Nano-modified recycled aggregates via vacuum impregnation: Towards stronger and durable recycled concrete

For the first time, this study aimed to enhance the quality of recycled aggregates (RAs) by employing nano-silica (NS) and the vacuum impregnation technique. Specifically, RAs experienced water immersion, ordinary and vacuum impregnation with 2 % NS slurry, and vacuum impregnation with 4 % NS slurry. Subsequently, these nano-modified RAs were incorporated into concrete mixes, and their strength and durability were assessed. Following this, an examination of the pore structures and properties of the interfacial transitional zones (ITZs) in recycled concrete was conducted. The results demonstrate that in contrast to ordinary pretreatment methods, concrete containing nano-modified recycled aggregates after vacuum impregnation exhibits better compressive strength (+18.39 %) and reduced chloride ion penetration (−17.90 %), which is attributable to a more compact pore structure and enhanced ITZs. The findings prove that vacuum impregnation significantly enhances the modification impact of NS on RAs when compared to conventional impregnation methods, owing to the reduced agglomeration effect of NS in concrete. •Vacuum impregnation improves the modification of NS on RC.•RC strength and durability enhanced owing to refined microstructure.•Vacuum impregnation outperformed other methods based on ITZs features.•Reduced NS agglomeration explains vacuum impregnation's benefits.