Experimental studies and numerical analysis of the dynamic mechanical properties of concrete at low temperatures

Concrete building structures in cold regions are frequently exposed to low-temperature environments and inevitably subjected to impact loads during service. This study aimed to investigate the water–ice phase transformation process of concrete at low temperature and its response to impact loads ranging from 20 °C to −30 °C, using nuclear magnetic resonance and a split Hopkinson pressure bar. Concrete mesoscopic model, with mortar, aggregates, interfacial transition zones (ITZs), and ice particles, was developed to carry out numerical simulation. Under impact loads, the dynamic compressive strength of concrete exhibited an exponential strain rate strengthening effect, with an average increase of 18% at −30 °C compared with 20 °C. Based on the T2 spectrum, bound water in the concrete took up above 80% of the pore water, while 50% of the pore water remained unfrozen at −30 °C. The concrete was primarily damaged by compression, with a tensile damage rate of less than 10%. The damage of each phase material is sensitive to the strain rate, but not to the low-temperature. Numerical simulations of concrete mesoscopic models can be used to analyze the damage evolution and crack propagation mechanisms of concrete at low temperatures, providing a reference for understanding the dynamic failure mechanisms of composite materials.