Roads & Paving
Technology improving paving: 3D machine control and beyond
By Andrew Snook
Tech companies and OEMs have been investing heavily in 3D machine control technologies in the roadbuilding sector to help paving and milling operations build longer-lasting roads. But how exactly have some of these technologies been improving operations?
For that answer, Rock to Road turned to Trimble’s Kevin Garcia, general manager for Trimble Special Solutions, and Brian Girouard, senior construction applications specialist for Trimble.
Before getting into the advantages of 3D machine control, let’s look at the difference between 2D and 3D technologies.
“2D milling or paving is a guidance to grade. A specific elevation or thickness. It could also be just slope, or it could be thickness or it could be slope and thickness. But the way to think about is 2D is from the ground up. We’re referencing a surface, or the existing pavement as it were, in a 2D system,” Garcia explains.
“3D milling and paving is for a specific grade and slope. It may be variable and changing throughout the job – maybe even changing every few feet. Think about that from top down. We design what we want the final surface to look like, and we offset vertically down to get the layers we’re looking for to get our final design.”
The shift towards 3D
Why are contractors gravitating towards 3D milling and paving in intelligent Construction (iC)?
“Ultimately, it’s to help us build better pavement structures,” Garcia says.
When engineers design roadways, specific layers are designed with engineering specifications (surface course, base course, subbase course, for example), and they each need to be a certain gradation with a certain thickness and have a specific density. The engineers intend for these layers to be constructed in a consistent manner, Garcia says.
“The more consistent we can hold these layers, the better the pavement structure, and that’s where machine control plays in,” he says.
Garcia says it’s very common to have contractors build their subbase and base course using 3D machine control in their earthworks operations, then shifting to 2D systems.
“Machine control in the world of earthworks is much more heavily adopted and prevalent than it is in the paving world. The adoption is growing every year, but it’s still not as prevalent as earthworks,” he says.
Depending on the job site and what the specifications are, sometimes contractors can use 2D paving technologies instead of 3D systems, but that’s not typically ideal.
“If it was greenfield construction and there was no milling involved, and you built your subbase and your base course with 3D dozers and a 3D motor grader for fine grading, and your job was to just place a consistent four inches of asphalt, then by all means use a 2D system – hang your sonic off the side, reference that surface and just pave for consistent thickness. It becomes easy to estimate your volumes for the day and you can certainly assure a pretty smooth surface, especially with an averaging beam,” Garcia says.
“But we don’t always have that luxury. Sometimes it’s rework, so we’re milling down and building back up. Maybe we’ve got some waves in that road that have occurred over time with variable settling of the subbase, and that’s where additional 3D machine control might come into play. Ultimately, we’re just trying to hold the consistency in all of our layers.”
Garcia warns contractors against using traditional 2D milling technologies with 3D paving technologies.
“It’s a square peg in a round hole, it doesn’t work,” Garcia says. “2D milling it to 3D pave it doesn’t make the most sense. It’s smarter to start with 3D mills and either 2D or 3D pave, depending on the job site and the specifications for that asphalt-paved surface. This is where your technology provider and a solid level of education around what solutions are available in the market can really help you pick the right solution for the right application.”
Why 3D mill?
Contractors can benefit significantly from adding 3D milling to their operations. It allows for companies to increase their production and lower costs by milling only where it is necessary.
“Just mill only where you need to mill, as opposed to milling a constant thickness,” Girouard says.
The 3D technology also assists contractors with removing longitudinal waves for improved smoothness, decreases asphalt usage; changing/fixing cross slopes and milling complex designs.
“The most important factor is that there are no stringlines or wires required,” Girouard says.
This helps reduce costs, offers better management of the trucks going in and out of a job site and removes potential tripping hazards.
Variable depth and slope milling is another advantage of 3D milling.
“This is important on some projects where you may have to mill more. This is typical for runways. There are certain areas off of centreline, especially in the middle, where you may have to remove 12 or 14 inches and as you get out to the edges maybe all you have to remove is two, four or six inches. The operator or the contractor can offset vertically from station to station and mill, more or less, a uniform surface so when they come back to fill it when they’re paving they just fill up the rectangles or blocks that are required and just do it to maintain the compaction.”
Smooth, safe operations
Using 3D milling for a profile design can significantly increase smoothness.
“If you were to place material down with your paver and use an averaging beam or 3D, there’s no doubt we’re going to place the material nice and even and smooth. The issue comes in the areas where you might have undulations or where you’re going to be placing more material, and ultimately when you roll it down it’s going to compact more, and that’s where we have our differential compaction issue,” Girouard explains.
