Asphalt membrane reduces air voids, improves performance
J-Band is a void-reducing asphalt membrane (VRAM) product. These products—mixes of asphalt binder, polymer, and modifiers—hold new asphalt in place and migrate upward into the asphalt layer, filling air voids. MnDOT and other agencies rely mostly on anecdotal evidence and manufacturer claims to judge VRAM products and applications.
In a MnDOT-funded project, researchers evaluated the use of J-Band in an asphalt pavement on State Highway 22. Tests showed higher bond strength, lower permeability and air void levels, and improved crack resistance.
Maintenance Operations Research kick-starts the study
Potholes and similar asphalt failures typically occur at the seams between lanes. At these edges, asphalt’s higher air void content makes it more susceptible to moisture penetration, freeze-thaw damage, and other failures.
Typically, the density within 6 inches of the longitudinal joint is lower than the density throughout the mat. To mitigate potential failures, crews can spray a VRAM product at the seam location before the asphalt paving.
In 2017, Jerry Geib and Charlie Kremer submitted a proposal to MnDOT’s Maintenance Operations Research (MOR) program. Geib, research operations engineer with MnDOT’s Office of Materials and Road Research, and Kremer, materials engineer in MnDOT District 7, requested $15,000 to test J-Band for longitudinal joint treatments. Their proposal was approved, and the funding was used to purchase the J-Band product.
In 2018, a 1-mile section was paved on TH 22 and treated with J-Band. At the test site, in Blue Earth County south of Mankato, J-Band was applied in an 18-inch-wide band at the longitudinal joint followed by a top layer of 1.5 to 2 inches. Another mile of pavement with no VRAM served as a control.
MnDOT then funded a study by Iowa State University to evaluate J-Band’s performance. Researchers gathered a sample of the hot-mix asphalt to determine binder and mix gradation and collected about 40 cores from the two sections. They conducted lab tests on the cores for a range of properties. They returned to the paving site in October 2019 to do a visual survey for signs of distress and examine the density of mat locations and joints.
Results: J-Band extends pavement service life
The researchers found that J-Band migrated up into the top asphalt layer and reduced air voids from 8.5 to 5 percent. The product reduced water incursion and improved pavement strength. In laboratory testing, VRAM outperformed control sections in terms of bond energy, fracture energy, work of fracture, and surface energy.
“This VRAM is performing as advertised,” says Eddie Johnson, research project engineer with MnDOT’s Office of Materials and Road Research and the technical liaison for the study. “It reduced water flow greatly. Mechanical tests indicated that J-Band strengthens the pavement structure.”
Cost savings over time could be significant. “Trying to solve longitudinal joint cracking through compaction effort is not really possible,” says Joseph Podolsky, bituminous materials scientist with Iowa State University and the study’s principal investigator. “Using VRAM products is easier. The material should benefit long-term pavement performance where it is used.”
Kremer notes that the cost of J-Band (or similar products) would be affected by product availability and application logistics.
MnDOT’s Office of Materials and Road Research is writing a special provision for VRAM use, Geib says.