A comparative study on strength, bond-slip performance and microstructure of geopolymer/ordinary recycled brick aggregate concrete

Abstract

Geopolymer recycled brick aggregate concrete (GRBC), which is a new kind of sustainable eco-friendly material, has the potential to be widely used in engineering applications. However, little research has been done on its basic mechanical properties and microstructures. Accordingly, a series of tests such as uniaxial compressive test, splitting tensile test and pull-out test were carried out in this paper. Taking recycled brick aggregate (RBA) replacement ratio (0%, 25%, 50%, 75% and 100%) as the main variable, 60 cubes and 40 pull-out specimens with steel bars were fabricated and tested. The compressive strength, tensile strength and bond-slip performance of GRBC were investigated and compared with the ordinary recycled brick aggregate concrete (ORBC). The analysis using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) was conducted to study the microstructure characteristics of GRBC and ORBC. The results show that the compressive strength, splitting tensile strength and bond strength between concrete and steel bar decrease with the increase of RBA replacement ratio, and the decrease rate of GRBC is faster than that of ORBC. For GRBC, when RBA replacement ratio varies from 0% to 50% and 100%, the compressive strengths decrease by 32.25% and 57.49%, respectively; the splitting tensile strengths decrease by 33.11% and 53.20%, respectively; while the bond strengths decrease by 19.91%–28.11% and 46.32%–49.63%, respectively, depending on different bond length. ORBC pull-out specimen is more prone to splitting failure than GRBC specimen. The aluminosilicate gel formed by the hydration of geopolymer matrix has a denser structure than the gel of ordinary concrete matrix. Incorporating the RBA results in the failure order change in weakness of GRBC and ORBC, and the failure of interfacial transition zone (ITZ) between matrix and aggregate is transformed into the failure of RBA.