First Findings from the Kansas Perpetual Pavements Experiment

To investigate the suitability of the perpetual pavements concept for Kansas highway pavements, the Kansas Department of Transportation (KDOT) constructed four thick, flexible pavement structures on a new alignment on US-75 near Sabetha, Kansas. They were designed to have a perpetual life and have layer thicknesses close to those recommended by KDOT's structural design method for flexible pavements, which is based on the 1993 AASHTO Design Guide. To verify the approach of designing perpetual pavements on the basis of an endurance strain limit, the four pavements were instrumented with gauges for measuring the strains at the bottom of the asphalt base layers. Seven sessions of pavement response measurements under known vehicle load were performed between July 2005 and October 2007, before and after the pavement sections were opened to traffic. The analysis of the strain data indicated that, even during hot summer days, the strains of all four test sections were smaller than the endurance limit of asphalt–concrete. As expected, the strains were affected by the temperature in the asphalt layers and the speed of the loading vehicle. The analysis of the strain signals revealed that the transverse strain under the front axle did not recover completely before the arrival of the rear axles, a situation causing the accumulation of dynamic transverse strain to values higher than those of the corresponding longitudinal strains. A comparison between the measured response and that predicted by a linear-elastic model indicated that the predicted transverse strains were close to half the corresponding measured dynamic transverse strains, while the predicted longitudinal strains were close to twice the measured dynamic longitudinal strains. Furthermore, the predicted vertical stresses at the top of the subgrade layer were close to five times the measured stresses.