Effect of Composite Impregnation on Properties of Recycled Coarse Aggregate and Recycled Aggregate Concrete

Round 1

Reviewer 1 Report

This paper discusses the effects of impregnation of various chemical strengthening agents on multiple behavior of recycled coarse aggregate and recycled aggregate concrete. The experiments in this paper are well designed and the results are clearly presented. The authors also illustrate possible mechanisms of the improvement in performances based on SEM analyses. Overall, this paper is of good quality and can be accepted after minor revisions.

1. In section 2.2, why are different mass fractions used for the three chemical reinforcing agents. What are the reasons for using 5%, 8%, and 10%.

2. Some acronyms in this articles are not clearly defined. For example, there is no explanation for PVA. Please give the definition for all the acronyms in this paper. For example, polyvinyl alcohol  (PVA).

3. Similar to question 1, why are the impregnation time different for different agents, and how are these time durations determined?

4. How many samples were tested to measure the physical and mechanical properties for each case? Please explicitly state the number of samples. Are the average values used to plot figure 4?

5. Just out of curiosity, why was the case S1S2P1 not tested?

The rest of this paper is written very well and I suggest accept this paper after the five questions above get addressed. 

Author Response

Response to Reviewer 1 Comments

Summary:

This paper discusses the effects of impregnation of various chemical strengthening agents on multiple behavior of recycled coarse aggregate and recycled aggregate concrete. The experiments in this paper are well designed and the results are clearly presented. The authors also illustrate possible mechanisms of the improvement in performances based on SEM analyses. Overall, this paper is of good quality and can be accepted after minor revisions.

We very much appreciate the favorable comments of the reviewer regarding the topic and significance of our manuscript. The comments are very helpful and have improved the overall quality of the paper. We have revised our manuscript as follows by referring the comments of the reviewer. The original comments are included verbatim in normal text, and our responses to each comment follow in blue and italicized text.

Specific comments:

1. In section 2.2, why are different mass fractions used for the three chemical reinforcing agents. What are the reasons for using 5%, 8%, and 10%?

In reference [34], RCA was soaked in 1 %, 3 %, 5 %, 7 % sodium silicate solution for 1h, 6h, 12h, 24h. RCA was soaked in 4 %, 6 %, 8 %, 10 % and 12 % silane solution for 24 h, 36 h and 48 h, respectively. RCA was soaked in PVA solution with mass fractions of 8 %, 9 %, 10 %, and 11 % for 24 h, 36 h, and 48 h, respectively. By testing the physical properties of aggregates, it is concluded that 5 % sodium silicate solution soaking for 1h, 8 % silane solution soaking for 24h, and 10 % PVA solution soaking for 24h can improve the physical properties of aggregates best. At the same time, Kou [32] also obtained10 % PVA as the best concentration of modified RCA. Relevant references have been cited and explained in chapter 2.2 of the experimental design. We added the following sentence to the revision: 'According to the research conclusion in [32,34]， in this test… '

2. Some acronyms in this articles are not clearly defined. For example, there is no explanation for PVA. Please give the definition for all the acronyms in this paper. For example, polyvinyl alcohol (PVA).

We've checked all the locations where the initial abbreviations appear and defined them. We apologize for the inconvenience of reading. Thank you for your suggestions, which make our article more rigorous.

3. Similar to question 1, why are the impregnation time different for different agents, and how are these time durations determined?

Based on the study in Reference [34], the impregnation time of RCA was set. The specific impregnation time has been explained and modified in question 1. Thank you for your suggestions to make our article background clearer.

4. How many samples were tested to measure the physical and mechanical properties for each case? Please explicitly state the number of samples. Are the average values used to plot figure 4?

Three samples were tested for each type. The number of samples for each type of test was supplemented in chapters 2.4 and 2.5 of the experimental design. We added the following sentence to the revision to explain the number of samples tested: ' Three samples were tested in each group and the average value was calculated. ' The average value of the test was used to draw Figure 4. Thank you for your suggestions, which will make our article more clearly displayed to the readers.

5. Just out of curiosity, why was the case S1S2P1 not tested?

In the experimental design process, considering the actual operation process of RCA, we did not adopt the scheme of S1S2P1. Thank you for your suggestions, and we will fully consider them in the future experiment.

References

[34] Xu, J. (2017). Study on Modification of Recycled Aggregate Concrete and Its Application (Master degree thesis, Anhui University of Technology).

[32] Kou, S. C., & Poon, C. S. (2010). Properties of concrete prepared with PVA-impregnated recycled concrete aggregates. Cement and Concrete Composites, 32(8), 649-654. [CrossRef]

Author Response File: Author Response.docx

Reviewer 2 Report

The reviewer recommend to accept the paper in the current format.

Author Response

Response to Reviewer 1 Comments

Summary:

The reviewer recommend to accept the paper in the current format.

We very much appreciate the favorable comments of the reviewer regarding the topic and significance of our manuscript. The comments are very helpful and have improved the overall quality of the paper.

