The greatest innovations often have the most humble beginnings. So is the story of the use of waste tire rubber in asphalt pavements. Charlie McDonald – dubbed the father of asphalt rubber¹ – pioneered this concept more than 70 years ago. 

McDonald’s camping trailer was leaking, and he needed a flexible material to effectively patch and seal.² His workaround – formulated with scrap tire rubber – served as the basis for a pothole application developed later in his career as an engineer for the City of Phoenix, Arizona.

In the 1970s and 80s, asphalt mix producers began adding large-sized recycled rubber to hot mix asphalt (HMA). However, roads paved with this early rubberized asphalt showed increased levels of failure because of mix design problems, including “insufficient binder, no production heating control, no dwell time control for produced mixes, compaction issues, [and] material handling issues.”³

Advancing the performance potential of recycled tire rubber

Forty-one million tires end up in landfills every year in the U.S.⁴ It is estimated that about 17% of the scrap tires produced in the U.S. in 2017 were used in modified asphalt binders.⁵ While that figure is encouraging, more needs to be done to upcycle the resources that are literally trashed. 

Innovations, such as our patented Rapid Digestion Process™, have helped push the needle in our industry. Through RDP, end-of-life tires are liquefied and blended with asphalt to create custom asphalt formulations – ones that include up to 50% tire rubber. 

States ahead of the curve

California and Texas, along with Arizona and others, have encouraged the practice of increasing percentages of tire rubber in pavements. At this time, Texas allows up to 20% TR while California allows 18-22%. In fact, approximately 31% of all HMA mixes placed in California by the end of 2010 were rubberized HMA.⁶ And, in Arizona, all high-volume highways have been surfaced with asphalt rubber open-graded friction course.⁷

Research in these states have confirmed the performance potential of using waste tire rubber with modified asphalt. California Department of Transportation (Caltrans) engineers reviewed the performance of over 100 recycled asphalt concrete (RAC) pavement projects in California and 41 Arizona DOT projects. Their study found that the progress of distresses in RAC pavements was much slower than that of structurally equivalent dense-graded asphalt concrete pavements. 

A study conducted for the Texas DOT in 2001 stated that “all asphalt rubber Porous Friction Course (PFC) projects are exhibiting excellent performance properties. Resistance to cracking and raveling in asphalt rubber PFC is particularly impressive. From [a] cost and benefits standpoint, PFC represents the best application for asphalt rubber.”⁸ In yet another Texas study, pavement evaluation results indicated that rubber modified HMA projects “had significantly better cracking resistance than conventional HMA.”⁹

A focus on life cycle cost analysis is key to progress

Of the state DOTs that do not allow waste tire rubber in asphalt mixes, 61% cited the higher cost as the main reason for not using it. However, a life cycle cost analysis indicated that the widespread use of asphalt rubber has been cost-effective in Arizona and California.¹⁰

Many states are collecting performance data to validate taking the leap. About two years ago, Oklahoma, a state that does not currently allow waste tire rubber in asphalt mixes, conducted a survey of rubberized asphalt roads that were put down in the 1970s and 80s and was impressed with the long-term performance. As a result, discussions about recycling and green technologies have increased at the state’s DOT. 

With further use, modification and study, we are confident that recycled asphalt pavements (especially those using waste tire rubber) will become more widely adopted. By pushing waste tire rubber percentages in mixes — and the limits of pavement performance — we can truly enter the next phase of a greener asphalt industry. In our upcoming post, we’ll discuss sustainable pavement designs and their impact on life cycle cost. Stay tuned.

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1.  https://www.rubberpavements.org/RPA_News/2011/201110_Father_of_Asphalt_Rubber_Article.pdf ↩︎
2.  HISTORY – Rubber Pavements Association ↩︎
3.  Technical Challenges of Utilizing Ground Tire Rubber in Asphalt Pavements in the United States – PMC (nih.gov) ↩︎
4.  PowerPoint Presentation (ustires.org) ↩︎
5.  Baumgardner G., Hand A.J., Aschenbrener T.B. Resource Responsible Use of Recycled Tire Rubber in Asphalt Pavements. U.S. Department of Transportation, Federal Highway Administration, Office of Preconstruction, Construction and Pavements; Washington, DC, USA: 2020. p. 41. Report No. FHWA-HIF-20-043. ↩︎
6.  Zhou H., Sri H., Vacura P. Caltrans use of scrap tires in asphalt rubber products: A comprehensive review. J. Traff. Transp. Eng. 2014;1:39–48. doi: 10.1016/S2095-7564(15)30087-8 ↩︎
7.  Shu X., Huang B. Recycling of waste tire rubber in asphalt and Portland cement concrete: An overview. Constr. Build. Mater. 2014;67:217–224. doi: 10.1016/j.conbuildmat.2013.11.027. ↩︎
8.  Tahmoressi M. Evaluation of Asphalt Rubber Pavements in Texas. PaveTex Engineering and Testing, Inc.; Dripping Springs, TX, USA: 2001. ↩︎
9.  Freeman T., Pinchett D., Haobo R., Spiegelman C. Analysis and Treatment Recommendations from the Supplemental Maintenance Effectiveness Research Program (SMERP) Texas Transportation Institute; College Station, TX, USA: 2002. ↩︎
10.  Hicks R.G., Epps J.A. Life cycle cost analysis of asphalt-rubber paving materials; Proceedings of the 1st World of Asphalt Pavements, International Conference; Sydney, NSW, Australia. 2 July 2000. ↩︎