Evaluation of In-Place Asphalt Mixture Density Using Pavescan RDM

Dielectric profiling systems developed under the US Federal Highways Administration Strategic Highway Research Program 2 (SHRP2) Solutions program provide a means to estimate the in-place compaction of asphalt concrete by correlation to the relative dielectric constant of the near-surface materials. The Pavescan™ system, a ground penetrating radar-based surface dielectric profiling system produced by Geophysical Survey Systems Inc., was used to continuously scan segments of an asphalt concrete pavement placed during two paving projects in 2019 that were constructed in Nova Scotia. The first project involved a paving trial of a C-HF asphalt mixture placed on 25 mm thick steel plates to simulate an orthotropic steel bridge deck.  Pavescan™ data was recorded over various sections which received different levels of compaction effort to create a wide range of in-place density. Excellent correlation was observed between the surface dielectric measured from the pavement surface reflection and the bulk density of core samples, yielding a coefficient of determination equal to 92.2%. The trial also indicated that the minimum mat thickness that could be tested without interference from the underlying steel plate was approximately 45 mm. The correlation developed for test data obtained on the steel plates did not accurately predict the bulk density of the same asphalt mixture compacted on granular base, indicating an interaction between compaction and the underlying base stiffness. Pavescan™ surveys were also completed on five segments of asphalt mixture placed on a rural roadway. The most accurate predictions of bulk density resulted when using daily calibrations of bulk density from cores and the measured surface dielectric constant with a 94.7% rate of correctly predicting air void contents above and below 7.5%. A comparison of the Pavescan™ results and quality assurance sampling within the same locations of the mat provided consistent measures of quality. However, contour plots of the surface dielectric or interpreted compaction were effective in mapping lower levels of compaction associated with transverse and longitudinal cold joints in the mat.