Degradation Mechanisms of Early Strength for High-Fluidization Cement Mortar under Magnesium Sulfate Corrosion

Round 1

Reviewer 1 Report

Dear authors,

Sorry that I'm telling you, but you can't use the same results as in previous papers. Fig.14-19 as in paper https://www.mdpi.com/1996-1944/14/20/6144/htm . As I understand it's a one of main results in this paper. Also there are no citation in the text to this previous results. This results were published at https://www.mdpi.com/1996-1944/14/20/6144/htm

Author Response

Reviewer #1:

Sorry that I'm telling you, but you can't use the same results as in previous papers. Fig.14-19 as in paper https://www.mdpi.com/1996-1944/14/20/6144/htm. As I understand it's a one of main results in this paper. Also there are no citation in the text to this previous results. This results were published at https://www.mdpi.com/1996-1944/14/20/6144/htm.

Authors’ Reply:

       Thank you for your comments. We have carefully checked the figures mentioned in the reviewer's comments. We verify that there is no any repetition in these figures (Figs.14 (c), 14 (d), 15, 16, 17, 18, and 19 in the origin manuscript) between this manuscript and the published paper mentioned by the reviewer. These figures are all original results. Fig. 14 (a) and 14 (b) in the origin manuscript are also redrawn based on new experiments. Please renewedly check and review our manuscript.

In addition, due to the comment of the 4th reviewer, the DSC curves (Figs. 14-18 in the origin manuscript) have been deleted in the revised manuscript and moved to the support file.

Author Response File: Author Response.pdf

Reviewer 2 Report

I consider that the manuscript is well organized and presented. The results may enrich the literature on magnesium sulfate's complex corrosion process. 

Author Response

Reviewer #2:

I consider that the manuscript is well organized and presented. The results may enrich the literature on magnesium sulfate's complex corrosion process. 

Authors’ Reply:

Thank you for your kind comments.

Reviewer 3 Report

The manuscript presents the results of a very well designed experimental campaign with focus on the effect of magnesium sulfate corrosion to the early term mechanical properties of high-fuidization cement mortar. Overall, the manuscript is well structured, the conclusions are supported by the analysis and it is worth to be considered for publication in Buildings after some necessary clarifications and corrections are provided by the authors.

-  2.2.3. It is not completely clear to me how the measurements of the outter and inner microstructures are performed. Are the microscopic samples taken from the surface and from the inner of the material to represent the two region? The authors should describe the two different groups (OUT and IN) of specimens.

-  2.2.4. The authors provide all the necessary information of the strength tests including the loading speed. Did the authors control the strength tests in terms of force? If yes, would the authors expect differences if the tests were controlled in terms of displacements? Additionally, did the authors observe any difference in the load displacement curves (if these are available) among the different tests?

- Figure 10 (a) - (b) and also in all figures that this applies. The authors denote the horizontal axis as erosion of time. For the case of 0% the time reflects just the aging/curing of the material properties is that correct? I would suggest that the authors use the term corrosion/aging time or  test at age which would cover also the case when no corrosion occurs.

- line 226. 'This is due to the corrosion is weaker...'. Change this to either 'This is due to the fact that the corrosion is weaker..' or 'This is due to weaker corrosion ...'.

- line 234.  '.. The HECM at different corrosion times..'. Again the authors should use better the term at different testing age in order to be consistent also for the case that c=0%.

- line 259. 'Figure 11 shows the inside (IN) and outside (OUT) ...'. How do the authors  measure the insided and the outside of the microstructure? see also previous comment.

- Figure 11. The authors should consider to add some notation of the different phases shown on the SEM figure as they do in Figure 12.

- Line 262. '...time is 3-day,'... should be 3-days.

- Line 280. 'As can be seen from ... is further intensified.' At which testing/corrosion time?

- Line 301. 'There is no obvious difference in the outside microstructure in the case of different 301 solution concentrations...'. Do the authors mean by comparing the figures of the outter microstructure for the different concentrations at 14 days or the differences between outter and inner microstructure at 14 days and for the same concentration? In the first case, I would say there are differences among the different percentages. The authors should clarify this. 

- Figures 19-20. Is there any correlation between the weight loss/gain and the mechanical properties of the HECM? Maybe plots weight loss vs flexural or compressive strength would provide a more clear view on the effect of the corrosion on the mechanical properties. 

- Conclusions. What are the authors recommendations for practical applications?

 

Author Response

Reviewer #3:

The manuscript presents the results of a very well designed experimental campaign with focus on the effect of magnesium sulfate corrosion to the early term mechanical properties of high-fuidization cement mortar. Overall, the manuscript is well structured, the conclusions are supported by the analysis and it is worth to be considered for publication in Buildings after some necessary clarifications and corrections are provided by the authors.

