By Vicki Speed
Equipment and associated hardware and software that streamlines and simplifies paving operations has advanced by leaps and bounds in recent years, so much so that the capabilities have changed the way contractors operate and how owners specify jobs.
In most cases, the differentiator has been the adoption of 3D paving control solutions that not only drive productivity, but deliver assured vertical and horizontal accuracies to within millimeters. Whereas 3D solutions were once used primarily for high performance surfaces, such as racetracks and airport runways, contractors have since recognized the ROI in the way of productivity and quality across all projects. With an accurate 3D design model and precise control, the paving contractor can complete the project faster, with a better material yield and minimal material waste, while producing a higher quality, longer lasting result.
These solutions work particularly well where there is variable depth and slope—and state transportation owners and the Federal Highway Administration have taken notice. As a result, some state departments of transportation are rewriting specifications to require lower International Roughness Index (IRI) percentages, while others are incentivizing smoothness with bonuses for IRI percentage improvements.
Perhaps even more exciting to some is that 3D paving technology has become a proving ground for more automated and autonomous operations in construction.
From a hardware perspective, a 3D paving control system incorporates machine specific sensors and other components, as well as specialized software algorithms to place material to a target 3D design elevation. These solutions utilize highly accurate instruments, such as total stations, and other guidance methodologies such as GNSS. With an x, y, and z (elevation) position, the software guides the machine to grade and slope according to the model. Put simply, it’s a sensor that sends 3D commands to the machine controller, which in turn controls the hydraulics of a machine to a defined 3D design elevation.
The software algorithms are a bit more complex. A 3D machine control system utilizes a 3D design to place material to a target elevation, often in multiple lifts, or layers, until the final design elevation is reached. Machine control systems, like Trimble Roadworks Paving Control Platform for Asphalt Pavers, sends 3D design information to the machine’s underlying controller to control the elevation and/or slope of the screed to achieve design elevation. Other machine control systems, like Trimble PCS900 Paving Control System for Concrete Pavers, are able to both control the pan of the machine to a certain elevation and steer the machine to a steering line, or main alignment within the design. The result is a more accurate and consistent surface with better rideability results that can meet today’s smoothness specifications and increase the contractor’s smoothness bonus.
For reference, Trimble total station based paving systems are accurate to +/- 3mm horizontally and +/-1mm vertically when at a distance of up to 100 m from a Trimble SPS930 Universal Total Station. PCS900 concrete paving systems are able to achieve this accuracy both by steering the machine according to a mainline alignment in a 3D design as well as vertical placement of concrete material by the paver pan. That consistent accuracy is a big reason for adoption by contractors all over the world.
Milling and paving contractor KUTTER GmbH & Co. KG Construction Company, headquartered in Memmingen, Germany, relied on its 3D paving workflows to support the Karl-Marx-Allee Boulevard modernization project. The project required the removal of the roadway’s concrete layer to a specified level. According to the site manager, the high points along the road were on average about 10 meters apart, so the milling depth changed continuously. In order to ensure the drainage of rainwater, engineers specified a swinging gutter profile over a length of approximately 800 meters and a width of 5.75 meters. Further, the engineering plans required the slope to vary between 2.5 percent and 3.0 percent at intervals of 3-5 meters. On the remaining 9.25-meter width of the roadway, the profile had to have a transverse gradient of 2.5 percent from the center to the edge of the roadway. This geometry resulted in a constantly changing milling depth between 0 and 12 centimeters.
The project team used a compact milling machine with a milling width of one meter equipped with the Trimble PCS900 Paving Control System for Milling Machines. With the 3D technology on the milling machine, crews were able to produce the profile exactly as planned. The deviations from the terrain model were at most 3 mm from the target value. The high accuracy of the milled surface made the placement of a constant thickness asphalt quick and easy without the need for time-consuming leveling or compensation layers.
