How dry is dry? Radiolysis reveals hidden water in cementitious materials

Assessing whether cementitious materials are truly free of adsorbed water after drying remains experimentally challenging, yet residual water can strongly bias measurements of radiolytic molecular hydrogen production. Here, we use radiolytic H 2 generation as a sensitive probe to quantify trace residual water and evaluate the efficiency of common desorption protocols. Non-porous model hydrates (portlandite and tobermorite) were subjected to freeze-drying, solvent exchange, or thermal treatment under vacuum, then irradiated with accelerated electrons and their H 2 yields measured. The results reveal clear differences between methods and minerals. Freeze-drying systematically left detectable surface-adsorbed water, while solvent exchange showed mineral-dependent limitations. Thermal vacuum treatment was the most effective, although complete desorption required harsher conditions than typically applied to cementitious materials. These findings establish radiolysis as a practical tool for detecting residual water and benchmarking drying procedures in cement-based systems. • Radiolysis detects trace residual water in “dried” cementitious materials • H 2 yields provide direct indicators of remaining adsorbed water • Drying methods show strong efficiency differences across minerals • Freeze-drying leaves detectable surface water under typical conditions • Thermal vacuum is most effective but requires harsher conditions