Revised Design Procedure for Thin and Ultrathin Bonded Whitetopping

Development of design procedures for bonded whitetopping overlays has been based on the assumption that failure mechanisms are a function of overlay thickness; namely, thin whitetopping results in longitudinal cracking and ultrathin whitetopping results in corner cracking. However, field data from whitetopping sections indicate that failure modes are dictated by slab size rather than overlay thickness. The revised procedure presented here for thin whitetopping and ultrathin whitetopping offers four primary enhancements to the Portland Cement Association and Colorado Department of Transportation procedures that traditionally have been used: (a) the failure mode is dictated by the joint spacing and not the overlay thickness, (b) the stress adjustments factors have been calibrated with an extensive data set, (c) the equivalent gradients to be used as the design input are defined according to the pavement structure and geographical location of the project and, (d) the effect of temperature change on hot-mix asphalt stiffness is considered. Comparisons of the predicted performance for the revised procedure with the actual performance for four separate projects showed that the predicted thicknesses are reasonable. It was also found that the predicted thickness obtained with the revised procedure was sensitive to the thickness of hot-mix asphalt, the level of traffic, and the modulus of rupture of the portland cement concrete, as expected.