Mechanical and Durability Performance of Concrete Made Using Waste Tyre Rubber as Coarse Aggregate

Waste tyres derived from automobiles are difficult to recycle due to a complex polymeric matrix and additives used in tyre manufacturing. This has resulted in more waste tyres being disposed in landfills or incinerated, while granulated waste tyre rubber (WTR) could have been used in construction as a replacement material for mineral aggregates in concrete. This study aimed to produce structural concrete (with a minimum characteristic strength of 25 MPa at 28 days) using 13 mm WTR as a partial replacement for the coarse mineral aggregate at replacement intervals of 5, 10, 20 and 30% by volume, while maintaining a constant water-to-binder (w/b) ratio of 0.40. Results indicate a significant reduction in the mechanical strength and durability (oxygen permeability and water sorptivity) index of concrete with increased WTR replacements. Portland cement (PC) was partially replaced with 15% condensed silica fume (CSF) by mass to enhance the strength and durability performance of concrete. Results showed that the strength of concrete made using PC decreased by 63.8% from 67.1 to 24.3 MPa when comparing the control mix and concrete at 30% WTR replacement. Furthermore, at 30% WTR replacement for concrete made using PC, the oxygen permeability index decreased by 13.5% from 10.19 for the control mix to 8.81, which indicates poor durability performance, while the water sorptivity index increased significantly at 20 and 30% WTR replacements compared to the control mix with the water sorptivity index of 9.35 mm/h(0.5). It was also observed that concrete mixes made using CSF had a higher strength and improved durability compared to those containing PC alone. The results from this study indicate that WTR could be used in concrete for structural applications, while reducing the demand for mineral aggregates mined and waste tyres incinerated or disposed in landfills.