Road surface and pavement condition assessment by high frequency GPR diffraction

The condition of roads and pavements near their surfaces is of interest to asset management, in particular of the roads and pavement assets, but also of assets buried under the roads or pavements such as cables or pipes. In many cases the decay of the near surface material results in small air or water filled regions within the tarmac/concrete/stone structure. The decay causes little change in the electromagnetic reflection or delay characteristics of these regions as measured by traditional GPR equipment. Signals launched along the surface are diffracted out of the surface by fractures and discontinuities within the surface. The change between a uniform and a fractured surface is seen to be more readily apparent in the direction normal to the surface, particularly at higher frequencies above about 3 GHz for fractures and for voids of the order of about 2 mm and above. Finite Difference Time Domain simulations and initial microwave frequency measurements indicate significant changes in diffracted signals levels are observed over sufficiently fractured regions.