SC 198 Over Norfolk Southern
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In 1992, the South Carolina Department of Transportation (SCDOT) constructed an overhead bridge and approaches carrying SC Rte. 198 over tracks belonging to Norfolk Southern Railway near Blacksburg, SC. The fill material used to construct the MSE walls in front of the north and south abutments did not appear to meet electrochemical requirements specified by AASHTO. These requirements are intended to limit the potential for corrosion of MSE reinforcements, and provide a basis for estimating metal loss over the service life of the structure. SCDOT retained ERTesting to implement a corrosion-monitoring program to observe in situ corrosion rates and estimate the remaining service life of the structure. ERTesting established a network of four corrosion monitoring stations at the site, took baseline measurements, trained maintenance personnel from SCDOT to obtain measurements of corrosion rate at prescribed intervals, and reviewed data as they were collected. Corrosion rates were monitored at six-month intervals over a twenty-month duration.
Measured rates of corrosion were found to be close to what is normally anticipated for MSE walls, and based on these measurements ERTesting estimated the remaining service life of the structure. The extrapolation presumes that steel corrosion rates will attenuate with respect to time, which is consistent with other observations available in the literature that form the basis for current metal loss models used in design.
