Yearning rubber

Feb. 19, 2010

Thousands of tires a day pound the pavement of I-80/94 (the Frank Borman Expressway) in northwest Indiana.

So perhaps there is no better resting place for 100,000 recycled tires than under the expressway’s widened lanes.

Shredded and mixed with sand, these old rubber wheel covers were placed under new concrete lanes as the perfect answer to a ground-stability challenge.

A stable challenge

Thousands of tires a day pound the pavement of I-80/94 (the Frank Borman Expressway) in northwest Indiana.

So perhaps there is no better resting place for 100,000 recycled tires than under the expressway’s widened lanes.

Shredded and mixed with sand, these old rubber wheel covers were placed under new concrete lanes as the perfect answer to a ground-stability challenge.

A stable challenge

Scheduled for completion in 2011, there is a $97 million project under way in northwest Indiana widening I-80/94 from six to 10 lanes with continuous ramp lanes. The project extends to either side of the heavily traveled I-65 interchange.

In the project’s design phase, a ground- stability challenge arose for widening eastbound lanes just east of I-65. Poor soil was rampant near the old riverbed of Deep River.

“The soil condition was bad for about 40 ft, so soil stabilization was cost-prohibitive,” said Brad Minnick, INDOT LaPorte District construction director.

In order to make the ground stable enough for a widened roadway, a mechanically stabilized earth (MSE) wall with air-cooled blast furnace (ACBF) slag was recommended in the plans. However, the available slag stone did not meet INDOT’s specific requirements for corrosion.

Slag, also a recycled material, is a byproduct of the steel production process.

“When the mills manufacture steel, the slag is a waste byproduct,” Minnick said. “Initially, it is a molten, fluid mass that takes the shape of the pit it is placed in as it cools to ambient temperature. Once cooled, it is broken up by mechanical means and crushed into a usable fractured aggregate.”

The LaPorte District often uses slag as a material source in concrete and asphalt paving, as well as for base or sub-base materials.

“We use it more in the northwest part of Indiana because of the proximity of the steel mills,” Minnick said. “It phases out the further south you go because of the trucking cost.”

In regard to the Borman project, the corrosive nature of the available slag was important because of the MSE wall straps going through the lightweight fill. Concerns arise if the slag is too corrosive, because it would cause the straps to rust and fail prematurely.

Also, the slag wasn’t passing resistivity specifications. It was less than desirable, meeting only 50% of the 3,000-ohm requirement.

Substandard slag could have led to a more expensive substitute, a costly redesign and a delay in project completion.

“It would have been a delay of at least two months,” Minnick said of the project with a fast-tracked schedule that would have been a political nightmare to delay. “It wasn’t going to be a viable option to wait on a redesign.”

Spinning tires

Prime contractor Walsh Construction and INDOT Research Division’s geotechnical laboratory in conjunction with Purdue University struggled to find suitable material.

Other lightweight material, such as expanded shale and extruded polystyrene, were considered. A layer of plastic foam (expanded polystyrene) was already planned for the fill, and adding more of it also was contemplated. But these all turned out to be more expensive and would have required a change order.

Then the project team recalled a research study about using a 60/40 mixture of tire shreds and sand as lightweight fill.

Athar Khan, manager for INDOT’s Office of Geotechnical Engineering, said that in the late 1990s the state of Washington built an embankment/retaining wall with tires. But before the project was complete, the tires caught fire.

“At the same time, we were trying to use shredded tires on INDOT projects,” Khan said. “As a result of this fire and awaiting its causes, we put our demo project on hold. In the meantime, we came up with the idea to mix shredded tires with sand in order to avoid the risk of fire.”

The first opportunity to implement the tire/sand mixture as a lightweight fill arose in 2001. INDOT’s LaPorte District had a project on U.S. 31 in Lakeville to remove an old railroad bridge and fill the void up to road level.

“This was a prime example of when the rubber meets the road,” Zeider said, “because the rubber became the road.”

Dillon Tire in North Liberty donated 50,000 tires for the study and Rieth-Riley Construction built the project.

After the tires were shredded and brought to the worksite, a 60/40 ratio of tire shreds to sand was developed.

“Because based strictly on volume, you have voids around the rubber tires,” Zeider said. “The sand needed to fill in the voids. They mixed the materials from adjacent stockpiles, and through trial and error with test batches, determined a 60/40 blend was the most suitable for the project.”

The research team installed some water- and stability-testing devices in the project.

“The end result of their testing over a couple years was that the material had not failed on a high-volume road (27,000 ADT) and the water wasn’t affected,” Zeider said. “Also, it was a very good use of rubber tires, good for the environment and resulted in cost savings.”

Kahn said it is now his department’s preference to utilize this application when it is available and applicable.

“Based on our findings, we believe that optimum mixtures are 50/50 and 60/40, which provide engineering parameters needed depending upon the application, such as normal or lightweight material,” Kahn said. “The tire weight is only 30 lb/cu ft, compared to soil which is 120 lb/cu ft. Also, a 6-in. size of shredded tire will provide the ideal mixture for our application.”

Zeider recalled how good it felt to protect the environment on his 2001 job.

“From the bridge structure to the steel, the road, the trees—everything became recyclable material,” he said. “Nothing went to the landfill. And actually, by using the tires, we took some material out of the landfill.”

Zeider drives this section of U.S. 31 often and is proud to see no cracks, dips or need for resurface construction.

“I go there eight years later and the pavement is as sound as the day we left the project,” he said. “And I can’t say that about every project we build. So I say, bring on the tires!”

A recycled resolution

On the present-day Borman project, Walsh Construction Superintendent Ron Wozniak heard the call for using tires. But this would be the first time Walsh’s Indiana office had worked with the material.

With assistance from Purdue University, the Indiana Department of Environmental Management, Reinforced Earth Co., tire recyclers and the INDOT Research Division, the improved MSE wall plans came through.

Elk Distributing in Elkhart and Liberty Tire in North Liberty responded well to the call for shredded tires.

“They’re excited about recycling tires and not just sending them to the landfill,” Wozniak said. “They want the state to be happy and want the state to continue it.”

Passenger-car tires were used because the treads are not as thick. Recycling companies also use tires to create playground mulch, but that process is more costly because a second stage of processing must take place to remove wires from the shredded material. Removing the wires is not required for the lightweight fill application.

In August, the shredded tire/sand mixture was installed.

“The most surprising part of it is you get an idea of how it’s going to look like: a pile of shredded tires,” Wozniak said. “But by the time the mixture is all said and done, it looks different. At first you might think this will be hard to compact. But once on the ground, it was easy to level off and get a smooth surface for keeping elevation and getting ready for the next lift.”

Wozniak is satisfied with the results.

“It’s something that you would definitely use again, especially in regard to the lightweight fill requirement,” he said. “It’s a good material to have as an option.”

LaPorte District Construction Director Minnick also is happy to have learned something new.

“This is the first time the shredded tire/sand mixture has been used as MSE wall backfill in Indiana,” he said. “It’s an innovative technique that helps the environment through recycling and saved the taxpayers approximately $180,000 on this project.”

About The Author: Bingham is a communication specialist with INDOT’s LaPorte District.

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