## 2 Flexural Tests on Corroded PC Beams  
### Fabrication of Test Specimens  
The studies relating to corroded PC beams fabricated for lab tests have mostly dealt with single straight strands. However, existing PC girders' tendons consist of a bundle of strands with a parabolic profile, so it is necessary to understand the behavior of corroded PC beams with multiple strands. Figure 1 shows a detailed drawing of the PC specimens. A total of five PC beam specimens were fabricated of dimensions \(380\times 280\times 3100\) mm. Two compressive rebars of diameter 13 mm and two tensile rebars of diameter 10 mm were used. Three strands of diameter 15.2 mm and a nominal area of 138.7 mm\({}^{2}\) (according to KS F 7002 [19]) were placed along the tendon profile shown in Figure 1.  
Figure 1: Detailed drawing of the prestressed concrete (PC) beam specimens. Prior to the strands being placed, they were artificially corroded using the impressed current method (ICM) as shown in Figure 2. This method has been adopted by some studies [20; 21] on strand corrosion and is known to cause corrosion relatively quickly compared to other methods. A strand and a copper plate are connected to the positive and negative electrode of a DC power supply supplying a certain level of current, and the copper plate is immersed in a 3.5% NaCl solution. In order to induce corrosion in a specific location, a cotton towel is hung on the strand, and the tip immersed in a 3.5% NaCl solution so that electric current flows continuously. A total of ten strands were corroded using this method, and the period of corrosion induction time was set randomly to achieve different levels of corrosion. A [PERSON] et al. [12] proposed hemispherical pit configuration to evaluate the cross-sectional loss of corroded strands using a pit depth, and the configuration was simplified with three idealized pit configurations in previous studies [16; 18] as shown in Figure 3 (when comparing the shape and Figure 3b, Figure 3b had larger cross-sectional loss up to a pit depth of about 2 mm and the model of [PERSON] et al. [12] became larger after that). The section loss measurement was conducted on six outer wires excluding the core wire which cannot be evaluated for section loss. The cross-sectional loss of a strand (called strand-unit section loss from here on) was defined as the sum of the section loss of each wire (called wire-unit section loss from here on). Likewise, a tendon-unit section loss was the sum of the three strand-unit section losses. Figure 3: Section loss measurement using (**a**) pit depth gauge and (**b–d**) three idealized pit configurations [16; 18]. Figure 2: Induction of electrochemical corrosion using the impressed current method (ICM). To define the most corroded section, the measuring technique was conducted every 20 mm along the length of corrosion. Among the measured strand-unit section losses, the biggest strand-unit section loss was selected as the degree of corrosion of the strand. This method has the benefit of being able to find the highest section loss among the length and apply this to practical inspection more easily than other measurement methods [18]. Equations (1)-(3) were mathematically derived from geometric shapes of the pit configurations so that section loss could be measured with only one variable, the pit depth. The corroded strands were placed on each specimen as shown in Table 1. Four PC beams with corroded strands, identified as CB, and a non-corroded PC beam, identified as RB, were prepared. CB1 only had corrosion in the middle of span, while the others had it located 300 mm from the support to the center. The cross-sectional loss of the wires and strands shown in Table 1 indicate those with the highest cross-sectional loss in the tendons of each specimen. After the strands had been placed, prestressing force was applied, and grout was injected. The corrosion has been found near the support in a case study [18], and the study conducted a PC beam test with single strand.