Evaluation of the Surface Performance of Mortar Matrix Subjected to Sodium Chloride Solution Modified with Hybrid Nanosilica Cement Paste

Round 1

Reviewer 1 Report

This paper focused on producing a cement paste modified by hybrid nanosilica (HMS) and investigated its properties to serve as a kind of surface treatment material. The manuscript is well written and organized, and we suggested it to be accepted for publication after some minor revisions. The review comments are as follows:

1.      Line 34, CO2 should be CO₂, Line 94, “mass ratio was1:3” should be “was 1:3” Line 99, 20mm should be 20 mm, Line 100, 1day should be 1 day, line 103, 14 days should be 14 days, etc. There are some other grammar and spelling errors, go through the manuscript and check it.

2.      Line 46-48, the sentence needs to be rewritten, Line 55-57, the sentence needs to be rewritten.

3.      Line 58-64, the abstract part needs to be polished up.

4.      Line 91 and 95, two water to cement ratios, 0.35 and 0.53, explain it

5.      Line 194, which is BK2?

6.      Line 197-198, have the authors done any examination of the pore structure using like MIP, or SEM? To support your findings? 

7.      Line 205-206, explain why only present the results of all samples subjected to 1mol/L NaCl solution, how about 0.5mol/L NaCl solution?

8.      Line 280-290, there some written errors on the chemical formula, check and revise it. 

9.      Line 267-308, in experiments, the nano SiO₂ was applied and why in thermodynamic modeling, the SiO₂ rather than nano SiO₂ was applied, explain it.

 

Author Response

This paper focused on producing a cement paste modified by hybrid nanosilica (HMS) and investigated its properties to serve as a kind of surface treatment material. The manuscript is well written and organized, and we suggested it to be accepted for publication after some minor revisions. The review comments are as follows: 1. Line 34, CO2 should be CO2, Line 94, “mass ratio was1:3” should be “was 1:3” Line 99, 20mm should be 20 mm, Line 100, 1day should be 1 day, line 103, 14 days should be 14 days, etc. There are some other grammar and spelling errors, go through the manuscript and check it. Response: Thank you for your comments! According to your comments, we went through the manuscript and revised the manuscript. See the revised manuscript. 2. Line 46-48, the sentence needs to be rewritten, Line 55-57, the sentence needs to be rewritten. Response: Thank you for your comments! We revised the manuscript according to your comments. See the revised manuscript. 3. Line 58-64, the abstract part needs to be polished up. Response: Thank you for your comment! The abstract part has been revised. See the revised manuscript. 4. Line 91 and 95, two water to cement ratios, 0.35 and 0.53, explain it Response: Thank you for your comment! The 0.35 was the water to cement ratio for the surface treatment materials (HSM) and 0.53 was the water to cement ratio for the matrix materials. They are different. 5. Line 194, which is BK2? Response: It is a mistake. We are sorry for making this mistake and we have revised it in the revised manuscript. See the revised manuscript. 6. Line 197-198, have the authors done any examination of the pore structure using like MIP, or SEM? To support your findings? Response: Thank you for your comment! We are sorry that we did not perform any pore structure analysis to examine the pore structure of the HSM. It is a common sense that the pore structure can be refined by nano particles and the results of the surface hardness test proved it. Moreover, this manuscript mainly focused on surface performance of the HSM materials. That is the reason we did not perform the pore structure examination. 7. Line 205-206, explain why only present the results of all samples subjected to 1mol/L NaCl solution, how about 0.5mol/L NaCl solution? Response: Thank you for your comment! The surface hardness properties of the HSM subjected to 0.1, 0.5, and 1 mol/L NaCl solution were all presented in the Section 3.1 and they all follow a rough changing trend that the modified samples are all obviously higher than the Ref sample. However, a drop (HSM-BK and HSM-B) was observed for when soaking time prolonged from 7d to 28d. It indicates that new phases may formed within the composites and that’s why we did the XRD test for the samples soaked in the 1 mol/L NaCl solution. We intended to find out the phase changes in the samples. 8. Line 280-290, there some written errors on the chemical formula, check and revise it. Response: Thank you for your comment! We revised the manuscript. See the revised manuscript. 9. Line 267-308, in experiments, the nano SiO2 was applied and why in thermodynamic modeling, the SiO2 rather than nano SiO2 was applied, explain it. Response: Thank you for your comment! Compared with SiO2, the nano SiO2 is with smaller size and higher specific surface area. It was accepted that, the nano SiO2 could have much profound pozzolanic effect, nucleation effect and filling effect.

