Field observations and numerical models of GPR response from vertical pavement cracks

High resolution ground-coupled GPR is useful for determining thickness, deterioration, jointing and cracks in pavements. Although only millimetres in width, vertical cracks can present a significant target in reflection profiles. On composite pavements, consisting of asphalt over concrete, we have observed responses at locations above joints in the underlying concrete that we attribute to cracks within the asphalt layer. On some asphalt pavement, we observed significantly stronger diffraction and waveguide effects responses at a 250 MHz centre frequency rather than at 1000 MHz, despite the small crack apertures. Using numerical modelling we show the importance of crack filling material, crack aperture, crack height, asphalt conductivity and the GPR centre frequency on the observed response. Our observations and models clearly show the potential of GPR to detect and characterise vertical cracks. We recommend a multi-frequency approach to GPR surveys of pavement: high frequency for crack characterisation and lower frequency for crack detection.

► GPR numerical modelling is important in understanding crack responses.
► Effects of crack width, dielectric properties and height were examined numerically.
► Existence of granular layer below the crack is important in enhancing its response.
► Numerical modelling results and results from actual GPR data are similar in character.
► We recommend high frequency for crack characterisation and lower freq. for detection.