# Performance Evaluation of Silane in Concrete Bridge Decks Using Transmission X-ray Microscopy
## 3 Results and Discussion
### Resistance of Outside Chemical Penetration  
Figure 6 shows typical concentration profiles for samples with and without silane. The iodide concentration profiles are the average from two samples for each project and two directions for each sample (a total of four concentration profiles). In each case, the measurement of the concrete without silane showed 2\(\times\) to 4\(\times\) the amount of iodide concentration at a comparable depth. Additional data for the other 14 locations are included in Appendix C.  
Figure 7 compares the iodide concentrations of all samples at a fixed depth of 2 mm for both silane and non-silane samples. A depth of 2 mm was chosen as the silane was found to penetrate to this depth in all samples investigated.  
Figure 5: Average depth of silane penetration for all samples.  
Figure 6: Iodide concentration profiles of Samples 3 and 9.  
The average of the iodide concentration from all samples without silane at a depth of 2 mm was 2.7%, while the average value for silane-treated samples at the same depth was 0.3%. These average values are shown with horizontal lines in Figure 7. This means that, on average, the outside salt solution penetrated 9\(\times\) higher into the depth of samples without silane compared to those that were coated with silane. This is a drastic difference in the performance of 14 different bridge decks when the samples were treated with silane vs. when they were not treated.  
For the non-silane samples, there existed a large variability among the samples. Some samples had iodide concentrations as low as 1% by weight, while some had concentrations greater than 4%. This may have been caused by the variation in the mixture design, casting practice, and curing methods employed for these samples.  
The range of iodide concentration change for silane-treated samples was 0.03% to 0.66%. This shows that the variation of the iodide concentration was low. A possible reason is that silane is a surface treatment coating material which acts as a barrier. The results show that the effectiveness of the silane was not dependent on the initial quality of the concrete. For example, Sample 13 had the lowest penetration of iodine in the untreated sample, while Sample 9 had the highest penetration of iodine. Regardless of the initial penetration level, both samples had the same amount of iodide penetration after being treated with silane. This is an important finding as it shows that silane has the potential to improve a wide range of concrete quality. By considering Figures 5 and 7 and by comparing Sample 4 (with silane penetration below the average) and Sample 1 (with the maximum silane penetration), it can be concluded that the performance of silane is not only related to the silane penetration but also some other factors such as surface preparation methods, application procedure, the influential environmental factors, and silane chemical properties. By comparing Samples 11 and 12, which had similar mix designs but different silane penetration depths, it can be concluded that, for a specific concrete, a greater depth of penetration provides better protection to concrete. Furthermore, by looking at the average values of iodide concentration for the treated and untreated samples, it can be concluded that silane can significantly reduce the penetration of outside chemicals of higher-permeability concrete.