An industrial applicable method to improve the properties of recycled aggregate concrete by incorporating nano-silica and micro-CaCO3

Reutilization of waste concrete is gaining worldwide popularity for promoting the sustainable development. To improve the properties of recycled aggregate concrete (RAC), in this work an industrial applicable mixing method was applied to strengthen recycled aggregates by using ultra-densified slurry. Nano-silica with high reactivity was incorporated in the strengthening surface-coating slurry. The nanoparticles accelerated cement hydration, promoted pozzolanic reaction, and increased the content of C–S–H gel. However, the strength enhancement of RAC diminished with time, for which CaCO3 microparticles were added to overcome this drawback. The combination of nano-sized and micro-sized particles not only improved the particle dense packing of binders but also promoted the multilevel hydration of cementitious materials. The phase compositions and thus the nanoscopic mechanical properties of both mortar matrix and new interfacial transition zone were subsequently improved. The proposed industrial applicable method that fully exerted the filling effect, activity effect and acceleration effect of nano-SiO2 and micro-CaCO3 optimized the microstructure of RAC and thus improved its properties.