Figure 18: Autonomous impact protection vehicle [44

Figure 18: Autonomous impact protection vehicle [44]

3 Selected Technologies

The tech scan provided over 23 remote-controlled technologies that showed promising benefits to improve worker safety in highway construction, inspection, and maintenance. It was determined by the project’s Technical Panel that the technologies chosen for the next phase should have a priority to paving work and inspection. Therefore, technologies that were not directly related to pavement work like roadside maintenance, drainage inspection, and land surveying were disregarded from further analysis.

The Technical Panel decided to farther investigate two technologies that are of substantial importance for asphalt pavement construction and inspection. The technologies selected focused on the quality control of asphalt paving. The first, Automated Real-Time Thermal Profiling for Asphalt Paving using Infrared Cameras, is able to determine the asphalt mat temperatures continuously during paving. Then, the Remote-Controlled Density Profiling System can provide quick and comprehensive density data for the asphalt layer during and after compaction. The final technology was chosen in leu of the country’s growing interest in connected and automated

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vehicles. The Technical Panel choose the Autonomous Impact Protection Vehicle due to its potential for safety improvement of an activity directly related to work zone safety.

Technology transfer workshops with leading experts and vendors were promoted for each selected technology. Field demonstrations for the DPS technology were also conducted. Appendix B presents a detailed account of the workshops. Video recordings of the presentations and discussions can be found in the IRISE website.

3.1 Thermal Profiling for Asphalt Paving

Asphalt paving has a heavy reliance on temperature especially when initially laid and compacted. Asphalt concrete loaded at a lower temperature will deform less and behave more elastically than at a higher temperature [45]. This is especially critical during compaction. Compaction occurs during a specific temperature range to create the optimal pavement with high density but still retaining the desired air void content. Compaction of hot-mix asphalt typically occurs between 185 – 300°F [45]. As the asphalt concrete cools, the binder will become stiffer until compaction is significantly reduced. No significant compaction occurs below 175°F. If the entire asphalt mix is at too low of a temperature or if there is a significant temperature difference in certain areas, the pavement will not be properly compacted leading to lower density [46]. This leads to excessive air void contents which decreases the durability of the mix and allows for more air and water to penetrate the pavement creating potential for premature aging and moisture damage [47]. An initial air void content, typically between 6 – 8%, is achieved through compaction. After opening to traffic, regular traffic will farther compact the asphalt to the desired air content of 3 – 5% which will remain to the end of the service life [45]. For a dense graded HMA, just a 1% increase in air content from a 7% base can lead to a 10% decrease in the pavement life [47].

There are two key terms to consider when discussing issues with asphalt mix temperature: temperature differential and temperature segregation. Temperature differential is the difference in average mat temperature between a cooler area and the bulk area. Temperature segregation is the isolated areas of the mat that have a significant temperature difference [48]. A 2013 study used thermal imaging cameras to highlight cold spots, areas with a significant

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