Three-Dimensional Mesonumerical Model of Freeze-Thaw Concrete Based on the Porosity Swelling Theory

To investigate the compressive behavior of concrete under a freeze-thaw environment, porosity swelling theory, a damaged plastic model, and an element removal technique are combined to propose a novel mesoscopic numerical model of concrete. The porosity swelling theory is employed to represent the pores evolution behavior of concrete under freeze-thaw cycles, and a novel calculation method for porosity expansion is presented to characterize freeze-thaw cycle times. The damaged plastic model is used to describe the tensile and compressive features of the mortar and interface transition zone. The element removal technique with maximum damage criterion is employed to implement crack propagation. It was demonstrated that the model could capture the freeze-thaw damage and compressive failure of concrete well. The uniaxial compressive behavior of five random mesonumerical models of freeze-thaw concrete was investigated. The results showed that freeze-thaw cycles can cause tensile damage to the mortar near pores and the spalling of surface mortar. With the increase of concrete freeze-thaw cycles, the dispersion degree of the compressive stress-strain curve gradually rises, and the peak stress and peak strain of the freeze-thaw concrete stress-strain curve decrease and increase, respectively. During the freeze-thaw cycles, the sustained preload will decrease the compressive strength because it causes the microcracks to accelerate the damage induced by the freeze-thaw cycles. Then, the influence of mortar and interface transition zone properties on the compressive strength of concrete under freeze-thaw cycles was analyzed. Under 100 freeze-thaw cycles, the maximum attenuation rates of concrete compressive strength increase by 9.39% and 34.26% with the increase of interface transition zone and mortar properties, respectively. Increasing mortar properties and decreasing the sustained preload will enhance the ability of concrete to resist freeze-thaw cycles.