In-Depth Exploration of the Behavior of UHPC in Subzero Conditions: Static and Dynamic Loading Scenarios

Ultrahigh-performance concrete (UHPC) is a suitable material for constructing nationally important structures such as military bunkers, storage structures, protective walls, and so forth. In many countries, these structures experience temperatures below 0°C. Thus, it is crucial to understand the static and dynamic performance of UHPC at such subzero temperatures (SZTs). This paper presents a comprehensive study of the behavior of UHPC under SZTs of −12°C, −24°C, and −36°C, (static and dynamic loading scenarios). Mechanical properties such as compressive strength, modulus of elasticity, flexural, and fracture performance of UHPC were assessed. The mechanical performance was enhanced with a decrease in temperature. Specifically, compressive and flexural strengths increased by 24% and 61.6%, respectively, at −36°C compared with room temperature (RT). Similar trends were found for flexural toughness, fracture energy (Gf), and the critical stress intensity factor (KIC) as well. The ballistic performance was assessed using different impact velocities of a projectile at different temperatures. Test results revealed that, with decreasing temperature, the velocity ranges for complete perforation of a UHPC slab increased and the loss of mass decreased. The energy absorption capacity improved by ∼270 J from RT to −36°C. A course of 32 cycles of freezing and thawing marginally affected the mechanical properties of UHPC. Additionally, the research highlights the role of steel fibers in enhancing UHPC’s performance at SZTs. The mechanism of the strength enhancement in UHPC at SZTs is discussed. These findings are critical for the design of military structures and other infrastructure in cold environments.