Molecular investigation of water sorption and the induced deformation in ASR products

Alkali-silica reaction (ASR) causes expansive deformation in concrete, yet the relative contribution of water adsorption to this expansion remains debated among several proposed mechanisms. This study employs a hybrid grand canonical Monte Carlo-molecular dynamics (GCMC-MD) method to evaluate the potential contribution of water-induced deformation in crystalline shlykovite, a mineral analog of products found in advanced stages of ASR. Bulk and slit-pore shlykovite systems are modeled under varying relative humidities (RHs) and pore sizes to distinguish the behavior of inter- and intralayer water from that confined in larger gel pores. In bulk shlykovite, water content varies by ~10–20%, producing up to ~10% swelling in flexible structures. In 1–2 nm slit pores, water adsorbs sequentially to form bridging films, with the critical humidity for capillary condensation increasing with pore size. The system volume initially contracts and then expands as capillary tension relaxes, consistent with Laplace pressure evolution. These results reveal how confinement, hydration, and structural flexibility govern the nanoscale deformation of shlykovite-like ASR products, providing molecular insight into the potential role of moisture uptake in concrete expansion.