Field trials around the country are generating results on alternative designs for improving high-performance concrete pavements.

To encourage the use of innovative technologies in concrete pavement, the Federal Highway Administration (FHWA) is testing and evaluating new concrete pavement designs and construction concepts through field projects around the United States. An FHWA program, High Performance Concrete Pavement (HPCP), has the overall objective of providing long-lasting, economical portland cement concrete pavements that meet the specific performance requirements of their particular application.

Since the program's inception in 1995, more than 23 projects in 13 States have been constructed or approved. Projects include joint sealing alternatives, alternative load transfer devices, durable concrete mix designs, and alternative surface finishing techniques. Although many projects are relatively new, several have produced preliminary or final reports. The results fall into five general categories: joint sealing, fiber-reinforced concrete, durable concrete mixtures, alternate dowel bars, and surface texture and noise.

Joint Sealing

The purpose of joint sealing is to provide a way of keeping rainwater from entering the pavement and causing erosion of the base and subsequent faulting and joint distress. New joint sealing technologies are intended to provide a longer-lasting and cost-effective seal. Some in the concrete pavement community believe that leaving joints unsealed will provide equal pavement performance at a reduced cost.

Projects in Kansas and Ohio evaluated joint sealing technologies, including hot poured asphalt, silicone, pre-formed compression seals, unsealed joints, and alternate joint geometry.

"Results to date indicate that the pre-formed compression seals are performing better than the hot poured asphalt or silicone sealants," says Anastasios M. Ioannides, associate professor of civil engineering at the University of Cincinnati. "Many joints sealed with the latter exhibit adhesion failures, although several continue to perform well. The easier a material is to apply on the site, and the less demanding it is for elaborate field procedures, the more likely it is to perform well."

Ioannides continues, "To answer the question of whether to seal or not to seal, however, many other pavement performance factors must be considered, and these do not appear to be related to sealant performance per se. The test site will be a resource for future observations over many years."

Fiber-Reinforced Concrete Pavements

The perceived benefits of using fiber reinforcement on concrete pavements include increased fatigue resistance, decreased shrinkage cracking, and increased joint spacing.

Projects in Maryland, Missouri, and South Dakota investigated fiber-reinforced concrete for pavement. The technologies tested include steel fibers, polyolefin, and polyester fibers at various dosage rates.

The results to date in South Dakota indicate no significant performance differences between the 20.3-centimeter and 16.5-centimeter (8-inch and 6.5-inch) fiber-reinforced concrete pavement and the 20.3-centimeter Jointed Plane Concrete Pavements (JPCP) control sections. The unjointed fiber-reinforced concrete pavement experienced transverse cracks at approximately 26-meter (85-foot) spacing. The initial cost of the 20.3-centimeter fiber-reinforced concrete pavement was $28.90 per square yard compared with an initial cost of $15.35/yd2 for the JPCP control section.

In Missouri the 12.7-centimeter and 15.2-centimeter (5-inch and 6-inch) fiber-reinforced concrete pavements exhibited significant transverse cracking soon after construction. The steel fiber pavement experienced transverse cracking within 0.3 meter (1 foot) of the transverse joint, while the polyolefin fiber pavement experienced transverse cracking near mid-panel. According to reports, the12.7-centimeter thickness test sections were removed and reconstructed due to transverse cracking and spalling.

According to Tim Chojnacki, director of research at the Missouri Department of Transportation, "While there were some thin test sections, the fibers in the other sections are doing what they should, keeping cracks closed, and the ride is excellent."

The 22.9-centimeter (9-inch) polyolefin and steel fiber-reinforced test sections exhibited some minor transverse cracking while the 22.8-centimeter and 27.9-centimeter (9-inch and 11-inch) control section without fibers experienced no cracking to date. In terms of cost, the steel and polyolefin fiber added approximately $47 per cubic yard and $60/yd3 to the cost of furnishing concrete for this project. Based on the experience in South Dakota and Missouri, it does not appear that fiber-reinforced concrete pavements are cost-effective, but the long-term benefits, if any, cannot yet be discounted.

Durable Concrete Mixes

Aspects of concrete that can lead to increased durability include larger top-sized aggregate, low water/cementitious ratio (w/c), fly ash, ground granulated blast furnace (GGBF) slag, and two-lift construction. Larger aggregates will reduce the paste fraction of the concrete, thus reducing the shrinkage potential. The objective of using lower w/c ratio, fly ash, and GGBF slag is to create a dense concrete with lower permeability. Two-lift construction allows the use of a lower-cost material on the bottom of the concrete slab, while a durable, higher-quality concrete can be used on the wearing surface.

Projects in Kansas, Ohio, and Virginia used pavements with concrete mixes thought to be more durable than typically used. The results from the Virginia project illustrate that air-entrained paving concrete with satisfactory strength, low permeability, and volume stability can be prepared using concrete with Class F fly ash or slag, and with 2.5-centimeter and 5-centimeter (1-inch and 2-inch) maximum size aggregates.

"Results indicate that the specified strength and durability are achieved," says Dr. Celik Ozyildirim, principal research scientist at the Virginia Transportation Research Council, "and the early performance is satisfactory."

