Abstract
The efficiency of a nano-silica (NS) treatment method, namely pre-spraying NS suspension on the surface of recycled aggregate (RA), in enhancing strength of recycled aggregate concrete (RAC) was evaluated and compared with that of a traditional NS treatment method by premixing NS with water. Various dosages and particle sizes of NS were considered. Microhardness and scanning electron microscopy tests were performed to investigate the microstructural properties and mechanism. Tests results showed that the NS pre-spraying method had superior effect over the NS pre-mixing method. The optimal NS suspension dosages of 4% and 6% by mass of aggregate were identified for the NS pre-spraying method and the NS pre-mixing method, respectively, whilst NS particle size had little influence on the performance. Such superior performance of the NS pre-spraying method could be ascribed to the better enhanced interfacial transition zone (ITZ) between RA and new mortar, as evidenced by the distinctive increase in microhardness and the formation of low Ca/Si ratio C-S-H in the ITZ.
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