Properties of crumb rubber concrete

Crumb rubber is a material produced by shredding and commutating used tires. There is no doubt that the increasing piles of used tires create environmental concerns. The long-term goal of this research is to find means to dispose of the crumb rubber by placement of the rubber in portland cement concrete and still provide a final product with good engineering properties. The Arizona Department of Transportation and Arizona State University have initiated several crumb rubber concrete (CRC) test sections throughout Arizona over the past few years. Laboratory tests were conducted to support the knowledge learned in the field and enhance the understanding of the material properties of CRC. Concrete laboratory tests included compressive, flexural, indirect tensile strength, thermal coefficient of expansion, and microscopic matrix analyses. The unit weight and the compressive and flexural strengths decreased as the rubber content in the mix increased. Further investigative efforts determined that the entrapped air, which caused excessive reductions in compressive strength, could be reduced substantially by adding a deairing agent. The higher tensile strains at failure observed from the tests were indicative of more ductile, energy-absorbent mix behavior. The coefficient of thermal expansion test results indicated that CRC was more resistant to thermal changes. The CRC specimens tested remained intact after failure and did not shatter as a conventional mix did. 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 in places where high-strength concrete is not required is recommended.