The Effect of Chloride Ions Morphology on the Properties of Concrete Under Dry and Wet Conditions

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

I have reviewed your manuscript and suggest making several improvements to boost its clarity and scholarly impact. The methodology section, in particular, needs further elaboration to ensure that readers can thoroughly grasp your processes. Additionally, broadening your reference base would solidify your arguments and enrich the research context. Furthermore, certain parts of the results section require more explicit explanation. Enhancing the detail in these areas will undoubtedly enhance both the credibility and the clarity of your findings.

Lines 73-82: Given the focus of your study on the impact of different forms of chloride ions on mixed sand concrete under wet-dry cycles, how do you differentiate the effects of various chloride forms in your experiments? Specifically, what methodologies are employed to isolate and measure the impact of these chloride forms on concrete durability and resistance to chloride ion penetration? Could you elaborate on the types of indoor environmental simulation tests and microstructural experiments you are conducting? How do these tests simulate the real-world conditions of salt lake and marine environments, and what parameters are you specifically monitoring? How do your findings intend to enhance the application of mixed sand concrete in such challenging environments, and what practical recommendations might your study yield for construction projects in salt-affected and marine areas?

Lines 130-157: In the context of your microstructural analysis of mixed sand concrete, incorporating references to recent scientific articles will strengthen and validate the methodologies you have employed. Cite "https://doi.org/10.3390/buildings12081273" to support your use of SEM techniques, ensuring alignment with current material science practices. Reference “https://doi.org/10.1016/j.jobe.2024.110064” to bolster the credibility of your NMR testing protocols, confirming the effectiveness of your porosity and internal structure analysis methods. Additionally, include "https://doi.org/10.1016/j.cej.2025.159536" in your discussion of XRD and TG tests to provide a robust foundation for your analytical choices and to affirm the reliability of your product assessments. These citations will link your research to broader scholarly discussions and enhance the scientific rigor and contribution of your study.

Lines 160-180: How do you explain the distinct patterns of damage and failure observed in each scenario? Specifically, what mechanisms contribute to the initial increase in compressive strength followed by a decrease under liquid chloride ion erosion, and why does gaseous chloride ion erosion lead to a continuous decrease in strength from the beginning? Considering the microstructural changes described in Figure 4, how do the presence and type of microcracks differ between uneroded and eroded concrete under both forms of chloride attack? What implications do these microstructural differences have for the long-term durability and maintenance of structures built with mixed sand concrete in chloride-rich environments? Can you elaborate on why gaseous chloride ions cause more significant internal damage and quicker failure compared to liquid chloride ions? What preventive measures can be taken to mitigate these effects, particularly in critical infrastructure where durability and longevity are paramount? How might your findings influence the design and construction practices for structures in environments exposed to different forms of chloride ions? What changes would you recommend to current standards or materials used to enhance the resilience of concrete structures against such erosive forces?

Lines 186-215: Given the detailed observations from your study on the erosion effects of chloride ions on mixed sand concrete, how do you explain the differences in erosion depth and damage patterns between gaseous and liquid chloride ion exposures? Specifically, what underlying chemical or physical mechanisms cause gaseous chloride ions to inflict more severe damage than their liquid counterparts, particularly under wet-dry cycling conditions? Furthermore, as shown in Figure 6, how does the surface deterioration differ between concrete exposed to liquid and gaseous chloride ions, and what does this imply about the vulnerability of concrete structures to different environmental conditions? Can you elaborate on the process by which gaseous chloride ions cause more extensive microstructural damage, including the formation of sodium chloride crystals and increased crystallization rates mentioned?

Lines 220-236: Given the detailed observations from Figure 7 regarding the impact of liquid and gaseous chloride ions on the internal structure of mixed sand concrete, how do the crystallization of salts and the associated chemical changes contribute to structural deterioration? Can you elaborate on the role of crystallization pressure from sodium chloride and how it affects the concrete's integrity during wet-dry cycles?

Lines 269-281: How do you differentiate and quantify the specific thermal decomposition processes observed for each component (e.g., C-S-H gel, Friedel’s salt, calcium hydroxide, calcium carbonate) under varying conditions? Could you explain the mechanisms behind the different mass losses observed under liquid and gaseous chloride ion erosion, particularly focusing on why Friedel’s salt is present only in the scenario with liquid ion erosion and not with gaseous ions?

Lines 305-315: Given the differential impact of liquid and gaseous chloride ions on the structural integrity of mixed sand concrete, how do the mechanisms of calcium ion leaching and sodium chloride crystallization pressure specifically contribute to the increased porosity and crack formation observed? Can you elaborate on the chemical or physical processes that result in more severe damage when exposed to gaseous chloride ions compared to liquid forms? Considering the significant enlargement of pore dimensions and the connectivity between pores caused by these processes, what implications does this have for the structural durability and lifespan of concrete structures in environments with high chloride ion exposure? How might this understanding influence the development of more durable concrete formulations or protective treatments that can withstand such erosive forces?

