Performance Optimization and Synergistic Mechanism of Ternary Blended Cementitious System Composed of Fly Ash, Slag, and Recycled Micro-Powder

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

To improve the sustainable use of solid waste materials in mortar manufacturing, this study explores a ternary blended cementitious system made of fly ash, slag, and recycled micropowder. We carefully assessed how different replacement amounts affected workability, mechanical strength, shrinkage performance, and microstructure, especially at 10% and higher. The paper needs to be revised as per the following:

 

The authors should elaborate the importance of this study for the literature in the last part of Introduction.

 

There should be balance between the papers written by Chineese and non Chineese authors.

According to the statement, the reference group's hydration products are comparable to those at low dosages. Could the authors support the hydration products' chemical similarity with more thorough XRD or thermogravimetric analytical data?

 

The findings mention enhanced brittleness as a result of a higher ratio of flexural to compressive strength. Could the authors elaborate on the importance of this ratio increase for structural performance and the potential effects on real-world application scenarios?

 

How about the repeatability of the tests performed? No error bars in the figures.

One significant finding is the decrease in drying and autogenous shrinkage. Could the authors elaborate on the possible processes by which 10% recycled slag and micropowder result in this kind of shrinkage reduction and whether or not this impact lasts over prolonged curing?

There is a brief discussion of the longer setting periods and improvements in workability. Could the authors elaborate on how these fresh-state attributes are impacted by the blended materials' powder shape and particle packing characteristics?

 

What are the limitations of the present study?

 

The study's findings for mortar samples taken in a lab setting are encouraging. How would the authors verify the system's performance in more complicated scenarios, and have they taken into account issues with scale-up or compatibility with actual concrete mixtures (including aggregates)?

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In this work, the influence of the ternary blended cementitious system has been studied in detail. In particular, the influence of the recycled micro-powder on their structure and properties have been examined. In my opinion, it is an interesting work from a structural point of view. The manuscript can be published but requires minor revision.

1. Techniques used should be mentioned in the Abstract.
2. I recommend standardizing the citation of names and surnames in the introduction, indicating the full name and surname or the surname and the first letter of the name.
3. In the introduction you write that "Research on multi-component solid waste cementitious materials (fly ash–slag–recycled micro-powder) has become a hot topic", but you do not cite any studies that use this particular composition (fly ash–slag–recycled micro-powder) of materials. Please supplement the introduction with other authors' works that investigate this system, or emphasise the novelty of your work more.
4. In Table 3, it is unclear from the marked samples (e.g., FM0.5) what the dosages were based on, and how they were calculated.
5. Why was 0.5% of plasticiser chosen? Isn't this amount too low? Have other amounts of this additive been tested?
6. In Section 2.2, the text does not specify under what conditions (temperature, humidity, curing duration, etc.) the samples were stored during curing.
7. It would be better to indicate "(see Figure 1(a))" in page 3, line 109 after ...cement mixer..., since the picture shows the equipment, but not the mixing process.
8. I recommend changing the title of Figure 1(a) to "Paste Mixer" (120 line).
9. I recommend you clarify what specific curing age you have in mind (line 144). It is unclear whether the samples were analysed by XRD only after 28 days or after a shorter period as well.
10. No dimensions are specified in Figure 2 (b and c).
11. From Figure 2 (c), the compressive strength test should have used specimens with dimensions of 40x40 mm. The text in subsection 2.3.2 states that the mentioned test was performed with a half-prism. Why were the tests not performed with specimens of the specified dimensions? Micro-damages may have occurred during the flexural strength of the prism, which could negatively affect the compressive strength. Please edit Figure 2(c).
12. I recommend you clarify what specific curing age you have in mind (line 177). The same problem as mentioned in question 9.
13. It is challenging to relate Figure 7 to Table 3 and the text in lines 195-200. In Figure 7 amount of micropowder is given in wt%. You can supplement the table by additionally indicating the amount (wt%) of regenerated micropowder, or, in Figure 7, by additionally marking the sample designations used in Table 3(C0, FM0.5, etc.).
14. Line 200 and line 203 – there aren’t spaces after numbers (1) and (2).
15. The same problem with Figure 8 as in Figure 7 (Question 13).
16. Lines 223 - 224 – there aren’t spaces after numbers (1), (2), and (3).
17. Misleading sentence and paragraph. It is difficult to understand when reading at what dosages of the additive the increase/decrease in strength is visible. I would recommend rewriting the paragraph (lines 245-250) with a clearer description of the data in mind.
18. I recommend modifying the sentence (Lines 260-263) and adding which samples show an increase and which show a decrease.
19. Section 3.3. The reasons and criteria for selecting the specific specimens for further research should be stated.
20. I recommend providing explanations of the abbreviations used in Figure 11 (AFt?) and Subsection 3.3.1 text, including the names of compounds, their chemical formulas, and the d-spacing Additionally, it is recommended to use at least three main diffraction peaks in the XRD pattern for accurate identification of each compound. For some compounds, only one is marked.
21. The abbreviations of the compounds in Figure 11 and text (Line 279) need to be unified (in the figure - "C-H-S", in the text - "C-S-H"). Are these different compounds?
22. I recommend adjusting the quality of the photos in Figures 12-14 and the brightness of the markings used, as it is impossible to read and see the text and lines.
23. Figures 15-17 are not cited in the text (Lines 308-316).
24. Line 312 “…Ca/Si ratio rises significantly...” - I recommend adding specific values indicating how the aforementioned Ca/Si ratio changes.
25. For what reasons was sample FM2 included in the pore structure analysis? Why was sample FM0.5 not included in this and other analyses?
26. Mistake in Figure number (Line 345).
27. Please verify the citation style and ensure that all authors' names and surnames are formatted consistently.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

