Properties of Crumb Rubber Concrete (05-0598)**
Kamil Elias Kaloush, Arizona State University
George Way, Scottsdale, Arizona
Han Zhu, Tian Jin University

Crumb rubber is a material produced by shredding and commutating used tires. There is no doubt that the increasing piles of tires create environmental concerns. The long term goal of this research is to find means to dispose of the crumb rubber in Portland cement concrete and still provide a final product with good engineering properties. The Arizona Department of Transportation and Arizona State University initiated several crumb rubber concrete (CRC) test sections through out Arizona over the past few years. Laboratory tests were conducted to support the knowledge learned in the field, and enhance the understanding of CRC material properties. Concrete laboratory tests included compressive, flexural, indirect tensile strength, thermal coefficient of expansion, and microscopic matrix analysis. The unit weight, compressive and flexural strength decreased as the rubber content in the mix increased. Further investigative efforts determined that the entrapped air, causing excessive reductions in compressive strength, could be substantially reduced by adding a de-airing agent. Higher tensile strains at failure observed from the tests were indicative of more ductile, energy absorbent, mix behavior. The coefficient of thermal expansion tests results indicated that the CRC are more resistant to thermal changes. The CRC specimens tested remained intact after failure, and did not shatter compared to a conventional mix. Such behavior may be beneficial for a structure that requires good impact resistance properties. If no special considerations are made to maintain higher strength values, the use of CRC mixes are recommended in places where high strength concrete is not required.