Investigation of the high-temperature resistance of glass aggregate enhanced sprayed high-performance concrete

With increasing demands on tunnel lining performance, the application of high-performance shotcrete has expanded rapidly, though its susceptibility to spalling under elevated temperatures remains a critical concern. To address the early thermal instability of conventional glass sand concrete under complex tunnel conditions, a heat-resistant and self-sensing shotcrete was developed by incorporating 0.9% carbon fibers, adjusting polypropylene fiber content (0%, 0.2%, 0.3%, 0.4%), and replacing 75% of manufactured sand with recycled glass sand. Specimens were exposed to temperatures ranging from 20 °C to 800 °C for two hours, followed by evaluations of mass loss, mechanical properties, and self-sensing performance. Polypropylene fibers enhanced thermal resistance, with 0.4% identified as the optimal dosage. Strength increased moderately up to 600 °C due to continued hydration (maximum compressive, splitting tensile, and flexural strengths of 124.54 MPa, 8.44 MPa, and 11.69 MPa, respectively), followed by a sharp decline beyond this threshold. The self-sensing capability diminished with temperature and disappeared entirely at 800 °C. Scanning electron microscopy confirmed the correlation between fiber melting, hydration changes, and mechanical degradation. Numerical simulations using ANSYS APDL indicated that fire exposure beyond one hour may cause compressive stress at the tunnel crown to exceed the concrete’s design strength, posing a risk of failure. Limiting fire suppression time within one hour and prioritizing post-fire crown inspection are recommended. This study provides new insights into fire-resistant design and repair strategies for tunnel linings.