Optimization of Asphalt Concrete Performance Using Waste Plastic Bottles (WPB) as a Sustainable Bitumen Modifier: A Comprehensive Rheological and Mechanical Assessment

This study investigated the potential of utilizing Waste Plastic Bottles (WPB) as a sustainable modifier in asphalt pavement mixtures, systematically examining the characteristics of aggregates, the WPB-modified bitumen binder, and the resulting asphaltic concrete mix. Detailed analysis of the aggregate gradation revealed the coarse fraction to be a well-graded gravel, characterized by a uniformity coefficient (Cu) of 2.47 and coefficient of curvature (Cc) of 1.14, indicative of optimal packing density for structural stability. These aggregates exhibited high durability, with an Aggregate Crushing Value (ACV) of 18.3% and Aggregate Impact Value (AIV) of 16.9%, ensuring resistance to abrasion and impact under traffic loads. In contrast, the fine aggregate was poorly graded (Cc = 0.45), highlighting the need for binder modification to enhance overall mix cohesion. Modification of pure bitumen (initial penetration 69 mm) with WPB progressively induced desirable hardening effects and superior high-temperature performance. Penetration values decreased markedly from 69 mm to 33 mm at 25% WPB incorporation, while the softening point rose substantially from 52°C to 81°C, demonstrating enhanced rutting resistance and thermal stability critical for tropical climates like Nigeria's Lagos region. Additional rheological improvements included increased viscosity (up to 2984 p.a.s), flash point (289°C), and specific gravity (1.13), with minimal ductility loss, collectively affirming WPB's role in creating a more resilient binder. Marshall performance testing on the WPB-modified asphaltic concrete further validated these enhancements. The mixture achieved maximum Marshall Stability of 19.74 kN and peak Marshall Quotient of 4.32 kN/mm at 15% WPB content— a 78% stability increase and 34% quotient gain over the control mix (11.05 kN and 3.22 kN/mm). Flow values remained controlled (3.43–4.57 mm), balancing stiffness with workability. These outcomes, aligned with prior pelletized WPB concrete data showing optimal 10–15% thresholds, confirm WPB's efficacy in boosting stiffness, load-bearing capacity, and deformation resistance. Overall, WPB modification yields a mechanically superior, eco-friendly alternative to conventional asphalt, promoting waste valorization while meeting geotechnical standards for durable pavements in sustainable infrastructure projects.