Modification of asphalt binder by the blend of chemically grafted thermoplastics and SBS: Influence of blend composition, chemical grafting, sulphur content, and MFI value

Thermoplastic elastomers, such as styrene–butadiene–styrene (SBS), significantly enhance the properties of asphalt binders. This study first highlights the drawbacks of binder modification using chemically grafted polyethylene (g-PE) and then demonstrates the process by which g-PE can be used in combination with SBS. The important role of chemical grafting, sulphur content, and melt flow index (MFI) value in obtaining practically usable ‘g-PE/SBS’ modified binders have been illustrated. The results show that ungrafted and g-PE produces modified binders with highly inferior properties, and the polymers phase separate from the binder within few hours of preparation. % Elastic recovery of the ungrafted and g-PE modified binders was < 30%, and the softening point was 10 to 25 °C lower than SBS modified binders. Modification using the ‘50/50’ g-PE/SBS blend also resulted in inferior modified binders. On the other hand, the ‘25/75’ g-PE/SBS blend resulted in modified binders with properties similar to SBS modified binders. Chemical grafting, sulphur content of 0.21 wt.%, and melt flow index value > 2 are the essential factors that resulted in acceptable ‘25/75’ g-PE/SBS modified binders. Cost analysis shows that the use of g-PE can reduce the overall cost of asphalt pavement. The strategy illustrated in this study can be adopted for low-cost polymers and the effective utilization of waste plastics.