During the last few decades, many efforts have been made to assess the reliability of nondestructive evaluation (NDE) technologies used for the detection of subsurface damage in concrete bridge decks. During these efforts, reliability of NDE technologies has either been described anecdotally, or been solely relegated to the probability of detection (POD) or accuracy estimation. Although these indices are important, most of the previous work did not take into account the probability of false alarm (POFA) of NDE technologies, nor did they investigate the reliability considering multiple threshold settings throughout test results. In addition, the existing body of research has used a limited physical sampling such as coring to validate NDE results. Consequently, the assessments were rather controversial, and there was no general agreement about the reliability of such technologies. Because most diagnosis systems are characterized by noisy data and less than perfect detection characteristics, reliability is to be carefully assessed considering all possible diagnosis output with multiple threshold settings within practical range of applications. In other words, when NDE data do not fall into either of the two obviously defined categories: true positive (TP), meaning the NDE data indicates a defect and there is a defect, or true negative (TN), meaning the NDT data indicates no defect and there is no defect, reliability analysis should also include the two types of incorrect indications: failure to give a positive indication in the presence of a defect (false negative, FN) and giving a positive indication when there is no defect (a false alarm or false positive, FP). The \three decades of NDI reliability assessments" report developed by Karta Technologies, Inc. in 2000 under supervision of the Air Force NDI Office stated that POD alone cannot describe the reliability of NDE technologies unless the probability of false alarm (POFA) is also considered in the analysis. POFA may be induced by noise with several possible sources: human, nature of phenomenon to be measured, and environmental conditions. The report covered nearly 150 reports and manuscripts from over 100 authors. However, a review of research literature reveals that little theoretical work on the reliability assessment in terms of both POD and POFA has been undertaken since then. In this research, the reliability of impact echo (IE), infrared thermography (IRT), and ground penetration radar (GPR) technologies for the detecting of subsurface damage in concrete plate-like members is assessed by using a statistical analysis method called receiver operating characteristic (ROC). The proposed analysis method has the capability to integrate POD and POFA indices over a wide range of decision threshold settings in a single curve, which is useful in assessing trade-off in choosing a threshold and for quantitatively comparing the performance of NDE technologies. This methodology for assessing NDE reliability is intended to provide a more effective means of comparing different technologies used in civil engineering applications, to make the evaluation process of a quantitative scheme, to reduce subjectivity and variability in interpreting NDE data, and to improve sensitivity to extract more information from NDE data. Area under ROC curve (AUC), which is interpreted as the probability of correctly classifying an arbitrarily pair of negative and positive test points, can provide for the desired quantitative reliability index, which can be used to compare the performance of one NDE technology to another. Results of this research obtained from ROC analysis indicate a great ability of IE and IR in detecting subsurface fracture damage such as delamination and debonding. In both technologies, there exist some threshold settings that can provide for a relatively high POD with very low POFA, and consequently, the areas under their ROC curves were very high. Data obtained from GPR testing, on the other hand, indicates that GPR technology has a very limited ability to detect physical damage such as subsurface delamination. This conclusion contrasts with that been argued by a large body of the previous work. However, GPR showed a good sensitivity to the presence of corrosive environments such as moisture and chloride when the concentrations of these factors are above some threshold values that may facilitate the initiation of steel reinforcement corrosion.

The state of Wyoming alone has 13.1 million square feet of bridge deck, and evaluation of those decks has become an important part of the Wyoming Department of Transportation's (WYDOT) management of bridge repairs. The authors believe that development and advancement of nondestructive evaluation methods over the past 25 years may provide a more efficient, standardized, and accurate method for evaluating bridge deck conditions compared with current practices. A study was performed on three bridge decks in Wyoming: the First Street Bridge in Casper, the Douglas I-25 Bridge, and the Remount I-80 Bridge. For each bridge, an investigation was done using standard WYDOT practices for chain dragging. In addition, the bridges were evaluated using impact echo, thermal imaging, and ground-penetrating radar (GPR) techniques. All three methods considered were successful, and the damage locations between the impact echo, thermal imaging, and GPR generally correlated well. Based on this study, a complete bridge deck evaluation should combine impact echo with GPR testing to provide the most accurate predictions of delamination and debonding in support of optimal maintenance decisions.

An objective view of the relative advantages and limitations of the nondestructive testing and evaluation methods that are currently used in the inspection of bridge decks is presented and discussed. The three main nondestructive testing technologies that were evaluated are impact-echo, ground penetrating radar, and infrared thermography. Nondestructive testing and evaluation procedures, including methodology and equipment to evaluate concrete bridge decks with asphalt overlays, are also presented and discussed. Current results indicate that a combination of ground penetrating radar and infrared thermography would provide the best methodology for evaluating the structural integrity, e.g., delaminations, of concrete bridge decks with overlays. Furthermore, current results also indicate that the impact-echo method shows promising future development towards the nondestructive evaluation of bridge superstructures.