Development Of Design Guide For Thin And Ultra Thin Concrete Overlays Of Existing Asphalt Pavements Task 2

The existing ultra-thin whitetopping (UTW) and thin whitetopping (TWT) design methods are reviewed so that any gaps in the design process can be identified. Four design methods are included, namely the Colorado Department of Transportation (CDOT) method, the New Jersey Department of Transportation method, the Portland Cement Association (PCA) method, and the Illinois Centre for Transportation (ICT) method. The structural response and performance models used in these methods are evaluated using field data from the whitetopping sections at MnROAD. Based on these evaluation, the PCA structural model developed for the calculation of stress in the corner and at the top of the overlay seems more suitable for the prediction of the structural response of UTW and the CDOT structural model developed for the calculation of stress at the lane/shoulder edge and at the bottom of the overlay is more suitable for TWT. It is also found that the use of a temperature-dependent asphalt modulus of elasticity results in significantly higher fatigue damage in the overlay, which is ignored by all four methods. Finally, the asphalt fatigue analysis incorporated in some of these design procedures is does not result in fatigue failure of the hot mix asphalt and therefore need not be considered when designing these overlays.