Bond Performance of Corroded Steel Reinforcement and Recycled Coarse Aggregate Concrete after Freeze–Thaw Cycles
Othman Hameed Zinkaah
Round 1
Reviewer 1 Report
Two issues require clarification in this article:
1. No chemical test data for recycled coarse aggregate has been reported. If this aggregate contains high amounts of chloride, this would have a major impact on the results of the freeze-thaw cycles. And the freeze-thaw cycles were crucial in the inference.
2. An accelerated process of reinforcement corrosion with a constant current density was very reasonably assumed. However, in the literature there are many discussions about the value of the current density, which causes electrode processes close to natural. There was no discussion in the article why the value of 0.02 mA/mm2 was adopted, nor was the literature data included.
Author Response
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Reviewer 2 Report
The manuscript should be reconsidered after proposed changes. please look at the attached file.
Comments for author File: Comments.pdf
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Reviewer 3 Report
Comments
The literature review in the manuscript is concise but describes the main topics and reasoning of the manuscript. The objectives of the study, however, are not clearly defined. I’d suggest adding a paragraph focusing on the specific objectives of the research.
The term “concrete composition” should be changed to “mixture proportions.”
The term “experiment” should be substituted with “test” if the testing followed industry accepted standards (Chinese or international, such as ASTM standards). Although some standards are referenced (e.g., China specification GB/T 50082-2009 65, for pull-out test) I could not find the standards for the following test:
- Fabrication of concrete cube specimens
- Electromechanical accelerated method for corrosion
- Compressive strength
- Dynamic modulus
- Freezing and Thawing cycles
If the tests were performed in accordance with industry-accepted standards, which seems to be the case, the authors should clearly report that. In addition, the standards documented in the text of the manuscript are not included in the list of references. Authors should add all standards in the list of references at the end of the manuscript.
The test methodology was appropriate for establishing the bond performance effects. Tests and procedures are adequate to the topic. In addition, the prediction model developed by the authors concurred with the experimental data.
All the figures in the manuscript are relevant and should be included in the final version, however, I found some difficulty in reading a few of these curves, such as Figures 15 and 16. I understand the space limitation of these manuscripts, however, I’d suggest increasing the size of such figures as much as it would be possible given the limitations.
The research methodology is well described and performed. The results of the study are informative and relevant. I believe the authors’ efforts should be recognized and the manuscript should be published with minor modifications.
Author Response
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Reviewer 4 Report
In this manuscript, bond performance of corroded steel reinforcement and recycled coarse aggregate concrete after freeze-thaw cycles has been investigated. The topic is worthy for investigation; however, some below aspects need to be clarified/modified as follows:
1-In many places of the introduction, authors only reported the results of others rather than giving discussions, comparing, and analysing the results.
2-There are many numbers found in the manuscripts. Are these numbers referring to the references? If so, theses references are not organized in order and need to be according to the template of the journal.
3. What is the new scientific knowledge generated in this article? Authors need to show the novelty of the topic.
4. A proofreading is strongly required to enhance the readability of the manuscript.
5. The value of sand (8220) shown in table 5 needs to be checked.
6. The paper did not provide a deep discussion for the parameters investigated.
Author Response
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Reviewer 5 Report
In this manuscript, the freeze-thaw resistance of the recycled coarse aggregate concrete (RAC) and the bond performance of the corroded steel reinforcement and the RAC after the freeze-thaw cycles are assessed. However, the research work is not very revealing and the results are not soundly interpreted. The following comments should be considered:
1) Is the RAC sand weight in Table 5 incorrect? Does the amount of water in the RCA include pre-absorption? Please explain it.
2) The specific location and dimensions of the PVC pipe in Figure 2 need to be clearly marked.
3) All citation superscripts in the manuscript should have parentheses.
4) The tiny cracks in the steel reinforcements in Figure 5 should be marked.
5) Why is the specimen after the freeze-thaw cycle test not dried before weight the mass? In this way, the factor of water infiltration leading to mass increase can be avoided.
6) It is not clear from Figure 8 that there is any difference in the rate of strength decline between RAC and NAC.
7) What is the specific value of the dynamic elastic modulus?
8) The fitting coefficient itself is derived from the test results, which in turn verifies that the test is correct. It is suggested to supplement the data of other researchers for verification.
Author Response
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Reviewer 6 Report
The submitted work deals with the experimental and analytical investigation of the freeze-thaw resistance of recycled aggregate concrete (RAC) and the bond performance of corroded steel reinforcements and RAC after freeze-thaw cycles. For this research program, pull-out tests and cubic concrete specimens where constructed and tested to investigate the development of the application of RAC structures in the mid-high latitude marine environment. The Authors propose two analytical expressions to estimate the bond performance under the coupled effect of the freeze-thaw cycles and the steel reinforcement corrosion. The analytical results agreed with the experimental data.
