Nondestructive Testing to Identify Concrete Bridge Deck Deterioration (2012)

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29 C h a p t e r 4 In Chapter 3, all promising NDT techniques for bridge deck evaluation were summarized and described in terms of their principles of operation and their applications in the detection and characterization of certain defects. Limitations of the tech- nologies were also described. This chapter describes the catego- rization, grading, and ranking of these promising technologies, according to a number of selected performance measures. Vari- ous steps in this process are illustrated in Figure 4.1. Five performance measures, including accuracy, precision (repeatability), ease of use, speed, and cost were defined for each of the identified techniques and graded for the ultimate ranking of the technology. The ranking was based on a par- ticular deterioration type and the overall value in evaluating and monitoring concrete bridge decks. Each performance measure was assigned a weight factor, on the basis of its importance in assessing deterioration in bridge decks. The overall grade for a technology in detecting a particular deterioration or defect was calculated as the weighted sum of the grades for all performance measures. For techniques that can detect multiple types of deterioration and defects, the grade was determined for each of the deterioration or defect types. The overall value of the technology for concrete bridge deck evaluation was calculated as the weighted average from the grades for different deterioration types. The weight fac- tors for different deterioration types are identified in the pro- cess as significance factors. performance Measures and Deterioration types Selection The evaluation of NDT technologies was carried out for the following four deterioration types: 1. Delamination; 2. Corrosion; 3. Cracking; and 4. Concrete deterioration. The rationale behind limiting the deterioration types into only four categories is the following. Although there are differ- ent causes for deterioration, in most cases the causes cannot be determined by NDT technologies; only their consequences can be determined. For example, corrosion and shrinkage- induced cracking will result in material degradation, which can be detected through reduced velocity, modulus, and so forth. In addition, from the list of all possible deterioration types and mechanisms, the four deterioration categories con- sidered are of the highest concern to transportation agencies. The following are the five performance measures selected for categorizing and ranking the technologies: 1. Accuracy; 2. Precision (repeatability); 3. Ease of data collection, analysis, and interpretation; 4. Speed of data collection and analysis; and 5. Cost of data collection and analysis. The rationale used for concentrating on only five performance measures is the following. Although the description of a par- ticular performance provides a more detailed description of that performance in terms of a large number of measures, for most technologies there is either no information regarding a specific performance measure or the measure is not applicable to that particular technology. In addition, analyses in terms of a smaller number of performance measures are believed to be of higher interest and practical value to transportation agencies and industry. Description and Definition of Main Deterioration types The descriptions of the deterioration categories below are based on the ability of the NDT technologies to detect them and thus do not include the causes of the deterioration. • Delamination. Detection is targeted toward predominantly horizontally oriented cracks, whether those cracks are Criteria and Methodology for Evaluating NDT Methods for Assessment of Bridge Decks

30 factors are compared in the same table to the average weights provided by five DOT bridge engineers. The two groups similarly identify delamination and corrosion of primary significance and vertical cracking and concrete degradation evaluation of secondary significance. elements Constituting performance Measures To rank the five major performance parameters in an accu- rate, repeatable, and practical manner, they were further sub- divided into up to three subcategories, resulting in a total of 12 factors. These 12 factors, which are mapped into the major five performance measures in Table 4.2, can be summarized as follows: 1. Detectability extent; 2. Detectability threshold; 3. Evaluation of severity of deterioration; 4. Repeatability of measurement; 5. Speed of data collection; 6. Speed of data analysis and interpretation; 7. Expertise needed for data collection; 8. Expertise needed for data processing and data inter- pretation; 9. Extent and potential for automation and improvement; 10. Cost of data collection; 11. Cost of data analysis and interpretation; and 12. Cost of equipment, supplies, and equipment maintenance. For each factor, a grade of 1, 3, or 5 was assigned, with 1 being the least favorable and 5 being the most favorable for a given technology. The definitions of these grades for each factor are summarized in Table 4.3. On the basis of the above descriptions, the performance of each selected technology was graded for each of the four dete- rioration types. The final grades obtained for all the selected technologies and for all deterioration types are summarized in Table 4.4. Identification of Most Important Deterioration Types and Corresponding Significance Factors Performance measure Delamination Corrosion Cracking Concrete Deterioration Accuracy Precision Ease of Use Speed Cost Definition of Performance Measures for Different Deterioration Types Performance measure Performance Parameter Weight Factor Definition of Parameter Definition of Grades Accuracy Precision Ease of Use Speed Cost Definition of Performance Parameters Used in Forming Performance Measures and Corresponding Grades Performance Parameters N D T Te ch no lo gi es Description and Grading of NDT Technologies for All Performance Parameters and for Each of the Four Deterioration Types Deteriora- tion Type Accuracy Precision Ease of Use Speed Cost Overall Grade ND T Te ch n o lo gi es Summary Grading of NDT Technologies for All Four Deterioration Types Evaluation of the Overall Value and Ranking of NDT Technologies in Concrete Deck Deterioration Detection Figure 4.1. Flowchart of the categorization and ranking process of NDT technologies. Table 4.1. Significance Factors for Deterioration Types Significance Factor Deterioration Type SHRP 2 Team DOT Bridge Engineers Delamination 0.42 0.39 Corrosion 0.35 0.38 Cracking 0.10 0.12 Concrete degradation 0.13 0.11 a result of rebar corrosion, overloading, or other types of deterioration. • Corrosion. Detection is directed toward two main objectives: detection and evaluation of the intensity of active corrosion, and the severity of existing corrosion. • Cracking. Detection concentrates on the detection and eval- uation of dominantly vertically oriented cracks. • Concrete deterioration. Detection involves measuring the change or variability of material properties, regardless of the cause (e.g., corrosion, ASR, carbonation, DEF). Because various deterioration types have different impacts on the serviceability of the bridge deck, significance factors, presented in Table 4.1, were assigned to each deterioration type. The factors used in the technology ranking represent a consensus of the SHRP 2 Renewal Project R06A team. These

