Influence of Non-Melting Waste Plastics on Volumetric Properties and Performance of Asphalt Mixtures

Abstract

The main objective of the study is to evaluate the impact of using polystyrene (PS) and polyethylene terephthalate (PET) plastics as an additive in asphalt mixtures. For this purpose, volumetric modification, moisture susceptibility along with performance variation at high, intermediate, and low temperature conditions were evaluated. Initially plastics were subjected to calorimeter analysis for assessing their melting characterization. Both PS and PET are included as dry mix additives individually at dosage levels of 3%, 6%, and 9% by weight of asphalt binder. Further, the changes in thermal properties of plastics occurring during mixture preparation were correlated to better understand the volumetric modification. PS, owing to its glass transition and partial amorphous nature, exhibited minimum deviation (<1%) from design air voids (4 ± 0.5%). PET was observed to increase the volumes of voids in mineral aggregate (VMA) and air void, owing to its crystalline nature. As regards performance, PS and PET modification enhanced the moisture resistance by 1.05 to 1.11 times the control mixture. The rutting tolerance index (RT_index) value increased for all plastic modified mixtures from the indirect tensile asphalt rutting test (IDEAL RT) performed at 58°C. However, the intermediate temperature cracking tolerance index (CT_index) at 19°C conveyed the high embrittled nature from plastic modification making the mixtures more susceptible to cracking. From the G_f versus l₇₅/m₇₅ interaction diagram, it was conveyed that although addition of plastics improves the fracture toughness of asphalt mixtures, the ductile nature of mixtures is compromised. Also, PS and PET modification could not improve the ability of asphalt mixtures to resist thermal cracking, evaluated at −18°C.