Reviewer 2 Report

The surface treatment materials in this investigation were hybrid nanosilica modified cement pastes (HMS). Several experiments were conducted to determine the effect of HMS on the chloride resistant ability of the matrix. The paper is interesting and could be published in the Journal of sustainability in the reviewer's view if the following comments and other reviewers, comments to be fulfilled.

 

- Abstract needs to be clarified in a sense to differentiate this study from other published work in this field. The objectives of this work are evidently given in the abstract but the sentence could be modified to give more clarity.

- Abstract: The abstract should be a precise and short summary of the whole manuscript. The authors focused more on few of the (previous mentioned) points. Please improve/rewrite it.

- Please use some innovative keywords.

- The introduction needs to be more emphasized on the research work with a detailed explanation of the whole process considering past, present and future scope. How the present study gives more accurate results than previous studies? It needs to be strengthened in terms of recent research in this area with possible research gaps. It is strongly recommended to add a recent literature. 

- Some of the selected references are quite old, which from the one point of view is good, since the authors cited necessary references to define a research problem, while from the other hand, lack of recent references may indicate an insufficiently performed literature review. Try to refer to some recent and up-to-date research papers related to the topic, especially in recent years like those related to cement:

- Reduction of cement consumption by producing smart green concretes with natural zeolites

- Experimental investigation on the effect of cementitious materials on fresh and mechanical properties of self-consolidating concrete

- Portland cement structure and its major oxides and fineness

- In section 1, after the State of the Art (SoA), the Authors should clarify what are the key novelties of this paper and the main contributions of this work beyond the current SoA. They are barely addressed.

- The novelty of the current work should be highlighted in the introduction.- Please try to mention a problem that needs solving - in other words, the research question underlying your study more clear.

- Please provide a reference for figure 1 (if applicable)

- Could you please explain a little about RCM method?

- Please provide more information for each graph and try to compare your results with related papers.

- Explain figure 6 in more detail. Please do the Rietveld refinement to get the crystallinity of different phases at different samples.

- Compare figures 8 and 9 with each other.

- Did you investigate the chemical effect of NS on HMS?

- Can NS enhance the chloride resistance of cement pastes at the early stage?

- Explain the drop phenomenon in HSM-BK and HSM-B.

- Why do HSM-A and HSM-B have a lower peak than HSM-BK?

- Please compare your results with some papers in the related field and explain the similarity and differences between your results and theirs.

- The discussion of the comparison results may be strongly extended, by providing proper considerations to each plotted graph

Major Comment: The conclusion should be an objective summary of the most important findings in response to the specific research question or hypothesis. A good conclusion states the principle topic, key arguments and counterpoint, and might suggest future research. It is important to understand the methodological robustness of your study design and report your findings accordingly. Please improve your conclusion section.

- Please mention your study limits and suggest some future research topics.

- The authors are advised to write the conclusion in a comprehensive way, it should contain key values, suitability of the applied method, contributions and possible future work. 

- The discussion of the comparison results Section may be strongly extended, by providing proper considerations to each plotted graph

- The "Conclusions" may be provided as a "uniform text", rather than using bullet points. The weaknesses of the work and the future improvements should be added in this section

 

Author Response

The surface treatment materials in this investigation were hybrid nanosilica modified cement pastes (HMS). Several experiments were conducted to determine the effect of HMS on the chloride resistant ability of the matrix. The paper is interesting and could be published in the Journal of sustainability in the reviewer's view if the following comments and other reviewers, comments to be fulfilled.

 

1. Abstract needs to be clarified in a sense to differentiate this study from other published work in this field. The objectives of this work are evidently given in the abstract but the sentence could be modified to give more clarity.

Response: Thank you for your comment! The abstract part has been revised. See the revised manuscript.

 

2. Abstract: The abstract should be a precise and short summary of the whole manuscript. The authors focused more on few of the (previous mentioned) points. Please improve/rewrite it.

Response: Thank you for your comment! The abstract part has been revised. See the revised manuscript.

3. Please use some innovative keywords.

Response: Thank you for your comment! We revised the keywords. See the revised manuscript.

 

4. The introduction needs to be more emphasized on the research work with a detailed explanation of the whole process considering past, present and future scope. How the present study gives more accurate results than previous studies? It needs to be strengthened in terms of recent research in this area with possible research gaps. It is strongly recommended to add a recent literature. 

