Investigating the applicability of storage stability test for waste plastic modified bitumen: Morphological analyses

Abstract

Plastics have proven as effective modifiers for asphalt binders; however, significant knowledge gaps exist around appropriateness of standard method of storage stability test and phase separation mechanism. These gaps are even more critical when using waste plastics containing polymeric cross-contamination. This study addresses these gaps through the application of asphalt tests, fluorescence microscopy (FM) and image processing techniques. The FM and image processing results showed that there is a relationship between elevated plastic swelling rates and plastic dispersion in bitumen matrix. Quantitative analysis of the images indicated that LDPE and LLDPE modified binders exhibited the lowest level of phase separation (5 %), followed by HDPE modified binder (13 %), and PP modified binder showed the highest level (20 %). Furthermore, cross-contamination of LDPE, LLDPE, and HDPE with PP notably worsened the storage stability of the resulting modified binders by approximately 10 %. The findings from FM and image processing indicated that the softening point test conducted through the storage stability tube test is insufficient for assessing the storage stability of plastic modified binders. To further validate this point, asphalt performance was examined for asphalt mixtures made with the binders before and after storage stability test. The findings demonstrated a substantial influence of phase separation of binder on key properties of the resulting asphalt mixture.