Cellulose derivatives as renewable resources gain in importance in a time of growing energy and resource demand and ecological awareness. The most important applications are pharmaceuticals, cleaning agents as well as building materials, where they are used as thickening and water retaining agents. In masonry coatings formulations, cellulose ethers are introduced in order to control fresh mortar properties, rheology and application performance as well as the final strength of the render. Water retention is a key property imparted by the cellulose ether in a cement render formulation. Indeed, when applied on highly absorbent support and / or submitted to evaporation, the material must retain the necessary amount of water which is required for proper setting of the cement. In consequence, the hydration process took place in good conditions leading to hardened mortar with high mechanical strength. The aim of the study is to better understand the fundamental mechanisms of water transports in fresh cement-based materials. In this frame, three types of cellulose ethers were used (HydroxyEthyl Cellulose, HydroxyEthylMethyl Cellulose, and HydroxyPropylMethyl Cellulose). Several features were studied, such as the admixtures structural parameters (weight-average molecular mass and substitution degrees), particle size, concentration, and mortar consistency. Using well-characterized molecules, it will be possible to understand their way of action on mortar water retention. They could provide strong capacities thanks to the possible superposition of several phenomena such as a rheological effect similar to that caused by polysaccharides (increasing the viscosity). Another effect, specific to cellulose ethers, remains to be defined. This could be caused by a modification of the porous network in the fresh state, or the presence of polymer layer acting as a diffusion barrier. In this frame, using nuclear resonance magnetic techniques, the effect of cellulose ether on water mobility in fresh cement based materials was explored.
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