Experimental Study on Axial Compressive Load-Bearing Performance of RC Short Columns Strengthened by All-Light Ceramsite Concrete

Round 1

Reviewer 1 Report

The paper deals with an interesting and relevant topic and the authors have invested considerable effort for the preparation of this paper.

But I think that the experimental tests performed did not fulfill the stated purpose of the examination ('Therefore, the purpose of this study is to comprehensively investigate the axial compressive load-bearing performance of RC columns strengthened with all-light ceramsite concrete with different bonding interface treatments.').

In particular, I believe that the test program is not appropriate if the goal is to apply the test results to the columns as constructive elements because of the selected:

1. dimensions of the specimens (columns as structural elements are slender elements, and the tested samples definitely are not)

2. load type (the columns in the tests are exposed to uniaxial pressure, while in reality they are exposed to oblique eccentric compression).

I recommend that the authors adjust the purpose of the paper (and consequently the title of the paper) so that it fits more closely with the results of the research.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Dear Authors,
thank you for your paper focused on strengthening of RC column with ceramsite concrete. Columns are one of the most used elements in construction, and in many cases, existing elements need to be strengthened, including columns. So the topic is current. My comments are:
- I recommend improve English,
- page 1, abstract, there is given in the second line "It is a good reinforcement material ..." - reinforcement is a steel (reinforcing bar), do you mean "material for strengthening?
- page 1, abstract, there is given in the third line "... when reinforcing ..." - use "strengthening", not reinforcing, if you need to improve the quality and resistance of a member, you strengthen the member, nor reinforce, "reinforcement, reinforcement steel" is used for steel bars,
- use "cross-section", not only "section",
- page 4, chapter 2.2., there is given "solidified concrete" - what is solidified concrete? Concrete usually hardens (concrete solidified in the first stages). Do you mean "concrete for strengthening"?
- page 4, chapter 2.3., there is given "encrypted area" - what does encrypted area mean? Is it a secret area? Or do you mean the end areas where the load is introduced? Do not use "encrypted area",
- chapter 2.3. - missing information on the slenderness of the samples - were they slender elements? What was the slenderness ratio? Or massive elements? I assume that after strengthening they were massive, but before strengthening (section 150x150mm)?
- page 7, chapter 2.4., the first sentence is incomprehensible - how can be a pressure tester for a column long (of length) 2000kN? The maximum force can be 2000kN and the maximum length of columns can be ... (2 3 meters ...).
- page 8, chapter 3, there is given "minute cracks" - what are minute cracks? The cracks that appear in the first minutes? This term is not used.
- page 8, chapter 3, there is given "penetration cracks" - what are penetration cracks? What do you mean? What is the difference between "crack" and "penetration crack"? Crack is only on the surface and penetration crack goes deep? All cracks go deep. Or are these only cracks in the strengthening layer? Please explain.
- page 9, chapter 3, there is given "(i) The specimen did not show cracks belonging to the linear elastic stage" - in the case of massive elements (which the samples probably were), even with centric compression, the formation of cracks in the linear elastic stage is not expected. Cracks only appear at the plastic stage (or elastic-plastic stage) before the failure of the element. This statement is probably unnecessary to write, or it is necessary to refine it as the author intended.
- Fig. 5 - yellow text outside the image cannot be read,
- Fig. 5 b) and f)- shouldn't the red markings of the cracks be moved?
- page 11, chapter 4.1., there is given "(iii) After reaching the peak load, the curve decrease rapidly until ..." - this statement can probably only be said about sample C1 (non-strengthened), because in other samples (strengthened) the branches are not so steep down and the failure occurs almost only at twice the deformation (12-15 mm) than the deformation at the peak (approximately 6 mm),
- pages 13-14, Fig. 9, the text above the figure states that the results for C5-C6 are shown, the caption of Figure 9 states that the results for C2-C6 are shown together, but the figure shows the results for C1-C4 and C6-C5 is missing. It needs to be reconciled, I recommend supplementing the results for C5 as well and stating everywhere that these are the results of C1-C6.
- paragraph 4.1 is followed by paragraph 3.2 - all paragraphs after 4.1 must be renumbered - these are paragraphs 3.2, 3.3, 3.4, 3.5, and 3.6 to paragraphs 4.2 to 4.6,
- page 17, conclusions, there is given "strength of the load-bearing capacity" - incomprehensible what is meant by that. The load-bearing capacity does not have strength, the concrete (any material) has strength. The load-bearing capacity satisfy or does not satisfy and you can specify it e.g. in kN (MPa, kNm ...)
- the paper is focused on new-to-old concrete cross-section and contact between them. To that problem are focused also kinds of literature (contact between concrete and fiber concrete), which I recommend see:
a) Kotes, P. - Vavrus, M.: Strengthening of Concrete Column by Using the Wrapper Layer of Fiber Reinforced Concrete. Materials 13(23), 2020, Article Number 5432,
b) Vavrus, M. - Kotes, P.: Numerical comparison of concrete columns strengthened with layer of fiber concrete and reinforced concrete. 13th international scientific conference on sustainable, modern and safe transport (Transcom 2019), Transportation Research Procedia, vol 40, 2019, 920-926.

Best regards.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The authors performed the experimental study on the reinforcement effect of RC columns reinforced with all-light ceramsite concrete. One unreinforced column, one RC column strengthened by ordinary concrete and four RC columns strengthened by all-light ceramsite concrete with different interface treatments were produced. Axial pressure tests were conducted on them. The experiments indicated that all-light ceramsite concrete had the characteristics of lightweight and high strength. It is proven to be a good reinforcement material and has a good application prospect when reinforcing the existing RC column by the enlarged section method. In general, the paper is well written, and the reviewer recommends publication, requesting the following comments to be duly handled.

1. The authors performed the external reinforcing study and concrete experimental research, which is a great work. The following papers related to the external reinforcing study and concrete experimental research can be included into the contents if possible.10.1016/j.conbuildmat.2008.12.003; 10.1177/1056789519900783; 10.1007/s10518-021-01222-w; 10.1016/j.jobe.2022.103988; 10.1016/j.jobe.2022.104904.

2. How do the authors design the specimens in the experimental study and what is the consideration? Maybe some explanations are needed in the contents.

3. The conclusions are given according to the six specimens and experimental results. Do the authors consider the uncertain factors (e.g. casting uncertainty, curing uncertainty, dimension uncertainty) and their corresponding influence in the results?

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Dear Authors,

thank you for improving your paper. I have no further comments.

Best regards.