Waste tyres crumb rubber as a sustainability enhancer for polymer-modified and hybrid polymer-modified bitumen

The increasing amount of waste vehicle tyres has already proved to be hard to dispose of properly and lead to environmental problems, such as soil contamination and toxic blazes. This study aimed to use recycled tyre rubber material (crumb rubber - CR) and combine it with well-known polymers in road engineering, such as styrene–butadiene-styrene (SBS) and/or a combination of SBS and ethylene-vinyl acetate (EVA) to develop hybrid recycled polymer modified bitumen (PMB). Most of the times, CR is only added to neat bitumen at high contents to enhance its properties despite some drawbacks. Physical, chemical, thermal and rheological tests were conducted to evaluate the overall performance of the blends with and without the addition of stabilising agents. CR has shown to increase the viscosity of the bitumen. The addition of EVA into CR/SBS blends has simultaneously improved the rheological properties specifically at intermediate and high temperatures. To conclude, the utilisation of small percentages of recycled tyres in PMBs and hybrid PMBs did not negatively affect the satisfactory performance of SBS-modified bitumen. This consequently encourages greater usage of CR which also mitigates the waste disposal problem at landfills.