# Effect of Corrosion on the Hysteretic Behavior of Steel Reinforcing Bars and Corroded RC Columns
## 3 Experimental Results and Discussion
### Corrosion Damage of Steel Reinforcing Bars
For higher levels of corrosion, corresponding to a mass loss in steel bars greater than 6%, the type of corrosion changes to pitting corrosion due to the appearance of local large pits on the surface of the steel bars. On that occasion, the assessment of the corroded steel reinforcement, expressed in the terms of either mass loss or corrosion penetration depth, needs special attention, since intense pits lead to a significant deviation of the effective reduced diameter (deff) in reference to the mean reduced diameter (dred) calculated on the basis of uniform corrosion penetration (x). In the following graph in Figure 9, the values of the mean reduced diameter (dred) and the actually effective diameter (deff) are depicted to emphasize the differences between uniform and pitting corrosion of steel reinforcement. More specifically, as observed in Figure 9, for a theoretical corrosion level of 6.5-7% of mass loss, the actual effective diameter may deviate from the mean uniform diameter by 9.3% to 31.3%, while for higher levels of damage, at about 11.0-11.5% mass loss, may differ from 8.6% up to 46.9%. Focusing on the reduction in the cross-section, a term which is taken into account in the design of RC elements, these deviations between dred and deff demonstrate at a greater level the huge negative impact of pitting corrosion on steel reinforcement. The percentage decrease in the actual residual cross-section (calculated by deff) in reference to the reduced cross-section (calculated by dred)was calculated by Equation (3). In detail, for a mass loss of about 6.5-7% the effective cross-section of corroded steel bar dropped by 17.7% up to 54.1% in reference to the mean reduced cross-section, while for mass loss of about 11-11.5% the reduction was recorded from 16.5% up to 71.8%. The obtained results agree with the results of previous studies on pit geometry measurements, where the statistically significant deviation between the mean (uniform) pit depth and the maximum (effective) pit depth is referred to [30; 31; 32; 33; 34]. \[\text{Cross-section deviation}\ =\frac{\text{d}_{\text{eff}}-\text{d}_{\text{red}}}{ \text{d}_{\text{red}}}\cdot 100[\%] \tag{3}\]  
Following the above observations, the effective residual diameter due to pitting corrosion has great significance especially in the case of dual phase steel reinforcement. As is well known, the outer ring of the martensitic phase in the circumference of dual phase steel reinforcing bars, such as class of Tempcore B500c, is responsible for the strength capacity. Thus, the reduction in or the absolute loss of the martensitic layer due to pitting corrosion has a negative impact on the mechanical response of this type of steel bar. Several studies have demonstrated the reduction in the mechanical response due to either uniform corrosion or pitting corrosion and have introduced the term pitting factor in order to express the severity of localized material damage in the latter case [35; 36; 37]. In this framework, [PERSON] et al. [38] collected several experimental data [30; 39; 40; 41; 42; 43] of corroded steel reinforcing bars and proposed degradation laws of mechanical properties for uniform and pitting corrosion. Figure 8: Area of uniform corrosion (in red range) in certain parts of the length of the steel reinforcing bar.