(1) - 2.2.3. It is not completely clear to me how the measurements of the outter and inner microstructures are performed. Are the microscopic samples taken from the surface and from the inner of the material to represent the two region? The authors should describe the two different groups (OUT and IN) of specimens.

Authors’ Reply:

Thank you for your constructive comments.

The outer and inner specimens are prepared as follows. Firstly, prepare the standard cuboid specimens (4 cm × 4 cm × 16 cm) according to the Chinese test standard “Test Method of Cement and Concrete for Highway Engineering” (JTG E30-2005). Secondly, cut the cuboid specimens into some cubic specimens (1 cm × 1 cm × 1cm), and put the cubic specimens into the corrosion solution until the target corrosion age. Thirdly, put the cubic specimens after corrosion into anhydrous ethanol for seven days to stop the hydration. The anhydrous ethanol must be replaced three times at least in the seven days. Finally, break the cubic specimens into pieces. The outer and inner specimens of SEM tests can be prepared via selecting from these pieces. The outer and inner specimens of XRD and DSC tests can be prepared via pulverizing the selected pieces.

The above has been supplemented in the revised manuscript (Line 162-174).

 

(2) - 2.2.4. The authors provide all the necessary information of the strength tests including the loading speed. Did the authors control the strength tests in terms of force? If yes, would the authors expect differences if the tests were controlled in terms of displacements? Additionally, did the authors observe any difference in the load displacement curves (if these are available) among the different tests?

Authors’ Reply:

Thank you for your constructive comments.

The strength tests are in accordance with the Chinese test standard “Test Method of Cement and Concrete for Highway Engineering” (JTG E30-2005). In the standard, strength tests are stipulated to implement based on the force-controlled mode using specified loading speed. Moreover, we think there is the difference between strength tests with force-controlled mode and displacement-controlled mode. It will be discussed in detail in future studies.

The above has been supplemented in the revised manuscript (Line 180-189 and 545-546).

 

(3) - Figure 10 (a) - (b) and also in all figures that this applies. The authors denote the horizontal axis as erosion of time. For the case of 0% the time reflects just the aging/curing of the material properties is that correct? I would suggest that the authors use the term corrosion/aging time or test at age which would cover also the case when no corrosion occurs.

Authors’ Reply:

Thank you for your kind suggestion.

The horizontal axis has been corrected to “Testing age” in the revised manuscript (Fig. 10 (a) - (b), Fig. 13 (a) - (b), Fig. 15 (a) - (b), Fig. 16 (a) - (b), Fig. 17 (a) - (b), and Fig. 18 (a) - (b)).

 

(4) - line 226. 'This is due to the corrosion is weaker...'. Change this to either 'This is due to the fact that the corrosion is weaker..' or 'This is due to weaker corrosion ...'.

Authors’ Reply:

Thank you for your kind suggestion.

The sentence has been corrected to ‘This is due to the fact that the corrosion is weaker…’ in the revised manuscript (Line 220-221).

 

(5) - line 234.  '.. The HECM at different corrosion times..'. Again the authors should use better the term at different testing age in order to be consistent also for the case that c=0%.

Authors’ Reply:

Thank you for your constructive comment.

“corrosion time” has been corrected to “testing age” in the revised manuscript (Line 26, 218, 224, 228, 333, 336, 369, 374, 396, 411, Fig. 10, Fig. 13, Figs. 15-18, and Table 7).

 

(6) - line 259. 'Figure 11 shows the inside (IN) and outside (OUT) ...'. How do the authors measure the insided and the outside of the microstructure? see also previous comment.

Authors’ Reply:

Thank you for your constructive comment.

Please find the preparation method of the outer and inner specimens in the 1st comment.

 

(7) - Figure 11. The authors should consider to add some notation of the different phases shown on the SEM figure as they do in Figure 12.

Authors’ Reply:

Thank you for your great suggestion.

The notations of different phases (e.g., CH crystal, C-S-H gel, and Aft crystal) have been supplemented into some typical SEM images in the revised manuscript (Fig. 11). In addition, it should be explained that some SEM images are deleted in the revised manuscript according to the comment of the 4th reviewer.

 

(8) - Line 262. '...time is 3-day,'... should be 3-days.

Authors’ Reply:

Thank you for your constructive comment.

The “3-day” has been corrected to “3-days” in the revised manuscript. Other similar contents also have been revised (Line 219, 220, 222, 230, 231, 265, 277, 278, 282, 283, 293, 294, 301, 308, 309, 337, 375, 376, 378, 397, 398, 401, 406, and Fig. 11).