31 Table 4.2. Definitions of Performance Measures for Different Deterioration Types Performance Measure Delamination Corrosion Cracking Concrete Deterioration Accuracy •  Estimation of boundaries  (extent) of the delamina- tion in the horizontal  direction •  Determination of the depth  of the delamination •  Detectability threshold  and assessing the degree  (severity) of delamination •  Detection of active  corrosion •  Determination of the  depth and boundaries of  corroding rebars •  Detectability threshold •  Determination of the  degree (severity) of exist- ing corrosion •  Determination of  the crack depth  and width •  Determination of the lateral  boundaries and thickness  of the deteriorated concrete •  Detectability threshold •  Determination of degree  (severity) of deterioration Precision •  Repeatability of the mea- surement in estimating  boundaries, depth,  detectability threshold,  and severity of  delamination •  Repeatability of the mea- surement in detection  and evaluation of severity  of active corrosion, exist- ing corrosion degree, and  depth of corroded rebars •  Repeatability of the  measurement in  evaluation of crack  depth and width •  Repeatability of the mea- surement in detection,  determination of deterio- rated zone boundaries,  and evaluation of severity  of deterioration Ease of use •  Ease and expertise level needed for data collection •  Ease and expertise level needed for data analysis •  Expertise level needed in interpretation (relating results of analyses to relevant engineering parameters) Speed •  Speed of data collection •  Extent and potential for automation/improvement of data collection •  Speed of data analysis •  Extent and potential for automation/improvement in data analysis Cost •  Cost of the data collection (including traffic control and other) •  Cost of the data analysis and interpretation •  Cost of the equipment (initial), supplies, and maintenance Table 4.3. Definitions of Performance Parameters and Corresponding Grades Major Categories Parameter Weight Factor Definition of Parameter Definition of Grades Very Favorable = 5 Favorable = 3 Not Favorable = 1 Accuracy Detectability extent—A1 0.3 Minimum extent of  deterioration that  should occur before it  can be detected Localized  deterioration can be detected Extensive  deterioration can be detected Indirectly evaluated  with low certainty Detectability threshold—A2 0.3 Stage of deterioration at  which it can be  detected Onset of  deterioration Advanced deterioration Indirectly detected  with low certainty Severity of deterioration—A3 0.4 Ability of the method to  quantify different  degrees of  deterioration Fully/continuously  quantifies Quantifies one or  more degrees Cannot distinguish  different degrees Precision Precision/ repeatability—R1 1.0 Repeatability of data  collection (even under  changed environmental  conditions), data  analysis, interpretation,  and so forth High repeatability  in all aspects High repeatability  only under cer- tain conditions Low repeatability  for any reason (continued on next page)

