Tensile behavior of steam-free UHPC under tensile stress in extreme cold environments from 20 °C to − 165 °C

Axial tensile tests on 42 UHPC specimens (2 mixes) across temperatures from 20 °C to −165 °C showed that non-steam-cured UHPC's tensile strength increased at low temperatures compared to room temperature. This strength improvement peaked at −120 °C before declining with further cooling. The study also proposed a strength ratio equation and a strain softening model for UHPC under ultra-low temperature tension.The tensile behavior of ultra-high performance concrete (UHPC) in LNG tank operational conditions at ultra-low temperatures (−165 °C) was investigated.The influence of two UHPC mix proportions and seven temperatures from 20 °C to −165 °C on the tensile performance of the material was explored by conducting uniaxial tensile tests on 42 sets of 100 mm × 100 mm × 300 mm dogbone-shaped tensile specimens. Experimental data indicated enhancement in UHPC tensile capacity when temperature decreased from 20 °C to −165 °C, reaching its peak at −120 °C, i.e., an increase of about 32 % (Group A) and 47 % (Group B) compared to room temperature. Further, a strength ratio-based equation was developed to calculate the uniaxial tensile strength of UHPC in ultra-low temperatures environments while constructing a theoretical model equation to characterize the axial tensile behavior of UHPC materials. The results showed that low temperatures can form an ice mesh structure inside UHPC, which densifies the matrix and improves the axial tensile strength of UHPC. In addition, steel fiber reinforcement significantly enhances the post-cracking ductility of UHPC under cryogenic conditions, thereby establishing theoretical foundations for implementing UHPC in full-concrete LNG tank structures.