PONE-D-23-35135Influence of Pozzolanic Addition on Strength and Microstructure of Metakaolin based ConcretePLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: I Don't Know

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3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

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4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The intent of this study is to explore the physical properties and long-term performance of concrete made with metakaolin (MK) as a binder, with the utilization of micro silica (MS) and nano silica (NS) as substitutes for a portion of the cement content. The dosage of MS was varied from 5% to 15% for OPC-MS-MK blends and dosage of NS was varied from 0.5% to 1.5% for OPC-MK-NS blends. Incorporation of these pozzolans accelerated the hardening process and reduced flowability, consistency, and setting time of the cement paste. In addition, it produced a denser matrix, improving the strength of the concrete matrix that was confirmed with SEM and XRD analysis. The use of MS enhanced strength by 10.37% and the use of NS enhanced strength by 11.48% at 28 days. It also reduced the matrix penetrability and enhanced the resistance to sulphate attack. Based on the results, 10% MS in presence of 10% MK for OPC-MS-MK blends and 1.0% NS in presence of 10% MK for OPC-MK-NS blends is considered as optimal dosage in cement composites.

This paper is well-organized and written well. But, it cannot be published in this present form. The authors need to address the following comments before possible publication.

1. The authors have stated that “10% MS in presence of 10% MK for OPC-MS-MK blends and 1.0% NS in presence of 10% MK is considered as the optimum dosage” which has already been carried out by many researchers. Clarify and clearly state the novelty of this paper.

2. What are the key parameters which are uniquely different when comparing the previous work done by [33] K. Nandhini, V. Ponmalar, Investigation on nano-silica blended cementitious systems on the workability and durability performance of self-compacting concrete, Mater. Express. 10 (2020) 10–20. https://doi.org/10.1166/mex.2020.1618.

3. There are no codal recommendations or provisions compared with the results observed from this study. For example, IS 4031-2019 part 4 & part 5 on page 6-Citation missing.

4. The equation on page 19 is wrongly marked as (1) change it to (2).

5. The English language for the entire manuscript needs to be thoroughly checked using a proof-reader. Say on page 15; “Fig. 6 illustrates the surface microstructure depicted in SEM images of the MB-1 concrete specimen along with the specimen having the highest compressive strength among OPC-MK-MS specimens (MB4) and OPC-MK-NS specimens (MB9)” which is the right way of representing the context. Similarly do a thorough check during the revision.

6. The introduction part needs to be specific with the literatures pertaining to cement + MK+MS+NS or a combination of either of these 3 SCM which would-be worthwhile for the readers to understand.

7. Section 2-Materials separate into sub-sections for each of the materials used with their physical and chemical properties.

8. Section 3- Various tests conducted like Fresh properties, hardened properties, durability studies etc.

9. Section 4- Results and discussion of section 3.

10. Fig. 1. What is IST and FST? Setting time period falls within the codal recommendations?

11. What is the reason for the ternary binder requiring more water with the increasing percentage level of NS at a constant dosage of MK?

12. Legends are missing in Figs 3-5, 8,9.

13. Fig. 6. Microstructural images are with respect to which day of curing and testing has not been reported.

14. Present the durability studies also as sub-sections so that the readers would understand the uniqueness that irrespective of the test conducted both M4 and M9 concrete mix performs well.

15. What is the primary objective behind the incorporation of pozzolanic substances into metakaolin-based concrete, and how does this impact its strength and microstructural characteristics?

16. Elucidate the alterations in the microstructure of metakaolin-based concrete when pozzolanic materials are introduced, and how do these modifications influence the material's performance?

17. What are the primary methodologies or approaches utilized for the evaluation and assessment of the microstructure of concrete incorporating pozzolanic agents?

18. In what manner does the curing process impact the strength and microstructure of metakaolin-based concrete containing pozzolanic supplements?

19. In the context of enhancing strength and microstructure, which practical applications or construction scenarios are most positively impacted by the utilization of metakaolin-based concrete with pozzolanic additives?

