Triaxial compressive performance of recycled aggregate/glass sand concrete: Experimental study and mechanism analysis

Abstract

In real-world applications, concrete is often subjected to triaxial compression combined with pore water pressure. Understanding the mechanical properties of the concrete made with recycled coarse aggregate (RCA) and recycled glass sand (RGS) under complex stress states can enhance its practical application. This study first investigated the microscopic properties of interfacial transition zones (ITZs) using nanoscratch and backscattered electron-based (BSE-based) image analysis. Subsequently, mechanical properties under confining pressures ranging from 0 to 14 MPa and pore water pressure ranging from 0 to 13 MPa were assessed based on the stress-strain behaviours. The results reveal that the chemical activity and specific surface areas of aggregate were closely related to ITZ microscopic properties. Despite with the same water-cement ratio, the ITZs between RCA and the paste matrix displayed better cohesion performance than the ITZs between RGS and the paste matrix. Confining pressure was found to increase the internal friction angle of concrete, thereby improving mechanical strength and ductility. The poor cohesion of the RGS-paste matrix interface resulted in a decrease in the peak stress and an increase in the peak strain under triaxial compression. Pore water pressure played a dual role in triaxial compression, providing support and promoting crack expansion. The supporting effect enhanced the initial stiffness of concrete, while the crack expansion effect reduced the peak stress. The William-Warnke failure criterion was proven to be suitable for describing the failure surfaces of concrete with RCA and RGS under various complex stress states. To accurately predict the stress-strain curve, it is essential to comprehensively consider the influence of ITZs in concrete and the effect of pore water pressure.