Bringing the Smooth
Innovative solutions improve ride for motorists on section of major northwest interstate.
Until recently, motorists traveling southbound on I-5, in an area about a half-hour north of Portland, Oregon, were accustomed to making sure objects in the car were secure, beverages were covered and, afterward, any loose fillings were intact. While that may be a bit of an exaggeration, concrete pavement in that 1.5 mile area — between the Washington State towns of Woodland and La Center — was so badly worn that it was singled out by Washington State Department of Transportation (WSDOT) for rehabilitation.
Heading up WSDOT’s effort to make traveling that area comfortable again, Granite Construction turned to an innovative paving solution from Topcon Positioning Systems (Livermore, Calif.) called SmoothRide and refined the finishing process using intelligent compaction, also from Topcon. The end result of those efforts was a significant improvement in rideability, a bonus for achieving those impressive numbers, and a mile and a half section of pure driving heaven — which is a nice bonus for the motoring public.
First created in 1956 as part of the nation’s Interstate Highway System, Interstate 5 (I-5) is the most significant north-south freeway for freight on the West Coast. In its nearly 1,400-mile trek, it passes through a number of major U.S. cities including San Diego, Los Angeles, Sacramento, Portland, and Seattle, making it critical to economies on the regional, state and national levels. It is the also busiest commuter roadway in western Washington, handling more than 274,000 vehicles per day.
Though traffic volumes are slightly lower near the Washington-Oregon border, they are significant enough to result in a steady wearing down of the pavement, resulting in cracks, ruts and potholes in many areas of the highway’s concrete surface. It was determined that the structural integrity of the roadway in that 1.5 mile stretch was questionable, leading to the $7.6 million contract with Granite, according to Logan Cantrell, the company’s material and construction quality manager.
“The concrete panels that made up this pavement were in rough shape before this project began,” he said. “The IRI — a number by which roughness of the road is measured — was about 117 which, though it falls into the ‘acceptable’ category, was still a very rough ride. While it would have been easy to simply overlay asphalt on top of the failing concrete to smooth out some of the rougher areas, there would still be high and low spots which needed real correction. An overlay alone was not the answer.”
“That is the real beauty of this process, its ability to correct for high and low spots.”
Lowering the Boom
The first step Granite took in rehabbing the substandard pavement was contracting with Antigo Construction (Antigo, Wisconsin) to crack & seat it, a process which, according to Matt Shinners, Antigo’s president, minimizes the risk of reflection cracks in the subsequently overlaid material.
“We were at the I-5 site for a couple of days and drove the full length of the project with a T8600 Badger Breaker,” he said. “That unit features a 12,000 lb. hammer which is repeatedly dropped onto the concrete to fracture it. The cracking process was followed by Granite’s team making several passes with a 50-ton, pull-type, rubber-tired proof roller to accomplish the necessary re-seating. To verify the depth of the fracturing, we took periodic 6” core samples.“
With the panels sufficiently prepped, Granite moved on to the actual paving facet of the job. According to Cantrell, it was one of their construction managers, already using intelligent compaction on several projects throughout the area, who contacted Topcon about the SmoothRide solution.
“He’d seen SmoothRide demonstrated at a recent ConExpo and wanted to see if it was a good fit for WSDOT projects moving forward,” said Cantrell. Working with Topcon, and Topcon Solutions Store, they set up the I-5 project as a demo.
Under the Hood
SmoothRide is a multi-faceted solution that begins with a detailed laser scan of the road surface, conducted using a vehicle-mounted RD-M1 scanner. Using this method, not only is a wealth of data compiled quickly and safely, it can be done without the need for costly lane closures. With millions of points of data downloaded and processed, designers can immediately begin the process of reviewing the existing surface, identifying problematic areas and creating the 3D model that will be exported for use in the milling or, as was the case on I-5, the paving equipment.
