Rapid and Non-intrusive Measurements of Moisture in Road Constructions using Passive Microwave Radiometry and GPR - Full Scale Test

High groundwater tables and moisture in road materials strongly reduce the service life of pavements. Two types of non-intrusive instruments have been tested for their potential to detect moisture in road constructions: a passive microwave radiometer (MIRA scanner), and a 900 MHz Ground-Penetrating Radar (GPR). Measurements were made at the surface of a 2.5 m x 2.5 m x 1.5 m full scale model of an asphalt pavement on a granular road base and a sand subgrade. The model allowed the controlled raising and lowering of the groundwater table. The moisture conditions in the subgrade and road base were monitored in observation wells and using Time Domain Reflectometry sensors for the validation of the non-intrusive measurements. This paper describes the non-intrusive instruments and the test setup. The response of the instruments to raising the groundwater table in the full scale model is analysed. It is shown that the MIRA scanner is capable of detecting variations in moisture in the upper 0.40 m of the road construction, while the GPR clearly detects the groundwater table at greater depths. An analytical model is presented that is well capable of predicting moisture conditions during the test. Finally, the paper discusses the potential of both non-intrusive instruments in practice.