“VDOT has basically dedicated themselves to placing SMA type asphalt on all of their interstate rehabilitation and maintenance work,” says Owen Lanier. “To accomplish this there were changes, modifications and upgrades in their highway construction specifications. We have been fortunate to have been awarded a number of these contracts including projects on I-95, I-295, I-64 and on the downtown expressway in the City of Richmond . In the beginning we began placing the SMA mix with our conventional pavers, and we quickly found that to get the proper density on the material we would need to employ a high frequency roller working very close behind the paver’s screed. Even then we found that the rideability suffered because of the high amount of compactive effort that had to be placed upon the newly laid mat.
“The rollers tended to push the mat horizontally as well as compact it vertically,” continues Owen Lanier. “This, in our opinion, was due in part to the weight of the compactor, the vibration frequency, the additional amount of binder asphalt in the mix, and the high temperatures that were needed to achieve the specified compaction density. It was at about that time we went looking at the tamper bar screed type pavers. Our first attempt at this involved a Dynapac machine as well as an ABG paver.
“We found the double tamper bar paver that was offered by ABG tended to give adequate compaction, with the added benefit that it put down a smoother mat because of the mechanics involved in the pre-compaction of the asphalt prior to it flowing under the screed,” he continues.
“This is an extremely important factor. Today most state and federal SMA project contracts contain an incentive/disincentive clause to be determined by the results of rideability.
“We have fortunately been able to maintain most of our SMA smoothness and rideability in the bonus mode. To a large degree this has been brought about through the use of our Ingersoll-Rand double tamper bar pavers with their high-density Duotamp vibratory screeds and the use of material transfer vehicles (MTV).
“Another important factor in this equation is that we also own two asphalt plants and produce our own SMA mix,” continues Owen Lanier. “In so doing, we maintain absolute control of the aggregate and asphalt binder. In placing this material with the use of an MTV we also avoid both thermal and material segregation.”
Lee Hy Paving’s experience
“We’re also very pleased with our new Ingersoll-Rand Model 326 Titan Duotamp paver with the double tamper bar screed,” says Stanley Snelling, Lee Hy Paving Corp.’s vice president and comptroller. “In fact, the results have been excellent. Test results indicate that we are achieving up to a 90-percent density at the screed. That has enabled us to affect a cost savings by eliminating one roller from our equipment spread.”
Lee Hy Paving Corp. of Rockville , VA primarily works (60 percent) on roads under the jurisdiction of VDOT. Another 30 percent is done on commercial paving projects in the private sector. The company also does some sitework, principally stonework for asphalt paving preparation. Lee Hy Paving owns and operates six Blaw-Knox pavers and one new ABG Model 326 Titan Duotamp. They also operate 21 rollers. The ABG Triton paver was acquired in March 2005 primarily for use on VDOT paving projects involving SMA.
Lee Hy Paving’s current SMA project involves both concrete patching and a two course, 3 ½-inch thick overlay and resurfacing of I-195/I-295. The 2-inch intermediate course consists of 25,000 tons of IM 19mm SMA. The 17,000 tons of top 1 ½-inch surface mix is SM 12.5mm SMA.
“The key to a successful SMA mix starts with the correct stone gradation,” says Snelling. “We have our own asphalt plant which provides us with tight control of the aggregate and binder. We purchase our stone from Vulcan Materials Co. Being the largest aggregate producer in the country, they know how to crush the special stone specified for SMA mix and do an excellent job.”
“The Ingersoll-Rand ABG Titan double tamping bar paver, in my experience, does a very good job in getting the majority of the required SMA mat density right up close behind the screed. We follow this up with a pair of heavy duty rollers in the vibratory/static mode and a pneumatic tire compactor as a finish roller,” says Danny James.
A mechanical supervisor for Virginia Paving Co., James has been closely involved with the ABG pavers ever since the asphalt contractor took delivery on its first one. In his position he supervises the heavy equipment, including the pavers and rollers. He also designs, builds and modifies equipment for the company’s special projects.