Prevent Temperature Segregation with a Thermal Profile
BY Sandy Lender
Paver-mounted thermal profiling scanning (PMTPS) is one facet of intelligent construction. Most readers of AsphaltPro Magazine are familiar with intelligent compaction, wherein data about the mat assists the roller operator in achieving optimum density.
In PMTPS, a thermal “camera” is affixed to the back of the paver for the purpose of assisting the paving crew in monitoring, and thus lessening the chances for, temperature segregation in the mat. The researchers at Transtec Group Inc., Austin, Texas, shared at their intelligentconstruction.com site:
“Normally, every 50-meter section of full-width temperature profiles is analyzed to determine the levels of temperature segregation. Example methods are the US AASHTO PP80 standard…and an improved Thermal Segregation Index (TSI) method developed by the Minnesota Department of Transportation (MnDOT) and The Transtec Group’s Veta team.”
Daniel Oesch, P.E., field materials engineer for the Missouri Department of Transportation (MoDOT), explained: “MoDOT has awarded 69 projects to date with both IC and PMTPS technologies. The effort gained momentum in 2016 after receiving an Accelerated Innovation Deployment grant from the Federal Highway Administration providing additional resources for the first 13 projects. During the 2020 construction season, 29 projects will be underway utilizing these technologies. This year, we have deployed a fleet of agency owner GPS tracking units, which are being circulated on the IC rollers in order to perform quality assurance (QA) on the data being collected by the contractors’ equipment. In addition to spot temperature readings, this year thermal images will also be used for QA of the PMTPS systems.”
Henry Polk of BOMAG Americas, Ridgeway, South Carolina, explained that the MOBA thermal imaging system is the preferred vendor Bomag recommends for use with its paving equipment. He shared that the MOBA thermal camera captures and stores the readings from across the width of the mat, allowing the foreman to download and share the data via a USB stick. While the thermal cameras available today don’t penetrate the mat, the temperatures measured and recorded from the surface give contractors a data point not easily available before.
“It only shows the surface temperature, but it’s still relative to segregation,” Polk said. “Thermal segregation is far worse than material segregation. Being able to see it on the surface is better than not being able to see it at all.”
The team at Caterpillar Paving Products, Peoria, Illinois, has a similar explanation. They state on their website: “Thermal mapping monitors the surface temperatures of the asphalt utilizing an infrared camera and a Global Navigation Satellite System (GNSS) enabled by RTK accuracy. Viewing real time temperatures, contractors can identify variations and take action to manage the plant-to-paver delivery process and fine-tune paving practices for more uniform lay-down temperatures.”
At the Wirtgen Innovation Days event in the fall of 2018, product managers discussed the merits of the Vogele RoadScan. This infrared temperature measurement system was also on display at CONEXPO-CON/AGG 2020 in Las Vegas. It’s designed to make quality measurable by verifying you’re paving at a constant temperature. It’s a non-contact temperature measurement system that scans the whole of the asphalt pavement behind the screed. A GPS receiver is also mounted in the housing for the infrared camera, to record the exact position of the temperature data. External parameters affecting paving are recorded as well. The maximum measuring width of 10 meters is made up of 40 squares measuring 25 by 25 centimeters. Each of these grid squares contains up to 16 individual measuring points, from which a mean value is calculated. The measurable temperature range is between 0 and 250 degrees C, with a tolerance of +/- 2 degrees C. RoadScan saves the measured data in the paver operator’s ErgoPlus 3 console. After paving, the data can be transferred to a memory stick.
As part of its Pavelink system, Topcon Positioning Systems offers the thermal mapper, which affixes to any paver to monitor the temperature of the entire width of the mat. It shows the operator, in real time, the average temperature of the previous lot as well as thermal segregation and for the overall jobsite. This means the foreman can see immediately if there’s a temperature problem creeping into the operation.
Preventing segregation is one step toward quality control for contractors. Equipment that can re-blend mix to keep cool spots from making their way through the train and to the mat is a helpful tool. “Our remix machine re-blends it and does away with the thermal segregation,” Polk said.
To ensure remixing machines ahead of the paver—or at the paver—have done their jobs, or to ensure all trucks have delivered consistent loads to the process, the thermal cameras offer an extra QC/QA measure. If the foreman and paver operator monitor the temperature readings gathered moment-by-moment, they can monitor temperatures in real time and make adjustments as needed.
This ensures the mix being delivered from the plant, to the head of material, and to the mat has a uniform temperature and a consistent, top quality.
This article originally appeared as a sidebar alongside this article about NB West’s award-winning mill-and-fill project on I-44, that required paver-mounted thermal profiling scanning (PMTPS).