Understanding the Storage Stability of Polyethylene Modified Binders: A Laboratory Case Study Using Waste Plastics

The aim of the study is to understand and achieve storage stable, compatible plastic-modified asphalt binders. In view of global plastic accumulation, the potentiality of polymeric waste plastics is evaluated as an asphalt binder modifier; providing an alternate recycling option. However, due to phase separation issues between asphalt and plastic, the usage of waste plastic is preferred through dry mixing in asphalt mixture. In this study, the compatibility of polyethylene-modified asphalt binder was assessed along with appropriate parameters that can explain the actual phase separation occurring during storage stability testing. Two types of plastics including low-density polyethylene (LDPE) and high-density polyethylene (HDPE) were blended with a PG 58-28 neat binder after assessing their melting behavior along with polystyrene (PS) and polyethylene terephthalate (PET). The impacts of polyethylene size (2.36-1.18 mm, 0.6-0.3 mm, less than 0.3 mm), blending time (30, 60, 120, 180 min), hot storage duration (0, 24, 48 h), and compatibilizers (styrene-butadiene-styrene, nanosilica, corn oil, polyphosphoric acid) on the storage stability were assessed. G*/Sin delta was used as an initial measure to assess the separation index (SI) value. The results concluded that polyethylene is observed to be inert to asphalt and phase separation persists irrespective of size and compatibilizer. Nanosilica at a dosage of 0.5% was able to partially compatibilize (SI value improved from 5.4 to 1.87) PE with asphalt. Also, in the need for better parameters to better understand the phase separation, percentage recovery, fluorescence microscopy, and black space analysis were identified as proper tests to detect phase separation.