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

International audienceThe study presented in this paper is devoted to improve the knowledge on the influence of cellulose ethers (CE) on the freshly-mixed mortars water retention. Indeed, this crucial property is the most important imparted by these polysaccharides. One of the assumptions proposed to explain this phenomenon is that CE acts as diffusion barrier to the water. To test this hypothesis, the CE effect on the self-diffusion coefficient of water in solution and on the water mobility between two fresh cement pastes was studied by Nuclear Magnetic Resonance. CE does not significantly modify the water self-diffusion coefficient in CE solution or in admixed cement pastes. Moreover the interdiffusion imaging experiments demonstrated that the water diffusion at the paste/paste interface is not affected by the presence of cellulosic admixture

International audienceWe show how nuclear magnetic spin-lattice relaxation dispersion of proton-water (NMRD) can be used to elucidate the effect of cellulose ethers on water retention and hydration delay of freshly-mixed white cement pastes. NMRD is useful to determine the surface diffusion coefficient of water, the specific area and the hydration kinetics of the cement-based material. In spite of modifications of the solution's viscosity, we show that the cellulosic derivatives do not modify the surface diffusion coefficient of water. Thus, the mobility of water present inside the medium is not affected by the presence of polymer. However, these admixtures modify significantly the surface fraction of mobile water molecules transiently present at solid surfaces. This quantity measured, for the first time, for all admixed cement pastes is thus relevant to explain the water retention mechanism

We show how nuclear magnetic spin-lattice relaxation dispersion of proton-water (NMRD) can be used to elucidate the effect of cellulose ethers on water retention and hydration delay of freshly-mixed white cement pastes. NMRD is useful to determine the surface diffusion coefficient of water, the specific surface area and the hydration kinetics of the cement-based material. In spite of modifications of the solution's viscosity, we show that the cellulosic derivatives do not modify the surface diffusion coefficient of water. Thus, the mobility of water present inside the medium is not affected by the presence of polymer. However, these admixtures modify significantly the surface fraction of mobile water molecules transiently present at solid surfaces. This quantity measured, for the first time, for all admixed cement pastes is thus relevant to explain the water retention mechanism.