Integrated Mechanical and Volumetric Evaluation of Plastic Modified RAP Mixtures Using Marshall Parameters

This study investigates the combined influence of plastic waste modification and centrifugal extraction on the mechanical and volumetric performance of reclaimed asphalt pavement (RAP) mixtures. Five plastic types (LDPE, HDPE, PET, PP, and PVC) were incorporated at 0–8% by asphalt weight, and performance was evaluated through standardized centrifugal extraction and Marshall testing in accordance with Bina Marga 2018. Extracted asphalt contents ranged from 4.22% to 5.87%, demonstrating reliable binder recovery within the RAP system. Plastic incorporation significantly improved mechanical performance, with maximum Marshall stability reaching approximately 1300 kg and Marshall Quotient exceeding 350 kg/mm, indicating enhanced stiffness and deformation resistance. Despite increased rigidity, flow values remained within the specified 2–4 mm range, and density values (2.28–2.33 g/cm³) showed minimal variation, confirming stable compaction behavior. Volumetric parameters generally complied with specification limits, although higher plastic contents slightly affected air void balance. Moderate plastic contents (4–6%) provided the most balanced performance. The findings establish a comprehensive framework for evaluating plastic–RAP interaction and demonstrate the technical feasibility of integrating plastic waste into RAP mixtures for sustainable pavement applications.