High-strength concrete exposed to fire is prone to strength reduction and possible explosive spalling due to thermo-mechanical and thermo-hydral processes; however, recovery is possible under water re-curing depending on the degree of fire damage. This research investigated the relationship between degradation and self-healing capability by examining the surface microstructure of high-strength mortar after fire in order to explore re-curing as a new repair method. Morphology properties and the shape of external and inner pores in the specimens were examined by microscopy, SEM-EDS, TG-DTA, and MIP after heating. The results show that degradation is driven by the interaction of the dehydrated zones at the surface, and spalling at the microstructure level can be attributed to build up of vapor pressure in entrained air pores. Self-healing capability was clearly observed in the dry/dehydrating and quasi-saturated zones, but is limited in dry/dehydrated, sintered areas. From these results, utilization of the dry/dehydrating and quasi-saturated zones may have high potential for a new repair method for firedamaged concrete.

Keywords: Self-healing, Degradation, Pore pressure, Fire-damaged concrete.