Condition assessment of reinforced concrete bridge decks as conductive media using GPR

Abstract

Bridge and overpass infrastructure are crucial parts of transportation networks that must be adequately maintained to ensure minimal repair costs and traffic disruption. The majority of the bridges and overpasses in North America are constructed with a concrete deck, with many of these decks acting as the wearing surface. It is well known that these types of steel reinforced concrete structures are susceptible to corrosion damage, especially when in environments rich in chlorides. In order to identify areas at risk of chloride-induced corrosion, this research aims to correlate chloride content in bridge decks with material properties determined using ground penetrating radar. It has generally been accepted that areas of a concrete deck showing high levels of signal attenuation indicate high chloride levels. While low signal loss conditions are often assumed in modeling wave propagation through concrete, this research aims to improve the detection of chloride laden areas using a conductive media approach. By assuming a constant moisture content throughout the structure and measuring the relative attenuation in each scan, the conductivity of the deck is determined. To determine the validity of this method, the conductive model was employed for the evaluation of five bridge decks surveyed in previous research. By accounting for both power fluctuations and geometric spreading, signal attenuation was isolated and conductive properties were determined. Conductive results were then compared to half-cell and chain drag reference tests from each of the five bridge decks investigated. The areas with the highest conductivity levels were strongly correlated with both half-cell and chain drag results, confirming that the conductive model is capable of identifying concrete in need of repair. Finally, determined conductivities were compared to chloride contents measured from cores taken from each deck at the time of testing. Conductivity was shown to increase linearly with chloride content, confirming the ability of ground penetrating radar to detect chlorides. This relationship can be used to map chloride content across a bridge deck and estimate the time to corrosion, greatly increasing the efficiency of bridge deck inspection.