Production and use of crumb rubber for bitumen modification from end-of-life passenger car tyres in comparison with truck tyres: a comprehensive study on bitumen and asphalt performance

Abstract

The use of crumb rubber (CR) from shredded end-of-life vehicle tyres in road engineering practices has become increasingly popular as a method of enhancing sustainability. Historically, crumb rubber produced from end-of-life tyres only used sources of rubber with high natural rubber content. This approach was believed to enhance the final properties of the crumb rubber modified binder, hence also providing betterments to the asphalt mix. The presence of a lower volume of textile fibre in radial truck tyres (TT) also contributed to the recycling of these type of tyres for road applications. However, with the development of more efficient recycling machines, and with the raised awareness that passenger car tyres are available in a much larger quantity, new research is needed to explore the suitability of recycling passenger car tyres (PCT) for bitumen modification. This study aims to evaluate the possible use of PCT in bitumen by studying its performance and comparing it to the performance of the same bitumen modified with TT and S45R (a commercial crumb rubber modified binder). Different percentages of PCT CR and TT CR were added to a neat binder, and their composition and performance were analysed through a series of physical, chemical, and rheological tests. The results indicate that adding PCT CR to neat bitumen can significantly improve the temperature susceptibility, elasticity, hardness, and stiffness of the binder, thus improving the rutting performance and resistance to fatigue similar to what TT CR can do. From a direct comparison, the performance of PCT CR modified binders is very similar to TT CR, especially at lower CR content (i.e. below 10%). Additionally, PCT CR in the approximate range of 13–16% by weight of bitumen would provide similar results to the commercially available S45R binder for most of the tests conducted. Consequently, selected binders and modified binders (with 15% and 20% CR) with a warm mix additive were used to produce a gap graded asphalt mix for mechanical behaviour evaluation on compactability, moisture resistance, non-damage viscoelastic behaviour, cracking, and rutting resistance. The study found minimal differences between the two sources of rubber (PCT and TT). Overall, PTC were found to be suitable to produce CR for bitumen modification through the wet process.