Deterioration process and damage constitutive model of concrete under freeze-thaw circumstance of severely cold regions

For concrete used in severely cold regions such as the Qinghai-Tibet Plateau, the Northeast China, and the Arctic region, it will inevitably be subjected to the freeze-thaw (FT) cycles close to-40 degrees C. However, the lowest temperatures of the conventional concrete FT cycle tests are not lower than-20 degrees C. To investigate the differences in concrete damage between the conventional FT cycle circumstance and the severely cold FT cycle circumstance, there are two kinds of the FT cycle test circumstances in this study:-18 degrees C +5 degrees C (FTC-18) and-40 degrees C +5 degrees C (FTC-40). The results indicate that, under both FT cycle circumstances, the deterioration rate of concrete escalates as the increase in the FT cycle number. Based on numerical simulation, after the same FT cycle number and under the same stress, the quantity of cracks formed by the load inside the concrete under FTC-40 exceeds that under FTC-18. The results from multi-scale experiments and numerical simulation consistently show that the damage effect of FTC-40 on concrete is more significant than that of FTC-18. The reason for this is that at-40 degrees C, more pore water freezes compared to-18 degrees C. In addition, the FT damage constitutive models for concrete exposed to both FTC-18 and FTC-40 are developed. The stress-strain curves obtained from the theoretical models exhibit good alignment with the experimental stress-strain curves, thereby confirming the validity and accuracy of the established models.