Noise Reduction with Asphalt-Rubber

The proven advantages of using Asphalt-Rubber as the binder in hot mix include:

Increases pavement Life
Resists rutting, aging and reflective cracking
Reduces pavement thickness
Provides optimum skid resistance

Another major benefit is traffic noise reduction of 65- to 85-percent, eliminating the need for expensive sound barriers.

Numerous noise level studies in the United States and abroad prove use of Asphalt-Rubber as the binder in Asphalt-Rubber hot mix reduces traffic noise levels dramatically.

This phenomenon was first noticed in Brussels, Belgium, in 1981, in an Asphalt-Rubber hot mix called "Drainasphalt." Since then, there have been noise studies conducted in three continents on Asphalt-Rubber hot mix pavements. Results of these evaluations are documented in technical papers published and are briefly reported here, summarized in the conclusion.

Decibel (dB) is a unit for expressing the relative intensity of sounds on a scale from zero, for the average least perceptible sound, to about 130 for the average pain level.

The decibel scale is a logarithmic function. An increase of 3 dBs doubles the energy or intensity, and an increase of 6 dBs quadruples the energy or intensity.

Noise Reduction Studies

Drainasphalt (Asphalt-Rubber open graded hot mix) study conducted on the Motorway South of Ghent, Belgium, on the Brussels Loop, 1981, reported by Professor E. Nakkel, President of a technical Committee on "Asphaltstrasen," Bonn, Germany. He advises of the high cost of reducing noise levels by using sound barriers. His investigation also reveals Asphalt-Rubber hot mix provided a noise reduction of 8 to 10 dBs, a 75-percent reduction in noise.
Michel Amilhat of the Société des Autoroutes du Nord et de l'Est de la France, Paris, 1988, presented a paper at the Austrian Conference on Asphalt-Rubber in Graz, Austria, on studies conducted in Paris, France.

An investigation was made to determine hydrostatic pressure in and under Drainasphalt placed on city streets along the Seine River in 1984. A significant noise reduction of 3 to 5 dB with no trucks, and 2 to 3 dB reduction with five percent trucks, were recorded, a 50- to 75-percent noise reduction. As a result, a recommendation was made to overlay the Paris Loop with open graded Asphalt-Rubber.
Dipl. Ing. Horst Pochhacker of West Germany, presented information on the many advantages of Asphalt-Rubber, at the 10th Anniversary International Conference in Graz, Austria, 1988, on Drainasphalt, placed in Bonn, Germany in 1980.

He spoke on the cost of sound barriers compared to Asphalt-Rubber overlays, stating savings were in excess of ten times the cost of constructing sound reduction structures.

Egil Nakkel, Director of Prof. and Pres. D. Techn Komitees der A.I.P.C.R., Bonn, Germany, informed attendees at these meetings, the thicker the overlay using Drainasphalt, the greater the noise reduction. He said that 4 cm is quieter than 2 cm, and reported a minimal 3 dB reduction in noise, which is 50-percent. Nakkel also discussed the high cost of sound barriers in comparison to 4 cm of Asphalt-Rubber drain mix, which is called FlüsterAspahlt."
Test Road in Dordrecht, Belgium. Paper presented at the national Seminar on Asphalt-Rubber, Kansas City, Missouri, 1989, by Ir. J.C.P. Heerkens and Ir. A. Von Meier. A 2.3 inch (6 cm) layer of Asphalt-Rubber hot mix placed in 1988 had a noise reduction of 3.5 dB as compared to dense asphalt concrete, and a 9 dB in comparison to portland cement concrete at 72 mph (120 km). This represents a reduction of 60- to 80-percent.
Test conducted in Europe, reported at the national Seminar on Asphalt-Rubber, Kansas City, Missouri, 1989, by Hugo Ban de Veld paper titled, "The Use of Asphalt-Rubber Bitumen in Road Construction," (Draining Mix), presented by Jacques G. Bardot. Van de Veld reported draining mixes using Asphalt-Rubber significantly reduce traffic noise. Three to ten dB reductions with speeds of 35 mph (60 km) to 60 mph (100 km) were recorded, representing 50- to 90-percent reduction in noise levels.
City of Phoenix, 7th Street Sound Level Survey, 1990, of a one-inch, gap-graded, Asphalt-Rubber hot mix overlay placed in 1989. Conducted by Western Technologies Inc., of Phoenix, Arizona, the study disclosed a noise reduction of 10 dB. This correlates to a sound intensity reduction of eight times, or 88-percent.
Arizona Department of Transportation (ADOT), Interstate 19, South of Tucson, open graded Asphalt-Rubber hot mix overlay, placed on a portland cement concrete pavement in 1989. Studies conducted be Western Technologies Inc., Phoenix, Arizona, in 1989, reported an 80.4 dB on the existing portland cement pavement, and a 73.7 on the Asphalt-Rubber overlay. The 6.7 dB difference is a nose level reduction of 78-percent.
At the 1988 Asphalt-Rubber Conference in Graz, Austria, Helmut Prager, Eng. of Austrian Highways and Bridges, Vienna, Austria, presented a paper on research conducted on Highway A-9, the Pyhrnam Autobahn and A-123, the Inntal Motorway.