Results from the Kansas project indicate that the two-lift construction process using either recycled asphalt pavement or local polishing limestone in the base and an igneous rock or low w/c ratio concrete in the top layer can be constructed effectively. The two-lift construction technique added approximately $25/yd2 to the overall construction cost. The two-lift construction costs included a second batch plant, extra hauling of material, a concrete belt placer/spreader, and extra labor for hauling.

The Ohio project led to the conclusion that "The use of GGBF [Ground Granulated Blast Furnace] slag in concrete pavement produces a higher durability concrete with lower permeability while maintaining constructability and reducing cost," according to Shad M. Sargand, professor of civil engineering at Ohio University and associate director of the Ohio Research Institute for Transportation and the Environment. "Slag cement slows down the concrete curing process.To prevent early cracking, special attention should be given to be environmental conditions during the first 48 hours of the curing process."

Alternate Dowel Bars

Alternate dowel bar systems reduce the distress from corrosion that is characteristic of epoxy-coated dowel bars. Projects evaluating alternate dowel bars were constructed in Illinois, Iowa, Kansas, Ohio, and Wisconsin. Alternate dowel bar technologies evaluated included fiber-reinforced composite (FRC), grout-filled FRC, stainless steel, stainless steel-clad, and grout-filled stainless steel tubes.

Results from all the States indicate satisfactory performance to date from all alternate dowel bar systems. The FRC dowel bars typically have lower deflection load transfer efficiency, however, than the conventional technology epoxy coated steel or stainless steel dowel systems, an alternative technology. This lower deflection load transfer can be attributed to lower bending stiffness of the FRC dowels.

"Significant stresses were generated in the dowel bars and in the concrete surrounding them after the concrete was placed," says Sargand. "Temperature gradients in the concrete slabs caused high stresses in the bars, and stress levels generated in the fiberglass dowel bars were less than those generated in the epoxy-coated steel bars."

FRC dowels typically cost between $7-10 each, while stainless steel-clad dowels cost approximately $14 each, and solid stainless steel dowels cost more than $20 each. The typical cost of epoxy-coated steel dowels is approximately $3 each. This cost difference is significant because of the number of dowels used in a jointed concrete pavement. A typical 3.6-meter by 4.6-meter (12-foot by 15-foot) jointed concrete pavement slab will contain 12 dowels, so an increase of $1 for each dowel will increase the finished cost by $0.75/yd2.

Surface Texture and Noise

Adding texture to concrete pavement provides a safe, durable pavement surface. Some uniform transverse tined texture, however, can produce an annoying "whine" under traffic. Projects in Colorado, Iowa, Michigan, Minnesota, North Dakota, and Wisconsin that evaluated surface texture and noise investigated alternatives to uniform transverse tined texture that do not exhibit a whine while still providing adequate surface friction. The texturing techniques evaluated included uniform transverse tined, random transverse tined, random skewed tined, longitudinal tined, and exposed aggregate surface.

"The difference between the loudest and quietest pavement was about 7 to 8 decibels," says David Kuemmel, P.E., adjunct professor of civil and environmental engineering at Marquette University in Milwaukee, WI. "That's a 100 times difference in noise pressure."

The results indicate that quiet pavement surfaces that also provide adequate surface texture for wet-weather safety can be constructed on concrete pavements. "Within concrete pavements," says Kuemmel, "we found that the more texture you put for safety, the more noise you get. But if you texture in a longitudinal pattern instead of traverse tine, you can get as quiet as or almost as quiet as an asphalt pavement with the same amount of texture."

The recommended surface texture pattern from the research in Wisconsin is a random skewed tine spacing with the spacing varying from 10-millimeters to 57 millimeters (0.4-inch to 2.25-inch) over a 3-meter (10-foot) pattern. The specific pattern recommended is important and can be obtained at the following Web site: www.trc.marquette.edu/noise&texture/index.html.

WisDOT has implemented the recommended pattern, with the option of skewing given to the contractors. "The safety aspects of longitudinally tined PCC pavements are currently being investigated," says Debra Bischoff, technology advancement engineer with WisDOT's Bureau of Highway Construction. "The results of that study will dictate whether or not WisDOT approves the use of longitudinal tining on Wisconsin highways."

In summary, the FHWA program to test and evaluate innovations in concrete pavement technology through field trials demonstrated that we can produce longer-lasting high-performance concrete pavements. In terms of cost, the results are mixed. Surface texture technologies and durable concrete mixes hold the promise of being cost-effective, while fiber-reinforced concrete pavements have not been shown to be cost-effective to date. Based on the work done in this project, no definite conclusion was reached on joint sealing, and the jury is still out on alternate dowel bars as well.

Summary of High Performance Concrete Pavement Projects

Mark Swanlund is the pavement design engineer for FHWA in Washington, DC. His responsibilities include pavement design, rehabilitation, performance evaluation, and surface characteristics. Responsibilities within surface characteristics include developing policy and technical guidelines for surface texture, pavement/tire noise, and roughness. Swanlund is leading a broad agency initiative to improve pavement condition on the National Highway System through research, development, and technology transfer to State highway agencies and the pavement industry. He has worked for FHWA for 15 years and is a registered professional engineer in Colorado.

For more information concerning high-performance concrete pavement technologies, contact Mark Swanlund at 202-366-1323 or mark.swanlund@fhwa.dot.gov. For supporting material, see the online version of the article at www.fhwa.dot.gov/research/tfhrc/.