This work deals with the relative efficiency of polysaccharides and their influence on cement hydration. Several parameters such as the structure, concentration, average molecular weight, and soluble fraction value of polysaccharides were examined. Cement hydration was monitored by isothermal calorimetry, thermogravimetry (TGA), and infra-red spectroscopy (FTIR). Results clearly show that retardation increases with higher polysaccharide-to-cement weight ratio (P/C). Low molecular weight starch showed enhanced retarding effect on the hydration of cement. The retardation effect of polysaccharides is also dependant on the composition of cement.

International audienceCellulose ethers (CE) are commonly used as additives to improve the quality of cement-based materials. As admixtures, they improve the properties of mortars such as water retention, workability, and open time. Also, polysaccharides such as starch derivatives are used to improve the consistency of the fresh material. The properties of cement-based mortars at fresh state were investigated. The effect of CE and their physico-chemical parameters (molecular weight, substitution degrees, etc.) on both water retention and rheological properties of mortars were studied. Moreover, some starch derivatives were also examined in order to better understand the water retention mechanisms. Rheological measurements showed that CE have a thickening effect for a content of 0.27 wt.%. Besides, a fundamental effect of CE molecular weight on mortar consistency and its water retention capability was highlighted. Finally, the comparison with starch ethers proved that, for those admixtures, water retention is not directly linked to mortar's viscosity

a b s t r a c tThanks to their refractoriness, carbides are sensed as fuel coating for the IVth generation of reactors. Among those studied, the Ti 3 SiC 2 ternary compound can be distinguished for its noteworthy mechanical properties: the nanolamellar structure imparts to this material some softness as well as better toughness than other classical carbides such as SiC or TiC. However, under irradiation, its behaviour is still unknown. In order to understand this behaviour, specimens were irradiated with heavy ions of different energies, then characterised. The choice of energies used allowed separation of the effects of nuclear interactions from those of electronic ones.

International audienceCarbide-type ceramics, which have remarkable thermomechanical properties, are sensed to manufacture the fuel cladding of Generation IV reactors that should work at high temperature. The MAX phases, and more particularly titanium silicon carbide, are distinguished from other materials by their ability to have some plasticity, even at room temperature. For this study, polycrystalline Ti3SiC2 was irradiated with ions of different energies, which allow to discriminate the effect of both electronic and nuclear interactions. After characterization by low-incidence X-ray diffraction and cross-sectional transmission electron microscopy, it appears that Ti3SiC2 is not sensitive to electronic excitations while nuclear shocks damage its structure. The results show the creation of many defects and disorder in the structure, an expansion of the hexagonal close-packed lattice along the c axis, and an increase in the microstrain yield

International audienceCellulose ethers such as hydroxyethylmethyl cellulose (HEMC) and hydroxypropylmethyl cellulose (HPMC) are common admixtures in factory made mortars. Nevertheless, their use principally remains empirical, and no cement-admixture interaction mechanism has ever been rigorously demonstrated. The main issue of this publication deals with the control of secondary effects generated by these admixtures such as the retardation of cement hydration. In this frame, a study of the impact of HEMC and HPMC molecule parameters on the modification of cement hydration was carried out. Minor influence of the molecular weight and of the hydroxypropyl or the hydroxyethyl group content was observed. On the contrary, the results emphasize that the methoxyl group content appears as the key parameter of the hydration delay mechanism

Low energy ion irradiation was used to investigate the microstructural modifications induced in Ti 3 SiC 2 by nuclear collisions. Characterization of the microstructure of the pristine sample by electron back-scatter diffraction (EBSD) shows a strong texturing of TiSi 2 , which is a common secondary phase present in Ti 3 SiC 2 . A methodology based on atomic force microscopy (AFM) was developed to measure the volume swelling induced by ion irradiation, and it was validated on irradiated silicon carbide. The swelling of Ti 3 SiC 2 was estimated to 2.2 ±0.8 % for an irradiation dose of 4.3 dpa at room temperature. Results obtained by both EBSD and AFM analyzes showed that nuclear collisions induce an anisotropic swelling in Ti 3 SiC 2 .

The aim of the present study was to investigate the rheological properties of microfibrillated cellulose/lignosulfonate hydrogels and to use them for the manufacturing of carbon objects by 3D printing and carbonization. To this purpose, both flow mode and thixotropic mode were used to characterize the hydrogel rheological behaviour which was subsequently used to search for formulation/processability correlations during 3D printing of square cuboids. At a concentration of 2%, microfibrillated cellulose (MFC) displayed excellent printability, i.e. a shear thinning behaviour with high yield stress and a viscoelastic response to a step-down shear rate variation. The addition of lignosulfonate (LS) induced a drop in the yield stress and, above a LS mass fraction of 30%, the MFC/LS hydrogel displayed an inelastic thixotropic response with a drop in printability (viz. the printed cuboids underwent a continuous deformation until hydrogel complete spreading). Above 50% of LS, the high viscosity slowed down the flow of MFC/LS hydrogels and printed cuboids had minor deformation. Freeze and air drying of cuboids printed with LS mass fraction lower than 20% and higher than 50%, respectively, allowed keeping the original shape and their carbonization under inert gas led to the production of highly conducting objects. In line with the high density of air dried samples, carbonized samples displayed an irregular structure with pores and crackles generated during drying and carbonization, whereas freeze dried samples had the typical lamellar structure of icetemplated materials.

The goal of this study was to elucidate the influence of the intrinsic properties of roughness, porosity, and surface pH on the susceptibility of mortars to biodegradation by phototrophic microorganisms. An accelerated fouling test was performed allowing a periodic sprinkling of an algae suspension on sample surfaces. The green alga Klebsormidium flaccidum was chosen due to its representativeness and facility in culturing. The biofouling of sample surfaces was evaluated by means of image analysis and color measurement. Two porosities, three roughnesses, and two surface pHs were examined. The colonization by algae of sample surfaces was not influenced by porosity because of the specific conditions of testing that led to a constant high level of moistening of mortar samples. The roughness, in contrast, played an important role in biological colonization. A rougher surface facilitates the attachment of algal cells and so favors the extension of algae. The surface pH was the most important parameter. A lower surface pH accelerated considerably the development of algae on the samples surface.