Figure 48. Average GPR cover depth collected from multiple rounds of data collection periods 5.3.3 Electrical Resistivity (ER) ER technology has long been used to assess the corrosive environment inside concrete specimens. The low resistivity of concrete is often a consequence of high moisture and chloride concentration. High electrical resistivity allows only low corrosion current to pass between the anodic and cathodic areas of the reinforcing steel, and thus does not facilitate the corrosive processes. To quantify the overall deck condition with respect to the corrosive environment and anticipated corrosion rate, the following expression has been introduced: ER index 𝐴𝑉𝑒𝑟𝑦 𝐿𝑜𝑤 × 100 + 𝐴𝐿𝑜𝑤 × 75 + 𝐴𝑀𝑜𝑑𝑒𝑟𝑎𝑡𝑒 × 50 + 𝐴𝐻𝑖𝑔ℎ × 25 + 𝐴𝑉𝑒𝑟𝑦 𝐻𝑖𝑔ℎ × 0 = 𝐴𝑇𝑜𝑡𝑎𝑙
(13)
where 𝐴𝑉𝑒𝑟𝑦 𝐻𝑔𝑖ℎ , 𝐴𝐻𝑔𝑖ℎ , 𝐴𝑀𝑜𝑑𝑒𝑟𝑎𝑡𝑒 , 𝐴𝐿𝑜𝑤 and 𝐴𝑉𝑒𝑟𝑦 𝐿𝑜𝑤 = areas with ER in ranges of <5 kΩ.cm, 5-10 kΩ.cm, 10-20 kΩ.cm, 20-30 kΩ.cm; and >30 kΩ.cm, respectively. 𝐴𝑇𝑜𝑡𝑎𝑙 corresponds to the total surveyed area. Figure 49 below plots the variation of condition index for the different rounds of ER data collection efforts from BEAST and compares it against the performance curve of the representative bridge. The condition index variation is somewhere between 0-30% and the trend in the data does not support the expected decrease of condition index versus the increase of deck age. Similar to GPR amplitude, this conclusion was expected given the fact that the level of moisture in the deck was not controlled due to the level of exposed brine solution. Therefore, the ER result might hold some levels of significant variability. Figure 50 subsequently plots the defect index estimation based on the approach previously discussed. As it is clear from this figure, the damage index is increasing by the age of the specimen, indicating that a more corrosive environment is present in the deck as a result of chloride penetration and rebar corrosion.
