The specifications at Salt Lake City International Airport required paving to an elevation. Granite Construction used echelon paving to minimize the number of cold joints.
Specified tolerances for the repaved surface were 2/100th of a foot. Quality control surveyors worked behind the screed to double check tolerances.
As they moved down the runway, the pavers received information from robotic total stations that directed the screed to be raised or lowered to meet elevation requirements. All screed adjustments were automatic.
Elevation data for the 3D paving process was created digitally and referenced during both milling and paving.
Granite Construction used its local Cat dealer to train the paving crew on the 3D paving process. Training included paving with sand to provide the crew with hands-on experience.
Four of the six compactors used on the project were equipped with intelligent compaction. This allowed the operators to easily see how many passes had been completed and adjust speed based on mat temperatures.
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, but a very different plan.
“A lot has changed in 10 years,” says 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.”
Paving Gets an Added Dimension
The project called for profile milling and resurfacing of a runway and all the taxiways. Crews removed 4 in. of asphalt during milling and replaced it in two 2-in. lifts. During the job, 80,000 tons of asphalt was placed.
Time, of course, was a factor. 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 says. “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 states. “The technology itself is not new to our surveyors.”
However, it was new to paving crews, and changed their roles. Smith acknowledges starting the process was stressful, particularly given the strict FAA standards. Granite arranged training through the local Caterpillar 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.
Keeping Pace with Cooling Mix
The preparation for 3D paving takes a great deal of work, says Smith, but once work starts, it moves along quickly. “The prep work is all basically done by building the model,” he explains. “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 38-ton capacities transported the mix from the plant to the jobsite 30 minutes away. Paving began in April — with snow still in the mountains — so quickly cooling mix was a concern.
The Caterpillar AP1055D and AP1055B pavers received information from up to 12 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.
The pavers worked at a pace of 20 to 25 fpm during the early, cooler days. “That pace is driven by surface temperatures,” Smith notes. “With the 2-in. 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 onboard display to ensure the screed is responding properly.
The pace was slowest at the start of the project as 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 is a challenge,” Smith says. The pavers worked within 100 ft. of each other. Mix was 320° F when it left the plant, between 300° to 310° F when it arrived, and between 280° to 290° F behind the screed.
Specified tolerances were 2/100th of a foot, and the crews consistently hit or exceeded that goal. Quality control surveyors worked behind the screed, double checking tolerances.
The pavers worked at a width of 15 ft. on the first 2-in. lift and 19 ft. on the second lift. “We started with a narrow approach so the crew could become comfortable with the 3D system while working with a more traditional width,” Smith says.
Compaction Gets Smarter
Compaction was a concern early in the project because of the cool temperatures and relatively thin lifts. But it also marked the crew’s introduction to another technological change: intelligent compaction.
Six compactors were used, with three behind each paver. The two breakdown and two intermediate rollers used the Cat Compaction Control.
“The intelligent compactors have GPS,” Smith says. “We utilized pass counts and mapped temperatures. Operators had screens on their rollers. They could easily see where they had been, and they knew the mat temperatures and whether they should be working faster or slower to avoid the tender zone.” The quality control supervisor also had access to the data and could make adjustments to improve consistency.
Each compactor has a wireless transmitter that relays information as part of Product Link, a remotely monitored fleet management system. The machines were also equipped with a Trimble wireless modem that relays pass count and temperature information in real time. That data is then accessed through VisionLink, which enables it to be analyzed by crew leaders on the jobsite and others back at the office. Both long- and short-term adjustments are made from that data.
The project specified the use of two IC rollers, but Granite chose to use four. “We saw this as a testing ground,” Smith comments. “Intelligent compaction is something we can utilize across our fleet. It can have an impact on highway and other paving projects. Quality control incentives on DOT jobs can be substantial, and intelligent compaction should help us reach those targets.”
Four of the compactors were Caterpillar CB64s, and the fifth was a CB564D. All rollers made three passes, with a movement forward and back counting as a single pass.
Breakdown and intermediate rolling was done with full vibration, as was the first pass or two of finish rolling. The mat temperature was between 210° to 230° F after completion of breakdown rolling; between 180° to 200° F after intermediate compaction; and between 160° to 180° F after finish rolling.
The FAA specs mandated cutting off a 3-in. edge on all longitudinal joints. This was accomplished through a cutting wheel option on the CB64. “The last roller operator cut all the joints per project specifications,” says Smith. “He completed his pattern, then dropped back and cut the edge.”
Technology as a Necessity
While much has changed in 10 years, in some ways, Smith feels like technology is helping Granite keep pace more than break new ground.
“As technology is introduced, I think the specs are getting tighter and tighter, too,” he says. “Customers are requiring more from us in terms of tolerances, and they’re asking us to work faster. The new technologies help us meet their expectations and — somewhere along the way — become necessities.” ET