Use of nano-silica as a supplementary cementitious material in recycled aggregate concrete: Hydration characteristics, mechanical properties and microstructure assessment

Abstract

Abstract Replacement of natural coarse aggregate (NCA) with recycled coarse aggregate (RCA) is an ideal solution to recycle and utilize the huge amount of construction and demolition wastes (CDW). However, due to the relatively higher porosity and cracking of RCA, its application in the construction industry is restricted. In this study, the RCA was used to completely replace natural coarse aggregate (NCA) for preparation of recycled aggregate concrete (RC). The effects of nano-SiO2 (NS) on the hydration characteristics, mechanical properties and permeability and microstructure of RC were investigated by a range of analytical techniques. The results indicated that the incorporated of NS promoted the hydration progress and enhanced the compressive strength at different ages, while it adversely affected the fluidity. Moreover, the microstructure showed less content of calcium hydroxide and dense interfacial transition zone (ITZ) between RCA and matrix in the RC reinforced by NS due to the nucleation effect and the pozzolanic reaction, thus increased the resistance to chloride penetration and capillary water absorption. The maximum efficiency was obtained when 3% NS was used. This method provides the possibility to use 100% RCA in concrete and helps to maintain the better mechanical properties and durability of RC for a longer period.