Technical Challenges of Utilizing Ground Tire Rubber in Asphalt Pavements in the United States

Abstract

At least 275 million scrap tires exist in stockpiles in the U.S. The practice of dumping scrap tires in landfills has been an environmental concern. To address this concern, many industries—and regional and national environmental protection agencies—have taken major initiatives to recycle scrap tires. One of the major uses of recycled scrap tires is in crumb rubber products, including rubberized asphalt. Rubberized asphalt is produced by blending ground tire rubber with asphalt to beneficially modify its properties for highway construction. The ground tire rubber (GTR) can be used either as part of the asphalt rubber binder (also known as asphalt rubber), seal coat, cap seal spray, joint and crack sealant or as substitute aggregate (rubber-modified asphalt concrete). Therefore, the largest single market for GTR is asphalt rubber, which consumes approximately 12 million tires, annually. Currently, several Departments of Transportation (DOTs) in the U.S. do not allow use of GTR in asphalt mixes. This is partly due to lack of information, laboratory test data and specifications or special provisions on the use of GTR in asphalt pavements. The current study was undertaken to summarize the available wealth of knowledge, identify research needs, and document the major findings of previous pertinent studies focused on GTR use in asphalt. Significant study findings—consisting of laboratory test results, field observations, and common practices—were documented, including: the use of GTR in asphalt mixes, wet and dry processes, characterization of hot mix asphalt (HMA) containing GTR and GTR performance when combined with virgin materials. In order to promote successful use of GTR, it is imperative to help DOTs develop specifications/special provisions for utilizing rubberized asphalt by collecting data, common practices and specifications utilized by other state DOTs. As a part of this effort, we conducted a survey of construction specifications used by different DOTs that currently allow the use of GTR in asphalt. Since some DOT practices are not readily available in the open literature, this survey proved to be an effective tool for gathering data on the current practices, methods and specifications associated with DOT use of GTR in asphalt pavement.

Review and Perspectives of End-of-Life Tires Applications for Fuel and Products

“…44 Rubberized asphalt results in higher carbon sequestration than conventional asphalt pavements using 1,600−2,000 tires per lane-mile. 45 Today, almost 12 million discarded tires are repurposed annually for rubberized asphalt, 46 a number that could substantially increase given the growing network of asphalt paved roads worldwide. 47 It has also been reported that rubberized asphalt enhances durability and performance while reducing noise, thus augmenting economic and social benefits.…”

Effect of Desulfurization Process Variables on the Properties of Crumb Rubber Modified Asphalt

“…Rath et al investigated the effects of a chemically engineered dry-process ground tire rubber modification in bitumen and mixtures, and the cracking and rutting performance of all the field sections was good-to-excellent [ 20 , 21 ]. However, for wet-process modified rubber asphalt, because the crumb rubber powder used in ordinary crumb rubber modified asphalt was treated by a vulcanization process, it had a relatively solid three-dimensional network structure and low activity, which makes the crumb rubber powder difficult to be compatible in asphalt and often accompanied by a large number of crumb rubber particles [ 22 , 23 , 24 ]. The ordinary crumb rubber modified asphalt prepared from vulcanized crumb rubber powder has a series of shortcomings, such as poor high temperature storage stability, easy segregation, high viscosity, and difficult construction, which limits its development and application [ 25 , 26 , 27 ].…”

Ground Tire Rubber Modification for Improved Asphalt Storage Stability

“…Terminal blending occurs at a designated plant and is shipped to the construction site. Tank blending may have lower quality control because of the time limitation in the chemistry kinetics, while terminal blending may have separation issues if not addressed appropriately …”

“…In a 2016 state DOT survey of 37 states plus one Canadian DOT, 54% use GTR (Figure ). The remaining states do not provide a technical reason, such as unsuccessful implementation in the past . The top three listed responses for incorporating GTR are better performance, cost effect, and incentives (by local departments of health, etc.).…”

“…Results of 2016 state DOT survey. A total of 54% of respondents use GTR in asphalt, and here are the listed responses for the reasons …”