## 5 Applicability of NDT Methods to ABC Closure Joints
### Quantitative Comparison among the Most Promising NDT Methods  
To substantiate the basic conclusions of the above analyses with quantitative measures, a statistical survey of the applicability of NDT methods to specific types of defects/damage was performed. A total of 50 literature sources were reviewed and evaluated for this purpose. The defects considered for this evaluation as described above were delamination, cracks (includes debonding), voids, and corrosion of the embedded steel. The criteria or measure considered for this evaluation was the number of citations of a specific method deemed applicable to a specific defect. In other words, to derive a quantitative measure for comparison among various NDT methods and their applicability to each defect type, results of the literature search were analyzed to find the number of sources that identified a method as being applicable to a defect type. Information for each defect type is summarized in Table 3. In this table, the first column lists the four groups of expected defects for closure joints. The second column of this table lists the NDT methods recognized as being promising for closure joints. Subsequently, the sources/references that have identified each NDT method for applicability to a certain type of defect are listed in the third column in a row corresponding to the NDT method and the row corresponding to the type of defect. N and M in the fourth and fifth columns of the table refer to the total number of sources (for each NDT method applicable to the type of defect) and the percentage of the number of sources in comparison with the total sources cited, respectively. The results are also illustrated in Figures 6-9 for clarity. The charts clearly show the NDT method(s) that is (are) most appropriate for each damage type in closure joints, as denoted by the higher percentage(s). Each chart shows the results for one of the four common types or groups of damage or defects. \begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Type of** & & **References** & **N** & **M** \\
**Defect** & IE & [20, 26, 27, 29, 30, 40, 41, 43–45, 48, 53, 55, 56, 61, 62, 68] & 17 & 34\% \\  & GPR & [19, 20, 22–27, 29, 31–35, 38, 40, 43, 45, 46, 48, 50–53, 55–57, 59–6] & 35 & 70\% \\  & UT & [20, 40, 48, 55, 58, 61, 64, 68] & 8 & 16\% \\  & IR & [22, 26–30, 33, 41, 42, 48, 51, 53, 54, 59–61, 63, 65, 67] & 19 & 38\% \\  & IRT & [21, 40, 48, 51] & 4 & 8\% \\  & RT & [32] & 1 & 2\% \\  & MFL & — & 0 & 0\% \\ \hline  & IE & [26, 56] & 2 & 4\% \\  & GPR & [19, 20, 24, 26, 27, 31, 34, 37, 38, 44, 45, 48, 55, 62] & 14 & 28\% \\  & UT & [47, 56] & 2 & 4\% \\  & IR & [27] & 1 & 2\% \\  & IRT & — & 0 & 0\% \\  & RT & — & 0 & 0\% \\  & MFL & [28] & 1 & 2\% \\ \hline  & IE & [27, 29, 47, 48, 55, 61] & 6 & 12\% \\  & GPR & [19, 34, 35, 52, 55] & 5 & 10\% \\  & UT & [20, 23, 26, 28, 32, 36, 39, 40, 48, 53, 55, 58, 60, 61, 64] & 15 & 30\% \\  & IR & [20, 28, 29, 47, 48, 61, 65, 67] & 8 & 16\% \\  & IRT & [47, 48, 51] & 3 & 6\% \\  & RT & [26, 47] & 2 & 4\% \\  & MFL & [49] & 1 & 2\% \\ \hline  & IE & [27, 29, 47, 48, 53, 61, 62] & 9 & 18\% \\  & GPR & [19, 20, 23, 26, 28, 29, 32, 36, 46, 48, 50, 53, 60, 65] & 14 & 28\% \\  & UT & [20, 23, 26, 39, 40, 53, 61] & 7 & 14\% \\  & IR & [20, 26, 29, 42, 47, 48, 51, 60] & 8 & 16\% \\  & IRT & [21, 47, 48, 51] & 4 & 8\% \\  & RT & [26, 32, 47, 53] & 4 & 8\% \\  & MFL & — & 0 & 0\% \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Statistical survey of applicability of NDT methods to defects in ABC closure joints [19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 40, 41, 43–45, 48, 53, 55, 56, 61, 62, 68]. Figure 6: Statistical representation of NDT methods most applicable to detect delamination. The charts in Figures 6-9 can be used as a selection guide and allow bridge owners/operators to select the most-applicable NDT method for detecting each type of specific damage/defects.