Abstract
A 2.38-mm (No. 10) mesh crumb rubber from waste passenger tires was pretreated with a low-viscosity petroleum-based product and used as an aggregate replacement in asphalt concrete mixtures. The preconstruction testing consisted of the development of an appropriate aggregate gradation, mix design information, and fundamental mixture properties such as temperature susceptibility, moisture sensitivity, low temperature behavior, and permanent deformation characteristics. Five crumb rubber modified (CRM) asphalt concrete plus two control test sections were placed in Babbitt, Minnesota, in the fall of 1993. Variables in the CRM sections include pretreated and untreated crumb rubber and CRM mixtures in just the wear course or throughout the 150-mm (6-in.) pavement section. Laboratory results indicated that there was little difference in the temperature susceptibility between the mix design and behind-the-paver mixtures. Although the mix design samples indicated some increase in the moisture sensitivity of the CRM mixtures, no difference was seen in the behind-the-paver materials. There was some indication that the CRM mixtures would exhibit a greater ability to dissipate thermal stresses through a better ability to strain at cold temperatures. Some slight to moderate improvements were seen in both moisture sensitivity and low temperature behavior when the crumb rubber was pretreated. Falling weight deflectometer results were used to backcalculate the layer moduli for all of the test sections. Results indicate no difference in any of the layer moduli; these results agree with the laboratory resilient moduli results. After two winters, all test sections are performing equally well. Anticipated damage by snowplows to the coarser gradation used with the CRM mixtures did not occur.
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