Driving towards better pavements: Through ground tire rubber modification and novel tools for material characterization

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2023-08
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Hallmark-Haack, Brittany
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Cochran, Eric
Williams, R. C.
Tessonnier, J.P.
Mallapragada, Surya
Buss, Ashley
Anderson, Jared
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Chemical and Biological Engineering
Abstract
Over 90% of the roads in the United States are paved with asphalt. Asphalt binder is preferred because its’ adhesion, flexibility, and waterproofing make it valuable for paving purposes. However, in recent years, as traffic grows in load and volume, asphalt binder variability increases, and petroleum refining techniques continue to evolve, unmodified binder is not capable of handling the increasing stress, so it is imperative to improve asphalt properties, such as strength, fatigue, rutting, aging resistance, low temperature cracking. Polymer modification has been proven to help with rutting and cracking resistance, as well as improve aging resistance and thermal susceptibility. Rather than use raw feedstock, Ground tire rubber (GTR) as an asphalt binder additive has proven to be a sustainable, cost-effective way to improve the resilience of the road as well as its viscoelastic properties. Although GTR has many advantages, it is not under widespread use due to its tendency to separate from the asphalt during storage at elevated temperature due to density disparity between the two materials. Simple compounding techniques can produce a GTR product that meets softening point and separation index requirements for storage stability. The first part of this work focuses on optimization of material properties and processing conditions to minimize separation differences, as well as investigate the use of computed tomography scans for increased understanding of separation behavior. The second half of this work focuses on new techniques for material characterization. To produce higher quality, sustainable asphalt pavements, it is not enough to simply explore alternative modifiers. It is important to have tools to effectively describe the structure-property relationships of asphalt binder to fully capitalize on the benefits of asphalt binder. To do this, the asphalt binder composition and properties needs to first be well understood. This can be accomplished by investigating the mechanical and chemical properties of asphalt binder. Flash chromatography for asphalt binder fractionation is investigated to demonstrate the viability of this technique. Stress relaxation curves constructed from measurements obtained by a dynamic shear rheometer in compression mode are compared to bending beam rheometer results for the determination of low temperature properties.
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