Review Reports - The Effect of Magnesium Chloride on the Macroscopic and MI-Croscopic Properties of Phosphate Cement-Based Materials

Round 1

Reviewer 1 Report

The manuscript, “coatings-1613123” presents an interesting study, however, the paper needs a major revision to improve the quality of the paper.

In the abstract, Phosphate cement-based materials are fast hardening cement materials which can be applied in the rapid repair of concrete structure engineering, here engineering word is unnecessary. Please delete it.
Instead of bonding strength, please write bond strength throughout the paper.
Dry shrinkage should be replaced with drying shrinkage.
Please revise the first line of the introduction, it does not sound good.
Page 2, In the introduction, can meet the requirements of opening to traffic 6 hours after construction, the sentence is grammatically incorrect. Please revise it.
Page 2, The triethanolamine possessed excellent retarding effect, need a reference.
Figure 13, the gap between the initial and final setting time is lower when MgCl content is less than 2%, please give reasons for that.
In figure 4, the axis title “Slump flow/mm” should be replaced with slump flow (mm). Also, this type of change applies to all figures.
Writing and data presentation is poor, consider revising the whole paper and maintaining scholarly article writing standards.
The flexural and compressive strength of the mortar is too high, please add some photos of the specimens and justify this high strength based on the related published literature.
In conclusion, the first line “In this study, the influence of magnesium chloride on the working performance and the following mechanical properties of phosphate cement paste” is an incomplete sentence, please revise it.
The microscopic properties were determined to research the mechanism of the properties, this also does not make any sense.

Author Response

Comments and Suggestions for Authors

The manuscript, “coatings-1613123” presents an interesting study, however, the paper needs a major revision to improve the quality of the paper.

In the abstract, Phosphate cement-based materials are fast hardening cement materials which can be applied in the rapid repair of concrete structure engineering, here engineering word is unnecessary. Please delete it.

----Thank you for your suggestion. The word “engineering” has been deleted.

Instead of bonding strength, please write bond strength throughout the paper.

----This is a very good point. “bonding strength” has been revised to “bond strength” throughout the paper.

Dry shrinkage should be replaced with drying shrinkage.

----This is a very good comment. “Dry shrinkage” has been replaced with “drying shrinkage”.

Please revise the first line of the introduction, it does not sound good.

----Thank you for your suggestion. The first line has been revised; you can find the revision in the revised manuscript.

In recent years, the damage of cement concrete building structures is frequently reported. For some critical structures, such as bridges and roads, it is always needed to recover their function.(Page 1)

Page 2, In the introduction, can meet the requirements of opening to traffic 6 hours after construction, the sentence is grammatically incorrect. Please revise it.

----This is a very good point. This has been revised, you can find the revision in the revised manuscript.

Research showed that it could be opened to traffic after paving within 6 hours [8] .(Page 2)

Page 2, The triethanolamine possessed excellent retarding effect, need a reference.

----Thank you for your suggestion. Ref [25] supporting this viewpoint has been added in the reference part of the manuscript.

Figure 13, the gap between the initial and final setting time is lower when MgCl content is less than 2%, please give reasons for that.

----This is a very good comment. The reasons has been given in the revised manuscript. You can find the revision in Page(6), just as follows:

Moreover, the gap between the initial and final setting time was small at an MgCl content of less than 2%, which can be attributed to the fact that the addition of MgCl can significantly change the pH value of phosphate cement paste. It can inhibit phosphate particles' dissolution and thus retarding the early hydration reaction speed of phosphate cement paste. However, when the content of MgCl was less than 2 %, the retarding effect of MgCl was insignificant [31, 32].

In figure 4, the axis title “Slump flow/mm” should be replaced with slump flow (mm). Also, this type of change applies to all figures.

----Thank you for your suggestion. This type has been revised according to your suggestion. You can find the revisions from Figure 4 to Figure 10.

Writing and data presentation is poor, consider revising the whole paper and maintaining scholarly article writing standards.

----Thank you for pointing this out. The paper has been revised thoroughly with the help of all authors. You can find our revision and effort in the revised manuscript.

The flexural and compressive strength of the mortar is too high, please add some photos of the specimens and justify this high strength based on the related published literature.

----Thank you for pointing this out. The flexural and bond strengths of magnesium phosphate cement mortar were reasonable and related published literatures(Refs[31-33]) have been provided. Some errors occurred to the compressive strength during calculation and now were corrected (Figure 7). All data were checked repeatedly and carefully. Figure 1 includes some photos of the specimens is added in the revised manuscript.

In conclusion, the first line “In this study, the influence of magnesium chloride on the working performance and the following mechanical properties of phosphate cement paste” is an incomplete sentence, please revise it.

----This is a very good comment. This sentence has been revised to “In this study, the influence of magnesium chloride on the working performance and the following mechanical properties of phosphate cement paste was investigated”. The revision has been added to the Section conclusion of the revised manuscript.

