Influence of Oxidative Aging on the Chemistry and Rheology of Asphalt Cement From Bolivian, Canadian and Costa Rican Sources
The objective of this thesis is to validate existing specification protocols, to monitor the chemical and rheological properties of Bolivian, Canadian and Costa Rican samples after being environmentally exposed for a year and compare these with samples subjected to standard and modified protocols that simulate long-term aging in the material. The project focuses on the chemical changes obtained in the material after exposure to rigorous oxidation processes and its relation with the deterioration in the ability to release the distresses at low temperatures causing premature cracking and loss of pavement integrity. Within the chemical analysis, Fourier transform infrared spectroscopy and X-ray fluorescence spectroscopy were employed to quantify the degree of oxidation and corroborate the presence of metals originating from recycled engine oil bottoms, respectively. Rheologically, the samples were analyzed in the dynamic shear rheometer, the regular bending beam rheometer (BBR), and the Extended BBR (EBBR), to obtain information related to fatigue and rutting resistance, rheological behavior at low, intermediate and high temperatures, and measure the stiffness at low temperatures after prolonged conditioning times. The ductile failure analysis was carried out using the double-edge-notched tension protocol which provides information about the critical crack tip opening displacement parameter, which is related to fatigue resistance. Finally, using modulated differential scanning calorimetry, the change of the glass transition with the different aging states and different cooling rates is studied. The appearance of unsaturation and increases in oxygen content in the environmentally aged samples lack correlation with the methods that simulate long term aging in laboratory making it impossible to validate the standard protocols. It is necessary to correlate the changes in the chemical structure of asphalt, the susceptibility to the oxidation of its molecules and the performance in service of the material. Besides, it was found that the modification of the binder with REOB and subjecting the asphalt to blowing processes to comply with the specification causes the asphalt to accelerate its oxidation and directly affect its performance in service. Modifications of the existing protocols generated great benefits when it comes to correlating and conditioning the samples more realistically to their state in service.