Mechanical properties and microstructure of nano-SiO2 and basalt-fiber-reinforced recycled aggregate concrete

Abstract

Abstract In this study, nano-SiO2 (NS) and basalt fiber (BF) were used to improve the quality of recycled aggregate concrete (RAC). The crushing value, water absorption, and apparent density of NS-modified recycled coarse aggregate (RA) were determined, and the effects of BF with different contents and lengths on the slump, compressive strength, splitting tensile strength, and flexural strength of RAC and BF-reinforced RAC containing NS-modified RA were analyzed. Finally, the filling effect of NS, the toughening and crack resistance mechanism of BF, and the micro-composite effect between NS and BF were analyzed based on scanning electron microscope (SEM) and energy-dispersive detector (EDS) measurement. The results show that the optimum modified concentration of NS solution is 2%, the content of BF is the main factor affecting the mechanical properties of concrete, and the optimum length and content of BF are 12 mm and 0.2%, respectively. For BF-reinforced RAC containing NS-modified RA, the 28 day compressive strength, splitting tensile strength, and flexural strength of RAC increase by 34.28, 40.55 and 54.5%, respectively. Based on SEM and EDS measuring, NS can react with Ca(OH)2 crystal to form flocculent C–S–H gel, which makes RAC compact and enhances the bonding properties of the interfacial transition zone (ITZ) between BF and the matrix.