Comparing traffic speed deflectometer and noise-modulated ground penetrating radar data for rapid road pavement investigations

The measurement of deflection under load is fundamental to the assessment of road pavement strength. Many authors have described the benefits of using GPR data to enhance assessment of deflection measurements made by devices such as the Falling Weight Deflectometer (FWD). However while GPR investigations can be undertaken quickly, FWD and other existing deflection methods are much slower which in turn limits productivity. This paper describes a 2010 field trial comparing data from two highway speed road measurement devices: the Danish made Traffic Speed Deflectometer (TSD) and the Australian made 3-D noise modulated ground penetrating radar (NM-GPR) system used in the `Roadscout' vehicle. Around 350 lane-kilometers of data from these devices were compared, showing a clear correlation. The methods were found to be particularly useful when used in combination - the TSD indicating where the pavement was weak, strong or variable and the GPR providing additional information to indicate why. In many cases changes in the data from both methods coincided, providing a direct indication of the cause of the change. In other instances either the TSD or GPR varied and the other method did not, indicating a different type of cause. It quickly became clear that the methods were complementary, providing two independent measurements of pavement response on which to assess current conditions. Overall the correlation between the NM-GPR and TSD data from this trial indicates great promise for using these methods in combination in the future. These methods provide key data needed to achieve rapid, large scale road pavement investigations, collected without public disruption at highway speeds.