Bender Element Field Sensors for Base Course Stiffness Measurements in Airport Pavements

This paper presents the field installation in an airport pavement and early results of a bender element (BE) field sensor recently developed at the University of Illinois for direct in situ local stiffness measurement and assessment of layer moduli of pavement base/subbase layers. The BE field sensors were installed in a ‘Smart Runway’ pavement; an extensively instrumented and monitored runway at Hill Air Force Base in Utah. The instrumentation project was undertaken by the US Army Engineer Research and Development Center (ERDC) for monitoring responses of in-service airport pavements subjected to aircraft loadings. Three BE field sensors were installed at different depths in the base layer along the gear path of a heavy cargo aircraft, and a fourth BE sensor was placed in a non-trafficked area of the pavement for comparison. Shear wave velocities were measured immediately after sensor installation in the base and after the construction of the asphalt surfacing. The modulus of the aggregate base was estimated from the measured shear wave velocities. Test results indicated a significant increase in shear wave velocities after proper compaction of the base layer and the placement of the asphalt surface course. The stiffening of the base due to higher confinement could be reliably determined by the shear wave measurement method. In addition, heavy weight deflectometer (HWD) and dynamic cone penetrometer (DCP) tests were also conducted on the test pavement. Comparisons between the moduli obtained from HWD backcalculation, the DCP-based assessment, and those measured by the innovative BE field sensors indicated that the layer moduli from the BE field sensors and DCP testing were relatively similar; whereas the modulus values backcalculated from HWD tests were notably higher.