Acoustic emission behavior and damage evaluation of recycled aggregate concrete under compression

Abstract

Application of recycled coarse aggregate concrete (RAC) will generate considerable environmental benefits. However, the properties of RAC must be studied before being adopted in structures. In this research, the failure process and damage assessment of RAC under compression were investigated by applying acoustic emission (AE) technology. The variables include loading rates, maximum coarse aggregate sizes, and water–cement ratios (w/c). Meanwhile, an innovative approach called stage cumulative proportion (SCP) analysis of AE result was put forward. Subsequently, the damage of RAC under compression was evaluated based on the rate process theory. The results demonstrated that void compaction and original crack expansion occurred first in the test and then the stable microcracking in interfacial transition zone (ITZ) and unstable cracking in mortar, and finally, there is the macrocrack expansion followed by the fracture. It was found that AE counts and energy were mainly produced before the peak stress was reached. The increase in loading rate caused the AE counts and energy to increase in stable microcracking of ITZ but decreased in unstable cracking of mortar. Increasing the w/c would also affect the AE results in these stages, but the effect was the opposite to the loading rate. Besides, an increase in coarse aggregate sizes would increase the AE counts and energy in unstable cracking of mortar and decrease in macrocrack expansion. In addition, a polynomial expression of the relationship between AE parameters and stress level was established. Then, an evaluation criterion was proposed based on the expressions and the rate process theory.