Effect of HCSA expansive agent and SAP on deformation of cement paste with low water binder ratio

In order to solve the problem that the shrinkage compensation effect of high performance calcium sulpho aluminate (HCSA) expansive agent was not significant at a low water to binder ratio, this study used super-absorbent polymer (SAP) as the internal curing agent to study the influence of HCSA, SAP, HCSA and SAP together on the volume deformation (autogenous shrinkage, drying shrinkage, deformation in water) of cement paste with a low water to binder ratio (0.25), and the synergistic effect of HCSA expansive agent and SAP was discussed. The results show that both HCSA expansive agent and SAP reduce the autogenous shrinkage and dry shrinkage of cement paste, and increase the expansion deformation when immersed in water. The expansive effects of HCSA under sealed and immersed condition are more significant than that under drying condition. HCSA and SAP have synergistic effect, i.e. the pre-absorbed water by SAP could promote the effectiveness of HCSA. Under sealed condition, the synergistic effect mainly occur before about 1 day, and then it still work slowly. When immersed in water, HCSA and SAP also show synergistic effect. But under drying condition, the synergistic effect of HCSA and SAP mainly takes effect after 7 days. SAP could not promote the effectiveness of HCSA at early ages, and the addition of HCSA and SAP together increases the drying shrinkage of cement paste with low water to binder ratio.