To investigate the suitability of the Perpetual Pavements concept for Kansas highway pavements, the Kansas Department of Transportation has constructed four thick flexible pavement structures on a new alignment on highway US-75 near Sabetha, Kansas. They were designed to have a perpetual life and have layer thicknesses close to those recommended by the KDOTs structural design method for flexible pavements, based on the 1993 AASHTO Design Guide. To verify the approach of designing perpetual pavements based on an endurance strain limit, the four pavements were instrumented with gages 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 indicates that, even during high summer days, the strains of all four test sections, are smaller than the endurance limit of asphalt concrete. As expected, the strains are 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 does not recover completely before the arrival of the rear axles, 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 indicates that the predicted transverse strains are close to half the corresponding measured dynamic transverse strains while the predicted longitudinal strains are close to twice the measured dynamic longitudinal strains. Also, the predicted vertical stresses at the top of the subgrade layer were close to five times the measured stresses.
Abstract