Study on Frost Resistance of the Carbon-Fiber-Reinforced Concrete
Round 1
Reviewer 1 Report
The reviewed work is an experimental research report. The use of carbon fibers in research is nothing new, nor is it innovative. The effects of using both metallic and non-metallic fibers in concrete mixtures have been well known for many years. The results presented are simply the result of tests carried out on a specific sample population. Nevertheless, the authors' special care and concern for the precision of the research and a detailed analysis of the results deserves attention. In the final version of the work, it is necessary to: 1) explain the practical purpose of the research, 2) indicate what the actual situation corresponds to the simulated tests, 3) whether the elements in which this type of distributed reinforcement would in fact be used, will not be exposed to solar radiation, and if so why in the simulation tests of aging processes no UV radiation was used, 4) explain why such a large number of frost resistance cycles (up to 300 cycles) were carried out, when usually up to 50 cycles are performed during material tests. Ultimately, it is necessary to apply ISE, whether similar tests should not be carried out for concrete operating in difficult operating conditions, i.e. for oily concrete (equivalent to construction elements in an industrial plant - laboratory simulation by soaking in oil), for chemically contaminated concrete (equivalent to construction elements in a sewage treatment plant - laboratory simulation by soaking in artificial urea), for biologically contaminated concrete (equivalent to construction elements in a farm - laboratory simulation by soaking in diluted horse / cow / pig faeces). In addition, consideration should be given to the possibility of numerical simulation of the aging processes of carbon fiber concrete
Author Response
Thanks to the editors and reviewers for their constructive comments. We have revised the article according to the comments. The detailed amendments and replies are as follows:
1) explain the practical purpose of the research.
Reply: This paper provides a scientific reference for improving the frost resistance of concrete under cold conditions. And we add this sentence to the revision.
2) indicate what the actual situation corresponds to the simulated tests,
Reply: To simulate cold and wet situations, this research was carried out. And we add this point in the proper placement.
3) whether the elements in which this type of distributed reinforcement would in fact be used, will not be exposed to solar radiation, and if so why in the simulation tests of aging processes no UV radiation was used.
Reply: As said in the question 2, in the cold and wet situations, the freeze-thaw damage is prior to aging damage, so freeze-thaw cycles were used rather than UV radiation.
4) explain why such a large number of frost resistance cycles (up to 300 cycles) were carried out, when usually up to 50 cycles are performed during material tests.
Reply: For the general case, 50 cycles is sufficient. For those repeated freeze-thaw situations, more freeze-thaw cycles should be considered.
5) Ultimately, it is necessary to apply ISE, whether similar tests should not be carried out for concrete operating in difficult operating conditions, i.e. for oily concrete (equivalent to construction elements in an industrial plant - laboratory simulation by soaking in oil), for chemically contaminated concrete (equivalent to construction elements in a sewage treatment plant - laboratory simulation by soaking in artificial urea), for biologically contaminated concrete (equivalent to construction elements in a farm - laboratory simulation by soaking in diluted horse / cow / pig faeces). In addition, consideration should be given to the possibility of numerical simulation of the aging processes of carbon fiber concrete.
Reply: The reviewer gave a very perfect suggestion, but these simulations cannot be realized in a short time. At the same time, the most important factor of freezing and thawing damage is number of times of freeze-thaw cycles. These effects on concrete resistance are secondary. Therefore, at present, we cannot carry out these experiments and simulations. Thank you again for your valuable comments.
Reviewer 2 Report
Manuscript ID: applsci-1629292
Title: Study on Frost Resistance of the Carbon-Fiber–Reinforced Concrete
In the introductory part, a very limited review of publications related to the topic of the paper is presented.
The conducted experiment presents a minimum set of tests of concrete mix and concrete - consistency, compressive strength, frost resistance after a variable number of freeze-thaw cycles. The concrete mixes use a variable amount of carbon fibers. The use of this type of micro-reinforcement is not new - there are many publications on carbon fiber reinforced concrete.