 

(9) - Line 280. 'As can be seen from ... is further intensified.' At which testing/corrosion time?

Authors’ Reply:

Thank you for your constructive comment.

The corrosion time is 7-days, which has been supplemented in the revised manuscript (Line 283).

 

(10) - Line 301. 'There is no obvious difference in the outside microstructure in the case of different 301 solution concentrations...'. Do the authors mean by comparing the figures of the outter microstructure for the different concentrations at 14 days or the differences between outter and inner microstructure at 14 days and for the same concentration? In the first case, I would say there are differences among the different percentages. The authors should clarify this.

Authors’ Reply:

Thank you for your constructive comment.

We want to express the second meaning. The sentence has been rewritten in the revised manuscript (Line 274-275, 284-286, and 304-306).

 

(11) - Figures 19-20. Is there any correlation between the weight loss/gain and the mechanical properties of the HECM? Maybe plots weight loss vs flexural or compressive strength would provide a more clear view on the effect of the corrosion on the mechanical properties.

Authors’ Reply:

Thank you for your constructive comment.

The correlation analysis between weight loss and strengths (compressive and flexural) has been supplemented in the revised manuscript (Line 415-419 and Fig. 19).

 

(12) - Conclusions. What are the authors recommendations for practical applications?

Authors’ Reply:

Thank you for your constructive comments.

This study is conducive to pinpoint the evolution process of mechanical strength and hydration products of the HECM under the magnesium sulfate corrosion. It is helpful to specifically adjust and control the composition of the HECM during the material design aiming at some special engineering conditions.

The above has been supplemented in the section of “Conclusions” (Line 447-451).

Reviewer 4 Report

The work submitted for review is in the form of a Laboratory Test Report. Despite the fact that the laboratory tests performed are elementary experimental works, the diligence of their implementation and a wide range of experiments (due to the large number of variable parameters) mean that the reviewed article can certainly be considered a work containing scientific elements. It is completely incomprehensible why as many as 11 people are Co-authors, it is hard to believe that so many people were involved in the preparation of the paper, or if someone only performed research and did not carry out any analysis of the results obtained, it is difficult to consider him a Co-author. In practice, there are no papers with 11 co-authors.

Objections are also raised by the lack of clear indication of the purposefulness of the performed laboratory tests - of course, the article deals with the issue of sulphate corrosion, but the content of the article does not clearly indicate why this issue is so important. It is not known where the analyzed mixtures with high fluidity and early strength will find / are used. In addition, the content of the article does not indicate what is new in this article in relation to other publications on this subject.

In addition, the article does not contain any economic and technological analysis - whether these types of mixtures will be used on an industrial scale and what will be their production costs in relation to the mixtures used today. There is also no information about the main purpose of using this type of mixtures.

In terms of the edition page - Figs. 10-11 and Figs. 13-22 require re-edition - this number of graphs is unreadable. The number of photos in Fig. 11 is definitely too large and makes the paper difficult to read.

The reviewer suggests introducing the corrections described above in order to increase the scientific value of the paper.

Author Response

Reviewer #4:

(1) The work submitted for review is in the form of a Laboratory Test Report. Despite the fact that the laboratory tests performed are elementary experimental works, the diligence of their implementation and a wide range of experiments (due to the large number of variable parameters) mean that the reviewed article can certainly be considered a work containing scientific elements. It is completely incomprehensible why as many as 11 people are Co-authors, it is hard to believe that so many people were involved in the preparation of the paper, or if someone only performed research and did not carry out any analysis of the results obtained, it is difficult to consider him a Co-author. In practice, there are no papers with 11 co-authors.

Authors’ Reply:

Thank you for your constructive comments.

In the original manuscript, we listed all the people who participated for the experiments in the author list. According to your kind suggestion, we only retain the author who has the contribution to both the experiments and the manuscript in the revised manuscript (Line 5-16, and 460-468).

 

(2) Objections are also raised by the lack of clear indication of the purposefulness of the performed laboratory tests - of course, the article deals with the issue of sulphate corrosion, but the content of the article does not clearly indicate why this issue is so important. It is not known where the analyzed mixtures with high fluidity and early strength will find / are used. In addition, the content of the article does not indicate what is new in this article in relation to other publications on this subject.

Authors’ Reply:

Thank you for your constructive comments.

