# Assessment of Mechanical Properties of Corroded Prestressing Strands
## 3 Tensile Test of Corroded Strands  
### Test Specimens  
A total of 100 corroded strands taken from Bridges A and B were investigated for corrosion. Among the specimens, a total of 86 seven-wire strands (47 strands from Bridge A and 39 strands from Bridge B) were selected for this study after exclusion of specimens that were too corroded to be used in the tensile test. Figure 8 shows two section profiles of the seven-wire strands. The strands from Bridge A had a nominal diameter of 15.2 mm and a sectional area of 138.7 mm. The diameter of the core wire was 5.2 mm, and the diameter of the outer wires was 5.0 mm. The strands from Bridge B had a nominal diameter of 12.7 mm and a sectional area of 98.7 mm. The radius of the core wire was 4.4 mm, and the radius of the outer wires was 4.15 mm. In this study, these two strands are referred to as the 15.2 type and 12.7 type, respectively.  
Before tests were conducted, the strands were cleaned with a steel brush and rust remover. An inspection to evaluate the section loss was also conducted along the length of the specimens, using a pit-depth gauge to determine the location of the most corroded section. For the quantitative corrosion comparison, the extent of section loss, denoted as \(\eta\), was expressed as follows.  
\[\eta=\frac{A_{sl}}{A_{0}} \tag{4}\]  
where \(A_{0}\) is the sectional area of the wire, and \(A_{sl}\) is the loss of the sectional area from Equations (1)-(3).  
After inspection of the corroded strands, it was found that the wire-unit section losses were different between strands, even though their strand-unit section losses were very similar. Figure 9 shows the relationship between wire-unit section loss of the most corroded wire and strand-unit section loss, considering the number of corroded wires. The figure also shows an example of how the data was collected. If the number of corroded wires was three, for example, the strand consisted of three corroded wires and four non-corroded wires. The maximum number of corroded wires was six because the remaining wire (core wire) was impossible to inspect.  
As Figure 9 shows, it was found that strands with a higher number of corroded wires tended to have higher strand-unit section losses as well as higher wire-unit section losses. A higher strand-unit section loss is a natural result, because the strand-unit section loss is the sum of the wire-unit section losses. However, the higher levels of corrosion in the wires have a special meaning. When all wires are exposed to corrosive environmental conditions, they will corrode simultane  
Figure 8: Section profiles of seven-wire strands.  
have different conditions due to insufficient grout or local contaminant penetration. This can cause corrosion reactions on some wires, as shown in the section picture of Figure 9, and then other wires begin to corrode when a certain level of corrosion occurs.  
In addition, a higher number of corroded wires tends to produce more widely scattered data. This means that pitting corrosion can develop differently in the wires; therefore, the maximum wire-unit corrosion in a strand can be very different between corroded strands, even though they have the same level of strand-unit corrosion. If the strand fracture is defined as the moment of a single wire fracture [15], it is necessary to consider the cross-sectional loss in the wire after at least a 2% section loss in a strand.