Figure 3 : Distribution of dielectric value
It helped that Maine DOT had a crew that was already familiar with GPR, making it a relatively easy transition to get up to speed. The crew found the PaveScan RDM equipment to be easy to set up and use. The only limitation they found is that the Figure 1: Typical density profile shows data collected with PaveScan RDM three- sensor system Figure 2 : Calibration of dialectric versus air voids at battery does not last several pilot study locations long enough for a full day of data collection. Other recent adjustments include a laser pointer that can be attached to the equipment to help operators align the scan- ning equipment, especially for use in night work. Operators found the extra lighting to be very helpful. However, Peabody notes that the technology does have some boundar- ies. It is affected by surface moisture, does not work as well when temperatures dip below 40°F, and can be affected by mix constituents, which may happen with a change in aggregate source. Measurement accuracy for layers of less than 1-inch may be affected by the under- lying layer, while layers that are 2.5 to 3-inches may be affected by density gradients within the layer. Maine DOT is also looking for further enhancements. For example, some users are adapting the technology for use with vehicle mounts. This issue is one that GSSI is actively pursuing for Spring 2019. Other items on the wish list are better ways of using the technology for lon- gitudinal joints; incorporation into the Veta intelligent construction software – a map-based tool for viewing and analyzing geospatial data; and better data analysis of intelligent compaction, thermal profile, and GPR density data. Peabody’s colleague, Rick Bradbury, has presented the positive results of the pilot studies at several SHRP2 workshops and has shared the information with New England DOT colleagues. He also recently presented the information at the 2018 North East Asphalt User/Pro- ducer Group (NEAUPG), which is focused on improving the quality and performance of asphalt pavement applications in the Northeastern United States by promoting communication, knowledge, technology, and uniform solutions.
Special focus on data analysis While not unique to this technology, one of the key factors affect- ing whether Maine DOT would want to implement the technology statewide is the issue of data analysis. “Who is going to collect all this data?” asks Peabody. “If there are 20 projects, you can’t have just one crew collecting data. We have thought about asking the contrac- tor to purchase the equipment and use it but we are not ready for that, because for it to work you have to have people who really understand the technology.” Ultimately, he believes it would be best if this type of data could be collected in a moving vehicle; the vehicle could then go project to project and collect data. However, Peabody acknowledges that this ap- proach would have a downside – the lack of real time data contractors could use to make adjustments as they are going along. “If they collect data but don’t look at it until the next day, that does not really give the contractor a chance to make adjustments if there are density issues. I’d like a way to share data with the project team in real time, other than only being able to show the display on the Toughpad.” According to Peabody, the larger question that must be answered is how to effectively manage the data to make near-real time changes during production, and to get timely reports to project personnel. “Cur- rently, there is no good way to get data in the right people’s hands so they can make adjustments on the fly. There is a lot of benefit to having that ability. They could collect data and then go back to specific points on the road. They could select locations of high and low dielectric/ density and then cut a core there and send it to the lab to determine the actual density.” GPR surveys show good correlation between dielectric and air voids The PaveScan RDM surveys show a good correlation between the dielectric value and the air void contents. Maine DOT can use the sur- veys to quickly identify and investigate low density areas and to check the compaction consistency. While data management is a huge effort, they believe the surveys will be very useful, in conjunction with other new technologies, including intelligent compaction and pave IR.
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october 2020
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