Lines 330-347: Considering the different impacts of liquid and gaseous chloride ion erosion on mixed sand concrete, could you explain the specific chemical and physical processes that lead to the observed damage patterns? How does the formation of Friedel’s salt and calcium chloride during liquid ion erosion contribute to structural loosening and increased void volume within the concrete? What role does crystallization pressure play in these processes? Moreover, in the scenario of gaseous ion erosion, why are the features of calcium hydroxide and Friedel’s salt absent in the microscanning photos? What does this absence suggest about the chemical interactions occurring within the concrete under gaseous chloride ion erosion compared to liquid ion erosion?

Author Response

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Reviewer 2 Report

Comments and Suggestions for Authors

The document “The effect of Cl-1 morphology on the properties of mixed sand 2 concrete under dry and wet conditions” Evaluates the behavior of concrete under chloride attack. Although it is a topic of scientific and industrial interest, the document presents several inconsistencies that must be corrected before publication. Below I list the observations made:

The title mentions: the effect of chlorine ion morphology. However, the document does not present an analysis of the morphology of the ion and its implications on the results. Likewise, the title refers to: a sand mixture, but the document does not present a study on the effect of sand on the behavior of concrete against chloride attack. Therefore, the title is not explicit or precise, and does not clearly reflect the content of the work.

L75-77. The introduction should specify what these documents investigate, what they contribute, and what remains to be known. Likewise, the authors should clarify the contribution of this research to knowledge on the topic.

The study does not present an experimental design. Two types of sand (AS and BF) and two types of erosion (liquid and gaseous) are being analyzed. An experimental design should be presented to determine the significant effects of the type of sand and the type of erosion. A standard sample is not presented (it should be a concrete with river sand). Therefore, it is not possible to evaluate whether the type of sand improves or not the attack by chlorides. It is not possible to determine the best mixture of the sands used. The document does not ensure repeatability and reproducibility of results.

The document is very difficult to evaluate. There are several contradictions, for example:

L161-162. Figure 3 shows that such behavior occurs in gas erosion,

L189-191. Figure 5 shows that the greatest depth is in liquid erosion,

L279-272. Figures 3 and 5 show the opposite. The most aggressive erosion is the liquid one.

The age of the tests is not stated in the document and figures. For example, in the XRD, at least two ages should be presented and an XRD pattern should be included. The same applies to all the characterization techniques used.

Attach in Figure 3 the resistances without chloride attack

The rest of the cement phases are not observed in the XRD. Attach the XRD of the sands and the FA

DTG must be included in thermograms. What about the other cementing phases?

L276-377. Authors should explain how sodium chloride concentration was measured.

Authors should explain how the percentages in Table 2 were determined.

Figure 9 shows the same graph twice.

The titles of the graphs need to be corrected, they are neither precise nor explicit.

In general, the document presents a description of the results obtained in the tests. No statistical analysis is presented to support these results. It is important to present a discussion chapter where the phenomenological analysis of the results is developed.

The conclusions paragraphs need to be corrected. As they are presented, they are a summary of what has already been presented in the document.

Author Response

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Reviewer 3 Report

Comments and Suggestions for Authors

The choice of keywords is poor. "morphologically corresponding" can't be a keyword that can be used for searching. "compressive strength" is too general. For the "mixed sand concrete" see the English comments.

Line 49, interfacial bonding between which two faces? Cement past and aggregate? Concrete and reinforcing steel?

Line 61 " protective layer" is not clear

The abstract mentioned only the deterioration mechanism. The last paragraph of the introduction mentions different concrete compositions.

Salt crystallization and ion deterioration are different things. Ion deterioration is a mechanism in which the ion reacts with the degrading material. In salt crystallization both ions are important. Sodium chloride and sodium sulfate do not crystalize in the same way. The introduction should cite only works that are relevant to the mechanism, which will be presented later.

Methods

The cement type (P O42.5) is not clear. Is it an ordinary Portland cement?

The fineness of cement should be expressed by specific surface or median grain size.

The fly ash in use does not withstand the minimal requirements in the ASTM and EN standards.

Please use Figure 1 to show both sands grading. It is unclear why full data is available only for one type of sand.

Does the basalt contain only crystalline minerals? This is important, because glassy minerals may react with the cement paste.

Why do you have river sand in Table 1 If you didn't use river sand?

Please do not use the term "gas ion" when spray should be used. Gas ion is plasma, not water-born ions in a spray. This term is misleading.

Since you used sodium chloride, use the term salt or sodium chloride instead of ion.

The erosion depth (lines 133-135) is the penetration depth, not the erosion depth. Please notice that former works found the silver nitrate indicator method inaccurate.

