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1Providing the means for the rapid, nondestructive, and accurate condition assessment and per- formance monitoring of bridge decks will significantly reduce the necessary resources and expenditures for bridge renewal. Aside from reducing the duration of traffic interruption during field operation, the more dense measurements yield a more accurate characterization of the condition of the bridge deck, a better prediction of the deterioration progression, and a better assessment of the rehabilitation needs. Such comprehensive and accurate assessments could also reduce the frequency of detailed regular and follow-up inspections. In addition, data collected from the nondestructive testing (NDT) of bridge decks should complement other information in our search to better understand life-cycle costs, deterioration mechanisms, and the effective- ness of preservation techniques at various stages of the aging process. Most important, the infor- mation gained should prevent the premature and unexpected failure of bridge decks. The dominant practice used by state departments of transportation (DOTs) in the evaluation of bridge decks has been visual inspection and simple nondestructive methods such as chain dragging and hammer sounding. Modern NDT for concrete and concrete bridge decks exploits various physical phenomena (e.g., acoustic, seismic, electric, electromagnetic, and thermal) to detect and characterize specific deterioration processes or defects. In general, the objective of all NDT techniques is to learn about the characteristics of a given medium from its response to an applied excitation. The ultimate goal of this research was to identify and describe the effective use of NDT tech- nologies that can detect and characterize deterioration in bridge decks. To achieve this goal, the following four specific objectives needed to be accomplished: 1. Identifying and characterizing NDT technologies for the rapid condition assessment of concrete bridge decks; 2. Validating the strengths and limitations of applicable NDT technologies from the perspectives of accuracy, precision, ease of use, speed, and cost; 3. Recommending test procedures and protocols for the most effective application of the promising technologies; and 4. Synthesizing the information regarding the recommended technologies needed in an electronic repository for practitioners. This report summarizes all the tasks conducted during the project. The first part concentrates on the elements related to the identification and selection of technologies included in the NDT technology validation tasks. This part provides a synthesis of the common concrete bridge deck deterioration types and the NDT technologies used to evaluate them. The methodology devel- oped for the grading and ranking of NDT technologies is also presented. The second part con- centrates on the tasks related to the validation of the promising NDT technologies. These tasks Executive Summary
2are the plan for validation testing, including the selection of the test beds; the conduction of the validation testing; and the analysis of the results of the validation testing. The analyses of the information provided by the participants in the validation testing, and the associated efforts and costs, are also included in the second part. Finally, the third part concentrates on the formulation of the generic features of the NDT technologies for bridges and the development of an electronic repository for practitioners, a web-based tool named NDToolbox. All the research tasks were described in more detail in the project progress reports. One of the early deliverables of the project was a comprehensive literature synthesis report on the deterioration processes in concrete decks and the most important NDT technologies for their detection. The synthesis concentrated on four groups of NDT technologies that use acoustic/ seismic, electromagnetic, electrochemical, and thermal principles of operation. More tradi- tional and commonly used techniques, such as visual inspection, chain dragging, hammer sounding, and chloride concentration measurements, were also described. The principle of operation and types of structural and material defects that can be detected and characterized with each technology were synthesized. The application and performance parametersâ accuracy, precision, ease of use, speed, and costâwere also summarized. Clear information about the advantages and limitations of each technology was provided whenever available in the literature. The conclusion of this search was that a single technology cannot detect or provide information about all the deterioration processes and defects of interest. Also, it was obvious that the technologies significantly differ in terms of the ease of use, cost, level of expertise needed in data collection, analysis and interpretation, speed of data collection, and accuracy of the provided information. All of this provided a clear need and justification for this research study. A methodology for categorizing and ranking the most promising NDT technologies was the first essential part in the development of the recommendations. Such a methodology was structured in a way so that information relating to (1) the value of the technology with respect to the detection of a particular deterioration type and (2) the overall value to an agency in bridge deck deterioration detection can be qualified. Technologies that could detect and char- acterize four deterioration typesâcorrosion, delamination, vertical cracking, and concrete degradationâwere of interest in the grading and later selection for validation testing. The NDT technologies were evaluated from the perspective of five performance measures: accuracy, precision (repeatability), ease of use, speed, and cost. The methodology was first imple- mented to identify the most promising NDT technologies, based on the literature search. The ranking developed served as the basis for the solicitation of participants in the validation testing. The validation testing and the follow-up analysis of the results were the most important and, at the same time, the most challenging parts of the project. The first step in the validation testing was identifying and planning the validation test beds. The validation test beds were identified, and the corresponding validation test plans were developed to enable an objective assessment of the previously defined performance measures. The first validation testing included an evaluation under controlled laboratory conditions. The controlled laboratory validation included a concrete slab with built-in defects and simulated deteriorations. In addition, a section of a deck removed from a highway bridge was used in the laboratory validation. The main foci of the laboratory validation were on the assessment of the accuracy and repeatability of the NDT technologies because broad ground truth information was available from cores and conducted autopsies. Field testing was supposed to enable the testing under actual, production-level conditions; there- fore, the field validation testing concentrated on the evaluation of speed, ease of use, precision, and cost. It was expected that it would be possible to evaluate the accuracy of NDT technologies to a lesser extent because of limited ground truth information. The field validation testing was first conducted in late October and early November of 2010 on a bridge over I-66 in Haymarket, Virginia, in coordination with the FHWAâs Long-Term Bridge Performance (LTBP) Program. The LTBP Program evaluated the same bridge in 2009, which provided a wealth of information from preliminary evaluations, using destructive and non- destructive means, and assisted in identifying the most suitable area for the validation testing.
