Residual mechanical and self-sensing properties of polypropylene fiber-reinforced waste glass aggregate UHPS after high-temperature exposure

To enhance the sustainability and high-temperature resistance of tunnel lining materials, this study prepared an ultra-high-performance shotcrete (UHPS) incorporating polypropylene fibres (PPF) and used waste glass aggregate as a substitute raw material. The effects of PPF content (0-0.4%) and high-temperature exposure (20-800 °C) on the residual mechanical properties, flexural toughness, and self-sensing capability of UHPS were systematically investigated. At 20 °C, adding PPF reduces strengths; relative to 0% PPF, 0.4% PPF lowers compressive, splitting-tensile, and flexural strengths by 13.28%, 23.04%, and 29.28%, respectively. In addition, PPF reduces flexural toughness indices and self-sensing capability at room temperature, with more pronounced reductions at higher fibre dosages. However, under elevated temperatures, PPF significantly suppresses the risk of spalling and enhances the residual mechanical properties of UHPS, with the optimal effect observed at 0.3% PPF. As the temperature increases, the mechanical strength of UHPS first increases and then decreases, while flexural toughness continuously deteriorates. Moreover, high temperatures weaken both pressure-sensitive and bending-sensitive properties, with self-sensing capability showing a marked decline above 400 °C. Microscopic analysis indicates that the decomposition of hydration products, fibre oxidation, and crack propagation are the main mechanisms underlying performance degradation at high temperatures.