Evaluation of Hybrid Fiber Multiscale Polymer Composites for Structural Confinement under Cyclic Axial Compressive Loading
and Alessandro Pegoretti 4Round 1
Reviewer 1 Report
please see the attachment
Comments for author File: 
Comments.pdf
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 2 Report
This paper presents very useful work on the topic of hybrid FRP confined concrete with cyclic compressive loading. Please consider the following comments to improve the quality.
Normally, if we do cyclic loaded testing, the target load of unloading is not zero. We keep a small load value for the end of unloading and then start reloading. Please tell the reason for this issue in the paper.
The unconfined strength was 24.36 MPa (Line 323), but in Eq. (3), f'co=25.047. Why? Normally we keep one decimal place for concrete strength in MPa.
More discussions and introductions on the k1 coefficient value in Eq. (2) are needed. For example, it is also related to other factors like aggregate (please refer to "Strength enhancement due to FRP confinement for coarse aggregate-free concretes"), and cross-section (e.g., "Effect of corner radius on the performance of CFRP-confined square concrete columns: Test").
How did you measure and obtain the strain data in the stress-strain relationship analysis? I did not see the LVDTs or strain gauges in the test setup figure.
More references with very the related topic of this paper are recommended:
"Effects of predamage and load cyclic on compression behavior of fiber reinforced polymer‐confined concrete"
“FRP-confined concrete under axial cyclic compression”
“Stress–strain model for FRP-confined concrete under cyclic axial compression”
"PET FRP-concrete-high strength steel hybrid solid columns with strain-hardening and ductile performance: Cyclic axial compressive behavior"
"Stress–strain behavior of actively and passively confined concrete under cyclic axial load".
Author Response
Please see the attached document
Author Response File: Author Response.pdf
Reviewer 3 Report
Evaluation of hybrid fiber multiscale polymer composites for structural confinement under cyclic axial compressive loading
This paper presents the performance of sisal fiber-reinforced polymer (SFRP), hybrid sisal basalt fiber-reinforced polymer (HSBFRP) and multi-walled carbon nanotube (MWCNT) restrained structures under cyclic loading. The article investigates the load-carrying capacity, strength, ultimate strain, damage warning and damage morphology of the restrained loads under cyclic loading. Based on the test results, it establishes a prediction model for predicting the peak compressive strength of FRP-constrained concrete. This paper guides applying an NWCNT-epoxy-based hybrid restrained system in structural strengthening and retrofitting. However, some issues still need to be addressed in the article.
(1) There need to be more citations in the article. For example, there is only one or no source for the characterization of MWCNT in 3.1.1 and the discussion of the test results in the subsequent summaries.
(2) In the introduction section, it is suggested to add an introduction of MWCNT to show the performance of MWCNT and its application in engineering.
(3) The authors may add more state-of-art articles for the integrity of the introduction. For axial compression, please refer to Axial compression behavior of recycled-aggregate-concrete-filled GFRP–steel composite tube columns; An experimental investigation and machine learning-based prediction for seismic performance of steel tubular column filled with recycled aggregate concrete.
(4) In section 3.1.2.2, it is mentioned that “homogeneous dispersion of nano-filler particles” has improved the “fracture toughness”, But in section 3.1.1, it is also mentioned that “agglomeration of nano-filler”. It is suggested that "the epoxy resin modified with MWNCT enhances its homogeneous dispersion and thus the fracture toughness”.
(5) It is suggested to add microscopic tests to investigate the generation of “polymer chains” and their role in MWCNT, and then explain the upgrading effect of MWCNT on epoxy resin chains.
(6) The confidence level of the fitted straight line of Fig.15 is not given, and it is suggested to provide the confidence level of the fit.
(7) The English language logic of this paper should be further improved. For example, there is a wrong line in Table 1 in line 195; Fig.10-Fig.14 are too simple and need more scale, and it is suggested to add the curve information in the figure.
Author Response
Please find the attached document
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
All major comments were adequately addressed and the Authors have done an admirable job of improving the quality of the manuscript. Therefore, it can be accepted without any structural modification.
Reviewer 2 Report
The paper looks okay now and can be accepted.
Reviewer 3 Report
accept
