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82 C h a p t e r 9 The primary objective of this research was to identify NDT technologies that can effectively detect and characterize dete- rioration in bridge decks. The research activity had the fol- lowing five specific objectives: ⢠To identify and characterize NDT technologies for the rapid condition assessment of concrete bridge decks; ⢠To validate the strengths and limitations of applicable NDT technologies from the perspectives of accuracy, pre- cision, ease of use, speed, and cost; ⢠To recommend test procedures and protocols for the most effective application of the promising technologies; and ⢠To synthesize the information regarding the recom- mended technologies needed in an electronic repository for practitioners. The first phase of the project consisted of a thorough litera- ture search to identify deterioration processes of concrete decks and existing and emerging NDT technologies for detect- ing deck defects. From a number of deterioration types, the following four types were given the highest priority for con- crete bridge decks because of their importance to the trans- portation agencies: delamination, corrosion, vertical cracking, and concrete degradation. Of those four types, higher priority was given to the detection of delamination and corrosion. On the basis of their capability to detect a certain type of defect, the technologies were categorized as follows: ⢠Delamination: impact echo, chain dragging and hammer sounding, ultrasonic pulse echo, infrared thermography, and ground-penetrating radar. ⢠Corrosion: half-cell potential, electrical resistivity, and gal- vanostatic pulse measurement. ⢠Vertical crack: visual inspection, ultrasonic surface waves, ultrasonic pulse echo, and impact echo. ⢠Concrete degradation: ultrasonic surface waves and pulse echo, impact echo, and ground-penetrating radar. Ten teams from research institutions and industry elite in the field of nondestructive evaluation of bridge decks partici- pated in the validation phase of the project to assess the per- formance of each of the above-mentioned techniques. The following five performance measures were used in the evalu- ation of technologies: accuracy, precision, speed, ease of use, and cost. Accuracy and precision were given the highest importance, followed by speed, ease of use, and cost. The vali- dation testing had two main components: field and labora- tory validations. The field validation enabled testing under actual, production-level conditions. The main focus of the research team during field testing was on the evaluation of speed, ease of use, repeatability, and cost. The laboratory vali- dation was conducted on samples with artificially introduced deterioration and defects at known locations providing broad ground truth information. Therefore, the laboratory validation concentrated on the evaluation of accuracy and repeatability of the NDT technologies. The field and laboratory testing results confirmed the litera- ture findings that there is no particular technology that is capa- ble of detecting all four major deterioration types. Although a number of technologies can provide detailed and accurate information about a certain type of defect, complementary use of multiple technologies is required. Until new breakthrough technologies are available for production-level testing, a selec- tion of technologies must be used for bridge deck condition evaluation. The selection of technologies must be primarily based on the accuracy of information they provide regarding the most important deterioration types. Those technologies should also meet or exceed certain criteria regarding the speed, ease of use, and cost. These performance measures were exam- ined in this research study. The following conclusions were drawn from this research study: 1. For each of the main deterioration types, there are tech- nologies that have demonstrated fair-to-good abilities of Summary, Conclusions, and Recommendations
83 detection. However, there is not a single technology that has shown capability in evaluating all deterioration types. 2. Four technologies were identified that can detect and char- acterize delamination with a fair-to-good level of confi- dence. Those are impact echo, chain dragging and hammer sounding, infrared thermography, and ground-penetrating radar. 3. Four technologies were identified as having fair-to-good capabilities for corrosion detection or characterization of corrosive environment. Those include half-cell potential, electrical resistivity, galvanostatic pulse measurement, and ground-penetrating radar. 4. Only one technology, surface wave testing, was validated as a fair technology in the vertical crack characterization. 5. Three technologies were identified as having capabilities in concrete deterioration detection and characterization. Those are ultrasonic surface waves, impact echo, and ground-penetrating radar. 6. The top technologies based on the overall value in detec- tion and characterization of deterioration in concrete decks are impact echo, half-cell potential, ultrasonic sur- face waves, ground-penetrating radar, chain dragging and hammer sounding, electrical resistivity, infrared thermog- raphy, and galvanostatic pulse measurement. 7. The overall value and ranking were to some extent influ- enced by the selected performance measures and the applied weights and significance factors in the grading process. One of the encouraging outcomes from the validation test- ing is that a number of NDT technologies can generate data at a production rate that is comparable to the current practice of chain dragging and hammer sounding. The speed of operation is certainly going to improve as new technologies are being developed. In addition, the cost of evaluation using some of the NDT technologies is gradually approaching that of chain drag- ging and hammer sounding. Considering the benefits of more accurate assessments and reduced traffic interruptions, trans- portation agencies should be moving toward implementing modern NDT technologies. Both the documented benefits and limitations of the NDT technologies justify the strong need for investing in their con- tinued development. Some of the promising technologies include seismic and ultrasonic tests, such as impact echo and surface waves, and ground-penetrating radar. Their potential especially increases as the technologies are being used in an air-coupled mode, thus increasing their speed and reducing the cost. Transportation agencies that would like to build their own capability should select tools on the basis of the deterioration type of the highest concern and constraints related to lane clo- sures, available funds, and so forth. If delamination is of great- est concern and is guiding agency decisions, impact echo with a higher degree of automation should be the NDE technology of choice. If corrosion is the deterioration type of greatest con- cern, either electrical resistivity or half-cell potential measure- ments are recommended because of their simplicity, low cost, and relative speed. The advantage of the electrical resistivity measurement is that it does not require an electrical connec- tion to the rebar mesh. However, half-cell potential provides information on corrosion activity that might be of greater interest to the agencies. With respect to the assessment of the quality of concrete, the ultrasonic surface wave technology provides the best results. Finally, if the objective of the agency is to obtain the overall condition assessment on the network level, GPR is the recommended tool because of its speed and ability to identify delaminations and describe the corrosive environment. Ideally, the agencies should have access to four out of the five mentioned technologies.
