On the sustainable use of recycled plastics in flexible asphalt pavements

Reusing plastic waste in asphalt has been an ongoing practice because of potential environmental and economic benefits. However, most research has come to contradictory conclusions about the merits of using plastic in road construction. As part of a pre-engineering study for a major pavement trial utilizing recycled plastics in the Regional Municipality of Durham, Ontario, this report documents and discusses test results on plastic-modified binders and mixtures. Locally sourced high density polyethylene (HDPE), low density polyethylene (HDPE), polypropylene (PP) and polystyrene (PS) waste plastics were used to modify asphalts. It was found that high temperature binder grades improved while low temperature grades were relatively unaffected. Plastics increase strength but reduce strain tolerance in ductile failure. Hence, only binder course layers should be modified to prevent undue risk for premature and excessive surface cracking. Hamburg wheel tracking tests on mixtures showed rather uneventful findings at 50 degrees C. In contrast, modified mixes were significantly less strain tolerant in ductile failure. In order to accommodate significant amounts of plastic and realize overall improved performance, it is proposed that the base asphalt is adjusted to a softer grade. This facilitates high additive contents to produce a rut resistant mix without sacrificing ductile failure properties.