Utilization of waste polyethylene terephthalate (PET) as partial replacement of bitumen in stone mastic asphalt

Stone mastic asphalt (SMA) is known for its superior performance and durability compared to other forms of asphalt concrete mixtures. However, it requires high asphalt binder, typically 6-7% of the dry mix weight and the modified binder is always essential for further improvement of its performance. These two requirements make SMA mix more expensive than other forms of asphalt mixes and hinder its selection despite superior performance properties. At the same time, several studies have been done trying to lower the investment cost for SMA and other forms of asphalt mixes. One promising option is incorporating recycled plastics in the mix by dry or wet processes. Whereas several studies incorporated recycled plastics as additives or part of the filler materials in SMA mixes, this study evaluates the viability of partially replacing asphalt binder by using recycled Polyethylene Terephthalate (PET). Unmodified asphalt binder was used, and its optimum content (OBC) was established by marshal design method, and appropriate PET value to partially replace part of OBC without jeopardizing the mix performance properties was established. The mix with PET was further evaluated against moisture damage, rutting and fatigue failure. After the extensive mix laboratory testing, the results show that 10% of PET by weight of the binder can replace the binder without affecting the mix performance requirements. Moreover, the SMA mix with 10% of PET by binder weight shows satisfactory resistance against moisture damage. Similarly, the well-compacted mix shows a long fatigue life. Dynamic modulus test shows a promising performance at low to medium temperatures and high loading frequency. However, it shows a poor performance against rutting at high temperature and low loading frequency, highlighting the necessity of a modified binder.