32 Table 4.3. Definitions of Performance Parameters and Corresponding Grades (continued) Major Categories Parameter Weight Factor Definition of Parameter Definition of Grades Very Favorable = 5 Favorable = 3 Not Favorable = 1 Speed Speed of data collection—S1 0.6 Production rate in terms  of area coverage (test  point number) per hour  for “good” quality data More than 500 ft2/h  or 120 test points More than 100 ft2/h  or 25 test points Less than 100 ft2/h  or 25 test points Speed of data analysis—S2 0.4 Production rate in terms  of area coverage (test  point number) for  preprocessing and  postprocessing  analyses More than 200 ft2/h  or 50 test points More than 50 ft2/h  or 12 test points Less than 50 ft2/h  or 12 test points Ease of use Expertise data collection—E1 0.2 Expertise needed in set- ting up instrumenta- tion, consideration of  environmental and other effects, and sur- vey conduct for high- quality data collection Basic training and little experience  needed Medium expertise  and experience  needed High expertise  and extensive experience  needed Expertise data analysis—E2 0.5 Expertise needed in pre-  and postdata process- ing and delineation and classification of the  deteriorated areas Basic training and little experience  needed Medium expertise  and experience  needed High expertise  and extensive experience  needed Extent and potential for automation—E3 0.3 Further potential for auto- mation in data collec- tion, analysis, and  interpretation in the  future High potential  for both data  collection and data analysis High potential for  either data col- lection or data analysis Little or no poten- tial for auto- mation of either  data collection or data analysis Cost Cost of data collection—C1 0.5 Overall cost is based on  direct data collection cost and need for  traffic control Low cost (<$1/ft2) and no need for  traffic control Low cost (<$1/ft2) and required  traffic control High cost (>$1/ft2) and required  traffic control Cost of data analysis—C2 0.3 Overall cost is based on  the expertise level and  time needed to analyze  and interpret Low cost per unit  area (<$2/ft2) Medium cost per  unit area ($2–4/ft2) High cost per unit  area (>$4/ft2) Cost of equipment—C3 0.2 Overall cost from equip- ment purchase and  maintenance, and  supplies per year of  operation Less than  $5,000/year Less than  $10,000/year More than  $10,000/year Conclusions The most important conclusions derived regarding the per- formance and overall ranking of the selected NDT technolo- gies are provided below. It should be emphasized that these conclusions are only based on the literature search, which served as a guideline in the identification of NDT technolo- gies for the validation testing. • Even though several technologies have shown potential for detecting and evaluating each of the main deterioration types, there is not a single technology that can potentially evaluate all deterioration types. • Six technologies were identified as having a good potential for delamination detection and characterization. Those are impact echo, chain dragging and hammer sounding, ultra- sonic pulse echo, impulse response, infrared thermogra- phy, and ground-penetrating radar. • Three technologies were identified as having a good poten- tial for corrosion detection and characterization. Those are half-cell potential, electrical resistivity, and galvano- static pulse measurement.

33 Table 4.4. Overall Value and Ranking of NDT Technologies Delamination Corrosion Cracking Concrete Deterioration Deterioration Type WF21 5 0.42 WF22 5 0.35 WF23 5 0.10 WF24 5 0.13 Overall Value Ranking Impact echo 4.7 1.0 2.5 3.1 3.0 1 Ultrasonic pulse echo 3.6 1.0 2.6 3.4 2.6 1 Half-cell potential 1.0 4.9 0.0 1.0 2.3 2 Impulse response 3.6 1.0 0.0 2.6 2.2 2 Ultrasonic surface waves 2.5 1.0 3.0 3.4 2.2 2 Ground-penetrating radar 3.0 1.0 1.0 3.1 2.1 2 Chain dragging/hammer sounding 3.7 1.0 0.0 1.0 2.1 2 Electrical resistivity 1.0 3.9 0.0 1.0 1.9 3 Infrared thermography 3.2 1.0 0.0 1.0 1.8 3 Galvanostatic pulse measurement 1.0 3.0 0.0 1.0 1.6 3 Visual inspection 1.0 1.0 3.7 1.0 1.3 3 Microwave moisture technique 0.0 1.0 1.0 1.0 0.6 4 Chloride concentration 0.0 1.0 0.0 1.0 0.5 4 Eddy current 0.0 1.0 1.0 0.0 0.5 4 Note: Shaded areas indicate higher performance of the technology in detection and characterization of a particular deterioration type. • Four technologies were identified as having a good poten- tial for vertical cracking characterization. Those are visual inspection, ultrasonic surface waves, ultrasonic pulse echo, and impact echo. • Five technologies were identified as having a potential in concrete deterioration detection and characterization. Those are ultrasonic surface waves and pulse echo, impact echo, ground-penetrating radar, and impulse response. • The ranking of the technologies was to some extent influ- enced by the selected performance measures, weight fac- tors, and significance factors. The closeness of some of the results necessitates validating the rankings through a series of field and laboratory testing.