Performance of normal strength reinforced concrete slabs after hydrogen-air explosion: Effects of cryogenic freeze-thaw cycles exposure

The blast resistance of reinforced concrete (RC) structures under extreme environmental conditions remains a significant concern, particularly for energy storage infrastructure systems. This study investigates the response of reinforced normal strength concrete (NSC) slabs subjected to hydrogen–air explosions, with particular emphasis on the effects of cryogenic freeze–thaw (FT) cycles. A comprehensive experimental programme was conducted to evaluate slab behaviour under hydrogen explosions with varying gas volumes (1 × 1 × 1 m³, 1.5 × 1.5 × 1 m³, and 2 × 2 × 1 m³) at a concentration of 30% within a confined space. Prior to testing, the specimens were exposed to 0, 4, and 8 FT cycles at low and cryogenic temperatures (−70°C and −160°C) to examine the coupled effects of thermal degradation and blast loading. Key response parameters, including explosion pressure, structural deflection, and damage patterns, were measured and analysed. The results indicate a strong dependence of structural vulnerability on temperature exposure and FT cycling. Compared with the control specimen, slabs subjected to 4 and 8 FT cycles between ambient temperature and −160°C exhibited 55 and 237 times higher residual deflection, respectively, under identical explosion conditions. In addition, the slab exposed to 8 FT cycles between ambient temperature and −70°C showed a 71% greater deflection than that exposed to 4 cycles. A numerical model incorporating FT-induced material degradation was developed and shown to reproduce the experimental responses with good agreement. The numerical results further highlight the increased vulnerability of FT-degraded structures to blast loading and suggest that the proposed modelling approach can provide a useful basis for the safety assessment of energy infrastructure under extreme conditions.