Program for Sustainable Pavement Engineering and Research

PROSPER project also addresses reuse of plastic waste

Geosynthetics can offer a promising solution for road base stabilization. In addition, utilizing geosynthetics made from recycled materials can benefit everyone since plastic waste poses a significant environmental challenge.

An in-progress project from the Program for Sustainable Pavement Engineering and Research (PROSPER), led by its director Halil Ceylan, aims to determine the structural benefits and environmental suitability of using recycled plastics as a base stabilization agent.

The project began in 2022, and the first test section was built in late September. To mark the occasion, demonstrate the technology, and discuss the research, PROSPER organized an open house on September 26 held in Independence, near the test section site.

“This here is like a triple win,” said Buchanan County Board of Supervisors Chair Clayton Ohrt to kick off the event that included more than 20 people.

He cited the project’s potential provide environmental benefits from using upcycled plastic waste, the creation of jobs and business opportunities in the county, and to address infrastructure issues related to freeze-thaw cycles as the triple benefits.

It’s fitting that Buchanan County is the location selected for the test sites for the project, as the research is a direct result of Ohrt asking about the potential to use recycled plastics as a base stabilizer.

Five years ago, a short message Ohrt sent to Buchanan County Engineer Brian Keierleber included the question, “Would using a percentage of plastic with base stabilization be an option?” Keierleber’s response back included the sentence, “A very good question for Dr. Ceylan.”

From there, the idea was submitted to the Iowa Highway Research Board, which is now sponsoring the PROSPER project along with the Iowa Department of Transportation (DOT).

The problems with plastic

It’s estimated that Americans throw away 2.5 million plastic bottles every hour, which means that during the course of the open house, about 10 million plastic bottles were tossed out.

These sometimes single-use items fill up landfills and too often make their way into the wild, affecting plants, wildlife, and humanity. It’s estimated that plastic film, wrap, and bags are the second-most landfilled category of items in Iowa, per a 2017 Iowa Department of Natural Resources study.

So much waste is generated that the United States had been exporting it to China, which has now banned importation of plastic waste.

Base stabilization as solution

One solution to all the plastic waste is using plastic waste in transportation infrastructure applications. Its use has been well-documented in asphalt and concrete, though less so in base stabilization.

Independence’s Frost Avenue offered an ideal ground for one of the research project’s demonstration site because of its silty soils. Ceylan said that though Iowa is blessed with fertile soils for agriculture, those soils also present challenges for infrastructure.

Though the site has an average daily traffic of about 200 vehicles, Keierleber said most of the vehicles he saw during a recent visit were semi-trucks.

One motivation for the research was the impact of frost boils during a particularly difficult spring for the transportation industry. The frost boils made transporting livestock and grains almost impossible on rock roads during spring 2019, and the lives of many farm animals depended on the transportation of grains.

Keierleber said to continue to transport grains on these problem roads, they ended up using four-wheel tractors to drag semi-trucks with supplies.

Geosynthetics can help provide stabilization, while also reducing the amount of aggregate needed for granular roads. Depending on the subgrade California bearing ratio (CBR), the amount of aggregate needed for an unstabilized road can be as much as 30 inches but can be anywhere between 15 and 6 inches for a stabilized road using geosynthetics.

Utilizing geosynthetics made from upcycled plastics can provide an innovative, environmentally friendly, less expensive, and more sustainable and resilient alternative to strengthen the bases of Iowa’s granular roads. They also provide high durability to freeze-thaw cycles and help the Buchanan County and Iowa economy.

An appropriate geogrid made from upcycled plastics, used in a well-designed road infrastructure system, will combine the use of plastic waste with the least amount of resources (such as aggregates, concrete, or asphalt) to support the maximum life span of the road system, playing a key role in sustainability.

The successful outcomes of this research will not only reduce landfill waste but also mitigate the adverse impact of microplastic pollution caused by plastic waste In Iowa and elsewhere.

What’s next

As part of the project, two additional test sites will be constructed in Buchanan County, with different soils and additional sensors. The additional sites are expected to be constructed next spring, likely in May 2024, at which time Ceylan expects to hold another open house or similar event to update on the progress of the research.

Ultimately, the project result in the development of a practitioner’s guide to document best practices to implement such a solution in Iowa’s gravel road network.

“The successful outcomes of this research will not only help reduce landfill waste but also provide an innovative and less expensive alternative to strengthen the bases of Iowa’s granular roads,” Ceylan said.