Falling Weight Deflectometer Testing to Determine Relative Damage in Asphalt Pavement Unbound Aggregate Layers

Abstract

Falling weight deflectometer (FWD) testing is a nondestructive pavement structural evaluation technique routinely performed on highway and airfield pavements to estimate pavement layer properties from measured deflection basins. This paper presents a methodology based on analyzing FWD test data between trafficked and nontrafficked lanes to determine the degradation and rutting potential of flexible pavement unbound aggregate layers in comparison to the subgrade damage. The validity of the approach is demonstrated by analyzing the heavy weight deflectometer (HWD) data obtained from the FAA's National Airport Pavement Test Facility (NAPTF) flexible airport pavement test sections built with substantially thick unbound aggregate base–subbase courses. The modified base damage index and base curvature index defined from HWD pavement deflection basins were used to determine relative base-to-subgrade damage, which clearly showed evidence of the increased base damage induced in the NAPTF airport pavement layers during trafficking partly due to the applied aircraft gear load wander. This was in accordance with both the individual pavement layer recovered and unrecovered (inelastic or residual) deformation trends identified from analyzing the multidepth deflectometer data collected during trafficking and the post-traffic forensic analysis results, which indicated that a majority of the permanent deformation occurred in the unbound aggregate layers and not in the subgrade. The methodology presented for the detailed analyses of the FWD (or HWD) test data between trafficked and nontrafficked lanes can be effectively used in flexible pavements to detect unbound aggregate layer deterioration and the pavement damage potential due to that deterioration.