The microscopic properties were determined to research the mechanism of the properties, this also does not make any sense.

----This is a very good point. This sentence has been revised to “The microscopic analysis was carried out to investigate the mechanism of the macroscopic properties.”

Reviewer 2 Report

Authors have attempted to evaluate the effect of MgCl and borax on the properties of phosphate cement paste. The authors need to take care the following points:

Unit must be included in Table 2.
Needs language editing and proof reading. For example, "Then the mixed uniformly water, K2HPO4"; "measurement of for the setting
time of phosphate cement paste"; "Cement standard consistency setting time tester (standard favicat tester) cement Vicat"
Check the sentence "The compressive and flexural strengths of specimens were tested by the YAW-300 microcomputer full-automatic universal."
It should be "ordinary Portland cement" and not "Portland ordinary cement".
“It can be acquired from Figure 6, the magnesium chloride could reduce the mechanical strengths of phosphate cement paste when the curing age was lower than or equal to 1 d and improve the mechanical strengths when the curing age reached 3 d.” Justify this statement.
What about the rate of increase in the strength properties with MgCl?
Check the sentence"The compressive and flexural strengths of specimens were tested by the YAW-300 microcomputer full-automatic universal."
It should not be "Portland ordinary cement", it should be "ordinary Portland cement"
Even the title mentioned the effect of MgCl and Borax, nowhere the discussion has been made on the effect of Borax on the properties of cement paste.

Author Response

Comments and Suggestions for Authors

Authors have attempted to evaluate the effect of MgCl and borax on the properties of phosphate cement paste. The authors need to take care the following points:

Unit must be included in Table 2.

----Thank you for pointing this out. The unit has been added in Table 2.

Needs language editing and proof reading. For example, "Then the mixed uniformly water, K2HPO4"; "measurement of for the setting
time of phosphate cement paste"; "Cement standard consistency setting time tester (standard favicat tester) cement Vicat"

----Thank you for your suggestion. The language has been edited with the help of all authors. All problems including your suggestion have been revised.

After that, water, K2HPO4 and water-reducing agent were added to the cement mixer and stirred for another 3 minutes with a stirring speed of 285±10 r/min.

Check the sentence "The compressive and flexural strengths of specimens were tested by the YAW-300 microcomputer full-automatic universal."
It should be "ordinary Portland cement" and not "Portland ordinary cement".
“It can be acquired from Figure 6, the magnesium chloride could reduce the mechanical strengths of phosphate cement paste when the curing age was lower than or equal to 1 d and improve the mechanical strengths when the curing age reached 3 d.” Justify this statement.

----Thank you for pointing this out. All these language problems were revised. You can find the revisions in Pages (4 and 8)

What about the rate of increase in the strength properties with MgCl?

----This is a very good point. The rate of increase in the strength properties with MgCl have been added in Figures 7(b), (d) and (f) of the revised manuscript.

Check the sentence"The compressive and flexural strengths of specimens were tested by the YAW-300 microcomputer full-automatic universal."

----Thank you for your suggestion. This sentence has been checked and revised, you can find the revision in the Section 2.3.2, just as follows:

The compressive and flexural strengths of specimens were tested by the YAW-300 microcomputer controlled full-automatic universal testing machine.

It should not be "Portland ordinary cement", it should be "ordinary Portland cement"

----Thank you for pointing this out. All of these were corrected. You can find the revision in the revised manuscript.

Even the title mentioned the effect of MgCl and Borax, nowhere the discussion has been made on the effect of Borax on the properties of cement paste.

----This is a very good point. The original title was unreasonable, and the title has been revised to “The effect of magnesium chloride on the macroscopic and microscopic properties of phosphate cement-based materials”.

Reviewer 3 Report

The manuscript entitled "The effect of magnesium chloride on the macroscopic and microscopic properties of phosphate cement-based materials" presents an interesting experimental study conducted on the obtaining and characterization of concrete with different amounts of MgCl2. However, the results section includes general affirmation without a clear/in-depth evaluation of the presented graphs and other issues must be addressed. The paper needs minor revisions before it is processed further, some comments follow:

Experimental Section

Table 1 – Chemical composition, the sum of the oxides isn’t 100. Please check your experimental results. Also, two types of iron oxides have been detected in concrete, therefore, please replace Fe2O3 with FexOy.

Results and Discussion Section

"At this dosage, phosphate cement's initial and final settings were 33.5 min and 56.8 min, respectively, which was suitable for construction." – As presented in Figure 4, each measurement has a standard deviation value, therefore, please present these values in the text. For example, the final setting time was 33.5 min ±1 min.

Thermal analysis.

Figure 8 – Please introduce figure labels to highlight the areas of interest for the readers- please provide a clear correlation between each peak presented on the curves and the chemical reactions that occur. Currently, only general affirmations have been introduced about the thermal behavior. Please provide a much detailed description.

