Drop hammer flexural impact performance of concrete with different moisture states in severe cold environments

In cold regions, concrete infrastructures are subject to prolonged subzero temperatures, which considerably change their mechanical properties owing to complex physical changes such as pore water freezing and matrix cold shrinkage. While existing studies have focused on quasi-static properties, the dynamic impact resistance of concrete under humidity-temperature conditions remains unexplored. This study investigates the effects of subzero temperatures (−20, −40, and −60 °C) and moisture content states (saturated, semi-saturated, dry) on concrete performance using quasi-static mechanical tests (compressive, split tensile, and flexural strengths), drop hammer impact experiments, and high-speed camera analyses. The quasi-static mechanical properties and dynamic flexural strength of concrete increased considerably under subzero temperatures. Fracture energy peaked at −20 °C but decreased at −60 °C owing to ice crystal brittleness. The dynamic increase factor (DIF) corresponded with predictions from the Malvar and Ross model. High-speed imaging confirmed that crack propagation at −60 °C exhibited typical brittle failure. These findings offer valuable theoretical insights for the impact-resistant design of concrete structures in cold regions. • Investigation of moisture states (saturated, semi-saturated, dry) and subzero temperatures (−20°C to −60°C) on concrete’s quasi-static and dynamic flexural impact performance using drop-hammer tests and high-speed imaging. • Enhanced strength and dynamic modulus in saturated concrete due to ice-matrix densification and pore-filling effects, validated via Browne & Bamforth and Goto & Miura models. • Dynamic strength increment factor (DIF) aligned with the Malvar & Ross model, while ice bridging at −20°C improved fracture energy.