How States Preserve Concrete Pavements
CPR pays off in extra pavement life.

by the Staff of the American Concrete Pavement Association

From Georgia to the Pacific Northwest and California, state transportation departments are recognizing that concrete pavement restoration (CPR) is a cost-effective pavement preservation strategy. And for good reasons. CPR provides several benefits that an asphalt overlay cannot accomplish:  CPR addresses the root cause of a pavement distress, minimizing further deterioration. Covering a distress with an asphalt overlay does not correct the real distress, which can manifest itself again in the form of a larger, more expensive problem.

• CPR costs less and lasts longer than an asphalt overlay. CPR projects typically last between 7 and 12 years, and some have performed for more than 17 years before a second restoration.

• CPR is quicker and causes less traffic disruption. CPR repairs only those areas that need improvement, such as the driving lane of a pavement.

• CPR preserves the safety of concrete pavements.

With shorter joint spacing, load-transfer dowels, and improved designs, today’s concrete pavements are designed never to need CPR. But no pavement lasts forever, so we need CPR to preserve our investment in concrete pavement. This article looks at CPR strategies in Kansas, Missouri, Georgia, Texas, and Washington.

The Kansas experience

Kansas maintains about 1,100 centerline miles of concrete pavement. Annually, the state does a distress survey of all its pavements. “Normally, we don’t have to repair our concrete pavements,” says Andy Gisi, a geotechnical engineer with the Kansas Department of Transportation. “We can just build them and leave them alone.”

However, from 1976 to 1988, most of the state’s new concrete pavements had no load-transfer dowels at the joints. “For about the last five years, we’ve been doing dowel bar retrofitting and diamond grinding on those pavements,” says Gisi. “If the faulting isn’t too bad, we just do diamond grinding. We have just one more un-doweled project to CPR, and then we’ll have completed all those projects.”

Lack of air entrainment in the concrete — caused by human error — caused some longitudinal joint spalling in another Kansas location. “For the spalling, we do partial-depth repairs,” says Gisi. “We saw-cut to delineate the area, and the contractor can either use a chipping hammer or a milling machine to remove the deteriorated concrete.” That is followed by cleaning the hole, sandblasting it, filling it with concrete, sawing the joint, and resealing it.

For some cracks, Kansas practices two types of stitching. Diagonal holes can be drilled through the pavement section, in the shape of an X across the crack. Epoxy and bars are then inserted into the holes. Or with horizontal stitching, crews cut parallel slots along a crack, remove the concrete, place bars in the slots, and grout them back.

“We do horizontal stitching primarily in areas of longitudinal cracking,” says Gisi. “Usually, that’s caused when the contractor didn’t saw the joints soon enough after construction.”

Kansas also does under-sealing, or slab stabilization. If voids develop under a pavement, holes can be drilled through the slab into the void. Crews then inject grout (fly ash, portland cement, and water) or high-density polyurethane foam into the hole and under the slab. “We try not to move the slab,” says Gisi. “If you’re not careful you can build pillars into the slab. We’re just trying to fill the voids.”

If slab stabilization is not performed in time, serious cracks can develop. They can call for full-depth repair or slab replacement, Gisi says.

Dowel bar retrofits

In Texas, U.S. Route 287 was an un-doweled concrete pavement with 60-foot joint intervals. An expansive clay sub-grade made problems worse. Cracks and rocking slabs developed, and the state decided to do CPR on a 4.9-mile stretch, in two lengths, in the towns of Childress and Quanah. It is a five-lane pavement. For $3.2 million, the contractor, J.L. Steele Incorporated, performed dowel bar retrofits, diamond grinding, and a small amount of drum profiling (using a drum cutter).

The project was completed in September of 2004. “We’re hoping to get 10 to 15 years more from that pavement,” says Ronald Hatcher, district laboratory supervisor in the Childress District of the state DOT. “The diamond grinding gave us a really good ride. It rides really well. We got a very good job out of it.”

