## 4 Experimental Numerical Study of Corrosion Cracks and their Reproduction
### Specimen  
RC beam specimens with a 20-mm cover depth were fabricated to simulate Specimen 3 in Figure 8. The cover portion could have become markedly nonuniform because of the coarse aggregate in the cover portion when the concrete was applied, mainly because a region with a relatively sparse void  
Figure 14: Crack width versus expansion step of reinforcement (Specimens 3 and 5). Figure 13: Damage distribution of a cross-section of Specimen 5.  
structure, called a transition zone, forms around the coarse aggregate to cause uneven corrosion. Therefore, a test specimen using mortar was chosen. Ordinary Portland cement was used for the mortar, and crushed sand (surface dry density = 2.56 g/cm\({}^{3}\); water absorption ratio = 1.96%; fineness modulus = 2.62) from the town of Saita in the Mitoyo district of the Kagawa prefecture of Japan was used as the fine aggregate. The water to cement ratio of mortar was 70%. The specimens were demolded immediately after being allowed to stand for 24 h and were then kept wet for 28 d under a wet cloth. Next, tests were conducted, as outlined in Figure 15, to generate early reinforcement electrolytic corrosion. A photograph of the actual test setup is shown in Figure 16.  
A stainless-steel plate (80 mm \(\times\) 200 mm \(\times\) 0.3 mm) was installed in the center of the bottom of the test piece, and a porous water-absorbing foam (80 mm \(\times\) 20 mm \(\times\) 200 mm, length \(\times\) width \(\times\) height) was sandwiched between it and the test piece, followed by a large plastic tray filled with a 3% aqueous sodium chloride solution. The fulcrum of the test piece was then provided at a position where half of the sponge installed in the bottom of the piece was immersed. A direct current stabilized power supply was prepared, and the anode of the apparatus and the reinforcing bar, as well as the cathode and the stainless-steel plate installed at the bottom of the test piece, were connected by a lead wire. Following the connection, a 100-mA steady-state current was applied to initiate corrosion, and anodic reactions were generated in the reinforcing bars to corrode the structures. To prevent the stirrup from electrolytic corrosion, as illustrated in Figure 15, only the main reinforcement in the 300-mm section of the center of the test specimen was corroded by applying epoxy resin on the stirrup around the main reinforcement, followed by electric insulation of the resin. Ten cases with different current application times were set up, and each specimen was subjected to electrical corrosion at a set time. Electrolytic corrosion was performed for 48 h in Cases 1-3, 161 h in Cases 4 and 5, 355 h in Cases 6 and 7, and 403 h in Cases 8-10. After the electrolytic corrosion test, the width of the corrosion cracks on the test specimens was measured by a crack width ruler. After measuring the crack width, the corroded reinforcing bars were collected from the test specimens and cut by electric cutters to divide the 300-mm section corroded by the reinforcement into three sections, each approximately 100 mm in length. Figure 17 shows the positions and numbers of collected and cut bars. To measure the loss on the cut bars due to corrosion, they were immersed in a 10% aqueous ammonium hydrogen citrate  
Figure 16: Photograph of electrolytic corrosion test. Figure 15: Electrolytic corrosion test setup. solution for 24 h at 60 \({}^{\circ}\)C, mainly to remove the corrosion products, after which the mass and length of each bar were measured. The corrosion amount \(W_{r}\) [mg/cm\({}^{2}\)] per unit area was calculated from (i) the difference between the mass \(W_{0}\) [mg] of the healthy reinforcing bar before the electric corrosion experiment and the mass \(W\) [mg] after rusting, divided by (ii) the product of the length \(L\) [cm] and nominal circumference \(\varphi\) [cm] of the cut reinforcing bar, namely  
\[W_{r}=\frac{W_{0}-W}{L\varphi}. \tag{15}\]  
Table 1 indicates the amount of corrosion for each reinforcing bar position.