Asphalt wear surfaces cover 1,378 of Minnesota's timber bridges. This study assessed the magnitude of premature asphalt
deterioration on timber bridges; identified the primary mechanisms responsible for wear surface deterioration; and suggested
methods for improving asphalt pavement performance on timber bridges.
Research methods included surveys, meetings with several county engineers and tours of their timber bridges, interviews with both
asphalt and timber bridge industry professionals, and literature reviews. The study revealed that approximately 50 percent of
counties experience some problems with premature reduced serviceability of the asphalt pavement wear surfaces that cover their
Possible pavement failure mechanisms include low-temperature cracking, reflective cracking from deck fault lines found at deck
panel joint lines and deck lamination separations, asphalt fatigue fracturing, and asphalt de-bonding due to oil preservatives
interference. The report presents the following proposed solutions for controlling timber bridge asphalt pavement cracking: asphalt
pavement saw & seal, asphalt pavement fabric or material underlay, removal of extruded oil-type preservative before surfacing,
conditioning of bridge timbers to the expected equilibrium moisture content before bridge installation, and tightening of timber
decks through maintenance practices.
Larson, Timothy D.; Seavey, Robert; Lange, Douglas A..
Relationship between timber bridge characteristics and asphalt pavement wear surface performance.
Minnesota Department of Transportation.
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