Review Reports - Nanocomposites Produced with the Addition of Carbon Nanotubes Dispersed on the Surface of Cement Particles Using Different Non-Aqueous Media

Round 1

Reviewer 1 Report

Dear Authors

The manuscript describes the inclusion of carbon nanotubes (CNTs) in cementitious composites due to the enhancement of their electrical, thermal, and mechanical properties. The manuscript presented concerns an interesting and actual subject.

The following suggestion and comments should be taken:

1. The overall English needs to be improved. Please seek guidance from a native English speaker if possible ("the" "a", commas, plural form and others could be corrected).

2. The introduction section needs enhancement few sentences about the other CNT composites and their different applications. Please cite

(1) Microsyst Technol (2021). https://doi.org/10.1007/s00542-021-05211-6

(2) Materials (2021), 14(9), 2448; https://doi.org/10.3390/ma14092448

(3) A review on the development and application of graphene based materials for the fabrication of modified asphalt and cement (2021) https://doi.org/10.1016/j.conbuildmat.2021.122885

3. Figure 1. Please correct this image for better quality (the inscriptions).

4. Please answer the question in the comments: What do you think, are you have cement particles in or out of nanotubes? Do you have the encapsulation process in tubular structures?

5. Could the authors include the standard deviation of the used methods?

6. Could authors add some HRTEM or SEM images of materials?

7. Raman spectroscopy. Could authors add Raman spectroscopy and a table with an intensity ratio? Please add sentences about intensity and potential defects in the structure of carbon material.

8. What authors said about the quality of used CNTs.

9. Authors are suggested to describe some future plans in conclusions.

Author Response

The authors are very grateful for the thorough revision of the manuscript and for the comments. The responses to the specific questions may be found as follows.

1. The overall English needs to be improved. Please seek guidance from a native English speaker if possible ("the" "a", commas, plural form and others could be corrected).
Thank you for the suggestion. In order to meet the quality standards of the journal, the text went through a professional English language revision.
The introduction section needs enhancement few sentences about the other CNT composites and their different applications. Please cite

(1) Microsyst Technol (2021). https://doi.org/10.1007/s00542-021-05211-6

(2) Materials (2021), 14(9), 2448; https://doi.org/10.3390/ma14092448

(3) A review on the development and application of graphene based materials for the fabrication of modified asphalt and cement (2021) https://doi.org/10.1016/j.conbuildmat.2021.122885

We appreciate the attempt to enhance the literature review of the manuscript. The suggested papers were included as references.
Figure 1. Please correct this image for better quality (the inscriptions).

We increased the font of the inscriptions to achieve a better image quality.
Please answer the question in the comments: What do you think, are you have cement particles in or out of nanotubes? Do you have the encapsulation process in tubular structures?

Thank you for introducing this interesting question on encapsulation of the hydration products. The nanotubes used do not have a control whether they have open or closed tips, therefore it is not possible to control our production process in that sense. At the same time we believe that there is no significant encapsulation of hydration products inside the CNTs. This belief is based on the incompatibility of size of both unhydrated cement particles (sizes in the range between ~1-10 microns) and cement hydration products (forming normally agglomerates in the size range of hundreds of nanometers or even more) compared to the inner diameter of the CNTs (up to ~10-20nm). Besides that, even if there is compatibility in size, the precipitated hydration products have low mobility within the cement paste and therefore they may not penetrate within the tubular structures of CNTs.
Could the authors include the standard deviation of the used methods?

Thank you for the valuable contribution. A reference regarding the reliability of the methods was included in the manuscript.
Could authors add some HRTEM or SEM images of materials?

SEM and TEM images besides the thermogravimetry (TG) analysis of the carbon nanotubes used were added to the manuscript.
Raman spectroscopy. Could authors add Raman spectroscopy and a table with an intensity ratio? Please add sentences about intensity and potential defects in the structure of carbon material.