3The testing area was about 1,000 ft2. A 2-ft by 2-ft grid was marked on the deck, identifying seven survey lines in the longitudinal bridge direction, with 43 test points along each line. The par- ticipants were required to take measurements and report results at all test points. They were also required to repeat the measurement along one of the survey lines. The laboratory validation was conducted at a site near the main campus of the University of Texas at El Paso in early to mid-December 2010. Two test sections were prepared for the validation testing. The first test section was a newly fabricated concrete slab with simulated defects, and the other test section was a section of bridge along I-10 in El Paso demolished earlier in that year. The fabricated slab was 20 ft long, 8 ft wide, and about 8.5 in. thick and was supported by three 1.5-ft-wide prestressed girders. Delaminated areas of different sizes and depths of embedment, vertical cracks of different depths, and a corroded section were artificially created. The distressed highway bridge section consisted of a 9-ft by 14-ft arch-type concrete sec- tion. For the fabricated bridge section, the grid test points were 1 ft apart, while they were 1.5 ft apart for the actual bridge section. Altogether, 10 teams participated in the validation testing, five of them from industry, four from academia, and one from an agency. The ten technologies rep- resented in the validation testing were ground-penetrating radar, impact echo, ultrasonic surface waves, impulse response, half-cell potential, electrical resistivity, galvanostatic pulse, infrared thermography, ultrasonic pulse echo, and chain dragging and hammer sounding. Some of the technologies were represented by multiple participants, each using a different system. The results from the validation testing were analyzed to evaluate the performance of the par- ticipating NDT technologies with respect to the five performance measures: accuracy, precision, ease of use, speed, and cost. Grades used in the evaluation of technologies varied between 1 and 5, where 5 was used for excellent and 1 for poor performance. The accuracy was in most cases obtained from the percent of test points where the technology provided an accurate assessment. The precision, or repeatability, of technologies was examined through the coefficient of variance of the submitted results from triplicate tests during both field and laboratory testing. The chal- lenge in making an objective comparison among technologies and participants was that the repeatability results provided were for different levels of data analysis and interpretation and, in some cases, only graphical presentations of raw data. The speed of NDT technologies was evalu- ated with respect to the data collection and data analysis and interpretation. The data collection speed grades were assigned on the basis of the actual time measurements of the field surveys. The data analysis and interpretation speed were graded on the basis of information provided by the participants regarding time needed. Similarly, the ease of use of technologies was evaluated. The data collection ease-of-use grade was defined on the basis of the observed, or perceived, physical effort and level of expertise needed to accomplish the task. The data analysis and inter- pretation ease-of-use grading, however, relied on the provided information and perceived con- clusions regarding the expertise needed to successfully accomplish the task. Finally, the cost was defined and graded on the basis of the information provided by the participants. The following conclusions were drawn regarding the performance and overall value of the examined NDT technologies for concrete bridge deck deterioration detection: 1. For each of the main deterioration types, there are technologies that have demonstrated a fair- to-good potential for detection. However, there is not a single technology that has shown potential for evaluating all deterioration types. 2. Four technologies were identified as having a fair-to-good potential for delamination detection and characterization. Those are impact echo, chain dragging and hammer sounding, infrared thermography, and ground-penetrating radar. 3. Four technologies were identified as having a fair-to-good potential for corrosion detection or characterization of a 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.
45. Only one technology, ultrasonic surface waves, was validated as having a good potential in concrete deterioration detection and characterization. 6. The top technologies, based on their overall value in detecting and characterizing deterioration in concrete decks, include ground-penetrating radar, impact echo, and ultrasonic surface waves. However, the ultimate decision on which equipment to acquire and which technology to use will primarily depend on (1) the type of deterioration that is of the highest concern to the agency and (2) whether the evaluation is being done for network-level condition monitor- ing or for project-level maintenance or rehabilitation. 7. The overall value and ranking were to some extent influenced by the selected performance measures and by the applied weights and significance factors in the grading process. Finally, an electronic repository of NDT technologies for bridge decks that targets practition- ers was developed as the ultimate goal of SHRP 2 Renewal Project R06A. The electronic repos- itory or NDToolbox is a web-based open-source database system that allows users to easily navigate through the content and find the information they seek. The NDToolbox primarily allows a user to explore different NDT technologies and examine their use in the deterioration detection. The NDT technology information includes a description of the technology, physical principle behind it, applications, performance, limitations, equipment, test procedures and protocols, and sample results. The NDToolbox also provides recommendations regarding the best technologies for a particular deterioration detection application.
