The benefits in utilizing PRAS are numerous, says Tucker.
- The ability to keep waste materials from entering landfills and reusing the products in the manufacturing process
- Lowering the amount of “virgin” liquid asphalt that has to be purchased
- Achieving density more quickly
- Continuing to be an environmental steward in the construction industry
"PRAS is really the next big thing after WMA for our industry," he notes. "The number one benefit for our bottom line is saving money on the liquid asphalt. Achieving density more quickly was a nice surprise. We didn't anticipate that."
Tucker says the quality control personnel on the project weren't sure why the densities were achieved more efficiently. "We ran the mix for eight days and densities were consistent throughout the project," says Tucker. "One theory was that the fiber that holds the shingle together acted almost like a fiber injection mix, creating the faster density."
Rock Hill Church Road was a good candidate for a PRAS mix, and it was also a good project to try the FHWA's Safety Edge technique. " Since this was going to be another 'pilot' project for Boggs' and NCDOT because of the PRAS mix design, State Construction Engineer Ron Hancock requested that we utilize the FHWA safety edge to see how effectively it would work to eliminate shoulder drop-off issues," says Tucker.
The FHWA recommends that states use the safety edge technique – particularly on two-lane roads with unpaved shoulders. According to its website, during the normal paving process, pavement edges are formed vertical or near vertical. The recommended practice of bringing the adjacent graded material (unpaved shoulder or stabilized soil) flush with the top of the pavement only lasts for a short time and requires frequent maintenance. The exposed vertical edge can contribute to drivers losing control of the vehicle when attempting to recover from a roadway departure.
Recent updated research has shown that almost all drivers and vehicles can recover if the edge is tapered to 30 degrees from the horizontal. Safety Edge is easy to include in the paving process and provides a safer roadway edge and a stronger interface between the pavement and the graded material, notes the website. The additional cost of the asphalt edge is minimal when included as part of resurfacing project.
Tucker notes that the FHWA is starting to require the Safety Edge in contracts for mixes greater than 2 inches.
"Basically the Safety Edge is installed on the outside gate of the paver and slopes the edge of the pavement on a 30-degree angle," says Tucker. "This will assist motorists when they run off the edge of the pavement and have to correct back on to the roadway. It works very similar to the Transtech Notched Wedge Joint Maker for centerline joints, which we used on this project as well."
Rock Hill Church Road was a pilot project for both PRAS and Safety Edge, but the project went off "without a hitch," says Tucker, who sees the company increasing its use of PRAS in the future.
"Boggs’ plans are to utilize the PRAS mixes on all possible projects," says Tucker. "NCDOT specifications currently allow RAS mixes on all projects, however, the NCDOT Construction Unit staff has been instrumental in allowing the use of PRAS. Ron Hancock and Todd Whittington have led the charge for the Department by initiating green components in new and existing contracts. The ability to have environmental stewards on the front lines of the Department will be a benefit to the taxpayers of the State of North Carolina for years to come."