Comparing Wet Mixed and Dry Mixed Binder Modification with Recycled Waste Plastic

Recycled plastic is now recognised as a potential bituminous binder extender and modifier, with various studies demonstrating the potential to improve asphalt mixture properties, including resistance to cracking and resistance to deformation. Many waste plastic products are intended to be dry-mixed into the asphalt production plant, but wet mixing into the bituminous binder is also possible. Laboratory tests for fracture resistance, moisture damage resistance and deformation resistance were used to compare otherwise identical wet-mixed and dry-mixed recycled plastic modified asphalt, as well as comparison to nominally identical control (unmodified) asphalt. The binder was also extracted from tested specimens and compared using common index properties, including elastic recovery, softening point and penetration. The effect of recycled plastic on the asphalt mixture properties and the binder properties was a generally significant improvement in deformation resistance, with no reduction in fracture resistance. Importantly, the wet-mixed and dry-mixed results were generally not significantly different, indicating that the two mixing processes are equally effective. Further research should focus on the practical issues of distribution and digestion of recycled plastic through the asphalt mixture during dry-mixing, as well as digestion and storage stability of wet-mixing into bituminous binder.