Properties of asphalt rubberized with shredded waste tires

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Properties of asphalt rubberized with shredded waste tires

Ghaly, A.M. / Barth, K.R. / Parlakian, M.

The effect of adding shredded waste tires on the performance and the mechanical characteristics of asphalt mixtures was investigated. Adding a percentage of tire rubber to asphalt pavement has long been considered beneficial in addressing a solid waste disposal problem, and in reducing the negative environmental hazard of billions of stockpiled tires. Currently (1997), a Federal mandate requires all fifty states to use rubber modified asphalt in 20% of total asphalt tonnage laid each year. In this study, crumb rubber made from old tires has been used in hot mixed asphalt (HMA). The asphalt mixture was designed using Marshall method, and crumb rubber was added using the dry process. Specimens were designed and prepared with crumb rubber content of 0, 4, 7, and 10% of total weight. Measurements of mix stability, flow, unit weight, air voids, and specific gravity were recorded. Furthermore, compression tests on confined specimens with different percentages of asphalt and rubber contents were conducted to determine the effect of crumb rubber on the magnitude of the stress-strain relationship. It is concluded that rubberized specimens containing 4% rubber and 5% asphalt cement by weight of total mix nearly satisfy the stability and flow limits of the specifications. The controlling characteristic of the rubberized asphalt mixture was found to be the air voids within the specimen. A rubber content of 2.6% by weight satisfies the stability, flow, and air void specifications. This amounts to 24 kg (52 lb.) of rubber per ton of asphalt paving mix.