A novel approach to warm mix asphalt additive production from polypropylene waste plastic via pyrolysis

Abstract

The utilization of waste plastics as an additive in warm mix asphalt (WMA), which is an environmentally friendly technology, by pyrolysis method is an emerging concept. In this study, WMA additive was synthesized from char (C) and wax (W) products obtained from the pyrolysis of polypropylene (PP) type waste plastics. Seven different pyrolysis modified bitumen were prepared as PP 6%C, PP 6%C-3%W, PP 6%C-6%W, PP 6%C-10%W, PP 3%C-6%W, PP 1%C-6%W and PP 6%W. Base bitumen and Sasobit® 3% (by weight of bitumen) modified bitumen were used as control groups. The rheological properties of the binders were investigated by Rolling Thin Film Oven, Pressure Aging Vessel, Rotational Viscometer, Dynamic Shear Rheometer and Bending Beam Rheometer tests, and the morphological properties were analyzed by Scanning Electron Microscope, Fourier Transformed Infrared Spectroscopy and Zeta Potential analysis. Asphalt mixture performance characteristics were evaluated by Marshall Design, Hamburg Wheel Tracking and Thermal Stress Restrained Specimen Tests. Binder test results demonstrated that with the addition of PP 6%C-6%W and Sasobit® 3%, the viscosity of bitumen decreased significantly and accordingly the plant temperature reduced by 14ºC and 9ºC. Besides, PP 6%C-6%W modified bitumen performed better than base bitumen at low, medium and high temperatures. Sasobit® 3% improved the high temperature performance of the bitumen. The additive-bitumen modification mechanism involved physical process. Furthermore, the additives were well distributed in bitumen and no agglomeration was observed. WMA-1 (PP 6%C-6%W) and WMA-2 (Sasobit® 3%) have 5% and 9% higher Marshall stability than hot mix asphalt (HMA), respectively. Moreover, the addition of PP 6%C-6%W and Sasobit® 3% increased the rutting resistance of the mixture by 9% and 21%, respectively. Moreover, PP 6%C-6%W improved the low temperature performance of the mixture by decreasing fracture temperature by 3ºC and increasing the fracture strength by 15%. All in all, PP pyrolysis products have strong indicators to become a WMA additive. © 2023 Elsevier Ltd