It was 10 years ago that Granite Construction milled and resurfaced the middle runway at Salt Lake City International Airport. The work is mandated to occur about every decade, so earlier this spring Granite crews were back at the airport. It was the same city, same airport, same runway — and a very, very different plan.
“A lot has changed in 10 years,” said Kyle Smith, project manager at Granite. “Ten years ago, we completed this job with one crew and wireline. This time we used two crews, a wireless system and 3D paving in echelon — and we are using intelligent compaction.”
The project called for profile milling and resurfacing of a runway and all the taxiways. Crews removed 4" of asphalt during milling and replaced it in two 2" lifts. During the job, 80,000 tons were placed. Time, of course, was a factor as well. The entire project had to be completed within 60 days.
Specifications required paving to an elevation, and echelon paving was used to minimize the number of cold joints. The echelon requirement meant wireline could not be utilized for elevation control.
This led Granite to launch the use of a Trimble 3D paving system. “We use 3D grading all the time,” Smith said. “As we looked at the need for echelon paving, and the tight tolerances of the FAA, we concluded that 3D paving was our best option.”
The 3D paving process required surveying technology that Granite had utilized on previous projects. The elevation was created digitally and referenced during both milling and paving. “We had been using it on motor graders for finish grading for years,” Smith said. “The technology itself is not new to our surveyors.”
It was new to paving crews, and changed their roles. The pavers—a Cat AP1055D and AP1055B—received information from up to twelve robotic total stations as they moved down the runway. That information directed the screed to be raised or lowered to meet the elevation requirements. All screed adjustments were automatic.
Smith acknowledged starting the process was stressful, particularly given the strict FAA standards. Granite arranged training through the local Cat dealer, which spent more than a week on the jobsite ensuring all crew members were up to speed. The training included paving with sand to provide the crew with hands-on experience.
The preparation for 3D paving takes a great deal of work, Smith said, but when work starts it moves along quickly. “The prep work is all basically done by building the model,” Smith said. “We don’t need surveyors setting elevations and installing wireline. That prep work is done prior to the start of the project, so we can just get out there and pave.”
FAA specs required the utilization of transfer material vehicles. Belly dump trucks, with capacities of 38 tons, delivered mix to the jobsite.
The trucks were 30 minutes from the plant. The paving began in April—“There was still snow in the mountains,” Smith said—so quickly cooling mix was a concern.
The paver worked at a pace of 20-25' per minute during the early, cooler days. “That pace is driven by surface temperatures,” Smith said. “With the 2" mat, we can’t let the paver outrun the rollers. The pace is strictly a function of compaction and has nothing to do with the technology.”
The paver operator steers the machine and sets the pace. The screed men are responsible for switching the signal reception from one station to the next as the paver moves down the runway. They also monitor an on-board display to ensure the screed is responding properly.
The pace was slowest at the start of the project while crews adjusted to the echelon paving process, and the volume of machines and personnel that go with it. “Trying to get two pavers to work side-by-side, it’s a challenge,” Smith said. The pavers worked within 100' of each other. Mix was 320° when it left the plant, between 300°-310° when it arrived, and between 280°-290° behind the screed.