A similar solution has been developed for asphalt paving. For instance, last year Trimble introduced its Trimble Roadworks 3D Paving Control Platform for Asphalt Pavers. The technology lets operators accurately control the screed to pave with variable depth and slope based on a 3D design. It can take out high and low areas on the first layer as the screed follows the design for slope and thickness. The system automatically lays the right amount of asphalt for improved accuracy and increased productivity.
By avoiding excess asphalt placement, the system increases road smoothness, which can also lead to potential bonus pay on projects that offer such incentives. It also means not having to spend time setting out and taking up stringline.
While 2D paving solutions are well adopted in the industry, 3D can be a difficult investment decision for contractors, despite the proven ROI. It’s one reason why technology developers are introducing subscription-based models to help contractors transition.
Subscription-based services such as Trimble Platform as a Service (TPaaS), available in North America, give contractors the ability to purchase certain hardware and software solutions for a set monthly price and get full technology assurance, including hardware upgrades, throughout the agreement. A subscription investment also turns a capital expenditure into an operating expense, which could also help contractors benefit from federal infrastructure spending.
Moving forward, OEMs continue to advance machines with more technology, including the addition of integrated temperature sensors, compaction sensors, safety sensors and even GNSS positioning. At the same time, operator assist functionality such as 3D machine control steering and other advancements in machine automation are a focus area for machine control providers and OEMs. These organizations are building new lines of machines that will be capable of more autonomous features, either by adding aftermarket technology designed for that purpose, or delivering “technology ready” applications.
However, autonomous construction – and specifically removing an operator or overriding the operator – is a hot and emerging technology direction but is likely many years out.
For now, the advantages derived by automatic and semi-autonomous operations are clear, helping contractors greatly improve productivity, manage labor shortages, more efficiently use materials and deliver higher quality products.
The 3D Advantage Helps Hawaiian Contractor Meet Spec, Reduce Waste
Jas. W. Glover, Ltd. (Glover), a locally owned and operated Hawaiian general contracting company specializing in concrete and asphalt paving, found similar advantages when tasked with the re-construction of Runway 8R-26L, also known as the Reef Runway at the Honolulu International Airport on the island of Oahu.
The FAA and the Hawai’i Department of Transportation (HDOT) required that each section of the runway take no longer than 15 days to complete, with stiff penalties written into the contract for missing deadlines. To increase milling and paving production at the Reef Runway, Glover added a 3D paving control system on an additional Roadtec RX-900 mill and Cat AP1055D paver. The system included four more total stations and two rovers for topos, layout and checking grade. The firm ran two 12.5’ wide 3D mills and two 25’ wide 3D pavers to keep up with production. The ability to control the milling elevation, and placing material to elevation with the pavers while maintaining slope and smoothness without stringline or wires was key to the project success. Each machine was controlled by a total station, and Glover crews used additional total stations to leapfrog every 1,000 feet without having to stop the machine.
The company built the 3D models in Trimble Business Center software. The 3D design is then transferred to the machine and displayed to the operator to show areas that are on, above, or below ideal grade comparing the actual drum position and slope with the digital design. The system automatically guides the milling drum to cut the ideal depth and slope without stringlines or manual adjustments. Not only did the paving control system on the milling machines provide a smoother base for paving, that smarter milling means they have to remove less waste material and mill off the minimum depth only.
According to the company executives it would have been nearly impossible to mill everything to the new profile without using 3D technology because of the existing variable slopes of the runway. They say the technology saved crews huge amounts of time and manpower in terms of layout, topos and establishing where the grades should be.
The owner was also pleased with the smoothness of the runway surface, noting that there were zero grinds on the finished product and elevation was within specification. In fact, Glover met the half-inch grade tolerance, quarter inch up or down for the entire length of the runway.
With 3D milling and paving machine control from Trimble, the company was able to lay 5,000 tons of asphalt to grade and slope per night, in a 12-hour shift compared to 2,000 or 2,500 tons per shift, on other jobs.
Vicki Speed is a freelance writer covering the construction industry.