Author Response File: Author Response.docx

Reviewer 3 Report

The manuscript deals with an interesting topic of single and combined impregnation of RCA with sodium silicate, silane, and PVA solution chemical reinforcement. The results of the experimental tests shown appear to be correct. The article is generally at a sufficient level but there are some shortcomings that need to be improved:

 1) The conclusion contains a sentence that is worthless because it contains knowledge which is generally well known: “Different chemical strengthening agents and different impregnation treatments can effectively improve the physical and mechanical properties of RCA.“ - this has been known for a long time :-) I recommend deleting this sentence and focusing on comparing individual impregnation materials with each other.

 2) In chapter 2, there is necessary to insert photos from the tests and a photo of the whole series of samples. There must be proof that the tests have been carried out to a sufficient extent.

 3) In chapter 3, I am missing an explanation why the water absorption of the S2 sample in the graph in Figure 4b is higher than the other treated samples? Please provide an explanation (hypothesis).

 4) The manuscript lacks several important articles mentioned in the introduction section that deal with recycled aggregate concrete - especially these three:

- Çakır, Ö., Dilbas, H.: Durability properties of treated recycled aggregate concrete: Effect of optimized ball mill method (DOI: 10.1016/j.conbuildmat.2020.121776)

- Pavlu, T. et al.: Improvement of the Durability of Recycled Masonry Aggregate Concrete (DOI: 10.3390/ma13235486)

- Pavlu, T. et al.: The Structural Use of Recycled Aggregate Concrete for Renovation of Massive External Walls of Czech Fortification (DOI: 10.3390/buildings12050671)

 Author must comment on the results of the above three articles and cite them in references.

Conclusion:

After incorporating the comments into the text (according to the above instructions) I recommend the manuscript for publication.

Author Response

Response to Reviewer 3 Comments

Summary:

The manuscript deals with an interesting topic of single and combined impregnation of RCA with sodium silicate, silane, and PVA solution chemical reinforcement. The results of the experimental tests shown appear to be correct. The article is generally at a sufficient level but there are some shortcomings that need to be improved:

We very much appreciate the favorable comments of the reviewer regarding the topic and significance of our manuscript. The comments are very helpful and have improved the overall quality of the paper. We have revised our manuscript as follows by referring the comments of the reviewer. The original comments are included verbatim in normal text, and our responses to each comment follow in blue and italicized text.

Specific comments:

1. The conclusion contains a sentence that is worthlessbecause it contains knowledge which is generally well known: “Different chemical strengthening agents and different impregnation treatments can effectively improve the physical and mechanical properties of RCA.“ - this has been known for a long time:-) I recommend deleting this sentence and focusing on comparing individual impregnation materials with each other.

The conclusion contains well-known knowledge, thank you for your suggestions. We deleted ' Different chemical strengthening agents and different impregnation treatments can effectively improve the physical and mechanical properties of RCA. ' in the concluding section.

2. In chapter 2, there is necessary to insert photos from the tests and a photo of the whole series of samples. There must be proof that the tests have been carried out to a sufficient extent.

We thank the reviewers for their proposal to insert test images into the article. It is necessary to make readers understand the progress of the experiment more clearly. The field preparation flow chart and test diagram of concrete have been inserted in chapter 2.

3. In chapter 3, I am missing an explanation why the water absorptionof the S2 sample in the graph in Figure 4b is higher than the other treated samples? Please provide an explanation (hypothesis).

We thank the reviewers for raising the important issue that S2 water absorption is higher than other treated samples. The reason why the water absorption of S2 is higher than other samples is that the organic alkyl generated by silane is accumulated in the cracks and pores of RCA, but it cannot completely seal the pores and fill the cracks. Sodium silicate reacts with the cement hydration products of the old mortar in RCA to form C-S-H gel, which can well repair the internal cracks and reduce the water absorption of S1 and S1S2. PVA formed a hydrophobic membrane on the outer surface of RCA effectively reducing the water absorption of P1, S1P1, and S2P1. We added the following sentence to the revised version to explain that S2 absorption was higher than other treated samples: ' The higher water absorption of S2 compared with the other treated samples is due to the organic alkyl groups produced by the silane accumulating in the cracks and pores of the RCA, but not completely closing the pores and filling the cracks. '.

4. The manuscript lacks several important articles mentioned in the introduction section that deal with recycled aggregate concrete.

We thank the reviewers for pointing out these issues in the introduction. We add the following sentences to supplement the references on the durability of recycled concrete: ' Çakır et al. [22] found that the durability of concrete prepared with 60 % RCA after the optimized Ball Mill Method was generally higher than that of untreated RCA. ' and ' Pavlu et al. [25,26] showed that crystal admixtures could fill the pores in recycled masonry aggregate, thereby improving the mechanical and durability of recycled masonry concrete.  '.

References

[22] Çakır, Ö., & Dilbas, H. (2021). Durability properties of treated recycled aggregate concrete: Effect of optimized ball mill method. Construction and Building Materials, 268, 121776. [CrossRef]

[25] Pavlu, T., Pazderka, J., Fořtová, K., Řepka, J., Mariaková, D., & Vlach, T. (2022). The Structural Use of Recycled Aggregate Concrete for Renovation of Massive External Walls of Czech Fortification. Buildings, 12(5), 671. [CrossRef]

[26] Pavlů, T., Fořtová, K., Řepka, J., Mariaková, D., & Pazderka, J. (2020). Improvement of the durability of recycled masonry aggregate concrete. Materials, 13(23), 5486. [CrossRef]

Author Response File: Author Response.docx