Can RAP from Crumb Rubber-Modified Asphalt Mixtures be Recycled Seamlessly as Standard RAP? A Comprehensive Laboratory Study

Abstract The recycling of end-of-life tyres such as crumb rubber (CR) in asphalt mixtures for roads addresses landfill and environmental issues. However, if a reclaimed crumb rubber asphalt mixture (CR-RAP) cannot be recycled, it may defer waste issues rather than offering a true eco-friendly solution. In this work, the future recyclability of dense graded CR-modified asphalt mixtures is investigated. In particular, this work examined the performance of a dense-graded asphalt mixture prepared with CR-RAP added at 15% and 30%. CR-RAP was manufactured in the laboratory by artificially ageing a CR asphalt mixture at two different ageing levels, equivalent to approximately 10 and 20 years of field ageing. Construction aspects, as well as key performance indicators of moisture damage, cracking and rutting resistance, were evaluated. The study revealed that adding more CR-RAP tends to reduce compactability. However, the asphalt mixtures with 15% and 30% CR-RAP added in this study had sufficient compactability. The study revealed that the inclusion of CR-RAP in a mixture does not generate additional moisture resistance issues; instead, it enhances the moisture resistance of the asphalt mixture. Compared with standard RAP, the inclusion of 30% CR-RAP can reduce cracking while improving rutting resistance in the asphalt mixture. Overall, the study suggests that CR-modified asphalt mixtures can be effectively recycled as conventional RAP in dense-graded asphalt mixtures. However, a high content of CR-RAP in dense graded asphalt mixtures might lead to compaction issues during construction if a proper mix design method is not employed.