Permanent deformation characteristics of modified thin overlay bitumen mixtures comprising waste polymers

Abstract

Using Thin Asphalt Overlay (TAO) as a maintenance or preservation layer is a promising technology supporting the development of the sustainable paving industry; any upgrades to such techniques in terms of mechanical, volumetric, and durability characteristics of the resulting pavement are thus extremely valuable. Permanent deformation represents one of the main mechanical characteristics of asphalt mixtures; thus, the aim of the current research was to evaluate the permanent-deformation characteristics of modified TAO mixtures utilizing waste polymers. Processing the investigation involved preparing the polymer modified asphalt (PMA) with dual additives kinds: Crumb Rubber Modifier (CRM) and Low-Density Polyethylene (LDPE). The Superpave design method was followed to determine the resistance to permanent deformation parameters in each mixture using the Wheel Tracking (WT) test. The prepared PMAs were comprised of 5 to 25% of 250-µm crumb rubber with or without the adding of 0, 2.5, 5.0, 7.5, and 10.0% LDPE. The results demonstrated that the addition of 15% CRM to the asphalt binder created a binder that was better able to resist permanent deformation while offering acceptable binder characteristics in term of workability. Asphalt binder was seen to become harder, having a higher viscosity with such additions, increasing the stiffness of binder and creating a consequent stiffening of the mixture. Similarly, when LDPE was added, an increase in resistance to permanent deformation was clear, with the laboratory work and the data analysis both showing that for different ratios of LDPE, an increase in the rut depth occurs at 5% LDPE, while increased proportions of polyethylene reduce rut depth and improve rutting resistance performance. Utilizing this effect is supported by the general trend to reuse larger quantities of waste materials to reduce the damage of collection and storage of such materials.