Response: Thank you for your comment! The introduction part has been revised according to your suggestions. See the revised manuscript.

5. Some of the selected references are quite old, which from the one point of view is good, since the authors cited necessary references to define a research problem, while from the other hand, lack of recent references may indicate an insufficiently performed literature review. Try to refer to some recent and up-to-date research papers related to the topic, especially in recent years like those related to cement:

Reduction of cement consumption by producing smart green concretes with natural zeolites

Experimental investigation on the effect of cementitious materials on fresh and mechanical properties of self-consolidating concrete.

Portland cement structure and its major oxides and fineness

Response: Thank you for your comment! According to your suggestions, we cited some newly published references. See the revised manuscript.

 

6. In section 1, after the State of the Art (SoA), the Authors should clarify what are the key novelties of this paper and the main contributions of this work beyond the current SoA. They are barely addressed.

Response: Thank you for your comment! We have revised the introduction part and clarified our key novelties. See the revised manuscript.

7. The novelty of the current work should be highlighted in the introduction.

Response: Thank you for your comment! We have revised the introduction part and highlighted our current work. See the revised manuscript.

8. Please try to mention a problem that needs solving - in other words, the research question underlying your study more clear.

Response: Thank you for your comment! We have revised the introduction part. See the revised manuscript.

 

9. Please provide a reference for figure 1 (if applicable)

Response: Thank you for your comment! The Figure 1 was drawn by ourselves.

10. Could you please explain a little about RCM method?

Response: Thank you for your comment! The RCM method was a world widely used method for evaluating the chloride diffusion coefficient. Some more text was added to the RCM test, as well as the explanation of the RCM results. See the revised manuscript.

11. Please provide more information for each graph and try to compare your results with related papers.

Response: Thank you for your comment! We tried to add more discussion for each graph and comparison with related papers. However, not for each graph. See the revised manuscript.  

12. Explain figure 6 in more detail. Please do the Rietveld refinement to get the crystallinity of different phases at different samples.

Response: Thank you for your comment! More discussion has been added to explain the figure 6. See the revised manuscript. For another comment, we have to admit that we did not notice that we should do the quantitative XRD test. However, the samples are all over the curing age and we are afraid that we could not further do the Rietveld XRD test. We thought that the peak height could roughly reflect the composition of the related phases and it helped to illustrate the NS on the chloride immobilization. It is a good comment and we will do the Rietveld refinement in our following research if XRD is needed. Thanks again!

13. Compare figures 8 and 9 with each other.

Response: Thank you for your comment! The figure 8 and figure 9 basically described same thing, in which figure 8 is the differential curve and figure 9 is the cumulative curve. We added some text to each graph. See the revised manuscript.  

14. Did you investigate the chemical effect of NS on HMS?

Response: Thank you for your comment! We added some text about the how NS influences the microstructure formation of HSM. As well, some text was added to illustrate how NS influence the chloride immobilization. See the revised manuscript.

15. Can NS enhance the chloride resistance of cement pastes at the early stage?

Response: Thank you for your comment! For the enhancement of the chloride resistance of cement paste, it should be addressed from three aspects: blocking resistance, physical binding, and chemical binding. At early ages, the NS could act as micro filler and help to refine the pore structure of the cement paste, which is considered to contribute to the block resistance. Physical binding and chemical binding are not considered at early ages. That’s our opinion. We also added some text to the revised manuscript. See the revised manuscript.

 

16. Explain the drop phenomenon in HSM-BK and HSM-B.

Response: Thank you for your comment! When the samples were soaked in the NaCl solution, the chloride ions can penetrate into the sample. Part of the chloride ions can be immobilized by the hydration products, and other chloride ions could transport within the composites through connected pores. When considering the chloride ions immobilization, three aspects should be addressed: migration resistance, chemical binding, and physical binding. For the sample BK, when subjected to 0.5 NaCl solution, three factors work together to immobilize the chloride ions. The AFm-liked phase can chemically bind the chloride ions and be transformed into F salt, which could enhance the microstructure. That’s why an increased surface hardness could be witnessed in the figure 3 for BK samples at 7 day. When the soaking time keeps increasing, with soaking time increased, the chloride ions were continuous immobilize the chloride ions and the microstructure of BK was constantly enhanced and an increased surface hardness could be observed for with increasing soaking time. However, when subjected in 1 mol/L solution, the BK do not have the capacity to continuously immobilize penetrated ions, and the ions will transport within the composites, which will weaken the microstructure of BK, and that’s why a decrease could be observed for BK when soaking time extended from 7d to 28d. We added some text to the revised manuscript to illustrate it. See the revised manuscript. 

