PSI - Issue 17

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

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Fig. 6. SEM micrographs of cross-sections of 316L rebars after cyclic polarization in a slightly alkaline electrolyte containing Ca(OH) 2 , acid rain simulating solution and (a) 0 wt.% fly ash ; (b) 20 wt.% fly ash; insets: EDX maps for Ca, O and Si.

Fig. 7. SEM cross-sectional micrographs of 316L rebars embedded in concrete with (a) 20 wt.% FA, (b) 25 wt.% FA, after 4 m of salt spraying.

However, on a high magnification (Figure 8), pits can be seen in the steel embedded in the 25% FA concrete (extremely scarcely though) containing Cl - . The detection of S in the pits associates the pits with high amounts of FA. As aforementioned, agglomerates of FA don’t interact in a pozzolanic way with Ca(OH) 2 , as a consequence of their low specific surface area. Therefore, a uniform film is not formed on the surface of the steel. Instead, deposits of the agglomerates are locally formed on the surface of the steel, causing deposit corrosion below the agglomerates.

Fig. 8. (a) Cross-sectional micrograph of 316L rebar embedded in concrete cube containing 25 wt.% fly ash, after 4 m of salt spraying, showing pitting; (b) EDX mapping for Ca and Cl; (d) Point EDX in a pit.