In general, the paper is extremely well written, the results are clearly presented, and the conclusions are supported by the results. The introduction is quite complete, and the problem is well established. In the opinion of this Reviewer this study is worthy of publication after minor revision and is very useful for scientific research. However, this Reviewer has some recommendations and questions, as described below:
1. Abstract: The Authors should improve the abstract. In lines 14-16 the Authors wrote “The freeze-thaw resistance of the recycled coarse aggregate concrete (RAC) and the bond performance of the corroded steel reinforcement and the RAC after the freeze-thaw cycles are assessed”. With what way? According to this Reviewer’s opinion the Authors should mention in abstract that this work is an experimental and analytical research of the freeze-thaw resistance of the recycled coarse aggregate concrete (RAC) and the bond performance of the corroded steel reinforcement and the RAC after the freeze-thaw cycles or something equivalent.
2. Introduction: The way the Authors referred to the previous research papers of the listed references is not correct and creates misunderstandings. Please follow the Journals’ guidelines.
3. Section 2: It would probably be better that section 2.1 includes specimen preparation instead of materials and concrete composition or before section 2.1 (materials and concrete composition) to write an introductory paragraph describing the experimental program.
4. Section 2, page 5, table 5: sand content of RAC = 8220 (kg/m3). Is it correct?
5. Section 2, page 5, table 5: Why do the Authors finally select to replace the total content of the natural aggregate coarse with recycled aggregate coarse? According to the introduction “Fernandez et al. 58 presented a different opinion, they indicated the effects of the replacement ratio of RCA on the bond performance of the RAC structures with 50% replacement ratio of RCA, was slight, while the effects became great for the RAC structures with 100% replacement ratio of RCA.
6. Section 2, page 5, lines 160-161: For what purpose do the Authors constructed six concrete prismatic specimens? It does not become clear throughout the text.
7. Section 3, Figures 7-11: The x-axis of these figures refer to the number of freeze-thaw cycles. It is clear. However, the Authors should write it and use the same caption in all figures.
8. Sub-section 3.5, lines 410-411: According to Table 8 and lines 405-408 the freeze-thaw cycles and steel reinforcement corrosion rates show negative relativity with the ultimate bond strength. Why do the Authors refer to positive relativity in line 410?
9. Sub-section 3.8: Give same extra information about the prediction bond – slip model proposed by Xiao et al. The referenced research paper is in Chinese so it could not be understood by people who do not know Chinese. Why do the Authors select these model as a base to extract the modified expressions? Could the modified expressions be used in other cases as well? In specimens with different bar diameter, concrete mixture or specimens which fail due to another form? In this point of view this Reviewer would like to encourage the Authors to prepare a future research paper concerning a parametric analysis to verify the validity of these expressions. Considering this work, the analytical and the experimental curves are in a very good agreement.
Author Response
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Reviewer 7 Report
The authors investigate bond performance of corroded steel bars after freeze thaw cycling. They also utilized recycled coarsa aggregate. The paper is generally good but it needs improvement. Followings should be carried out before acceptance:
The abstract should contain important results of the study.
Authors mentioned recycled coarse aggregate as if only it is obtained from demolished waste concrete. However, there are other ways to obtain recycled aggregate. Authors should add a paragraph to introduce recycled aggregate. The authors should state that there are other ways to obtain RCA such as glass, marble, PET, marble and etc. In order to support this sentence, the following studies can be utilized: use of recycled coal bottom ash in reinforced concrete beams as replacement for aggregate; concrete containing waste glass as an environmentally friendly aggregate: a review on fresh and mechanical characteristics; mechanical behavior of crushed waste glass as replacement of aggregates;flexural behavior of reinforced concrete beams using waste marble powder towards application of sustainable concrete; investigation of the physical-mechanical properties and durability of high-strength concrete with recycled pet as a partial replacement for fine aggregates; effects of waste powder, fine and coarse marble agregates on concrete compressive strength.
How this recycled materials for this study is obtained?
Novelty is not clear. Very same studies are already exists. What is the difference?
The reason for selecting design mixture should be added.
The design of reinforced concrete should be declared. Why did use sttirrups with 50mm spacing. Is it too low?
Why did you chose fi8? What is the reinforcement ratio and balanced ratio?
Add photos of aggregates
Title of fig4b should be changed
Add some summary for conclucision
Add recent studies on this subject to introduction. There are many studies on the introduction for this topic.
Conclusion should be improved. The recommendation consdiering all test should be given for engineers.
Author Response
Thank you for your comments. The response to your comments has been given, and the confirmation certificate of the English language editing provided by MDPI was included in it. Please see the attachment.
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Round 2
Reviewer 2 Report
The revised version satified me.
Reviewer 4 Report
Authors did the required corrections..
Reviewer 7 Report
The paper can be accepted
