Issue 50

A.G. Lekatou et alii, Frattura ed Integrità Strutturale, 50 (2019) 423-437; DOI: 10.3221/IGF-ESIS.50.36 429 Figure 2 : Comparison of the polarization behaviors (forward scans) of 304L rebars in two electrolytes (an acidic one and an alkaline one) containing Ca(OH) 2 , acid rain simulating solution and fly ash at different contents. Figure 3: Comparison of the polarization behaviors (forward scans) of 316L and 304L rebars in an electrolyte containing Ca(OH) 2 , acid rain simulating solution and fly ash at different contents. 304L rebars as compared to the 316L rebars is mainly attributed to the absence of Mo and the higher content of S. Mo in- creases the pitting corrosion resistance in chloride containing solutions, whilst sulfur (as sulfides) promotes stress corrosion cracking and pitting [44]. The relative electrochemical trends of both steels, as far as the FA content of the solution is concerned, are similar: Increasing FA contents lead to slower corrosion kinetics. This trend is reversed at 25 wt.% FA. The most interesting observation though, is that even 10 wt.% or 15 wt.% replacement of Ca(OH) 2 with FA has led to notably slower corrosion kinetics of 304L as compared to 316L in Ca(OH) 2 solution free of FA. Hence, the potential of using the relatively inexpensive 304L (as compared to 316L) in the restoration of ancient monuments, provided that fly ash is employed as a corrosion inhibitor, is herein indicated. Microstructure of corroded rebars This section attempts to elucidate the deterioration of the electrochemical behavior of the 304L rebars at the 25 wt.% FA (case of acidic electrolyte). To start with, Fig.4 illustrates micrographs of rebars after cyclic polarization in the acidic electro- lyte, at relatively low magnifications. A fine surface state has been maintained, in all cases of FA contents. -2000 -1500 -1000 -500 0 500 1000 1500 2000 0.000001 0.00001 0.0001 0.001 0.01 0.1 1 10 Potential (mV, Ag/AgCl) Current density (mA/cm 2 ) 304L, Ca(OH) 2 + fly ash + acid rain 0% FA-low pH 0% FA-high pH 10% FA-low pH 10% FA-high pH 15% FA-low pH 15% FA-high pH 20% FA-low pH 20% FA-high pH 25% FA-low pH 25% FA-high pH