Reactive powder concrete (RPC) is widely used in fire-critical infrastructure due to its high strength and dense microstructure; however, its post-fire behavior under realistic firefighting conditions remains underexplored. Specifically, the combined effects of hybrid fiber reinforcement and water quenching (thermal shock) during fire suppression are not well understood. This study investigates the residual mechanical properties and microstructural degradation of hybrid steel–polypropylene fiber reinforced RPC exposed to temperatures of 200, 400, 600, and 800 °C, followed by either natural air cooling or water quenching. Residual compressive, splitting tensile, and flexural strengths were measured, and damage mechanisms analyzed using SEM and XRD. Predictive models were developed for the degradation of mechanical properties under thermal shock. Results showed compressive strength increased by up to 19% at 200–400 °C due to enhanced hydration, with severe degradation above 600 °C. Water quenching caused greater strength loss than air cooling, particularly at 600 °C, due to thermal shock-induced microcracking. Hybrid fiber reinforcement with optimal steel fiber content (2%) improved post-fire performance. Microstructural analysis indicated that strength loss during water quenching was driven more by microstructural disruption than phase transformation. The proposed models and insights aid in post-fire assessments and fire design of RPC structures.
Abid et al. (Mon,) studied this question.