# Influence of Cracking on Oxygen Transport in UHPFRC Using Stainless Steel Sensors
## Materials and Methods
### Methodology and Experimental Program in Cracked State  
#### 2.3.1 Concept and Experimental Program  
It is clear that the UHPFRCs matrices display superior mechanical and durability properties if compared with those of traditional concrete types from the characterization results. This work aims to study whether these superior durability properties are also extended to the cracked state. To this purpose, small reinforced beams (Figure 2) were cast and pre-cracked (see Section 2.3.3) at three levels of severity, and its oxygen availability was analyzed in two experimental campaigns that are summarized in Table 4.  
The first campaign was defined to compare the concretes evaluating the difference in oxygen availability while using one stainless steel sensor that was located in a fixed position at the lower part of the beam, as displayed in Figure 2. The four concrete types were all studied in uncracked state (Ref). HPC and UHPFRCs were studied in both low and high strain levels (HS). The comparison of the  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multicolumn{6}{c}{**Experimental Campaign 1**} & \multicolumn{3}{c}{**Experimental Campaign 2**} \\ \hline \multicolumn{2}{c}{_Single Crack Pattern_} & \multicolumn{3}{c}{_Multiple Cracks Pattern_} & \multicolumn{3}{c}{_Correte_} & \multicolumn{1}{c}{_Crack Level_} & \multicolumn{1}{c}{_No._} & \multicolumn{1}{c}{_Concrete_} & \multicolumn{1}{c}{_Crack Level_} & \multicolumn{1}{c}{_No._} \\ \hline \multirow{2}{*}{SQC} & Uncracked & 3 & \multirow{2}{*}{UHPFRC} & Uncracked & 3 & HPC & High Strain & 1 \\ \cline{3-5}  & Uncracked & 3 & & Low Strain & 3 & UHPFRC & High Strain & 1 \\ \cline{3-5}  & Low Strain & 3 & & High Strain & 3 & UHPFRC-n & High Strain & 1 \\ \cline{3-5}  & High Strain & 1 & & & Uncracked & 3 & & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Summary of the distribution of beams for the experimental campaigns performed and number of specimens per case (No.).  
Figure 2: Beams scheme for the two experimental campaigns showing the position of the sensors.  
results that were obtained in these levels will allow for discerning the potential durability of cracked UHPFRCs as compared to traditional concrete types (SQC or HPC) in uncracked or low strain levels. Three beams were evaluated for each concrete and Table 4 shows the cracking level.  
The second campaign was a detailed study that was performed on three beams that suffered high damage levels to evaluate the sensitivity of the result that was obtained when changing the position of the reference electrode. It aimed to determine whether the sensors are able to differentiate the cracking or damage levels in different areas of a same beam. In this case, each beam contained three sensors located at three heights (sensor H, M and L) and four sectors were studied, named S4, S3, S2, and S1, as displayed in Figure 3. The bottom surface will be tensioned while the upper surface will be compressed, since the pre-cracking method is a four-points bending test. The cracks are expected to be mainly produced in the middle span (sectors S2 and S3), and will be V-shaped, with the maximum crack opening in the tensioned surface (location of sensor L) and decreasing towards the compressed area (sensor H).