Acoustic emission characteristics of recycled brick-concrete aggregate concrete under freeze-thaw-load coupling action and damage constitutive model

Abstract

Replacing natural aggregate with construction waste to prepare concrete is an effective way of its resource utilization, which is in line with China 's " carbon peaking and carbon neutrality " strategy and the green development needs of the construction industry. Due to the existing technology is difficult to completely separate waste bricks and waste concrete, this paper mixes recycled brick aggregate and recycled concrete aggregate in a ratio of 1:1 into a mixture, and replaces the natural aggregate with a replacement rate of 30% to prepare Recycled Brick-Concrete Aggregate Concrete (RB-CAC). Concrete in northern China is often subjected to freeze-thaw and load coupling, which accelerates the damage degradation of RB-CAC. Therefore, it is necessary to study its damage constitutive model. In this paper, the effects of different stress levels (0%, 20%, 40%, 60% of flexural strength) and freeze-thaw cycles (0 times, 40 times, 80 times, 120 times, 160 times) on the apparent morphology, mass loss, relative dynamic elastic modulus and acoustic emission characteristics of RB-CAC were analyzed by freeze-thaw-load coupling test, constitutive relation test under uniaxial compression and acoustic emission characteristic test. The dynamic evolution of its frost resistance and damage process was analyzed and evaluated. Finally, combined with the knowledge of damage mechanics, the elastic modulus is defined as the damage variable generated by the freeze-thaw-load coupling effect. Based on the mesoscopic damage theory, the ratio of the number of failure interfaces to the total number of interfaces is defined as the damage variable generated by uniaxial pressure. The damage evolution equation of RB-CAC and the damage constitutive model of freeze-thaw times and stress level are established.