Uniaxial tensile stress-strain model of UHPC at low temperatures: Experimental and mesoscale analysis

Ultra-high-performance concrete (UHPC) has been increasingly applied in engineering structure exposed to extremely low-temperature environments. The mechanical properties of UHPC at cryogenic temperatures urgently need scientific research. To investigate the uniaxial tensile behaviors of UHPC at low temperatures, a series of physical tests and mesoscale simulations were conducted. The effects of low temperatures (ranging from 20 °C to −90 °C) and steel fiber contents (ranging from 0.0 % to 3.0 %) on failure modes, stress-strain curves and tensile performance indices of UHPC were discussed. Results showed that the uniaxial tensile behaviors of UHPC at low temperatures still exhibits multi-crack ductile failure. As the temperature decreases, the crack width widens and the slope of post-peak stress-strain curve becomes steeper, indicating an increased brittleness. Furthermore, the increasing steel fiber content significantly enhances the post-cracking tensile behavior of UHPC at low temperatures. Notably, from 20 °C to −90 °C, the elastic modulus and tensile strength of UHPC increase by 97.1 % and 42.3 %, respectively, while the peak strain and toughness index decrease by 27.8 % and 46.3 %, respectively. Finally, a simplified tensile stress-strain model considering the combined effects of low temperature and steel fiber content was proposed and verified, which can accurately predict the nonlinear tensile behaviors of UHPC at low temperatures.