Slippage Failure of a New Hot-Mix Asphalt Overlay.

A premature pavement overlay failure had occurred only 1 day after it was opened to traffic. Crescent-shaped cracks were intermittently spread over a section about 3 mi in length. Dynamic cone penetrometer results demonstrated that the slippage cracks were not linked to weak base or subgrade. Loss of overlays on structurally sound pavements due to poor bonding is an expensive error. A tack coat is considered a simple, relatively inexpensive, yet essential step in the pavement construction process. It is theorized that the ineffective bonding due to poor quality tack coat and/or inappropriate application rate is the primary factor that led to the slippage cracks. Other contributing factors include low asphalt content and high aging ratio that reduced the effectiveness of the bond. The aging ratios exceed the maximum allowable 3.5 specified. Based the investigation results, the contractor did remove and replace the top 50 mm hot-mix asphalt (HMA) overlay at his own expense. Although selection of proper tack coat materials and quantities is essential, there is a lack of proper construction quality control and quality assurance procedure to ensure appropriate surface preparation prior to application of a HMA overlay. [ABSTRACT FROM AUTHOR]