Impact of crumb rubber modifier type and blending temperature on asphalt binder and mixture properties

Document Type

Conference Proceeding

Publication Date

1-1-2019

Abstract

As the price of asphalt binder continues to rise, state agencies are looking for sustainable ways to reduce the cost of asphalt pavements without compromising performance. One such alternative is the use of crumb rubber (CR), derived from waste tires, in binders of asphalt mixtures. Blending virgin asphalt binder at 170° and 190°C with ambient or cryogenic ground crumb rubbers along with E-rubber (free flowing rubber pellets) to produce sustainable asphalt mixtures was studied. Thermogravimetric analysis (TGA) was used to determine the natural rubber to synthetic rubber ratio in the ground tire rubbers. Gel permeation chromatography (GPC) was used to investigate the molecular structure and changes occurring in the asphalt binder upon blending with rubber/modifier. Mixtures prepared from modified asphalt binders were characterized using a semi circular bend (SCB) test at intermediate temperatures and Hamburg wheel tracking test at higher temperatures. Correlation of physical properties of crumb rubber (CR) asphalt binder with apparent molecular weight of binder components was examined. Ground CR particles were comprised of favorable polyisoprene contents (minimum natural rubber percentage was 50%) for blending with asphalt binder. About 73-87% of the E-rubber particles dissolved in the asphalt binder during blending confirming that E-rubber had great compatibility with the binder chemistry and hence has the ability to improve performance. Asphalt mixtures containing 10% (by weight of binder) ambient ground crumb rubber blended at 170°C and 190°C did exhibit acceptable mixture intermediate temperature cracking performance as measured by the SCB Jc parameter. However, similar mixtures containing 10% cryogenically ground CR exhibited acceptable SCB Jc parameter when blended at 170°C, but failed when blending was conducted at 190°C. Addition of either 5% or 10% E-rubber to the asphalt binder at 190"C also yielded acceptable intermediate temperature cracking performance of the corresponding mixtures. The presence of crumb rubber in asphalt binder contributed to an increase in percent high molecular weight species that provided enhanced mixture rut resistance.

Publication Source (Journal or Book title)

Asphalt Paving Technology: Association of Asphalt Paving Technologists-Proceedings of the Technical Sessions

First Page

515

Last Page

543

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