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The main objective of this study was to improve some properties (physical, mechanical, hydric and thermal) of earth renders amended by cow dung, as such amendment is an ancestral practice in Burkina Faso. For this purpose, raw clayey material from Kodeni (in western Burkina Faso), mainly composed of kaolinite (62 wt.%), quartz (31 wt.%) and goethite (2 wt.%) and having adequate geotechnical properties was used to elaborate earth renders reinforced with up to 6 wt.% of cow dung. The cow dung studied was mainly made up of small vegetable fibres, clayey minerals and quartz consumed by cows. Cow dung incorporation limits the spread of cracks and hardens the material thanks to the good adhesion of cow dung to the clayey matrix, which is linked to the rough surface of fibres contained in cow dung. The presence of cow dung in an earth render influences its mineralogy through the formation of insoluble amine silicate (Si(OH)4. 4NH3). This compound is formed during the reaction between fermented cow dung with mainly fine crushed quartz and feebly kaolinite in basic medium. The molecule formed links isolated raw material particles through free electronic doublets on the oxygen atoms and especially on the nitrogen atoms. The consequence of this effect is an improvement of the microstructural, physical and mechanical properties of earth renders. In particular, their thermal conductivity is reduced as the fibres present in the composite materials are rich in cellulose (molecule with thermally insulating properties), and their resistance to abrasion and to water is good. The earth renders elaborated in this way help to provide water resistant housing with good thermal comfort.

International audience; This research aims at the seismic assessment and understanding of a traditional loadbearing system incorporating horizontal timber elements into earth brick masonry walls. In order to characterize the global behavior of the loadbearing device, an experimental campaign was performed on the constituents (i.e. bricks and mortar) and on masonry samples. Compression tests were carried out on four geometries of earth brick samples and three geometries of earth mortar samples. As the methods to obtain the compressive strength of earth material are still discussed within the scientific community, a focus was made on different configurations tested. Uniaxial compression tests were performed on two earth brick wallets. Then, two brick walls (with and without horizontal timber reinforcement) were submitted to lateral quasi-static cyclic load. A LVDTs system and a stereo correlation image system were coupled to study the experimental response of the reinforced and unreinforced walls. This investigation led to estimate the lateral strength, the stiffness degradation and the dissipated energy of both reinforced and unreinforced masonry walls. Moreover, it allowed the comparison between the failure modes of the two types of wall. This analysis brings light on the mechanical impact of the horizontal reinforcement.

International audience; The starting premise of this article is that it is not environmentally consistent to stabilize earth by using more than 4% of mineral binder (cement or lime). Thus, this paper presents a study of the effects of low mineral binder contents (2 and 4%) on the properties of earth bricks. The results obtained on two different soils show that the effects are not observable for dry compressive strengths or for dry thermal conductivities but the addition of small amounts of mineral binders significantly modifies the resistance to water and the Moisture Buffer Value.

International audience; Earth is a material presenting good hygric properties, which is an important point as comfort and indoor air quality have become major issues. Nowadays, the energy efficiency of a construction is also crucial, but the thermal insulation provided by an earth brick is quite low. Therefore, some plant aggregates were added to lighten the material, thus decreasing its thermal conductivity. The hygrothermal properties of seven formulations made of earth with 0, 3 or 6% by weight content of barley straw, hemp shiv or corn cob were assessed. The properties determined were thermal conductivity, specific heat capacity, water vapour permeability, and sorption-desorption isotherms measured with the saturated salt solution and DVS methods. The theoretical MBV was also calculated. The study showed a large decrease in thermal conductivity when a large volume of plant aggregates was added while plant aggregates incorporation conversely affected the thermal inertia parameters. Concerning water vapour permeability, as earth is a very permeable material, the addition of plant aggregates did not improve this property. The sorption capacity of bio-based earth materials was slightly increased in comparison with earth alone. Finally, the calculated MBV showed the excellent buffering capacity of this kind of material, with and without plant aggregates.

Earth is perfectly suited for indoor plastering purposes thanks to its numerous technical, ecological and economic assets. The quantity of clay is frequently evoked to explain fresh and mechanical performances of earthen coatings but this indicator fails to give full account of the diversity of earth behaviour encountered in earth construction. This paper aims to examine plaster properties from the point of view of their geotechnical and mineralogical composition. Four types of soil were employed to design earthen plasters with variable earth to sand ratios. The behaviour of coatings was assessed through their water requirement, linear shrinkage, and flexural and compressive strengths. A noteworthy relationship was detected between the water requirement of earth plasters and the liquid limit of the raw earth employed. The mechanical resistances of plasters were found to be linked to the cation exchange capacity of the soils. The correlations between linear shrinkage, or compressive strength, and percentage passing at 2 µm were strong, justifying the widespread use of texture and clay content for soil classification, and assessment of the properties of earth-based building materials.

As a building material, earth is known to be a natural humidity regulator and to improve comfort inside buildings, making it a good choice for indoor plastering. The clayey phase ensures the sorption capacity of the material and its global cohesion by acting as a binder for the sand grain skeleton. However, clay also induces drying shrinkage of the mortar, leading to cracking of the plaster. Additives or stabilizers are typically used to address issues such as mechanical resistance and drying shrinkage in earthen building materials. To promote the development of eco-building materials, this paper pays particular attention to the potential of organic admixtures (vegetal or animal). The effectiveness of such admixtures could depend largely on the type of soil used and on the amount and nature of the clay minerals involved. Four types of soils were investigated. Based on consistency, shrinkage, visual and numerical detection of cracking, and flexural, compressive and shear tests, the characteristics of mortars in fresh and hardened states were evaluated. The results show that the clay content is a key parameter of both fresh properties and mechanical performances of plasters but is not sufficient by itself, especially when organic admixtures are involved. The potential of seven admixtures was evaluated. Although the deflocculants enabled a water reduction in mixes as well as a mechanical improvement, and the cohesion strengtheners were able to enhance mechanical properties at the hardened state, only flax fibre-based mortars demonstrated sufficient adhesion to their application substrate and, above all, no cracking as they dried.

Earth masonry is a good alternative to more conventional materials in order to reduce the environmental impact of building materials. However earth construction techniques mostly rely on bricklayers’ experience, which is a hindrance to industrial development of this traditional know-how. This article proposes a methodology for the mix design of unstabilized earth bedding mortar based on mechanical criteria of the masonry and rheological criteria of fresh mortar. A test to characterize the shear strength of the masonry interface is specially investigated. The mechanical performances of the formulated mortar are then validated with laboratory scale characterization.

