Influence of Partial Rust Layer on the Passivation and Chloride-Induced Corrosion of Q235b Steel in the Carbonated Simulated Concrete Pore Solution
, Yunze Xu 1 and Yi Huang 1,*
Round 1
Reviewer 1 Report
Abstract:
L16-17 “The results 16 show that the passive film generated on the pre-rusted steel area is more fragile than that formed on the fine polished steel area”, add “in carbonaceous media”
L 18-19 Nevertheless, the pitting corrosion resulting from the presence of Cl- or provoked by Cl- (should be added) still prefers to occur on the fine 18 polished steel surface due to the local acidification process that was hindered by the rust layer.
Introduction
L41-42 “However, few studies considered the role of surface states on rebar depassivation”. Add more references coming from R. Rodrigues, S. Gaboreau, J. Gance, I. Ignatiadis, S. Betelu, Reinforced concrete structures: A review of corrosion mechanisms and advances in electrical methods for corrosion monitoring, Constr. Build. Mater., DOI https://doi.org/10.1016/j.conbuildmat.2020.121240(2020) 121240”.
“The role of mill scale and native rust layer on the corrosion resistance of steel in still unclear [67–69]. Some studies indicate that it does not affect the corrosion rate or may have a beneficial effect due to the protective behaviour of the layer in the case of a dense and uniform mill scale [70,71], but most studies affirm that it has a negative effect on the corrosion rate as it inhibits the development of an effective passive layer on the rebar or decreases its electrical resistance [72–77]. It was also shown that the corrosion rate is greater for rebars exposed to natural weathering (pre-rusted rebars) than for the as-received rebars [78]. The initial surface state of the rebar and the distribution of native rust are thus major parameters controlling the corrosion susceptibility, and a non-uniform mill scale layer can create weak points for corrosion initiation [79,80]. Hence, as for cement-based materials, a detailed description of the rebar grade, composition, microstructure and initial surface condition is necessary for a correct interpretation of the data and the development of database for the assessment of corrosion mechanisms. exposed to atmospheric conditions must be investigated to determine the corrosion susceptibility in concrete”.
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[76] J.A. González, E. Ramírez, A. Bautista, S. Feliu, The behaviour of pre-rusted steel in concrete, Cem. Concr. Res. 26 (1996) 501–511. https://doi.org/10.1016/S0008-8846(96)85037-X.
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[78] M.J. Martinez-Echevarria, M. Lopez-Alonso, D. Cantero Romero, J. Rodríguez Montero, Influence of the previous state of corrosion of rebars in predicting the service life of reinforced concrete structures, Constr. Build. Mater. 188 (2018) 915–923. https://doi.org/10.1016/j.conbuildmat.2018.08.173.OK
[79] L. Michel, U. Angst, Towards understanding corrosion initiation in concrete – Influence of local electrochemical properties of reinforcing steel, MATEC Web Conf. 199 (2018) 04001. https://doi.org/10.1051/matecconf/201819904001.
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Materials
L96-97 “The dimensions of each electrode were machined as 2× 2 × 10 mm” Remove microelectrode from the text and replace by electrodes or milli-electrodes.
Provide dimensions in figure 2
Results
Figure 4 shows the surface morphology of two pre-rusted coupons after the introduction of chloride ions into the carbonated SCPS for (a) t = 0 h, (b) t = 6 h, (c) t = 12 h, (d) t = 24 h, (e) t = 48 h; i.e. fig 4 (a) shows the surface morphology of the electrode just after step 2. The reader do not have any information of the surface morphology before step 1 neither after step 1. Thus, sentence L160-162 “It is seen from Figure 4 that the steel surfaces show no obvious changes after 24 h of immersion in the carbonated SCPS of pH 10, indicating only the carbonation of the pore solution would not induce corrosion on a fine passivated steel” can not be verified. Authors have to remove it or to show more coupon morphologies, at least after step 1.
L173: Authors should also describe the “surface cleaning” observed at the center of the coupons after 24 hours into carbonated SCPS + 0.5M of NaCl. They should further link this behavior with the role of the rust layer which behaves as cathode into SCPS + 0.5M of NaCl.
Figure 5C. Provide the scale of the Local 3D morphology, between 0 and 80.
Table 1: Please give all the c2. Plase also calculate Yon and discuss the result if possible.
Explain why a value of Rf > 100 kΩ·cm2 allows suggesting that the pre-rusted steel could keep a passive state. Insert some references. Isn’t a value of 10 kΩ·cm2 enough to suggest such a behavior?
What is more, L241, 242: “It is seen that all the selected microelectrodes have a large Rf which is higher than 100 kΩ·cm2”. This sentence is not thue for W5,1 (Pr) and W7,8 (Pr). For pre-rusted electrodes, this sentence is only true for W7,4. “It suggests that the pre-rusted steel could keep a passive state in carbonated SCPS of pH 10”. This conclusion not thus not true, with regards of what is written before which should be reformulated. Moreover, this conclusion could be done if authors measured, analyzed and compared Rf before Step 1, before Step 2 et after Step 2 (the later is done) and verified that Rf in the same order of magnitude.
