We report on the structural transformations of Bioglass ® during thermal treatments. Just after the glassy transition, at 550 °C, a glassy phase separation occurs at 580 °C, with the appearance of one silicate-and one phosphate-rich phase. It is followed by the crystallization of the major phase Na 2 CaSi 2 O 6 , from 610 to 700 °C and of the secondary phase, silicorhenanite, at 800 °C. The latter evolves from the phosphate-rich glassy phase, which is still present after the first crystallization. In order to control the processing of glass-ceramic products from Bioglass ® , crystallization kinetics were studied via differential scanning calorimetry measurements in the range of 620-700 °C and temperature-timetransformation curves were established.

International audienceThe purpose of this study is to investigate the influence of torrefaction on wood grinding energy. Wood chips were torrefied at different temperatures and durations. The energy required to obtain fine powder was measured. Particle size analyses were carried out on each powder sample. It is showed that torrefaction decreases both grinding energy and particle size distribution. A criterion to compare grindability of natural and torrefied wood is proposed. It takes into account both grinding energy and particle size distribution. It accounts the energy required for grinding particles to sizes inferior to 200 μm, for given grinding conditions. Torrefaction is characterised by the anhydrous weight loss (AWL) of wood. For AWL inferior to around 8%, grinding energy decreases fast. Over 8%, grinding energy decreases at a slow rate. Particle size distribution decreases linearly as the AWL increases. Both for spruce and beech, the grinding criterion is decreased of 93% when the AWL is around 28%

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

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.

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This work compares the effects induced by polysaccharides on the hydration of cement. It also brings new insights into the interaction mechanisms between these two components. Several parameters such as structure, concentration, average molecular weight, and the soluble fraction value of the polysaccharides were examined. The hydration of cement was monitored by conductivity measurement, and ionic chromatography. The influence of polysaccharide structure on the kinetics of cement hydration was revealed. The extent of retardation increases when polysaccharide concentration rises. Dextrins with lower average molecular weights compared with starches favor a higher soluble fraction value and further retard hydration. The growth of hydrates seemed to be more affected by the presence of these admixtures than did the dissolution of anhydrous particles or the nucleation of former hydrates.1 Keywords : C Ionic conductivity, Cement, B Composites, C Chemical properties, Polysaccharides , Hydration. 1.IntroductionAmong the organic admixtures widely used in the formulation of mortars and concrete, polysaccharides are polymers which can be equally classified in water-reducers, set-retarders, and water retention agents.Numerous authors have demonstrated that the properties of mortar and concrete can be significantly modified at fresh state as well as at hardened state by the addition ofSeveral mechanisms were proposed to explain the interactions between cement and set-retarders (i.e. sugars or carboxylic acids) [9][10][11][12][13][14][15]. Some authors focused their studies on interaction with anhydrous surfaces. For Hansen [16], the adsorption onto anhydrous particles could occur and protect surfaces from initial attack by water. Susuki [17] proposed that the retarding action of admixtures could be linked to the precipitation of insoluble calcium salts at the surface of anhydrous particles even though a clear correlation between solubility and retarding ability of carboxylic acids was not established.Other studies pointed out that interactions between admixtures and hydrates could also exist. According to Thomas and Birchall [18], the retarding action of sugars is explained in terms of adsorption onto and poisoning of hydrates surfaces. Young [19] suggested that an incorporation of admixtures into crystal lattices could occur. For example, in the case of C 3 A hydration, he proposed that organic compounds could enter 2 the interlayer region and stabilize hexagonal hydrates like C 4 AH 13 at the expense of the cubic form C 3 AH 6 . However, in the case of C 3 S hydration, Popova [20] showed that polymer-CSH interaction was restricted to adsorption. Indeed no significant structural modification of CSH were observed by 29 Si NMR characterization.Hence a mechanism describing the influence of set retarding admixtures on cement hydration is still not well elucidated. In order to bring new insights, the present study focuses on the hydration of cement in presence of compounds widely used in mortars i.e.polysaccharides. Th...

International audienceCellulose ethers are polymers frequently introduced into mortar formulations. This study allows to assess the potential role of cellulose ethers degradation on the alteration of the cement hydration kinetics. A retardation mechanism based on the calcium binding capacity of chelates is often proposed to describe the effects of some polysaccharides (e.g. sugars) on cement hydration. The alkaline stability of cellulose ethers has been poorly studied and may represent one way to understand the hydration delay induced by such admixtures. Identification and quantification of the hydroxy carboxylic acids generated during alkaline degradation were performed. The results indicate that cellulose ethers are very stable in alkaline media. We also show that the ability of cellulose ethers to complex calcium ions is negligible. Finally, degradation of cellulose ethers and its impact on the cement hydration kinetics does not seem to be significant