NEW TECH
PaveScan MDM Offers Real-Time Density Data BY SARAH REDOHL
I
magine being able to know the density of the entire pavement without having to take a single core. That’s the ultimate goal behind the new PaveScan MDM (Mixed Design Module) from Geophysical Survey Systems Inc. (GSSI), Nashua, New Hampshire. When used along with GSSI’s PaveScan RDM (Rolling Density Meter) or RDM 2.0 systems, PaveScan MDM is used to correlate dielectric values with the known densities from gyrotory pucks directly from the asphalt plant to the PaveScan RDM system. In layman's terms, dielectrics refers to how permeable/permitive the substance is. The dielectric constant of a surface (for our purposes) is the ratio of how permeable it is compared to the permeability of free space—and this is expressed by how much electric flux is involved. For a scientific, in-depth explanation of dielectrics, visit www.vedantu.com/physics/dielectric-constant.
Paving Consultant Bryce Wuori of Wuori Consulting has used PaveScan RDM 2.0 since 2019 and has tested out the MDM system on more than 30 projects in 15 states since 2020. “I use PaveScan RDM 2.0 as a real-time quality control tool, whereas the MDM system is the calibration kit from dielectric to density. I consider it the link between PaveScan RDM and the asphalt mix being produced.”
FROM DIELECTRIC TO DENSITY
Since the launch of GSSI’s first PaveScan RDM model in 2016, the RDM system can be used to calculate the asphalt dielectric values for the entire pavement in real time. The dielectric values are based on the pavement’s void content, a relative indication of density. Visit theasphaltpro.com/articles/ gssis-pavescan-rdm-asphalt-density-assessment-tool/ for a full explanation of how PaveScan RDM works. “The dielectric maps can help show pavement uniformity and areas that are lower or higher in density,” said GSSI Business Development Manager Rob Sommerfeldt, “but alone it can’t tell you density values.” In the past, it was possible to convert dielectric data into density only after the job was cored. Only after the density of the cores was matched to the dielectric values that PaveScan RDM collected at the coring locations could a calibration curve be created, which converts the dielectric map to a density map. Since the launch of GSSI’s PaveScan MDM calibration system in January 2022, it is possible to use the RDM system to map the density of the entire pavement while there is still time to resolve potential issues. PaveScan MDM can be used to convert dielectric to density using pucks instead of cores. “Then, instead of seeing the dielectrics when using the RDM on the job site, the crew and DOT will be able to see 44 | JUNE 2022
These charts from the Ohio Department of Transportation shows how PaveScan RDM’s results correlate with nuclear and non-nuclear density gauges. Courtesy of GSSI
the density displayed on the RDM’s screen from day one of the job,” Sommerfeldt said. It’s even possible for this calibration to be done during the winter for a variety of common mix designs, so long as the same mix from the same plant gets used. Although Wuori has been using ground penetrating radar (GPR) technology for many years and has grown familiar with dielectric data, he said being able to see density data on the RDM’s screen, when used alongside MDM, is useful for those with less familiarity with dielectric data. “Dielectric doesn’t mean anything to many people in the asphalt industry,” he said. “Converting dielectric into a term they’re more familiar with helps the user better understand what’s happening with the asphalt.”
QUALITY CONTROL, QUALITY ASSURANCE
Not only can PaveScan RDM and MDM be used as quality assurance tools by agencies, the systems can also be used as quality control tools by contractors. “Contractors are making tons of decisions every day,” Sommerfeldt said. “This is a tool that can help them evaluate the job immediately.” For example, PaveScan RDM was used on a recent job in Texas where the crew realized they were seeing a pattern of low density. They were able to stop the job to diagnose and resolve the issue (the temperature on the auger of the paver wasn’t hot enough). This is how Wuori prefers to use the PaveScan RDM system. In fact, he uses RDM to set up roller patterns for all his projects, but also to adjust roller patterns as needed. “Since it produces real time data, we can walk behind the intermediate roller and look at rolling consistency in real time, to see density from the centerline to the shoulder in real time,” he said. If an area isn’t achieving the density required to satisfy a percent within limits (PWL) specification, Wuori and his contractor client can change the rolling pattern immediately to ensure uniform compaction.
