Study on the Dynamic Properties of Concrete under Freeze-Thaw Cycles and CT Fine View Damage

In order to study the dynamic mechanical properties of concrete under freeze-thaw cycles, uniaxial impact compression tests were conducted on concrete specimens with different number of freeze-thaw cycles (0, 25, 50, 75, and 100) using a 50 mm diameter split Hopkinson pressure bar (SHPB) test device at an impact air pressure of 0.4 MPa and combined with a CT scanning system to analyze the internal fissures of concrete specimens before and after freeze-thaw cycles. The results showed the following. (1) The concrete specimens were divided into linear elastic stage, plastic stage, and damage stage under the freeze-thaw cycle, and the macroscopic mechanical parameters of the specimens were weakened with the increase of the number of freeze-thaw cycles. (2) Freeze-thaw intensified the expansion and penetration of the internal fracture of the specimens, and the CT scan results showed that the internal fracture parameters of the concrete specimens were increased with the increase of the number of freeze-thaw cycles, and the structural characteristics of the internal fracture show gradually complex expansion and evolution characteristics. (3) The degree of damage was defined at the fine level, which increased with the number of freeze-thaw cycles, establishing an intrinsic link between the fine deterioration of concrete specimens and the loss of macroscopic parameters under freeze-thaw cycles. The results are of great significance to further elucidate the internal structural characteristics of concrete material damage under freeze-thaw conditions and to reveal the damage deterioration mechanism.