Experimental investigation on the performance of waste plastic-modified hot mix asphalt in dry and wet processes

Waste plastic materials have become a current environmental issue, while conventional flexible pavement designs need to improve their appreciable pavement performance by incorporating compatible waste Polyethylene Terephthalate (PET) plastic materials as a bitumen binder modifier. A study experimentally investigated the performance of waste PET plastic-modified hot-mix asphalt in dry and wet processes. The selected plastic material as a partial replacement of bitumen binder of the hot mix asphalt (HMA) is polyethylene terephthalate (PET). Tests based on international test techniques are addressed for bitumen, aggregates, and PET waste plastic materials processing. Gradation, specific gravity, water absorption, aggregate crushing value, flakiness, and soundness are among the tests for aggregates, while specific gravity, ductility, penetration, and softening point tests were bitumen tests established to meet the specifications set in the standards by ASTM, AASHTO, BS, and ERA (Ethiopian Road Authority). After characterization of the materials, the conventional Marshall Mix design of the hot mix Asphalt was performed to get the optimum plastic content of dry and wet processes plastic-modified hot mix asphalt. Plastic-modified asphalt mixture tests, such as moisture susceptibility, flow, volumetric properties, Marshall Stability, indirect tensile strength, and rutting resistance, were conducted and evaluated with respect to the controlled conventional asphalt mixtures. The plastic modified HMA resulted with amended tensile strength, Marshall Stability, and resistance to moisture compared with the conventional control HMA. Under the experimental conditions investigated, Plastic Modified HMA in the wet Process showed uniform binder modification, but the dry process resulted in better stability. The results indicate modified hot mix asphalt with optimum PET plastic content showed enhanced mechanical properties, which can improve its performance and engineering application of the HMA pavement. Later on, optimization of dry and wet process performances was conducted. The methods to optimize these processes, multi-criteria decision analysis, particularly TOPSIS, are implemented. The closeness coefficients of the dry and wet process are 0.97, and 0.49 respectively. Within the scope of this study, the dry process has greater value hence it is selected for its performance over the wet process. Therefore, PET plastic-modified HMA enhanced the Engineering performance of flexible pavement.