Composite Asphalt Modification with Waste EPDM Rubber and Tire Pyrolytic Oil: Rheological, Chemical, and Morphological Evaluation

Abstract

Waste ethylene-propylene-diene monomer (EPDM) rubber and tire pyrolytic oil (TPO) derived from waste tire pyrolysis have shown promising results for their use in asphalt binder modification. However, their incorporation has shown improvements mainly either on rutting or fatigue behavior of the resultant asphalt binders. Composite modification may be a viable option to achieve improved performance with these two materials. The aim of this study was to evaluate the rheological, morphological, and chemical properties of asphalt binders produced through both individual and composite modifications using waste EPDM rubber and TPO. For composite modification, two different blending schemes were used: (1) sequential addition of TPO and EPDM rubber to the heated base asphalt binder; and (2) premixing of TPO and EPDM rubber prior to addition to the heated base asphalt. In the latter case, before being added to the base asphalt, TPO premixed EPDM rubber was conditioned at two temperatures (25°C and 90°C) to see the effect of different conditioning temperatures in composite modification. Firstly, the conventional properties of all the binders in the unaged state were assessed, followed by the evaluation of short-term-aged binders for Superpave and Shenoy rutting parameters, frequency sweep, zero shear viscosity, multiple stress creep and recovery, and Burger’s modeling. The long-term-aged binders were evaluated through the Superpave fatigue parameter, Glover-Rowe parameter, and linear amplitude sweep. Fourier transform infrared (FTIR) spectroscopy and optical microscopy were used for chemical and morphological analyses. The premixing of EPDM and TPO accompanied with conditioning at 90°C imparted a synergistic effect with improvements in both rutting and fatigue performance of binder. The improvement in performance attributes was ascribed to the preswelling of EPDM rubber with TPO, which was evident from the morphological analysis. FTIR provided evidence of chemical interaction between EPDM rubber and TPO during the conditioning and blending processes.