**9.5 Evaluation of corrosion-induced risk and deterioration of concrete slabs using ground-penetrating radar and ultrasonic pitch-catch techniques**

This project aims at evaluating corrosion-induced deterioration of RC bridge deck slabs using two non-destructive evaluation techniques, UPC and GPR. Experimental testing on RC slab specimens with pre-planned artificial defects was conducted to

#### **Figure 6.**

*Two bridges in West Virginia Department of Transportation's inventory. (a) East Street Viaduct Bridge (curtesy of WVDOT - WVDOH bridge inspection reports 2012 and 2017); (b) Flag Run Bridge (curtesy of WVDOT - WVDOH bridge inspection reports 2016).*

*Environmentally Influenced Risk and Sustainable Management of State Controlled... DOI: http://dx.doi.org/10.5772/intechopen.98232*

**Figure 7.**

*Basic principles of the UPC technique: (a) transmitting and receiving transducers in UPC configuration; (b) the first channel transmit signals and the other channels receive the signals; and (c) the second channel transmit signals and the other channels receive the signals.*

**Figure 8.**

*3D visualization of the test specimen using NDT/NDE GPR and MIRA.*

understand merits and disadvantages of each NDE technique. **Figure 10** illustrates the points at which data was collected for the RC slab using the UPC technique. **Figure 11** shows the signal amplitude versus depth of the delamination. The collected NDE data were used to generate both 2D and 3D images of layouts of reinforcements in the RC slabs [36]. The GPR effectively identified corrosion.

Potential areas of defects were generated using B-scan data. NDE data fusion approach was used to interpret the NDE data and to reconstruct the 2D/3D images. The GPR technique is not likely to be detect corrosion-induced concrete delamination. On the other hand, the UPC technique was found to be quite effective in determining and locating delamination, voids, reinforcing rebars, and pre-stressing tendons in the RC slabs. Major limitation of this technique is its sensitivity to the electrical properties of concrete such as the resistivity and dielectric constants. Therefore, the UPC is not suitable for detecting early signs of reinforcing bars corrosion. In addition, it requires a substantial amount of time to complete data

**Figure 9.**

*Two-dimensional reconstructed image at an artificial delamination location.*

#### **Figure 10.** *Data collection on the RC slab using the UPC technique.*

**Figure 11.** *Signal amplitude versus depth of the delamination.*

collection. The GPR technique rapidly detected the highly corrosive regions in RC structures while the UPC technique can be used for in-depth evaluation and inspection of likely active corroding areas found by the GPR technique.

The project team recommended the combined use of GPR and UPC techniques for comprehensive assessment of corrosion-deteriorated bridge deck slabs [36].

## **9.6 Asset evaluation of concrete bridge deck slabs rehabilitated with composite Fiber-reinforced polymers**

Fiber-reinforced polymer (FRP) materials have been widely accepted as an effective method in retrofitting deteriorated infrastructure (in shear, flexure and confinement

*Environmentally Influenced Risk and Sustainable Management of State Controlled... DOI: http://dx.doi.org/10.5772/intechopen.98232*

applications). Despite the fast-growing and advanced technology in FRP materials and strengthening techniques, the monitoring and quality control of the FRP construction and installation remain challenging. For externally FRP-rehabilitated newly constructed and existing structures, it is critical to evaluate the potential for debonding failure and defects including cracks and voids surface on the concrete surface.

Accurate detection and evaluation of these defects is important to verify the structural capacity and to ensure appropriate durability of the FRP-strengthened structures. Experimental and theoretical non-destructive studies were conducted for concrete bridge deck slabs externally bonded with glass FRP, carbon FRP, and the combination thereof. **Figure 12** shows a sample reinforced concrete bridge deck slab specimen. Ground-penetrating radar (GPR) and infrared tomography (IRT) methods were utilized.

The results showed that the in-house developed software using an enhanced image reconstruction technique could provide high-resolution images of the FRPstrengthened reinforced concrete slabs in comparison to those obtained from the device's original software [37].

**Figure 13** shows reconstructed images of the sample bridge deck slab specimen. The results obtained from the IRT camera indicated that this technology could accurately detect and locate near-surface defects such as debonding, cracks and voids. The study suggests that the combination of the GPR and IRT methods is effective in imaging internal defects of FRP-strengthened concrete structures.

**Figure 12.** *Details of a sample reinforced concrete bridge deck slab specimen.*

**Figure 13.** *Reconstructed images of the sample bridge deck slab specimen.*
