Electrochemical Diagnostics of Sprayed Fiber-Reinforced Concrete Corrosion
Round 1
Reviewer 1 Report
The paper is well written. Consideration of the following comments and suggestions will improve the comprehension of the presented material.
Review comments
· The authors should write in the introduction the purpose of this research clearly.
· In line 149 “…shrinkage measured after min. 90 days…”. The authors should replace the abbreviation min. with the whole word.
· The authors should explain the meanings of Est, Θ, icor of table 2.
· Minor English mistake on lines 312-313 “….reduced shrinkage and provides earlier…”. The authors should use the same tense.
· In Figure 13 the x-labels are not easily visible. The authors should increase the font and make them clearer.
Author Response
Response to Reviewer 1 Comments
The authors thank you for all comments and remarks that helped us to improve the manuscript.
The changes are marked in red in the text.
Point 1: The authors should write in the introduction the purpose of this research clearly.
Response 1: The aim of the research has been described more clearly in the introduction. (lines 87-90)
Point 2: In line 149 “…shrinkage measured after min. 90 days…”. The authors should replace the abbreviation min. with the whole word.
Response 2: The whole word “minimum” replaced the abbreviation “min.”. (line 153)
Point 3: The authors should explain the meanings of Est, Θ, icor of table 2.
Response 3: The meanings of the reinforcement stationary potential (Est), the resistivity of the concrete cover (Θ) and the corrosion current density (icor) have been explained. (lines 167-175)
Point 4: Minor English mistake on lines 312-313 “….reduced shrinkage and provides earlier…”. The authors should use the same tense.
Response 4: The above sentence has been improved. (line 336)
Point 5: In Figure 13 the x-labels are not easily visible. The authors should increase the font and make them clearer.
Response 5: The labels in the Figure 13 have been increased. (line 311)
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Paper titled ‘Electrochemical diagnostic of Sprayed fiber-reinforced concrete corrosion’ by W. Raczkiewicz and P. Kossakowski
The paper evaluates the effect of sprayed fiber concrete on the corrosion of the main reinforcement in concrete structures and whether it leads to increase of corrosion of the main bars. While this is a good topic to research given the different opinions on the effect sprayed FRC on corrosion, there are few questions that I would like the authors to respond and comment on related to their study
Specific comments:
1. The study was limited to specimens with long fibers (lw = 60 mm or l/d = 60). Could using shorter fibers (lw = 30 mm or l/d= 30) or other fibers with different aspect ratios-which will have larger distribution, different orientation, and different microstructure lead to different results? Can the authors comment on that? I believe this is an important parameter.
2. The specimen size is small. Is this size adequate to validate the results? Could there be size effects if larger specimens were tested.
3. Did the specimen have transverse bars (like bar grid)? If only bars in one direction were used, I wonder if having both long and transverse bars would have made a difference in the reported results?
4. Are the criteria in Table 2 on page 6 for assessing reinforcement corrosion accurate criteria for assessing corrosion risk levels? How do they compare with other criteria?
5. Is the thickness of the specimen 50 mm? Please indicate the thickness.
6. Can the authors include a photo of the test similar to the sketch given in Fig. 5?
7. The resistivity values are very low and as the authors indicated are not reliable. It would have good to have good results from the resistivity tests to relate them to corrosion risk. Did the authors tried to do more tests to get good results from concrete resistivity?
8. In Conclusion No (4), the authors conclude that the scanning results show no corrosion in the steel fibers. It will good to show a sketch showing how the NaCl solution was applied. Were the sprayed fiber concrete layer exposed to the NaCl solution? If it was, one would expect some corrosion of the steel fibers. Could the authors clarify?
9. What suggestions or recommendations the author have for addition studies related to this topic?
Author Response
Response to Reviewer 2 Comments
The authors thank you for all the comments that helped us to improve the manuscript, as well as to better plan our research in the future.
The changes are marked in red in the text.
Point 1: The study was limited to specimens with long fibers (lw = 60 mm or l/d = 60). Could using shorter fibers (lw = 30 mm or l/d= 30) or other fibers with different aspect ratios-which will have larger distribution, different orientation, and different microstructure lead to different results? Can the authors comment on that? I believe this is an important parameter.
Response 1: The Reviewer rightly noted that the study was limited to the specimens with only one type of fibers in the amount of 1 % vol. of the mixture. It is likely that the use of another type of fibers and / or other amount of fibers will affect the results. For this reason, final conclusions apply only results obtained from tests of SFRC specimens with 1% fiber addition. (lines 344-347)
This issue is worth further research. (lines 346-347).
