In-Place Determination of Stiffness of Subsurface Reclaimed Layers in Thin Surface Hot-Mix Asphalt Pavements

Abstract

Seismic testing and analysis using a nondestructive method was developed to determine the moduli of reclaimed layers in thin surface hot-mix asphalt pavements. This method is particularly useful when accurate backcalculation of moduli is difficult because of the existence of unknown layers and when the extraction of intact cores for laboratory testing is impossible. Sixteen Maine Department of Transportation projects with foamed asphalt and plant-mixed recycled asphalt pavement reclaimed layers were tested according to this method using a portable seismic property analyzer. Layer thickness uniformity was checked with a ground-penetrating radar, and falling weight deflectometer was used at multiple load levels to acquire deflection data. Seismic test data were analyzed to estimate layer moduli. The collected data were found to have very low variability. The deflections calculated with the predicted moduli and actual deflections were found to compare well, and the use of predicted moduli as seed moduli resulted in backcalculations with relatively low root-mean-square errors. The moduli were corrected for temperature, and design moduli were recommended. This newly developed method can be used effectively to determine the moduli of subsurface layers, and its use is important for collecting a large amount of data, specifically because of the highly variable nature of the reclaimed layers. A logical next step will be to develop artificial neural networks to automate the process of data reduction from seismic testing. This would allow departments of transportation and industry to fully use the benefits of this fast, nondestructive testing method.