Non-explosive spalling UHPC mediated by synergistic regulation of thermal stress and vapor pressure

Abstract

The explosive spalling of UHPC critically limits its application in fire-prone scenarios such as tunnels and nuclear facilities. Addressing the theoretical gap of thermal stress effect in existing studies, this research uncovers the synergistic damage mechanism of thermal stress and vapor pressure through experiments and thermo-mechanical coupled modeling. This research leverages polyethylene fiber (PEF) phase transitions to concurrently alleviate vapor pressure and thermal stress. A 12-min temperature plateau (the cross-section temperature stabilized at 155 ± 2 °C) suggest that PEF has a beneficial effect on thermal stress. Meanwhile, the melting and vaporization of PEF introduce extra pore channels with total porosity of 5.89 % at 400 °C for vapor pressure dissipation. Consequently, PEF-modified UHPC eliminates explosive spalling at 1000 °C, while the compressive strengths are maintained at 98.3 MPa and 36.0 MPa under 400 °C and 800 °C, respectively. Moreover, a spherical pore theory inspired model has been established to quantitatively validate that the synergistic regulation, where the results reveal that thermal stress and vapor pressure contribute 43.6 % and 56.4 % to the explosive spalling. This research proposes a novel approach to eliminate the explosive spalling, achieving theoretical breakthroughs for the fire-safe design of UHPC.