International audience; Bio-aggregate based building materials offer promising perspectives thanks to their low environmental impact and interesting hygrothermal behaviour. In this paper, different formulations of bio-aggregate concrete are proposed and analysed. We focus on two types of locally available bio-aggregates, namely maize and sunflower bark chips, and two types of binder matrices, based on respectively metakaolin and lime. The study specifically focuses on the pore structure of the composite material, as this quantity has a decisive impact on the insulating properties (thermal conductivity), the hygric behaviour (sorption isotherms, water vapour permeability and moisture buffer value) as well as on the mechanical performance (compressive strength). The results underline the impact of the constituents' porosity on the complex porous structure of the bio-concrete and the influence of porosity on its performance. The findings demonstrate that metakaolin and sunflower are high-potential raw materials for the design of a bio-aggregate based concrete.

The structure of a [Cu(SiF6)(C10H8N2)2]n coordination polymer with ordered 4,4′-bi­pyridine and water mol­ecule channels is described., The coordination polymer {[Cu(SiF6)(C10H8N2)2]·2C10H8N2·5H2O}n, systematic name: poly[[bis­(μ2-4,4′-bi­pyridine)(μ2-hexa­fluorido­silicato)copper(II)] 4,4′-bi­pyridine disolvate penta­hydrate], contains pores which are filled with water and 4,4′-bi­pyridine mol­ecules. As a result of the presence of these ordered species, the framework changes its symmetry from P4/mmm to P21/c. The 4,4′-bi­pyridine guest mol­ecules form chains inside the 6.5 × 6.9 Å pores parallel to [100] in which the mol­ecules inter­act through π–π stacking. Ordered water mol­ecules form infinite hydrogen-bonded chains inside a second pore system (1.6 × 5.3 Å free aperture) perpendicular to the 4,4′-bi­pyridine channels.

International audience; Nowadays, for environmental reasons, the demand for bio-based building materials is increasing. The number of studies focusing on earth building bricks with addition of plant aggregates is growing. In this study, barley and lavender straws were considered as bioaggregates in an earth matrix. Their characterization revealed distinct shape, size and porosity. Composites including 3% and 6% by mass of each bioaggregates were then elaborated. Their performances were investigated and compared in terms of mechanical and thermal properties, durability of the composite materials and resistance to fungal growth. The mixture with 3% of lavender straw showed satisfactory durability results while barley straw brought better thermal properties.

International audience; This study deals with the influence of fonio straw on the physical, thermal and mechanical properties of adobes. The raw materials (soil and fonio straw from Burkina Faso) were characterized from the chemical (ICP-AES), mineralogical (XRD, DSC-TGA, IR), geotechnical (particle size distribution, Atterberg limits, methylene blue value) and microstructural (SEM-EDS) points of view. The physical (thermal conductivity, capillarity water absorption, porosity, erodibility) and mechanical (compressive and flexural strength) properties of the adobes were studied with specific attention paid to their damage and fracture behavior. Because of the biochemical composition of fonio straw (presence of quasi-crystalline cellulose and hemicelluloses, which are hydrophilic compounds), its association with the clay matrix increased water absorption and was accompanied by a significant porosity due to the air trapped during mixing. The insulating character of the cellulose and the low density resulting from the high porosity contributed to an appreciable reduction of the thermal conductivity of these adobes. The use of small amounts of fonio straw improved the mechanical properties of the adobes and made them less brittle. This improvement was linked to the good adhesion between fonio straw and the clay matrix, greatly reduced propagation of fissures in the composites and the high tensile strength of fonio straw because of its cellulose content. Thus, fonio-straw-reinforced adobes have interesting properties for use as cheap construction materials in the Sahelian zones and could contribute significantly to the thermal comfort of the inhabitants in this hot climate.

International audience; 12 Expanding the use of low-environmental impact materials in the field of building materials is a 13 major aim in a context of sustainable development. These alternative materials should be 14 non-polluting, eventually recycled, and locally available. Bioresources are already used in 15 some building materials but few studies have investigated their relevance in such 16 applications. The aim of this paper is to evaluate the suitability of three kinds of vegetal 17 aggregates: barley straw, hemp shiv and corn cob. The availability of these bioresources, 18 extracted from a French database, is discussed, as are their physical properties and 19 chemical compositions. Their microstructure is described with SEM images and their particle 20 size distributions are provided through image analysis. Sorption-desorption isotherms are 21 measured by a Dynamic Vapour Sorption system. Bulk density, thermal conductivity and 22 water absorption are also quantified. The results highlight a tubular structure for the three 23 different aggregates, with low bulk density and thermal conductivity (0.044, 0.051 and 0.096 24 W.m-1 .K-1 respectively for straw, hemp shiv and corn cob) and high water absorption, 25 especially for barley straw and hemp shiv (414 and 380% vs. 123% for corn cob). Their 26 hygric regulation capacity is also sufficiently good, with a water sorption of between 20 and 27 26% at 95% of relative humidity. These plant aggregates could therefore be used as 28 additions in an earth matrix, or a hydraulic, pozzolanic, air lime or gypsum binder, or just as 29 loose-fill insulation material. However, future research should focus on their resistance to fire 30 and bacterial growth to validate this approach. 31 32

WOS:000379589500010; International audience; In developing countries, most of the population cannot afford conventional building blocks made with the sand-cement mixture. In addition, these blocks do not provide thermal comfort and have a high embodied energy compared to vernacular materials. The main objective of this work was to produce low cost, resistant and durable (good resistance to water) blocks with a thermal behaviour enabling quality comfort indoor. For that purpose, the effects of cow-dung on microstructural changes in earth blocks (adobes) are investigated by means of X-ray diffraction, thermal gravimetric analyses, scanning electronic microscopy coupled with energy dispersive spectrometry, and video microscopy. The effects of these changes on the physical properties (water absorption and linear shrinkage) and mechanical properties (flexural and compressive strengths) of adobe blocks are evaluated. It is shown that cow-dung reacts with kaolinite and fine quartz to produce insoluble silicate amine, which glues the isolated soil particles together. Moreover, the significant presence of fibres in cow-dung prevents the propagation of cracks in the adobes and thus reinforces the material. The above phenomena make the adobe microstructure homogeneous with an apparent reduction of the porosity. The major effect of cow-dung additions is a significant improvement in the water resistance of adobe, which leads to the conclusion that adobes stabilized by cow-dung are suitable as building materials in wet climates.

