Optimisation of ground penetrating radar testing at traffic speed for structural monitoring of pavements

Resumo

Transport infrastructures have a high socio-economic impact on every country. For the last years, the investment priory made for new construction has been refocused for maintenance and support activities, which have high demands in terms of time, money and personnel. Therefore, optimized pavement management strategies, with reliable and accurate up to date real pavement information, are fundamental to enhance maintenance interventions, to reduce costs and to improve safety. Ground Penetrating Radar (GPR) is a non-destructive technique (NDT) that operates at traffic speed and can be used to obtain continuous data concerning pavement structure. However, GPR is a method that is used only in a few countries, and mainly for research proposes. This happens due to the complexity in the analysis of the results, associated with difficulties in data collection and signal processing. This thesis identifies the advantages and current limitations of GPR application for pavement monitoring and promotes its use at different stages of the pavement lifecycle and in combination with other NDT methods. The main goals are to increase the confidence level of the data obtained and to promote a more efficient data processing. The research starts with a state of the art regarding the application of GPR for road inspection, not only for thickness measurement but also for the detection of cracks, voids, delamination and moisture, pathologies typically associated with the loss of pavement bearing capacity. The following works combine GPR with other NDT techniques first to analyse the condition of the pavement subgrade during the construction and then to evaluate the bearing capacity of a rehabilitated pavement. The first study analyses different antenna setups together with two load NDT techniques to detect anomalous areas that can lead to future failure of the pavement, at the subgrade level. Results from a real scale model show that integration of GPR with load tests helps improve the interpretation. Another study, following the same line of research, presents a combination of GPR with Falling Weight Deflectometer for pavement structural evaluation of a rehabilitated flexible highway. This work focuses on the sensitivity of the estimated elastic moduli to layers thicknesses. It highlights the need for accurate continuous data on layer thickness as input for bearing capacity evaluation and to better support maintenance interventions. Lastly, this thesis proposes a new approach for a coreless GPR calibration method, aiming to provide accurate data on layer thickness measurement. This method applies the Common Mid-Point approach to air-coupled antennas measurements. It focuses on asphalt layer thickness assessment, as it is the most relevant for the structural evaluation of flexible pavements. Results from the GPR tests performed on three real scale physical models, with different flexible pavement structures, show the improvement of this new methodology, in comparison to existing calibration methods, especially for thinner asphalt layers. As a follow-up, the proposed methodology was implemented for an in situ pavement evaluation, as a case study. The main challenges of the implementation of the proposed methodology, conclusions, and future research lines are also presented herein.