A Concrete Comeback?

Concrete Paving Industry Promoters See a Growing Market

By Scott Judy

The pending update of the American Association of State Highway and Transportation Officials' pavement design guide, the emergence of pervious concrete paving and improvements in equipment could give the Southeast's concrete paving industry a boost, regional officials say.

For many years, the Southeast's market for concrete pavements has been limited, at best.

In Florida, for example, transportation and concrete and asphalt association officials have estimated that asphalt accounts for roughly 97 percent of the state's overall pavement market.

And in Georgia, Wouter Gulden, formerly with the Georgia Department of Transportation and currently director of engineering and training for the Southeast Chapter of the American Concrete Pavement Association, said the concrete pavement market had all but "disappeared" until the last couple of years.

There is a potential for change here, though, Gulden added. He said that in Georgia, the DOT has started utilizing a variety of concrete paving methods to rebuild interstate mainline and shoulders - so much so that Gulden estimated that "it's gone from almost zero to over 2 million sq. yds. for this year. And there's a lot of work coming up in the next couple of years."

Gulden's counterpart in Florida, Dr. Jamshid Armaghani, director of paving for the Florida Concrete & Products Association in Gainesville, was also optimistic about the state of concrete paving in his state. "It's going to continue to improve in the next five years," he said.

However, Gulden was less optimistic about expanded opportunities in the Carolinas due to the funding issues both states are currently facing.

Going Good in Georgia

The Georgia DOT has taken steps to try concrete paving in various situations. One of the first notable efforts it undertook, a few years ago, was the full-depth replacement - including the base material - of 4.2 mi. of Interstate 75 south of Atlanta.

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At the time, Jeff Vinson, area engineer for GDOT, said the department "had never done anything like this. I had to see it to believe it." (Southeast Construction, August 2003.) The $18.1 million Gilbert Southern contract required complete slab removal and a high-early strength concrete mix to quickly replace the old 10-in.-thick slabs in a section-by-section basis over several months.

Gulden said GDOT is now taking that technique to other areas of the Atlanta metro, including a major project on Interstate 85 currently under way near the airport. Also, APAC-Southeast recently used this method to reconstruct a section of I-75 near Macon.

The agency also has recently used roller-compacted concrete to reconstruct 16-in.-thick shoulders along Atlanta's Interstate 285.

Though RCC has been around since the late 1970s, it's only been recently that improvements to the method have resulted in sufficient quality for highway pavements, Gulden said. He added that the improvements have been in both RCC mix designs and equipment, which is more similar to asphalt equipment than typical concrete pavers.

"I think it's going to have a future for certain applications," he said, including, perhaps, state highways. "It's a lot less expensive than regular concrete. It competes with asphalt on a first-cost basis."

Gulden said GDOT's increased interest in concrete comes from the ever-increasing congestion in the metro Atlanta area, especially, and its impact on road construction.

"Every seven to eight years they're having to do mill and inlay of asphalt, and as the traffic is increasing, there's more and more congestion every time they go out there," he said. "It used to be you could go out there at night and no one would ever know you were there. But now you have major traffic backups no matter when you do it. There's no good time to do it any longer, so they're looking at a more durable solution."

New Design Guide

One major reason both men cited for their optimistic outlooks was the pending adoption of a new pavement design guide produced by the American Association of State Highway & Transportation Officials, the leading standard for pavement specifications.

The new guide is more modern and features computer modeling, which is built on more than 20 years of collected data and can predict future pavement performance based on numerous specific design and construction inputs - including pavement thickness, saw cuts, mix designs, base types and even weather.

"The new (AASHTO) design guide is going to be pretty powerful for concrete paving," Gulden said. "It's going to predict how many cracked slabs you're going to have in year 10, or what the ride's going to be like in year 10 or 12. You can see what the effects are going to be."

Armaghani said the new guide will help Florida's concrete paving promoters make the case for their product.

"The new AASHTO guide actually removes a lot of the conservative design methodology which was in the previous 1993 design guide," Armaghani said. "The overall program is excellent and a quantum leap improvement over the 1993 guide."

For example, this modeling should provide evidence of what Armaghani and others have been touting regarding the long-term durability of concrete pavements.

"We feel, based on existing concrete pavement projects, that concrete pavement doesn't need any rehab until 25 to 30 years, and many have shown much more than the 30 years," Armaghani said. He added that FDOT assumes rehabilitation will be necessary after 20 years, a factor that reduces concrete's advantages in a life-cycle cost analysis versus asphalt.

He said the new guide "will predict the year in which the first rehabilitation should be done based on your tolerances."

Additionally, Armaghani said that FDOT is updating its pavement selection manual, which he believes will allow greater consideration of concrete paving.

"The department has been very responsive in the effort to make a fair-and-balanced competition between the two products (concrete and asphalt)," he said. "We fully intend to stay engaged and compete for every life-cycle cost analysis and pavement type selection of new projects, widening projects and resurfacing projects.

"I think the level (of concrete paving) should increase (in Florida) over the next two years. The department is really doing a very good effort to make that happen."

Pervious Paving

In addition to along the highways and byways, the concrete paving industry is making a push for market share in the Southeast's parking lots and driveways. Those are the markets in which it is most aggressively pitching its pervious concrete product.

Literature from the Southeast Cement Association and the Portland Cement Association describes pervious as a mix of coarse aggregate, cement, water and a minimal amount of sand, the latter of which is a standard component of regular concrete mixes. This recipe creates what appear to be small aggregate particles, joined together by cement - or, as PCA more technically states: "a system of highly permeable, interconnected voids that drains quickly."

With the large gaps, or voids, in between the aggregate instead of a solid concrete mass, pervious concrete is able to capture rainwater and allow it to drain through it, thereby minimizing stormwater runoff. For this reason, the PCA says the Environmental Protection Agency recommends the use of pervious concrete as one of its "best management practices" for managing stormwater runoff.

PCA touts that properly designed and constructed pervious pavements should allow between 3 and 8 gallons of water per minute to pass through each square foot.

Technological Advances

Stringless slipform pavers are also coming. Both Terex/CMI and Gomaco are working on GPS-based technologies that will automatically control a paver's profile and theoretically keep the pavement as smooth as possible.

Armaghani and Gulden said that in addition to improving smoothness, these new machines should allow greater productivity.

"It shows a lot of promise," Gulden said. "The technology's advanced quite a bit, and I think they're getting pretty close." He added that APAC recently experimented with Gomaco's Smoothness Indicator system, which he said provides the paver operator "an almost instant indication of what the smoothness is."

Armaghani added: "That (GPS control) makes the surface very smooth, because now you're working in a very tight tolerance, and the machine is not going to be affected by any abnormalities in the base layer, or the stringline sagging and dipping and having these highs and lows. That would be a major innovation in manufacturing."

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