Bridge deck survey with high resolution Ground Penetrating Radar

Ground Penetrating Radar applications for structure surveying started to grow in the 1980s; amongst these, initial civil engineering applications included condition assessment of highway pavements and their foundations, with applications to structural concrete focusing on inspection of bridge decks. There are many factors that can cause or contribute to the damage of the top layer of concrete in bridge decks including the corrosion of steel rebar, freeze and thaw cycles, traffic loading, initial damage resulting from poor design and/or construction, and inadequate maintenance. When applied to the analysis of bridge decks, GPR can be successfully used for detecting internal corrosion of steel reinforcement within the concrete deck, which can be an indicator of poor quality overlay bonding or delamination at the rebar level. Therefore, this equipment has the ability to gain information about the condition of bridge decks in a more rapid and less costly fashion than coring and will perhaps yield a more reliable assessment than current geotechnical procedures. However, this application requires suitably designed equipment; for instance, optimization of antenna orientation to take advantage of signal polarization is an important feature for successfully locating reinforcing bars in a time-depth slice. Novel equipment has recently been developed to enable the nondestructive analysis of bridge decks; the IDS RIS Hi-Bright runs two arrays of high frequency sensors featuring a rapid, but very dense data collection, thus dramatically increasing the resolution of the GPR survey. Antenna dipoles in these arrays are deployed to collect two data sets with orthogonal antenna orientations, one with the electric field parallel to the scanning direction (VV), the other perpendicular to it (HH); in this way, the equipment is capable of collecting 16 profiles, 10 cm spaced in a single swath, thus collecting an incredible amount of information. Dedicated data analysis software provides- a 2-D tomography of the underground layers and a 3-D view of the surveyed volume. Main output include the determination of pavement and concrete thickness, the detection of moist areas as well as concrete damage and the location of rebars and ducts within the concrete slab.