PennDOT Studies Joints for Sustainable Pavements
BY Associated Asphalt
Researchers have established that longitudinal joint performance influences the lifespan of a pavement. If the joint is built with higher permeability and lower density compared to the rest of the pavement, water and air intrusion leads to accelerated damage, which often requires maintenance within three to five years.
This graphic shows the timeline for PennDOT’s road to a standard special provision for void reducing asphalt membrane use. All images courtesy of Associated Asphalt
Over the years, multiple agencies have investigated various strategies to enhance the performance of asphalt pavement longitudinal joints. Despite these efforts, high permeability remains a challenge. The void-reducing asphalt membrane (VRAM) has demonstrated its effectiveness as a solution that prolongs the life of longitudinal joints.
VRAM is a material-based solution involving the application of a thick layer of hot-applied, polymer-modified asphalt (PMA), rather than an emulsion. It is applied beneath the future centerline of the longitudinal joint. As hot-mix asphalt (HMA) is laid and subjected to heat and compaction by rollers, the VRAM gradually migrates from the bottom up, rendering the joint nearly impermeable to water and air. The VRAM “wicks” upward in the longitudinal joint area during paving, essentially filling the air voids remaining in the longitudinal construction joint.
Check out the January 2019 Here’s How it Works for a step-by-step guide to creating a joint with VRAM. Read the March 2021 “Innovate at Centerline Rumble Strips” for additional information on the membrane’s use.
Initial trials for VRAM occurred in Illinois in 2001 and 2002. In 2017, follow-up testing and observations by the Illinois Department of Transportation (IDOT) revealed the experimental sections exhibited lower permeability and higher asphalt content compared to the control sections, resulting in improved crack resistance.
In 2018, the Pennsylvania Department of Transportation (PennDOT) developed a work plan to investigate VRAM via 14 trials via a five-year period. One of the VRAM products selected for these trials was J-Band® and that’s what we’ll look at here.
First PennDOT Trial
PennDOT District 5 began its first trial on a 2.1-mile stretch of I-81 in Schuylkill County in October 2018. Annual visual assessments were conducted to examine the state of the VRAM longitudinal joint and the control joint.
In April 2023, Dave Powers, Associated Asphalt’s Northern Region performance products manager, along with representatives from PennDOT Central Office, District 9 and District 5, carried out a fifth-year evaluation.
In the VRAM experimental section, in line with expectations for the fifth year, they observed minor cracks present on the joint’s surface in a few areas. However, these cracks did not penetrate into the paving mat. The majority of the experimental section remained devoid of cracks.
In the control sections built with traditional joint methods, they observed the project faced issues stemming from underdrain and material failures. The northbound control area underwent milling and replacement in July/August 2019, which is nine to 10 months after the trial began. Nonetheless, District 5 managed to avert the replacement of the experimental VRAM section. Instead, the new joint installed in 2019 was treated as the “control joint” for this pilot project. Despite the control section being paved subsequent to the experimental joint, the VRAM continued to demonstrate superior performance.
Second PennDOT Trial
PennDOT’s second VRAM trial was applied Oct. 17, 2018, on a 1.1-mile section of I-380 in Monroe County. This experimental section would be compared over time to approximately 0.5 miles of control sections.
A team visually reviewed the joints annually, and in 2021, cores were pulled from the 3-year-old joints in the control and VRAM sections. These cores were sent to Rutgers University Center for Advanced Infrastructure & Transportation (CAIT) for complete testing. While the annual visual inspections did not reveal substantial differences between the control and VRAM sections, the lab data showed differences in favor of VRAM.
Air Void Determination—The air void determination indicated that the control section had higher air voids than the VRAM section for the 9.5-mm SMA surface course with the butt joint longitudinal joint construction (10.4% vs 8.2%, respectively).
Falling Head Permeability (FM 5-565)—The application of the J-Band product significantly reduced the permeability of the compacted asphalt at the longitudinal joint. On average, the permeability of the J-Band-treated longitudinal joint was approximately 35 times slower than the conventional longitudinal joint. When permeability testing was conducted using the entire core provided (9.5-mm SMA plus J-Band plus binder course), the VRAM sections were determined to be impermeable, indicating the VRAM seals off the underlying asphalt layers below the longitudinal joint area.
IDEAL-CT Index—The application of the J-Band product significantly improved the cracking resistance of the longitudinal joint as determined using the IDEAL-CT Index test procedure. The application of the VRAM product increased the IDEAL-CT Index of the longitudinal joint by almost 4 times compared to the IDEAL-CT Index values measured in the control cores.
All trial cores for PennDOT resulted in these average IDEAL-CT Index scores. Graph courtesy of Associated Asphalt
Another visual inspection was completed in December 2022. The VRAM joint continued to show less cracking than the control joint.
Through the end of 2022, thirteen trials had been constructed, including four in District 5, two in District 4, and one each in Districts 1, 2, 3, 6, 8, 11 and 12. In total, six separate core tests were conducted, including the 3-year-old joints pulled from the second trial described above. The graphs included here summarize some of the data collected from the PennDOT test project by Rutgers University CAIT. Overall, VRAM effectively demonstrated an improvement in IDEAL-CT (crack resistance), as well as a reduction in permeability. VRAM improved the performance of the asphalt pavement mat at the longitudinal joints by reducing permeability and lowering air void content.
All trial cores for PennDOT showed these average air void percentage results. Graph courtesy of Associated Asphalt
New VRAM Standard Special Provision
In March 2023, PennDOT issued a new Standard Special Provision for Void Reducing Asphalt Membrane (VRAM). This SSP, which can be used on projects let on or after April 14, 2023, is recommended for use on limited access and expressway-type pavements where exceptional longitudinal joint performance is difficult to achieve. An added benefit of using the VRAM SSP is the joint density specification does not apply. As of August 2023, there have been six VRAM projects completed or scheduled to be completed in 2023, and seven confirmed for 2024.