WOS:000418212400009; International audience; The main objectives of this work were to manufacture adobes with good mechanical properties, even in a wet environment, and low thermal conductivity so as to give the population homes that provided better thermal comfort than cement-based constructions. For this purpose, clayey raw material from Burkina Faso, mainly composed of quartz (49 wt%), kaolinite (28 wt%), goethite (7 wt%) and muscovite (9 wt%) was mixed with up to 12 wt% of cement to manufacture adobes. Various characterization techniques were implemented to assess the microstructure of these materials: X-ray diffraction, infrared spectrometry, differential scanning calorimetry, scanning electron microscopy and energy dispersive spectrometry. Their physical properties were also investigated (through water absorption, spray test, apparent density, porosity and thermal conductivity) as their mechanical characteristics (compressive and flexural strengths). It was found that the addition of cement resulted in the formation of calcium silicate hydrate (CSH) (I), ettringite and calcite. The CSH was formed partly through the hydration of anhydrous cement compounds (alite and belite) and also through pozzolanic reactions strongly involving finely crushed quartz and, to a lesser extent, kaolinite. These cement-stabilized adobes were particularly distinguished by good mechanical resistance even in a wet environment, and low thermal conductivity. These results indicate that adobes stabilized with 2 wt% of cement are suitable for use as building materials for mass housing. (C) 2017 Elsevier Ltd. All rights reserved.

International audience; The effect of molds present in buildings on the health of the occupants is a major issue hence, when a building material is developed, its sensitivity to microbial growth should be assessed. However, few studies have investigated fungal growth on bio-based building materials with the resources available in a laboratory specializing in materials. The objective of this paper is thus to propose a simple and efficient experimental method useful for construction materials laboratories, adapted from methods proposed in the literature. For this purpose, fungal growth was investigated under different environmental conditions on earth-based material with or without the addition of straw or hemp shiv. Samples were inoculated with a strain of Aspergillus brasiliensis and were incubated for 12 weeks at 76, 84 or 93% RH, and 30 °C or 20 °C. Reproducible results showed that earth-based materials were more sensitive to fungi when they were enriched in plant aggregates. Fungal development was observed on earth material containing plant aggregates after 4 weeks of exposure at 93% RH and 30 °C, whereas it was observed after 8 weeks on raw earth material under the same conditions. Additionally, the possibility of quantifying fungal development with increased sensitivity by using image analysis is proposed. Due to the growth of fungal species other than A. brasiliensis, a natural inoculation approach is recommended. One of the conclusions is that liquid water is more favorable to mold growth than relative humidity alone. The addition of liquid water is thus recommended to accelerate the test.

WOS:000416767900015; International audience; A building material is mainly characterized by its mechanical performance, which provides proof of its quality. However, the measurement of the compressive or flexural strength of an earth-based material with plant aggregates, which is very ductile, is not fully standardized. The objective of this study is to determine the compressive and flexural strengths of a composite made of earth and 0, 3, or 6% of barley straw, hemp shiv, or corn cob. Given the manufacturing processes available, cylindrical compressed specimens were studied in compression, whereas extruded specimens were studied in flexion. Two protocols were tested for compressive strength measurements: one with direct contact between the specimen and the press and the other with reduced friction. The test with reduced friction engendered a huge decrease of the stress and a slight decrease of the strain. For both compressive and flexural strengths, the specimens made of earth alone were the most resistant, followed by composites containing straw. The influence of two different treatments applied to the straw is also discussed. (C) 2017 American Society of Civil Engineers.

International audience; 9 For Heat, Air and Moisture modelling, one of the most crucial hygrothermal properties of porous 10 construction materials is the sorption isotherm. Current techniques for measuring the sorption 11 isotherm rely on the standardized Saturated Salt Solution (SSS) method which is known to be time 12 consuming. Recently, a device called Dynamic Vapor Sorption was applied on building materials 13 allowing faster measurements but limiting the mass and volume of the sample. As this technique is 14 not yet standardized, an experimental procedure was developed and validated on barley straw. 15 Results were also in good agreement with the measurements from the SSS technique. 16 17

International audience; A new organic-inorganic hybrid material, 1-amonioethylpiperazine-1, 4-diium tetrachloridozincate(II) chloride, (C6H18N3)[ZnCl4]Cl, has been synthesized and characterized by various physicochemical techniques including UV-visible absorption, Infra-Red (IR), Raman and NMR spectroscopies. The compound crystallizes in the monoclinic system and P21 space group with Z = 2 and the following unit cell dimensions: a = 7.1728 (6), b = 12.4160 (11), c = 8.0278 (7) Å, β = 97.513 (1)°, V = 708.80 (11) Å 3. In this structure, the Zn 2+ ion, surrounded by four chlorides, adopts a distorted tetrahedral coordination geometry. The structure of this compound consists of monomeric 1-amonioethylpiperazine-1, 4-diium trications and monomeric [ZnCl4] 2-and Cl-anions. These entities are interconnected by means of hydrogen bonding contacts [N-H…Cl, C-H…Cl], forming a three-dimensional network. Intermolecular interactions were investigated by Hirshfeld surfaces. More than three quarters of the interaction surface in the crystal packing is constituted by attractive and favored H...Cl hydrogen bonds. The 13C and 15N CP–MAS NMR spectra are discussed and the vibrational absorption bands were identified by infrared and Raman spectroscopy

International audience; The electro-assisted self-assembly (EASA) of tetraethoxysilane (TEOS) and cetyltrimethylammonium bromide (CTABr) in hydro-alcoholic medium is now recognized to be a versatile method to generate highly ordered mesoporous silica films with unique orientation of mesopore channels normal to the underlying surface. In this work, we have evaluated the possibility to extend the method to aqueous media (i.e., without adding a cosolvent) and to determine the parameters affecting the EASA process and the resulting organization/orientation of the mesoporous framework by using electron microscopies and diffraction techniques. Contrary to water/cosolvent-based sols, the nature of the surfactant and supporting electrolyte counteranions (X-) was found to induce drastic variations on both the morphology and the mesostructural order of the deposits formed by electrochemically induced gelification (by pH increase) of CTAX/NaX-based silica sols. These changes are triggered by different surfactant assemblies arising from lower critical micellar concentration when passing from hydro-alcoholic to aqueous medium, and they are affected by the chaotropic-cosmotropic character of the counteranions. To be brief, cosmotropic anions (such as SO42-) promote the formation of thin films but suffering from poor or no ordering, whereas weakly bonded anions (such as Cl-) favor the mesostructuration but mainly in the form of particles or aggregates, while chaotropic anions (such as Br-) lead to rather thick deposits made of poorly organized aggregates. Mixing these anions, to get mixed micelles, enables compromises to be reached between these ``extreme'' behaviors and mesostructured thin films can be indeed obtained with the CTACl/Na2SO4 and CTABr/Na2SO4 media, exhibiting, respectively, some vertical or horizontal orientation of mesopore channels. This can be rationalized by taking into account the CTA(+), X- binding strength variations (Cl- < SO42- < Br-), thus affecting competitive binding of negatively charged silicate species, and sphere-to-rod transition abilities (SO42- approximate to Cl- < Br-) of the CTA(+)-based templates. Cyclic voltammetry was also used to characterize mass transport processes through the films. Finally, a preliminary work aiming at getting swelled pores of such electrogenerated films with mesitylene was carried out to evaluate the potential interest of the water-based EASA process for the entrapment of hydrophobic molecules inside the surfactant-silica phases.