20. In the conclusion state the optimised mix design and add a recommendation for the future studies using these SCM.

21. Please conduct an extensive literature review. Some of the most relevant references that need to be cited in the literature review section are:

a. Study on the addition effect of metakaolin and mechanically activated kaolin on cement strength and microstructure under different curing conditions

b. Influence of super absorbent polymer on mechanical, rheological, durability, and microstructural properties of self‐compacting concrete using non‐biodegradable granite pulver

c. Performance of sustainable insulated wall panels with geopolymer concrete

d. Influence of nano composites on the impact resistance of concrete at elevated temperatures

Reviewer #2: The authors have present a study to evaluate the combined effect of metakaolin (MK), micro silica (MS) and nano silica (NS) on the physical properties, strength and microstructural properties of concrete composites. During these studies the phenomenon of mutual synergy of microstructural interactions of materials used - for the potential production of sustainable concretes and their applications in concrete structures was taken into account. Paper is in the journal scope. However, there are some changes that need to be made to the manuscript in order to improve it, as follows:

(1) Abstract. Abstract were not formatted according to the paper's instructions. There should be a summary of both qualitative and quantitative findings in this section.

(2) Intruduction. There is a lack of clarity in the introduction section. A description of any relevant earlier work should be included in this section of the paper. It should be noted that there are various ways to modify concrete composites taking into account synergy between pozzolanic additions, in order to obtain a more durable and sustainable material. Therefore, please include recent literature that has been published during 2023 in the introduction, for example:

-“Mechanical properties and brittleness of concrete made by combined fly ash, silica fume and nanosilica with ordinary Portland cement, AIMS Materials Science 2023.

- „Editorial: Fabrication and properties of concrete containing industrial waste”, Frontiers in Materials, 2023.

- „Study of strength and microstructure of a new sustainable concrete incorporating pozzolanic materials”, Structural Engineering and Mechanics, 2023.

- „Concrete composites based on quaternary blended cements with a reduced width of initial microcracks”, Applied Sciences 2023.

- „The effect of the addition of coal fly ash (CFA) on the control of water movement within the structure of the concrete”, Materials, 2023.

- „Assessing of water absorption on concrete composites containing fly ash up to 30 % in regards to structures completely immersed in water”, Case Studies in Construction Materials, 2023.

- The role of pozzolanic activity of siliceous fly ash in the formation of the structure of sustainable cementitious composites”, Sustainable Chemistry, 2022.

(3) Methodology. The cost of nano silica should also be discussed as they are costly.

(4) Experiments. Please provide photos showing samples during preparations (in connection with the photo showing specimen during testing, Fig. 1b). The flowchart of the presented studies should also be presented. Fig. 1 is insufficient.

(5) SEM Studies. Descriptions of SEM studies should be improved. Please provide SEM images with higher magnifications of visible phases. Moreover, besides SEM images please provide also EDS charts. Phase identification is possible by analyzing the EDS diagrams. The morphology itself does not say everything. These studies should be supplemented. How can you tell from these pictures that there is a C-S-H or CH phase.

6) Conclusions. The conclusions are too general. More specific conclusions are needed

indicating the application of the work.

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Reviewer #1: No

Reviewer #2: No

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Influence of Pozzolanic Addition on Strength and Microstructure of Metakaolin-Based Concrete

PONE-D-23-35135R1

Dear Dr. Bahrami,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Kind regards,

Paul Awoyera

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: (No Response)

Reviewer #2: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: (No Response)

Reviewer #2: Yes

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: (No Response)

Reviewer #2: Yes

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4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: (No Response)

Reviewer #2: Yes

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: (No Response)

Reviewer #2: Yes

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The paper can be accepted for publication. The authors have addressed all my comments. Congratulations to the authors.

Reviewer #2: The paper is well revised. I have no further comments.The manuscript is improved and the questions are well addressed. so I think the article is accetable as it is.

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7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

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