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Condition Assessment of Bridge Deck Using Various Nondestructive Evaluation (NDE) Technologies

On October 6 and 7, 2014, the LTBP Program team performed a third round of inspections of the bridge selected for pilot testing of the LTBP Protocols in Virginia “Virginia Pilot Bridge”. The Virginia Pilot Bridge carries U.S. Route 15 over Interstate 66 in Haymarket, Virginia (figure 1). Nondestructive evaluation (NDE) technologies were used to perform a detailed condition assessment of the deck with respect to corrosion, delamination, and concrete quality. This was the third assessment of this bridge deck over the last 5 years; previous assessments were performed in September 2009 and August 2011.

Figure 1. Photo. Virginia Pilot Bridge, carrying U.S. Route 15 over I-66 in Haymarket, Virginia.
Figure 1. Photo. Virginia Pilot Bridge, carrying U.S. Route 15 over I-66 in Haymarket, Virginia.

This two-span bridge was constructed in 1979 with a reinforced concrete deck on continuous steel girders. The bridge has a small skew and is about 275 feet (ft) long. The bridge deck has two 12-ft lanes, a 10-ft-wide right shoulder, and a 4-ft-wide left shoulder, making the total deck area approximately 11,000 ft2. After 35 years of service, this assessment was a unique, final opportunity to evaluate the deck condition prior to demolition. The entire bridge is scheduled for replacement in 2015. Figure 2 clearly shows a bridge deck that has gone through numerous repairs.

Figure 2. Photo. Data collection on the deck of the Virginia Pilot Bridge.
Figure 2. Photo. Data collection on the deck of the Virginia Pilot Bridge.

The following suite of five NDE technologies, identified by the LTBP Program as appropriate technologies to achieve those goals, was deployed:

  • Half-cell potential (HCP) to assess corrosion activity.
  • Electrical resistivity (ER) to assess corrosion activity.
  • Impact echo (IE) to detect and characterize delamination.
  • Ultrasonic surface waves (USW) to assess concrete quality by measuring concrete modulus.
  • Ground penetrating radar (GPR) to provide a qualitative assessment of the deck condition, detect and locate corrosion induced damages, and to measure the concrete cover.

The data collection (figure 2) was conducted on a 2-ft by 2-ft grid.

The results from three of the deployed technologies are shown herein as an example. The selected assessment results unambiguously confirmed rapid progression of deterioration during the 5-year period. The ER condition map (figure 3) depicts the corrosive environment, which was becoming more aggressive and is shown encompassing larger areas with every new measurement. The increase in the aggressiveness of the corrosive environment is directly reflected in the rate at which reinforced steel corrodes, increasing the likelihood of deck delamination and spalling.

Figure 3. Contour Map. Electrical resistivity  (ER) condition maps from the 2009, 2011, and 2014 surveys.
Figure 3. Contour Map. Electrical resistivity (ER) condition maps from the 2009, 2011, and 2014 surveys.

The condition maps from the three GPR assessments paint a similar picture of deterioration progression (figure 4). Strong attenuation of the GPR signal in the zones plotted in hot colors (reds and yellows) is an indication of highly corrosive environment and likely indicates the presence of cracks and delamination. The condition maps from the three IE assessments clearly show the progression of delamination (figure 5). The red zones show the delaminated area on the bridge deck. The condition maps from the other NDE technologies further support these results, in both the deterioration progression and affected areas identified.

Figure 4. Contour Map. Ground penetrating  radar (GPR) condition maps from the 2009, 2011, and 2014 surveys.
Figure 4. Contour Map. Ground penetrating radar (GPR) condition maps from the 2009, 2011, and 2014 surveys.

Figure 5. Contour Map. Impact echo (IE) condition maps from the 2009, 2011, and  2014 surveys.
Figure 5. Contour Map. Impact echo (IE) condition maps from the 2009, 2011, and 2014 surveys.

The best illustration of the quantitative nature of NDE results are the calculated condition assessments, a weighted average of percentages of the deck area in various states of deterioration on a scale of 0 to 100. For example, delamination is calculated as an average of three assigned weight values: good or no signs of delamination (100), initial or incipient delamination (50), and fully developed delamination (0). Figure 6 shows the color-coded result of this calculation based on data from the 2009 testing. The top part shows the result based on IE, and the bottom part corresponds to HCP. The figure divides the bridge deck into different segments.

Figure 6. Contour Map. Segmentation grading of the deck based on IE and HCP data from 2009.
Figure 6. Contour Map. Segmentation grading of the deck based on IE and HCP data from 2009.

Table 1 shows corrosion, delamination, and concrete quality NDE condition assessment for the three surveys. The delamination condition of the assessed bridge deck dropped from 70 in 2009, to 60 in 2011, then to 40 in 2014, indicating a very rapid progression of deck delamination. The combined condition assessment also shows a rapid decrease in the overall condition of the deck. In contrast, the results of the visual inspections conducted during the same period do not indicate this rapid progression of deterioration. This is because NDE technologies provide information about deterioration processes and defects that typically are not visible. This ability to describe deterioration quantitatively allows for a more objective condition assessment of bridge decks and for more realistic deterioration models to better predict the service life of concrete decks and better manage them.

Table 1. NDE condition assessment of U.S. Route 15 over I-66 bridge.

NDE Condition Assessment 2009 2011 2014
Active Corrosion 40 30 25
Delamination 70 60 40
Concrete Degradation 50 35 25
Combined NDE Assessment 53 41 30

 

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