Effects of nano-SiO2 modification on rubberised mortar and concrete with recycled coarse aggregates

Abstract With the recent acceleration of industrialisation and urbanisation, increasing quantities of demolished construction waste and waste tyres are being produced. The production of recycled coarse aggregate (RCA) and rubber particles from this waste, for use as partial or full replacements of normal aggregate in cement concrete, is attracting attention as a solution to the problem of solid waste management. However, the greater incidence of defects in RCA and rubber particles than in normal aggregate limits their application in construction industries. This study evaluated an economic and environmental approach to optimise the performance of rubberised concrete with RCA. Two types of nanomaterials, nano-SiO 2 (NS) solution and NS sol–gel, were used to pretreat RCA and rubber. The effect of the treatment time on the physical properties of the RCA was tested, and the mechanical properties of the rubberised mortar prepared with pretreated rubber were investigated. In addition, a compression test for the rubberised recycled aggregate concrete (RRAC) was designed using the Taguchi method. The effects of four factors (water–cement ratio, rubber content, rubber size, and aggregate treatment) on the stress–strain curve, compressive strength, elastic modulus, specific toughness, and failure patterns of RRAC were also analysed. The results showed that the NS-treated RCA exhibited lower water absorption rate and better mechanical properties. Moreover, the NS-modified rubber enhanced the compressive and flexural strengths of the rubberised mortar by 35 and 17%, respectively. Interestingly, it was found that simultaneous treatment of both RCA and rubber could negatively affect RRAC. Scanning electron microscopy indicated that NS improved the interfacial transition zone separating RCA and rubber from the cement matrix, whereas the pretreated RCA tended to bond with the pretreated rubber in RRAC.