Departments of Transportation (DOTs) are forcing change in the road building industry. They want smoother rides and roadways that last longer. Pavement performs best when the surface has fewer bumps and dips, resulting in less vibration as vehicles pass. The challenge for contractors and engineers is to install flatter pavement surfaces more economically. That goal is being achieved through improved technology and smarter construction.
Changes are occurring in both layout and placing equipment. The introduction of robotic total stations, 3D laser scanners, and GPS surveying equipment with contractor-friendly software changes the preconstruction survey process and who executes the work. Going “stringless” changes the paving process and this is where the industry is headed.
Smarter, faster layout
In the past, engineering and surveying companies did the layout for construction. Contractors hired them to set all the control points and hubs. With the arrival of total stations and later robotic total stations in the mid-1990s some contractors began to handle these tasks in-house, calling on surveying companies only to verify bench marks. Equipment manufacturers, such as Leica Geosystems, Topcon, and Trimble, responded with software more easily understood by contractors. This software made it easier for contractors to set control points as needed, starting from the benchmarks established by the surveyors.
The different types of instruments used in the paving process today include:
Robotic total stations. This instrument automatically tracks the prism mounted on a surveyor’s rod or on a machine. They are the workhorse of the industry now, due to their accuracy, range, and versatility for any jobsite positioning task. Mike Reed, North American business manager for machine control, Leica Geosystems, Norcross, Ga., says robotic total stations were first introduced into the concrete paving market in late 1999. Today, companies can load plans into them by cellular network or via email—managing construction changes the same way.
GPS survey instruments. Commercially available GPS emerged in the mid-1980s, but the technology only became viable for construction applications in the late 1990s. The instruments locate themselves using satellite signals and then locate control points. GPS is better at locating plan position than elevation so it is used in combination with other equipment for setting control points or guiding stringless pavers.
Total stations. This equipment can be used to lay out points but requires two people—one at the instrument and one at the rod. It doesn’t automatically track the location of the rod so it’s not used to guide paving equipment.
3D laser scanners. Where a total station is used to locate a few points or elevations, a 3D laser scanner locates millions of points. These scanners, mounted on tripods, often are used to record original site conditions, providing topographic information for design processes. As they scan, they also can take digital pictures, making it easier to visualize a site than relying solely on the “point cloud,” produced by a scan. An increasing number of contractors also use them to document every stage of the construction process and provide as-built 3D models at the end of a project. In the future, we may see them guiding earthwork machines and concrete pavement operations.
LIDAR scanning. Laser detection and ranging (LIDAR) is a method for producing quick 3D surveys of an area. 3D laser scanners are moved through space as they collect topographic data. LIDAR scanning can also be accomplished from airplanes, but the speedy collection of data points reduces accuracy, so if LIDAR is used on a project, it’s usually to provide front-end topographic information.
Kevin Klein, vice president for Gomaco, Ida Grove, Iowa, says they had their first meeting with Leica in 1997 to discuss the possibility of stringless concrete slipform paving. Contractors were just starting to explore 3D machine control for site preparation at that time. “Our first production paving project was completed in 1999,” he says. “So the idea has been around a long time. I think it’s about to go mainstream.” Gomaco announced an exclusive distribution agreement for the Leica PaveSmart 3D system onto Gomaco equipment in January 2011, meaning Gomaco customers have support for both their machinery and their stringless systems.
A 3D stringless control system on a paving machine starts with the computer, which interfaces with the paving machine controller through a control area network (CAN). The computer has the 3D control software loaded with the project design file. The computer communicates with the total stations, lasers, or GPS instruments via radio link to collect machine position information, used to calculate where the machine is on the site. The information is relayed to the machine controller via the CAN network. Operators don’t direct the steering and elevation control of the machine during this process. The same technology is used to guide trimmers to ensure concrete thickness will be as specified. Klein says the accuracy of pavement location and surface elevation will be in the ±3 millimeter range—much better than the 1 to 2 centimeters expected from earth-moving equipment.
Stringless paving has many advantages:
- Project design files can be analyzed to ensure rideability before a project begins.
- Stringlines are eliminated, reducing cost, increasing jobsite maneuverability, and making the site safer for workers.
- Good control of pavement thickness (and thus of concrete consumption) is achieved by using 3D machine control to build a pavement from the subgrade up.
- 3D paving machine control can decrease the total time to complete a paving project.
- It’s quicker to move in and out of a paving project when you eliminate the time required to set stringlines.
Manufacturers of the 3D instruments for surveying and stringless paving think its time has finally come and they are preparing in a variety of ways. The manufacturers of paving equipment already include electronic controls wired to the machines’ hydraulics and are developing software to interface with 3D surveying instruments. Klein says their interface software currently works with Leica and Topcon instruments and will soon interface with Trimble products.
Stephen Bullock, vice president of sales and marketing for PowerPavers, Salisbury, N.C., says they are excited about the future of stringless paving and think there are opportunities for contractors. Their machines have an “open system,” so when contractors buy the package to do 3D stringless paving they can use the survey product of their choice.
