Mechanistic Design of Thin Whitetopping Pavements in Colorado

A mechanistic design procedure was developed for the state of Colorado to determine the required concrete thickness of thin [12.7 cm to 17.8 cm (5 in. to 7 in.)] whitetopping overlays on asphalt pavements. Field testing was conducted to evaluate critical load locations for whitetopping with joint spacing up to 3.66 m (12 ft). The load-induced flexural strains were used to calibrate fully bonded stresses computed by applying finite element analysis techniques to partially bonded stresses measured in the field. For each test section, load testing was conducted throughout the course of a day to develop a temperature correction for the critical stresses derived for zero temperature gradient (zero slab temperature curling). Equations predicting the critical concrete flexural stresses and asphalt concrete strains for use in whitetopping were developed. A mechanistic design procedure is described that allows the evaluation of trial whitetopping thicknesses and joint spacings. The procedure computes the concrete and asphalt fatigue life for specific material properties. Iterations are required to determine the appropriate parameters that provide the required design life for both concrete and asphalt layers. In addition to the design procedure, the effect of surface preparation during construction was studied by comparing identical slabs constructed on milled and unmilled asphalt. It was concluded that existing asphalt pavement should be milled and cleaned before concrete placement for an overall reduction of 25 percent in the critical load-induced stresses. However, new asphalt, such as that placed in repair patches, should not be milled before concrete placement to avoid a 50 percent increase in critical load-induced stresses.