Assessing the blending of recycled LDPE flakes with bitumen in mixtures using rheological and thermal properties: a case study

Despite growing interest in asphalt mixtures modified with low-density polyethylene (LDPE), the industry lacks clear guidelines to reliably produce these materials, particularly with the dry method where the role of melted plastic particles is unclear. This paper assesses the blending potential of recycled LDPE flakes with bitumen introduced by the dry method and develops a methodology to estimate how much plastic functions as a binder modifier. Five mixtures were compared: four laboratory-produced mixtures (0% and 1% LDPE, unaged and short-term aged) and one plant-produced mixture with 1% LDPE. Bitumens were extracted and recovered (E&R) to evaluate LDPE presence through rheological and thermal analyses. The results indicated that most LDPE remained dispersed as fibres/particles with aggregate, but a small fraction systematically modified the binder, notably in plant-produced mixtures. Workability testing further suggested LDPE primarily functions as a mixture modifier rather than as a bitumen modifier in the dry process.