Mitigating autogenous shrinkage in HPC by internal curing using superabsorbent polymers

When the water-to-cement ratio of concrete is lower than a critical value, a marked selfdesiccation may occur, leading to autogenous shrinkage. This volume reduction can induce stress when the shrinkage is restrained, and may cause microcracks, compromising the longterm durability of the concrete. For a more extensive use of high-performance concrete (HPC), it is essential to find appropriate ways to avoid such a risk of cracking at early ages. Methods based on the concept of internal concrete curing have been suggested in the literature. These methods consist in the formation of water-filled inclusions in the fresh concrete, which prevent self-desiccation of the hardening concrete. The additional internal water can be supplied by using relatively small amounts of pre-saturated, lightweight, fine aggregates (LWA) or superabsorbent polymer (SAP) particles in the concrete. This paper focuses on the reduction of autogenous shrinkage of HPC by means of the addition of SAP as an internal curing agent. Drying shrinkage and autogenous shrinkage tests were performed from the first hours after casting. The effects of different amounts of SAP on the properties of concrete are presented and discussed. Finally, the effectiveness of this internal curing method to mitigate autogenous shrinkage in HPC is compared to that of more conventional methods using other chemical admixtures, such as an expansive agent and a shrinkage reducing admixture.