## 2 Materials and Experiments
### Experimental Methods
#### 2.3.2 Electrical Accelerated Steel Corrosion  
Firstly, before RC specimen preparation, rust on the surface of steel bars should be removed; then all the steel bars should be cleaned with deionized water and dried in the drying device at 20 \({}^{\circ}\)C for 4 h. After that, the mass (\(m_{si}\)) and length (\(l_{si}\)) of each steel bar were tested using a sensitive balance and vernier caliper to obtain the average line density (\(\rho_{s}\)) of all the steel bars. \(\rho_{s}\) can be calculated by the following equation, and the value was tested to be 0.395 kg/m.  
\[\rho_{s}=\frac{1}{n}\sum_{i=1}^{n}\frac{m_{si}}{l_{si}} \tag{1}\]  
It takes a long time to obtain corroded beams due to the slow penetration process of chloride ions by immersing RC beams into chloride solution. Given that steel corrosion is an electrochemical process, electrochemical techniques can be used to accelerate steel corrosion [27]. The device for accelerating steel corrosion is displayed in Figure 3. Each specimen was placed into an electrolytic cell filled with 6 wt% NaCl solution. A 30 V direct current (DC) regulated power supply was used to provide impressed current. Each specimen should be vertically placed. In order to ensure the effective length of the corroded steel bar is 40 cm, the exposed part of the steel bar at the bottom of each specimen should be cut off. Additionally, the exposed parts of four steel bars at the top of the specimen were welded with copper wire and connected to the anode of DC regulated power supply in parallel mode, while the cathode was connected with a 15 cm \(\times\) 40 cm copper sheet. During the accelerated corrosion test, NaCl solution should not exceed the top of the specimen and touch the steel bars.  
Figure 3: Sketch of the device for accelerating steel corrosion.  
Figure 2: Experimental procedure.  
Furthermore, in order to determine the theoretical current value and electrified duration, [PERSON]'s law can be used for calculating the theoretical mass loss of steel bars when subjected to the impressed current no matter what medium is surrounding this kind of metal [28; 29]. The relationship between mass loss of steel bar, electrified duration and impressed current intensity is as follows:  
\[\Delta m=\frac{M\Pi t}{zF} \tag{2}\]  
where \(\Delta m\) is the theoretical mass loss of the steel bar, in g; \(M\) is the atomic weight of the metal (56 g or 0.1232 lb for Fe); \(I\) is the impressed current intensity, in A; \(t\) is the electrified duration, in s; \(z\) is the ionic charge number of steel (2); \(F\) is [PERSON]'s constant (96,500 A/s).  
In this study, the electrified duration for each steel bar to obtain a mass loss of 10% (corrosion ratio of steel bar equals 10%) was controlled at 24 h. Therefore, the applied current value for steel bars to reach the theoretical corrosion ratio can be calculated from [PERSON]'s law and is listed in Table 2.  
It was ensured that the corrosion ratio of four steel bars embedded in one RC specimen was the same. Therefore, it can be calculated that the accelerated corrosion system needs to electrified 0, 24, 48, 72, and 96 h for RC beams to reach the target corrosion ratio (percentage of mass loss) of 0%, 10%, 20%, 30%, and 40%; and the current value applied in the DC regulated power supply for corroding each specimen is 2.52 A.