These types of materials have a high content of water in different forms that will be removed during heating at different stages. Please improve the comments and discussions related to the thermal behavior considering previous studies, see DOI: 10.3390/ma15010202.

Figure 9 - XRD analysis- Please provide the phase ID, Why do the authors consider some peaks instead of others, there is no clear correlation between the peaks and the identified phases. Please provide full identification of the peaks. There are some clear peaks between 30 and 35 degrees.

Figure 10 - Please provide the experimental proof to support your affirmation, please provide the elemental mapping images and highlight the analyzed zone.

Conclusion:

The conclusion section can be improved since those are far too general.

Conclusions present some of the results discussed above in the paper with very limited discussion.

Please improve the conclusions and present them following the main recommendations by Academia of giving the conclusions of the study by points with highlights.

Please rewrite the conclusions in a more quantitative form.

Author Response

Comments and Suggestions for Authors

Experimental Section

----This is a very good comment. Table 1 has been checked carefully, the sum of the oxides and the Loss on ignition is 100 and some errors have been corrected. The Fe2O3 has been replaced with FexOy.

Results and Discussion Section

----Thank you for pointing this out. The sentence "At this dosage, phosphate cement's initial and final settings were 33.5 min and 56.8 min, respectively, which was suitable for construction." has been revised to：“At this dosage, phosphate cement's initial and final setting times were 33.5 ±0.018 min and 56.8±0.016 min respectively, which was suitable for construction.” The standard deviation values of Figure 4 have been added in the revised Figure 4 of Page 6 of the manuscript.

Thermal analysis.

----This is a very good point. The figure labels of the areas of interest for the readers have been highlighted. A clear correlation between each peak presented on the curves and the chemical reactions that occur has been provided. A much detailed description has been provided.

----Thank you for your comment. Different stages of the removed free water and other decomposition of crystal water have been added in Section 3.3 of the revised manuscript. Moreover, some important marks have been added in Figure 8, you can find the revision in Pages 9 and 10. The related paper“DOI: 10.3390/ma15010202”has been added in Section Reference of the revised manuscript.

----Thank you for pointing this out. The phase ID of XRD analysis has been added in Figure 9 of the revised manuscript. The clear correlation between the peaks and the identified phases and full identification of the peaks have been added in revised Section 3.3. You can find our revision in page 10 of the revised manuscript

Figure 10 - Please provide the experimental proof to support your affirmation, please provide the elemental mapping images and highlight the analyzed zone.

----This is a very good point. Energy dispersive spectrometer has been added to support my affirmation. You can find the results in Figure 11 and Table 4. The observing elements in mapping images can confirm the hydration products.

Conclusion:

The conclusion section can be improved since those are far too general.

Conclusions present some of the results discussed above in the paper with very limited discussion.

Please improve the conclusions and present them following the main recommendations by Academia of giving the conclusions of the study by points with highlights.

Please rewrite the conclusions in a more quantitative form.

----Thank you for your comment. The conclusions of this paper have been rewritten by all coauthors. The newly written conclusions are more quantitative. You can find the new conclusions as follows:

In this study, the influence of magnesium chloride on the working performance and the mechanical properties of phosphate cement paste were investigated. The microscopic analysis was carried out to investigate the mechanism of the macroscopic properties. The conclusions can be drawn as follows:

The addition of magnesium chloride increased the setting time and the slump flow of phosphate cement paste. The optimal content of 2 % magnesium chloride by the mass ratio of magnesium oxide showed the most effective retarding efficiency for phosphate cement paste. The initial and final setting times of 33.5 ±0.018 min and 56.8±0.016 min were observed, respectively. The relationship between the slump flow and the magnesium chloride content obeyed the positively correlated linear function.

The evaluation function for the drying shrinkage rate and the curing age could be expressed as a quadratic function. The addition of magnesium chloride negatively affected the mechanical strengths of phosphate cement pastes at a curing age lower than or equal to 3 d. Meanwhile, when the curing age was longer than 3 d, the addition of magnesium chloride could improve the mechanical strengths of phosphate cement paste. Additionally, magnesium chloride could decrease the drying shrinkage rate of phosphate cement paste.

The TG test showed that the free water in phosphate cement paste evaporated within the temperature from 20 ℃ to 150 ℃. The decomposition of hydrated potassium magnesium concentrated on two temperature ranges, including 150 ℃ ~ 424 ℃ and 424 ℃ ~ 918 ℃. The magnesium chloride could inhibit the hydration of phosphate cement and reduce cracks induced by drying shrinkage at a later curing age (higher than 3 d). The retarder composed of magnesium chloride and borax showed a positive effect on retarding phosphate cement setting and could improve the properties at a curing age longer than 3 d. (Pages 13 and 14).

Round 2

Reviewer 1 Report

The authors have addressed my comments sufficiently. So, I have no further comments.

Author Response

Comments and Suggestions for Authors

The authors have addressed my comments sufficiently. So, I have no further comments.

Thank you very much for your comments. The paper has been improved thoroughly with your help.