No questions.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript titled "Performance Optimization and Synergistic Mechanism of Ternary Blended Cementitious System Composed of Fly Ash, Slag, and Recycled Micro-Powder" presents an experimental study on the mechanical, microstructural, and shrinkage behavior of mortar systems incorporating fly ash, slag, and recycled micro-powder as ternary blends. The work addresses the potential of such combinations to enhance the performance and sustainability of cementitious materials, particularly in the context of solid waste utilization and low-carbon construction.

The study is based on a comprehensive experimental program that includes rheological tests, strength development (3, 7, 28 days), XRD, SEM/EDS, MIP, and shrinkage evaluations. Results indicate that low replacement levels (10%) of cement and fly ash with slag and recycled micro-powder result in mortar performance comparable to or better than the reference mix. However, higher replacement rates lead to increased porosity and decreased strength.

While the manuscript contributes valuable insights to the field of sustainable cement-based composites, several key issues require attention. These include inconsistent or imprecise technical terminology, unclear definitions (e.g., "defects of recycled powder"), lack of clarity in microstructural phase identification, and insufficient explanation of observed phenomena (e.g., unexpected high amounts of AFt or absence of visible C-S-H in SEM). Furthermore, the interpretation of some results does not always align with the presented data.

Please refer to the annotated PDF for detailed comments and suggestions.

 

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript investigates the performance of blended cementitious systems based on fly ash, slag, and recycled micro-powder. The topic aligns with current trends in sustainable construction materials and valorization of solid waste. The experimental design is extensive, including mechanical and microstructural characterization. However, there are several areas where clarification, further detail, or improvements are necessary.

• The introduction and the Discussion Sections can be improved by discussing/mentioning more recent studies on the use of Slags (e.g: https://doi.org/10.1016/j.conbuildmat.2025.142547 ) or RCP (e.g: https://doi.org/10.1007/978-3-031-53389-1_26 ) in cement mixes, not only Geopolymers. 
• It is essential to specify the type of slag used. Is it from a blast furnace (GGBFS), electric arc furnace (EAF), or ladle furnace (LFS)? Each type has significantly different chemistry and reactivity. Currently, the description is vague.
• The blended system described includes cement, fly ash, slag, and recycled micro-powder. If all four are present simultaneously, it constitutes a quaternary system, not a ternary!
• Please confirm the exact particle size distribution and surface area of each powder. Currently, only "less than 75 µm" is mentioned, which can be insufficient. If not available, it should be highlighted for future studies.
• Figures 1 through 6 show basic laboratory equipment (mixers, Vicat, etc.). While informative for beginners, such figures are unnecessary in a research journal and can be removed or moved to supplementary material. Their presence affects the professionalism and conciseness of the manuscript.
• Please cite all standard methods used explicitly within the text and match them with references.
• What is the maximum particle size of the fine aggregate? 
• The SEM images (Figures 12–14) are quite blurred. Please improve their quality and contrast. Marking key hydration products (C–S–H, CH, ettringite, etc.) would enhance their usefulness.
• Linking microstructure studies (e.g., Ca/Si) more directly with mechanical properties in the discussion would strengthen the argument.
• In future studies, I suggest investigating the reactivity of the slag and recycled micro-powder by thermogravimetric analysis (TGA) or bound water measurements, especially to support the observed microstructural evolution. This is particularly useful given the discussions around Ca(OH)₂ consumption and hydration degree.
• There are multiple minor grammatical and phrasing issues (e.g., "the hydration products are more favorable" is vague).
• The use of parentheses for itemized reasons (e.g., "(1)...", "(2)...") is overdone. Consider integrating them into a narrative form for smoother reading.
•  Ensure consistency and professional formatting in all figures. (Axis labels are occasionally too small or unclear)

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

revised as suggested

Reviewer 3 Report

Comments and Suggestions for Authors

Thank you for your thorough and thoughtful revisions. The manuscript has been significantly improved in both clarity and scientific rigor. The technical terminology has been appropriately refined, unclear expressions have been corrected, and key concepts—such as the role and characterization of recycled micro-powder—are now better defined. The microstructural interpretations are more consistent with the presented data, and the identification of hydration phases has been clarified. These improvements enhance the overall coherence and credibility of the study.

I find the revised version suitable for publication in Buildings and have no further comments.

Reviewer 4 Report

Comments and Suggestions for Authors

Thanks for addressing the comments.