 

17. Why do HSM-A and HSM-B have a lower peak than HSM-BK?

Response: Thank you for your comment! For sample A, the lower peak was witnessed at quite early ages. The HN is considered to have an effect on the HSM microstructure at a later age. And at quite early ages, the microstructure of the A and B is not as denser as that in BK due to the existence of HN particles, which is considered to have a negative effect on the fresh properties at early ages. That is why A is lower than BK. However, with extended ages, no lower peak of A than BK was observed. For sample B, the reason is similar to that of A at early ages. At extended ages, the formation of FS in B is lower than that in BK. Even though, the HN can help to refine the microstructure of HSM to form a denser microstructure. However, the densify of microstructure can not compensate the loss of decreased FS content. And it results in the lower peak of B compared to BK.    

18. Please compare your results with some papers in the related field and explain the similarity and differences between your results and theirs.

Response: Thank you for your comment! More comparison with related research has been added according to your suggestions. See the revised manuscript.

 

19. The discussion of the comparison results may be strongly extended, by providing proper considerations to each plotted graph

Response: Thank you for your comment! According to your suggestions, we extended our discussion part. See the revised manuscript.

20. Major Comment: The conclusion should be an objective summary of the most important findings in response to the specific research question or hypothesis. A good conclusion states the principle topic, key arguments and counterpoint, and might suggest future research. It is important to understand the methodological robustness of your study design and report your findings accordingly. Please improve your conclusion section.

Response: Thank you for your comment! We have revised the conclusion part according to your suggestions. See the revised manuscript.

 

21. Please mention your study limits and suggest some future research topics.

Response: Thank you for your comment! The limitations and future research topics have been added. See the revised manuscript.

22. The authors are advised to write the conclusion in a comprehensive way, it should contain key values, suitability of the applied method, contributions and possible future work. 

Response: Thank you for your comment! We have revised the conclusion part according to your suggestions. See the revised manuscript.

23. The discussion of the comparison results Section may be strongly extended, by providing proper considerations to each plotted graph

Response: Thank you for your comment! We have added more discussion to each graph according to your suggestions. See the revised manuscript.

24. The "Conclusions" may be provided as a "uniform text", rather than using bullet points. The weaknesses of the work and the future improvements should be added in this section

Response: Thank you for your comment! We don’t quite agree that the conclusions should be provided as a uniform text rather than using bullet points. We added some more text to the conclusion part according to your suggestions. See the revised manuscript. 

Reviewer 3 Report

This research proposed a methodology to fabricate a cement-based surface treatment materials and investigate related properties including surface hardness and anti-corrosion properties. The experimental and numerical methods were coupling applied. The manuscript is well written and the figures are well graphed. The manuscript is suggested to be accepted after minor revisions.

 

1.      The introduction part needs to be polished up.

2.      Line 79, detailed information of Polycarboxylate superplasticizer needs to be provided.

3.      Line 82-83, how about the dispersion conditions and which method was applied to obtain a well dispersion conditions of the hybrid nano silica?

4.      Line 96-97, how about the binding behavior between the matrix and the layer and will the moisture conditions of the matrix affect the binding behavior of them?  

5.      Line 162, 163, 178, etc., there should be a space between the value and the unit. Check for all manuscript.

6.      Line 205-207, the main peaks are similar which should imply that the incorporation of HMS should not change the mineral composition of the hydration products. Why you said would change? Explain why?

7.      Fig. 6, why only the mineral composition of the samples soaked in 1 mol/l NaCl solution was presented? How about soaked in 0.5 mol/L and 0.1 mol/L?

8.      Line 301-302, “3CaO·Al2O3·CaCl2·10H2O” should be “3CaO·Al₂O₃·CaCl₂·10H₂O”, there are some other similar errors, check for all manuscript.

9.      There are some grammar errors, like Line 67-70, Line 195-196, ration should be ratio. Check for all manuscript.

Author Response

This research proposed a methodology to fabricate a cement-based surface treatment materials and investigate related properties including surface hardness and anti-corrosion properties. The experimental and numerical methods were coupling applied. The manuscript is well written and the figures are well graphed. The manuscript is suggested to be accepted after minor revisions.

1. The introduction part needs to be polished up.

Response: Thank you for your comment! We have added some text to the introduction part. See the revised manuscript.

