Evaluating the Contribution of Asphalt Binder from Recycled Asphalt Shingles in Asphalt Concrete
Type of DegreeMaster's Thesis
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The use of Recycled Asphalt Shingles (RAS) to replace a portion of the virgin asphalt binder in asphalt mixtures has been increasing over the past several years due to environmental and economic motivations. Yet, since shingle asphalts are much stiffer than paving asphalts, there are concerns that the shingle asphalt may not be completely activated as a binding material which could result in under asphalted mixtures, or that the composite binder created by the blended shingle asphalt and virgin asphalt may not have suitable characteristics to resist cracking under load and environmental conditions in pavements. This research studied RAS using three approaches. First, the effects of the individual components of RAS on asphalt mixtures were studied by separating the shingle asphalt and shingle aggregates and fibers. These were used separately to replace a portion of a control virgin mixture and compared to a similar 5% RAS mixture. Second, the effect of mixing temperature on RAS containing asphalt mixtures was studied by mixing and compacting a 5% RAS mixture at temperatures ranging from 250°F to 350°F. Third, the mixtures described above were compared to the properties of plant-mixed laboratory-compacted mixtures. It was found that the shingle aggregates and fibers do not appear to significantly affect the cracking resistance of the mixture. The shingle asphalt may increase the stiffness and lower the cracking resistance of RAS containing mixtures. Also, increasing the mixing temperature increases the stiffness of the mixture. This increased stiffness may be caused by increased activation of shingle asphalt in RAS containing mixtures, and increasing the mixing time and/or storage time may additionally increase the percentage of activated shingle asphalt. Finally, further aging or increased mixing temperatures of laboratory produced RAS containing mixtures may be needed to better match to plant produced properties.