Wirtgen America, Antioch, Tenn., has staff that writes all their control software. Wade Bowman, their national sales manager–concrete slipform paving, thinks they are unique in this aspect. Their software interfaces with instruments made by machine control manufacturers such as Leica, Topcon, and Trimble. They also have a simpler and less expensive control package called Auto Pilot for smaller machines.
Terex Roadbuilding, Oklahoma City, makes a full range of concrete paving equipment. John Phillips, a senior project engineer, says they experimented with stringless technology 10 years ago, well ahead of contractor interest in the concept and today can fulfill contractor requests for pavers for stringless applications.
The instrument manufacturers are tuned into these developments as well. constantly improving their equipment and software to make stringless paving more accurate and efficient. Leica is merging their data formats so all equipment, earth moving machines, milling machines, trimmers, placers, and concrete slipforming machines, work off the same platform—every operation will use the same data.
Some also are making contractor-friendly software apps to make construction layout, grade checking, and machine control as simple and efficient as possible. Topcon, Livermore, Calif., promotes what they call Millimeter GPS systems to guide pavers. Brad Burgess, Topcon’s North American sales manager–laser scanners, says they combine GPS with rotating laser technology—GPS for steering and location, lasers for elevation control. Burgess adds that Topcon’s approach of integrating laser technology, along with other technologies, such as sonic, can result in a solution for the contractor that is more cost productive than buying dedicated robotic total stations.
Trimble, says its segment manager for paving products Jeroen Snoeck, has been deeply involed in the the earthmoving side of the business and now is focusing on the concrete paving industry. Its robotic total stations, along with the related software, will communicate with any manufacturer’s paving equipment. They also are continuing to develop software that will provide real-time communication to and from the field.
The road ahead
Although manufacturers are unwilling to share information about products in development, there are some general trends emerging. For example, Burgess says Topcon is exploring the benefits of building information modeling (BIM). Many contractors use BIM models for structural work and pavement also can benefit.
Cloud computing is starting to be used by the building community, including manufacturers of paving and survey equipment who are beginning to use the cloud to connect the office to the field in real time. Some manufacturers have set up their own cloud servers that include proprietary software contractors can use to manage their jobsite flow of information—sent and received in real time. Manufacturers also use these portals for product support.
Karl Soar, director of business development for construction, machine control, and paving systems at Leica Geosystems, confirms they are working on BIM. “The market also wants unified solutions for data exchange and data management,” he adds. So their goal is to have one software package to serve all types of instruments—robotic total stations, GPS survey instruments, 3D laser scanners, and machine-control applications. The goal is for the software to continue to become more contractor friendly, more graphical and intuitive.
Workers are becoming comfortable with information technology using smartphones, tablet PCs, and mobile internet services to manage data in the field. Equipment manufacturers will continue to focus on this trend.
Paving projects often are located in remote places in countries all over the world. Manufacturers are working to provide hardware and software their expert technicians can use to remotely troubleshoot breakdowns from anywhere. They will be able to run diagnostics on equipment and software so they can give customers a solution. Both manufacturers and equipment owners will be able to monitor regular maintenance schedules.
Koss Construction, Topeka, Kan., tries to keep up with the latest improvements in the pavement industry, according to its manager of quality and technical services, Robert Kennedy, and has invested in stringless paving. Last year they installed about 20% of their work using the technology with good success. He predicts they will soon be 100% stringless.
Kennedy says they set dual stringlines when they do traditional paving, with surveyors setting all the hubs. He doesn’t see significant cost advantages for going stringless yet, but there are technical and operational advantages. Robotic total stations are positioned about every 250 feet, stakes for stringline are set every 15 to 25 feet, so equipment and truck access is better with stringless. Although the initial investment is high, there are labor savings. He also says that the ride is good but doesn’t exceed what can currently be done with precisely set stringlines.
The Flynn Co., Dubuque, Iowa, primarily works on pavements and runways. With about 100 employees, they cover the Midwestern states. One of its project managers, Mark Gorton, says they started doing stringless paving using Guntert & Zimmerman paving equipment in 2010 and are sold on the concept. Their first experience was an overlay where they placed 200,000 cubic yards of concrete. This job required very accurate topographical maps of the existing road, which they generated using robotic total stations, not GPS equipment. They quickly realized they had to map both the top and the bottom of the pavement. After some initial problems, the project went well.
Gorton says they did two county road overlay projects: one with stringline and one stringless. The stringline project cost them 10% overage on concrete. On the stringless project the overage was only 1%, even though 15% was projected by the county engineer. Gorton says the primary advantages of stringless paving are convenience, reducing bumps in the pavement, and no broken strings to delay construction.
Cold Springs Construction, a heavy and highway contractor located in Akron, N.Y., bought two paving machines in 2010. Ryan Forrestel, its vice president, says there were kinks to work out during the first year—some theirs and some in the equipment—but by 2011 they were very pleased with the results: One-hundred percent of their business was stringless. He says it’s definitely cheaper than stringline paving, productivity is good, and they achieve a good ride on their pavements.