High-performance cementitious materials are sensitive to early age cracking, mainly due to the large magnitude of autogenous shrinkage, which is closely related to the internal relative humidity (RH) decrease and capillary pressure induced by self-desiccation in the cement matrix. However, there is debate about the determination of time-zero, the time at which autogenous shrinkage begins to develop, which causes great difficulty in comparing the results provided in the exiting researches.This study presents an accurate determination of time-zero based on the relationship between the internal RH and autogenous shrinkage of cementitious materials. According to the time-zero, the effect of replacements of cement by supplementary cementitious materials on the autogenous shrinkage was investigated for the early age cement pastes with low water/binder ratio.The autogenous shrinkage was conducted according to the standard method ASTM C1698. Internal RH was performed on the sealed cement pastes at very early age by conventional method of hygrometer. Setting time was determined by the Vicat needle apparatus according to the standard method ASTM C191. The results could potentially explain the mechanism of autogenous shrinkage at early age in mixtures with supplementary cementitious materials.
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