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.”