Paving Technology Helps Achieve Accuracy

Since as early as the 1970s, plans have been in place for a Western Wake Expressway around the bustling city of Raleigh, NC. This morphed into a 70-mile Interstate-grade beltway, known as the Raleigh Outer Loop, which will encompass Raleigh and the towns of Apex, Cary, Garner and Morrisville. To complete it, there will be three other segments in addition to the expressway.

NCDOT issued a $460-million contract for completing the western segment of the Raleigh Outer Loop to Raleigh-Durham Roadbuilders, a joint venture between Archer Western Contractors and Granite Construction. The newly constructed Western Wake Expressway will be a toll road once completed.

The Lane Construction Corp., based in Cheshire, CT, was subsequently awarded the $30 million contract to pave an approximately 14-mile stretch of the Western Wake Expressway running from Cary and looping south to Apex. “We were responsible for laying asphalt, which will seal the sub-grade before a finish course of concrete is placed,” notes Ryan Graham, project engineer.

Technology helps coordination

Lane dedicated a 12-worker paving crew, surveyor, project engineer and superintendent to the project. “We understood that the quality of the finished road surface is dependent upon the quality of the subgrade,” Graham says. “That’s why our asphalt paving quality was critical.”

Lane Construction was not only required to produce top-shelf asphalt paving but to coordinate well with the other contractors on the project. “With the help of Trimble technology, we had no problem keeping pace with the contractor establishing the stabilized dirt sub-grade,” Graham states. “We used the Trimble PCS900 3D paving control system on our paver, supported by four SPS930 universal total stations.”

Lane’s fleet includes a Roadtec RP-190 10-ft. rubber-tire asphalt paver with a hydraulically extendable vibratory screed that can pave as wide as 24 ft. with extensions. The paver was equipped with the PCS900 3D paving control system.

Since the project was fairly complex, with Y-lines, frontage roads and numerous exits and on-ramps, Graham used the total stations to more accurately measure position, cross slope and heading of the screed to automatically handle the transitions, super-elevated curves and frequently changing cross slopes. Two of the total stations were also used to grade check the laid mat to confirm accuracy.

“The contract called for the placement of 200,000 tons of asphalt, so we wanted to minimize waste and ensure accuracy across the three-lane highway,” Graham says. “We were looking at two 12-ft. lanes and a 14-ft. lane and all of the on-ramps and off-ramps and acceleration lanes, as well. The expressway widens out to four lanes temporarily in sections, expanding from 38 to 48 ft. wide.”

3D helps with smoothness

The PCS900 paving control system is a 3D automatic screed control system for paving in a stakeless environment. Smoothness is said to be improved because the machine is automatically implementing the design.

“The Trimble technology helped us immensely since our tolerances were very tight,” says Graham. “Technically, if we were more than 1/8-in. too high, we would have to go back and mill, and if we were 1/4-in. too low, we would have to pay for the extra concrete. So we had 3/8 in. of wiggle room. I don’t want to even think about it, but our milling and concrete costs would be substantial without the Trimble systems, just because the road was that complex.”

Lane Construction has complete capability internally to build digital 3D models. “Our company works on $1 billion worth of work annually, so we have 10 model builders on staff,” says Joe Grenier, GPS manager for Lane Construction. “We invested the time up front to topo the existing conditions every 25 ft. and compared that topo to the theoretical finish grade, and then added in the compaction factor of the asphalt. We created what we call an ‘un-compacted model’ to ensure we could hit within that 3/8-in. tolerance.”

Grenier admits that learning the un-compacted model procedure and getting it ironed out was probably one of the biggest challenges the company initially faced. A second challenge was mastering the Trimble system for pavers. “We’re very familiar with building models and running machine control systems on earthmovers, so taking advantage of that technology for asphalt paving was a natural extension, but still new to us,” Grenier says.

“Once we figured it out, the tangible benefits were apparent,” he continues. “By far the biggest benefit was to not have to go back and mill stretches of completed asphalt paving. With the tight tolerances on this project and all of its complexities, it would be expected to have the expense of a milling crew out there all of the time — but we didn’t.”

As a result of its success on this project, Lane Construction bought a PCS900 for a paver it has working in South Carolina and is looking at two additional systems.

According to Grenier, “The big reason the paving control system is so valuable is that concrete is so expensive. We save a lot of money on milling and concrete material. If we are too low with the asphalt surface, then we would need to fill that with the more expensive concrete.”

Lane’s portion of the project started at the beginning of 2011 and was completed by summer 2012. Unfortunately, once the Western Wake Expressway section is finished, motorists will never see the asphalt that Lane Construction laid.

“When people are driving on it, they probably won’t realize all the work that went into what’s under that concrete, because they’re just going to see the concrete surface,” Graham says. “But that’s fine; all of us who worked on it will know.” ET

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