The work presented in this paper studies the leaching of heat-cured mortars affected by delayed ettringite formation (DEF). For this, the expansion and the leaching of various elements (OH−, Ca2+, Na+ and K+) were monitored for more than 5 years in three mortars: a reference mortar and two compositions in which 3·11% of Na2SO4 (sodium sulfate) and 1·75% of NaOH (sodium hydroxide) were added to the mixture. The four mortars expanded but with different kinetics. pH, conductivity and leaching of calcium had the same global variation: a fast decrease during the first few days of curing, a strong increase after the beginning of the expansions and, lastly, a plateau of several months followed, or not (depending on the mixtures and the progress of the reaction), by a strong decrease in leaching. Finally, the results suggest that the reasons for DEF are not only related to the leaching of alkalis.

International audience; Multilayered and vertically-oriented mesoporous silica films are prepared by multiple electrochemically assisted self-assembly (EASA). This is achieved by consecutive potentiostatic EASA steps, implying the application of a negative potential to an electrode immersed in a sol solution containing silica precursors and surfactant molecules, disrupted by open-circuit periods targeted to rinsing of the electrode to avoid the precipitation of silica aggregates. The generated hydroxyl ions in each step catalyze the polycondensation of precursors around the surfactant template and film growth onto the electrode surface. Multilayered films with thicknesses of up to 400 nm are obtained, exhibiting a well-ordered hexagonal mesostructured normal to the underlying electrode support. Mass transport through the films and especially between each layer is demonstrated by cyclic voltammetry using a redox probe in solution. In addition, such multilayered films functionalized with ferrocene groups covalently attached to the internal mesopore walls exhibit long-range electron transfer by electron hopping. The charge transfer processes can be modulated by elaborating sandwich silica-ferrocene/silica-alone/silica-ferrocene multilayers in which insulating silica-alone acts as a barrier to electron hopping.

International audience; Earth as a building material is increasingly being studied for its low environmental impact and its availability. Plant aggregates and fibers have been incorporated into the earth matrix in the aim of enhancing performance for thousands of years but scientific studies began quite recently. The present paper reviews the state of the art of research on the influence of these various natural and renewable resources in unfired earth materials such as compressed earth blocks, plasters, and extruded and stabilized blocks. This review, based on 50 major studies, includes characterization of the particles and treatments, and recapitulative tables of the material compositions, and the physical, mechanical, hygrothermal and durability performances of earth-based materials. A lack of references on hygroscopic and durability properties was observed. Future research orientations are thus suggested to promote and develop this type of sustainable material, which provides a solution for saving energy and natural resources. Highlights  Earth-based products with plant aggregates as a sustainable material are reviewed.  Physicochemical and mechanical properties of plant aggregates or fibers are reviewed.  Mechanical, hygrothermal and durability performances of the composites are reviewed.  Further investigations are needed to promote these materials.

WOS:000374328800006; International audience; There is an increasing demand for earth construction in the world today but there is no consensus on the procedure to be used to measure the compressive strength of earth bricks. The study presented in this paper aims to propose a test procedure specific to earth bricks that would give the most realistic value of compressive strength while remaining as simple as possible. This study focused on four different bricks and consisted of measuring the compressive strength of these specimens by varying several parameters: specimen size, orientation, use of Teflon capping or not, and tests on dry sawn specimens, on half-bricks or on entire bricks. The results of the study show that the best compromise to achieve a simple and representative compressive strength test for earth bricks is to transform the bricks as little as possible before the test and thus to test entire bricks.

WOS:000209197400009; International audience; This paper deals with the valorization of wastepaper sludge ash (WSA) as the main component of Hydraulic Road Binder (HRB). The physical, chemical and mineralogical characteristics of this WSA were studied and this characterization was completed by a study of the reactivity of WSA in presence of lime and gypsum. This study led to the optimization of HRB rich in WSA whose characteristics were tested on mortars and on samples of treated soil. The characterization of WSA and the study of its reactivity showed that WSA had hydraulic properties because of the presence of hydraulic minerals: lime (CaO), mayenite (Ca12Al14O33) and alpha'-Ca2SiO4. The compressive strength of WSA-containing mortars was strongly penalized by the high water demand of the ash but this was not the case for the samples of treated soils. The results obtained on clayey soil treated by a binder optimized by the addition of 20 wt% of gypsum were better than those obtained with conventional commercial binders: their behavior was comparable in the long term but the optimized binder was more efficient in the short term. All the results obtained in this study permit us to conclude that WSA is suitable for use as the main component of HRB. This study is a good example of waste valorization: firstly, the calorific value of sludge produced by the paper recycling industry is recovered at the industrial plant and, secondly, the ash formed during this incineration process is reused as the main component of HRB with interesting added value.

This paper deals with the physical, chemical and mineralogical characterization of WSA in order to evaluate the interest of its potential reuse as a component in hydraulic binders. The results show that WSA contains hydraulic minerals such as lime (CaO), mayenite (Ca12Al14O33) and α′-Ca2SiO4 in addition to gehlenite, the main mineral. WSA can also be considered as a hydraulic mineral admixture, which is very encouraging for the potential reuse of this material in hydraulic binders. However, WSA has some characteristics that could be worrying for its reuse. Firstly, SEM observations show that its particles are very porous, and that could lead to problems of workability of cement-based materials containing WSA. Secondly, the presence of both lime and metallic aluminium could be responsible for swelling when WSA is introduced into cement-based materials. No swelling was observed visually during the hydration of WSA-containing paste in this study but this first qualitative test is not sufficient and further investigations of this specific characteristic will be necessary. Finally, the presence of lime in the WSA could be considered as a problem for its use in binder for construction (risk of expansion) but, from another point of view, it would be very interesting for applications in road works, especially for the stabilization of soil, in which lime is regularly employed because it has useful properties (drying and reinforcement of the mechanical strength of the soils).