We appreciate the interesting suggestion of the reviewer. The Raman spectroscopy is a well-accepted method for the evaluation of the quality of carbon nanotubes - amongst other materials. However, since the same type of CNT was used without any structural modification, i.e. no functional groups were attached covalently, we believe, that in the case of this study there is no relevant comparison that we could make regarding the CNT quality based on this technique.
What authors said about the quality of used CNTs.

Some comments regarding the quality of the nanotubes were included to the manuscript. The nanotubes were intended for industrial use, therefore probably with somewhat lower quality control (with respect to SWCNTs for example) in order to reduce costs.
Authors are suggested to describe some future plans in conclusions.

Thank you for your valuable contribution. Some future research opportunities have been indicated in the conclusions.

Reviewer 2 Report

Reviewer comments on the paper
“Nanocomposites produced with the addition of carbon nanotubes dispersed on the surface of cement particles using different non-aqueous media”

In this paper, authors analyze the influence of the addition of CNTs dispersed in the cited three types of non-aqueous suspensions on the cement paste's electrical and mechanical properties. The paper is not acceptable in this stage. A revised version may change my primary evaluation. The paper needs a revision before reconsideration. The reviewer comments are suggested as:

Although the title, materials and methods of the present paper are very interesting, however the main novelties of it are not clear for the reviewer. Authors are encouraged to add more comments on the novelties and main contributions of the present paper in Abstract and last paragraph of Introduction section.

What is application of the proposed method? Authors are suggested to provide some technical expressions on the application of the proposed method and needing to this new finding.

The Introduction section is very briefly organized. The Introduction section should be improve.

The variables and components should be defined after first appearance in the paper.

The abstract is very short and incomplete. The abstract should be enriched with addition of the materials and methods.

The discussion is not informative. It should be enriched with addition of some more important conclusions.

The results and discussion are very briefly organized. An extended result and discussion is required.

Authors should add the physical interpretations of the obtained results.

The results and discussion is very brief.

Resolution of the figures should be improved.

Author Response

We are very grateful for the thorough revision of our manuscript and for the comments of the reviewer. Please find the specific responses to your suggestions as follows.

Some addition information were included in the Abstract and the Introduction.

What is application of the proposed method? Authors are suggested to provide some technical expressions on the application of the proposed method and needing to this new finding.

Thank you for the valuable comment. The authors think that the findings of this paper may contribute to the better understanding of the production process of CNT-cement based composites, which – according to the literature – may have future as a more durable and sustainable material. These thoughts were included in the manuscript.

The Introduction section is very briefly organized. The Introduction section should be improve.

Thank you for revealing these weak points. The Introduction was enhanced and more information were included.

The variables and components should be defined after first appearance in the paper.

The variables and components were defined at their first appearance, according to your suggestion.

The abstract is very short and incomplete. The abstract should be enriched with addition of the materials and methods.

The abstract was enhanced according to your comment.

The discussion is not informative. It should be enriched with addition of some more important conclusions.

Thank you for the constructive critics. The discussion of the findings was enhanced.

The results and discussion are very briefly organized. An extended result and discussion is required. Authors should add the physical interpretations of the obtained results. The results and discussion is very brief.

Some addition information were included regarding the results and their discussion.

Resolution of the figures should be improved.

Thank you for the valuable contribution. The figures quality was improved in the manuscript.

Reviewer 3 Report

The manuscript is devoted to investigation of carbon nanotubes application in the cement production. The comprehensive study is presented with necessary technical details and discsussion. The manuscript may attract attention of the readers specialied in this particular area.

The necessary minor correction are marked in enclosed file with the manuscript text.

Comments for author File: Comments.pdf

Author Response

We are very grateful for the thorough review and the comments. The corrections suggested were executed in the updated version of the manuscript and the responses to the specific comments may be found in the attached pdf file.

