A 17-in., full-depth reconstruction is part of a massive $156 million rebuild and expansion of I-65 in the Indianapolis area. To place asphalt so thick, Milestone Contractors, L.P., prime contractor for the addition of a third lane in both directions, as well as the reconstruction, used 3-D paving.
A Cat AP1055F asphalt paver equipped with a Weiler SE10 and 3-D technology supplied by a Trimble PCS900 Paving Control System helped the Indiana-based contractor work more efficiently and meet tight tolerances, according to Josh Arthur, asphalt project superintendent.
The 3-D paving system utilizes the Trimble SPS930 Universal Total Station and onboard software to compare the screed position and slope with a 3-D digital design of the job. The system automatically guides the screed to lay a precise amount of material to achieve the specified thickness and slope.
String lines and stakes aren’t necessary. “This should save on labor and engineering, and we expect the mat to be more accurate,” Arthur said during the second week of paving on the job.
Better control
Machines working from the same set of data improved the accuracy of tolerances. For base lifts, crews aimed for a 0.25-in. tolerance. On upper lifts, where materials are finer, crews shot for a 1/4-in. to 1/8-in. +/- for smoothness and 92–93% for compaction density.
3-D technology enables contractors to more precisely control elevations and the amount of asphalt being placed to produce a high-quality, smooth mat.
“We take out more of the highs and lows than we can in traditional two-dimensional paving,” said Craig Atkins, operation manager for Sitech of Indiana. “It’s a big savings for contractors. They don’t run into penalties for thin asphalt lifts and bad densities. And they virtually eliminate wasteful spending on asphalt.”
Asphalt paving was completed in five lifts at a total depth of approximately 17 in. Mat depth varied, because 3-D paving focuses on elevation and not lift thickness. “We’re controlling to a precise elevation,” Atkins said.
Crews placed two base lifts using 1-in.-diam. aggregate, one lift of .75-in. open grade, a lift of .75-in. intermediate, and a final SMA surface lift of 1.5 in.
Model construction
A 3-D model that represented the completed reconstruction was loaded onto a 3-D display. The paver communicated via radio with the SPS 930 Total Station, which guided the screed to within 0.12 in. of the desired elevation for each lift.
Total Station controlled the asphalt screed to keep it at the proper elevation for each lift. A laser transferred information to the screed’s radio receiver. “It’s an automatic system,” Arthur said. “It controls both sides, the grade and the slope.”
Total Station eye levels were placed 1,000 ft apart to keep them in range with the screed at all times during paving. “All we have to do is maintain a line of site between Total Station and the machine, and it will guide the machine very precisely,” Atkins said.
Outside lanes are 12-ft-wide, and the inside lane is 14-ft-wide. Paver speed depended on the depth of the lifts.
“We’re doing a 6-in. compacted lift, and we’re running the paver at 18 to 20 ft per minute to achieve optimum placement and compaction,” Arthur said. “We’re targeting approximately 300 tons per hour to keep the plant, the trucking, and everything on the job moving nice and consistent.”
