Microstructure and physical properties of concrete containing recycled aggregates pre-treated by a nano-silica soaking method

In this work, the properties of nano-silica improved recycled aggregates (NS-RAs) and concrete containing these aggregates have been examined. First, RAs were soaked in nano-SiO2 solutions with five different concentrations (0, 1.0, 1.5, 2.0, and 2.5 wt%), after which the crushing indices and water absorptions of the resulting NS-RAs were determined to identify the optimal soaking conditions. The obtained results showed that the optimal concentration of nano-silica was 2%, which reduced the NS-RA crushing index by 28% as compared with that of untreated RAs. After adding this content of NS-RAs to concrete during preparation, its compressive strength was increased by 20%. Thus, the nano-silica soaking method was proven to effectively heal the defects of RAs and compensate for the loss of the compressive strength of RA-modified concrete.