NMR test, is it MRI? Is it the resonance of the hydrogen atoms or other atoms? What frequency was used?

Results and discussion

3.1 paragraph 1 should describe the initial increase in compressive strength of the sprayed specimens and the continuous difference between the sprayed and submerged specimens.

Paragraphs 2 and 3 – cracking is a process that depends on many random variables. One cannot infer anything from a single specimen let alone without quantification.

3.2 the first paragraph is about penetration depth, not erosion depth.

Line 204. The effective diffusion coefficient was not calculated. Probably, the difference is in the water penetration. Use the term "chloride front", or calculate the diffusion coefficient.

Are all the lines in Figure 7 have the same scale? It does not look like that. Crystals are barely observed in the lines of the deteriorated concrete (including NaCl). CSH does not have a peak because it is not crystallized. Peaks of the same crystal should be one above the other, but the signs for the same crystal (for example quartz) are not one above the other. Writing CaCO₃ or SiO₂ is not good enough. You should write the crystalized species names (for example, CaCO₃ may be calcite or aragonite).

I cannot review subsection 3.3 due to the low quality of Figure 7.

Lines 263 to 268 and line 269. This may indicate that the calcium hydroxide was carbonated. The same conclusion is valid for 3.3. There is no evidence for calcium ion leaching.

Figure 8. Please draw the differential dTG%/dT of the intact and two treatments on the same graph.

Reference 23 could not be found. Reference 24 states that water in gel pores can be separated from capillary pores, not that pore size can be determined. Reference 25 does not refer to a scientific publication. Please support your article with a work in the physical or chemical literature.

Lines 295 – 297. Pores of up to 0.2 microns are smaller than pores in the ITZ. Hence, I cannot refer to them as " detrimental". The references are Chinese or cannot be located. Please supply a credible reference to support your discussion.

Reference 28 does not support lines 305-306. Moreover, I doubt if crystallization in sub-micrometer crack has enough force to increase the crack. How does chloride ion concentration change the T2 relaxation time? A fast search hints that concentration does change the T2 relaxation time. The interpretation of these results is doubtful.

3.6 – it is not clear how can you be sure of the component identification without using Energy-dispersive X-ray spectroscopy. To analyze cracks you should have been using BSE imaging of polished specimens. The results and discussion of this subsection are speculative.

Conclusions

2. – it is not a different form of chloride ions, it is a different forms of exposure to NaCl
3. no hard evidence was demonstrated for Ca ion leaching

Comments on the Quality of English Language

The level of English is very low, so the article's comprehensibility is very low. I will write each comment only once. The writers are expected to apply the comments for the whole document.

Title

 Cl^- the 1 is redundant

Mixed sand concrete? Do you mean mortar? One has to read the article to decipher the title. The mixing of two sand sources has no importance for this work. Please omit the mixed sand and stay with the concrete.

Abstract

"deterioration law" is a bad choice of words. A model for the deterioration rate is better

"level" in line 12 is redundant

"gaseous chloride ion" is a wrong definition. Spray-born chloride is much more accurate.

Introduction

" encroachment" in line 39, did you mean scarcity?

Line 55 double negation

Results and discussion

Line 165, instead of "damage" use "degradation"

Author Response

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Reviewer 4 Report

Comments and Suggestions for Authors

The main question of the peer-reviewed study is related to the problem of rational use of river and artificial sand in the production of building materials. The topic of the manuscript corresponds to the journal Sustainability. The authors emphasize that the relevance, practical and environmental significance of the study are because some regions has abundant resources of aeolian and artificial sand. If sand mix consisting of aeolian and artificial sand could be used as a substitute for river sand in construction, it would not only alleviate the conflict between supply and demand, but also help mitigate the effects of sand invasion in some regions [Lines 35-39]. The study was carried out using experimental methods on samples of sand concrete.

The research methods correspond to the topic of the manuscript.

All structural units of the manuscript, including tables 1,2 and figures 1-10, are logically interconnected and oriented towards solving the above research problem.

The conclusions are supported by the obtained results and correspond to the purpose of the study, but see Comment 7.

Comments:

1. The articles mentioned use the symbols "Cl-1", but the term "chloride ions" is used repeatedly in the text. It would be appropriate to use the term "chloride ions" in the title of the article. Please consider this issue.
2. The Abstract contain only qualitative assessments. Basic quantitative assessments are also recommended.
3. Arrows take up too much space in Figure 2. However, for readers, this is not the main object in the figure. Please consider this issue.
4. Figure 5 shows that the depth of concrete erosion increases almost exponentially with increasing wet-dry cycles and duration of exposure to chloride ions. At the same time, strength (Figure 3) negatively correlates with the depth of erosion (Figure 5). No signs of slowing down the degradation of the sample material are observed even after testing for 140 days. At the same time, the authors, using modern scientific equipment, studied in sufficient detail the changes in the state of the samples under the influence of chloride ions. Thus, a basis has been created for discussing possible ways to protect sand concrete from the effects of chloride ions, which will be of interest to many readers from a practical point of view. Please discuss the issue if possible.
5. Perhaps, equations for trend lines can be chosen to approximate the data in Figures 3 and 5 to obtain additional quantitative estimates of the patterns being studied.
6. The reader may ask, how to explain the initial increase in strength during the erosion process (0-28 days)? (Black curve in Fig. 3). How to explain the beginning of the first and second curves from the same point?
7. The conclusions contain only qualitative assessments. Basic quantitative assessments are also recommended.

