Guidelines for Evaluation of Existing Pavements for HMA Overlay (0-5123-2)

This report discusses the application of nondestructive test (NDT) tools for evaluating existing pavements for hot-mix asphalt (HMA) overlays.The NDT tools covered in this report include ground penetrating radar (GPR), falling weight deflectometer (F WD), and rolling dynamic deflectometer (R DD). The GPR is used to estimate the thickness of existing pavement layers, and identify section breaks and potential trapped moisture problems. The FWD is used to evaluate the structural capacity of the existing pavement, and the in-situ layer modulus can be backcalculated from FWD data. In addition, for existing concrete pavements, the FWD can be used to determine load transfer efficiency (LTE) at joints and/or cracks. The application of the RDD to evaluate existing concrete pavements is also discussed. The major advantage the RDD has over other discrete NDT devices (e.g.,F WD) is that it provides continuous deflection profiles of the pavement, which can be used to identify joints with poor LTE. However, no software is available to automatically interpret the RDD data. After reviewing RDD data collected on several different concrete pavements, the researchers developed some basic interpretation criteria for the RDD data. Based on the measured RDD deflection data and the monitored field reflective cracking performance on IH20, threshold values for RDD Sensor 1 deflection and the differential deflection between Sensors 1 and 3 are recornmended. If either the Sensor I deflection or the differential deflection between Sensors I and 3 is larger than the proposed thresholds, the corresponding joint and/or cracks is recommended for pretreatment before placing a new HMA overlay. Finally, general guidelines for evaluating existing pavements for HMA overlays are proposed in this report.