This investigation confirmed 4 to 5 cm provides better noise reduction than 3 cm for Silent Asphalt Flüsteraspahlt. Also, a major noise reduction of 3 or more dB, with 50-percent or more nosie reduction, were verified on old stone city streets overlaid with Flüsteraspahlt.
Research reported by Dipl. Ing. E. Reinsih at the 1988 Austrian conference on Asphalt-Rubber on Concrete Autobahns overlaid with Drainasphalt in 1985 and 1987, provides significant mix design data.

Asphalt-Rubber surfaces tested in uphill and downhill grades, curves and hills, using Asphalt-Rubber with 6.6-percent binder indicated a need for 20-percent voids in Drainasphalt. Noise reduction values of 6 dB, or 75-percent noise reductions were recorded.
Noise Level Reduction through Silent Asphalt, by Neivelt, Stehno, Stickler and Ertle, a joint venture of CT-Bitument Gesellschaft, Vienna, ESSO-Specialbitumen, Vienna; Trainfeller Baugesekkschaft Scheibbs, on Inntal Motorway between Innsbruck and Angath.

Noise levels were reduced by 4.1 to 5.5 dB or 60 to 70 percent. The greatest reduction occurred at night, with a wet surface. The average noise level reduction was 4.8 dB or 65-percent.

The study advises a 3 dB or 50-percent reduction corresponds to:
- Reduction of the traffic volume by half
- Twenty-five percent reduction in speed
- Doubling of the distance from the noise source

Conclusion

Asphalt-Rubber offers many advantages that cannot be denied. Research, Demonstration Products, and 20 years of performance on thousands of lane miles of roads, attest to this fact.

Noise suppression qualities of Asphalt-Rubber were often overlooked in early research. However, work on the Brussels Loop revealed a very important advantage of using Asphalt-Rubber.

European Engineers discovered in th 1980's, Asphalt-Rubber reduces noise. In recent years, engineers in the United States have recognized the importance and value of this noise reduction quality.

Research has verified a significant noise reduction due to open graded design and the inclusion of crumb rubber from scrap tires. Several comparison studies indicate a 10 dB or 90-percent noise reduction. In all cases, noise has been reduced by no less than 50-percent.

Pavement surfaces can be designed to reduce noise by 3 dB without rubber. However, the addition of rubber in the binder increases the dB by 6 or more.

The maximum acceptable dBs highway and street designers expect is 64 dBs. Many streets and roads have 79 or greater dBs. A well-designed surface with Asphalt-Rubber can move noise factors back into acceptable comfort zone, and eliminate the need for noise abatement structures. Sound walls cost more than $400 per linear foot of centerline pavement. Asphalt-Rubber hot mix overlays cost $12 per linear foot, per one 12-foot lane per inch.

Noise abatement is only one of the many advantages in resurfacing city streets and urban roads with Asphalt-Rubber.

References

Proceedings National Seminar on Asphalt-Rubber, Kansas City Missouri, October 1989.
Asphalt-Rubber Conference in Graz, Austria, March 1988.
1990 Sound Level Survey, City of Phoenix Streets, by Western Technologoes, Inc.
A Noise-absorbing road surface made of Prorelastic Asphalt concrete, Dr. Ing A. Con Meier and Ir J.C.P. Heerkens, 1986.
Silent Asphalt-Research Project "Noise Level Reduction through Highly Elastomeric Asphalts," by Gottfried Neivelt, Gerhard Stehno, Helmut Stickler and Johann Ertl.

[home library membership newsletter FAQ links contact events]