According to Tim Tometich, Project Manager-Manatts–Brooklyn, Iowa, 42% of their projects involved concrete overlays in 2018. In 2016, workers with the diversified heavy highway construction firm placed a 6-inch unbonded concrete overlay on nearly 11 miles of existing asphalt on a Guthrie County highway in western Iowa. That $3.9 million overlay is among a rising number of concrete overlay projects used to construct, rehabilitate, and extend the life of road pavements. He said, “I’d say we have almost as many overlays as we do full-depth paving jobs, so it’s pretty split. It seems like more counties and states are getting on board, using overlays a lot more, especially to cover up the asphalt. Appears to be a longer lifecycle for these roads if you can use concrete overlays.”
Concrete experts agree, including Gary Fick, Project Manager-The Transtech Group and Dale Harrington, HCE Services who co-authored the “Guide to Concrete Overlays” (National Concrete Pavement Technology Center (CP Tech Center)–Iowa State University)—a technology partner of the International Society for Concrete Pavements (ISCP) and the American Concrete Pavement Association (ACPA). Harrington said that thin concrete overlays–defined as less than 6 inches thick–can extend performance life up to 20 years on existing concrete, asphalt, or composite pavements.
Statistics from state bid lettings show concrete overlays have increased steadily over the past 12 years, according to ACPA. Use of U.S. concrete overlays has risen from about 4% to an average of 13% of the volume of concrete pavement, said Gerald Voigt, President and CEO–ACPA. From 2012 through 2017, concrete overlays accounted for an average of 12.5% of the overall yearly concrete pavement volume nationwide. The increasing use of overlays for pavement resurfacing has fueled the biggest improvement in the concrete market in the last five years—with the volume of mainline concrete pavement generated projected to reach about 55 million square yards in 2018. Voigt said the pace is expected to hold and may even climb slightly once they’ve received the 2018 data.
“It’s become a pretty good segment of ACPA’s work, and it’s been an opportunity for us to obtain market share from asphalt because the concrete overlays that we’re placing are being built on top of existing asphalt pavements. That’s an industry market enhancement, because in the past, there would have been … another asphalt overlay. We’re seeing more designs that are 6 inches or less in thickness, the trend is towards thinner sections and shorter joint spacing—contractors are using 6-by-6-foot squares for joints on concrete overlays, correspondingly more joints placed in the pavement. Also important for our industry, we’ve seen higher numbers of those placed on high-volume-traffic interstates that are a lot thinner than previous concrete pavements. With the overlay technology along with the inclusion of fibers in some of the sections that we’re doing, we’re able to pull down the thickness and shorten the joint spacing,” Voigt said.
Using macro-synthetic fibers to reinforce concrete:
New developments include 1.5- to 2.25-inch-long macro-synthetic structural fibers that strengthen the concrete. A technical overview on using fiber-reinforced concrete for pavement overlays is set for release in early 2019. It’s funded by the National Concrete Consortium (NCC), composed of engineers from 32 state highway agencies, Harrington said.
Also, there are the nonwoven polypropylene fabrics used as interlayers to separate an unbonded concrete overlay from the existing concrete pavement surface—all married together, with no patterns. The existing concrete pavement becomes a base layer, blocking cracks in the concrete below from being reflected up into the concrete overlay. The biggest use for it now is unbonded overlay, mostly over concrete but also over asphalt. The fabric can act as a drain to wick away moisture—adequate drainage of either the geotextile or asphalt interlayer is important.
Harrington added, “A 1-inch asphalt separation layer has two problems:
1 – The asphalt interlayer is about twice as expensive as fabric
2 – It takes a different kind of/additonal contract for an asphalt contractor to come out and put it down, versus a concrete contractor who’s doing the paving.”
More options to meet your priorities
“DOTs were asking for options to bid either concrete or asphalt overlays. They want the options mainly so there’s not a monopoly on one or the other because the prices can rise,” Harrington said.
With thinner overlays, engineers can avoid having to raise the grade, redo the shoulders, possibly guard rails, and reworking around bridge entries, he added.
He pointed out, “Training is also important because they need to develop their own in-house expertise so they can train their people.”
Harrington, who has developed countless technical briefs, guides, workshops, and webinars on concrete overlays and preservation, and Fick have trained thousands of contractors and engineers in about 30 different states since 2008. Harrington said that for contractors, priorities include:
- Training for installations
- The way projects are constructed
- Having adequate vertical clearance
- Traffic maintenance during construction
In addition, a document, currently being developed, titled “Development of Concrete Overlay Construction Documents” could help contractors get uniformity in plans so they know how to best bid overlay projects.
Harrington explained, “Most states bid concrete in square yards, and asphalt in tonnage. With concrete overlays, we’ve been encouraging highway agencies to allow contractors to bid two items for concrete overlays for: 1) placement, or square yards, which is typical, and 2) cubic yards for the material they use. Because, when you put an overlay on top of a roadway, it changes in thickness because the roadway underneath is not necessarily uniform.”
Harrington said for the states that bid only by square yards, a contractor must guess if it will be thicker in certain areas and adjust the price accordingly to try to cover that volume.
Harrington said, “We’ve been encouraging the states to bid it both by placement of square yards and by material in cubic yards. We bid it for the materials the contractor’s placed with one bid item for placement and the other for materials used because of the variance in thickness. That’s a big deal for contractors.”
Tometich, Mantas spoke of an Ida County overlay project in which contractors provided two separate bids-either asphalt or concrete, noting that “it was a comparable bid as far as life cycle—and concrete was the low bid.”
States bidding overlays
Across the nation, concrete overlay project construction are being let, including in states that have never done this, such as Kentucky and West Virginia, said Voigt. Big projects have also been recently completed in North Carolina, Minnesota, Iowa, Kansas and California. Using concrete overlays enables owner agencies to take maximum advantage of existing assets. “The pavement they already have out there becomes the structure for supporting the overlay, providing excellent value,” Voigt said.
Voigt also notes a key benefit: concrete overlay does not deform or rut the way asphalt can. He said, “You add more structure with a concrete overlay than an asphalt overlay just by the nature of the materials being stronger. They last longer; they’re stronger inch by inch. We can build them smooth, comparable to an asphalt overlay with no appreciable difference to the user. You get excellent skid resistance with a concrete overlay. From a user-impact standpoint, you’re getting 20-plus years out of a concrete overlay versus 8-10 years out of an asphalt overlay. You’re not getting back in there as frequently to replace the overlay, so you’re not impacting traffic as much. You’re not shutting down lanes. And you’re not exposing workers to work zones as frequently.
For the entire Equipment World article, please go to: https://www.equipmentworld.com/concrete-overlay-roadbuilders-new-options-opportunity/
For the ISCP article on the 3-part webinar series titled “Fiber Reinforced Concrete (FRC) Overview for Concrete Pavement & Overlays”, please go to: https://www.concretepavements.org/2018/11/26/cp-tech-center-sponsored-webinar-series-fiber-reinforced-concrete-frc-overview-for-concrete-pavement-view-1-2/
AND, for the 3 videos of the webinar series, please go to: https://vimeo.com/channels/cptech
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