There is no microstructure analysis in the paper - for example SEM. I propose to supplement the paper with this type of research. If this happens, the assessment of the behavior of concretes with carbon fibers in the frost resistance test will be more reliable. In the present situation, the presented analysis regarding the freeze-thaw resistance of the analyzed concretes is rather an assumption.
In my opinion, the paper is not of good quality. It needs to be redrafted and supplemented with microstructural studies.
Figures 2, 3 and 4 are not useful in the paper.
Comments for author File: 
Comments.pdf
Author Response
1) the introductory part, a very limited review of publications related to the topic of the paper is presented.
Reply: We improve the introduction of the revision and we also seek help from our colleague.
2) the conducted experiment presents a minimum set of tests of concrete mix and concrete - consistency, compressive strength, frost resistance after a variable number of freeze-thaw cycles. The concrete mixes use a variable amount of carbon fibers. The use of this type of micro-reinforcement is not new - there are many publications on carbon fiber reinforced concrete.
Reply: Because there's been a lot of research on mechanical properties of carbon fiber-reinforced concrete except frost resistance, it's important to find out the frost resistance of that.
3) There is no microstructure analysis in the paper - for example SEM. I propose to supplement the paper with this type of research. If this happens, the assessment of the behavior of concretes with carbon fibers in the frost resistance test will be more reliable. In the present situation, the presented analysis regarding the freeze-thaw resistance of the analyzed concretes is rather an assumption.
Reply: I would like to carry out the microstructure analysis, but it is difficult to conduct this test due to limited time. Honestly, I had intended to do this test, but the COVID-19 pandemic seriously hampered my plan, even my graduation. In the further, I will continue to do this test at convenient time.
4) In my opinion, the paper is not of good quality. It needs to be redrafted and supplemented with microstructural studies.
Reply: We are very sorry for that. The reviewer gave us a lot of useful suggestion, which are very helpful. In this revision, we rewrite some part to improve the quality of the paper.
5) Figures 2, 3 and 4 are not useful in the paper.
Reply: The Figure 2 is adjusted. The Figure 3 is deleted. The Figure 4 could visually display the data, so it was retained.
Reviewer 3 Report
Dear Authors,
thank you very much for the opportunity to review.
The topic of frost resistance of carbon reinforced concrete is quite recent and deserves research.
Manusrcipt presents a material study with the results of 6 concretes with increasing amounts of carbon fiber from 0 to 0.2%. This range and amount is certainly encouraging and commendable.
Individual sections:
Title in order.
The abstract is very technical and full of clear information, but is completely uninteresting and tells the reader nothing.
You have to find a balance between a good abstract and a technical one.
The introductory chapter contains a lot of general facts without citations, but this is not appropriate in technical literature. You need to clearly define the reasons and objectives of the general research composite right at the beginning, as it does not justify your research. For inspiration and citations, see for example:
10.3151/jact.19.771
10.1617/s11527-020-01535-3
Similarly, general information on fibre concrete is insufficient and further literature needs to be added in terms of the durability of these materials:
10.1016/j.cscm.2022.e00939
10.3390/math10020229
I can conclude that there really are not many studies with your topic and therefore it is worthy of interest.
The description of the material is concise and clear.
In general please make the pictures bigger.
Have you discussed the effect of HRWR and DA on frost hardiness results?
The description of the concretes is clear. Preparation of sample quantities is understandable and meets expectations - how did you ensure fibers were dispersed evenly throughout the sample?
Did you perform compressive strength testing on non-frozen samples to nullify the effect of hardening, as compressive strength should increase significantly up to at least 91 days?
Figure 8 is misleading because in Figure 6 we see the differences in strength of the concretes at 0 cycles, so Figure 8 shows the wrong results - how do you explain this discrepancy?
The strength at 0 must be different for each concrete, right?
The conclusions are rather abrupt and brief.
The importance of the study needs to be more emphasised.
Author Response
1) The abstract is very technical and full of clear information, but is completely uninteresting and tells the reader nothing. You have to find a balance between a good abstract and a technical one.
Reply: Thanks to reviewer. The abstract is modified in the revision.
