Assessment of air void content of asphalt using dielectric constant measurements by GPR and with microwave radar

In this report, we have presented microwave radar and GPR measurements as well as laboratory tests conducted in 2014-2016. The microwave radar was tested in three different construction sites. In addition, GPR measurements were obtained for comparison. Laboratory tests included traditional density measurements and 7-17 GHz VNA scanning of drill cores obtained from the test sites. A new laboratory measurement method using cavity resonator principle was introduced with promising results. Testing of this new method will be continued. The results indicate no clear correlation between air void content and GRP permittivity measurements. Permittivity is sensitive to the changes in the relative permittivity of aggregates and volume portions of aggregates and bitumen. The relative permittivity of the aggregates determines the base level for permittivity measured with radar or VNA. In the course of this research, it has become apparent that a new calibration procedure for the GPR measurements is needed. The aim in further research is to extract core samples from pavement areas with different densities to obtain a local calibration model