Regulating thermal damage evolution of concrete under prolonged dry-thermal exposure: Insights into moisture retention, crystal filling and crack restraint

Prolonged dry–thermal exposure induces multiple deterioration processes in concrete, including dehydration, pore coarsening, and microcrack development, ultimately resulting in late-age strength deterioration. To explore a microstructure-based regulation strategy, this study investigated the effects of a graphene oxide (GO)–calcium carbonate whisker (CW) composite system on concrete subjected to long-term exposure at 50 °C. GO–CW improved long-term strength retention, with the 90 d heat resistance coefficients for compressive and splitting tensile strengths being 16.9% and 5.9% higher, respectively, than those of the reference concrete. This improvement was primarily associated with the regulation of thermal damage evolution. Mechanistically, GO enhanced moisture retention within hydration products and promoted CH crystal growth for pore filling, while CW restrained microcrack development through its bridging effect. This regulation largely confined pore coarsening to the 100–1000 nm range, reduced macropore content by up to 65.8%, and limited pore–microcrack connectivity during prolonged thermal exposure. These findings provide a mechanistic basis for improving the long-term performance of concrete under prolonged dry–thermal exposure through microstructural regulation.