Damage constitutive models of concrete under the coupling action of freeze-thaw cycles and load based on Lemaitre assumption

In cold environments, concrete structures are subjected to a combined action of load, freeze-thaw cycles, and salt attack. The performance degradation of some concrete structures in such areas is serious, thus shortening their service life. In this study, a macro-mesoscopic coupling damage model was established to determine the durability of concrete under the coupling action of freeze-thaw cycles and load based on the Lemaitre strain equivalent assumption. Meanwhile, the an indoor accelerated test was conducted to verify the rationality of the model. Results indicated that the damage in different kinds of concrete under freeze-thaw cycles and load can be predicted by the theoretical model. The structural coupling damage was determined by the meso-damage caused by the freeze-thaw cycles and the macro-damage caused by the applied load, which showed a nonlinear superposition relationship. The evolution laws of coupling damage were entirely different because of the freeze-thaw cycles and strain. The coupling damage and peak strain increased with the increase in number of freeze-thaw cycles but the variation range of damage and peak stress decreased. The peak strain can be the critical point of the coupling damage when the number of freeze-thaw cycles was constant. The growth of coupling damage was not significant before the peak strain. When the deformation approached the peak strain, the coupling damage increased considerably, and the concrete was destroyed rapidly.