For sustainable pavement construction, this research paper aims to investigate the feasibility of using Waste Cooking Oil (WCO) and Waste Engine Oil (WEO) as rejuvenators on the rheological properties of aged bitumen extracted from Reclaimed Asphalt Pavement (RAP). The aged bitumen was extracted from milled RAP recruited from an old pavement. The rheological characteristics of the rejuvenated bitumen were determined by penetration, softening point, Brookfield viscosity, Dynamic Shear Rheometer (DSR), and Bending Beam Rheometer (BBR) tests. In addition, the chemical composition of virgin (control), aged and rejuvenated bitumen by WCO, and WEO was investigated using Fourier Transform Infrared Spectroscopy (FTIR) and Energy Dispersive X-ray (EDX). The quality of the rejuvenated bitumen was also evaluated by the Scanning Electron Microscopy (SEM) imaging technique. Based on penetration and softening point testing results, the optimum percentages of the waste oils were found to range from 3.5 to 4.0% for the WCO and from 5.5 to 6.0% for the WEO. The aged bitumen properties were significantly improved by rejuvenators as evidenced by the chemical analysis (FTIR and SEM/EDX) along with the ratio of asphaltenes to maltenes. Furthermore, the surface morphology was renovated as well as the fundamental physical properties of the rejuvenated aged bitumen. Additionally, the rejuvenated bitumen showed less tendency to short-term aging as confirmed by the DSR results. BBR results of rejuvenated aged bitumen samples exhibited comparable performance to those of the control samples at different low temperatures having a performance grade of PG 64-28. Moreover, rejuvenated 100% RAP mixes were found to cope with Egyptian requirements for heavy traffic as binder courses and medium traffic as wearing courses in terms of Marshall stability and flow. Finally, Indirect Tensile Strength (ITS) results were within the specification limits.

Introduction

Despite the limited resources, about 110 million tons of bitumen are used annually in the highway industry worldwide [1]. Bitumen is an organic hydrocarbon material with high thermal sensitivity. Exposure to elevated temperatures during mixing and placement of the Hot Mix Asphalt (HMA), and the environmental conditions throughout the pavement service life, lead to aging of the asphalt binder. The loss of volatiles and oxidation of bitumen (as bitumen is a hydrocarbon material) are the main causes of aging, which result in higher viscosity and stiffer bitumen [2]. Aged bitumen tends to lose its flexibility and turns into a brittle material that is prone to crack easily [3]. There has been an enormous increase in the use of Reclaimed Asphalt Pavement (RAP) worldwide as an economic and environmentally sound alternative for sustainable pavement construction [4–۶]. However, some road authorities are hesitant in encouraging the use of RAP in pavement construction on a large scale due to some limitations. The barriers that limit the use of high RAP percentages (more than 15%) are the high variability in milling processes, mixing RAP from different sources, different properties of aged bitumen than required for virgin bitumen, in addition to one more additional material to care about during HMA manufacturing [6,7].