## 4 Damage and Repair of Girder Ends  
To induce realistic damage to the tested girders in pattern to that is sustained at the end regions of girders in service, the concrete cover was removed from the web and the bottom flange. For all the cases except the control case, concrete cover was removed to approximately the centerline of the stirrups. To remove the cover, a grid of holes was drilled first (Figure 5a) to control the depth of the concrete cover to be removed, and to weaken the concrete and ease the removal process. Next, a hammer drill with a chisel was utilized to remove the cover. A picture of the beam end after cover removal is depicted in Figure 5b.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Test** & **Cover Damage** & **Mortar Repair** & **FRP Repair** & \
\begin{tabular}{c} **Concrete Compressive** \\ **Strength, MPa** \\ \end{tabular} &
\begin{tabular}{c} **Mortar Compressive** \\ **Strength, MPa** \\ \end{tabular} \\ \hline Control & n/a & n/a & n/a & 60.3 & n/a \\ Damaged & X & n/a & n/a & 60.3 & n/a \\ Mortar & X & X & n/a & n/a & 41.7 \\ CFRP & X & X & X & n/a & 54.1 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Test matrix.  
Figure 4: Three-point bending testing instrumentation (1:27).  
Figure 5: Concrete cover removal (1:27): (**a**) grid of drilled holes and (**b**) girder after cover removal.  
After the cover was removed, the exposed surface was air blasted and vacuumed to provide a clean surface for the following mortar repair. It was essential to restore the shape of the damaged end before any other repair material such as FRP laminate was applied. Rapid mortar mix was used to obtain a fast repair. A trovel was used to place mortar layer on the concrete surface and to smooth the surface for following FRP laminate application. Due to its high Young's modulus and ultimate strength, carbon FRP (CFRP) laminate was selected as the repairing material. The CFRP laminate was manufactured with unidirectional carbon fibers saturated in resin and had an elastic modulus of 86.9 GPa and tensile strength of 930 MPa. One layer of CFRP laminate had a thickness of 1.24 mm. Due to the blockage of the support bearing plate and the limited space under the girder near end region in the field, an externally bonded U-wrap scheme was not feasible. As a result, the 2-sided FRP repair approach was adopted, where FRP laminates were only applied at the girder sides and not the bottom side. After the mortar was set, FRP laminates with vertical fiber orientation were applied to the girder sides using the wet layup method. Figure 6 depicts a schematic and picture of the applied repair scheme. As illustrated in the figure, four panels of one layer of the FRP sheet with a width of 279 mm were applied starting from the center of the support bearing plate and spaced at 25.4 mm. Three longitudinal strips of CFRP laminate were placed atop the panels to serve as anchors to prevent the debonding of the vertical CFRP panels as shown in Figure 6. Each strip was 1498 mm long and 76.2 mm wide. The longitudinal strips extended to 152.4 mm beyond the first and last panel. Vertical strain gage was attached to the third FRP panel to monitor the strain developed within the FRP laminate. Since the slip of strand was not anticipated, the strand slip of the control case was not monitored. After the strand slip was observed during the testing of the control girder, the slip of the strand during loading was monitored for the rest of the cases by attaching one LVDT to one of the prestressing strands.