# Performance Evaluation of Silane in Concrete Bridge Decks Using Transmission X-ray Microscopy
## 2 Materials and Methods
### Diffusion Test
To start the diffusion test, samples were transferred to separate cells, which were filled with a 0.6 mol/L KI solution. The salt solution was kept on the samples for 28 days. In this period, the KI solution was changed every 5 days to keep the concentration constant. During the experiment, the cells were covered to prevent any evaporation and change in the solution concentration. All samples were kept at room temperature (23 \({}^{\circ}\)C) during the experiment. The samples were scanned at a number of time periods up to 28 days after ponding to get the secondary radiographs. Results represented in this paper were extracted from radiographs taken after 28 days of ponding. To analyze and compare the taken radiographs, a software programming code with minimal user intervention was prepared in Matlab to apply local displacements on each image and align the secondary radiographs with the reference radiograph of each individual sample. Then, the central region of the samples with an approximate width of 100 pixels (0.88 mm) was used to find the average gray value at each depth, as shown in Figure 4. The center region was used to eliminate artefacts caused by a nonuniform cross-section. The obtained gray value profiles for each timeseries radiograph were subtracted from the gray value profile obtained from the reference images to quantify the changes in gray values because of mass transport in the samples. The Beer-Lambert law (Equation (1)) [41; 42] was used to determine the subtracted gray values in attenuation at different depths of each sample. \[(\Delta\mu)_{x}=\ln{(I_{\text{ref}})_{x}}-\ln{(I_{\text{t}})_{x}}, \tag{1}\]  
where \((I_{\text{ref}})_{x}\) is the transmitted X-ray intensity (gray value) at depth \(x\) on the reference profile, and \((I_{\text{t}})_{x}\) is the transmitted X-ray intensity at the same depth at other intervals. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **TXM Setting** \\ \hline Pixel size (mm) & 8.8 \\ Voltage (keV) & 100 \\ Current (mA) & 100 \\ Filter & 0.5 mm Al + Cu \\ Acquisition time & 8 s \\ Chamber condition & Air \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Settings used in TXM technique. Figure 4: Considered region for data analysis in each radiograph. To convert the calculated attenuations to concentration, calibration curves were applied. Calibration curves plotted concentration vs. attenuation. To develop the calibration curves, standard samples made with known iodide concentrations added to the mixtures during mixing were used. These standard samples were scanned with the setup provided in Table 1. After scanning the standard samples, the attenuation correlated to each concentration was calculated. Ultimately, a curve was fitted to the obtained spots to obtain an equation which converts the attenuation to the concentration. By using the obtained equation, concentration profiles correlated to different durations of ponding were plotted for each sample. In these profiles, the ion concentration in terms of the weight percentage of the paste was calculated and plotted against the depth. The obtained concentration profiles give information about the concentration at each depth, and the slope of the profiles gives an idea about the rate of penetration. This work used the concentration of iodide at a given depth as a method to quantitatively compare the different samples. The diffusion coefficients were not used because these values for the silane-treated samples were nearly zero.