A lightweight, durable, and traction-resistant material is needed as a replacement for anexisting two-layer timber wearing surface. The surface to be replaced is 30 ft (9.2 m) wide and isattached to an orthotropic closed-cell steel deck. The orthotropic steel deck is supported by twosteel box girders that are 61 in. (155.9 cm) wide by 163 in. (414 cm) deep. The bridge is 2295 ft(699.5 m) long with six spans. The structure crosses the Yukon River at a 6% grade on theDalton Highway, a gravel road about 50 mi (80 km) north of Fairbanks, Alaska. This structure isexpected to support the oil pipeline, a future gas line, heavily loaded trucks and respondfavorably to mild summers and harsh winters. Air temperature extremes are -58°F (-50°C) to100°F (40°C).A 5 in. (127 mm) two-layer timber wearing surface was installed in 1976. The top layer wasreplaced in 1981, 1993, 1999, and 2007. Both layers were replaced in 1993 and 2007. Becauseof excessive costs, the Alaska Department of Transportation is seeking alternatives. Thermalcracking, abrasion, durability, flexural strain, traction, weight, and a secure fastening method tothe steel deck are important in selecting a replacement surfacing material. The driving surface maybe dry, wet, icy, snow-covered or some combination. During the winter, the driving surface issubjected to snow plow removal and because of the steep grade, trucks typically cross using tirechains.Prior to this study, several different wearing surfaces have been installed and evaluated for fieldperformance by AKDOT as part of an FHWA experimental feature. We were asked to evaluate in thelaboratory several systems that were being considered. Some of the samples were installed on the bridgeand others were only evaluated in the laboratory. Samples were laboratory tested for structuraldurability, traction, and resistance to tire chains. In addition to laboratory test results, fieldperformance for several experimental wearing surfaces was evaluated and compared with thelaboratory results. Laboratory test results are presented and each wearing surface is ranked forstructural integrity (evaluated for compliance with the flexibility of the orthotropic deck),traction, resistance to chain damage, and field performance. Cobra X (no longer available) wouldlikely provide more than a 15-year satisfactory service life. All other wearing surfaces tested inthis study including the existing timber wearing surface are less than satisfactory for long term use.Another study has begun in which samples of wearing surfaces solutions that are proposed bycompetitive companies are tested and pre-qualified for use for field evaluation. The results arepromising.
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