Explain why a value of 700 ≤ Rf ≤ 900 kΩ·cm2 allows suggesting that the pre-rusted layer could also inhibit the corrosion process. Add references.
Author should take care because L248: “The Rr of the PR-wires is quite high ranging from 700~900 kΩ·cm2 which means the rust layer could also inhibit the corrosion process. This sentence is wrong. From table 1, it ranges from 258 to 719 kΩ·cm2. The conclusion is thus not true with regards of the written text. Isn’t a value of 10 kΩ·cm2 enough to suggest such a behavior?
L245-248: The Qf-n of the FP-wires maintained at 0.95 which suggests that the passive film on the FP-wires is relatively uniform. However, the Qf -n of PR-wires is lower than 0.9 which means the passive film formed beneath the rust layer is homogeneous. What is for the authors the difference between uniform and homogeneous? Is it a synonym for the author? If yes, because 0.9 ~0.95, why do the authors use the word “However” between the two sentences. If not, because the authors use the word “However” between the two sentences, would the author clearly explain the difference between uniform and homogeneous. Does the authors mean that the passive film of the PR-wires is relatively homogeneous but with some more defects within the crystalline structure because of the decrease in n from 0.95 to 0.9?
Could the authors discuss the values provided by Yon ?
L250-252 “Overall, these EIS results reveal that passive film formed on the surface of pre-rusted steel is less stable and protective, which is possibly induced by the decrease of passive film thickness and the increased defects in the passive film”. How does EIS results reveal that passive film formed on the surface of pre-rusted steel is less stable? Would the authors explain it? The word “stable” better agrees with data provided by Fig 6-b.
The comparison of EIS data before Step 1, before Step 2 et after Step 2 could reinforce the sentence “which is possibly induced by the decrease of passive film thickness and the increased defects in the passive film”. The determination of Yon should also help the authors : Yon of the passive film increases from [3.1-3.4] to [6.9-12.5] 10-5×Ω-1·cm-2·sn (to be transformed in µF). The increase of the capacitance could be in agreement with the decrease of coating thickness.
Figure 9 (b): Indicate the x axis title.
L 283-287 : “Small K values of the three fine polished microelectrodes, indicate the uniform dissolution of the passive film”. Please, insert reference(s) – Please provide the K values. This sentence is true in the range from 10-3 to < 10-1 Hz. In the range from 10-1 to 100 Hz, higher K values are observed for the three fine polished microelectrodes. Would the authors interpret such a phenomenon?
While larger K values of the three pre-rusted microelectrodes indicate that the passive film formed beneath the pre-rusted area would undergo a local rupture process besides the uniform dissolution. Use “higher” than “larger”, no? This is right in the range from 10-3 to < 10-1 Hz, no?
What does bibliography tells about K values? Are there any ranges, in K values and/or in Hz values to affirm such processes? Because in the range from 10-1 to 100, higher K values are observed for the three fine polished microelectrodes? Is there another process? In that in agreement with the reparation of the weakened passive film?
L302-305 “It is worth noted that the main cathodes are distributed in the pre-rusted region, while the cathode current in the fine polished region is negligible. It could be inferred that the rust layer would promote the cathode reaction, indicating that the rust layer might take part in the cathodic reduction as reducer’. “As reducer ?” Do authors mean that the rust layer oxidizes while O2 reduces? That is not in agreement with the schematic Fig. 11. If yes, authors should refers to a “virtual” diffusion of Fe2+ that can still occur across this layer through electron transfer in the Fe(III) layer, i.e. sorption of one Fe2+ on one side and release of another Fe2+ on the other side, as proposed for Fe diffusion at the steel-bentonite interface. J. Hadi, P. Wersin, V. Serneels, J.-M. Greneche, Eighteen years of steel–bentonite interaction in the FEBEX in situ test at the Grimsel Test Site in Switzerland, Clays Clay Miner. 67 (2019) 111–131. https://doi.org/10.1007/s42860-019-00012-5. Authors should thus introce it into the schematic Fig. 11 and O2 should be reduced at the top of the layer.
L321-322 “It is clearly seen from the test results that the surface morphologies of the corrosion coupons and WBE are similar in carbonated SCPS without Cl-“. That is not demonstrated. What is demonstrated is: It is clearly seen from the test results that the surface morphologies of the corrosion coupons and WBE are similar in carbonated SCPS in the presence of Cl-“; i.e. A similar surface morphologies behavior is observed for the corrosion coupons and WBE in carbonated SCPS in the presence of Cl-.
L 322 “The cathode sites and the anode sites are randomly distributed in the pre-rusted region” , right, but add in the absence of Cl-.
