Nondestructive Testing to Identify Concrete Bridge Deck Deterioration (2012) / Chapter Skim
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12 The literature review provided a number of NDT technologies that have the potential to detect and characterize deterioration in concrete bridge decks. The following 14 techniques were considered for grading and ranking on the basis of the literature search and possible inclusion in the validation testing program: • Impact echo; • Ultrasonic pulse echo; • Ultrasonic surface waves; • Impulse response; • Ground-penetrating radar; • Microwave moisture technique; • Eddy current; • Half-cell potential; • Galvanostatic pulse measurement; • Electrical resistivity; • Infrared thermography; • Visual inspection; • Chain dragging and hammer sounding; and • Chloride concentration measurement.
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13 Different authors interpret the severity of the delamination in a given deck with the IE method in various ways. One of the ways used in this study is shown in Figure 3.2.
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14 in the audible frequency range, unlike responses from the deck with incipient delamination that may exist only in the higherfrequency ranges (Gucunski et al. 2006; Cheng and Sansalone 1995; Lin and Sansalone 1996)
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15 Possible delaminaon Backwall Backwall Backwall Backwall Figure 3.4. Bridge deck survey using MIRA ultrasonic system.
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16 Limitations Ultrasonic pulse echo surveys require very close spacing between test points to develop images of the tested medium, making it time-consuming. The data quality depends strongly on the coupling of the sensor unit, which may be difficult on rough surfaces.
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17 waves. This is illustrated in Figure 3.6, where the arrival of the surface (Rayleigh)
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18 an indication of the presence of a delamination or other anomaly. A schematic of the USW (SASW)
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19 Even though the concept behind impulse response and impact echo is similar, there are significant differences in bridge deck testing. Impact echo is based on the excitation of particular wave propagation modes above the probable anomalies within the deck or between the top and bottom of the deck, which is typically in a frequency range of about 3 to 40 kHz.
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20 continually reflected back to the receiver from other interfaces until it is diminished. GPR measures specific signal responses caused by variations in the electrical properties of the materials making up the deck.
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21 some other NDE methods or limited destructive sampling (cores, chloride sampling and testing, or other ground truth)
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22 between the two metals can be measured as a voltage with a high-impedance voltmeter (Figure 3.13)
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23 underestimated because of concrete electrical resistance (Elsener et al. 1996; Böhni and Elsener 1991; Klinghoffer et al.
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24 Limitations High electrical resistivity in concrete cover leads to unstable measurements and, therefore, prewetting of the measurement area is essential. To avoid potential shifts due to wetting effects, the first reading should be recorded after a few minutes.
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25 environment (Figure 3.17)
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26 Figure 3.18. Infrared thermography testing.
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27 owners for the detection of delaminations in concrete bridge decks. The objective of dragging a chain along the deck or hitting it with a hammer is to detect regions where the sound changes from a clear ringing sound (sound deck)
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28 Physical Principle Chain dragging and hammer sounding are categorized as an elastic wave test. The operator drags chains on the deck, listening to the sound the chains make.
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