Development of nano-silica treatment methods to enhance recycled aggregate concrete

The reuse of recycled aggregates (RA) for producing recycled aggregate concrete (RAC) is a promising way to alleviate the environmental impacts and improve construction sustainability. Because of the inferior properties of RA than natural aggregate, pre-treatments of RA are commonly considered to improve the performance of RAC. In this study, three nano-silica (NS) treatment methods, i.e., pre-spraying plus air-drying, pre-spraying without air-drying and pre-soaking plus air-drying, were adopted and evaluated systematically by varying the dosage and the particle size of NS suspension. The mechanical properties and durability of RAC such as compressive strength, elastic modulus, rate of water absorption and chloride penetration resistance were evaluated. For the microstructural assessment, the micro-hardness test was conducted to investigate the influence of these NS treatment methods on the old mortar and the new mortar near the interface. The experimental results showed that the NS pre-spraying treatments were superior to the NS pre-soaking method and the pre-spraying without air-drying was the best in terms of the enhancement in mechanical properties and durability. The optimum dosage of NS suspension for pre-spraying was 3% of RA by mass and a larger particle size of NS would be more effective. In addition, the microhardness of both the old mortar and the new mortar near the interface were enhanced after using the three NS treatment methods, and the microstructure enhancement of the latter played a more important role for the enhancement of the performance of RAC.