Long life in Georgia

About 5 to 7% of Georgia’s state road network consists of concrete pavement, says A.J. Jubran, state pavements engineer with the DOT. “Under the life cycle we assign to concrete pavements, we figure to get 20 years until the first CPR, then 10 years, then seven or five years,” says Jubran. “It depends on the traffic, and whether or not the pavement was overloaded. The state has one 5-mile section of Interstate 85, located near South Carolina, that was built in the early 1960s and is “still in pristine condition,” says Jubran.   

Not long ago Georgia completed a $19.13-million project on 14.7 miles of Interstate 75 south of Macon. Some $7.2 million of the cost went for concrete pavement, and the project included lane replacement, safety upgrades, and extensive CPR work. “We used full-depth slab replacement, diamond grinding, and joint resealing,” says Myron Banks, materials and research branch chief, Georgia DOT. “We reconstructed the outside lane, but on the two interior lanes we did restorative work.” The highway has eight lanes divided in one portion, and six lanes in another.

A second CPR-and-lane-replacement project, on Georgia’s Interstate 85 in metro Atlanta, began in June last year and will continue through November. One inside lane will be added, and the state will do CPR on the two outside lanes. The existing pavement is three-lanes wide, and the original inside lane needs no work. The 6.9-mile-long project will cost $39.7 million.  

Beefing up CPR

In Missouri, the past two years have seen the state DOT add partial-depth repairs and dowel bar retrofits to its CPR bag of tricks, says Mark Shelton, assistant state construction and materials engineer. Before that, the state had specifications for full-depth repairs and diamond grinding.

“Over the past two or three years, we’ve probably done nearly 10 CPR projects,” says Shelton. “We’ve done projects with up to several miles of diamond grinding. We regard CPR as a cost-effective way to restore concrete pavements. The earlier you catch the pavement distresses and do something about them, the more years you will get from the pavement.

“We saw some successes with partial-depth repairs and dowel bar retrofits in other places, and those looked like technologies that made sense for us,” says Shelton. To perfect the DBR techniques, Shelton says the state worked with the Missouri-Kansas chapter of the American Concrete Pavement Association. As for partial-depth repairs, Missouri observed the success that Minnesota has had with that technology.

“On a lot of our contracts we do the PDR work ahead of the diamond grinding,” says Shelton. For the partial-depth repairs we try to identify areas that are still structurally sound but have spalling that’s less than half-way through the pavement thickness.

“For dowel bar retrofits we do three saw cuts in the wheel paths and use 1.5-inch dowels,” adds Shelton. “We like to use DBR while transverse cracks are still in the early stages — while we still have some load transfer due to aggregate interlock.

Current or recent CPR projects in Missouri include PDR and DBR on Interstate 435 near Kansas City, and DBR and diamond grinding on Interstate 370 near St. Louis.

Money for CPR

In Washington, the DOT has a budget for preserving pavements, and, says pavement design engineer Jeff Uhlmeyer, “Obviously concrete gets the least priority because it can last longer.” Still, the DOT has identified needs for more than $400 million of CPR work.

Pavement surveys and evaluations show the need for 380 lane miles of DBR work, 230 lane miles of diamond grinding, and 530 lane miles of reconstruction, says Nadarajah (Siva) Sivaneswaran, state pavement management engineer. The DOT uses $330,000 per lane mile as the budgeted figure for DBR work, which it has performed steadily since 1992.

CPR is expected to add 10 to 15 years of life to a concrete pavement, Uhlmeyer says. “We don’t do asphalt overlays on concrete pavements,” says Uhlmeyer. “DBR has been doing very well for us. Typically we DBR the outside lane and diamond grind the inside lanes. You don’t have to DBR all the inside lanes.”

Will the DOT get the money it needs for concrete repair? In April, the state Senate was considering $406 million for existing concrete pavements. The House had not publicized its proposal. “The $406 million only partially covers the need,” says Uhlmeyer. “All the lane miles have been prioritized and broken into projects that we sent to both houses of the legislature. We’ll see how much we get!”

