Due to more sophisticated asphalt mix designs, increasing quality expectations and ever-tighter schedules, compaction requirements on paving projects are more complex than ever. This is where intelligent compaction (IC) can help.
Currently used on 66 in. wide and larger rollers, IC monitors the stiffness of the mat, the mat surface temperature and the roller passes as it’s compacted.
“IC is an equipment-based technology for better quality control that results in longer pavement lives,” says George Chang, PhD, PE, with the Transtec Group. “IC machines are vibratory rollers with accelerometers mounted on the axle of drums, GPS, infra-red temperature sensors (for asphalt) and onboard computers that can display color-coded maps in real time to track roller passes, asphalt surface temperatures and stiffness of compacted materials. In short, intelligent compaction is a smarter way to get things done.”
IC comes to Utah
The Utah Department of Transportation (UDOT) was learning how IC could help improve operations, reduce impacts to the public and deliver a higher-quality product. It contacted the Federal Highway Administration’s (FHWA) Intelligent Compaction research team in February 2012 to express interest in participating in a national IC field study.
“UDOT was interested in the FHWA research on this technology and whether or not it would benefit our state,” says Muriel Xochimitl, M.A., with UDOT, Region 3.
In February 2012, FHWA conducted an IC National Workshop in Salt Lake City, UT. “Following the workshop, UDOT partnered with the FHWA to host an IC demonstration in August 2012, after the technology was used on our US-89/SR-180 Pavement Rehabilitation Project,” says Xochimitl.
The demonstration project was located at US-89 and SR-180 in American Fork and Lehi, UT. The total length of the project was approximately six center lane miles, with the target section for the study being approximately three lane miles.
The US-89/SR-189 Pavement Rehabilitation project was a mill-and-fill asphalt paving job for one lane in each direction. Four inches were milled from the existing pavement.
The new layers included a 2.5-in.-thick warm mix asphalt (WMA) base course and a 1.5-in.-thick stone mastic asphalt (SMA) wearing course with a cross slope of 2%. The WMA was produced using the foaming method.
Staker & Parson was the contractor on the US-89/SR-189 Pavement Rehabilitation project, and was the first company to use IC technology in Utah.
“Our organization was just introduced to IC thanks to this demonstration,” says Jonas Staker, estimator and project manager with Staker Parson Companies. “Through this demonstration, the biggest benefit was learning about IC and what this new IC process and its long-term benefits can provide. It seems this might really help our industry.”
Staker & Parson used two rollers on three paving shifts during the demo: a HAMM HD+120 double-drum IC roller and a Sakai SW880 double IC roller. The Sakai IC roller used a Trimble GPS system, while the HAMM IC roller used an OmniStar GPS system. A MOBA Pave-IR system was also used to help detect thermal segregation in the asphalt pavement in real time.
The benefits of IC
Staker appreciates the time and cost savings of using IC. “Having real-time feedback to the roller operator with compactions and densities is a huge benefit,” he says. “With the GPS system mapping out rolling passes, the benefit of rolling the pavement (or aggregate) evenly will lead to pavements that will be compacted to optimum strength without being over or under compacted. These factors will increase the life of the pavement.
“From a cost perspective, having the roller measuring the stiffness of the pavement in real time could eliminate the cost of having a field technician on site and/or possibly alleviate destructive testing,” he adds.
Another benefit is the ability to monitor pavement stiffness over a larger area. “In the compaction process, IC technology continuously measures asphalt stiffness,” Xochimitl notes. “Real-time data allows the project team to track and consistently compact the entire work area, which improves the overall quality of the asphalt on the roadway. The consistent pavement densities result in greater roadway smoothness and lower maintenance costs. Over time, the roadway’s higher quality will result in cost savings to the department and the taxpaying public.”
Staker agrees, noting, “IC is a system that measures 100% of the road surface, instead of cores/nuclear gauge tests that only test a very, very small sample of the area. IC will lead to a smarter way of constructing a roadway, which will increase the life of the pavements. I think this technology is something we need to grasp as an industry.” ET