Influence of Matrix Strength on Bridging Performance of Fiber-Reinforced Cementitious Composite with Bundled Aramid Fiber

Round 1

Reviewer 1 Report

This research reports on an investigation into the effect of matrix on bridging performance of fiber reinforced composite materials. To do so, uniaxial tension tests as well as pullout tests were conducted on FRP composite.     This is an interesting study with potential application in composite design and manufacture. However, in my opinion, this can't be published unless the manuscript is revised as per my comments below:   1) The deception of experimental apparatus and test procedures are poor. It is not clear how many samples have been used, whether there's been a test calibration, and most importantly if the data extracted is reliable. The authors must also discuss their measurement technique, whether there's been increasing randomization to reduce sample bias.    2) Please explain why there is a material discontinuity in the setup of loading and measurement for uniaxial tension test? The reviewer doesn't agree that this is a proper way to measure tensile failure as there is a huge stress concentration in the region where the material discontinuity exists. Why not one uniform sample under tensile load? This way, you can guarantee that the stress concentration is not the cause of failure.    3) Another important issue is the novelty of this work. There have been numerous works in the literature in which the effect of matrix + Fiber + volumetric fiber fraction of fiber + etc. has been thoroughly investigated. Please discuss what makes your research unique as compared to similar ones in the literature!   4) The literature review doesn't provide sufficient information into the core objective of this research. The authors are apparently not much familiar with some of the leading research regarding experimental studies conducted on material characterization, failure and fracture of composite materials. AS such, the introduction is currently not concise and informative. The author must discuss the following references in the introduction portion of the revised manuscript.    "Localized failure analysis of internally pressurized laminated ellipsoidal woven GFRP composite domes: Analytical, numerical, and experimental studies", Archives of Civil and Mechanical Engineering, Vol:19, pp:1235-1250.   "A semi-empirical approach to evaluate the effect of constituent materials on mechanical strengths of GFRP mortar pipes", Structures, Volume 36, February 2022, Pages 493-510.   Some useful testing methods have been introduced in the above-mentioned papers which must be discussed in the introduction of the revised manuscript.   5) What does the results of uniaxial tension test tell us? What is the relationship between the maximum load and load at the first crack?    6)  Example of pulled-out fiber is unclear in Fig.11c. It doesn't demonstrate any fiber pullout has occurred.   I believe responding to the above-mentioned comments and revising the manuscript accordingly are essential before considering the paper for publication.                  

Author Response

The authors sincerely thank the reviewers for their constructive comments, thoughtful suggestions and advices. Our responses to each of them are detailed below and changes to the manuscript are indicated by highlights (The revised parts suggested from other reviewers are also highlighted).

Comment 1:
This research reports on an investigation into the effect of matrix on bridging performance of fiber reinforced composite materials. To do so, uniaxial tension tests as well as pullout tests were conducted on FRP composite.     This is an interesting study with potential application in composite design and manufacture. However, in my opinion, this can't be published unless the manuscript is revised as per my comments below:   
1) The deception of experimental apparatus and test procedures are poor. It is not clear how many samples have been used, whether there's been a test calibration, and most importantly if the data extracted is reliable. The authors must also discuss their measurement technique, whether there's been increasing randomization to reduce sample bias.
Response:
Thank you so much for your valuable comments. In the uniaxial tension test, five specimens were manufactured for nine series, so the total of 45 specimens were tested as described in lines 131-133. In the pullout test, the specimen number is same as that in the uniaxial tension test as described in lines 234-236. In the uniaxial tension test, obtained data from the specimens, in which failure mode was detected to be bending failure, are not used for the evaluations as described in Section 3.3. In the pullout test, only one specimen was not tested due to the damage of the specimen at the detaching of the mold as described in lines 255-256. The number of specimens such as three or five is considered to be common in the research of the cementitious materials such as concrete.

Comment 2:
2) Please explain why there is a material discontinuity in the setup of loading and measurement for uniaxial tension test? The reviewer doesn't agree that this is a proper way to measure tensile failure as there is a huge stress concentration in the region where the material discontinuity exists. Why not one uniform sample under tensile load? This way, you can guarantee that the stress concentration is not the cause of failure.
Response:
Thank you so much for your valuable comments. The notched prism is one of the popular specimens in the field of cementitious materials such as concrete. The following sentence and two references are added in lines 125-127: “The notched rectangular prism specimens with slit have been generally utilized to investigate the tensile characteristics of cementitious materials such as FRCC as same as concrete [26, 27].”
[26] International Standard, ISO 19044 Test methods for fibre-reinforced cementitious composites — Load-displacement curve using notched specimen, 2016.
[27] Japan Concrete Institute Standards Guidelines, JCI-S-001-2003 Method of test for fracture energy of concrete by use of notched beam, 2003.

Comment 3:
3) Another important issue is the novelty of this work. There have been numerous works in the literature in which the effect of matrix + Fiber + volumetric fiber fraction of fiber + etc. has been thoroughly investigated. Please discuss what makes your research unique as compared to similar ones in the literature!
Response:
As described in lines 67-74, there are few previous studies investigating the influence of matrix strength on bridging performance of FRCC. The following sentence is added in lines 79-82: “Within the knowledge of the authors, however, there is no previous study in which the mixture proportion was selected as the experimental parameter because of the difficulties of the control the fresh properties of cementitious matrix.”