Owing to complex service conditions, some diseases (e.g., crack, void, etc.) will invariably occur in civil engineering structures. The grouting is one of the most efficient and common methods for the rapid repairment and reinforcement of civil engineering structures. The high-fluidization and early-strength cement mortar (i.e., the HECM) mentioned in this study is one type of grouting materials. As stated in the manuscript, owing to complex engineering environments, the civil engineering structure is inevitably corroded by sulfates. Moreover, according to the literature review, it can be found that the sulfate corrosion plays a significant and complex effect on strengths and mechanisms of cement-based materials, especially for the magnesium sulfate. Obviously, as the repair material used in civil engineering structure, the HECM will also be subject to the corrosion by the magnesium sulfate. Hence, in order to ensure the engineering quality, it is necessary to reveal the corrosion mechanisms of the HECM under the magnesium sulfate corrosion. However, the previous studies mainly focus on the corrosion mechanisms of conventional cement-based materials. Considering the characteristics of high-fluidization and early-strength of the HECM, the hydration process and strength formation of the HECM under the magnesium sulfate corrosion are consequentially different from the conventional materials, while there are few studies on it. Hence, the objective of this study is to reveal the degradation mechanisms of strength formation of the HECM under the magnesium sulfate corrosion.

The above has been supplemented in the revised manuscript (Line 36-44, 68-74, and 91-97).

 

(3) In addition, the article does not contain any economic and technological analysis - whether these types of mixtures will be used on an industrial scale and what will be their production costs in relation to the mixtures used today. There is also no information about the main purpose of using this type of mixtures.

Authors’ Reply:

Thank you for your constructive comments.

The technological parameters of the HECM have been supplemented in the revised manuscript (Line 110-113, 543-544, and Table 5).

The main purpose of using the HECM are explained in the answer of the above comment. Moreover, this study is conducive to pinpoint the evolution process of mechanical strength and hydration products of the HECM under the magnesium sulfate corrosion. It is helpful to specifically adjust and control the composition of the HECM during the material design aiming at some special engineering conditions.

In addition, we want to explain that this study mainly focuses on the analysis of corrosion mechanisms, while does not yet face on the industrialization. Hence, the economic parameters will be analyzed in future studies and is not discussed in this study. On the other hand, the compositions of the HECM are all common raw materials (i.e., ordinary Portland cement, water reducing agent, accelerating agent, and expansion agent). The cost of the HECM is not too expensive to restrict its application.

The above has been supplemented in the revised manuscript (Line 447-458).

 

(4) In terms of the edition page - Figs. 10-11 and Figs. 13-22 require re-edition - this number of graphs is unreadable. The number of photos in Fig. 11 is definitely too large and makes the paper difficult to read.

Authors’ Reply:

Thank you for your constructive comments.

The SEM images have been simplified in the revised manuscript (Line 253-258 and Fig. 11). We only retain the SEM images those have significant difference of micro-structure features under different conditions.

Moreover, due to that the figures in Figs. 14-18 of the origin manuscript are original results of DSC tests, in which the data can be found in Figs. 19-22 (Figs. 15-18 in the revised manuscript). These figures have been deleted in the revised manuscript and moved to the support file. Only a typical DSC curve is retained to illustrate the DSC results (Line 354-355 and Fig. 14).

 

The reviewer suggests introducing the corrections described above in order to increase the scientific value of the paper.

Authors’ Reply:

Thank you for your time. We have revised the manuscript according to your comments. We hope our answers are OK, and your favorable consideration will be appreciated.

Round 2

Reviewer 1 Report

Dear authors,

The article looks nice now and you have done a lot of work on it.

I have only one remark. The article clearly has novelty. However, in order to emphasize this with a larger number of world authors, I would advise adding sources to the list of references.

For example:

10.1016/j.engstruct.2006.09.004   10.3390/ma14102638   10.3390/ma14216612
10.15587/1729-4061.2021.237954   10.1617/s11527-017-1131-6 10.1007/978-981-13-9008-1_48 10.1016/j.conbuildmat.2018.08.040

In my opinion, this will highlight a world problem and its insufficient study.

With best regards

 

 

   

 

 

Author Response

The article looks nice now and you have done a lot of work on it.

I have only one remark. The article clearly has novelty. However, in order to emphasize this with a larger number of world authors, I would advise adding sources to the list of references. For example: 10.1016/j.engstruct.2006.09.004, 10.15587/1729-4061.2021.237954, 10.1016/j.conbuildmat.2018.08.040, 10.3390/ma14216612, 10.1007/978-981-13-9008-1_48, 10.1617/s11527-017-1131-6, and 10.3390/ma14102638.

In my opinion, this will highlight a world problem and its insufficient study.

With best regards

 

Authors’ Reply:

Thank you very much for your comment.

We have reviewed these references. Some of them has been supplemented in the revised manuscript (Line 39, 447, 471-472, and 524-525).

Reviewer 3 Report

No further comments.

Author Response

No further comments.

 

Authors’ Reply:

Thank you very much for your kind comment.