Moving Forward on Surface Texture Issues
The FHWA issues a new policy; the ACPA leads the way
in several research efforts across the country.

by the Staff of the American Concrete Pavement Association

The concrete pavement industry is working full speed ahead to proactively address issues centering on concrete surface characteristics, including tire pavement noise, texture, smoothness, and friction.

Today, the concrete pavement industry not only offers existing solutions to the tire/pavement noise issue, but is working to find new answers in the form of improved surface textures for new pavements. Pavement texture, however, is decidedly not a one-dimensional noise issue, says Gerald F. Voigt, ACPA President and CEO.

“We will not trade off safety or long-term performance, and we will strive to avoid significantly increasing initial costs or life-cycle costs,” Voigt said. The industry is drawing from experience in European countries, with the goal of optimizing a texture for the United States.

FHWA’s new position

Research studies have revealed that much of the perceived problem with concrete pavements results in a pure tone, or whine that occurs when noise with a certain discrete frequency emanates from the tire/pavement interface. Almost always, those frequencies are set up by a concrete pavement with uniformly spaced transverse tining. It so happens that in the late 1970’s, in an effort to improve safety, the Federal Highway Administration mandated tining of concrete pavements. In response, many states placed concrete pavements with uniform transverse tining.

Now, the FHWA has dropped the requirement for transverse tining. In a new Technical Advisory dated June 17, 2005, the FHWA writes, “While safety considerations are paramount, tire/surface noise should be considered when specifying pavement and bridge surfaces.” And the FHWA opens the door to a variety of concrete pavement texture treatments that can be used, including:

• Tining, preceded by a burlap drag. “Spacing, depth, width, and orientation of the tine pattern have a significant influence on the friction and tire/surface noise characteristics of the completed surface,” says the FHWA.

• An exposed aggregate surface, which has been shown to provide a lower noise surface for concrete pavements.

• If adequate safety performance is demonstrated, the FHWA recommends a broom or artificial turf drag finish for concrete surfaces where the design speed is 50 miles per hour or greater.

• Diamond grooving has been shown to be an effective method for providing macro-texture to new concrete pavements. Again, spacing, depth, width, and orientation of the grooves have significant influence on the friction and tire/surface noise characteristics of the completed surface.

• The FHWA recommends diamond grinding of new concrete pavements for the purpose of imparting macrotexture, provided adequate safety performance is demonstrated.

• Burlap drag surface texture should only be considered for surfaces where the design speed is less than 50 miles per hour.

• Other techniques may be used if research indicates that long-term safety performance is achieved.

The research effort

Texture modifications to existing concrete, or novel constructions for new concrete, can bring about substantial reductions in tire/pavement noise, writes Paul Donavan of Illingworth & Rodkin Inc., a Petaluma, California-based noise authority. In a research paper that the ACPA’s Scofield calls “one of the best,” Donavan concludes that concrete surfaces have been found to span a range of as much as 16 decibels — a very significant number.

“As a result, there is the potential to achieve large noise reductions depending on the existing and final surfaces,” says Donavan. “In California, grinding of bridge decks and elevated structures has been found to reduce tire/pavement source levels by 3 to 10 decibels with comparable reductions in wayside measurements. In Arizona, grinding of (concrete) has reduced source levels up to 9 decibels relative to some transversely tined surfaces.”

Donavan documents the frequency issue. He says four new test sections, all of them diamond ground, were used in constructing a demonstration project sponsored by the ACPA, the Arizona DOT, the International Grooving and Grinding Association, and the local cement industry.

“From the worst-case random transverse-tined section to the ground section, the reduction is almost 9 decibels,” Donavan writes. Furthermore, he says most of the improvement between the tined and ground surfaces occurs at frequencies below 1,600 Hertz. In this region, reductions of 10 to 12 decibels occur.

Donavan’s frequency finding was confirmed by tests run on a section of concrete pavement in Santa Clara County, California. Sound intensity measurements were made to compare the original tining noise to the ground pavement. It was observed that the largest reductions in noise were found in bands around 1,600 Hertz.

“These frequencies are thought to be responsible for a higher frequency presence, or sizzle sound, that can be noticeable in the community,” the paper says. Its title is Quieting of Portland Cement Concrete Highway Surfaces with Texture Modifications, presented at Noise-Con 2005 in Minneapolis.

“Our message is that concrete has both a frequency and a noise component,” says Scofield. “And if we can eliminate the tonal whine related to frequency, then we don’t have to have the quietest pavement in town. Because you have one material, concrete, that doesn’t have frequency issues but is longer lasting, versus the alternative, which may be quiet when it’s built but builds up noise over time and doesn’t last as long.”

When the FHWA gave up the requirement for transverse tining, Scofield said, the frequency issue with concrete surfaces was resolved. “They still want a safe road,” he says. “If you want to use an artificial turf drag for surfaces designed for more than 50 miles per hour, you still have to demonstrate that it’s safe.

“We still have to resolve issues with existing pavements,” says Scofield. “We need to grind them to improve their noise performance. People need to know that concrete can be built to perform quietly — or ground to perform quietly. People want good friction qualities, a good ride, and good noise performance. And then you must consider the long-term performance of concrete itself. The economics of the alternative material are not going to be there in the long term.”

Pooled fund research

A three-part field research project is well under way under the leadership of the National Concrete Pavement Technology Center at Iowa State University in Ames. The research is being supported by the ACPA, Iowa State University, and the FHWA, with some funds from the Iowa Highway Research Board.