“We did the scan very early on a Wednesday morning,” said Cantrell. “We attached the RD-M1 to one of our company vehicles and in roughly an hour, we had all the surfaces scanned and ready for processing. That was particularly important since WSDOT only gave us that long to scan the full three lanes of road.”
Because this was their first experience with SmoothRide, a Topcon specialist rode with Granite personnel to help explain the process and ensure they had everything they needed to proceed.
“It was a totally new experience for us so it was great to have them with us every inch of the way on this job,” said Cantrell. “Whether or not we commit to a solution like SmoothRide is largely dependent on WSDOT attaching additional bonuses to future projects for improving smoothness, so it was important that we got this right.”
“This year we’ve been moving the IC around the state, having a number of different crews try it out doing various types of projects.”
A Lifting Experience
With the 3D model for the project loaded into their Cat AP-1055F paver, Granite proceeded to lay down 9” of asphalt in four separate lifts measuring 2”, 3” and a pair of additional 2” lifts. According to Cantrell, the initial lift was actually slightly variable in depth to allow for any necessary correction.
“That is the real beauty of this process, its ability to correct for high and low spots,” he said. “Because what’s being laid is based on what’s been scanned, any bad areas on the surface are not just being paved over. They are actually being corrected, leaving a much better overall end-product — and increasing the life of the surface.”
As anyone involved in asphalt paving will attest, even the best laid road surface can be ruined at the hands of improper compaction. The problems caused by over- or under-rolling include but are not limited to material segregation, surface cracks and raveling. Granite is aware of these issues and, with its reputation and the satisfaction of customers like WSDOT on the line, has gone to great lengths to ensure they don’t impact their projects. One of the ways they are doing so is by employing what is actually an ideal compliment to SmoothRide, the intelligent compaction solution mentioned above.
Based around the concept that a better-informed roller operator is a better-performing one, intelligent compaction uses sensors to measure the temperature of the asphalt being compacted with each pass of the machine and graphically depicts it on screen in the cab. In this way, the operator also has no doubt as to what areas they’ve already completed. The effect it has had on Granite’s compaction crews’ performance has been impressive — and measurable — according to Cantrell.
“This year we’ve been moving the IC around the state, having a number of different crews try it out doing various types of projects,” he said. “Our ultimate goal is to try to improve standard deviation, that is, maintaining uniformity, on our WSDOT work. That is the factor that most directly affects our compaction-related bonus pay. Though it varies from job to job, we’ve probably seen that number drop by about .5% already. If we can be at 1% we would be assured of getting full bonus and we are currently in the 1 ¼ and 2% range; so we’ve definitely seen an improvement. And we can trace it to our use of IC because when we’ve taken it off the rollers, we’ve seen those numbers go back up. There’s no doubt it’s helping.”
As is often the case with new technology, Cantrell said that some of their seasoned operators hesitate to embrace IC at the outset. As they use it, however, he said their attitudes begin to change.
“They are initially opposed to anything that takes them out of their comfort zone,” he said. “But then I’ll catch them looking at the screen to verify what they’ve done and haven’t done, where they’ve stopped, and so on. And that’s understandable — sometimes it’s hard to see, especially when you’re not in the breakdown roller and seeing that immense compaction at the beginning. If you’re toward the back and losing sight of roller marks, particularly at night, it can be a challenge. But the IC solution eliminates that, which wins them over.”
The combination of SmoothRide and IC at the I-5 Woodland site accomplished Granite’s goals which were to gain familiarity with the solution and, at the same time, better position them for the possibility of capturing future project incentives. Cantrell said the improvement definitely turned some heads.
“The project turned out great for us,” he said. “After completion, that IRI value of 117 had been reduced to 40 — an almost 300% improvement in smoothness. As a result, we should get about an 80% bonus for IRI on this job. While we really like the SmoothRide system, we would need to see changes in WSDOT’s specifications to allow for variable depth milling/paving and IRI bonus on more jobs. But this was a great opportunity for both organizations to see the changes SmoothRide can bring.”