The authors chose this type of fibers because they are widely used fibers; in addition, longer fibers seemed more exposed to corrosion. The content of fibers in the mixture (1%) resulted from their efficiency as well as the workability of the mixture and its use as a spraying concrete. (lines 208-210)
Point 2: The specimen size is small. Is this size adequate to validate the results? Could there be size effects if larger specimens were tested.
Response 2: The size of the specimens is not large, however, according to the authors, it seems sufficient to carry out this type of research. The layer thickness of the shotcrete used is usually 25-30 mm (sometimes more, e.g. 120 mm). The 100 mm thick specimen and the 25 mm concrete cover meet these assumptions. The specimen surface dimensions (210 x 228 mm) and fiber length lw = 60 mm (assuming a uniform application of the concrete mix) also seem sufficient to obtain reliable results. Nevertheless, the Reviewer's question is interesting and worth researching in terms of scale effect.
Point 3: Did the specimen have transverse bars (like bar grid)? If only bars in one direction were used, I wonder if having both long and transverse bars would have made a difference in the reported results?
Response 3: There were no transverse bars in the specimens (line 215).
In real reinforced concrete structures there are generally longitudinal and transverse rods.
However, the construction of the apparatus and existence of the so-called guard ring in the measuring electrode allows (according to its creators) to make reliable measurements of a given reinforcement section. The author tested the reinforced concrete slab (with reinforcement arranged in two directions), and the results seemed reliable - adequate to the results of testing samples of material taken from the element. Although, it is worth to perform two types of specimens: specimens with reinforcement in two directions and specimens with longitudinal reinforcement only and compare the results.
Point 4: Are the criteria in Table 2 on page 6 for assessing reinforcement corrosion accurate criteria for assessing corrosion risk levels? How do they compare with other criteria?
Response 4: The criteria given in Table 2 allow (with a certain probability) to indicate the areas where the reinforcement is likely to corrode and estimate its rate in time. (lines 167-175)
It should be noted that other corrosion measuring devices have a different reference scale and the results can’t be directly compared. (lines 182-184)
Point 5: Is the thickness of the specimen 50 mm? Please indicate the thickness.
Response 5: The thickness of the specimens was 100 mm. (line 213)
Point 6: Can the authors include a photo of the test similar to the sketch given in Fig. 5?
Response 6: The photo has been included. (line 185)
Point 7: The resistivity values are very low and as the authors indicated are not reliable. It would have good to have good results from the resistivity tests to relate them to corrosion risk. Did the authors tried to do more tests to get good results from concrete resistivity?
Response 7: All measurements of concrete cover resistivity, which the authors made on young specimens using galvanostatic pulse method, gave similar results (it was described, among others, in [19,25,29]). This is probably due to the fact that the specimens were still fresh and the hardening process probably did not end. (lines 279-280)
Currently, the authors are working on this issue.
At the same time, it should be added that in-situ studies of decades-old elements (reinforced concrete ramp, columns, pillars) gave reliable results - adequate to the age of the elements, environment conditions and degree of the concrete cover damage [40].
Point 8: In Conclusion No (4), the authors conclude that the scanning results show no corrosion in the steel fibers. It will good to show a sketch showing how the NaCl solution was applied. Were the sprayed fiber concrete layer exposed to the NaCl solution? If it was, one would expect some corrosion of the steel fibers. Could the authors clarify?
Response 8: The sketch showing how the NaCl solution was used would be very useful, but if the Reviewer does not mind, the authors will try to describe it.
The specimens were immersed in the NaCl solution so that the chloride ions could penetrate into the concrete cover in the direction of reinforcement, which was supposed to simulate the processes taking place in reality. (lines 220-222)
Of course, on the surface of the specimens corrosion products appeared around several of the fibers fragments found there. However, the analysed sample was taken from a depth of about 20-25 mm (near the reinforcing bar) and no corrosion products were found at this point, which may suggest that chloride ions have not penetrated into this place. (lines 303-310; 342-343)
Point 9: What suggestions or recommendations the author have for addition studies related to this topic?
Response 9: In reference to the Reviewer's suggestions, it is worth performing similar tests with a different type of fibers and / or a different amount of fibers. (lines 344-347).
It is also worth examining the effect of the scale, i.e. determine the size of specimens on the obtained results. These problems are particularly important also in the context of the production of industrial floors, where the impact of the aggressive environment is very significant. The authors are also investigating this issue.
On the other hand, it is also important to recognize the measurement capabilities of the GalvaPulse apparatus depending on the age of the tested sample, the distribution of reinforcement or environmental conditions. This is also the subject of the authors' research.
Author Response File: Author Response.pdf
