Asphalt Review, Technology Update

New Cat AP1055F Asphalt paver makes its mark

Automated systems and 3D paving capabilities on the new Cat® AP1055F Asphalt paver are improving accuracy and efficiency for contractors working on major road projects in Indianapolis in the United States.

Automated systems and 3D paving capabilities on the new Cat® AP1055F Asphalt paver are improving accuracy and efficiency for contractors working on major road projects in Indianapolis in the United States.Sections of Interstate 65 in the Indianapolis area that were built in the 1960s and 1970s are now being rebuilt and expanded to meet the demands of the 21st century. Three projects worth a combined $156 million are currently underway in the Indianapolis metropolitan area.

Milestone Contractors, L.P. is the prime contractor on the I-65 reconstruction and road-widening project at the southern edge of the metro area. Work includes the addition of a third lane in both directions, and 0.43 metres (17 inches), full-depth reconstruction.

A Cat AP1055F Asphalt Paver equipped with a Weiler SE10 and 3D technology supplied by a Trimble PCS900 Paving Control System is helping the contractor work more efficiently and meet tight tolerances, says Josh Arthur, Asphalt Project Superintendent.

The 3D paving system utilises the Trimble SPS930 Universal Total Station and onboard software to compare the screed position and slope with a 3D 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.

With 3D paving, string lines and stakes aren’t necessary. “It will be more efficient, and there should be a cost saving.” Mr. Arthur asserts. “Anytime there are strings, you have to set them and you have to worry about people getting into the them and making adjustments. This should save on labour and engineering, and we expect the mat to be more accurate.”

Tighter tolerances 

Tolerances are expected to be more accurate because machines are working from the same set of data.

“We shoot for a quarter-inch tolerance, plus or minus, for the thicker lifts. The base lifts are a little bit thicker and a little bit bigger rock, so the tolerances are a little more,” he says. “As we build the lifts up and the materials are finer, we tighten the tolerances. We shoot for a quarter- to an eighth-inch plus or minus for smoothness and 92 to 93 per cent for compaction density.”

The use of 3D 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,” says Craig Atkins, operation manager for Sitech of Indiana. “In the long run, it amounts to 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.”

The I-65 project is Milestone’s first using the Cat AP1055F, Weiler SE10 and the 3D paving system. “We really like the paver. It’s doing a good job,” says Mr. Arthur. “The screed set-up is very operator-friendly. They can see what is happening on the opposite side, so one person can control everything.”

The paver’s dual operator stations provide excellent control and visibility from either side of the operating platform. The press of a button transfers control from one station to the other. Eco-mode utilises 1650-rpm engine speed, which reduces fuel burn. Automatic engine speed control reduces speed to 1000 rpm when in neutral or to 1300 rpm when screed heat is active.

Paving began in August last year with crews working 24/7. Two crews were each working 12-hour daily shifts. The comfort of the paver’s air-ride seat and controls that are easily within the operator’s reach help make the long shifts possible.

Asphalt paving is being done in five lifts at a total depth of approximately 0.43 metres (17 inches). Depth of the mat varies because 3D paving focuses on elevation and not lift thickness. “We’re controlling to a precise elevation,” Mr. Atkins says. “The Milestone crews are doing a great job.”

Crews are placing two base lifts using 25 millimetres (one inch) diameter aggregate, one lift of 19 millimetres (0.75 inches) open grade, a lift of 19 millimetres (0.75 inches) intermediate, and a final stone mastic asphalt surface lift of 38 millimetres (1.5 inches).

Automatic system

A 3D model that represents how the reconstruction will look when completed has been loaded onto a 3D display. The paver communicates via radio with SPS 930 Total Station, which guides the screed to within three millimetres (0.12 inches) of the desired elevation for each lift.

Total Station takes control of the asphalt screed to keep it at the proper elevation for each lift. “It’s an automatic system,” Mr. Arthur says. “It controls both sides, the grade and the slope.”

Total station eye levels are placed 305 metres (1,000 feet) apart to keep them in range with the screed at all times during paving. “All we have to do is maintain a line of sight between Total Station and the machine, and it will guide the machine very precisely,” Mr. Atkins adds.

A laser transfers information to the screed’s radio receiver. “With GPS systems using satellites, tolerances are 19 millimetres (0.75 inches). With the laser, we’re expecting to get within one-quarter inch,” Mr. Arthur says.

Outside lanes are 3.66 metres (12 feet), and the inside lane is 4.27 metres (14 feet). Paver speed depends on the depth of the lifts. “We’re doing a 15.24 centimetres (six inches) compacted lift, and we’re running the paver at 5.5 – 6.1 metres (18 – 20 feet) per minute to achieve optimum placement and compaction,” Mr. Arthur says.

Milestone crews received training from Caterpillar and Sitech, including the proper set up of the stations, 3D display, and how to calculate screed offsets. “Everybody is really getting the hang of it. There are details that you must pay attention to. We’re doing that,” says Mr. Arthur.

To ensure the subgrade was placed precisely, Total Station-guided motor graders were used. “We know that if the underlying elevation is correct and the technology achieves a precise elevation on top of that, our depth is going to be right. That equates to good cores, good samples and good densities,” adds Mr. Atkins.

Not Too Cool 

A pair of Cat CB64B rollers are being used for compaction. “With this thick base lift we’re running high amplitude and high frequency. We’re making around 10 vibratory passes, with one static pass, in order to achieve our maximum density of 92 to 93 with each roller,” says Mr. Arthur. “The breakdown roller usually stays within a load of the screed for temperature and safety reasons.”

The rollers feature infrared temperature gauges, which make it easy for operators to know when the mat has reached the optimum temperature for compaction. “For the breakdown roller, there’s a temperature zone when it starts to cool off and starts to get a little tender. We want to stay out of that zone,” explains Mr. Arthur. “The temperature gauge lets the finish roller operator know when to get on it and when to leave it alone to achieve maximum density and compaction.”

Operators don’t need to guess or stop the machine to use a temperature gun to know how hot the mat is. “The technology frees them to concentrate on their jobs. It speeds the process up, and keeps them moving,” he adds.

Thanks to the capabilities of the new Cat AP1055F Asphalt Paver and the automated systems employed on the I-65 reconstruction and road-widening the Milestone crew is paving more efficiently and accurately than in the past.

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