A modified Parrot–Killoh model for cement hydration considering self-desiccation: Incorporating the coupled relative humidity-hydration mechanism

Self-desiccation is prone to occur inside engineering-scale concrete, leading to a reduction in internal relative humidity (RH) and thereby affecting the cement hydration process. Building upon the classical Parrot-Killoh (PK) model, this study develops a modified hydration model for cementitious materials considering self-desiccation by coupling the dynamic interaction mechanism between RH and hydration. The RH evolution is computed by incorporating the time-dependent behaviors of pore solution activity and the curvature radius of pore menisci. Specifically, the latter is determined using an improved pore size distribution model that incorporates the influence of the water-to-cement ratio (w/c) on the initial packing density of hydration products, as well as a correction for the volume of adsorbed water on dry pore walls. In addition, the mathematical expression describing the inhibitory effect of RH reduction on hydration rate is optimized. The modified PK hydration model is validated against multiple datasets from the literature, demonstrates high accuracy in predicting hydration degree, RH evolution, and capillary porosity. Furthermore, the sources of prediction error are systematically analyzed. This study enhances the applicability of hydration models in practical engineering, facilitates mix design optimization, and contributes to improved resource efficiency.