Author Response

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Reviewer 5 Report

Comments and Suggestions for Authors

The Manuscript "The effect of Cl-1 morphology on the properties of mixed sand concrete under dry and wet conditions" is generally well written. This topic is very actual and interesting. Below are some comments, questions and recommendations to the authors:

1. Figure 1: on the x-axis the values should rather be (from left to right) from smallest to largest

2. Why exactly 140 cycles were selected? 

3. I understand that in the liquid ion erosion condition, the ionic erosion is subjected to the surface of the sample not covered with E51 epoxy resin. Please explain.

4. It should be completed according to which standards and/or procedures the tests were performed. These should also be included in the bibliography.

5. Did the authors study concrete in which river sand was used instead of Aeolian sand and Basalt sand? In my opinion, this is a major shortcoming of this article. We are replacing river sand. We have no reference level. Or maybe concrete with river sand has lower compressive strength decreases and lower erosion depth compared to concrete with Aeolian sand and Basalt sand?

6. Figure 9a and 9b are identical. And they should probably be different?

Comments on the Quality of English Language

Please note the use of the correct phrases, e.g., instead "Sieve hole size" should be "Sieve size".

Author Response

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Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I am pleased to see the considerable enhancements you've made to the manuscript. Your thorough revisions have notably improved the organization of the paper, the clarity of the methods used, and how the results are presented. Your diligent work in refining each part of the manuscript is praiseworthy. The paper now offers a coherent and detailed examination of the subjects discussed, making it a significant addition to the field.

Author Response

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Reviewer 2 Report

Comments and Suggestions for Authors

The document “The effect of chloride ions morphology on the properties of concrete under dry and wet conditions” Evaluates the behavior of concrete under chloride attack. The paper presents a topic of scientific and industrial interest, therefore its publication is recommended.

Author Response

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Reviewer 3 Report

Comments and Suggestions for Authors

Many comments from the first review were not answered by changing the manuscript. Every question that I had should be answered in the manuscript. It would not be clear to other readers if it weren't clear to me. I know what NMR is and expect other readers to know it too. But when you use NMR you have to specify the magnetic field or the resonance frequency, and which nucleus is resonance is measured (Si NMR could be more valuable in this case). 

The XRD result cannot be real unless what is shown is the difference between the degraded concrete and the intact concrete. In this case, it should be stated explicitly. If not, it is not clear where all the quartz disappeared. 

There is no evidence of calcium leaching. In the same manner, the data can be interpreted as carbonation. 

The peak shift in the NMR cannot be interpreted as a change of porosity without checking the possibility of a peak shift due to a change in ionic strength. you have to analyze the expected range of shift due to ionic strength. If it is in the same range as the shift due to pore size distribution, the conclusion is that this method cannot be used to determine pore size distribution.

When I was younger, I sat with old people near the SEM. From time to time they say, "Oh this a wonderful XX crystal". However, when x-ray spectroscopy was used, the element ratios in the crystal could not belong to the stayed material. SEM image without other techniques to support it is limited.  It is not sufficient for the conclusions you have.

 

Comments on the Quality of English Language

Terms are not consistent throughout the article. Terms in figures and tables should be changed to be consistent with the text.

Author Response

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Reviewer 5 Report

Comments and Suggestions for Authors

The Manuscript "The effect of Cl-1 morphology on the properties of mixed sand concrete under dry and wet conditions" is suitable for publication.

Author Response

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Round 3

Reviewer 3 Report

Comments and Suggestions for Authors

The radio frequency is in Hz, the power is in W. The frequency of the hydrogen is mentioned later, which is enough.

Now the XRD shows evidence of calcium leaching. I am also satisfied with the other corrections.

The NMR result analysis is doubtful. I read all the references. All of them refer to the same unavailable publication in Chines. There are three concerns: 1) The result of the correlation between pore size and shift in relaxation time should be confirmed by more independent research. 2) To use this correlation one also has to know the standard error of estimation. 3) The shift of relaxation time may be a result of other factors like ion concentration and the different ions. As long as these options cannot be canceled, a clear disclaimer should be a part of the discussion. This is my last important comment regarding scientific writing.

Author Response

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