Surface modified used rubber tyre aggregates: effect on recycled concrete performance

Although research has found that using rubber in concrete will enhance its resilience and reduce its density, the significant loss of strength owing to lack of bonding has remained unresolved. This study considers how to minimise the loss of strength of concrete with used rubber tyre crumb aggregates and investigates the improvement of water permeability resistance that may consequentially develop. A surface of rubber crumb was modified by soaking in the saturated sodium hydroxide solution or silane coupling agent (SCA) before using. Up to 20% of natural fine aggregate was volumetrically replaced with treated rubber crumb. Experimental results show higher compressive and flexural strengths, Young's modulus and water permeability resistance from the samples with SCA-treated rubber than with as-received or sodium-hydroxide-treated rubber. X-ray diffraction pattern analyses indicate almost no change in crystalline phase for the rubber surface modification. Microscopic inspections show an enhanced rubber-matrix adhesion with the use of SCA. Results of mercury intrusion porosimetry reveal that concrete with SCA-treated rubber has a similar pore size distribution to the other three mixes, but achieves the lowest porosity and highest tortuosity, resulting in the best water permeability resistance. A brief cost analysis suggests that this method of surface modification is economically viable.