L326 : “With the increase of immersion time, the pitting area continued to expand”, in the region FP region (to be assed), step by step, just next to the first oxidized region (to be added, to be reformulated probably), and there are no new pits formed in other areas of the specimen.
L 328 : “and the pitting damage only could expand on the fine polished area”. I am not sure about that because W 4,1, W4,2 and W7,1 areas become anodes. Authors should discuss it.
L330: Many researchers consider that the protectiveness of the passive film and its initial 330 breakdown are the critical factors of pitting corrosion[33]. Many researchers??? and only one reference. Add more references please !!
L 348-349: “the OH- directly in the reaction process”. The verb is missing
Comments for author File: 
Comments.pdf
Author Response
We would like to express our great appreciation to you for your helpful comments and suggestions. We have now gone through all your comments point by point and modified the manuscript accordingly. Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
The manuscript presents interesting experimental research, however, some remarks arise.
1. The tests did not reproduce the conditions of contact of steel reinforcing bars with the liquid filling the pores of the concrete, which are close to reality. In fact, the side surface of ribbed rebar has a very complex shape. There are numerous crossing ribs, on which a rapid change of shape or kinks can additionally be a potential place of activation of corrosive processes. The research on small, flat lamellae is quite a simplification of the experiment.
2. Discussing the problem of the influence of polishing the surface of sheets in terms of corrosion development is not substantively justified in the context of steel reinforcing bars in concrete. It should be strongly emphasized that the polishing of the surface of reinforcing steel is never used in practice. At the construction site, during concreting, uncleaned reinforcing bars with slight corrosion raids are placed.
3. All the alkali components of cement, such as sodium, calcium and potassium, dissolve in the concrete pore liquid. There are numerous examples in the literature of the composition of the synthetic concrete pore liquid, which contains all three of the above-mentioned elements. Why in the experimental studies it was not decided to more accurately reproduce the pore liquid of concrete? It was also possible to use crushed concrete mixed with distilled water.
4. Corroded rods in concrete are mentioned in the introduction to the manuscript. However, it was not specified how the corrosion products affect the adhesion of reinforcing steel to concrete, which is key in the operation of reinforced concrete. This should be completed.
5. The conclusions should show a slightly broader perspective on the problem of steel corrosion in the pore liquid of concrete. Narrowing this problem down to local effects on small sheet fragments simulating steel reinforcing bars is insufficient.
6. In many figures, the markings (a), (b) are abnormally large and this should be corrected.
Author Response
We would like to express our great appreciation to you for your helpful comments and suggestions. We have now gone through all your comments point by point and modified the manuscript accordingly. Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
The present manuscript discusses the effect of partial rust on the passivation and the evolution of corrosion by Cl on steel rebars. The paper is well structured, and overall easy to understand. The results are adequate and the conclusions well supported. I only have two remarks on the technical and scientific side.
The first, why was the coverage of half of the electrodes of the WBE not carried out? In each of the zones, one of the reactions, anodic or cathodic, prevails, so if one of the areas is reduced, one of the processes can be favored.
For the same reason, why were the corroded and polished areas not distributed symmetrically?
To prevent an unequal distribution of potential from affecting the result, the most appropriate would be a symmetrical distribution of the corroded and polished areas, and not placing one of them in the center
Another question is related to the cleaning of the samples after being covered with silicone.
Normally, before electrochemical tests are carried out, the samples are washed and degreased using solvents such as alcohol or acetone in an ultrasound bath to eliminate any organic residue that may affect the measurements.
The text indicates that it was removed mechanically with a plastic knife. I understand that the use of a solvent can be adsorbed in the corroded area, but how has the correct removal of the silicone from the polished areas been verified? If organic substances remain on the surface, the growth of the passive layer may be slowed down, affecting the results obtained.
Author Response
We would like to express our great appreciation to you for your helpful comments and suggestions. We have now gone through all your comments point by point and modified the manuscript accordingly. Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
The article contains some mistakes that should be removed:
- - Figure 1.: Error in marking of the images in the description of Figure 1.
- - Page 5, line 160: The sentence “It is seen from Figure 4 that the 160 steel surfaces show…” should be “It is seen from Figure 4a that the 160 steel surfaces show…”.
- - Figure 4.: should be “Pit propagation”
- - Figure 5.: The designation in description (d, e) does not correspond to the designation in figure (b, c). Moreover, it is not clear which cases from Figure 4 are "(a)" and "(b)" in Figure 5.
- - Page 8, line 241: “It is seen that all the selected microelectrodes have a large Rf which is higher than 100 kΩ·cm2.” This statement does not correspondent with Rf values in Table 1.
- - Chapt. 5: The first conclusion is too brief and it does not capture the obtained results related to the passivation behavior of WBE in carbonated SCPS.
Author Response
We would like to express our great appreciation to you for your helpful comments and suggestions. We have now gone through all your comments point by point and modified the manuscript accordingly. Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 4 Report
The article was corrected. I recommend to accept it in present form.
