Assessing the influence of moisture on the dielectric properties of asphalt

The presence of moisture in asphalt can reduce the cohesion between binder and aggregate, and can thus lead to premature deterioration of the pavement structure. This issue is particularly relevant in the UK, as well as other areas around the world, where records suggest climatic trends showing increased total rainfall, and increased frequency of periods of very wet weather. Detection of locations where excessive moisture may be present, or where moisture ingress may be occurring, is important for the maintenance of asphalt pavements. The dielectric properties of asphalt are heavily influenced by the amount of water in the material. Data from ground penetrating radar (GPR) investigation can be used to estimate asphalt dielectric properties, and hence to assess areas of relative moisture content, although it is often difficult to quantify absolute moisture amounts. This paper describes a series of laboratory tests conducted using asphalt core samples taken from road pavements, to establish the relationship between moisture content and the dielectric values determined from GPR data. It has been possible to observe and quantify the asphalt dielectric constant as it changes as a result of changing moisture content. The results of this study can be used to improve estimates of moisture amounts from GPR data obtained from asphalt pavements, and to quantify the effect on dielectric values that increases in moisture content may produce. The findings from the work can assist in producing more confident and accurate outputs from GPR pavement moisture investigations.