INDEPENDENCE – County Engineer Brian Keierleber and County Supervisor Clayton Ohrt recently met with engineering professors from ISU and DNR staff to discuss the possibility of using recycled plastic in rural road construction. The material may mitigate extreme frost boils.
The meeting came about after Ohrt read an article about using recycled plastics and improving the performance of the pavements.
“About 300 million tons of plastics are produced annually, a quantity nearly equivalent to the weight of the entire human population,” said Keierleber. “Only about nine percent of all plastics ever produced are being recycled.”
Keierleber presented the idea to improve the road bases with recycled plastics to Dr. Halil Ceylan, a professor in the civil, construction, and environmental engineering (CCEE) department and the director of the Program for Sustainable Pavement Engineering and Research (PROSPER) at Institute for Transportation (InTrans) at Iowa State University (ISU).
“Dr. Ceylan and his staff did a literature review and found where recycled plastics have been studied with promising results in India, the United Kingdom, Australia, New Zealand, Canada, the Netherlands, and other countries,” said Keierleber. “The use of the recycled plastics has improved the engineering properties of the asphalt mixes, concrete mixes, and geomaterials for unpaved roadways, including subgrade soil.”
According to Keierleber, the Indian government made it mandatory in 2015 for road developers to use waste plastic along with bituminous mixes for road construction in urban areas. Bitumen is the liquid binder that holds asphalt together.
“Dr. Ceylan presented the concepts to the Iowa Highway Research Board (IHRB) as a problem statement,” said Keierleber.
“He is optimistic that between them as well as the Iowa Department of Natural Resources (DNR) that some funding might be obtained to study the possibilities of using recycled plastics in asphalt mixes, concrete mixes, and unpaved road base/subgrade stabilization. The literature review found only limited studies on using the recycled plastics as base stabilizers and then appeared mainly as soil nails for roadway slope stability. However, there are numerous studies showing that use of plastic fibers improves the performance of geomaterials/soils significantly. It is also well-known that polypropylene fibers can significantly improve the performance of concrete pavements. Such results would be similar for recycled plastic fibers when used in the same applications,” Keierleber continued.
“The clayey and silty soils that encompass much of Iowa are excellent for growing crops, but when combined with the extreme weather conditions with significant amount of annual precipitation and large number of freeze-thaw cycles create some of the most difficult conditions for maintaining a road,” said Keierleber.
“Economical solutions must be developed given the limited resources available for the use of local agencies. Agriculture has dramatically changed over the past 50 years, but the way the rock roads are maintained basically has not. Moving loads on the unpaved roads are much heavier and much more frequent, and the existing bases when impacted by frost boils cannot sustain the loads. The old answer of treating a frost boil by staying off it is not always a viable answer.
“Historically the solution has been to pave over the frost boil and it will not bother, but the funds are not available to pave all the roads that should be. This past spring, even six-inch-thick hot mix asphalt was failing due to the frost boils and heavy loads. The goal is to treat the road base with the recycled plastics and strengthen it sufficiently that when frost boils occur the stabilized base can bridge over the frost boils much like a pavement does.”
Keierleber also stated a major concern for the research coalition, comprised of ISU engineers, Iowa DNR, Iowa Department of Transportation, and Buchanan County personnel, is to find a use for the recycled plastics that is not harmful to the environment.
“We have the right expertise and knowledge to find innovative ways of utilizing recycled plastics in Iowa’s road infrastructure system,” said Dr. Ceylan, “but we need research funds to come up with a detailed research plan for laboratory and field work so that we can develop guidelines for the transportation agencies to successfully implement the research findings and recommendations in full-scale projects.”
“With high and heavy loads on our roads in today’s world, they are under extreme stress,” said Ohrt. “We need to look beyond the present road maintenance procedures and look at the long-range economics and safety. By finding a use for waste plastic products would be a double win.”