Damage characteristics and constitutive model of concrete under uniaxial compression after Freeze-Thaw damage

In order to study the uniaxial compressive damage characteristics and stress–strain behavior of concrete with different degrees of freeze–thaw (F-T) damage, and then effectively evaluate the mechanical properties of concrete under different F-T damage degree. The rapid F–T cycle test was performed on different groups of concrete specimens, and an F–T damage evolution equation was established according to the change law of the relative dynamic elastic modulus. Uniaxial compression tests were performed on specimens with different F–T cycles, and damage evolution during compression was studied using an acoustic emission (AE) system. Finally, the AE characteristic parameters were used to establish a uniaxial compression constitutive model of concrete considering F–T damage. The results showed that the degree of F–T damage increased as the F–T cycles increased. During the concrete compression failure, the AE amplitude showed a more obvious and rapid rising trend when it was close to the critical state point. The proportion of low-amplitude AE events (≤50 dB) gradually decreased, whereas that of medium- and high-amplitude events exhibited a corresponding upward trend. These results indicate that the concrete after F–T damage exhibited more brittle characteristics during the compression failure process. The damage constitutive model established in this study can accurately reflect the damage evolution law of concrete during the entire process of uniaxial compression after F–T cycles. Moreover, the model was sufficiently consistent with test data, providing a reference for the design and safe operation of concrete structures in cold regions.