Effect of Fibre Reinforcement on Creep in Early Age Concrete

Round 1

Reviewer 1 Report

1. In Table 3, the authors need to clarify additive that employed in this study.
2. In Table 4 and at the lines 126-129, the authors need to explain why the difference in loading rates (40% and 50%) were applied.
3. Since the colors selected for presenting normative prediction and experimental results are different in the legend of Fig. 9, it is difficult to understand when this reviewer looked at it. Thus, please, unify those colors. Also, it is necessary to revise "(a) 24?" in Fig. 9 capture (line 242).
4. In Table 4, there are specimen codes. However. Figures 6, 7, 8, 9, 10, 12, and 14 show only test data for four specimens. Please, add the detail explanations regarding this part.

Author Response

Responses to the reviewers’ comments to the manuscript ID: applsci-1504644

 

Effect of fibre reinforcement on creep in early age concrete

 

Dear reviewer,

We greatly appreciate the opportunity you gave us to improve the paper with the valuable comments of the reviewers.

Below you can find the detailed answers to the comments and resulting modifications.

Best regards,

The authors

 

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Reviewer #1 (changes in blue)

The authors would like to thank the reviewer for the time and effort in reviewing our paper.

1. In Table 3, the authors need to clarify additive that employed in this study.

Thanks for your comment. It is now clarified in the table and in a previous sentence:

A superplasticizer additive, Master Ease 5025, was added, in the proportion of 1% wt. of cement.

Material	Mix [kg/m3]
FA0-2	480
FA0-4	480
CA4-12	480
CA10-20	480
Cement	390
Water	165
Additive Master Ease 5025	3.9 (1% wt. cement)
Fibres	35
w/c	0.45

 

2.In Table 4 and at the lines 126-129, the authors need to explain why the difference in loading rates (40% and 50%) were applied.

The following text was added to clarify it:

“In the case of 24 h and 3d age specimens, the load was chosen to be sufficiently representative at 3d, but to be able to be supported by 24h age specimens. In the case of 7 and 28 d age specimens, a load of 50% of its compressive strength was considered adequate to see a significant evolution in the concrete.”

3.Since the colors selected for presenting normative prediction and experimental results are different in the legend of Fig. 9, it is difficult to understand when this reviewer looked at it. Thus, please, unify those colors. Also, it is necessary to revise "(a) 24?" in Fig. 9 capture (line 242).

Thank for the comment. The problem of colours has been corrected and “24h(a)” was added.

4.In Table 4, there are specimen codes. However. Figures 6, 7, 8, 9, 10, 12, and 14 show only test data for four specimens. Please, add the detail explanations regarding this part.

To clarify this, this sentence was added before Fig.6:

“In the following figures, the joint results of each age rage are shown as the average evolution experienced by the two test specimens.”

 

Author Response File: Author Response.docx

Reviewer 2 Report

Review Report

This study reports the long-term and short-term mechanical behaviors of fibre-reinforced concrete with loading ages.

The authors spent great effort on the long-term creep experiment of FRC and it is really a challenging work, however, the importance and the knowledge gap of current study were not fully explained by line 50-55. According to the reference[1], there are plenty of studies on the creep behavior of FRC. The necessity of current study should be emphasized.

There are also some details which should be paid attentions to:

