Shrinkage-reducing admixtures and early-age desiccation in cement pastes and mortars

摘要

Fundamental studies of the early-age desiccation of cement -based materials with and without a shrinkage-reducing admixture(SRA) have been performed.Studies have been conducted under both sealed and drying conditions .Physical measurements include mass loss, surface tension.X-ray absorption to map the drying profile ,internal relative humidity(PH),and autogenous deformation.Interestingly,although, the SRA accelerates the dryig of bulk solutions in, cement paste with a water -to - cement(w/c) ratio of 0.35 ,it actually reduces the measured drying rate.Based on the accompanying X-ray absorption measurements and a simple three -dimensional microstructure model ,an explanation for this observation is proposed .In sealed systems,at equivalent hydration times ,the SRA maintains a greater internal RH and reduces the induce autogenous deformation .Thus these admixtures should be beneficial to low w/c ratio concretes undergoing self-desiccation ,in addition to their normal usage to reduce drying shrinkage .