Exploring the Rheological Behavior of LDPE-Modified Bitumen: Influence of Plastic Source

ABSTRACT Using plastic waste as a polymer substitute for modification of bitumen presents a promising avenue to improve the sustainability of road infrastructure. This approach is cost-effective and aligns with the sustainability approach of the circular economy. This research assesses the impact of various plastic sources on the rheological behavior of the modified bitumen in both linear viscoelastic (LVE) and nonlinear viscoelastic (NLVE) domains. Conventional viscosity grade (VG 30) bitumen has been modified using low-density polyethylene (LDPE) waste plastic from four distinct sources (named as LDP, LDF, LDPU, and LDS). The weight ratio of sulfur and LDPE is 1:3. The combination of both has been referred to as plastic modifier, and the combined modifier content was 6 % by weight of modified bitumen, as optimized based on storage stability. Results indicate a minimal influence of plastic sources on LVE behavior, whereas a significant effect is observed in the NLVE domain. Among the four modified bitumen types (LDP, LDF, LDPU, and LDS), LDPU exhibits superior resistance to permanent deformation, whereas LDF shows higher elasticity at high temperatures. Additionally, LDS has the highest fatigue life, followed by LDF. This research finds a significant influence of plastic sources on rheological performance, particularly evident at intermediate temperatures. Prior literature emphasizes the dominance of the degree of crystallinity (DOC) of polymers in defining modified bitumen rheology, where higher DOC corresponds to higher resistance to permanent deformation and lower resistance to fatigue damage. However, this study identifies that DOC is not the only parameter that dominates the behavior; the melt flow index (MFI) of polymers also plays a crucial role in defining the rheological properties of bitumen in the NLVE domain, although the relative dominance between DOC and MFI remains undetermined. Overall, the modified bitumen exhibits improved performance at higher and intermediate service temperatures.