1. The bottom line should be added to Table 1, 2 and 3.
2. The figure 2 should be improved. A schematic diagram of hooked-end fibres may be presented with specific dimensions and a picture of hooked-end fibre could be place aside as fig(b) to make it clear to the readers.
3. According to the contents of Figure 3, Figure 3 should be clearly labeled as Fig 3(a) and Fig 3(b); and the resolution of Fig3(b) should be improved as the readers could not figure out the labels of Fig3(a).
4. Fig 6(a) and 6(b) give out the opposite experimental results. The authors declare that “similar behaviour is observed in the specimens loaded at 15 and 20 MPa” (line 171-172). There is a great difference between Fig 6(a) and 6(b) which has been neglected, intentionally or unintentionally, by the authors. The creep curve of specimen loaded at shorter loading age in Fig 6(a) shows a smaller creep strain while the creep curve of specimen loaded at shorter loading age in Fig 6(b) shows a greater creep strain. A smaller creep strain of specimen loaded at shorter loading age in Fig 6(a) may be contradictory to our common sense and I think the authors should address the discrepancy of Fig 6(a) and 6(b)。
5. The formula in the manuscript is better edited by Mathtype but not the build-in tool by Microsoft. The symbols in formula [1] to [4] are not clearly explained.
6. According to Fig 5, the starting point to the curve is the compressive strength of loading age at 24h. However, according to line (89), the first point is compressive strength of loading age at 10h. I think this discrepancy should be explained.
7. Line 206 to 210 is the caption of Fig 7 and there is no figure at all, while there is another Fig 7 from line 213 to 217.
8. Fig 7 and 8 are abrupt. As a reader, I could how the curves of the coefficients "α (t0)" and "α (t-t0)" are obtained. I think the authors may provide a more detailed explanation.
9. The labels of Fig 9(c) should be carefully checked as the experimental results was wrongly labeled as normative prediction. What’s more, the caption of Fig 9 is incomplete for the loading age 24h is missing.
10. In Fig 10(b) the specimen loaded at 7d shows a larger elastic modulus, while in Fig 11, the elastic modulus increases with the loading age. The authors should clearly explain this discrepancy.
11. To clearly show the trend of elastic modulus with loading age, the range of vertical axis in Fig 13 should be better narrowed to 30 MPa-50 MPa.
12. In line 243 to 244, the authors stated “The normative prediction fits relatively well with the experimental results in FRC loaded at 28d of age.” Comparing to Fig 9(b) and (c), such a statement is apparently not objective as in Fig 9(b) and (c), the normative prediction gives better performance.

 

Comments for author File: Comments.docx

Author Response

Responses to the reviewers’ comments to the manuscript ID: applsci-1504644

 

Effect of fibre reinforcement on creep in early age concrete

 

Dear editor,

We greatly appreciate the opportunity you gave us to improve the paper with the valuable comments of the reviewers.

Below you can find the detailed answers to the comments and resulting modifications.

Best regards,

The authors

 

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Reviewer #2: (Changes in green)

This study reports the long-term and short-term mechanical behaviours of fibre-reinforced concrete with loading ages.

The authors spent great effort on the long-term creep experiment of FRC and it is really a challenging work, however, the importance and the knowledge gap of current study were not fully explained by line 50-55. According to the reference [1], there are plenty of studies on the creep behaviour of FRC. The necessity of current study should be emphasized.

The authors thank you for your time and effort in reviewing our paper.

There are also some details which should be paid attentions to:

The bottom line should be added to Table 1, 2 and 3.

Thank for the comment. This has been corrected.

The figure 2 should be improved. A schematic diagram of hooked-end fibres may be presented with specific dimensions and a picture of hooked-end fibre could be place aside as fig(b) to make it clear to the readers.

A diagram was added:

According to the contents of Figure 3, Figure 3 should be clearly labeled as Fig 3(a) and Fig 3(b); and the resolution of Fig3(b) should be improved as the readers could not figure out the labels of Fig3(a).

A label was added and the resolution of Fig3 (a) was improved.

