United States Department of Transportation
i
Evaluation of Crumb Rubber Modification of Louisiana Mixtures
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2023-11-01
[PDF-741.15 KB]
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Edition:Final Report November 2023
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Abstract:Since 2008, the Louisiana Department of Transportation and Development (DOTD) has permitted the use of crumb rubber modifiers (CRM) in hot mix asphalt (HMA) mixtures in accordance with its specifications. However, crumb rubber (CR)modification has presented unique challenges during the design and production of the mixtures. Louisiana DOTD district shave reported early cracking for dense-graded (DG) mixtures containing CRM. Adhesion and stability issues have been reported for Open-Graded Friction Courses (OGFC) and Stone Matrix Asphalt (SMA) mixtures modified with CR. Currently, Louisiana DOTD specifications allow the contractor to switch asphalt cement without re-designing the mixture during CR modification. This study evaluated different CR-modified mixture designs to address design and performance concerns. Additionally, the study assessed the volumetric and mechanical properties of DG, SMA, and OGFC mixtures prepared with unmodified and Styrene-Butadiene-Styrene-modified asphalt binders as well as crumb rubber from five different sources. Superpave volumetric parameters were evaluated to ascertain the impact of CR modification on the design of CR-modified mixtures. Rutting and intermediate temperature cracking resistance were determined by conducting the Hamburg Loaded Wheel Tracking and Semi-Circular Bend Tests, respectively. Further, solvent extraction and ignition test methods were used to determine the asphalt binder content of the modified mixtures. The results showed that CR modification resulted in increased rutting resistance and decreased cracking resistance. The volumetric parameters were also found to be affected by CR modification. Based on the analysis of the results, it is recommended that additional asphalt content, reduced CR dosage, and polymer additives be used to enhance the cracking resistance of CR-modified asphalt mixtures. Contractors are advised to redesign mixtures if they anticipate using CR-modified asphalt binder.
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