Search

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

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

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; 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; 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.

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.