Tire-Derived Aggregate Modified Using Postconsumer Recycled Plastics for Subsurface Pavement Applications: A Study of Absorption and Swelling Effects

The major objective of this research study, believed to be the first of its kind, was to explore the swelling and absorption rate of tire-derived aggregate (TDA) modified using postconsumer recycled (PCR) plastics in optimum blend proportions. Further, TDA was utilized in developing plastics-modified rubberized asphalt mixtures through an innovative semi-dry approach aimed at applications in subsurface layers, such as the base or subbase of a pavement system. The research included: (i) physical and thermochemical characterization of raw materials; (ii) blending of 16 combinations of PCR plastics-modified asphalt (PA) binder; (iii) rheological assessment of PA blends, including performance grade, multiple stress creep recovery, and optimization; (iv) preparation of 18 combinations of modified TDA (MTDA) products utilizing optimized PA blend; (v) asphalt absorption tests on TDA and MTDA to determine swelling and asphalt absorption rates; and (vi) microscopy of MTDA particles. Thermochemical characterization revealed promising binding compatibility of TDA, PCR plastics, and hydraulic lime (HL), owing to their distinct thermal and chemical properties, while rheological assessment confirmed that PA blends with higher polyethylene terephthalate dosages significantly improved rutting resistance and elasticity for TDA modification. Additionally, the inclusion of PCR plastics and HL in MTDA reduced the absorption capacity and uncontrolled swelling of the unprocessed TDA three- or four-fold. It is envisioned that this study will promote a feasible waste management solution to address recycling of both waste tires and plastics by conserving natural resources and pave the way to create perpetual and resilient infrastructure.