## 2 Experimental Procedure
### Chloride Ion Penetration  
To measure the chloride ion penetration of the base concrete, the ASTM C 1202 \"Standard Test Method for Electrical Indication of Concrete's Ability to Resist Chloride Ion Penetration\" and the NT Build 492 \"Chloride Migration Coefficient from Non-Steady-State Migration Experiments\" were used. The use of two different testing procedures was to comprehensively understand the chloride ion penetration resistance of the fiber reinforced base concrete because the amount of charge passed was found to be affected by the presence of the conductive material (steel fiber) in the concrete [10].  
The cylindrical base concrete test specimen was cut into the size specified in both standards (100 mm \(\times\) 50 mm). Subsequently, the sliced specimen was inserted into the cell designed for each of the standard test procedures. For the ASTM C 1202 test, a 0.3 N NaOH solution was injected into the anode, a 3% NaCl solution was injected into the cathode, and a voltage difference of 60 V (DC \(\pm\) 30 V) was maintained for 6 h using PERMA(tm) (Giatec Scientific, Ottawa, ON, Canada).  
The test configuration of the NT-Build 492 is shown in Figure 3. In this case, a 0.3 N NaOH solution was placed into the anode (on top of specimen) and 10% NaCl solution was poured into the cathode (outside container). The test was conducted using PROOVETT (Germann Instruments, Copenhagen, Denmark). A 30 V (DC \(\pm\) 30 V) voltage was applied to the cell and the initial current amount was measured. The voltage for the overall measurement was adjusted according to the recommendation in NT-Build 492. The results from the initial current measurements (at 30 V) and adjusted voltage values that were used for the overall measurement are summarized in Table 3. The test was conducted for a total of 24 h after the initial measurement process was completed.  
To measure the penetration depth of chloride ions, the tested specimen (by NT-Build 492) was split into two pieces using a compression testing machine after the test was  
Figure 3: Test configuration for the NT-Build 492 test procedure.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & \multicolumn{5}{c}{**Volume Proportion of Polyolefin Fiber in Hybrid Fiber \({}^{*}\)**} \\ \cline{3-7}  & & **0\%** & **25\%** & **50\%** & **75\%** & **100\%** \\ \hline \multirow{2}{*}{0.54 vol\%} & Initial current (mA) & 110 & 88 & 79 & 68 & 52 \\ \cline{2-7}  & Test voltage (V) & 20 & 25 & 25 & 25 & 30 \\ \hline \multirow{2}{*}{1.08 vol\%} & Initial current (mA) & 161 & 153 & 132 & 72 & 58 \\ \cline{2-7}  & Test voltage (V) & 15 & 15 & 15 & 25 & 30 \\ \hline \hline \end{tabular}  
* The volume proportion of steel fiber in hybrid fiber is opposite to that of polyolefin fiber, thereby following the order of 100%, 75%, 50%, 75%, 0%.  
\end{table}
Table 3: Initial current of the specimens at 30V and adjusted voltage for overall measurements.  
completed. A 0.1 M silver nitrate solution was sprayed onto the surface of the split specimen. In this case, the free chloride ions present inside the base concrete react with silver nitrate to form insoluble silver chloride (silver color), making it easier to measure the penetration depth of chloride ion. The average penetration depth was used to calculate the diffusivity of chloride ion by Equation (2).  
\[D_{nssm}=\frac{0.0239(273+T)L}{(U-2)t}\left[x_{d}-0.0238\sqrt{\frac{(273+T)Lx_{ d}}{U-2}}\right] \tag{2}\]  
where, \(D_{nssm}\): non-steady-state migration coefficient (\(\times 10^{-12}\) m\({}^{2}\)/s), \(U\): absolute value of applied voltage (V), \(T\): average value of initial and final temperatures in the anolyte solution (\({}^{\circ}\)C), \(L\): thickness of the specimen (mm), \(x_{d}\): average value of the penetration depths (mm), and \(t\): test duration (h), respectively.