This paper deals with the use of a weathered basic oxygen furnace (BOF) slag as a main constituent in hydraulic road binder. The original idea of this study was to associate the BOF slag with ground granulated blast furnace slag (GGBFS). The free lime contained in BOF slag activated the GGBFS. Small amounts of catalyst were added to the mixtures in order to accelerate the setting of this ternary blended binder. Before studying the characteristics and the influence of the proportion of each constituent, the chemical, mineralogical and physical characteristics of BOF slag were analyzed. X-ray diffraction showed that the main minerals present were calcium silicates (βC 2 S and C 3 S), dicalcium ferrite (C 2 F), lime (CaO), a solid solution of magnesium iron oxide (MgO x FeO y ), an alumino ferrite calcium phase (C 4 AF) and, due to the weathering, calcite (CaCO 3 ) and portlandite (Ca(OH) 2 ). The activity of BOF slag in cement-based mortars was evaluated and the results show that BOF slag has little hydraulic activity and apparently no pozzolanic properties. These results were confirmed by XRD on hydrated BOF slag. Only CaO, C 3 S and C 4 AF react with water and, as the C 3 S and C 4 AF contents were relatively low, the hydraulicity of the BOF slag under study was low. However, BOF slag contains 7% of Ca(OH) 2 and, in spite of the weathering, still 5% of CaO. The production of a ternary blended binder containing a mixture of BOF slag, GGBFS and catalyst was a success. The optimization of the binder composition showed that it was possible to produce an HRB10 (the compressive strength of standardized mortars higher than 10 MPa at 56 days) by mixing 52.5% of GGBFS, 42.5% of BOF slag and 5% of catalyst. Moreover, the stability study showed that there was no problem of expansion with such a binder.

The development of innovative materials has to respond to both environmental and energy concerns. Bio-based materials are relevant because they are made from renewable raw materials and are carbon neutral. Similarly, unprocessed earth has a very low embodied energy. In this paper, the basic hygrothermal properties of straw-clay samples provided by two French companies were determined. Mixes with densities lower than 450 kg m−3 would be suitable for use as self-insulating material in current construction. In addition, the material showed a high sorption capacity and very high water vapour permeability. The measurements were then implemented in a numerical model in order to simulate the hygric response of a small room. The straw-clay mixture was found to have a moisture buffering effect of the same magnitude as walls made of hemp concrete and largely higher than conventional walls. The influence of various indoor finishing materials was investigated through additional simulations.

WOS:000369190800006; International audience; The use of bio-based materials in the construction field is of great interest to society and the scientific community because of its highly sustainable character. They are formed by plant fibres and a binder, usually cement, lime or pozzolanic additives. Among the new vegetable fibres used, hemp-based biomaterials have attracted great attention in the recent years due to its excellent thermal and hygroscopic properties. However, they present a very low mechanical performance, which has intensified the search for better alternatives. In this research, the use of magnesium phosphate cement (MPC) as binder with different hemp additions (8%, 12%, 16% and 20% by weight) was evaluated. Thus, a new material made of hemp and MPC (heMPC) was developed. According to the results obtained, the heMPC could be used in floor or pre-cast structural applications since it presented enhanced mechanical (sigma(max) = 0.714 +/- 0.11 MPa with a 20 wt.% of hemp content) and thermal (lambda(D) = 0.103 W . m(-1) . K-1, density = 600 kg . m(-3)) properties with respect other lime-based hemp biomaterials. Furthermore, the material exhibited good hygroscopic properties (water absorption by capillarity). Accordingly, this preliminary study allowed opening a new research line in the use of hemp bio-composites, in which other important properties are currently under investigation. The MPC used as a binder in this study was formulated with a by-product from the MgO industry, which increases the sustainability and recyclability criteria of the material developed. (C) 2015 Elsevier Ltd. All rights reserved.

WOS:000366652100032; International audience; Earthen plastering mortars are becoming recognized as highly eco-efficient. The assessment of their technical properties needs to be standardized, but only a German standard exists for the moment. An extended experimental campaign was developed in order to assess multiple properties of a ready-mixed earth plastering mortar and also to increase scientific knowledge of the influence of test procedures on those properties. The experimental campaign showed that some aspects related to the equipment, type of samples, and sample preparation can be very important; although others seemed to have less influence on the results and the classification of mortars. It also showed that some complementary tests can easily be performed and considered together with the standardized ones, whereas others may need to be improved. The plaster satisfied the requirements of the existing German standard but, most importantly, it seemed adequate for application as rehabilitation plaster on historic and modern masonry buildings. Apart from their aesthetic aspect, the contribution of earthen plasters to eco-efficiency and, particularly, to hygrometric indoor comfort should be highlighted. (C) 2015 American Society of Civil Engineers.

Physicochemical characteristics of Hibiscus cannabinus (kenaf) fibers from Burkina Faso were studied using X-ray diffraction (XRD), infrared spectroscopy, thermal gravimetric analysis (TGA), chemical analysis and video microscopy. Kenaf fibers (3 cm long) were used to reinforce earth blocks, and the mechanical properties of reinforced blocks, with fiber contents ranging from 0.2 to 0.8 wt%, were investigated. The fibers were mainly composed of cellulose type I (70.4 wt%), hemicelluloses (18.9 wt%) and lignin (3 wt%) and were characterized by high tensile strength (1 ± 0.25 GPa) and Young’s modulus (136 ± 25 GPa), linked to their high cellulose content. The incorporation of short fibers of kenaf reduced the propagation of cracks in the blocks, through the good adherence of fibers to the clay matrix, and therefore improved their mechanical properties. Fiber incorporation was particularly beneficial for the bending strength of earth blocks because it reinforces these blocks after the failure of soil matrix observed for unreinforced blocks. Blocks reinforced with such fibers had a ductile tensile behavior that made them better building materials for masonry structures than unreinforced blocks.

This paper intends to present applications of experimental charge density research in physics, chemistry and biology. It describes briefly most methods for modelling the charge density and calculating and analyzing derived properties (electrostatic potential, topological properties). These methods are illustrated through examples ranging from material science and coordination chemistry to biocrystallography, like the estimation of electrostatic energy in a zeolite-like material or the relation between electrostatic energy and spin density to macroscopic magnetic properties in a ferrimagnetic molecular material. The accurate structure and charge density of a coordination compound exhibiting LIESST effect is also described, together with an exemple of transferability of charge density methods to macromolecular science and protein crystallography.

