Volumetric stability of polymer-containing cementitious materials under aqueous and thermal aging

Volumetric stability is a key performance parameter of polymer-containing materials exposed to aqueous environments and thermal cycling, as polymer–water interactions and time-dependent structural rearrangement processes, including relaxation phenomena described for polymer systems, induce dimensional changes that compromise interfacial integrity. Comparative evidence across cementitious systems with differing polymer architectures under combined hygrothermal conditions remains limited. This in vitro study investigated the volumetric stability of polymer-containing cementitious materials with differing polymer architectures during aqueous storage and thermal aging. Five restorative materials were examined, including a crosslinked dimethacrylate-based alkasite, polymer-modified glass ionomer cements containing elastomeric polyethylene glycol–polyurethane (PEG–PU) micelles, a glass hybrid system, and conventional glass ionomer cements. Standardized cubic specimens were stored in distilled water (up to 30 days), followed by thermal aging (5000 thermocycles). Volumetric changes were quantified using Archimedes-based measurements. Mass changes were analyzed in parallel to enable mechanistic interpretation of volumetric behavior. Material-dependent differences in volumetric behavior were observed (p 0.05). The glass hybrid (EQF) demonstrated initial expansion (+5.62%) followed by stabilization. The results demonstrate that hygrothermal dimensional stability is strongly associated with polymer architecture and matrix-related properties.