Pilot Instrumentation of a Superpave Test Section at the Kansas Accelerated Testing Laboratory

Pilot Instrumentation of a Superpave Test Section at the Kansas Accelerated Testing Laboratory

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    Final ReportAugust 1998 – November 2000
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    Two Superpave test sections were constructed at the Kansas Accelerated Testing Laboratory (K-ATL) with 12.5 mm (2 in) nominal maximum size Superpave mixture (SM-2A) with varying percentages (15 and 30 percent) of river sand. A 150 kN (34 kip) tandem axle with dual wheels was used for 10,000 repetitions. Next the sections were loaded by three different tandem axle loads and three single axles for more than 30 repetitions in each configuration to estimate the relative pavement damage in the SM-2A layer due to different axle loads and configurations. All load application was done at a temperature of approximately 38o C (98o F) at the middle of the SM-2A layer. The test sections were instrumented at three locations on each test section with (i) transverse strain gages at the bottom of the SM-2A layer, (ii) pressure cells on the top of the subgrade, and (iii) temperature gages in the aggregate base, subgrade and SM-2A layers (mid-depth and bottom). Data was collected during load applications by the K-ATL tandem axle and a Falling Weight Deflectometer (FWD). After 80,000 applications of the 150 kN (34 kip ) tandem axle loading, severe rutting was observed on both test sections with no visible cracking, and the testing was terminated. The theoretical pavement responses were also calculated with a multi-layer elastic analysis program, ELSYM5 and compared to the test results. The measured vertical stresses on the top of the subgrade and tensile strains at the bottom of the SM-2A layer due to FWD loads are generally very close to those calculated by ELSYM5. However, measured tensile strains and vertical stresses on both sections were higher than those calculated by ELSYM5. In general, the measured tensile strains under the K-ATL wheel loads were found to increase with increasing number of wheel load repetitions, but the measured vertical stresses remained relatively constant. Fatigue tests were conducted on the beams fabricated from the loose SM-2A (15) mixtures sampled during construction. Fatigue and rutting damage analyses were also conducted on a set of test beams sawed from that section. The rutting and fatigue results were consistent with observed and predicted damage. The AASHTO load equivalency factors were found to be much higher than those calculated in this study. Finally, based on the measured pavement temperature data and the longitudinal profile data (dipstick measurement), a temperature variation along the depth of Superpave pavements and pavement deterioration based on International Roughness Index values were analyzed and reported. Several recommendations based on this study have also been made.
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