Molecular structure and dynamics of water on the surfaces of cement hydration products and associated Minerals: Nanoscale wettability behavior

Wettability is crucial to the performance of cement-based materials in coastal environments, where saline exposure accelerates deterioration. Understanding the wetting behavior of key hydration products at the molecular level is essential for enhancing material durability and developing effective repair solutions. This study examines the wettability of four principal substrates in cement-based materials: ettringite (AFt), anhydrite (CaSO₄), calcium carbonate (CaCO₃), and calcium silicate hydrate (C-S-H), utilizing molecular dynamics simulations to analyze contact angles, dipole orientations, interfacial bonding, and energy interactions. Results indicate substrate-specific wettability, with contact angles of 8.04° for AFt, 10.75° for CaSO₄, 15.61° for CaCO₃, and 10.06° for C-S-H. Notably, AFt and C-S-H allow deeper water penetration due to robust hydrogen bonding with hydroxyl and silicate groups, facilitating high wettability. In contrast, CaSO₄ and CaCO₃ display limited water molecule diffusion, driven by ionic interactions, with CaCO₃ exhibiting strong water adsorption that constrains droplet mobility. The distinct hydrogen bond and dipole angle distributions of H₂O molecules elucidate the varied wetting behaviors on each substrate. These findings advance the molecular-level understanding of wetting mechanisms, offering valuable insights for designing durable cementitious materials for coastal applications, especially in sulfate-resistant, rapid-hardening marine repair scenarios.