Determination of the compaction of hot mix asphalt using high-frequency electromagnetic methods

Abstract

The main objective of this work is to assess the capability of electromagnetic (EM) methods based on wave propagation to determine the compaction of hot mix asphalt (HMA) specimens. It is to be recalled that rocks are the main component of HMA. We begin by performing a dielectric characterization of rocks with cylindrical resonant cavities. This experiment shows that the rocks, and consequently HMA, may be considered as low-loss materials. We then use the same electromagnetic devices to assess the complex permittivity of cylindrical HMA samples implemented in the laboratory and controlled with standard tests. The level of compaction is estimated according to a complex refractive index (CRI) model that takes into account all HMA components in addition to the measured permittivity. During a final stage, we conduct an experiment on HMA slabs, whose permittivity is measured with a step-frequency radar (SFR) along with an ultra-wideband antenna. These experiments reveal that the electromagnetic approach is capable of assessing compaction to within a few percent of the standard test compaction value and with a similar standard deviation. The main outcome of this work is the possibility it raises of replacing the standard nuclear gauges currently used in the laboratory and in the field by EM-based systems.