# Effect of Corrosion on the Hysteretic Behavior of Steel Reinforcing Bars and Corroded RC Columns
## 3 Experimental Results and Discussion
### Test Set-Up and Results of the Cyclic Behaviour of RC Columns  
Based on the previous experimental work of the authors [19], the behavior of two reinforced concrete columns under dynamic loading was investigated as a simulation of seismic events, in corroded and non-corroded conditions.  
The columns of a square section 300 \(\times\) 300 mm\({}^{2}\) had a height of 1600 mm, while the base had a rectangular section of 1200 \(\times\) 800 mm\({}^{2}\) with a height of 600 mm. The materials that were used were C20/25 concrete class and B500c grade of steel reinforcement. The longitudinal reinforcement of each column consisted of four corner bars of nominal diameter 16 mm (4016), while the transverse reinforcement consisted of stirrups of a nominal diameter of 8 mm at 250 mm intervals (\(\Sigma\)O8/250). The thickness of the concrete cover was equal to 25 mm (Figure 16).  
In order to evaluate the mechanical behavior of a typical column, before and after corrosion, a laboratory-accelerated corrosion experiment was conducted on one of the columns, at a height of 600 mm from the base, in the presence of a 5% NaCl solution.  
After the accelerated corrosion tests, mechanical tests were carried out applying repeated loads that gradually increased, with imposed displacements of the top of each column (drifts) according to the following sequence: 0.2%, 0.8%, 1.0%, 1.25%, 1.50%, 2.0%, 2.5% and 3.5% to 5%, each with three repetitions with a simultaneous imposition of a constant axial load equal to 350 kN.  
The following force-displacement curves (Figures 17 and 18) were obtained from the cyclic loading of the columns, which reflect their mechanical behavior under seismic loads [19]. It is noteworthy that the failure of the tested columns (non-corroded and corroded) was due to the concrete crushing at the column base. Inelastic buckling of steel reinforcing bars was also observed [19].  
From the force-displacement curve of the non-corroded column (Figure 17), it was obvious that the loading history had a significant effect on bearing capacity of the RC element. More specifically, the maximum tensile load was recorded equal to 63 kN, corresponding to a drift equal to 1.75%, while the tensile load during the last loading cycle dropped to 42 kN at a drift equal to 5%. Similarly, in the compressive branch the maximum load was recorded equal to 60 kN corresponding to a drift equal to 1.5%, while at the failure cycle (drift equal to 5%), the bearing capacity was degraded to 38 kN.  
In the case of the corroded column (Figure 18), a huge reduction in the bearing capacity and ductility was observed. The maximum tensile load decreased in contrast to non-corroded conditions, from 63 kN to 44 kN and the maximum compressive load from 60 kN to 45 kN, respectively. The maximum recorded loads were degraded due to corrosion by 30% and 25% in the tensile and compressive branch, respectively. Moreover, the failure of the corroded column occurred at a drift equal to 2.5%, i.e., a 50% reduction relative to the non-corroded column.  
Due to the loading history and significant inelastic buckling of corroded steel reinforcing bars, there was also an enormous drop in the strength capacity of the corroded column during the cyclic loading. In detail, the maximum tensile load at the failure cycle degraded by 66% and the corresponding compressive load by 60%, respectively. The overall degraded mechanical response of the corroded RC column in terms of both strength capacity and ductility indicates the negative impact of corrosion.  
Figure 16: Schematic illustration of the geometry of the column.