The Matthew effect in cement hydration: Hydroxylation-driven wetting of C2S mesopores

Water adsorption and capillary condensation in cementitious mesopores govern early transport and hydration kinetics, yet how surface chemistry couples to pore wetting remains unclear. Using grand canonical Monte Carlo simulations, we quantify water uptake and condensation in slit-shaped dicalcium silicate mesopores with varying surface hydroxylation degree. We identify a Matthew effect in hydration, i.e., a positive-feedback process in which water accumulation promotes surface hydroxylation, which in turn strengthens solid-liquid interactions and accelerates further uptake. The enhanced water adsorption on hydroxylated surfaces arises from more interfacial hydrogen bonds and shorter bonding distances, increasing the orientational ordering and structuring of interfacial water. Therefore, more reactive minerals develop more hydroxylated surfaces that increase water uptake and promote further hydration, exacerbating interphase heterogeneity in the hydration degree of cement paste. These results clarify the preferential transport and accumulation of water in cement mesopores and provide explanations for long-term hydration degree disparities of clinker phases.