Effects of surface treatments of recycled tyre crumb on cement-rubber bonding in concrete composite foam

The uptake of recycled tyre crumb (RTC) in concrete can result in a significant loss of strength because of weak adhesion between cement and rubber. Five RTC surface treatment methods (cement coating, silica fume coating, sodium hydroxide, potassium permanganate and sulphuric acid soaking) were used to mitigate strength loss in concrete composite foam with RTC. All five methods yielded strength improvements between 27% and 56%, with sulphuric acid and silica fume coating having the largest improvement. Silica fume coating, a treatment method used for the first time, improves strength because of the better adhesion between RTC and mortar. In addition, the formation of low Ca/Si gels was observed at the rubber mortar interface based on SEM-EDS analysis. A reduced water contact angle on rubber showed that the three soaking methods were able to successfully reduce the hydrophobicity of RTC. Microscopic analysis of sulphuric acid treated RTC revealed etching of the surface and possible formation of polar zinc sulphate crystals. Silica fume coating provides an economically feasible solution with less safety and environmental risks associated compared to the chemical treatments. (C) 2018 Elsevier Ltd. All rights reserved.