2. Line 79, detailed information of Polycarboxylate superplasticizer needs to be provided.

Response: Thank you for your comment! Detailed information of the Polycarboxylate superplasticizer has been added. See the revised manuscript.

3. Line 82-83, how about the dispersion conditions and which method was applied to obtain a well dispersion conditions of the hybrid nano silica?

Response: Thank you for your comment! The applied hybrid nano silica was a commercial product provided by Jiangsu Subote Materials Co., Ltd. It was well dispersed when purchased.

4. Line 96-97, how about the binding behavior between the matrix and the layer and will the moisture conditions of the matrix affect the binding behavior of them?  

Response: Thank you for your comment! Since the HSM and the matrix are both cementitious materials and they were well bonded. Also, the surface of the matrix was roughened with abrasive paper to strengthen the bonding behavior between the two materials. We did not pay much attention to the effect of moisture on the bonding behavior. The matrix was prepared and cured in the curing room (95%±5% relative humidity and 20 ℃±1 ℃) before the HSM layer was cast on its surface. This comment inspired us a lot and we will investigate the effect of moisture on the bonding behavior in our further research.

5. Line 162, 163, 178, etc., there should be a space between the value and the unit. Check for all manuscript.

Response: Thank you for your comment! We have revised the manuscript. See the revised manuscript.

6. Line 205-207, the main peaks are similar which should imply that the incorporation of HMS should not change the mineral composition of the hydration products. Why you said would change? Explain why?

Response: Thank you for your comment! We are sorry to make a mistake here and we have revised it. See the revised manuscript.

7. Fig. 6, why only the mineral composition of the samples soaked in 1 mol/l NaCl solution was presented? How about soaked in 0.5 mol/L and 0.1 mol/L?

Response: Thank you for your comment! The surface hardness properties of the HSM subjected to 0.1, 0.5, and 1 mol/L NaCl solution were all presented in the Section 3.1 and they all follow a rough changing trend that the modified samples are all obviously higher than the Ref sample. However, a drop (HSM-BK and HSM-B) was observed for when soaking time prolonged from 7d to 28d. It indicates that new phases may formed within the composites and that’s why we did the XRD test for the samples soaked in the 1 mol/L NaCl solution. We intended to find out the phase changes in the samples.

8. Line 301-302, “3CaO·Al2O3·CaCl2·10H2O” should be “3CaO·Al₂O₃·CaCl₂·10H₂O”, there are some other similar errors, check for all manuscript.

Response: Thank you for your comment! We have revised it. See the revised manuscript.

9. There are some grammar errors, like Line 67-70, Line 195-196, ration should be ratio. Check for all manuscript.

Response: Thank you for your comment! We have revised these mistakes. See the revised manuscript.

Reviewer 4 Report

This work studies the influence of mortar surface treatment with the organic/inorganic hybrid nanosilica on the durability of mortars against aggressive environments. Overall, the work is informative; however, there are several concerns that are recommended to be addressed before publication. The literature review is not complete, and the gap is not clear. Abstract needs revision to reflect both the qualitative and quantitative results in brief; in its current format, it just reports some of the experiments done and some qualitative results, which may not be considered novel. Further recommendations can be found below:

The title needs to be revised considering that “modified by hybrid nanosilica cementitious materials” refers to the mortar.

“Cement” may be too general as a keyword.

Line 21: “The results showed that HSM …”, please revise if it refers to “cement paste modified by hybrid nanosilica”; line 16 (“the cement paste modified by hybrid nanosilica (HMS)”), line 90: HN modified cementitious surface treatment materials (HSM), line 82: hybrid nanosilica (HN). Abbreviations need to be consistent throughout the paper. Also, line 18 (“… the influence of HMS on the chloride permeability of matrix …”) seems to need revision.

Line 32: “… the bridges and so on”, the text needs to be specific.

Line 35: “Prolonging serve life …” please revise if the authors mean service life?

Line 65-67: “To further explore hybrid nano-silica modified cementitious materials used as surface treatment materials, and investigated its effect on chloride resisting property of matrix.” Please revise.

Line 89: A table representing the proportion of ingredients used in the preparation of mixes in addition to some images from the tested samples, can be useful for the reader.

Figures need to be referred to before they appear in the text.

 The results need more robust justifications; for example, what is the reason that the series BK showed a different performance in 0.5 and 1 mol/L NaCl? And why the behaviour of the three series A, B, and BK is different at 7 days under 0.5 and 1 mol/L NaCl (figures 3 and 4).

