Internal curing of fine coral aggregate in cement mortars with low water-to-cement ratio: Difference in freshwater and seawater

Fine coral aggregate has a porous structure and high water absorption, which can be used as an internal curing medium. In this study, the pore characteristics and water absorption-desorption of fine coral aggregate were investigated, as well as the difference in internal curing of fine coral aggregate between freshwater and seawater mixed cement mortars with a low water-to-cement ratio. The results showed that the pore size of fine coral aggregates is mostly larger than 1μm. In addition, the seawater can promote the hydration of cement, improve the early strength, and increase autogenous shrinkage and later-age drying shrinkage of cement mortars. On the other hand, it can accelerate the release of internal curing water from fine coral aggregates into the matrix. Based on experiments, three stages of early autogenous shrinkage development were discussed and an autogenous shrinkage calculation model for cement mortars mixed with seawater and fine coral aggregates was proposed. Moreover, the optimal volume replacement content of fine coral aggregate in cement mortars mixed with freshwater or seawater was calculated, which indicates that it is necessary to modify the pore structure of fine coral aggregates.