Smooth Finishes: Paving, 3D and the Road to Autonomy
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 Interna - tional Roughness Index (IRI) percentages, while others are incentiv- izing 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 opera- tions in construction. Performance Focused 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 sta- tions, 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 ma - chine'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 de- sign. 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 Construc- tion Company, headquartered in Memmingen, Germany, relied on its 3D paving workflows to support the Karl-Marx-Allee Boulevard mod - ernization 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 place- ment 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
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May 2022 csengineermag.com
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