbial attack in sewer conditions; (ii) evaluate the impact of partially substituting PC with mineral additives, rich in aluminum and/or iron on the resistance of the materials; (iii) understand the mechanisms of interactions between the cement matrix, the aggressive environment and the biofilm; (iv) use and optimization of a numerical model, based on the coupling of materials’ chemistry and the transport of species in solution, to include biological transformations of sulfur species.The experimental work was carried out in laboratory conditions using an accelerated test. This test made it possible to create favorable conditions for the development of a sulfur-oxidizing activity at acidic pH on tetrathionate (S4O62-) substrate and to evaluate the behavior of various materials (based on PC, CAC, CSA and AAS).A performance indicator (PIeqOH) was developed by evaluating the leaching of chemical elements/compounds (in particular calcium, aluminum, iron, magnesium and sulfate which defines the neutralizing capacity of the materials). This performance indicator was used to establish a classification of materials according to their resistance to sulfuric acid attack in these exposure conditions.In the experimental conditions, Acidithiobacillus and Thiomonas genus were the main bacteria identified, with the latter being able to disproportionate tetrathionates in absence of oxygen. The disproportionation of tetrathionate was identified as responsible for the presence of elemental sulfur precipitation on the materials' surface.Certain CSA-based materials have shown better behavior than Portland cements in the experimental conditions. This resistance was mainly attributed to the formation of aluminum hydroxide and its chemical stability in acidic environments. Moreover, the mineralogical form of aluminum-bearing phases is critical regarding their resistance to the acid attack and the simple increase of the aluminum content by non-reactive mineral additives was shown to not improve the performance of the materials.Iron, non-reactive initially, remained relatively inactive during the very aggressive microbial attack. Neither the iron concentration nor the form in which it was present showed any impact on the development of microbial activities. Moreover, no improvement of the resistance of cement-based materials by iron enrichment has been obserbed maybe in relation with the absence of new Fe-bearing hydrated phases.In the conditions of the BAC test, the deterioration mechanisms of alkali-activated slag materials were similar to those of Portland cement based ones, and consisted of a strong decalcification of C-A-S-H, leading to the formation of an aluminosilicate gel on the surface., La biodégradation des matériaux cimentaires dans les réseaux d’assainissement est une préoccupation majeure pour des raisons sanitaires et économiques. Elle est principalement due à l'oxydation biologique de H2S en H2SO4 conduisant à une dissolution progressive de la matrice cimentaire ainsi qu’à la précipitation de produits expansifs susceptibles de provoquer des fissurations. Dans la littérature, il est établi que le ciment d'aluminates de calcium (CAC) a une meilleure résistance, dans de tels environnements, comparé au ciment Portland (PC). Les meilleures performances du CAC sont attribuées à la forte teneur en aluminium et aux propriétés physico-chimiques de la matrice cimentaire (phases minéralogiques, porosité…). D’autre part, des études récentes révèlent le potentiel rôle du fer dans la résistance des matériaux présents dans ces environnements, sans toutefois permettre de clarifier ce rôle.Cette thèse avait pour objet (i) d’étudier le comportement et les mécanismes de détérioration des différents matériaux cimentaires bas-CO2 (ciment sulfoaluminate (CSA) et laitier alkali-activé (AAS)) exposés à une attaque microbienne en condition d’assainissement; (ii) d’évaluer l’impact de la substitution d’une partie du ciment Portland par des additions minérales, riche en aluminium et/ou fer sur la performance des matériaux; (iii) de comprendre les mécanismes d’interactions entre la matrice cimentaire et le biofilm; (iv) d’optimiser un modèle numérique, basé sur le couplage de la chimie des matériaux et le transport des espèces en solution, par l’intégration des transformations biologiques des espèces soufrées.Le travail expérimental a été réalisé en laboratoire en utilisant le BAC test. Ce test vise à générer des conditions favorables au développement d’une activité sulfo-oxydante à pH acide sur un substrat de tetrathionate (S4O62-) et d’évaluer le comportement de différents matériaux (PC, CAC, CSA et AAS).Un indicateur de performance (PIeqOH) a été développé par l’évaluation de la lixiviation des éléments/composés chimiques (notamment le calcium, l’aluminium, le fer, le magnésium et le sulfate qui définissent le pouvoir tampon des matériaux). Cet indicateur a permis d’établir un classement des matériaux selon leurs résistances à l’attaque d’acide sulfurique dans ces conditions.Dans les conditions expérimentales, les espèces Acidithiobacillus et Thiomonas sont les principales bactéries identifiées, Thiomonas étant capable de dismuter les tetrathionates en absence d’oxygène. La dismutation du substrat soufré a été identifiée comme responsable de la présence de soufre élémentaire à la surface des matériaux.Le meilleur comportement des matériaux à base de CSA, comparé aux ciments type Portland, a été attribué principalement à la formation d’hydroxyde d’aluminium (AH3), phase chimiquement stable en conditions acides. La forme minéralogique des phases contenant de l’aluminium est un facteur clé de leur résistance à l’acide et la simple augmentation de la teneur en aluminium par des additions minérales non-réactives s’est avérée insuffisante pour améliorer les performances des matériaux cimentaires.Le fer, initialement non-réactif, reste relativement inactif pendant une attaque microbienne très agressive. Ni la concentration en fer, ni la forme sous laquelle il est présent n’ont montré d’impact sur l’installation de l’activité microbienne. De plus, l’ajout des additions minérales riches en fer non réactifs n'a pas amélioré la durabilité des matériaux cimentaires.Dans les conditions du BAC test, les mécanismes de détérioration des matériaux à base de laitier alcali-activé étaient très similaires à ceux à base de ciment Portland et ont consisté en une décalcification très forte des C-A-S-H, menant jusqu’à la formation d’un gel silicoalumineux en surface.