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Heat the Longitudinal Joint For Optimum Density AsphaltPro discusses the continuing trend of heating longitudinal joints during construction, a practice that allows the contractor to improve density at the joint and achieve full pay. BY SARAH REDOHL
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aving Consultant Bryce Wuori of Wuori Consulting, Bismarck, North Dakota, estimates that roughly half the jobs he consults on face a longitudinal joint density specification. “If you include the airport jobs I’m on, it’s up to 70 percent,” he said. Wuori said that the majority of states in which he works now have incentives for density on the longitudinal joint, anywhere from $0.60 to $1 per linear foot. Not only can that add up to quite a bit of incentive for contractors, Wuori said, but improving density on the longitudinal joint also produces a better road for the owner. “The longitudinal joint is typically the first place that fails,” he said, “so if you can make that last as long as the rest of the road, you’re going to get longer lasting roads.” “Pavement deterioration always starts with cracking,” said Michael Blake, marketing manager at KM International, North Branch, Michigan. “And the main cause of cracking is water penetration, which usually starts at the centerline joint.” Density issues at the longitudinal joint are nothing new, Wuori said. What is new is the growing number of agencies specifying longitudinal joint density. In the next three to five years, Wuori believes almost all jobs will specify longitudinal joint density. “In the past, we didn’t have the tools to achieve better density at the longitudinal joint,” Wuori said. “Now that contractors have the tools available to improve joint density, agencies are feeling more comfortable implementing density specifications because contractors have a good chance of achieving them.”
METHODS TO IMPROVE JOINT DENSITY
Although longitudinal joint density specifications are becoming more common, Wuori said the process by which a contractor achieves density on the longitudinal joint often isn’t specified. One solution is the process of heating the longitudinal joint during construction. “When you reheat the joint, you’re making the bitumen and aggregates thermal again so their ability to bond increases,” Wuori said, which decreases air voids at the joint. “By heating the joint, you are ensuring the joint is around 300 degrees Fahrenheit at compaction, instead of 80 to 100,” Blake said. With an infrared heater, he added, contractors can install hot asphalt against hot asphalt, “which is going to create a seamless weld between the two lanes.” Although Wuori most often recommends to his clients the use of a notched wedge to improve joint density, he said heating the joint is also a good option. “The notched wedge is the cheapest and easiest option and one that almost always allows the contractor to hit that joint density,” Wuori said. However, he added, “from what I’ve seen, if you can reheat the joint you’re going to see better, more consistent density than with a notched wedge.” 56 | MARCH/APRIL 2022
Wuori gave this theoretical comparison: If a contractor paved a 2-inch lift with a standard dense-graded Superpave mix with a standard vertical joint, Wuori estimates they might hit the average longitudinal joint density spec of 90.5 percent density half the time. All else equal, if the contractor added a double shot of tack or J-Band at the joint (which Wuori requires on all his projects), he estimates they could hit that density 70 percent of the time. If they used a notched wedge, he estimates they could hit density 90 percent of the time. If they use both a double shot of tack or J-Band plus a notched wedge joint, Wuori estimates the contractor could be successful 100 percent of the time. He estimates the use of a double shot of tack or J-Band plus reheating would be similarly successful. And, if they used a double shot of tack or J-Band, plus a notched wedge joint, and reheating, “they will max out the incentive for longitudinal joint density every time,” he said.
LEARN MORE HERE’S HOW J-BAND CAN HELP Void reducing asphalt membranes (VRAM) beneath the longitudinal joint of a course of hot-mix asphalt (HMA) pavement are designed to assist in joint construction. One such VRAM is J-Band, a hot polymer-modified asphalt product from Asphalt Materials Inc., Indianapolis. “VRAM is a materials solution to centerline permeability and joint density issues,” said Jeffrey Ball, executive director of marketing and communications for Asphalt Materials. “It’s like an insurance policy to minimize the need for agencies to have to repair these joints because of longitudinal cracking, potholes, raveling, etc.” J-Band is applied by a distributor truck immediately before paving, usually as an 18-inchwide strip under the eventual location of the longitudinal joint along the final lift. As HMA is applied, J-Band will migrate upward through the new HMA to fill voids up to 75 percent of the overlay height to fend off future water infiltration. “The heat of the hot mix activates the VRAM,” Ball said. “The heat along with the pressure of the rollers helps the VRAM migrate up into the hot mix. If you core the longitudinal joint area and test the permeability, you’ll see that it's much lower because the VRAM has filled those air voids.” This process can help roads last up to five years longer, Ball added.
