Deformation mechanisms of cement paste with ultra-low water-to-cement ratios under different curing conditions at early ages

Abstract

Cement-based materials with ultra-low water-to-cement ratios (w/c) swell with external water supply, which may cause cracking and strength reduction. Studies on the volumetric stability of cement-based materials ignore the possible expansion occurring in the material before the starting point, standard curing (20 ± 2 ℃ and relative humidity (RH) > 95 %) for 28 d. Thereby, the deformation and mechanical properties of cement paste cured under standard and sealed conditions at early ages were compared. Deformation mechanisms were investigated by thermogravimetric analysis, 1H nuclear magnetic resonance relaxometry, and pore structure measurement. The saturation degree and hydration degree were both estimated. The results show that swelling occurs in cement-based materials with ultra-low w/c under standard curing, with increasing flexural and compressive strength. Gel water and capillary water contribute to large proportions of the total absorbed water. Cement paste with low w/c produces higher swelling when absorbs the same amount of water. Deformation mechanisms are attributed to the mitigation of self-desiccation shrinkage, calcium-silicate-hydrate gel swelling due to water absorbed, and solid volume increase of solids after hydration.