Fig 6(a) and 6(b) give out the opposite experimental results. The authors declare that “similar behaviour is observed in the specimens loaded at 15 and 20 MPa” (line 171-172). There is a great difference between Fig 6(a) and 6(b) which has been neglected, intentionally or unintentionally, by the authors. The creep curve of specimen loaded at shorter loading age in Fig 6(a) shows a smaller creep strain while the creep curve of specimen loaded at shorter loading age in Fig 6(b) shows a greater creep strain. A smaller creep strain of specimen loaded at shorter loading age in Fig 6(a) may be contradictory to our common sense and I think the authors should address the discrepancy of Fig 6(a) and 6(b)。

Thank you for the comment. The authors referred to the fact that the evolution of the specimens, analysing separately the different loads, follows a similar trend. However, the authors agree that the explanation given is misleading. Therefore, the phase has been modified as follows: “Analysing the evolution of the deformation of the FRC due to the creep episode to which it was subjected during the test, differences in strain rates are observed according to the age in the specimens loaded at 15 and 20 MPa”

The fact that specimens loaded at short ages have less deformation was later explained. : “the deformation of the specimens loaded at a younger age is greater. This is because the cement in the younger specimens has not hydrated sufficiently and deforms more in the first days of loading”

The formula in the manuscript is better edited by Mathtype but not the build-in tool by Microsoft. The symbols in formula [1] to [4] are not clearly explained.

An explanation of these symbols has been included:

                                                    [1]

                                                                                                  [2]

                                                                             [3]

Where:

• σ(to) is the stress on specimens during creep test.
• E_c,to is the initial modulus of elasticity in specimens.
• E_c,28 is the modulus of elasticity of the specimens at 28 days.
• ϕ_HR is the coefficient of influence of relative humidity [22].
• β(fcm) is the coefficient of influence of concrete strength [22].
• α(t0) is the coefficient associated with the loading age proposed by the authors;
• α(t-t0) is the coefficient associated with the evolution of creep with time proposed by the authors.

                                           [4]

Where:

• ɛ_e,i is the instantaneous elastic strain.
• ɛ_e,d is the delayed elastic strain.
• t_d is the unloading age.
• E_c,td is the modulus of elasticity of the specimens at unloading age.

According to Fig 5, the starting point to the curve is the compressive strength of loading age at 24h. However, according to line (89), the first point is compressive strength of loading age at 10h. I think this discrepancy should be explained.

It was an error. Thank you for the appreciation. It has been corrected in section 2.2. methods (it’s correct at 24h).

Line 206 to 210 is the caption of Fig 7 and there is no figure at all, while there is another Fig 7 from line 213 to 217.

In the Lines 206 to 210 (219-220 in the new version) is presented the Fig7 for the analysis. In Lines 213-217 (228-229 in the new version) in the caption, food of the figure 7.

Fig 7 and 8 are abrupt. As a reader, I could how the curves of the coefficients "α (t0)" and "α (t-t0)" are obtained. I think the authors may provide a more detailed explanation.

Thank you for the comment. To clarify it, the following explanation has been added (Line 233-235):

“To determine the optimal creep coefficients, the authors have scanned all possible combinations of values of these coefficients and have obtained the error of the final proposed formulation for each load age analysed in the study.”

The labels of Fig 9(c) should be carefully checked as the experimental results was wrongly labeled as normative prediction. What’s more, the caption of Fig 9 is incomplete for the loading age 24h is missing.

Thanks four your comment. It has been corrected.

In Fig 10(b) the specimen loaded at 7d shows a larger elastic modulus, while in Fig 11, the elastic modulus increases with the loading age. The authors should clearly explain this discrepancy.

There was an error in the graph corresponding to the load of the specimens loaded at 7 days and at 28 days. This error has already been corrected and updated the stress / strain curve in the manuscript.

To clearly show the trend of elastic modulus with loading age, the range of vertical axis in Fig 13 should be better narrowed to 30 MPa-50 MPa.

Thanks for your suggestion. It was modified:

In line 243 to 244, the authors stated “The normative prediction fits relatively well with the experimental results in FRC loaded at 28d of age.” Comparing to Fig 9(b) and (c), such a statement is apparently not objective as in Fig 9(b) and (c), the normative prediction gives better performance.

We agree. The labels of this figure were wrong, according to a previous comment. The legend was corrected and it can be shown that the proposed model fits better than the normative.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

It has been revised to fully reflect what I pointed out.