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Evaluation of Tire Rubber-Modified Asphalt Mixtures
AdvisorSebaaly, Peter E.
Civil and Environmental Engineering
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In the late 1960’s, the use of scrap tire rubber (TR) started in Arizona, USA with the intent to modify the properties of asphalt binders used in paving applications. Nevertheless, few States allowed its use in selected application types such as open-graded asphalt mixtures, gap-graded asphalt mixtures, and surface treatments. However, its use in dense-graded asphalt mixtures has been very limited because of the lack of performance records.This thesis focuses on evaluating the engineering properties and performance characteristics of Terminal Tire Rubber (TTR) asphalt mixtures when compared with asphalt mixtures manufactured using neat and polymer-modified asphalt binders. Mix designs were performed using seven asphalt binders: one neat, 3 modified at various % TR (i.e., 10, 20, and 28%), 3 modified at various %TR and Styrene-Ethylene-Copolymers (SEC) (i.e., 10, 20, and 28% TR with 3% SEC per binder). All mixtures were manufactured using recycled asphalt pavement (RAP material with 25% content) and hydrated lime (as an additive). The mix designs were conducted following the Superpave standard method and evaluated using Tensile Strength Ratio (TSR) test for moisture sensitivity. Moreover, all mixtures were evaluated in terms of engineering property using the dynamic modulus test, resistance to permanent deformation using the repeated load triaxial (RLT) test, resistance to reflective cracking using the Texas Overlay test, and resistance to fatigue cracking using the bending beam fatigue. For the sake of brevity and limitation in time, results related to fatigue cracking were not presented in this document. Based on results from the asphalt binders and mixtures tested in this study, it was recommended that the TTR binder be considered for further pavement application due to its noticeable homogeneity during testing and ease of pumping without any segregation. Moreover, the lime percentage should be increased in order to meet the minimum TSR requirement as per Superpave. On one end, the engineering property and rutting performance life mixtures with 28%TR and 3% SEC are expected to exhibit optimal performance when placed on heavy trafficked roads. However, further analyses remain needed to evaluate the fatigue performance life of such mixtures characterized with high stiffness. On the other end, the reflective cracking results showed that mixtures with 10% TR and 3% SEC exhibited an optimum performance when used in overlay applications.