Dynamic mechanical properties and constitutive model of concrete under low-temperature conditions

In extremely cold regions, the mechanical properties and failure behavior of concrete are considerably altered by low temperature. In this study, the effects of low temperature on the dynamic mechanical properties of concrete were investigated. The unfrozen water content at different temperatures was quantitatively measured using low-field nuclear magnetic resonance. Dynamic stress–strain relationships under varying temperatures and strain rates were obtained using split Hopkinson pressure bar tests; high-speed photography captured the fracture process of the specimens. The results showed that decreasing temperature reduced the unfrozen water content and increased the ice content within the concrete pores, thereby slightly increasing the initial equivalent elastic modulus and enhancing the dynamic compressive strength. Both lower temperatures and higher strain rates enhanced the dynamic compressive strength. Additionally, macroscopic crack development was considerably suppressed at lower temperatures. By considering the combined influences of temperature and strain rate, a damage evolution equation was formulated. Based on damage mechanics and elastoplastic theory, a dynamic constitutive model for concrete under low temperatures was developed. The effectiveness of the proposed model was verified through comparison between theoretical predictions and experimental results. Quantitative analysis demonstrates that the prediction error for dynamic compressive strength is strictly controlled within 5%.