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Comparing Effects of Crumb Rubber and Synthetic Polymers on Hot Mix Asphalt Performance

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Date:

October 23 , 2012

Author(s):

Hussain Bahia, Ph.D.; Amir Golalipour, MSc.; Aaron R. Coenen, Ph.D.

Source:

Asphalt Rubber Conference 2012 Munich

Description:

One of the most widely used bitumen additives is styrene-butadiene-styrene (SBS) polymer. Addition of this polymer has been shown to improve asphalt binder properties; however, there has been growing uncertainty about the future supply of SBS due to the fluctuation of prices in crude oil versus natural gas. This uncertainty has caused a need to find alternate modification techniques. In addition to introducing other new synthetic polymers, a concept with growing popularity in many parts of the world is the addition of recycled ground tire rubber (GTR). GTR is a vastly available resource produced from used vehicle tires. Modification with GTR however is not accepted yet within the PG (Performance Grading) system. Several highway agencies remain skeptical and believe that superior pavement performance incorporating GTR is only applicable in specific climates. This study is intended to summarize findings of important past studies regarding the degree of digestion of GTR in asphalt binder. Also mechanical performance and aggregate structure evaluated by image analysis of GTR mixtures are compared to unmodified mixtures as well as mixtures produced with SBS-modified (elastomeric polymer) and plastomeric-modified binders. Results indicate that GTR-modified binder has the capacity to meet and even exceed the performance of some more widely used synthetic polymer-modified asphalt binders. The GTR-modified mixtures show a lesser degree of plastic deformation, specifically at increased stress levels. The results are encouraging and confirm the potential of successful use of GTR to deliver good performance at reasonable cost with less risk of supply shortages experienced with other additives.

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