Early Detection of Near-Surface Void Defects in Concrete Pavement Using Drone-based Thermography and GPR Methods

Near-surface (i.e., less than 4 in deep) voids that are 1/2” or larger in diameter (in both horizontal and vertical directions) is a common consolidation issue during the construction of concrete pavements. This issue was observed by Nebraska Department of Transportation (NDOT) in concrete pavements constructed by different contractors, on different roads (highways and local roads), and with different thicknesses (9-14 in). These voids can be caused by improper vibration, overly dry mix, and/or long wait time between concrete batches (Legg 1974). These large voids or concentrations of smaller voids can be detrimental to the durability and/or strength of the pavements (Freeman and Zollinger 2008). Being able to detect these voids at an early stage will enable NDOT to direct timely correction orders during the construction process. As a result, costlier repair and maintenance actions can be avoided. Non-destructive testing (NDT) methods, including ground penetrating radar (GPR) and Thermography have been used in detecting concrete defects for a long time, including the detection of pavement delamination, deterioration, spalling and pumping issues (Sebest and Scullion 2005; Morcous and Sekpe 2010) with varying levels of success. However, very few reports were found on using these two NDT approaches to detect defects during the hydration time due to many constraints and challenges, including weak compression strength during the early hydration process for heavy inspection vehicles or equipment. The primary project goal is to develop a reliable and efficient early detection tool for near-surface voids and to enhance NDOT’s capacity of quality control during concrete pavement construction. More specifically, early detection means during the curing stage, 2 to 72 hours after the concrete pavement is casted in place. This will give NDOT field personnel sufficient time to request corrections before the contractors complete the job.