Comment 4:
4) The literature review doesn't provide sufficient information into the core objective of this research. The authors are apparently not much familiar with some of the leading research regarding experimental studies conducted on material characterization, failure and fracture of composite materials. AS such, the introduction is currently not concise and informative. The author must discuss the following references in the introduction portion of the revised manuscript.    "Localized failure analysis of internally pressurized laminated ellipsoidal woven GFRP composite domes: Analytical, numerical, and experimental studies", Archives of Civil and Mechanical Engineering, Vol:19, pp:1235-1250.   "A semi-empirical approach to evaluate the effect of constituent materials on mechanical strengths of GFRP mortar pipes", Structures, Volume 36, February 2022, Pages 493-510.   Some useful testing methods have been introduced in the above-mentioned papers which must be discussed in the introduction of the revised manuscript.
Response:
Thank you so much for your valuable information. However, this study focuses on Fiber-Reinforced Cementitious Composite (FRCC) in which the short discrete fibers with low volume fraction are distributed in the cementitious matrix (mortar or concrete) randomly. It is considered that the fundamental properties of FRCC are very different from those of composites reinforced with FRP in which the continuous fibers and/or polymers are used. So, the authors did not include the suggested literatures.

Comment 5:
5) What does the results of uniaxial tension test tell us? What is the relationship between the maximum load and load at the first crack?
Response:
“Fiber bridging” transfers the tensile force through cracks after cracking of cementitious matrix as described in lines 24-29. As described in Section 3.4, FRCC tested in this study shows tensile strain-hardening property that load increases after the first crack generated.

Comment 6:
6)  Example of pulled-out fiber is unclear in Fig.11c. It doesn't demonstrate any fiber pullout has occurred.   I believe responding to the above-mentioned comments and revising the manuscript accordingly are essential before considering the paper for publication.
Response:
Thank you so much for your valuable comments. Figure 11(c) was modified to see the fiber clearly that was pulled out from the matrix.

Author Response File: Author Response.pdf

Reviewer 2 Report

The aim of the study was to determine matrix strength of FRCC composites containing Aramid fiber bundles. The authors presented the article in an organized way. However, it seems to me that there is major correction that should be clarified.

• Mention the standards used for the tension and compression test
• Specimens cured upto maximum of 45 days. During the curing process how authors controlled interaction of water with Aramid fibers
• Mention the standard deviation for the average tensile strength in Table 4.
• Figure 8 represents the maximum load vs compressive strength for different volume fractions of Aramid fiber. Why authors not considered the different series of samples (Fc24, 36 and 48) for this particular analysis.
• Figure 11(c) shows the complete pull out of the fibers. Is that same for all specimens? Or any test showed fiber failure between the matrix interphase?
• Modify the conclusions section by adding the major findings of the article. Also, discuss conclusion in terms of applications of these kind of structures. Mention few points related to future scope of the study.

 

 

Author Response

The authors sincerely thank the reviewers for their constructive comments, thoughtful suggestions and advices. Our responses to each of them are detailed below and changes to the manuscript are indicated by highlights (The revised parts suggested from other reviewers are also highlighted).

Comment 1:
The aim of the study was to determine matrix strength of FRCC composites containing Aramid fiber bundles. The authors presented the article in an organized way. However, it seems to me that there is major correction that should be clarified.
*Mention the standards used for the tension and compression test
Response:
Within the knowledge of the authors, the unified standard or specification of the uniaxial tension test method for FRCC does not exist. The following sentence is added in lines 117-120: “Since the unified standard or specification of the uniaxial tension test method for FRCC does not exist within the knowledge of the authors, the prism specimen shown in Figure 2 is prepared considering the ease of specimen setup and measuring the axial deformation at crack position.”
The compression test was carried out in accordance with JIS A 1108, Method of test for compressive strength of concrete, and JIS A 1149, Method of test for static modulus of elasticity of concrete, as described in lines 139-140.

Comment 2:
*Specimens cured upto maximum of 45 days. During the curing process how authors controlled interaction of water with Aramid fibers
Response:
Specimens were cured in the natural environment without any controlled interactions of water. The following sentence is added in lines 140-141: “The cylinder-specimens were also cured in the natural environment until the days of the loadings.”

Comment 3:
*Mention the standard deviation for the average tensile strength in Table 4.
Response:
The values of standard deviation were added in column “Average max. load” in Table 4.

Comment 4:
*Figure 8 represents the maximum load vs compressive strength for different volume fractions of Aramid fiber. Why authors not considered the different series of samples (Fc24, 36 and 48) for this particular analysis.
Response:
Thank you so much for valuable comments. The relationship between the maximum load and fiber volume fraction was added as Figure 8(b). The corresponding sentence was modified in lines 208-209.

Comment 5:
*Figure 11(c) shows the complete pull out of the fibers. Is that same for all specimens? Or any test showed fiber failure between the matrix interphase?
Response:
In all specimens, the fiber was pulled out from the matrix without observing clear rupture of the fiber as described in lines 253-254. Figure 11(c) was modified to see the fiber clearly that was pulled out from the matrix.

Comment 6:
*Modify the conclusions section by adding the major findings of the article. Also, discuss conclusion in terms of applications of these kind of structures. Mention few points related to future scope of the study.
Response:
Thank you so much for valuable comments. The following sentences are added in lines 367-372: “It is considered that these findings will be valuable to evaluate the tensile properties of FRCC by the matrix strength, that is generally exhibited by compressive strength in the design of structural elements such as coupling beams, columns, seismic walls, and beam-column joints. The authors also consider that simple calculation methodologies for tensile strength and toughness of FRCC will provide the effective use of FRCC in the structures, and those will be studied in the future.”

Author Response File: Author Response.pdf