# Curable Area Substantiation of Self-Healing in Concrete Using Neutral Axis
## 2 Experimental Setup
### Specimen  
A prismatic specimen measuring L400 \(\times\) W100 \(\times\) D100 mm was used in this study, as specified in the JCI standard (JCI-S-001-2003). RILEM specifies a longer specimen for the three- or four-point bending test, but small specimens are convenient from the viewpoint of the most essential curing process in self-healing [38]. Ordinary Portland cement was used as the base material, and additional materials that can aid the healing process were not included because we sought to focus on the crack itself. The water-cement ratio (W/C) was set to 45%. Detailed specifications of the concrete mix are listed in Table 1.  
All specimens were fabricated at the same time and with the same materials, and the notch was also created at the same time and cured for seven days. All specimens were cast in steel molds, and they were demolded and cured in fresh water at 20 \({}^{\circ}\)C for the following 24 h. Five different cases were considered in this study, and the faster loading process (1 st loading) of these cases was planned on the seventh day after fabrication. Therefore, the notches in all specimens were sawed on the seventh day of the curing process. A wet concrete cutter with a diamond blade was used for sawing the notch. The notch depth depends on the maximum load capacity of the specimens. If the notch is too deep, there would not be sufficient space to measure the neutral axis. Considering these aspects, the notch depth was set to 33 mm, which is one-third of the specimen depth, and the notch width was set to 3 \(\pm\) 0.5 mm. Cracks occur near the peak load and begin to propagate, and the crack propagation speed is generally higher with a higher peak load. As a preliminary experiment, 25% of the load specified in RILEM or 30% of the load specified in the JCI standard was found to be too high as peak loads from the viewpoint of controlling crack propagation easily. These were three loading processes per case. The 1 st loading induced the crack in each specimen. The 2 nd loading just followed the 1 st loading. The 2 nd loading was limited to the extent that the crack induced in the 1 st loading was no longer advanced, and it measured performance before healing. After the 2 nd loading, specimens entered the healing process. The healing process was done in different healing conditions (freshwater and air) and in different periods of time (21 days, 42 days and 63 days). The 3 rd loading was performed after the healing process. We were able to determine the degree of healing effect by comparing the 2 nd loading and the 3 rd loading performed before and after the healing process. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**W/C (\%)**} & \multicolumn{3}{c}{**Unit Content (kg/m\({}^{3}\))**} \\ \cline{2-5}  & **Water** & **Cement** & **Sand** & **Gravel** \\ \hline
45 & 175 & 389 & 780 & 879 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mixing proportions of the specimen. Figure 1: Schematic of the experimental setup. Five different cases were planed; 7-28 case, 7-49 case, 7-70 case, 28-49 case and 49-70 case. The first number of case names indicates when the 1 st loading and the 2 nd loading took place. Both of them was done at the same days because the 2 nd loading was just followed the 1 st loading. The second number of case names indicates the date when the 3 rd loading was made, and the healing period could be calculated from the difference between two numbers in the case name. For example, 28-70 case means that the 1 st loading and the 2 nd loading was done on the 28 th days and the 3 rd loading was done on the 70 th day with a 42-day healing period. Finally, the letters W and A at the end of the case name represent the healing condition; healing in freshwater at 20 \({}^{\circ}\)C and healing in air in a curing room maintained at 20 \({}^{\circ}\)C.  
The effect of the healing period would be investigated comparing 7-28 case, 7-49 case and 7-70 case.