2) The introductory chapter contains a lot of general facts without citations, but this is not appropriate in technical literature. You need to clearly define the reasons and objectives of the general research composite right at the beginning, as it does not justify your research. For inspiration and citations, see for example:10.3151/jact.19.771,10.1617/s11527-020-01535-3 Similarly, general information on fiber concrete is insufficient and further literature needs to be added in terms of the durability of these materials: 10.1016/j.cscm.2022.e00939, 10.3390/math10020229
Reply: Thanks to the reviewer. You give very detailed recommendations and specific references. The references are cited in the revision.
3) Have you discussed the effect of HRWR and DA on frost hardiness results?
Reply: Surely, the HRWR and DA could yield the effect on frost resistance of the concrete. In this paper, the usages of HRWR and DA are fixed, it would not disturb assessing the effect of fiber on concrete. In the further, we would like to carry the research about the effect of HRWR and DA on concrete.
4) How did you ensure fibers were dispersed evenly throughout the sample?
Reply: The carbon fiber, dispersant, and water were mixed and dispersed by the vibration of ultrasonic waves for 5 min to produce a carbon fiber solution.
5) Did you perform compressive strength testing on non-frozen samples to nullify the effect of hardening, as compressive strength should increase significantly up to at least 91 days?
Reply: The test process for the frost resistance of each concrete specimen strictly complied with Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete. This standard does not consider the effect of hardening. Reviewer gives us a very important information, and we will consider this point in the further.
6) Figure 8 is misleading because in Figure 6 we see the differences in strength of the concretes at 0 cycles, so Figure 8 shows the wrong results - how do you explain this discrepancy? The strength at 0 must be different for each concrete, right?
Reply: In order to distinguish Fig. 6 from Fig. 8, Fig. 8 uses the relative compressive strength, that is, the compressive strength under freeze-thaw cycles compared with the initial compressive strength.
7) The importance of the study needs to be more emphasized.
Reply: We emphasized the importance of the study in the revision.
Round 2
Reviewer 2 Report
To the Authors
Thank you for taking into account the amendments indicated. This improved the quality of the paper.
I wish you continued success in your scientific work.
Author Response
Thank you for taking into account the amendments indicated. This improved the quality of the paper. I wish you continued success in your scientific work.
Reply: We are truly grateful to you. Your suggestion not only improves the quality of the article, but also gives inspiration to our future work.
Reviewer 3 Report
Dear Authors,
You've made some changes, but not all of them are as recommended in the first review. Respectively, I see in the text that you have not modified everything as you write in your replies to the reviewers.
Please check in depth point no.
and implement all recommendations in the article.
Then I recommend the article for publication.
Author Response
Reviewer two: You've made some changes, but not all of them are as recommended in the first review. Respectively, I see in the text that you have not modified everything as you write in your replies to the reviewers.
Reply: Thank you again for your valuable comments. The reviewer gives us several professional and profound suggestions. We make responses to all of these suggestions, but we must confess that some replies are superficial and inadequate. Thank the reviewer for giving us another chance to improve the quality of the article. We have carefully revised the article, and it is necessary to provide supplementary answers to some suggestions.
The original question 1) The abstract is very technical and full of clear information, but is completely uninteresting and tells the reader nothing. You have to find a balance between a good abstract and a technical one.
Reply: Thanks to reviewer. The abstract is modified in the revision. It was totally rewritten. Please see the revision.
The original question 2) The introductory chapter contains a lot of general facts without citations, but this is not appropriate in technical literature. You need to clearly define the reasons and objectives of the general research composite right at the beginning, as it does not justify your research. For inspiration and citations, see for example:10.3151/jact.19.771, 10.1617/s11527-020-01535-3 Similarly, general information on fiber concrete is insufficient and further literature needs to be added in terms of the durability of these materials: 10.1016/j.cscm.2022.e00939, 10.3390/math10020229
Reply: Thanks to the reviewer. You give very detailed recommendations and specific references. The references are cited in the revision. And this part was largely changed on the comments.
The original question 7) The importance of the study needs to be more emphasized.
Reply: We emphasized the importance of the study in the revision.
The others please see Round 1.
Thank the reviewer again for your constructive and insightful suggestions.
