Using waste oils in bitumen modification for sustainable asphalt pavements

In today's context where sustainable transportation objectives have come to the forefront, minimizing the environmental impacts of materials used in road construction and ensuring more efficient resource utilization have become increasingly significant. Particularly, the environmental concerns associated with the production and use of bituminous binders have intensified interest in alternative material solutions. In this regard, research efforts have focused on the reuse of waste materials and the extension of existing materials' service life. The use of waste oils as rejuvenators in bituminous binders presents an environmentally friendly approach and has proven to be an effective method in mitigating performance deterioration caused by aging. This thesis aims to develop a sustainability- and performance-oriented solution by refunctionalizing aged bituminous binders through modification with waste oils. The study investigates the rejuvenation of both short-term and long-term aged bituminous binders using waste cooking oil, industrial oil, and motor oil. Considering the inadequacy of existing laboratory methods in reliably simulating aged binders, a novel laboratory method—a forced air circulation oven system—was developed to produce sufficiently homogeneous and consistently aged binder samples. In addition to the reference pure binder and binders artificially aged in the laboratory using the newly developed method, a total of 21 binder samples were prepared, including three different modification ratios (1%, 3%, and 5%) for each waste oil type. The physical properties of the binders were analyzed using standard binder tests. The physicochemical and structural characteristics of bitumen and waste oils were characterized using Fourier Transform Infrared Spectroscopy (FTIR) for functional group analysis, Scanning Electron Microscopy (SEM) for surface morphology, Energy-Dispersive X-ray Spectroscopy (EDS) for elemental composition, and X-ray Diffraction (XRD) for crystalline structure determination. To evaluate rheological performance, Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR) tests were conducted in accordance with the Superpave system, enabling analysis of high-temperature rutting resistance and low-temperature cracking susceptibility. At the mixture level, aggregate gradations were selected following Superpave mix design guidelines, and optimum binder contents were determined. The durability of prepared mixtures under moisture conditions was assessed through Indirect Tensile Strength (ITS) and Tensile Strength Ratio (TSR) tests. Moreover, Hamburg Wheel Tracking (HWT) tests were performed to investigate rutting resistance in detail. The experimental findings revealed that the effects of different waste oil types and modification rates on bituminous binders vary significantly depending on aging conditions. Waste cooking oil demonstrated superior rejuvenation performance, particularly in terms of physical and chemical properties, whereas waste motor oil exhibited superior results in critical mixture performance parameters such as strength, moisture sensitivity, and rutting resistance. In short-term aging, the highest TSR values were obtained with waste cooking oil, while in long-term aging, the highest TSR value of 110.5% was recorded with 1% waste motor oil. Furthermore, the best rutting performance, indicated by the lowest rut depth of 1.71 mm, was also achieved with 1% waste motor oil, highlighting the long-term performance advantages of this modification.