Laboratory-Accelerated Versus Outdoor Weathering for Retroreflective Sheeting Specifications

Abstract

Laboratory-accelerated weathering tests are used instead of outdoor weathering tests in specifications for products intended for long-term outdoor use because they provide fast results. These accelerated tests are used as a measure of acceptable weathering performance for a material. Acceptance of results from laboratory-accelerated tests in product specifications is based on two major assumptions: (a) materials that pass the requirements of the laboratory-accelerated test meet outdoor durability requirements, and (b) results from laboratory-accelerated tests are much more consistent than those from outdoor exposures. Numerous examples illustrate the errors that occur when these assumptions are wrong. Material with good outdoor durability can fail to meet the requirements of a specified laboratory-accelerated test, or material with poor outdoor durability will pass the requirements of the specified laboratory-accelerated test. Between-lab variability can cause a product to be rejected by a specifier although the same test run by the supplier produced acceptable results. For retroreflective sheeting, outdoor exposures are actually more consistent than the laboratory-accelerated exposure most commonly used in specifications. To assure minimum acceptable durability, 36-mo outdoor exposures are recommended for most retroreflective sheeting specifications. However, results from these exposure tests do not predict the ultimate service life of retroreflective sheetings.

Get full access to this article

View all access options for this article.

References

ASTM G23, Standard Practice for Operating Light-Exposure Apparatus (Carbon-Arc Type) With and Without Water for Exposure of Nonmetallic Materials. Annual Book of ASTM Standards. Vol. 14.02, American Society for Testing and Materials, West Conshohocken, Pa.

Federal Specification for Sheeting and Tape, Reflective, Non-Exposed Lens. LS300 C. Superintendent of Documents, U.S. Government Printing Office, Washington, D.C., 1979.

ASTM D4956, Standard Specification for Retroreflective Sheeting for Traffic Control. Annual Book of ASTM Standards. Vol. 4.03, American Society for Testing and Materials, West Conshohocken, Pa.

ASTM G53, Standard Practice for Operating Light- and Water-Exposure Apparatus (Fluorescent UV-Condensation Type) for Exposure of Nonmetallic Materials. Annual Book of ASTM Standards. Vol. 14.02, American Society for Testing and Materials, West Conshohocken, Pa.

Specification for Reflective Sheeting for Highway Signs. Report T-14-94. State of Illinois Department of Transportation, 1994.

ASTM G26, Standard Practice for Operating Light-Exposure Apparatus (Xenon-Arc Type) With and Without Water for Exposure of Non-metallic Materials. Annual Book of ASTM Standards. Vol. 14.02, American Society for Testing and Materials, West Conshohocken, Pa.

Specification for Reflective Sheeting Signs. State of California Department of Transportation, Office of Purchasing and Warehousing, June 1996.

Ellinger

M. L.

Weathering Tests. Progress in Organic Coatings, Vol. 5, 1977, pp. 21–34.

Sherbondy

Accelerated Weathering. Paint and Coating Testing Manual, 14th Edition of the Gardner-Sward Handbook ( Koleske

J. V.

, ed.). American Society for Testing and Materials, West Conshohocken, Pa., 1995.

10.

Schiers

, Ketola

, and Fischer

. Weathering of Polymers (Methodology and Limitations of Accelerated Testing). Polymeric Materials Encyclopedia. Vol. 11 ( Salamone

J. C.

, ed.), CRC Press, New York, 1996.

11.

ASTM G7, Standard Practice for Atmospheric Environmental Exposure of Nonmetallic Materials. Annual Book of ASTM Standards. Vol. 14.02, American Society for Testing and Materials, West Conshohocken, Pa.

12.

ASTM E810, Standard Test Method for Coefficient of Retroreflection of Retroreflective Sheeting. Annual Book of ASTM Standards. Volume 6.01, American Society for Testing and Materials, West Conshohocken, Pa.

13.

ASTM E1349, Standard Test Method for Reflectance Factor and Color by Spectrophotometry Using Bidirectional Geometry. Annual Book of ASTM Standards. Volume 6.01, American Society for Testing and Materials, West Conshohocken, Pa.

14.

USPS-S-1087, U.S. Postal Service Specification, Sheeting and Printed Markings, Retro-Reflective. United States Postal Service, Washington, D.C., May 30, 1996.

15.

Daro

, Trojan

, Jacobs

, and David

. Degradation of Polymer Blends IV, Natural Weathering of Low-Density and Linear Low-Density Polyethylene. European Polymer Journal, Vol. 26, No. 1, pp. 47–52.

16.

Simms

J. A.

Acceleration Shift Factor and Its Use in Evaluation Weathering. Journal of Coatings Technology, Vol. 53, 1987, pp. 45–53.

17.

Fischer

, Ketola

, and Murray

. Inherent Variability in Accelerated Weathering Devices. Progress in Organic Coatings, Vol. 19, 1991, pp. 165–179.

18.

Ketola

Durability Testing for Retroreflective Sheetings. In Transportation Research Record 1230, TRB, National Research Council, Washington, D.C., 1989, pp. 67–76.

19.

Ketola

, and Fischer

. Use of Reference Materials in Accelerated Durability Tests. VAMAS Report Number 30, ISSN 1016-2186. National Institute for Standards and Technology, Gaithersburg, Md., 1997.

20.

Fischer

Results of Round Robin Studies of Light- and Water-Exposure Standard Practices. Accelerated and Outdoor Durability Testing of Organic Materials. ASTM STP 1202 ( Ketola

W. D.

and Grossman

, eds.), American Society for Testing and Materials, Philadelphia, Pa., 1993.

21.

Association of Automobile Industries’ Working Group on Test Methods for Paints. Journal of Coatings Technology, Vol. 58, No. 734, 1986, pp. 57–65.

22.

Catalog of Fees and Services, South Florida Test Service, Miami, Fla., 1996.