Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper explores the effects of sulfurized CO2 on the mechanical properties, pore changes, and microstructural characteristics of alkalized coal gangue. It delves into the impact of modified coal gangue on concrete in terms of pore distribution and hydrated components. This research topic is highly innovative and possesses significant practical application value. The method of carbonizing aggregates after alkalization, combined with the use of the High-temperature Steam Carbon Mineralization Enhancement Device, represents a novel approach to strengthening coal gangue and provides a theoretical foundation for the engineering application of coal gangue, aligning with the scope of "Sustainability." The paper contains minor issues that the authors should address. Specific suggestions are as follows:

 

1.        The country of origin for the coal gangue used in the study is not specified. Please add this information to facilitate reader understanding.

2.        The authors' topic has the potential to address pollution issues in coal mines and thermal power plants. However, to my knowledge, exhaust gases from thermal power plants are currently subject to desulfurization treatment. Please explain the rationale behind the existence of "SO2 content of approximately 96 mg/m³."

3.        In Figure 13 of the paper, chemical formulas should adhere to proper subscript and superscript formatting.

4.        More specific details should be provided regarding materials, equipment, and testing methods. Information such as the model of testing equipment, the number of test samples, and the dimensions of specimens will enhance the manuscript.

5.        MIP testing is a traditional method for pore structure analysis widely adopted by researchers. Compared to MIP, what are the notable advantages of NMR? It is recommended to briefly supplement the advantages of NMR testing over MIP testing.

6.        Consistency in terminology should be maintained throughout the paper, and abbreviations should be defined when they first appear.

7.        An explanation is needed on how alkalized coal gangue aggregates of different concentrations affect the pore distribution and porosity changes in concrete.

 

8.        On page 8, line 266, the mention of the constitutive relationship of concrete should be removed. The paper does not investigate the constitutive relationship but establishes a connection between pore structure parameters and strength based on statistical analysis.

Comments on the Quality of English Language

Well writen.

Author Response

Please see attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The article discusses important and topical issues related to the study of the strength and microstructure of concrete from coal vein.

The presented new method improves the physical and mechanical properties of coal rock from the suburbs of Inner Mongolia for its further use as an environmentally friendly material for work on slopes. The method is based on the controlled transfer of moisture into the porous rock using high-temperature steam. This approach provides air sequestration, realized due to the economical gas outlet of the loading of sulfided composite gases CO2.

Experimental studies have shown an improvement in the properties of the material after treatment. Thus, the microhardness of the surface and transition zone increased by 24.3% and 36.4%, respectively, after three-hour treatment. Compressive strength and compositions of concrete based on a coal base increased to 4.8-27 MPa and 0.4 MPa, respectively. At the same time, a decrease in porosity to 3.6% and a decrease in the proportion of harmful pores from 11.22% to 6.54% were observed. Positive correlation between the addition of harmless/low-harmful pores and the strength of the material to confirm the effectiveness of the proposed method.

The proposed method can effectively improve the physicochemical properties of coal gangue, increasing its stability for use as a building material. Coating treatment with surface activity and degree of moisture, which has a positive effect on strength characteristics. The results of the study are impressive prospects for the use of this method to solve environmental problems, areas with the utilization of coal gangue and land reclamation in the coal mining regions of Mongolia. Further research will be aimed at optimizing the process parameters and scaling up the technologies for industrial application.

The work presented by the authors is of interest to readers in the field under consideration.

 

However, the work has the following comments:

 

1. The paper discusses various methods of processing coal wood (coating, heat treatment, chemical activation, carbonization), but does not provide a detailed description of these methods. For a scientific publication, it is necessary to describe in detail the technologies used, specify the processing parameters (temperature, time, pressure, reagent content) and justify the choice of specific methods.

2. The introduction should dwell in more detail on the methods for improving the characteristics of concrete after processing gangue, but does not provide specific data (tensile strength, bending, modulus of elasticity, water absorption, etc.). To confirm the effectiveness of the proposed methods, it is necessary to provide test results with recording of measurement errors. The analysis of the microstructure of the material should be supported by artificial images and data.

3. In section "2. Materials and Methods" the description of the materials used is too concise. It is necessary to describe in more detail the properties of coal gangue, including the chemical composition, particle size distribution, and other relevant characteristics.

4. The description of the experimental setup is not detailed enough. It is necessary to provide a setup diagram, as well as a detailed description of the process parameters, such as temperature, pressure, and processing time.

5. The analysis of the X-ray diffraction (XRD) results is not detailed enough. It is necessary to describe the phase composition of the samples in more detail and analyze the change in phase composition depending on the alkali concentration.

6. The work should provide a more detailed description of the devices and methods used to determine microhardness, porosity, and other characteristics. X-ray phase analysis should be considered in more detail, as one of the most popular methods.

7. The description of the micromorphology of the samples is not detailed enough. It is necessary to provide more information on the structure and morphology of hydrate products.

8. It is necessary to provide more information on the effect of carbonation process parameters on the microstructure and properties of concrete.

9. It is necessary to explain how the change in water absorption is related to the blocking of pores. A more convincing justification is required. 10. The conclusions should present prospects for further research on the topic under consideration.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

In this study, the optimization of coal gangue performance through sulfurized CO2 composite gas-steam carbon sequestration of harmful coal gangue was explored, and the properties of coal gangue concrete and elucidate its underlying mechanisms were analyzed. The variations of exhaust gas composition, type, and treatment conditions on mechanical properties and microstructure characteristics were investigated. The paper may be interesting to some readers related to waste materials recycling in concrete. However, some major revisions should be conducted. The detailed comments are as follows:

(1) The abstract should be concise to include the key information. The background is presented excessively, but the research gaps are not illustrated clearly. It should be noted that sentences should be easy to understand by readers.

(2) The objective should be restated and highlighted.

(3) Authors have analyzed many previous publications, while the research gaps are not well highlighted. The literature review and comments should be further improved.

(4) Authors have conducted so many experiments, while the detail explanations are not presented why these tests should be conducted. It should be always noted that the investigations should be done with specific objectives.

(5) The figures should be optimized. The font size is too small.

(6) More discussions should be provided to explain the results, and the correspond references are also needed.

(7) It is difficult to see the application scenario of concrete after the concrete was optimized by the fixed carbon and improved performance. It is very important to show the applications, like buildings, pavement. The performance requirements under different applications are considerably different.

(8) The conclusions should be concise to include the main findings, and it should be meaningful and effective.

(9) The reviewer suggests the manuscript should be double checked and revised for some typos, grammar mistakes, and format errors (especially the use of a large number of Chinese symbols).

 

Comments on the Quality of English Language

The English Language must be improved in terms of typos, grammar mistakes, format problems.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

In general, the article has been revised by the authors and my comments have been taken into account. A few more minor corrections need to be made.

1. Format the list of references according to the rules.

2. Make full captions for figures 6-15. That is, write not just "Microstructure", but write in full "Microstructure of the material ... obtained ..."

3. Add a couple more specialized keywords on the topic of the work.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors has revised the manuscript favorably. The current version can be accepted.

Author Response

Dear Editor and Reviewer：

Thank you for your letter and for passing on the reviewers' constructive comments concerning our manuscript entitled, "Study on the strength and microstructure of coal gangue concrete by sulfurized CO₂ composite gas and steam carbon fixation" (Manuscript ID: Sustainability-3381710). We appreciate the recognition of our previous submission and the time and effort the reviewers have dedicated to examining our work.

Thank you once again for your consideration and the valuable feedback provided by the reviewers. We remain hopeful for the positive outcome of our revised manuscript.

Best regards.

Huanjie Su