A comparison of modified free-space (MFS), GPR, and TDR techniques for permittivity characterisation of unbound granular pavement materials
This paper reports on a laboratory experiment comparing permittivity measurements using a modified free-space approach to results using common-offset ground-penetrating radar and time-domain reflectometry on moist and compacted samples of unbound granular road pavement materials. In the first part of the experiment, unbound granular samples from the same source were prepared to varying moisture contents and a fixed target density. Separate samples were prepared for modified free-space and time-domain reflectometry testing, all of which were also measured using ground-penetrating radar. In the second part of the experiment, samples were mixed to a consistent gravimetric moisture content and varying densities before undertaking the modified free-space, time-domain reflectometry, and ground-penetrating radar measurements. Reasonably good agreement was found between modified free-space and ground-penetrating radar measurements, which also compared well with literature relations for crushed rock pavement materials. The time-domain reflectometry results were relatively consistent with those literature relations, although they appeared to deviate from the ground-penetrating radar and trend of modified free-space results for lower density and drier samples.