An overview on the effect of internal curing on shrinkage of high performance cement-based materials

High performance cement-based materials, such as high or ultra-high performance concrete (HPC or UHPC) have been widely used and still faces the risk of cracking caused by shrinkages, especially autogenous shrinkage. Internal curing is an effective method to reduce or even eliminate autogenous shrinkage and has effects on chemical shrinkage, dry shrinkage, etc. The commonly used internal curing materials include super-absorbent polymer (SAP) and porous materials. Porous materials refer to lightweight aggregate (LWA) and porous superfine powders. In this paper, the internal curing materials has been divided into two categories based on water absorbing mechanism. The effects of these two categories of internal curing materials on shrinkage of high performance cement-based materials are reviewed. The addition of internal curing materials releases internal curing water, postpones the drop of internal RH, and reduces autogenous shrinkage, but increase chemical shrinkage. The addition of internal curing materials with extra water increases drying shrinkage. The mechanisms of shrinkage on internal curing are also summarized and discussed. However, those mechanisms only focus on certain type of shrinkage. To reduce the risk of cracking more effectively, the relationship of different type of shrinkages should be established.