Found: A way to treat diamond grinding slurry

The Penhall Company, Minneapolis, recently found a solution to a challenge with diamond-grinding slurry. The challenge is to dispose of the slurry formed when the diamond blades’ cooling water mixes with the concrete cuttings from the pavement.

California regulations make it very expensive to haul away all of the wastewater and dispose of it off-site. “In California, it’s tougher to get rid of that slurry,” says Casey Holloway, contracts manager for Penhall.

The company has developed a method of treating the slurry that Holloway says Caltrans initially “likes a lot.” This spring Penhall found a chance to use the treatment method on a 141,000-square-meter grinding project near Torrance, California. The project generated 1.7-million gallons of slurry, Holloway says, and it required three 4-foot-wide Cushion Cut grinders to complete. The job is located on six- and eight-lane sections of Route 110, and all lanes need diamond grinding. To avoid heavy traffic, work has been limited to the hours of midnight to 4:30 a.m.

Oil field technology 

The slurry treatment equipment, sold by the Brandt Company, closely resembles that used to treat drilling mud used in the oil fields, Holloway says. The raw waste slurry first flows to a shaker screen that scalps off the heaviest particles of concrete. From there, the slurry drops into a 10,000-gallon agitator tank with paddles in it to keep the concrete in suspension.

Next, the material is pumped to a 12,000-gallon clarifying tank. Enroute to that tank, a polymer flocculant is added that drops out the heaviest particles to the bottom of the tank. The heavy material is pumped to a centrifuge, which consolidates it into a heavy clay-like material.

“You come out with a material that’s about 10% water,” says Holloway. It’s like a heavy clay. You can take it to a landfill. So instead of 1.7-million gallons of slurry that we’d have to put in a hole or in a berm, we’ll handle 100 end-dumps full of this clay-like and sandy waste.”

As of spring, the little treatment plant was “doing a good job of separating the material,” Holloway said. It may need a larger centrifuge, however, to keep up with the project’s production. The plant can be broken down and moved on two flat-bed trailers, and Penhall planned to move it around to various projects.

Standard Methods of CPR

1. Slab stabilization. This technique restores support to concrete slabs by filling small voids that develop underneath the concrete slab at joints, cracks, or the pavement edge. 

2. Full-depth repairs. This is a way to fix cracked slabs and joint deterioration by removing at least a portion of the existing slab and replacing it with new concrete.

3. Partial-depth repairs. These correct surface distress and joint-crack deterioration in the upper third of the concrete slab. Placing a PDR involves removing the deteriorated concrete, cleaning the patch area, placing new concrete, and reforming the joint system.

4. Dowel bar retrofits. This method consists of cutting slots in the pavement across the joint or crack, cleaning the slots, placing the dowel bars, and backfilling the slots with new concrete. Dowel-bar retrofits link slabs together at transverse cracks and joints so that the load is evenly distributed across the crack or joint.

5. Cross-stitching longitudinal cracks or joints. Cross-stitching repairs cracks that are in low-severity condition. The method adds reinforcing steel to hold the crack together tightly.

6. Diamond grinding. By removing faulting, slab warping, studded tire wear, and unevenness resulting from patches, diamond grinding creates a smooth, uniform pavement profile.

7. Joint and crack resealing. This technique minimizes the infiltration of surface water and incompressible material into the joint system. Minimizing water entering the joint reduces subgrade softening; slows pumping and erosion of the subgrade or subbase fines; and may limit dowel-bar corrosion caused by deicing chemicals.

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For more information, you can contact the American Concrete Pavement Association headquarters at 847-966-2272. ACPA maintains chapter offices throughout the country that stand ready to help with your concrete pavement questions. See also www.pavement.com.

Reprinted from Better Roads Magazine
August 2005

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