Editor's Report
Editor's Note: Barry Gantenbein, editor, Western Builder magazine, reports on recent efforts to reduce highway noise...
Silence Please
Quieter pavement is a common goal in the highway construction industry, but numerous roads are being traveled to reach this goal. The use of rubberized asphalt overlays is being explored in the Arizona Department of Transportation's Quiet Pavement Pilot Program. The program's preliminary results made a lot of noise at the American Concrete Pavement Association's (ACPA) July Mid-Year Committee Meetings in Chicago.
In 2003, the Arizona Department of Transportation (ADOT) began a three-year, $34-million Quiet Pavement Pilot Program, in cooperation with the Federal Highway Administration (FHWA) and the Maricopa Association of Governments (MAG), to surface about 185.07 km of Phoenix-area freeways with rubberized asphalt. The intent of the Quiet Pavement Pilot Program is to determine if sound walls can be replaced by pavement type to reduce noise alongside highways.
On Phoenix-area freeways, a 0.0254-meter layer of rubberized asphalt is being applied on top of the existing 0.305-meter-thick to 0.356-meter-thick concrete pavement. Rubberized asphalt consists of regular asphalt paving mixed with "crumb rubber," which is used tires ground to the consistency of ground coffee.
After about one year, overlays have resulted in up to a 12-decibel reduction, with a typical reduction of 7 to 9 decibels, according to a report at the ACPA Mid-Year Committee Meeting. However, a re-analysis could show that the level of noise reduction is not nearly as great as the early numbers indicate, said the ACPA's Larry Scofield.
Also, the use of rubberized asphalt overlays of concrete may be problematic in areas with harsh winter climates.
In addition to concerns about durability in climates with freeze/thaw cycles, the application of rubberized asphalt is sensitive to temperatures. The concrete pavement surface needs to be between 85 and 145 degrees Fahrenheit for the material to adhere properly, according to ADOT. As for eliminating sound walls, walls do more than reduce the noise from highways in adjacent areas, ACPA members said.
"Sound wall provide separation from the community from the corridors, so there's a safety component. Sound walls keep children, animals and other things off corridors," said one member.
Concrete Efforts
Efforts are being made to reduce noise from concrete highways. The texture of concrete pavements and the concrete mix used to build highways can be adjusted to reduce noise levels, members said at the meeting.
"You can make profound differences in the noise levels, without changing surface types," said Scofield. "We do have solutions; I don't want people to forget that." Texture is the main cause of noise on concrete highways, with transverse tine the noisiest texture, said one member. An Astro turf drag seems to work well in noise reduction, said another member. Scofield reported on efforts being made to reduce noise from concrete pavements. The ACPA now has Sound Intensity Measurement Capability to aid in determining the cause of highway noise.
"We can actually go out and measure roadways ourselves. If there's a noise issue, we can figure out if it's frequency based or overall noise measurement based," Scofield said.
An ISU/FHWA/ACPA partnership is examining a variety of test sections across the country. "They're doing surface characteristic measurements, looking at noise, friction, texture, and profile," said Scofield.
The Purdue Tire Pavement Test Apparatus (PTPTA) is being used to conduct three experiments — one studying the effects of joint widths and offsets on noise; a grinding parameter study; and an examination of innovative tining and textures.
"The advantage of this laboratory approach is that if you can cast it, you can test it. You can dream up any kind of texture you want, and get an idea what is quiet and what isn't quiet," Scofield said. The ACPA has a number of publications available online, including test results, on how to reduce noise levels on concrete pavements. Research includes a look at how truck traffic affects noise levels.
"How commercial vehicles create noise, and where it comes from, is a huge issue," said Scofield. Also, the FHWA has two task orders with consultants to look at innovative surface systems.
"This is coming from the manufacturing industry, where they're using etching and water jet blasting, and not worrying about whether it's a construction application. They may be able to come up with textures we would have never thought possible," Scofield said.
22-Jan-2006