Influence of waste clay bricks as fine aggregate on the mechanical and microstructural properties of concrete

To satisfy the demand of modern concrete and environmentally friendly society, the value-added utilization of waste clay bricks could be effectively improved without sacrificing the strength of sustainable concrete. This paper investigated the influence of variable replacement ratios (0%, 25%, 50%, 75% and 100%) and additional water volumes (no extra water, partially extra water and totally extra water) of fine aggregates made of waste clay bricks (WCBF) on the properties of recycled concrete (RBC). Based on the pore structure, microscopic morphology and chemical element of microscopic test results, the mechanism of the WCBF on the properties of concrete were analyzed. The results indicated that the density of RBC was gradually reduced with the increasing of additional water volume and replacement ratio of WCBF. The compressive strength of RBC with no extra water and partially extra water within 50% replacement ratio was comparable with normal concrete (NC), but the compressive strength of RBC with fully extra water and partially extra water beyond 50% replacement ratio was degraded. The splitting tensile strength of RBC was comparatively increased or similar with the decrease of additional water volume, while the RBC yielded lower elastic modulus especially beyond 50% replacement ratio. The microscopic results revealed that the RBC porosity and total pore volume, as well as the pore content with diameter higher than 100 nm of RBC were increased. In addition, the interfacial transition zone was compacted because of the pozzolanic activity together with the penetration of cement matrix into the surface of the WCBF by about 120 µm.