PSI - Issue 10

A. Drakakaki et al. / Procedia Structural Integrity 10 (2018) 59–65 A. Drakakaki et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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Both dual and single-phase steel reinforcement have been used in existing structures. However, the different internal structure and the chemical composition (Table 2) of the two types of steel attribute different mechanical characteristics to each category. Both different mechanical characteristics and corrosion resistance result in unlike response of the two materials in long term. Given the differences among the two materials examined in the present study, as far as yield stress and vulnerability to corrosion is concerned, it is difficult to make a common prediction for the deterioration of existing structures. An effort was made to correlate the results received from the laboratory tests, for each steel bar category, to the environmental conditions.

Table 2. Chemical composition of S400 and S500s steel bar categories. C P

S

N

S400 S500s

0.35 024

0.013 0.055

0.026 0.055

0.01

0.013

In the existing literature an effort was made to correlate real coastal- corrosive- environment, XS1 exposure class, to the accelerated artificial corrosion method of salt spray fog chamber, by using S400 steel bar specimens. According to Papadopoulos et al. (2011), 1 day of exposure in the chamber corresponds to 79 days in real conditions. Moreover, Apostolopoulos (2007) and Koulouris et al (2016) describe the response of S500s and S400 steels, respectively, against corrosion. In the specific studies, are presented mass loss rates (Table 3) of specimens of both categories, after various exposure periods to the salt spray chamber. The exposed length of the specimens used is equal to 250 mm. In the present study, an effort was made to correlate electrochemical corrosion to the environment. For this reason, the correlation given by Papadopoulos et al. (2011) and the results presented by Apostolopoulos (2007) and Koulouris (2016), are combined with the results of the current study, concerning specimens of both categories, corroded for 300 hours, under constant current density equal to 0.5 mA/cm 2 (Table 4). The correlation is taking place according to the mass loss rates recorded for both steel classes, for each exposure period. Table 3. Mass loss percentages of S400 and S500s steel bars, after their exposure to corrosion in salt spray chamber, for various exposure periods. S400 S500s Exposure periods (days) Mass Loss (%) Exposure periods(days) Mass Loss (%) 0 0 0 0 10 1.44 10 1.50 20 2.27 20 2.00 30 3.43 30 3.03 45 4.71 45 4.89 60 6.57 60 6.65 90 7.71 90 10.4 Table 4. Mass loss percentages of S400 and S500s steel bars, after 300 hours of corrosion under 0.5mA/cm 2 constant current density. S400 S500s Mechanical Properties Values Mechanical properties Values Mass Loss (%) 4.23 Mass Loss (%) 3.18 According to the previously mentioned information, the damage recorded for S400 steel, after 300 hours of exposure to 0.5 mA/cm 2 current density, is corresponding to the damage occurred after 40 days of exposure to the salt spray chamber. Similar damage is recorded for S500s as well. Consequently, 1 hour of exposure to 0.5 mA/cm 2 current density in the electrochemical corrosion system, corresponds to 10.5 days of exposure to the real aggressive - coastal environment.