New Infrared and Radar Systems for Detecting Segregation in Hot-Mix Asphalt Construction

The first phase of Texas Department of Transportation (TxDOT) research project 0-4577, "Further Development of NDT Devices to Identify Segregation in HMAC," focused on evaluating non-nuclear density gauges for measuring hot-mix asphalt (HMA) density on paving projects and is documented in Report 0-4577-1. This report documents the second phase of that project. In this phase, researchers refined infrared methods for detecting segregation on paving projects, verified previously recommended limits on surface dielectric variations for different TxDOT paving mixtures, and developed new ground-penetrating radar (GPR) tools to more rapidly investigate the uniformity of a new overlay. To refine infrared methodology, the research team created an infrared sensor bar that gets pushed behind the paver. Data collection and processing software allow personnel to inspect and identify suspected segregated areas in real time. To verify the previously recommended limits on surface dielectric variations, the research team used GPR to inspect completed overlays for segregation on six TxDOT paving projects. Results matched well with the previously recommended guidelines. On projects using coarse-graded mixes, locations with surface dielectrics that are not within = 0.4 of the mean dielectric value should be investigated for segregation. A new software package, RadSeg, allows personnel to more rapidly analyze GPR data for segregation. A newly developed three-channel GPR system allows personnel to collect data over both wheel paths and the centerline in one pass for rapid assessment of the uniformity of a project.