Iowa City director of public works Rick Fosse heads up maintenance for some 280 roadway miles; he estimates 70% are concrete, and the remaining 30% are concrete overlaid with asphalt.
Iowa City's concrete pavement restoration (CPR) efforts consist of full- and partial-depth patching, diamond grinding, and sawing and sealing joints. Fosse uses diamond grinding to correct faulting, fix slab warping, improve the ride, and quiet tire-to-pavement noise. “Neighbors along our diamond-ground roads say they appreciate the lack of noise, and motorists like the improved ride,” he says, adding that the pavement where the city first performed CPR, eight years ago, is still holding up very well. “My advice to others is, ‘Be generous with your patching, both full- and partial-depth, and you'll be happier with the pavement in the long term,'” he says.
Like Fosse's team in Iowa City, road departments are increasingly turning to CPR to repair and prolong the life of their pavement. The technique's affordability, durability, and ease of use make it an appealing alternative.CONCRETE: TRIED AND TRUE
Founded in 1823, McDonough, Ga., had aging concrete pavement around the city square and on access roads from the north or south. Some entrance routes had been widened with concrete in the 1940s.
In 2003, officials scrapped plans to replace with asphalt—deciding the change would detract from the city's aesthetic appeal—and opted to keep it concrete. Because the project was state-funded, it needed state approval.
“We expressed our desire to the state DOT not to overlay the project with asphalt,” says James Lee, city administrator. “It worked. We restored some of the concrete and replaced other sections. We were very pleased with the project.”
To minimize traffic disruption, Conyers, Ga., contractor Pittman Construction performed most of the work at night. The $6.2 million project covered 11 lane miles and featured:
- Some construction on new alignment
- Grinding and resealing one section of concrete
- Completely removing and replacing some slabs
- Removingl an asphalt overlay and replacing the underlying concrete in another section.
In total, Pittman performed 25,000 square yards of full-depth slab replacements, 80,000 feet of joint sealing and resealing, and 68,000 square yards of diamond grinding. Use of a high-early-strength mix made it possible to open the area to traffic four to six hours after placement.SUCCESSFUL EXPERIMENTING
Douglas County, Colo., maintains 280 lane miles of concrete pavement, much of it on six-lane urban arterials with auxiliary lanes. In recent years the pavements—most more than 20 years old—have developed spalling and slab separation at the longitudinal joints.
Three years ago, the county experimented with Thermacrete, a patching material supplied by Deery American Corp., Grand Junction, Colo. In the past two years, the county has placed 33 tons of the polymerized material, which contains an aggregate and is heated inside a melter towed behind a truck. Hot liquid product flows from the melter; workers use shovels to scoop the material into place.
“On a 50° F day, we can open up to traffic in 20 minutes after we place the mastic product,” says Randy Teague, county road and bridge manager. “High-early-strength concrete would take several hours.” Typically a nine-man crew blocks off two lanes, jackhammers the spalls down to hard concrete, applies a conditioner, and places the Thermacrete.
By blocking off two lanes, Teague says, “In one day, we can apply one ton of Thermacrete in two longitudinal joints—one on each side of the slab for a half-mile. That's one mile of joint repairs in a day.”
The material costs $3.20 per pound, or $6400 per ton—enough to repair one linear joint mile. Teague figures the cost is just 3% of the cost to remove and replace a concrete panel.
— Brown is a freelance writer in Des Plaines, Ill.