Author Response File: Author Response.pdf

Reviewer 4 Report

The manuscript “Nanocomposites produced with the addition of carbon nanotubes dispersed on the surface of cement particles using different non-aqueous media” by Vanessa Vilela Rocha, Bruno Athaíde Bacelar, Isabela Domingues Coelho and Péter Ludvig is contributed to the study of cementitious nanocomposites reinforced by carbon nanotubes (CNTs), paying special attention to analyses of dispersion methods of the CNTs.

Lines 13 – 14 “Considering the hydrophobic characteristics of CNTs, these nanoparticles need to be well dispersed in the aqueous media in which they are inserted to guarantee those gains”. In fact, CNT is one-dimensional (1D) carbon allotrope and cannot be considered as nanoparticle, which is rather carbon nanodot.

Line 31 “young’s modulus” should be Young’s modulus (capital letter).

Lines 45 – 46 “On the other hand, the extremely high conductivity of CNTs may contribute to lower the overall electrical resistivity…” As a matter of fact, not all CNTs are electric conductors. Depending on their chirality, the single-walled carbon nanotubes (SWCNTs) are metallic (armchair (n, n) ones), semimetallic or semiconductors. This can also influence the conductivity of the nanocomposites under study and not only the method of the CNTs´ dispersion.

Lines 100 – 102 “…multi-walled carbon nanotubes (MWCNTs), with estimated tube lengths between 5 μm and 30 μm, 99% of external diameter between 0.8 nm and 30 nm…” How many layers (constituent SWCNTs) has a MWCNT with the outer diameter of 0.8 nm? It should be double-walled CNT with inner diameter of at about 0.45 nm, and such small nanotubes are difficult to produce. Were the MWCNTs with outer diameter of 0.8 nm frequent in this study?

Section 3.3. Compressive strength. The results of the compressive strength test should be influenced also by the mechanism of CNT-matrix load transfer, which is not discussed in the present manuscript. I suggest mentioning this issue in the discussion of results obtained.

Author Response

We are very grateful for the thorough revision of our manuscript and for the comments of the reviewer. Please find our responses to the specific questions as follows.

The authors are very grateful for the valuable contribution made by the reviewer. However the carbon nanotubes are often referred as “nanoparticles”, we agree that it is important to highlight their one-dimensional nature. On the other hand, the term “nanodot” would suggest a material that is point-like (has no extension). Therefore, the term “nanomaterial” was employed throughout the manuscript.

Line 31 “young’s modulus” should be Young’s modulus (capital letter).

Thank you for the comment, the error was corrected.

The reviewer is totally correct regarding the conductive nature of the carbon nanotubes. The nanotubes employed in this study had absolutely no control of chirality and one could consider that all of the cited types are present, also regarding the fact that MWCNTs may be composed of layers with different chiral orientations. Due to these fact, a mean (or bulk) conductivity of the nanotubes might be considered. At the same time, the conductivity of even the least conductive semiconductor CNTs is better than the components of a plain cement matrix, therefore we believe that their addition in this case had a positive effect on the overall conductivity. The text was corrected to better reflect to this context.

We are grateful for this valuable comment. In fact a commercially available MWCNT was used in this study produced at a local manufacturer, CTNano, Belo Horizonte, Brazil. The product that we employed in our study is the type of CNT with the lowest price mainly because of the intended use. This means that this type of nanotube has probably less control of quality and therefore the sizes vary over a larger range (at least when compared to other products of the same manufacturer). The indicated values refer to the extremes of diameter and length. We believe that the distribution of diameters is somewhat gaussian (additional information was added to the manuscript), therefore the quantity of such double- (or few-)walled CNTs is relatively low.

We appreciate the important contribution. Some additional discussion was included in the manuscript.

Round 2

Reviewer 1 Report

The authors have addressed all comments and the manuscript can be published as is.

Reviewer 2 Report

Reviewer 4 Report

The authors have improved the manuscript sufficiently. It can be published now.