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When cement-based materials with a low water-binder ratio are exposed to water, the internal unhydrated cementitious components undergo rehydration. Rehydration tests of paste samples with a low water-binder ratio were conducted to determine the hydration degree under water immersion conditions. A modified rehydration model was developed based on a thermodynamic model for cement hydration and used to predict the hydration degrees of samples at different times. The modified rehydration model closely agreed with the test data. The ambient temperature significantly impacted material rehydration. The temperature effect on the rehydration reaction rate constant follows the Arrhenius law.

The capillary absorption capacity exerts an important effect on the durability of cement-based materials and is closely related to the pore structure. In this study, a variety of cement-based specimens were examined. The capillary water absorption and pore structure of the samples were determined using a gravimetric method and mercury intrusion porosimetry (MIP), respectively. The capillary water absorption coefficients for different water–binder ratios, diverse types and dosages of mineral admixtures, and various preloads were measured. The experimental results were analyzed and compared with data available in the current literature. The test results showed that the capillary water absorption performance of cement-based materials increased with an increasing water–binder ratio, first decreased and then increased with an increasing fly ash dosage, decreased with an increasing mineral power dosage, and decreased when the preload was less than a critical value and increased rapidly when the preload was greater than the critical value. The relationship between the capillary absorption coefficient and porosity was nearly linear. Water absorption by cement-based materials mainly correlated with pore diameters in the range of 10~1000 nm. The capillary water absorption coefficient increased continuously with the increase of pore fractal dimension.