## 4 Experimental Results
### WEB Part of T-Shape PC Girder Bridge
The gray value profile along the line segment across the PC sheath and nearby reinforcing rods (see Figure 20) was obtained, as shown in Figure 14.0 Regions of \"A\" and \"B\" correspond to the PC wires and unfilled grout, respectively. A few wires are seen less to be dark in the region between them, as depicted in Figure 17a. Additionally, two lower peaks attributed to the two rods can be clearly observed as \"C\" and \"D\". Because this profile contains an ununiform background distribution of irradiating X-rays, it has to be compensated by using the data shown in Figure 14.1 The compensated profile is shown in Figure 14.2 We used these compensated profiles for the gray value analysis to evaluate the filled and unfilled grouts quantitatively. Figure 14.3 Gray value profile of the line segment in Figure 14.4  
Figure 14.5 Gray value profile analyzing line. Line segments for gray value analysis are indicated in Figure 23 in this X-ray image of the 200 mm thick WEB of the T-shaped PC girder bridge by the 950 keV X-ray source. The gray-value profiles are shown in Figure 14.6  
Figure 14.7 Line segments for gray value analysis for unfilled grout in the X-ray image of 200 mm thick WEB of the T-shape PC girder bridge by the 950 keV X-ray source. Figure 14.8 Original gray value profile of the yellow line in Figure 14.9  
Figure 15.0 Compensated profile of Figure 20 by subtracting the ununiform background due to the X-ray point source. By identifying the sheath range within the gray value profile, gray values could be obtained. The evaluated values are summarized in Figure 15.1 As predicted above, the average ratio of \(K\) is clearly higher than 1 and is approximately 1.4. Moreover, we plotted another set of gray values for the unfilled grout. Figure 25 shows the original image of the same WEB part (200 mm-thick T-shaped PC girder bridge) taken by the 950 keV source. The inspection location is different from that shown in Figure 23, as exhibited in Figure 12d. Line segments for gray value analysis are also indicated in the figure. \begin{table}
\begin{tabular}{c c c c} \hline
**Location** & \(\mathbf{G_{w}}\) & \(\mathbf{G_{no\_grant}}\) & \(\mathbf{K_{fw}}\) (\(\mathbf{G_{no\_gout}}\)/\(\mathbf{G_{w}}\)) \\ \hline Left & 148 & 210 & 1.42 \\ Center & 167 & 232 & 1.39 \\ Right & 152 & 214 & 1.41 \\ Average & 156 & 228 & 1.41 \\ \hline \end{tabular}
\end{table} 
Table 2: Gray values and \(K\) ratios for 200 mm PC, 950 keV and unfilled grout. Figure 24: Gray value profiles of (a) Left; (b) Center; (c) Right in Figure 22.  
The gray value distributions on the line segments in Figure 25 are shown in Figure 26. Table 3 lists the gray values and \(K\) ratios. The average ratio of \(K_{max}\) is approximately 1.5. Meanwhile, \(K_{max\_few}\) is lower at \(\sim\)1.1 This is because the parts of many and a few wires look dark and less dark, that is, \(G_{w\_few}>G_{w}\). Figure 26: Gray value profiles of Figure 25. (**a**) Left; (**b**) center; (**c**) right. Figure 25: X-ray image of unfilled grout in a 200 mm thick T-shape PC girder bridge taken by the 950 keV source. (**a**) Left; (**b**) center; (**c**) right. Line segments for gray value analysis are also indicated. After looking into the unfilled sample, we proceeded to the filled grout case. Figure 27 shows an image taken from the same WEB part (200 mm-thick T-shaped PC girder bridge) by the 950 keV source. The lower half of the PC sheath appears to be dark compared to that in Figures 23 and 25. Line segments for plotting the gray values are also observed. In the same way, the profiles were plotted as shown in Figure 28, and the \(K\) ratios are calculated in Table 4. The average ratio of \(K_{flux}\) is -1.3, which is lower than the \(