This article focuses on the effects of metallic aluminum contained in municipal solid waste incineration (MSWI) fly ashes on cement-based materials in which they are added. The ash under study was treated by an industrial physicochemical process of neutralization. The paper also presents a method to quantify the metallic aluminum content of ash: it consists in measuring the amount of hydrogen gas produced by the oxidation reaction of metallic aluminum. This method is simple and fast. Results show that studied ash contains an appreciable amount of metallic aluminum. Investigations were carried out to study the incorporation of the ash in concrete: in this case, the presence of metallic aluminum is worrying because it could be responsible for disorders in concrete. In fact, swellings are observed on cement pastes and mortars containing ash during the first 24 h of hydration. A test based on hydrostatic weighing permits to quantify the swelling of fresh cement paste and to study the evolution of this swelling. Causes of swelling are analyzed. Results show that ettringite formation occurs after the end of the expansion reaction. So it can be concluded that metallic aluminum is the sole responsible for the observed swelling. Consequences of swelling are also analyzed by measuring compressive strength of ash-containing mortars: this swelling leads to cracks in the mortars and significant decrease of their compressive strength.

WOS:000372185700008; International audience; The impacts of buildings on the environment and on the health of the inhabitants are priority issues nowadays. For many environmental, social and economic reasons, the demand for building products made of materials such as earth and bio-based materials is increasing. Under certain conditions, mold growth can be observed on the surface of such materials, which raises many questions about their use in buildings. In the framework of the "BIOTERRA" ANR project, the aim of the study was to develop and characterize an earth based material incorporating plant fibers from both abiotic and biotic points of view. Compressive strength, thermal conductivity and water vapor permeability of this material were determined. Microorganism sampling methods intended for raw materials and cylindrical specimens were optimized, and the microflora profile of these materials was then obtained. The results showed that the straw addition led to a decrease of compressive strength and an increase of thermal insulation. However, it did not influence water vapor permeability coefficient. Raw materials and manufactured specimens contained mainly Bacillus sp., Aspergillus sp. and Penicillium sp. Other compositions of this bio-based material will be characterized. Sampling methods developing here can also be used to identify the microflora of existing earthen buildings.

Carbonation was applied to a Pb- and Zn-contaminated fraction of municipal solid waste incineration electrofilter fly ashes in order to reduce heavy metal leaching. Carbonation tests were performed in solution, by Na2CO3 addition or CO2 bubbling, and were compared with washing (with water only). The injection of CO2 during the washing did not modify the mineralogy, but the addition of Na2CO3 induced the reaction with anhydrite, forming calcite. Microprobe analyses showed that Pb and Zn contamination was rather diffuse and that the various treatments had no effect on Pb and Zn speciation in the residues. The leaching tests indicated that carbonation using Na2CO3 was successful because it gave a residue that could be considered as non-hazardous material. With CO2 bubbling, Pb and Zn leaching was strongly decreased compared with material washed with water alone, but the amount of chromium extracted became higher than the non-hazardous waste limits for landfilling.

WOS:000331424400009; International audience; There is an intense on-going search for less polluting materials and technologies, which consume little energy in their production, construction and/or utilization. Attention of the researchers has turned to materials, which found applications in engineering in pre-industrial times: local vegetable fibers and earth composites are one of the promising materials. This paper presents the results of an investigation in establishing the physical and mechanical properties of Hibiscus cannabinus fibers which have been used in the fabrication of Pressed Adobe Blocks (PABs). The PABs have been reinforced with 0.2-0.8 wt.% of 30 mm and 60 mm lengths of H. cannabinus fibers. The microstructural characteristics of the PABs composites were investigated using X-ray diffraction (XRD), thermal gravimetric analyses (TGA), scanning electronic microscopy (SEM) and video microscopy. It was established that the addition with 0.2-0.6 wt.% of 30 mm long fibers reduced the dimensions of the pores in the PABs with the improvement of their mechanical properties. However, the addition of 0.8 wt.% of 60 mm fibers had negative effects on the compressive strength. The elaborated Pressed Adobe Blocks specimens were suitable as building material with contribution for thermal comfort. (C) 2013 Elsevier Ltd. All rights reserved.

International audience; Internal Sulfate Attack (ISA) is a pathology that occurs under certain conditions in concrete having undergone heating above 70 °C at early age (through heating in pre-casting industry or due to hydration in large concrete parts). This reaction deemed very slow, numerous methods to speed up reactions leading to delayed ettringite formation have been developed. These methods are all based on the material damage. Another type of test is currently under development. It is based on rehabilitation techniques such as electrochemical chloride extraction (ECE) in order to accelerate the leaching of alkalis that could be one of the triggers of the pathology. The study presented in this paper focused on concrete specimens prepared from cement (CEM I 52.5 N) enriched with Na2SO4. These concretes have undergone a heat treatment typical of those used in precast plants (up to 24 hours with a maximum temperature of 80 °C). Various paths were explored for the development of the accelerated test. The first results showed that it was necessary to use a removable titanium anode ruthenium anode instead of stainless steel embedded in the concrete. Then tests with de-ionized water as the solute to the cathode did not accelerate the onset of expansions. The experiment has been modified and potassium carbonate was added to the solution. This modification didn't show any significant improvement, and other experiments are being carried out to explain this result.

International audience; One key challenge in inorganic mesoporous films is the development of oriented mesostructures with vertical channels, and even more challenging is their functionalization while maintaining accessible the selected surface groups. Combining the electrochemically assisted deposition of ordered and oriented azide-functionalized mesoporous silica with alkyne-azide click chemistry enables such nanostructured and vertically aligned hybrid films to be obtained with significant amounts of active organic functional groups, as illustrated for ferrocene and pyridine functions. A good level of mesostructural order was obtained, namely up to 40% of organosilane in the starting sol. The method could be applied to a wide variety of functional groups, thus offering numerous new opportunities for applications in various fields.

