A Critical Review on the Application of Recycled Carbon Fiber to Concrete and Cement Composites

Round 1

Reviewer 1 Report

The article "A critical review on the application of recycled carbon fiber to cement composites" is a well-written, interesting review with current content. The article aligns with the journal's theme, and publication is recommended after some revisions. These are mainly minor issues, but they can still enhance the reader's interest in finding essential information for their research.

1) Line 33, it is not clear what you mean by specific modulus. Could you rephrase the sentence?

2) Would it be possible to estimate the percentage of virgin fibers that would no longer be used and consequently provide an estimate of the reduction in production costs?

3) I suggest removing section two, "necessity of CF recycling," and moving the entire content before the sentence "This review deals..."

4) In subsection 3.1, do the percentages indicated for recycled fibers refer to the final composite or the strength of the individual fiber?

5) Subsection 3.2: The residual char on the fibers, as well as the ash, could be suitable in cementitious composites. I would add a sentence emphasizing this point.

6) For Tables 2 and 3, I would suggest adding a column with "improvement" instead of "findings," indicating only the percentage improvement compared to the respective reference sample. I would also add a "note" column to indicate special conditions, such as that in reference [50].

7) Subsection 5.3: The initial sentence is not entirely correct. Cement is not non-conductive but poorly conductive and is intrinsically a piezoresistive material. The addition of carbon fibers allows the creation of a sensor inside it. I would suggest modifying the first sentences to say: "...are very low conductive materials and cannot be used as self-sensors." "The use of carbon fibers improves the electrical properties of cement composites." At the end of the section, I would add a small note on the piezoresistivity of cement containing fibers.

8) In the section on dispersion, I would advance some suggestions, such as whether chemical functionalization of recycled fibers or another type of treatment could have a beneficial effect on increasing both mechanical and electrical properties.

9) The references section: Reference 71 needs to be reviewed.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comment 1: Lines 2-3:  The authors use the title "A critical review on the application of recycled carbon fiber to cement composites."  It is recommended to adjust this title to include phrasing such as "concrete and cement composites" due to the manuscript cites references from studies utilizing both cement and concrete composites.  

Comment 2: lines 344-362:  In addition to workability, are there any studies with RCF cement/concrete composites that have been conducted with rheological parameters taken into account? It is recommended to add some brief context distinguishing workability and rheological parameters in this section. 

Comment 3: lines 365 - 389  It is recommended to add some references and discussion of characterizing the RCF fiber itself. As an example, although smaller than the microstructural level, characterizations such as X-ray Diffraction and X-ray Scattering for RCF to identify small-scale level characterization of the fibers can be briefly mentioned here or another section with referenced studies.  

The quality of English used in this study is proficient.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

The review paper is well-written and structured, so I recommend accept after proper modification. Some comments are listed as below:

1. Section 3, improve the quality of Figure 3.

2. Section 4, please also mention the potential reasons for the poor mechanical properties of CF from mechanical recycling. 

3. Section 5, the length of CF is critical to the flexural and tensile strengths, and you must mention it with their contents in the following discussion. 

4. Some figures or tables are needed in the section on electrical properties. In addition, the following related studies are recommended: Powder technology 373 (2020): 184-194. Construction and Building Materials 184 (2018): 311-319. Cement and Concrete Composites 128 (2022): 104454.

5. Some figures illustrating the microstructural differences are recommended. 

6. Section 6, please summarize more in detail regarding the dispersion of CF.

The English expression is fine. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have resolved all the issues raised, and the article is recommended for publication.

Reviewer 2 Report

The authors satisfactorily addressed this reviewer's comments. 

The quality of English is fine and recommend a final grammar/spelling check.

Reviewer 3 Report

The comments from reviewers have been well-considered by the authors. Hence, I recommend accepting this manuscript.  

The English expression is fine.