Millimeter GPS Raises the Bar
Beauty to behold for the concrete contractor is the smooth, uniform surface of freshly-paved concrete. For them, Concrete Gray is the color of choice in the 64 pack of crayons and nothing feels better than leaving a durable, quality finished concrete paved job for others to experience.
The passage of time will reveal any flaws in workmanship, the invasion of water, or the wear from use. Discoloration, scaling, crazing, cracking, or curling will sometimes occur due to a poor ready-mix batch, inadequate curing procedure, subgrade settlement, or improper bonding of the finish-layer. Concrete surfaces are generally very durable, but like everything, they won't last forever--aging and surface wear due to the abrasion of use will have an effect.
Concrete paving is pretty complex and achieving quality, long-lasting results requires skill, the right equipment, and advanced technology. At its root, pavement is an outdoor floor...a hardscape surface covering that is driven or walked on. One of the major advantages of concrete pavements is they are typically stronger and more durable than other types of surfaces. They also can be grooved to provide a tough skid-resistant surface. A notable disadvantage is that they typically can be more time-consuming to construct. Thus, concrete contractors have turned to technology for production-enhancing efficiencies and improved results.
The Evolution of Concrete Paving
According to the American Concrete Pavement Association, the role of technology has been significant to the growth and evolution of concrete paving: "Since 1892–when the very first concrete pavement was placed in America–concrete pavement technology has been changing, continually evolving to meet current and future needs."
As part of this more than a century of improvement, the machines and methods have evolved. Today, technology has improved productivity and quality of results.
"We're seeing progressive contractors...early adopters embracing technology today, and the others realizing they will have to follow or settle for not being competitive," said Brian Lingobardo, systems manager, 3D road construction, Topcon Positioning Systems, Livermore, Calif. "We have the technology to provide contractors with millimeter paving accuracy, which is astounding."
Slipform Pavers Bring Efficiency
Slipform pavers have become indispensable in concrete paving because of their efficiency in the highly-automated production of concrete road pavements, airstrips, and other large surface sites. The track-mounted multipurpose machines are monster-size masters in the production of a countless range of poured, in-place profiles. Controlling their performance to ensure desired results is where machine control developers step in.
Topcon Positioning Systems offers a 3D paving capability through its Millimeter GPS paver system. According to Topcon, the product is the world’s first GPS-based millimeter accurate control for pavers. The system uses satellite positioning together with a zone laser reference. Mounted on the paver is a control box designed to send control to the hydraulics independently. The color, graphical screen displays the machine position on the job, and the sensors being used to control the left and right side of the pan, as well as the current elevation and slope.
The system has machine control positioning-zone laser receivers with integrated GPS antenna mounted on the rear of the paver. Other components on the paver include the machine control GNSS receiver and slope sensors to control the front or “draft” of the paver.
The Topcon Millimeter GPS paver system features a laser that transmits a unique signal and operates similar to a standard rotating laser. Unlike a standard rotating laser that only works in a flat plane, the Topcon LZ-T5 transmits a Lazer Zone signal that creates a measuring area 33 feet (10 m) in height. Therefore, positioned anywhere within the Lazer Zone, the Millimeter GPS paver system’s machine control sensor is designed to compute the precise vertical information. There is no need for a moveable mast, the technology is designed to determine elevation automatically. Even if the site has an elevation variance of 10 meters (33 feet), there is no need to reposition the instrument or receivers with this technology. For sites with significant elevations or large areas, up to four LZ-T5 Lazer Zone transmitters can be linked to cover a larger area and elevation change of more than 130 feet.
"Since we are free of stringlines, we like the efficiencies provided by the Millimeter GPS paver system," stated Kevin Gehring, owner/operator at Gehring Construction & Ready Mix Co., Columbus, Neb. "We're not needing to wait and pay for surveyors to be scheduled and pound hubs in ground. And we're no longer waiting and paying employees to set stringline."
Gehring believes he is also achieving better paving alignment and rideability because he is able to use actual radius data for horizontal and vertical curves instead of short tangent string line sections.
Agreeing with Gehring's conclusions, Scott Murchison, P.E., LEED AP, and chief engineer for RC Construction, Greenwood, Miss. stated: "We like the ease and flexibility that the system provides us, since we're no longer married to a stringline with all the time and effort required to get the slipform paver set up. We recently paved a new runway at Joint Base Andrews in Prince George's County, Maryland, for Air Force One. The 3,000-foot long by 250-foot wide runway with two intersecting taxiways had a specified 7-inch per mile profilograph testing tolerance. With our Topcon system, we achieved an incredible profilograph smoothness rating of less than 1-inch per mile. We couldn't be happier."
Improved Concrete Safety and Performance
The Topcon Millimeter GPS paver system appears to help with paving accuracy--both in material usage and concrete lay down.
"Our yields have been much better than expected," said Jacob Headrick, paving/3D manager, GLF Construction Corp., Miami, Fla. "We're dialed into the exact amount of material we need, which saves on material costs and eliminates rework.
"The accuracy with the Topcon Millimeter GPS system is phenomenal. We're achieving finished paved grade within a hundredth, and if you consider that a piece of aggregate can be bigger than that...that's pretty spectacular."
Headrick also cites savings and return on his technology investment as benefits: "With our first project, we saved enough to cover the cost of the Topcon system. On our second job, we saved enough on outside survey costs to purchase two Millimeter GPS systems if we wanted them."
Certainly, technology is becoming integral to concrete paver's desire for the smooth, uniform surface of freshly-paved concrete they all seek.
According to the Federal Highway Administration (FHA), "Today’s highway users expect a high-quality traveling experience on roads that are safe and well maintained with the least possible delay." The FHA has several ongoing programs that intend to ensure "that innovative technologies that can improve the safety and performance of the transportation system are deployed and implemented on the Nation’s roadways."
Clearly, one could expect that the technologies being adopted by concrete paving companies are consistent with the stated mission of the FHA and are directly contributing to the high-quality traveling experience highway users are expecting.
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