It is recommended to add the limitations of the study and draw potential future research directions.

Author Response

This work studies the influence of mortar surface treatment with the organic/inorganic hybrid nanosilica on the durability of mortars against aggressive environments. Overall, the work is informative; however, there are several concerns that are recommended to be addressed before publication. The literature review is not complete, and the gap is not clear. Abstract needs revision to reflect both the qualitative and quantitative results in brief; in its current format, it just reports some of the experiments done and some qualitative results, which may not be considered novel. Further recommendations can be found below:

Response: Thank you for your comment! According to your suggestions, we have revised the abstract and introduction part to make it appear novelty. See the revised manuscript.

1. The title needs to be revised considering that “modified by hybrid nanosilica cementitious materials” refers to the mortar.

Response: Thank you for your comment! The title has been revised. See the revised manuscript.

2. “Cement” may be too general as a keyword.

Response: Thank you for your comment! The key words have been revised. See the revised manuscript.

 

3. Line 21: “The results showed that HSM …”, please revise if it refers to “cement paste modified by hybrid nanosilica”; line 16 (“the cement paste modified by hybrid nanosilica (HMS)”), line 90: HN modified cementitious surface treatment materials (HSM), line 82: hybrid nanosilica (HN). Abbreviations need to be consistent throughout the paper. Also, line 18 (“… the influence of HMS on the chloride permeability of matrix …”) seems to need revision.

Response: Thank you for your comment! We are sorry for making these mistakes and we have corrected them in the revised manuscript. See the revised manuscript.

4. Line 32: “… the bridges and so on”, the text needs to be specific.

Response: Thank you for your comment! We have revised it. See the revised manuscript.

5. Line 35: “Prolonging serve life …” please revise if the authors mean service life?

Response: Thank you for your comment! We have revised it. See the revised manuscript.

 

6. Line 65-67: “To further explore hybrid nano-silica modified cementitious materials used as surface treatment materials, and investigated its effect on chloride resisting property of matrix.” Please revise.

Response: Thank you for your comment! The text has been revised. See the revised manuscript.

7. Line 89: A table representing the proportion of ingredients used in the preparation of mixes in addition to some images from the tested samples, can be useful for the reader.

Response: Thank you for your comment! According to your suggestion, we have added a table of detailed mix proportions. See the revised manuscript. For the images of tested samples. We are sorry that we are afraid that we could not provide it. We forgot about taking some images of the samples before they were tested. We do appreciate for your understanding. It is a good comment and we will take more images of the samples in our further research.

8. Figures need to be referred to before they appear in the text.

Response: Thank you for your comment! Figures have been moved before the text according to your suggestion. See the revised manuscript.

9. The results need more robust justifications; for example, what is the reason that the series BK showed a different performance in 0.5 and 1 mol/L NaCl? And why the behaviour of the three series A, B, and BK is different at 7 days under 0.5 and 1 mol/L NaCl (figures 3 and 4).

Response: Thank you for your comment! When the samples were soaked in the NaCl solution, the chloride ions can penetrate into the sample. Part of the chloride ions can be immobilized by the hydration products, and other chloride ions could transport within the composites through connected pores. When considering the chloride ions immobilization, three aspects should be addressed: migration resistance, chemical binding, and physical binding. For the sample BK, when subjected to 0.5 NaCl solution, three factors work together to immobilize the chloride ions. The AFm-liked phase can chemically bind the chloride ions and be transformed into F salt, which could enhance the microstructure. That’s why an increased surface hardness could be witnessed in the figure 3 for BK samples at 7 day. When the soaking time keeps increasing, with soaking time increased, the chloride ions were continuous immobilize the chloride ions and the microstructure of BK was constantly enhanced and an increased surface hardness could be observed for with increasing soaking time. However, when subjected in 1 mol/L solution, the BK do not have the capacity to continuously immobilize penetrated ions, and the ions will transport within the composites, which will weaken the microstructure of BK, and that’s why a decrease could be observed for BK when soaking time extended from 7d to 28d. We added some text to the revised manuscript to illustrate it. See the revised manuscript.  

10. It is recommended to add the limitations of the study and draw potential future research directions.

Response: Thank you for your comment! The limitations of the study potential future research directions have been added. See the revised manuscript.

Round 2

Reviewer 2 Report

All the comments are addressed suitably. 

Reviewer 4 Report

The authors have made modifications. The title can be further improved.