Expansion strain model and damage risk control for cement-based materials with low water–binder ratios under rehydration

Unhydrated cementitious materials in cement-based materials with low water–binder ratios undergo rehydration after re-exposure to water. Long-term rehydration not only damages cement-based materials but also influences their volume stability; however, the relationship between macroscopic strength and expansion strain remains unclear. In this study, rehydration tests were conducted on cement paste to analyse the influence of water soaking temperature and water–cement ratio on the expansion strain of specimens, and an expansion strain model was established based on a hyperbolic model form. The methods of assessment and control of damage risk induced by long-term rehydration for cement-based materials were developed on the basis of the established model and the correlation between compressive strength and expansion strain. Results showed that the expansion strain of the cement paste specimen increases with increasing water soaking temperature but decreases with increasing water–cement ratio. The values predicted by the model were in good agreement with the experimental results. The control effect for the damage risk caused by rehydration became more significant as the amount of silica fume increased. It provides experimental and theoretical bases for the application and life-cycle design of high-performance concrete (HPC) and ultra-high-performance concrete (UHPC) structures over long service periods in water environments.