Verification of High-RAP Mixtures Including Recycled Plastic Compound: From Lab-to Plant-Production

Discrepancies between the engineering properties of laboratory-optimised and plant-produced asphalt mixtures often undermine the validity of laboratory mix design studies. This may be particularly relevant in the case of innovative or unconventional mixtures, like those containing a great amount of recycled materials like RAP and waste plastics. This paper aims to bridge the gap between laboratory research and practical implementation by comparing lab-produced (LP) and plant-produced (PP) mixes containing 50% RAP and a recycled plastic compound (RPC). Different dosages of RPC were incorporated through the hybrid modification method. For comparison, a reference mixture containing a polymer-modified bitumen (wet modification) was prepared to assess differences between the hybrid and wet modification approaches. The study examined the validation of the laboratory mixing procedure, the effect of several RPC dosages, and the performance of different modification methods by analysing key engineering properties, including volumetric, workability, and mechanical characteristics. Similar stiffness and strength properties observed among all investigated mixtures confirmed the reliability of the mix design study and the adopted laboratory mixing procedure. However, all PP asphalt mixtures exhibited lower workability compared with their LP counterparts. Moreover, hybrid-modified mixtures outperformed the reference wet-modified mixture across all investigated parameters, with no adverse effects observed as the RPC content increased.