An Innovative Approach for Evaluating the Quality of Recycled Concrete Aggregate Mixes

Round 1

Reviewer 1 Report

1.     In 3.2. Adhered mortar quantification, I believe that when assessing the particle size distribution after ultrasonic bath treatment, the results should not be solely determined through visual observation.

2.     In the subsequent text, the manuscript roughly suggest that the results of particle size distribution before and after ultrasonic bath treatment are not significant. I believe that such a judgment cannot be solely based on visual observation methods. Secondly, if you consider the effectiveness to be inadequate, there should not be excessive emphasis on it in the earlier stages of the process.

3.     The color contrast in Figure 9 is relatively low.

4.      The analysis of Figure 11 is lacking. The rate of change for ACV is not linear; each segment exhibits a different trend.

5.     Line 448, your approximation is problematic; you've been consistently forcing it towards 45%, which is unreasonable.

6.     Line 461-469, please consider your expression carefully to determine if it is truly a milestone breakthrough.

7.     Carefully inspect all your charts and verify if the font formats used in the text are consistent.

Minor editing of English language required

Author Response

Response to Reviewers’ comments and description of changes in the revised Manuscript Number: buildings-2826394

General comments:

Authors’ general comments to the Editor and Reviewer:

We are grateful to the Editor and Reviewers for the time dedicated to revising our paper and their comments. We have done our best to implement all suggested changes to the manuscript and we are certain this has helped improve its quality. Our responses to the review comments are below, and the changes that we have made to the paper are highlighted in the revised manuscript submission.

1. In 3.2. Adhered mortar quantification, I believe that when assessing the particle size distribution after ultrasonic bath treatment, the results should not be solely determined through visual observation.

Response:

Thank you for your coment, here would be benefitial to clarify the process that was explained in section 2.2.2. using sentences that can be found in lines 206-208:

The ultrasonic cleaning process was repeated multiple times until the water in the bath was clear for each sample, after which the samples were dried in an oven. Steps six and seven of the above procedure were repeated.

Steps six and seven from the above procedure are described in lines 193-196 as:

6. Once a constant mass was achieved, the RA samples were sieved again.
7. To improve the identification of the quantity of adhered mortar, visual inspections were conducted on each sample. This involved separating and weighing the liberated aggregates from their unliberated counterparts.

Hence, the results are not based solely on visual observation but mainly on conducting sieving analysis.

2. In the subsequent text, the manuscript roughly suggest that the results of particle size distribution before and after ultrasonic bath treatment are not significant. I believe that such a judgment cannot be solely based on visual observation methods. Secondly, if you consider the effectiveness to be inadequate, there should not be excessive emphasis on it in the earlier stages of the process.

Response:

We appreciate your coment: The method was not based solely on visual inspection. The ultrasonic cleaning was assessed as an extra step for further cleaning the loosely attached mortar. Although some improvements are visible, as specified in Figure 7., the parts of the attached mortar which were high in mass such as in the case of unliberated aggregate type ii. and iii. (Figure 6.) stayed mainly intact. Nevertheless, ultrasonic cleaning was experimentally investigated as a possible step for further liberation but did not provide the substitutional improvement considering additional resources, time and energy.

Figure 7. A representative sample of RA starting from the untreated state (a.), after treatment using Na₂SO₄ solution (b.), and after ultrasonic cleaning (c.).

Figure 6. Examples of particles that characterized as liberated and unliberated after the treatments and based on classification by Kim

3. The color contrast in Figure 9 is relatively low.

Response:

Thank you for drawing attention to this. Modifications to both Figure 9 and 10 in the new version of the manuscript have done with regards to colouring.

4. The analysis of Figure 11 is lacking. The rate of change for ACV is not linear; each segment exhibits a different trend.

Response:

Thank you for the valuable observation. We improved the analysis of Fıgure 11 in the paragraph located between lines 393-397. Added sentences are highlighted with yellow color.

5. Line 448, your approximation is problematic; you've been consistently forcing it towards 45%, which is unreasonable.

Response:

Thank you for addressing this statement. We believe that the aggregate crushing value results are also dependent on the confinement effect, which could prohibit further liberation of attached mortar from aggregate due to the static load applied. Although this statement could not be verified experimentally in this study, it seems valid considering the nature of the test and the typical behavior of bulk aggregate. The added sentence in the manuscript supporting this between lines 463 and 465 is highlighted with yellow color.

6. Line 461-469, please consider your expression carefully to determine if it is truly a milestone breakthrough.

Response:

Thank you for your considerate comment. The sentence is changed, excluding milestone expression (see lines 480-483 in the updated manuscript).

7. Carefully inspect all your charts and verify if the font formats used in the text are consistent.

Response:

Thank you for calling attention to this matter.

Reviewer 2 Report

The article, entitled “An Innovative Approach for Evaluating the Quality of Recycled Concrete Aggregate Mixes”, is experimental in nature. Its aim was to present a method for evaluating the quality of RA-containing aggregate mixes, which adopted a holistic approach to take into account all possible physical variables of RA that affect the mechanical strength of aggregate mixes.

