Chloride Binding Capacity and Its Effect on the Microstructure of Mortar Made with Marine Sand

Round 1

Reviewer 1 Report

The subject is interesting and the paper is suitable for the Sustainability journal. The paper discusses the effects of three fine aggregate, with different chloride content in its composition, on chloride binding capacity and its effect on microstructure were investigated.

However, some suggestions are recommended in order to improve the clarity of the research and the findings.

The research idea (i.e. the effect of chloride ions on microstructure of the mortars) is not completely novel or original, but the methodology used gives clear insight of the issue.

The paper is in general well written; however, since the reviewer is not native English speaker, this not implies that correctness of the English language is adequate.

Some minor remarks which should be tackled by the authors are recommended, before publication can be considered:

• Introduction:
  • Line 36-42: Is said that the idea of use marine sands can be advantageous in terms of sustainability, since is an abundant resource and desalination technologies can be used to reduce the negative effects on the mortars. However, no study of the environmental impact of transport the marine sands to the distant areas of the coastline, as well as the environmental impact of using the desalination technologies is shown.
  • Line 44-66: This part of the introduction is not always clear and should be reformulated/clarified.
  • Line 55: “Chloride binding is relatively complex and is influenced by various factors.” Please avoid generic statements and briefly specify the factors.

• Materials and Methods:
  • In subsection 1 the authors do not report the particle size distributions of the different used sands. This should be added to support the interpretation of the results.
  • Should also be added the river sand source, as well as the desalination process used.
  • In subsection 2.3.6 the authors do not report the parameters used by MIP (i.e the pressure range, pore size range, surface tension and the contact angle). This should be added to support the interpretation of the results.
    

• Results:
  • I propose that this section should be moved to the Discussion, since there are some others results present in section 4.
  • Line 128-129: “The free chloride content in MS and WMS specimens increase first, then decrease and finally stabilize during the curing ages”. This behaviour should be clearly explained by the authors.

• Discussion:
  • I propose that this section should be the Results and Discussion, and the references to previous studies should only be made when necessary and related to results found in the authors' research.
  • Line 152-153: In the sentence “To clarify whether this process exits in the mortar made with MS, the chloride contents of several areas with different distances away from sand at 3 d were tested”. The experiment was performed only at 3 days? Why did the authors choose this age? Why was it not done at other curing ages? Please clarify this aspect.
  • Figure 2: The figure is related to the MS mortar or WMS mortar? Please complete the legend and add details of the morphologies of the main crystalline compounds growing in pores.
  • Line 196-197: “As shown in Figure 5, several evident endothermic peaks are observed in MS and WMS specimens at different curing ages, and the corresponding substances include C-S-H, AFt, AFm, Ca(OH)₂ and calcite.” I suggest that the authors should add the monoculture used in figure 5 (i.e calcite (CC); Ca(OH)2 (CH), etc).
  • Line 207-208: The results indicated that content of Friedel’s salt gradually increased with curing age”. The authors should explain the relationship with the results obtained in Figure 1 and how to connect to the content of Friedel’s salt, since the bound chloride content is constant from 28 days.
  • Figure 6: Very interesting figure, Please add details of the morphologies of the main crystalline compounds growing in pores to complete.
  • Figure 7 and Figure 8: what curing age was the analysis performed? Please complete the information since it is important to know if the samples measured by MIP were completely hydrated or not.
  • In the text is not referenced the Figure 8.
  • Line 231-232: “This result indicates that the introduction of chloride ions can reduce the total porosity of mortars by the chloride binding products” and Line 234-235: “The chloride binding products make the mortar structure more compact.” Please add the values of total porosity measured by MIP to support the interpretation of the results.
  • Line 233-234: “The curves illustrate that the volume of 10-100 nm fine capillary pores in the MS specimen was significantly the highest, followed by the WMS specimen and the RS specimen”. The presence of shell increases the CaCO₃ content due to the sand mineralogy, which involves a reduction of the volume of large pores (> 1µm) and generates the formation of amorphous and semi-amorphous calcium carbonate agglomerates which increase the volume of intrusion obtained in this range. Can the author comment the influence of shell in the results obtained by MIP.
  • Line 235-240: The authors suggest that the chloride ions introduced by fine aggregate can act as a filler in the pores of the concrete and refine the pore structure of the mortar but without clearly explaining what would be their effect on the measured MIP curves.
  • Moreover, in general, the large population of pores under 10 nm could be attributed to the formation of calcium silicate hydrates (C-S-H) and calcium aluminium silicate hydrates (C-A-S-H) compounds, and the measured by MIP in this range have significant limitations. It would be very useful to complement the work with nitrogen adsorption measured or microscopy observation on thin sections. These can provide relevant information.

• Conclusions
  • I suggest that the authors should also add some considerations about the durability and the applicability of the aggregates on the performance improvement of the cement mortars in order to predict the real sustainability of the use of these aggregates.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Manuscript entitled “Chloride binding capacity and its effect on the microstructure of mortar made with marine sand” submitted by Congtao Sun, Ming Sun, Tao Tao, Feng Qu, Gongxun Wang, Peng Zhang, Yantao Li, Jizhou Duan.

 

Here is a list of my specific comments:

1. General comment: The novelty and practical applicability of this study should be clearly highlighted in the manuscript.
2. Page 1, Abstract: This section is quite too short and too general. Include here the most important experimental results to highlight the importance of this study.
3. Page 1, line 36: “Given the advantages of abundant resources…”. Add here some references.
4. Page 2, line 69: “The chloride binding behavior…”. At the end of Introduction, the main objectives of this study should be clearly and detailed presented.
5. Page 3, 2.3. Test methods: Delete all subtitles from this section, and provide a detailed description of the experimental methodology used for this purpose.
6. Page 3, 3. Results: In my opinion, this title should be replaced by “3. Results and discussion”, because the number of experimental results is too low.
7. Page 4, 4. Discussion: Delete this title and include all observation in the section “Results and discussion”. Also, provide a detailed interpretation of the experimental results in agreement with the main objectives of this study.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

All my previous remarks and comments have been considered in this new version of the manuscript. In my opinion, the revised manuscript meets the criteria and can be published as original paper in Sustainability Journal.