“Our goal with 3D milling to get the surface smooth the first time, so that when we’re building it up – depending on what the spec requires – our initial lift, the structure of that material, is uniform and correct and ultimately to grade. So, once you roll it and compact it, it’s going to compact to whatever compaction factor you have.”
Another benefit of using a 3D milling technology is that the contractor ends up decreasing their asphalt usage on projects.
“We remove the waves of a surface, so you can save a lot of money on your materials,” Girouard says.
This results in creating smoother roads where motorists can control their vehicles easier at high speeds, while reducing the impact of heavier vehicles on the roads, such as transport trucks. This also allows for better drainage, reduced ponding/hydroplaning and better traffic control.
“We end up having longer lasting structures in the pavement, which in return gives us lower maintenance costs and better snow removal because plows aren’t beating up the asphalt where the pavement isn’t smooth,” Girouard says.
Why 3D pave?
The goal of 3D paving is to achieve the highest possible accuracy and smoothness levels to help manage materials and optimize material yields. It can also eliminate stringlines and reduce staking labour, downtime and errors, reduce costly rework, and help complete projects faster.
“If you have a project where, regardless of what the milled surface is – 2D or 3D – and you still have to place wire or stringline, 3D can help remove that part. If you have any specific deadlines where you have to mill and pave on a project where they have to shut down for a period of time – like when you have to pave at night – to go and set your stringline to provide an elevation guidance to your machine is very labour intensive and there’s potential errors in there when you’re setting that up that we can eliminate.”
3D paving technologies can also be used for variable depth and slope paving applications, including complex designs for roadways, airports and commercial surfaces; base material prior to asphalt to prevent segregation; asphalt; roller compacted concrete; and concrete-treated bases.
Managing differential compaction is another advantage of 3D paving. If an existing surface is not to grade or not level, low areas will compact more. 3D paving can manage differential compaction using an uncompacted design, Girouard says.
“There’s three key components we require to build an uncompacted design: We need to know the surface that we’re paving on; we need to know what the design surface is; and, what at the compaction factor is,” Girouard says. “The goal is to place the levelling course at the same time as the design grade. We’re going to place a little bit more material in the low areas, so when the compactor hits those areas, it gets compress or compacted at grade.”
Pavement thermal mapping or profiling can be used to measure, display and record asphalt mat temperatures directly behind the screed using a high-resolution thermal camera that is mounted on a pole on the back of a paver.
The thermal camera broadcasts in a fan-like shape and records temperature data with the help of GPS technology.
“It’s GPS referenced so that we can say we knew the temperature that mat was as it came out of the back of the screed, wherever it was on the job site,” Garcia says, adding that the cameras can pick up intolerance, whether a mat is too hot to be rolling on, or too cold or brittle so you could be damaging it with the compactor. “These cameras are so good that if you had a screed heater go out, you would start to see a blue or blue-green stripe start to form exactly behind the paver when you’re looking at it in your machine control station. It becomes very obvious what it is.”
Thermal mapping also allows contractors to identify truck loads that have been sitting for too long. It can offer insight into potential trucking issues, whether it’s getting consistently cold loads due to routes taking too long in terms of cycle times, or if it’s occurring sporadically.
“Maybe we’re getting poor loading practices at the asphalt plant and thermal segregation from how they’re doing their drops at the soils, any number of things,” Garcia says. “If you have multiple pavers running, they are capable of sharing that information between machines.”
Girouard says there are a few key ingredients to consider for pulling off a successful 3D project.
“Make sure you’re consulting with a qualified manufacturer and supplier prior to the project,” he says. “We always appreciate, even before the pre-construction, to discuss what the options are, and what the opportunity is to set the expectations. It’s very important, so when you start using this technology that you understand the ins and outs and what to expect.”
He adds that contractors ensure they receive the necessary training and support from a qualified distributor.
“Plan and prepare for training prior to production on the project. Just-in-time training doesn’t work. Just-in-time training can be dangerous from my perspective, especially when people don’t know what they’re doing. So, planning way before you get into production is extremely important to get everybody up to speed on their roles and responsibilities and the expectations,” Girouard says.
“We also expect that the contractor is committed to using the technology. The most successful contractors have a person that learns this, if they haven’t used it before. It is very important for the contractor to own this as much as possible. You’re making a product investment and an investment to change how you work, and ultimately, to be more productive and more efficient out in the field.”
It is also vital that contractors follow all machine manufacturer recommendations for operating the machines equipped with machine guidance, he notes.
“Just follow the procedures. There is no magic button. You still need to know how to pave, how mill and follow the procedures to be successful,” Girouard says, adding that matching the correct technology to each application is equally important. “It’s important you look at all the conditions to ensure success.”
This article appears in the July/August 2021 issue of Rock to Road. Read the digital edition.