Strength Recovery of Thermally Damaged High-Performance Concrete during Recuring.

High-performance concrete (HPC) experiences significant degradation in its mechanical properties after fire exposure. While various post-fire curing methods have been proposed to rehabilitate thermally damaged concrete (TDC), the physical and chemical changes occurring during these processes are not well-understood. This study examines the strength and microstructure restoration of HPC through water and water-CO cyclic recuring. HPC samples were initially heated to 600 °C and 900 °C, then subjected to water and cyclic recuring. Results indicate that the mechanical performance recovery of thermally damaged HPC is significantly better with cyclic recuring than with water recuring. The compressive strength of HPC samples exposed to 600 °C and 900 °C reached 131.6% and 70.3% of their original strength, respectively, after cyclic recuring. The optimal recuring duration for substantial recovery in thermally damaged HPC was determined to be 18 days. The strength recovery is primarily due to the healing of microcracks and the densification of decomposed cement paste. These findings clarify the physical and chemical processes involved in post-fire curing of HPC, highlighting the potential of water and water-CO cyclic recuring in the rehabilitation of TDC.