Search

Sorption processes are critical for the drying and durability of cement-based materials, directly affecting their thermal properties. Temperature can substantially influence these processes. This work uses molecular simulations to study sorption in C–S–H pores under varying temperatures and relative humidity, considering pore sizes from the gel to the interlayer scale (between 11.6 and 106 Å). We quantify the temperature and pore-size dependence of water cavitation and sorption hysteresis in the C–S–H pores. The critical pore sizes for the disappearance of hysteresis and the reversibility of capillary condensation are identified, with the former being directly associated with cavitation. We show that cavitation occurs only in gel (meso)pores when they are above the critical pore size and below the critical temperature for cavitation. Interlayer pores, a major class of micropores in C–S–H, are not subjected to cavitation. Cavitation in C–S–H pores is homogeneous, occurring in the bulk-like zone of mesopores. The hydrophilicity of the C–S–H surface increases with the temperature, making heterogeneous cavitation less likely to occur. The results above were obtained consistently with three different force field parametrizations, building confidence in their relevance to describe C–S–H interfacial behavior. Finally, we demonstrate that macroscopic considerations for pore emptying and filling, such as the Kelvin-Cohan and equilibrium Derjaguin-Broekhoff-de Boer equations, are not valid or inaccurate when desorption occurs through cavitation in C–S–H. These results are relevant to understanding the sorption processes in other nanolayered adsorbing materials.

(Oxy)hydroxides such as portlandite (Ca(OH)2), boehmite (γ-AlOOH), and gibbsite (γ-Al(OH)3) have been shown to produce and store dihydrogen or its precursor, the H·atom when subjected to ionizing radiation. In this study, we investigate the diffusion of H2and the associated lattice expansion within these three minerals using molecular simulations. The crystal structure of all three (oxy)hydroxides dilates linearly with the number of H2molecules introduced, up to approximately 0.5 H2per nm3. The energy barriers between hopping sites are compared with available data from quantum simulations for boehmite and gibbsite, and are provided for the first time for portlandite. H2diffusion in these materials is shown to be subdiffusive, which might explain why such systems have to be activated, for example, by heating, to release the H2molecules. Nevertheless, simulations also show that each system has its own specific behavior related to anisotropy in diffusion: H2is effectively trapped in gibbsite, shows one-dimensional (1D) diffusion in boehmite, and two-dimensional (2D) diffusion in portlandite. H2migration can be observed under experimentally attainable time scales in defect-free boehmite and portlandite, but not in gibbsite below 100 °C. The affinity of H2with the bulk mineral (quantified using a damping factor multiplied to the potential well energy of the H2force field) together with the considerations about the connectivity of interstitial sites explains the subdiffusive behavior in the minerals studied.