Effect of rolling thin film oven-aged binders and aging methods on the performance of hot mix asphalt

Age hardening of bitumen has long been perceived as one of the main factors that can significantly affect the durability of bituminous paving materials. When the bitumen is age-hardened, the asphalt mixture will become brittle and its ability to support traffic-induced stresses and strains may significantly reduce. Deterioration of the pavement by readily-induced cracking may follow. In addition, excessive hardening can also weaken the adhesion between the bitumen and aggregate, resulting in loss of materials at the surface layer and generating weakening of the asphalt mixture. Furthermore, the performance of asphalt pavements is found to be very poor in moisture induced situations. Considering this a lot of work has been done on the use of additives in bituminous mixtures as well as on modification of bitumen but none has studied the possibility of benefiting of this weak point. Research has indicated that the addition of polymers to asphalt binders helps to increase the interfacial cohesiveness of the bond between the aggregate and the binder resulting in enhanced properties of the asphalt pavements to help these increased traffic demands. However, the additive that is to be used for modification of mix or binder should satisfy both the strength requirements as well as the economic aspects. On the other hand, the properties of binders in asphalt mixtures change over time during mixing, transportation, and construction whereby as time increases, the stiffer and more brittle the binder becomes. It is generally agreed that aging is primarily associated with bitumen oxidation and the loss of volatile/oily components from the bitumen to the air and/or aggregates during asphalt mixture production (short-term aging) and in-place service period (long-term aging). Both factors cause an increase in viscosity (or stiffness) of the bitumen and consequential stiffening of the asphalt mixture. However, in terms of the effects of the RTFO aging method on asphalt binder aging, studies have shown that it is not only the exudation part of bitumen aging that appears to be of significance, the age time may have added effects on the aging of the asphalt binder. This thesis attempts to provide an improved understanding of the effects of aging methods and aging time on binder and mixture aging. Ethylene-vinyl acetate (EVA) was used to modify the asphalt binder, and asphalt mixtures were artificially aged in the laboratory at five ageing times. The tensile strength and fatigue crack resistance of the mixtures, the rheological properties and chemical composition of aged asphalt binders were determined after different durations of ageing. There were compared to EVA-modified asphalt binder and mixtures at five different proportions. This asphalt binder and mixtures ageing study, utilized two different ageing simulation methods (Short-Term Oven Ageing, STOA) with five ageing times of 45, 85, 125, 165, and 205 min and a new laboratory technique. Short-Term Steam Ageing (STSA) for binder aging by using Steam Cooker. This new technique was used to study the effect of steam and heat on asphalt during storage and asphalt pavement during its service life. Five steam aging duration (0, 15, 30, 45, 60, and 75min) with four steam aging stages at different pressure and temperature for each stage were selected to investigate the physical, rheological properties of steam-aged asphalt binder. Results of the study were subjected to comparative analysis in order to determine the effect of aging time and aging method on the test results in order to have a better understanding of the mechanism of asphalt binder oxidation, which is the main cause of asphalt age hardening Hence, a suitable asphalt binder aging time could be selected for asphalt mixtures in order to show clearer effects of aging time and aging method. Through physical, rheological and mixture tests the following results have been reached: 1. These methods show a well-defined condition and best performed using 2-holes opening with a pressure of 1.10 Milibar and a temperature of 98.8 for 30-minute conditioning time. 2. Increase in viscosity and inoculation in homogenous permeability in case of 2, 3 and 4 halls as compared with 1 hall due to the pressure disturbance of water drainage from the wall openings. 3. Through comparative results of TSR test for the four cases with the limits of specifications, the investigation found that 2-holes give the best result as compared to the other situation. Using RTFO Aged Binder instead of EVA Modified Binder is suitable for some cases especially for physical and rheological asphalt binder test.

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