The FHWA says it is committed to developing pavement surfaces that are safe, durable, and cost-effective, while providing a smooth ride and low tire-pavement noise. The National Concrete Pavement Tech Center, the ACPA, and several states are also interested in improved surface characteristics. So it makes sense that the parties come together to leverage their resources. “The resulting project is much more robust than any of the parties could have done individually,” says the FHWA in a statement.

As for goals of the three-part project, the FHWA would like to have definitive recommendations for concrete texturing methods that meet the owners and users needs and can be reliably constructed. The FHWA says it is their intention “to modify our current Technical Advisory on texturing pavements, as appropriate, based upon the results of this project.”

The first part of the project, writing a strategic plan, has been completed, says Paul Wiegand, research engineer for the center. The goals are threefold: to define the relationship between noise and concrete texture with current practices; to make the current practices as quiet and safe as possible; and to provide a specification that will control concrete pavement texture, and therefore, control the tire/pavement noise.

The second part, now ongoing, consists of field experiments including tire/pavement noise measurements. Last summer, the center began conducting noise research on existing pavements in a number of states nationwide. Also as part of part 2, the center is doing more detailed research on a 2.5-mile stretch of U.S. Highway 30 east of LeGrand, Iowa. Some 18 surface textures are being tested, including burlap drag, artificial turf drag, diamond grinding, and various forms of longitudinal and transverse tining.

Through the spring and summer of 2006, research will continue with measurements of noise, texture, and friction conducted on existing pavements in southern, eastern, and western states, including California and Washington. Field tests include texture measurements with a new line-laser based three-dimensional texture measurement system termed RoboTex. For noise, on-board sound intensity, in-vehicle testing, and wayside measurements are all being conducted. The sophistication in all of these measurements is allowing the research team to relate tire-pavement noise to texture at the exact same location. This type of data collection is first-in-the-world. With on-board sound intensity measurements, microphones are mounted near the tire, close to the pavement. The effects of engine noise and wind are virtually eliminated in this type of testing.

Friction tests are an important part of the center’s research as well. Friction is being measured in two ways: with a locked-wheel skid trailer and with a dynamic friction tester. The latter consists of a flywheel that is brought to speed and then lowered onto the pavement. The test measures friction by monitoring force as the wheel slows down.

“We hope to start the third phase this fall,” says Wiegand. “It consists of continuing field experiments and looking at innovative concrete surfaces. It is a pooled-fund study supported by various states, so we’re soliciting participation by the states now,” says Wiegand.

Preliminary results confirm that very strong relationships exist between concrete pavement’s mean profile depth and tire-pavement noise. “We’re looking at whether — and how — the depth and other texture characteristics affects noise.” This is particularly true given the large variability that is present,” says Wiegand. “One major discovery is that the actual texture on the pavement differs considerably from that which was specified. Trends are evident, but there are often exceptions. We need to look at how to attain a more consistent texture along the pavement.”

The center intends to investigate such innovative surfaces as porous concrete and exposed aggregate concrete, which often results from two-lift concrete construction with a specially cured surface. The two-lift construction is practiced in Europe and is called wet-on-wet construction, Wiegand says. It’s done in two separate paving operations. The first layer “doesn’t need to be of the highest quality,” Wiegand says. “You can focus your strength and durability requirements on the surface lift.”

Porous concrete has also been used in Europe to a limited extent, and it has excellent splash-spray and noise characteristics, Wiegand said. But porous concrete has not been proven to stand up structurally on high-load, high-speed roadways.

More research

With support from the ACPA and its affiliate, the International Grooving and Grinding Association, testing is being conducted at Purdue University using a custom-built grinding head, which is a key component of the Tire Pavement Test Apparatus. TPTA testing is conducted at 0 to 30 miles per hour, and the machine is capable of sound intensity testing (close to the wheel) or close proximity testing. “We have a noise microscope,” says Will Thornton, principal investigator at Purdue.

The special grinding unit can grind two 8-inch wheel paths in each sample. Initial tests at Purdue are evaluating the effect of blade spacer width, blade width, and groove depth on the noise-generating characteristics of the resulting texture. The test plan also evaluates the effect of pavement joints, groove effects, and tining and innovative surfaces.

The TPTA allows for quicker changes in the grinding head than could occur with a full-scale field grinding machine. And the laboratory eliminates traffic control or other environmental factors that would be present in field experiments. 

“We’re looking at optimizing the concrete surface with regard to friction and noise,” Thornton says. “We have a good feel for the direction we need to take.” He says it is still too early to issue any results from the Purdue tests.

In addition to the research programs at Purdue and Iowa State, the ACPA has conducted or participated in Whisper Grinding field experiments in Arizona, Kansas, and California. Noise tests were performed, for example, on three different surface textures on State Route 58 near Mojave, California. The surfaces included longitudinally tined, burlap drag, and longitudinally broomed pavements. Next, eight sections of the original pavements were ground and/or grooved to various texture geometries.

In a 2003 report prepared by Donavan of Illingworth & Rodkin, the best noise performance of the 11 surfaces tested on the Mojave Bypass was achieved with the 0.105-inch spacing texture grind surface. “Applied to the existing pavement surfaces on the Bypass, the 0.105 surface was well optimized to balance the high and mid frequencies while achieving a sizable reduction in the joint impulses,” says the report.

Across the nation, in summary, the ACPA is spearheading research that will lead to the optimum concrete pavement surface texture. The resulting surface will not only have optimum tire/pavement noise characteristics, it will be a superior material in terms of friction for safety, durability, and smooth ride.

Reprinted from Better Roads Magazine
August 2006

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