Workability of stone mastic asphalt and asphalt concrete made by waste plastic pyrolysis

Due to factors such as increasing consumption and changes in living standards associated with population growth, the consumption of plastics has significantly increased in today's world. However, the rapid depletion of existing resources leads to universal issues such as environmental pollution and visual pollution. For these reasons, the recycling of plastic waste is of great importance both economically and environmentally. This study aims to examine the effects of materials obtained from the pyrolysis of waste plastics on the workability of bituminous hot mixtures. Waste nylon bag plastics, including high-density polyethylene (HDPE), low-density polyethylene (LDPE), polyethylene terephthalate (PET), and polypropylene (PP) (weight percentages of 15% HDPE, 30% LDPE, 30% PET, and 25% PP), were subjected to pyrolysis. The solid material (NPP) obtained from the pyrolysis process was utilized to produce modified bitumens at 3% and 5% ratios. Asphalt concrete mixtures were then prepared with these modified bitumens, and the effects on the workability of bituminous hot mixtures were investigated. Additionally, in the study, solid material obtained from the pyrolysis of waste plastic polypropylene was used to produce 5% modified bitumen. Furthermore, 4.5% modified bitumen was obtained with SBS additive. Stone mastic asphalt mixtures were prepared with these modified bitumens, and the effects of these materials on the workability of bituminous hot mixtures were investigated. Penetration and softening point tests were conducted on both pure (B50/70) and all modified bitumens. The Marshall design experiment was conducted to determine the optimum bitumen content (OBC) of the mixtures and to assess their characteristics, including density, void ratio, flow, and stability. As part of the study, the workability of the mixtures was evaluated using the Gyratory Shear Machine (GSM). For Asphalt Concrete (AC), a total of 9 samples were prepared, including three mixture types (Pure, 3%NPP, and 5%NPP) with three samples each (OBC, OBC+0.5, and OBC-0.5). Similarly, for Stone Mastic Asphalt (SMA), a total of 9 samples were prepared, including three mixture types (Pure, 5%PP, and 4.5%SBS) with three samples each (OBC, OBC+0.5, and OBC-0.5), mixed at 155℃ and compacted at 145℃, all with a diameter of 15cm and compacted at 50 gyrations. The results were interpreted by calculating the workability indices using the formula WI = (1/A)*100 at 30 and 50 gyrations. NPP-inclusive hot mixtures demonstrated a positive impact on workability, suggesting its potential use to enhance the mixture's workability. Similarly, it was observed that PP-inclusive hot mixtures exhibited a positive effect on workability, indicating the material's suitability as an additive. However, SBS-inclusive mixtures did not show a significant impact on workability.