Multi-Analytical study of physical-mechanical variations induced by environmental aging on gypsum plasters

Gypsum plasters are highly sensitive to environmental fluctuations, yet their response to mild temperature and humidity conditions remains underexplored. This study investigates the onset and progression of the gypsum-to-bassanite transformation under near-real environmental conditions and assesses the cumulative effects of repeated thermal–hygroscopic cycling on plaster durability. Integrated thermogravimetric, calorimetric, X-ray diffraction, and infrared spectroscopy analyses show that dehydration can initiate at temperatures as low as ~45 – 50 °C and accelerates with successive dehydration–rehydration cycles, indicating progressive microstructural modification. A targeted accelerated aging protocol was developed to reproduce realistic environmental stresses through alternating hot–dry and mild–wet steps. Multiscale characterization strategy reveals substantial and irreversible deterioration after cycling, including increased porosity and specific surface area, higher air permeability, and a pronounced reduction in drilling resistance. Scanning electron microscopy further confirms extensive microstructural alterations leading to the formation of bulkier, less interlocked gypsum aggregates formed through solution-mediated recrystallization. Overall, the results demonstrate that moderate but prolonged exposure to thermal–hygroscopic stressors significantly weaken gypsum plasters, affecting both their microstructure and mechanical integrity. These findings underscore the importance of understanding material performance under evolving climatic conditions and support evidence-based conservation decision-making.