The research is very interesting. However, the reviewer is uncomfortable with several issues. Firstly, can such a study be performed for every concrete and mortar? Can cement-polymer concretes be tested in this way? Secondly, the testing seems time consuming and that every concrete that could be a potential aggregate needs to be tested in this way is difficult. Recycled aggregates would need to be tested using these methods before producing new concrete. This lengthens the time until construction work can begin.

It also seems to increase the cost of recycling itself. Waste management and the whole process of recovery and recycling already require financial investment. 

I would ask the authors to address these comments.

Minor editing of English language required

Author Response

Response to Reviewers’ comments and description of changes in the revised Manuscript Number: buildings-2826394

General comments:

Authors’ general comments to the Editor and Reviewer:

We are grateful to the Editor and Reviewers for the time dedicated to revising our paper and their comments. We have done our best to implement all suggested changes to the manuscript and we are certain this has helped improve its quality. Our responses to the review comments are below, and the changes that we have made to the paper are highlighted in the revised manuscript submission.

The article, entitled "An Innovative Approach for Evaluating the Quality of Recycled Concrete Aggregate Mixes", is experimental in nature. Its aim was to present a method for evaluating the quality of RA-containing aggregate mixes, which adopted a holistic approach to take into account all possible physical variables of RA that affect the mechanical strength of aggregate mixes.

The research is very interesting. However, the reviewer is uncomfortable with several issues. Firstly, can such a study be performed for every concrete and mortar? Can cement-polymer concretes be tested in this way? Secondly, the testing seems time consuming and that every concrete that could be a potential aggregate needs to be tested in this way is difficult. Recycled aggregates would need to be tested using these methods before producing new concrete. This lengthens the time until construction work can begin.

It also seems to increase the cost of recycling itself. Waste management and the whole process of recovery and recycling already require financial investment.

I would ask the authors to address these comments.

Response:

Thank you very much for the comments. Regarding the first question, it depends on the raw materials for sure. The literature has recognised that subjecting recycled concrete aggregate with various origins of virgin natural aggregate to freezing and thawing cycles while being submerged in sodium sulphate solution is one of the most harmless procedures for virgin aggregate. Here, care should be taken to ensure that adhered mortar is the one that is first detached from virgin aggregate. Since the porosity difference between the aggregate and adhered mortar would lead to their response to the stresses induced, we believe investigation regarding lightweight aggregate as a virgin aggregate would be important. Since there is also a variety of raw materials for cement-polymer concretes, we cannot confirm that the approach is applicable to (all of) them, but it is definitely something to be further investigated. Moreover, we are aware of the complexity of the process. This is why we propose developing prediction models and classifications based on aggregate crushing value. If the prediction models are developed based on the large dataset, the complexity of the process will be substantially reduced.

Reviewer 3 Report

1. The research significance of the article needs to be better elaborated in the last paragraph of the introduction, highlighting the research significance of the article;

2. Two types of coarse aggregate are used: RA and NA, whether to consider the influence of coarse aggregate shape on the research results of the article;

3. The conclusion of the article should be further refined and revised, and corresponding quantitative analysis should be conducted again;

4. There are still many grammar errors in the article, and it is recommended to make careful revisions and checks;

1. The research significance of the article needs to be better elaborated in the last paragraph of the introduction, highlighting the research significance of the article;

2. Two types of coarse aggregate are used: RA and NA, whether to consider the influence of coarse aggregate shape on the research results of the article;

3. The conclusion of the article should be further refined and revised, and corresponding quantitative analysis should be conducted again;

4. There are still many grammar errors in the article, and it is recommended to make careful revisions and checks;

Author Response

Response to Reviewers’ comments and description of changes in the revised Manuscript Number: buildings-2826394

General comments:

Authors’ general comments to the Editor and Reviewer:

We are grateful to the Editor and Reviewers for the time dedicated to revising our paper and their comments. We have done our best to implement all suggested changes to the manuscript and we are certain this has helped improve its quality. Our responses to the review comments are below, and the changes that we have made to the paper are highlighted in the revised manuscript submission.

1. The research significance of the article needs to be better elaborated in the last paragraph of the introduction, highlighting the research significance of the article;

Response:

Thank you for the valuable comment. The last paragraph has been modified (lines 96-99).

2. Two types of coarse aggregate are used: RA and NA, whether to consider the influence of coarse aggregate shape on the research results of the article;

Response:

We acknowledge that the effect of aggregate shape is not directly examined in this study, but based on experimental investigation focusing on packing density and mechanical resistance, the shape factor is certainly considered. The direct evaluation of aggregate shape could be a valuable input for future developments in machine learning tools. The aggregate shape influences important phenomena such as interlocking, which significantly impacts the mechanical behaviour of concrete.

3. The conclusion of the article should be further refined and revised, and corresponding quantitative analysis should be conducted again;

Response:

Your comment is appreciated, The conclusion part of the manuscript has been rewritten.

