Carbon Fiber Traces in Cracked Surfaces of Mortar Prisms

Round 1

Reviewer 1 Report

This paper present a study on the appearance and characteristics of five unique fiber traces (uprootedness, avulsion, separation, overlay and dividedness) of carbon fibers along the cracked surfaces of mortar prisms, aiming to analysis the changes of flexural strength of mortar prisms with different carbon fiber content. Overall, it is an interesting study. But it cannot be considered for publication in its current version.

The conclusions were drawn based on limited samples (only 2 mortar prisms for each mixture). In Table 1, it is clearly shown that the number of each trace observed in two prisms of same mixture varies a lot. More samples are needed to get more reasonable statistical data.

This paper focuses on the effect of the appearance and characteristics of five unique fiber traces on the flexural strength of mortar prisms. However, addition of fiber content would influence the hydration process and microstructure (pore structure for example), which in turn influence the development of mechanic properties of mortar (including flexural strength).

Language should be further checked by a native speaker. There are too many long sentences that hard to be understood.

There are many typo errors as well, for example,

Line 113-116: For the flexural strength measurement of mortar prisms comprising fibers, cement … admixture 1 % weight of the cement. Poor English.

Line 125, 131, 133: 20oC ± 2oC, 4.88 ㎛2, 0.8 ㎛2.

Line 626-628: The increasing numbers of (avulsions + separations) will reduce the strength of the prism samples, 5) the number of dividedness is 2 (CF 627 0.5), 7 (CF 1.0), 10 (CF 1.5) and 12 (CF 2.0).

Line 630-631: “As the fiber percentage increases further” to “As the fiber content increases further”.

Author Response

Dear Reviewer

Thank you for your review.

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors investigate effect of adding carbon fibers to mortar prisms. The procedure followed is simple but thorough. However the paper cannot be excepted in its current format because of poor writing and poor presentation of results. 

The authors need to be specific when writing about the experimental procedure,, camera placement, which specimen faces were monitored and rate at which camera images were captured. All the images should have scale. The writing is vague sometimes. Authors should add more tables and improve figures and describe the specifics in the manuscript.

Author Response

Dear Reviewer

Thank you for your review.

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

In this manuscript, the authors based on the microscopic structural analysis to explain why prisms of 1.0 vol% carbon fibers show the highest flexural strengths. Based on the experimental observation, the authors propose that the reduction in prism strength at high fiber volume is related to a reduction of the cohesiveness of the mortar. More specifically, at higher fiber concentrations, the cemented fiber bundles/chunks work as air pockets and inhomogeneities that reduces strength. This argument is nice and qualitatively supported by the experimental observation, however, it is not quantitatively confirmed. That is to say, the authors have not measured the strength of the fiber bundles/chunks and verified that they are indeed weak spots.

Some points to be improved:

1. My major concern about this manuscript is its presentation. I think many aspects of the presentation can be improved. For example, currently, the schematics in Figure 4 are hard to follow, and there is no description in the caption. Combining Fig.4 and 5 side by side may help to interpret the different microstructures proposed by the authors.
2. Again for the presentation, Fig. 8-Fig.11, there are too many marks - it is thus very challenging for the reader to compare the difference. Can the authors simplify the marks? It would be nice to also include a figure that directly and clearly shows the characteristic microstructural evolution as the fiber volume increases.
3. For the discussion, some contents are not necessary. I suggest the authors carefully go through and shorten the manuscript, removing some unnecessary descriptions, which help the reader to focus on the key message.
4. Is the main conclusion (fiber bundles/chunks and inhomogeneities reduce strength) related to the fiber-concrete adhesion strength. If the fiber-concrete adhesion becomes very strong, I wonder whether the conclusion will change? Please just comment.
5. The writing should be improved. I suggest the authors have a careful check.

For example:

- Abstract: “The percentage increase induces the more fibers to be clustered together and overlapped to each other to make more numbers of divided, ...” where the second “the” should be removed.

Author Response

Dear Reviewer

Thank you for your review.

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The changes incorporated are satisfactory.

Author Response

Dear Reviewer:

Thank you for the comments.

We tried to improve our English further.

You can find our changes by “Track Changes” function.

The changes incorporated are satisfactory: Thanks.

Jung-Young Son

Reviewer 3 Report

I do not have extra comments, thought I believe the presentation of the results can still be improved.

Author Response

Dear Reviewer:

Thank you for the comments.
We tried to improve our English further.
You can find our changes by “Track Changes” function.

do not have extra comments, thought I believe the presentation of the results can still be improved:

Thanks. I tried to improve our presentation by improving our English.

Jung-Young Son