Comparison of Ground Penetrating Radar Deck Surveys to Conventional Level 2 Deck Testing Results

A 1500 MHz Ground Penetrating Radar (GPR) survey was conducted on the Beaver River Bridge, located near Dapp AB. The bridge deck had previously been identified as being partially testable with regards to Alberta Transportation Level 2 Copper Sulphate Electrode (CSE) half-cell potential testing due to problems with the western pre-cast prestressed RD box girder span. The deck also included an overhead through-truss (TH) span with a concrete deck that was constructed using galvanized reinforcing steel. After adjustment to account for higher chloride concentrations required for corrosion initiation of galvanized steel versus uncoated steel, areas of elevated GPR signal attenuation were thresholded correlated closely with areas of CSE values more negative than -400 mV in the TH span. Areas of elevated GPR signal attenuation levels, assumed to be caused by increased chloride content in the concrete cover layer, correlated closely with CSE values more negative than -400 mV on the TH deck span, and with areas where cracking and corrosion staining were observed in all spans. The GPR results were effective in describing areas of longitudinal cracking in the RD spans along the grout keys which appeared to be impacted by high levels of chloride ingress. The GPR also indicated low but elevated levels of chloride ingress along multiple transverse cracks observed in all of the TH span panels. Level 2 CSE testing was not able to identify either of these issues. Both the CSE and GPR results indicated that the majority of the deck appeared to have a low risk of corrosion in most areas that were not cracked. After adjustment to account for higher chloride concentrations required for corrosion initiation of galvanized steel versus uncoated steel, the GPR results indicated that conditions for corrosion were unlikely at two locations where reinforcement had been previously exposed for inspection due to CSE values that were indicative of corrosion activity. GPR survey results can provide transportation agencies with a rapid and accurate means to quickly gather important parameters related to monitoring the condition and service life prediction of their reinforced concrete deck infrastructure or for quality assurance purposes for new construction or rehabilitation.