PAVING and 3D Machine Control (Part 2)

Randy Noland, Editor MCo Last month we summarized a brief history (at least a US snapshot) of the paving business and just how large and important the industry has become. The focus of this article is to discuss the application of 3D machine control to concrete paving and asphalt paving. First lets discuss some differences between earthmoving, the more traditional 3D machine control beneficiary, and paving. These differences create a unique challenge and approach for 3D machine control technology providers.

3D machine control has proven to dramatically boost productivity in earthmoving applications. Depending on the task, these increases can be as high as 200% over traditional methods. So in this case, 3D machine control technology’s main benefit is its positive impact on productivity.

Paving (roads and highways) is different in that the productivity is measured differently. In earthmoving, the goal is getting to grade in minimal passes and with minimal rework. For paving, productivity is feet per minute but faster is usually not better. If the desired paving speed is 40 feet per minute, high productivity would be achieving that speed continuously all day long without significant paving stops due to shortage of asphalt delivery. For best performance, increasing the paving speed is not better productivity (although it is easy to find naive disagreement with this point).

Accuracy and quality impact the smoothness or rideability of the finished product. Rideability is one of the key performance metrics for which the work is judged although not the only one. Compaction density is also a performance measure. That being said, 3D machine control technology must focus on how to make the rideability better, i.e., of higher performance. Many contractors earn bonuses for achieving this higher quality that can justify a technology investment.

The accuracy required on paving projects to achieve better performance is higher than that provided by GNSS (GPS) alone. 3D machine control providers have met this challenge in a couple of ways. Systems from Leica and Trimble offer robotic total stations with accuracy higher than +/- .02”. Topcon offers laser augmentation, as does Trimble, which supplements or augments the less accurate elevation component of GNSS (GPS). Thus the integration and convergence of additional sensor technologies address these challenges. I have posted links at the end of this article to the various positioning technology providers so please visit their site and explore what each offer.

Asphalt Paving vs Concrete Paving
Concrete paving machines and asphalt paving machines vary physically as do their methods of paving. These differences are important because the positioning technology is fundamentally different in terms of controlling the paver's hydraulics for steering and leveling. The asphalt paver with its floating screed is traditionally being controlled with mechanical or ultrasonic grade sensors referencing a physical surface such as the existing road, a curb or a stringline. Steering is typically done manually by the operator. The adoption rate for 2D systems (elevation only) in the asphalt industry is fairly high as it clearly helps the operator to achieve the major goals: superior smoothness and thickness based on volume.

The art of compaction, which also is a critical part of asphalt paving, is worth an article by itself. Some pavers can actually compact the asphalt up to 100%. However looking around the globe, compaction is looked at differently and so are the job specifications. Some countries using different material mixes which don't allow such a high compaction and some others allow for 97% compaction. Many roller manufacturers have their own high technology systems using GNSS (GPS). In any case, it is important to have a closer look at the rollers which work after the paver. Their contribution can raise the performance bar or destroy the paved surface if performed incorrectly.

Concrete pavers on the other hand work differently; having a fixed tool inside (or outside) a rigid frame which creates the concrete surface. Compared to the floating screed, the concrete pavers frame is rigid and has very sensitive hydraulic control systems on board to control level and steering of the machine. Traditionally nearly all of the pavers are controlled with wand sensor based on one or two-sided stringlines. When adding 3D control to this machine, you basically replace the stringline which brings some significant benefits to the table. Beside a constant accuracy and the ability to create more complex job designs, we are looking at up to 60% production increase just due to the fact that stringlines are not required any more. Of course there are other factors related to safety and machine handling which are important but the logistical benefits are the main drivers for this technology. Since nearly all the machines have automatic steering and full elevation control, this is a true 3D machine which can be controlled very precisely.

One of the early 3D systems was developed by Leica Geosystems and installed onto a Wirtgen SP 500 slipform paver (right) in 1997, based on a high-speed railway project in Germany. (click here to read more) Due to the the highly complex design of the railway the stringline stakeout would need to be much more dense than typical. It would have required a much more dense traditional stringline stakeout with pins closer than 1 ft apart was required. Additionally there was not a lot of space around the track to handle the concrete logistics and stringlines would have further reduced it. The project was overall 120km long and had six SP 500 pavers working in 3D at the same time.

GOMACO of Ida Grove, Iowa has also been at the forefront of 3D positioning systems since its inception. GOMACO, along with Leica GeoSystems, were a part history over 12 years ago when the first 3D road in the U.S. was paved. GOMACO has taken their role as a partnered innovator a step further by announcing the creation of an in-house 3D machine control group. This follows similar moves by other manufacturers such as Caterpillar and John Deere to name a few. I believe we will see deeper integration at the manufacturing level with each passing year, although there will be a strong retrofit market for years to come.

Milling Machines
Milling may offer the greatest opportunity in the paving realm for applying 3D machine control technology. I will address milling Machines and 3D machine control in an upcoming article. I hope you will join me.

Special Thanks
I would like to thank the following for their feedback in preparation of this article:

David Shelstad, Vice President of Sales, MOBA Corporation,
Kevin Klein, VP of Engineering, GOMACO Corporation,
Matthias Fritz, 3D Machine Control Manager, Wirtgen

Other References

Leica GeoSystems
MOBA Corporation
Topcon Positioning Systems
Trimble

*There are other manufactures of paving equipment and positioning systems. This list is representative of what I used for my research. I am happy to add links to other industry players. Please send me an email at This email address is being protected from spambots. You need JavaScript enabled to view it.

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