4. There are still many grammar errors in the article, and it is recommended to make careful revisions and checks;

Response:

Thank you for drawing attention to this, the article has been detailly reviewed.

Reviewer 4 Report

The work is relatively interesting, and the structure and language are well prepared. Some comments below need to be addressed or considered to improve the technical depth of the manuscript:

(1) In 2.2 Methods, “The methodology is based on an experimental investigation of the bulk aggregate”, the referenced standard should be added and explained.

(2) In 2.2 Methods, what is the basis for “A three-step approach”? The scientificity and rationality of this method should be explained.

(3) In 2.2.1. Packing density, “The aggregate was oven-dried (60 °C) until the constant mass”. The drying temperature should be set at 105-110 °C, only 60 °C in this test was used. How should the author consider this? Please supplement the reference standard.

(4) In 2.2.2. Adhered mortar quantification, “16 hours at approximately -17°C and 8 hours at about 80 °C”, why was such time and temperature chosen?

(5) In Figure 4, the red straight line and R2=0.8463 should be explained.

(6) In 3.2. Adhered mortar quantification, the result after Na2SO4 solution treatment and after ultrasonic treatment are similar. Please explain the reason.

(7) The conclusion is too long, please simplify it.

Minor editing of English language required

Author Response

Response to Reviewers’ comments and description of changes in the revised Manuscript Number: buildings-2826394

General comments:

Authors’ general comments to the Editor and Reviewer:

We are grateful to the Editor and Reviewers for the time dedicated to revising our paper and their comments. We have done our best to implement all suggested changes to the manuscript and we are certain this has helped improve its quality. Our responses to the review comments are below, and the changes that we have made to the paper are highlighted in the revised manuscript submission.

• In 2.2 Methods, “The methodology is based on an experimental investigation of the bulk aggregate”, the referenced standard should be added and explained.

Response:

Thank you for the comment: The methodology was developed in this study, so there is no reference standard for it. However for each respective step of the procedure (2.2.1., 2.2.2., 2.2.3) , applicable standards/literature are referenced.

• In 2.2 Methods, what is the basis for “A three-step approach”? The scientificity and rationality of this method should be explained.

Response:

Your comment is appreciated: The final paragraph of the 1. Introduction has been enhanced to clarify the rationale behind the method's development (see lines 85-103).

• In 2.2.1. Packing density, “The aggregate was oven-dried (60 °C) until the constant mass”. The drying temperature should be set at 105-110 °C, only 60 °C in this test was used. How should the author consider this? Please supplement the reference standard.

Response:

Many thanks for the comment: This was mainly based on the possible changes in the microstructure of recycled concrete aggregate. Since in the future work recycled aggregate concrete will be designed and tested, we decided to apply temperature, which will not affect the microstructure of the cementitious paste. We are aware that the usual drying temperature for aggregate based on, for instance EN 933-1 standard is 110 ± 5°C. However, reducing the drying temperature would only extend the time required to reach constant mass and would not affect the final results. Additionally, we provide a list of the effects that temperatures higher than 60°C can have on cementitious paste:

1. Gypsum dehydration beginning around 80°C ;
2. Initial decomposition temperature of ettringite at about 60°C;
3. Partial dehydration of C-S-H at 105°C [1].

[1]      C. Gallé, “Effect of drying on cement-based materials pore structure as identified by mercury intrusion porosimetry A comparative study between oven-, vacuum-, and freeze-drying,” Cem Concr Res, vol. 31, no. 10, pp. 1467–1477, 200AD, doi: https://doi.org/10.1016/S0008-8846(01)00594-4.

• In 2.2.2. Adhered mortar quantification, “16 hours at approximately -17°C and 8 hours at about 80 °C”, why was such time and temperature chosen?

Response:

We appreciate your comment: The method for deattachment of adhered mortar was adopted from Abbas et al.[2]. A series of approaches were considered, and this procedure was identified as the most effective. The sentence in section 2.2.2 of the manuscript, where the method reference is specified, is highlighted in pink (see lines 180-182). Additionally, the ASTM C 672 Standard Test Method for Scaling Resistance of Concrete Surfaces Exposed to Deicing Chemicals proposes subjecting concrete to a temperature of -17°C for 16 hours. Overall, the method is based on introducing both thermal and chemical stresses to the reycled concrete aggregate.

• In Figure 4, the red straight line and R2=0.8463 should be explained.

Response:

Thank you for the comment: The paragraph below Figure 4 extends the interpretation of the results. It can be found in lines 249-256.

(6) In 3.2. Adhered mortar quantification, the result after Na2SO4 solution treatment and after ultrasonic treatment are similar. Please explain the reason.

Response:

We appreciate your comment:

The interpretation of the results is expanded on page 9, where the added sentences are highlighted in pink (see lines 304-308).

• The conclusion is too long, please simplify it.

Response:

The conclusion has been shortened in the new version of the manuscript.

Round 2

Reviewer 3 Report

The article has been carefully revised and can be accepted

The article has been carefully revised and can be accepted