Figure 44. Defect index calculated based on IE dominant peak frequency
5.3.2 Ground-Penetrating Radar (GPR) GPR technology has been implemented to assess concrete quality. GPR can provide a qualitative assessment of concrete condition and describe potential concrete deterioration, delamination, and corrosive environment [63]. The GPR assessment is based on the measurement of attenuation of electromagnetic waves as they propagate through concrete layers. The condition index from the GPR surveys is calculated according to: GPR index =
𝐴𝐺𝑜𝑜𝑑 ×100+𝐴𝐹𝑎𝑖𝑟 ×70+𝐴𝑃𝑜𝑜𝑟 ×40+𝐴𝑆𝑒𝑟𝑖𝑜𝑢𝑠 ×0 𝐴𝑇𝑜𝑡𝑎𝑙
(12)
where 𝐴𝐺𝑜𝑜𝑑 , 𝐴𝐹𝑎𝑖𝑟 , 𝐴𝑃𝑜𝑜𝑟 , and 𝐴𝑆𝑒𝑟𝑖𝑜𝑢𝑠 = areas with GPR signal attenuation (normalized dB) ranges of > -15, -15 to -17, -17 to -20, and <-20, respectively [64]. 𝐴𝑇𝑜𝑡𝑎𝑙 corresponds to the total surveyed area. Figure 45 below plots the variation of condition index for the different rounds of GPR data collection efforts from BEAST and compares it against the performance curve of the representative bridge. While the condition index decreases by the age of the bridge, it should be noted the variation is not significant and only changes between 99% and 100%. In addition, Figure 46 plots the estimation of defect index that was thoroughly discussed in the previous section. The range of defect index variation is somewhere between 16-21% and the trend in the data does not support the increase of defect index versus the increase of deck age. This conclusion was expected given that the level of moisture in the deck was not controlled due to the level of exposed brine solution. Therefore, the GPR results might hold some level of significant variability.
