Construction of the new Tacoma Narrows Bridge (TNB) included a steel orthotropic bridge deck. The higher flexibility of an orthotropic deck causes pavement placed upon it to fatigue and crack more quickly than pavement placed on a normal roadway. The HMA (Hot Mix Asphalt) overlay placed on the new bridge incorporated Trinidad Lake Asphalt (TLA) to help resist the stresses of an orthotropic deck.
The performance of the overlay after eight years of traffic was disappointing. Problems with the mix design, achieving specified densities, temperature differentials, and issues with the paver resulted in a pavement with a higher than desired void content. The result was severe rutting caused by raveling in the wheel paths possibly exacerbated by wear from studded tires. Cracking and delamination, the initial concern which prompted the use of the TLA modified HMA, were not a problem on the bridge deck.
As a result of the severe raveling, consideration is being given to the use of a conventional HMA when replacement of the deck wearing surface becomes necessary.
Washington (State). Department of Transportation. Materials Laborabory
Paving materials, Trinidad Asphalt, Orthotropic plates, Overlays (Pavements), Pavement performance, Hot mix asphalt, Fatigue (Mechanics), Wear, Stripping (Pavements), Bridge decks, Steel bridges, Rutting.