Effect of internal curing on shrinkage of calcium sulfoaluminate cement concrete and calculation of the shrinkage stress at early age considering creep

Effect of internal curing on shrinkage of calcium sulfoaluminate cement (CSA) concrete in both sealed condition and dry/wet cycles was studied using four CSA concretes with water-to-binder ratios (w/b) of 0.62, 0.42, 0.30, 0.24 respectively corresponding to strength grade of CSA30, CSA50, CSA80, CSA100, and ceramsite as internal curing agent. Results indicate that lower w/b results in higher autogenous shrinkage and the total shrinkage of CSA100 at age of 14d under sealed condition reaches as high as 550 ga, while this figure is only 100 ga for CSA30. The concrete with lower w/b exhibits higher deformation amplitude during subsequent dry-wet cycles and the dimensional variations during dry-wet cycles for CAS100 and CSA30 are respectively 80 ga and 30 ga. It is found internal curing can effectively reduce both the autogenous shrinkage and the deformation amplitude during dry-wet cycles, especially for the concrete with lower w/b. The internally cured CSA100 exhibits 14d total shrinkage under sealed condition of 100 ga and the deformation amplitude during the subsequent three dry-wet cycles of 25 ga, with reduction rate of respectively 82% and 69% compared to its normally cured counterpart. Moreover, shrinkage stress of concrete cured for 3d under sealed condition and subsequently for 25d under drying condition was calculated based on ring test results considering creep behavior. It is shown that for CSA100 at Day 28, the shrinkage stress of the inner surface in the ring test is 2.32 MPa while this figure greatly drops to 0.43 MPa for its internally cured counterpart.