Study on the impact of recycled plastic introduction methods on the performance of asphalt mixtures

Each year, millions of tons of waste plastic are produced, yet the recycling rate remains low. Incorporating recycled plastics into asphalt pavement construction is a promising approach to utilizing waste plastics beneficially. Various methods exist for introducing recycled plastics into asphalt mixtures; however, most past studies have focused on laboratory-produced plastics-modified asphalt mixtures. Plant production conditions differ significantly from those in laboratory settings and may therefore affect the performance of plastic-modified asphalt mixtures. This study evaluated how plant- and laboratory-based introduction methods of recycled plastics influence asphalt mixture performance, particularly at high application rates. Recycled plastics, a blend of high-density polyethylene (HDPE) and low-density polyethylene (LDPE), were introduced into plant-produced loose asphalt mixtures in the plant and laboratory, respectively. Recycled PE was added at rates of 0%, 0.75%, and 1.5% of the total asphalt mixture mass, respectively. The results showed that the introduction methods had a significant influence on asphalt mixture performance in terms of rutting and fatigue cracking resistance. The addition of 1.5% plastics resulted in a 45.5% increase in cracking resistance for laboratory-introduced mixtures, whereas a 24.4% reduction was observed for plant-introduced mixtures. The absorption of maltenes by recycled PE and the reinforcing effects of recycled plastics are believed to play key roles in performance outcomes. This study demonstrated the importance of using realistic production conditions when evaluating the performance of recycled plastics-modified asphalt mixtures.