International audience; This paper presents the results of a compressive strength test carried out on an extruded earth block of dimensions 40.7x13.6x4.8 [cm 3 ]. The failure of the block was not detected by the press used, which reached its highest load (2500 kN). This would correspond to a compressive strength of the block greater than 45 MPa! This value is obviously an aberration and the discussion developed in the paper, based on results from the literature, aims to explain this result and propose solutions for measuring the compressive strength of such products. Highlights (3 to 5 bullet points (maximum 85 characters, including spaces, per bullet point) The compressive strength measured for an earth block was higher than 45 MPa. The direct measurement of the compressive strength on adobe plates is aberrant. Compressive strength tests on adobe plates are comparable to oedometric tests. A 3 point bending test could be a solution for measuring the UCS of adobe plates.

In the crystal structure of the title organic–inorganic hybrid material, (C10H22N2)[ZnCl4], the tetrachloridozincate anions and 1-cyclohexylpiperazine-1,4-diium dications are interconnectedviaN—H...Cl and C—H...Cl hydrogen bonds to form layers parallel to the (001) plane. The cyclohexyl groups from adjacent chains interdigitate, thus building the three-dimensional structure. The piperazinium and cyclohexyl rings exhibit regular spatial chair conformations. The title salt was also characterized by FT–IR and Raman spectroscopic analyses.

WOS:000316304800023; International audience; This paper deals with the utilization of a natural pozzolan as the main component of Hydraulic Road Binder (HRB). A study of its reactivity in presence of lime and gypsum leads to a proposal for an optimized binder composed of 80 wt% pozzolan, 15 wt% lime and 5 wt% gypsum. The characteristics of this binder were tested on mortars and on samples of treated soil and the results lead to the conclusion that it is possible to produce an HRB rich in pozzolan and without cement that can efficiently stabilize clayey soils. (C) 2012 Elsevier Ltd. All rights reserved.

International audience; Delayed Ettringite Formation (DEF) is an internal sulfate attack caused by early age heating to a temperature of over 70 degrees C. In this paper, the effect of natural Algerian pozzolan on the expansion of cement mortars caused by DEF was investigated. For this purpose, a portion of cement was replaced by natural pozzolan, with three different dosages (10%, 20% and 30%) and finenesses (fine, medium, and coarse). The results obtained highlighted the significant effects of natural pozzolan on DEF and the correlation existing between the expansion of the heat-cured mortars and the evolution of their mechanical properties.

International audience; The work presented in this article studies the effects of some parameters that can be considered, a priori, as important in the appearance of delayed ettringite formation (DEF). The parameters studied are the nature of the binder, the water/cement (W/C) ratio, the preliminary microcracking (wettingdrying cycles) and the curing conditions. The results presented show that the chemical composition of cement is one of the main parameters controlling the appearance of DEF. The other parameters studied, (W/C ratio, wettingdrying cycles and temperature of curing water) principally modify the kinetics of the expansion: it seems that, the more favourable the conditions are to ionic and hydrous transfers, the sooner the expansion starts. Finally, the renewal of the curing water strongly affects the start of DEF. In one case of the study, the renewal of the curing water only accelerated the start of the expansion. In the second, it led to late starting of DEF (fouryears) whereas the same mixture cured continuously in water that was not renewed still had not expanded after more than fiveyears.; L’étude présentée dans cet article a pour objectif d’observer les effets de certains paramètres que l’on peut qualifier a priori d’importants vis-à-vis de l’apparition de la DEF. Les paramètres étudiés sont la nature du liant, le rapport E/C des mélanges, le préendommagement des éprouvettes (cycles d’humidification-séchage) et, enfin, les conditions de conservation des échantillons. Les résultats présentés montrent que la composition chimique du ciment est l’un des principaux paramètres contrôlant l’apparition de la DEF. Les autres paramètres étudiés (rapport E/C, cycles d’humidi-fication-séchage et la température de l’eau de conservation des échantillons), modif-ient principalement la cinétique de l’expansion: il semble que plus les conditions sont favorables pour améliorer les transferts ioniques et hydriques, plus l’apparition des expansions est accélérée. Enfin, le renouvellement de l’eau de conservation affecte fortement le début de l’apparition de la DEF. Dans un cas d’étude, il n’a fait qu’accélérer le début de l’expansion. Dans un second cas, le renouvellement de l’eau de conservation a permis le déclenchement de la DEF au bout de 4 ans, alors que le même mélange conservé en permanence dans l’eau qui n’a pas été renouvelé n’avait pas encore montré de gonflement après plus de 5 ans.

Considering the lack of references dealing with the behaviour of clayey soil blocks subjected to freezing–thawing cycles, exploratory work has been carried out on such blocks to study the effects of freezing–thawing cycles on their mechanical properties. As the blocks were not stabilized, the procedures conventionally applied for freezing–thawing cycles, in which the samples are immersed, were adapted to this case of study: the specimens were humidified by placing them in a moist environment for 1 week (20 °C and 95% RH (relative humidity)) and were then subjected to freezing–thawing cycles without any re-humidification between cycles. The variations of weight and compressive wave velocity showed that freezing–thawing cycles led to the desiccation of the samples. The consequences of these cycles on the characteristics of the soil blocks were thus those of a conventional desiccation of specimens and, in particular, their hardening. This hardening was highlighted by the study of the mechanical characteristics of the clayey soil blocks (compressive strength and modulus).

This paper presents an original method developed to quantify the reactivity of mineral additions based on the measurement of the lime (CaO) and gypsum (CaSO4, 2H2O) consumed by mineral additions in a paste. Three mineral additions were tested: a Siliceous Filler (SF), a natural pozzolan (Poz) and a Wastepaper Sludge Ash (WSA). The results obtained on SF, considered as a reference, show the efficiency of this method. Its application to Poz and WSA permits the quantity of lime and gypsum consumed by these additions to be evaluated and, thus, the amount of each component to be optimized in Hydraulic Road Binders.

The objective of the work presented in this paper is the quantitative determination of the mineral composition of two complex mineral wastes: a sewage sludge ash (SSA) and a municipal solid waste incineration fly ash (MSWIFA). The mineral compositions were determined by two different methods: the first based on calculation using the qualitative mineralogical composition of the waste combined with physicochemical analyses; the second the Rietveld method, which uses only X-ray diffraction patterns. The results obtained are coherent, showing that it is possible to quantify the mineral compositions of complex mineral waste with such methods. The apparent simplicity of the Rietveld method (due principally to the availability of software packages implementing the method) facilitates its use. However, care should be taken since the crystal structure analysis based on powder diffraction data needs experience and a thorough understanding of crystallography. So the use of another, complementary, method such as the first one used in this study, may sometimes be needed to confirm the results.

