The root of it all

Feb. 5, 2016

Full-depth reclamation drives down cost and saves time on I-10 in Texas

A severely distressed section of I-10 in rural western Texas had structural failures that ran deep. Past maintenance for this 11-mile-long, 4-lane-wide stretch of I-10 near Balmorhea was purely surface level. The particular stretch of the highway was marred by sunken spots, rutting and other distresses, indicating an entire base failure.

I-10 is a major east-west highway that runs through much of Texas including major cities like El Paso, San Antonio and Houston. It is the longest continual untolled freeway in North America, measuring 880 miles long. 

With a speed limit of 80 mph, this specific span of I-10 was hazardous and detrimental to motorists. The foundation was the root cause of most of the issues. The base layer was made of crushed limestone with a small amount of rhyolite additive, a common rock found in the area and used for road aggregate.

The road was selected as a candidate for road reclamation by the Texas Department of Transportation (TxDOT) in August 2015, and its reclamation approach and successful application is what won the project a 2016 Roads & Bridges/Asphalt Recycling and Reclaiming Association Recycling Award.

It was determined by TxDOT that a full-depth reclamation (FDR) was the best course of action to stabilize the road, as it would provide a more permanent solution for road rehabilitation. 

A WR-250 at work on I-10, followed by a water tanker. 

The FDR method provided two crucial benefits to TxDOT: time and money. Material costs are low due to a reduced need for new material, instead crews would be mainly working with materials already present in the existing roadway. New construction of this rough patch of I-10 also would be time consuming. The FDR process allowed crews to complete construction in less than three months without impacting the traveling public with lane closures. 

The rural location didn’t help matters much. If a machine broke down, the nearest town was Balmorhea, with a population of 490 and not much in the way of heavy equipment replacement parts. Therefore, it was essential for the contractor to invest in preventive maintenance. 

“It was a challenge we had to overcome. If something breaks down and you’re in Dallas or Fort Worth, you can go to the shop and buy it right there. Here, it’s a day or more out. Really staying on top of our equipment and making sure we did our preventive maintenance to stop things like that from happening and slowing us down was the key to our success,” Project Manager Eric Fleps told Roads & Bridges.

When the project went to bid, Kiewit came in with the lowest price, which included a quote from Texas Roads Recyclers which provided the emulsion material as well as QC services for the road project. The contract was, in turn, selected by TxDOT to mend this stretch of I-10 because of its cost-effective value. 

Fleps said that the project required multiple testing points to get the mix design correct. “We had to run multiple points at different rates of emulsion to figure out what would be the optimum mix design for the existing material and would perform the best and meet the requirements of the TxDOT specifications.”

Kiewit and Texas Road Recyclers arrived at a mix design of 1.5% cement with a 4.5% emulsion. That was mixed into 2 in. of the existing asphalt pavement and 7 in. existing base at 97% compaction density.

The project used 22% RAP, 78% reclaimed base on FDR and 11% RAP on the HMA overlay, totaling a milling depth of 9 in.

The result was 315,000 sq yd of roadway that was reclaimed in 10 weeks, while meeting the original contract budget of $24.4 million. 

QC for this project also was critical to its success. With a roadway this size, the materials are bound to change as crews go along and constant monitoring of the mix design was imperative. 

“They’re [materials] not completely uniform throughout the length of the roadway so you have to run tests as you’re going along to make sure that the road material is staying within the limits put forth in the mix design,” Shane McDade, founder of Texas Road Recyclers, told Roads & Bridges. 

Measure twice, pave once

The field QC was a “moving target,” Fleps said, but one they were able to meet the requirements at the end of the day through the assistance of QC technicians provided by Texas Road Recyclers. 

Under the direction of McDade, technicians took samples from behind the mixer, checking the moisture and making any necessary adjustments. A second sample was taken to form a mold in order to determine that the processed material was meeting the 125.5-lb/cf density required by the mix design. 

“I take samples and make molds to check moistures and densities of the processed material at prescribed intervals during production. I also will take samples in addition to the prescribed intervals if there is a visible change in the nature of the material. If the processed material is out of spec at any point, we can make field adjustments to correct it,” McDade said.

Technicians performed density tests throughout the entire reclamation process to ensure they were meeting the specified compaction. 

As with all FDR projects, proper added moisture content is vital to achieving specified density. If the tested density on the processed material varies too far from that 125.5-lb mark then it can be varied by adjusting the water and/or emulsion content. In severe cases, you can speed up or slow down the reclaimer or adjust rolling patterns. 

Consistency was the key to providing a high level of QC and catching any deviations as they arose. It’s a lot of work, McDade acknowledged, but the only way to ensure project success. 

The highway was never, at any point, closed down to traffic. Work was done in 2-mile by one-lane sections, and traffic was diverted to another lane when crews were working.

This allowed for uninterrupted traffic flow for I-10 motorists. 

With time to spare

Meticulous and constant monitoring of the mix design can be a time-consuming process, but Kiewit managed to complete the project four months ahead of schedule, without any lane closures or nighttime construction. They did this by having reclaimers work in tandem.

Wirtgen WR-250 and WR-2500 reclaimers ran side by side, followed by two 13-ton vibratory sheepsfoot rollers and then a 30-ton pneumatic roller, a rare and tricky move to pull off, McDade explained. Kiewit perfected the dual-machine process by placing a water tanker behind the machine rather than spraying water from the front, allowing a faster and more efficient process.

The dual-machine technique processed materials to complete the job in a short period of time. 

“There were days on that project that we used 17 tanker loads of emulsion. I can’t think of any project that I’ve ever been associated with that used more than six in a day,” McDade said. 

The scope and coordination involved in the I-10 rehabilitation project were aspects both Fleps and McDade said were vital to the project’s success. 

“We had Texas Road Recyclers who was the supplier, we worked with them, they dealt with the emulsion refinery and the transport company. There’s a cement supplier and of course there’s us, the contractor. And all of those parties had to really be on point and do their part to make this a successful job,” Fleps said. 

“The scope and the speed of this project was a mile beyond what is typical. You know, it’s a big highway, I-10 is a big highway, it was a deep reclamation because it takes a lot of traffic. It was just a lot of square yards and a really big job for this type of project and they did it really, really fast,” McDade said. R&B

About The Author: Shoup is associate editor for Roads & Bridges

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