September 2021Vol. 29, No. 3

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Asphalt membrane reduces air voids, improves performance

rutted gravel road

A mound of fill indicates where a test core was pulled
from a joint that used J-Band.

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.

wheat field and blue sky next to a road

Researchers tested samples from an asphalt pavement
on State Highway 22 that included J-Band under the
longitudinal edge joints of asphalt lanes.

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.

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