PSI - Issue 17

S. Tsouli et al. / Procedia Structural Integrity 17 (2019) 268–275 S. Tsouli, A.G. Lekatou, C. Nikolaidis, S. Kleftakis/ Structural Integrity Procedia 00 (2019) 000 – 000

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The microstructure of the corroded 316L specimens (cross-sectioned at ribs by a diamond saw and polished) was inspected by SEM EDX (JeoL JSM 6510 LV SEM/Oxford Instr. X- Act EDX).

3. Results and discussion

3.1 Electrochemical polarization

Fig. 1 illustrates the polarization curves of 316L rebars during immersion in the electrolyte containing Ca(OH) 2 , FA and AR simulating solution. Table 1 includes electrochemical values extracted from the polarization curves.

Fig. 1. Cyclic polarization curves of 316L rebars in a slightly alkaline electrolyte containing Ca(OH) 2 , FA and an acid rain simulating solution.

Table 1. Electrochemical values of 316L rebars immersed in a slightly alkaline electrolyte containing Ca(OH) 2 , FA and AR simulating solution. Fly ash (wt.%) E corr (mV, Ag/AgCl) E a/c tr (mV, Ag/AgCl) E b (mV) i corr (mA/cm 2 ) 0 -267±6 -250±27 1065±27 0.0019±0.0006 10 -255±28 -232±65 1087±48 0.0012±0.0003 15 -251±65 -194±23 1054±93 0.0012±0.0001 20 -233±12 -158±35 1083±7 0.0010±0.0001 25 -254±40 -240±81 1050±21 0.0012±0.0007 The positive hysteresis loops of the anodic polarization curves for the “10 - 25 wt.% FA” polarization curves in Figure 1 suggest that 316L has not been subjected to localized corrosion. Only the voltammogram corresponding to 0 wt.% FA presents a negative hysteresis loop. Nevertheless, the high E b -E corr value and the very low E a/c tr -E corr value suggest that localized corrosion may not be the reason for the surface deterioration upon reverse scanning of the “ 0 wt.% FA ” steel. (Besides, only 1/3 of the tested “0 wt.% FA” rebars showed negative hysteresis loop.) All forward anodic polarization curves reveal passive regions of high potential range and very low current density values (<0.1 mA/cm 2 ), suggesting true passivity. The nobler E a/c tr values as compared to the respective E corr values (Table 1), indicate nobler surfaces at E a/c tr (reverse polarization) compared to those at E corr (forward polarization). Therefore, the high resistance to the localized corrosion is suggested for all different contents of FA. Fig. 1 shows that the positive hysteresis loops at 15 wt.% and 20 wt.% FA present the largest surface areas and the greatest E a/c tr -E corr values (positive) indicating the highest resistance to localized corrosion. On the other hand, the curve at 25 wt.% FA shows the smallest hysteresis loop surface area, which becomes slightly negative in the middle of the passive regime; moreover, it presents the lowest E a/c tr -E corr values (positive) indicating lower localized corrosion resistance than that implied by the 10, 15, 20% FA curves.