International audience; In this work, we describe a versatile approach to generate highly methylated mesoporous silica films exhibiting hexagonally-packed one-dimensional mesochannels oriented uniquely perpendicular to the underlying support. It involves the electro-assisted self-assembly (EASA) of tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) with cetyltrimethylammonium bromide (CTAB) under potential control. Transmission electron microscopy and grazing-incidence X-ray diffraction indicate that high level of ordering and vertical alignment of mesopores can be maintained at rather high MTES contents (up to 50–60 mol% with respect to total precursors in the starting sol). The rate of film growth decreased concomitantly to increasing the MTES/TEOS ratio, resulting in thinner films for higher functionalization degrees. This also led to more hydrophobic films (after template extraction), which tended to become less permeable to aqueous phase solutes, as pointed out qualitatively and quantitatively by several electrochemical methods and various redox probes. Effective rate constants for electron transfer were found to be several orders of magnitude higher than for other thin silica films on electrodes, explained by preferential porosity orientation.

International audience; This article, which deals with the effect of wetting–drying (W-D) cycles on materials affected by delayed ettringite formation (DEF), has two main objectives. The first is to observe whether W-D cycles pre-damage samples, by using the replica technique. Scanning electron microscopy (SEM) observations of replicas show that W-D cycles lead to microcracks in the samples. The second objective of the study is to observe whether the cycles are necessary for development of DEF or if they only accelerate DEF. A study of the expansion of the samples shows that cycles accelerate the appearance of expansion but they are not a prerequisite for triggering DEF.; Cet article, qui porte sur l’effet des cycles d’humidification-séchage des matériaux atteints de DEF, a deux objectifs principaux. Le premier objectif est d’observer par l’utilisation de la technique de la réplique, si les cycles d’humidification-séchage pré-endommageaient les échantillons. Les résultats obtenus par le suivi des répliques ont permis de conclure que les cycles pré-endommagent les éprouvettes. Le second objectif de cette étude, est d’observer si les cycles sont nécessaires au développement de la DEF ou s’ils ne font qu’accélérer la DEF. Le suivi des expansions a montré que les cycles permettent d’accélérer l’apparition des expansions, mais qu’ils ne sont pas un préalable nécessaire pour le déclenchement de la DEF.

International audience; Highly ordered and vertically oriented mesoporous silica films can be generated by electro-assisted self-assembly (EASA). The method involves the electrogeneration of hydroxide ions at an electrode surface immersed in an hydrolyzed sol solution (containing typically tetraethoxysilane, TEOS, and cetyltrimethylammonium bromide, CTAB) in order to catalyze polycondensation of the precursors and self-assembly of hexagonally packed one-dimensional channels that grow perpendicularly to the support. Vertically aligned mesostructures have been demonstrated by TEM imaging and by grazing incidence X-ray diffraction (GIXD), this latter technique enabling characterization of thin films directly on their underlying electrode surface. The influence of the electrosynthesis medium composition (precursor and surfactant concentrations, surfactant chain length) on the mesostructural order and film thickness has been thoroughly examined. It was shown that the highly ordered and oriented mesoporous silica films can be obtained over a wide composition of the starting sol (i.e., 10−200 mM CTAB and 50−350 mM TEOS) and that the lattice parameter can be moderately tuned by changing the chain length of the surfactant template. Thickness of these films can be accurately controlled by applying galvanostatic conditions and by varying the deposition time, which offer the versatility to be applied in the same way to electrodes of different nature without overpotential problems encountered in the potentiostatic mode. Thin mesoporous films are often covered with an additional byproduct made of particulate aggregates arising from bulk gelification at the electrode/solution interface. Getting aggregate-free thin films is possible by working in diluted solutions (i.e., [TEOS] < 125 mM and CTAB/TEOS ratio

International audience; This paper aims to open a discussion on the relevance of the laboratory studies on heat-induced internal sulphate attack. The results presented here show that specimens of mortars conserved in frequently renewed deionised water expand after 3 years and a half. The same specimens conserved in water that is not renewed still do not expand after more than 5 years of conservation. So, it seems that the appearance of the phenomenon is linked to the experimental conditions of the test. Moreover, the period before the beginning of the expansion is very long. These results raise two important questions: may the laboratory studies be used for the prediction of the field DEF behaviour and, if so, what minimal duration should formulation qualification tests have to ensure the durability of the constructions faced with this pathology?

International audience; This article, which deals with the study of the microscopic modifications of DEF-affected materials, has two main objectives. The first one is to study the influence of sample preparation on the microcracks of specimens observed in Scanning Electron Microscopy (SEM). From the results of this study, it can be concluded that direct observations of the samples are inappropriate because they produce cracks that are not ascribable to the pathology. It is therefore preferable to use an indirect technique of observation such as the replica technique. This technique was developed in the 1980s and used to study the evolution of microcracking due to mechanical damage to the concrete. The results presented in this article show that it is possible to use this technique to study the microcracking associated with delayed ettringite formation. The second objective is to study ettringite formation during the swelling of DEF-affected specimens. The main results show that secondary ettringite is initially formed in the paste–aggregate interface even at low levels of expansion. For these levels of expansion, there is no trace of secondary ettringite or microcracks observable in the paste. However, for higher expansions, cracks filled with ettringite appear in the paste.; Cet article, qui porte sur le suivi des modifications à l’échelle microscopique de matériaux atteints de DEF, a deux objectifs principaux. Le premier concerne l’étude de l’influence de la préparation des échantillons sur la microfissuration des éprouvettes observées au Microscope Electonique à Balayage (MEB). Les résultats de cette étude permettent de conclure que les observations directes des échantillons ne sont pas adaptées car elles produisent des fissures qui ne sont pas imputables à la pathologie. Ainsi, il est préférable d’utiliser une technique indirecte d’observation comme la technique de la réplique. Cette technique a été développée et utilisée il y a longtemps pour étudier l’évolution de la microfissuration provoquée par un endommagement mécanique du béton. Les résultats présentés dans ce papier montrent qu’il est possible d’utiliser cette technique pour l’étude de la microfissuration associée à la formation d’ettringite différée. Le second objectif de cette étude concerne le suivi de la formation de l’ettringite au cours du gonflement des éprouvettes. Les principaux résultats montrent que l’ettringite secondaire se forme d’abord à l’interface pâte-granulat même pour des niveaux d’expansion très faibles. Pour ces niveaux d’expansion, il n’y a pas de trace d’ettringite secondaire ou de microfissures observables dans la pâte. Par contre, pour des expansions plus importantes, des fissures pleines d’ettringite apparaissent dans la pâte.