PAVING CORNER

Full-depth reclamation with foamed bit gaining traction as cost-effective projects prove successful

Nearly 20 years ago, the Texas Department of Transportation (TxDOT) tested the full-depth reclamation (FDR) with foamed bitumen (foamed bit) process on an asphalt roadway to less-than-ideal results. Additional testing was put on hold; however, TxDOT decided to take another look at FDR recently, and the outcomes have been very positive, according to Kirby-Smith Machinery Key Account Product Specialist Gary Corley.

“One major reason for improved results is Wirtgen’s design using proven, proprietary technology that perfects the methodology,” Corley emphasized. “Each asphalt roadway is unique. Using a WLM 30 laboratory mixer, Wirtgen can duplicate specific road conditions, enabling an exact mix design for the material being reclaimed. That gives contractors the valuable information they need well in advance and sets up success.”

The FDR with foamed bit process utilizes in-place materials, replacing more traditional reconstruction that involves completely removing existing asphalt and reconditioning the subgrade or milling the old and laying new. Contractors performing foamed bit on TxDOT jobs have used multiple types of Wirtgen Group equipment, starting with a Streumaster SW 16 TC binding-agent spreader that lets operators distribute a precise amount of cement ahead of the “foamed-bit train.”

The primary machine in the train is a Wirtgen WR 250i cold recycler/soil stabilizer that creates the lab-design mix generated by the WLM 30. The WR 250i pushes a tanker truck with bitumen (hot, liquid asphalt – that, in the case, is heated to between 320 and 370 degrees) and pulls a water truck, both of which have hoses hooked to the recycler to supply liquids to the mixing chamber. As the WR 250i digs into the existing road and subbase – up to 12-inches deep – it combines the components to make a new base.

“As the elements are mixed, it creates what looks like shaving gel,” described Wirtgen Field Service Engineer John Riley. “During the foaming process, that expands and grabs fines from the cement. When it contracts again, it hardens into a firm, yet flexible base. The advantage is that it’s not rigid, so even with heavier traffic it’s likely to last longer than a traditional rip-out-and-replace or mill-and-fill operation.”

Shorter construction schedule

Next, operators compact the new subsurface with Hamm Padfoot and smooth-drum rollers. A course of asphalt is put on top to complete the roadway.

Wirtgen Recycling Product Manager Mark Stahl emphasized that FDR with foamed bit saves both time and money. “Because we are recycling existing roadway materials that have already been paid for, there is no need to bring in virgin aggregates or haul away asphalt, dirt or rock. We are seeing cost savings of 30 to 40 percent and a shorter construction schedule.”

The first of four recent foamed bit projects that TxDOT put out for contract was completed in 2018 on a two-lane, farm-to-market (FM) road when Big Creek Construction reclaimed eight miles followed by a two-inch overlay of hot mix asphalt. It was finished in 13 days and remained open to traffic throughout that time. Corley said the results were outstanding, with gradations and densities exceeding expectations.

Three more projects followed, including one completed by Gilvin-Terrell in the Texas Panhandle and two in eastern Texas near Texarkana. To prepare for the latter assignments, Kirby-Smith and Wirtgen held a conference with TxDOT personnel and contractors R.K. Hall Construction and Madden Contracting Co., which rented the Wirtgen Group equipment for their respective undertakings.

“We wanted to make sure everyone fully understood the technology and the FDR with foamed bit process. It was also to assure TxDOT and the contractors that both Kirby-Smith and Wirtgen were on-board to fully support them,” said Jim Powell, Kirby-Smith Machinery Director of Paving & Minerals. “It was a great way for all of us to build a relationship and ensure success from good pre-planning through the entirety of the projects.”

R.K. Hall Construction completed approximately eight lane miles on FM 3129 in Cass County. With the Wirtgen WR 250i, a crew chewed up approximately 12 inches of pavement and subgrade and then injected it with the proper mix of bitumen, cement and water to create a new base course. It followed with seal coat and layer of asphalt.

“The biggest takeaway for me was the time savings. For instance, one section that would normally take six days was reduced to two,” said R.K. Hall Construction Project Superintendent Brad Haugh.  “That’s huge, and we didn’t have to shut down the entire roadway for an extended period. Traffic was able to move in the opposite lane as we worked.”

Stretching the budget

Madden Contracting Co. saw similar results when it rehabilitated four miles of FM9 at a depth of 11 inches.

“Normally, this project would have taken about three months; however, with the foamed bit technology, we were able to do it in less than 20 days,” noted Owner David Madden. “It’s truly a game-changer for TxDOT’s FM roads and even some primary roads. This is an efficient way to restabilize them and give taxpayers in rural areas good roadways that could last decades.”

Stahl said that while the recent TxDOT projects were successful as were several others around the country, he cautions that not every roadway is a good candidate for FDR with foamed bit.

“Investigation is important. We need to know exactly what the pavement structure is like,” said Stahl. “FDR with foamed bit works best when the pavement design is consistent. When that’s the case, it’s a great alternative to traditional methods and can help DOTs rehabilitate more miles of road with a limited budget.”

Powell also noted the long-term benefits. “This offers a way to prolong an existing roadway at a fraction of the cost, up to 10 years by some estimates. We are fully committed to being a part of the process. I believe we are the only equipment dealer in Texas with a Wirtgen WR 250i in its rental fleet.”

Stahl added that Wirtgen is dedicated to being the leader in FDR with foamed bit.

“Wirtgen has more recyclers in the market doing this than any other manufacturer,” said Stahl. “We have the technology and research as well as written design specifications. In addition, Wirtgen supports customers, as well as DOTs or other agencies that specify these types of projects to ensure they understand how to do it and get a quality job. We have the machines and the people, and with partners like Kirby-Smith, we are confident that FDR with foamed bit will continue to grow.”

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