Advanced machine control technology has made its way into the paving and milling markets. "The most common type of 3D machine control on the market today is GPS," says Kevin Klein, vice president of engineering/research and development, GOMACO. Frequently used in earthmoving, Global Positioning System technology is now enabling contractors to move toward stringless and stakeless paving and pavement repair operations.
"3D technology on milling machines and asphalt pavers can help you build better roads for less," asserts Jeroen Snoeck, paving segment manager, Trimble. "With 3D technology, you can better control your yield, increase your smoothness, save valuable material and get rid of your stakes."
GPS by itself is not yet accurate enough for concrete paving. "GPS systems have a proclaimed accuracy of +/- 1cm. But in real life +/- 2cm or even worse is more likely on a day in and day out basis," Klein explains. "So we will use systems with robotic total stations (TPS or LPS) or a GPS system, which is augmented with some other technology such as lasers or total stations. With these types of systems, we can achieve accuracies up to +/- 3mm."
It's important to account for all the variables. "When applying the standard rules and limits of machine and system usage, you can fairly easily get a 3mm mean deviation on the milled surface," notes Matthias Fritz, Wirtgen. "The rules are basically good maintenance of the machine and tools (pics), reasonable milling speed (up to 15m/minute) and reasonable distances to the total station or laser."
"The advantages [of 3D] are similar to what you get in the earthwork industry, where you have stakeless grading," says Jim Cleary, Cleary Machinery. "However, in the milling and paving industry, we don't put grade stakes in the ground; we paint marks on the ground. [With 3D controls], we eliminate those." The entire job is on an electronic data file.
Not using stakes or string can take some getting used to. "At first, contractors may be concerned in not having the stringline to measure from to ensure the paving is in the correct place," says Klein. "Once paving has started, and they have learned how to operate the survey equipment used to do the as-built checks, they realize how much easier it is."
Cleary, who is one of the most experienced Topcon dealers in the paving and milling market, has been doing machine control applications since the 1980s. Many of his clients work on airport runways. "There are more runways within 50 miles of Manhattan than possibly anywhere in the world," he says. "Before GPS, we had to set up stringline on runways. Stringline is only as accurate as the surveyor who sets each pin. It can get hit. It can blow in the wind. Guys will try to step over it and kick it by accident. They might even walk away and not tell anybody."
Stringline also limits use of multiple milling machines. "If you are running one milling machine, you could set up stringline," says Cleary. "But if you are running three milling machines on a runway, you can't do it. It's a logistical nightmare for trucks to maneuver in."
Yet, Cleary has demonstrated that multiple milling machines can work at the same time using GPS. On a project this spring at the John F. Kennedy airport in Queens, NY, Intercounty Paving Associates had five Roadtec RX-900 milling machines operating simultaneously to speed production. Three of the GPS-equipped machines were used to bulk mill the job, leaving the last 1 1/2 in. to be profile milled using two Topcon Millimeter GPS-equipped machines.
"That is the beauty of GPS. You have the entire job on a stick and on the machine," says Cleary. "This is an incredible breakthrough product for the milling and paving industry as far as I am concerned."
Several tangible benefits arise from using 3D paver control. "Paving is all about the penalties," Cleary comments. For example, consider an airport runway where the spec is +/- .25 in. "You can't be more than a 1/2 in. out -- ever," he emphasizes.