Evaluation of the Refined Decomposition Effect of Reclaimed Asphalt Pavement Materials

Round 1

Reviewer 1 Report

A nice study that evaluated refined decomposition effect of reclaimed asphalt pavement material. Overall, the manuscript is generally well-written and organized.   Here are some suggestions for implementing:

1. Table 1, What does 30Hz mean?

2. Suggest replotting gradation curves on 0.45 Power graph.

3. Incorporating the full names of the abbreviations when they show up in the first time in the manuscript.

4. Figure 4 is a little hard to follow.

5. Minor editing of English language is required.

Minor editing of English language is required.

 

Author Response

Dear Editor and Reviewer:

Thank you very much to the editors and reviewers for hard work in this article. We consider and discuss the valuable suggestions put forward by the reviewers. We have carefully revised the manuscript according to the reviewer's comments. The revised content of the manuscript is shown below.

1. Table 1, What does 30Hz mean?

The reviewer's suggestion is very accurate. The refined decomposition effect of RAP is related to many factors, such as crusher rotor speed, RAP properties and temperature, crusher baffle position. The crusher rotor speed is the key factor. Moreover, since this test was conducted at the project site and the large refined decomposition equipment (120 t/h) was used in the test, it is difficult to change the position of crusher baffle, RAP property and temperature. Therefore, the collision strength of RAP was controlled by changing the frequency of centrifugal impact crusher.

According to the reviewer's comments, the authors added explanations before Table 1. "0Hz" represents the RAP without refined decomposition. The "30Hz", "40Hz" and "50Hz" are frequency parameters used by refined decomposition equipment to control the speed of centrifugal impact crushers, which are linearly related to the rotor speed.

2. Suggest replotting gradation curves on 0.45 Power graph.

According to the reviewer's comments, the gradation curves have been redrawn.

 

3. Incorporating the full names of the abbreviations when they show up in the first time in the manuscript.

According to the reviewer's comments, the abbreviations that first appeared have been checked and supplemented.

4. Figure 4 is a little hard to follow.

The authors revised Figure 4 according to the reviewer's comments. The modified image is shown below.

 

5. Minor editing of English language is required.

The authors checked the entire text according to the reviewer's requirements.

Reviewer 2 Report

This study assessed the RAP refined decomposition impact at three frequency parameters (30, 40, and 50 Hz).  The overall quality of RAP may be enhanced through the improved breakdown process, which also makes it possible to recycle RAP at a high level and for a high price.The author did an extensive literature review and it is a meaningful work. This manuscript can be accepted for publication after major revisions to address the following issues:

- The objectives of the study should be stated clearly at the end of the introduction

 

- The authors should describe the research limitations and contribution

- Please add more in depth discussions for all findings.

- The Conclusions section should be written in a discussion concept. Instead of directly giving the increase and decrease obtained as a result, some more controversial and evaluative comments should be made. Accordingly, the conclusions section should be expanded.

- The authors have stated in methods that the asphalt mixtures are evaluated at high and low temperatures, however, I could not find any results showing the evaluation of high and low temperatures in whole text

- the authors uses the phrase "significantly" in describing the increase of decrease the values, however, there was no statistical analysis to show whether the increase or decrease was significant

- Pls add table to show the composition of samples from 1 to 4 or add them in Table 1.

- Pls add the properties of aged asphalt in section 2.2.

Figure 7 (b) , pls add more easily understood chart.

- The number of references are not sufficient, Pls add more updated references (published last two years)

 

 

Author Response

Dear Editor and Reviewer:

Thank you very much to the editors and reviewers for hard work in this article. We consider and discuss the valuable suggestions put forward by the reviewers. We have carefully revised the manuscript according to the reviewer's comments. The revised content of the manuscript is shown below.

1.The objectives of the study should be stated clearly at the end of the introduction.

The authors revised the end of the "Introduction" according to the reviewer's comments. The end of the "Introduction" section points out the objectives of the study. The last paragraph of "Introduction" after modification is shown below.

This study focuses on the properties of RAP after refined decomposition and the impact of refined decomposition RAP on recycled asphalt mixtures. The study specifically includes the refined decomposition effect of RAP, and the effect of refined de-composition on the addition proportion of coarse RAP to recycled asphalt mixture. In addition, the influence of refined decomposition on the road performance of recycled asphalt mixture was studied. The research results provide a technical basis for the large-scale application of RAP in recycled asphalt mixture and the quality improvement of recycled asphalt mixture. The research is conducive to improving the utilization level of highway traffic solid waste and providing technical support for the construction of low-carbon and sustainable highway.

2.The authors should describe the research limitations and contribution.

The relevant content has been adjusted according to the suggestions of the reviewer. the research limitations of the references were placed after the relevant literature and the research contributions were added.

In refined decomposition process, RAP is crushed by collision and friction in the centrifugal impact crusher, and the RAP (after crushing) is divided into coarse RAP (≥ 5mm) and fine RAP (0-5mm). The coarse RAP surface contains little asphalt due to collision and friction, and most aged asphalt enters the fine RAP to realize the separation of aged asphalt and coarse aggregate. Coarse RAP can be directly used for recycled asphalt mixtures. The fine RAP can be used for recycled asphalt mixtures through cold addition and other methods. The fine RAP can also be used for asphalt mixture components, achieving high-quality reuse of RAP. Qiu et al. [23] applied refined decomposition RAP to recycled asphalt mixture at a proportion of 80%, and the road performance of the recycled asphalt mixture is equivalent to that of the new asphalt mixture. This study provides a reference for the high addition proportion of RAP to recycled asphalt mixtures based on refined decomposition. Wang et al. [24] applied the refined decomposition RAP to the highway reconstruction project, and the performance of SMA-13 recycled asphalt mixture was basically the same as that of the new asphalt mixture. They applied recycled asphalt mixture to the surface layer of highways based on refined de-composition. Current research pays more attention to the road performance of recycled asphalt mixture with refined decomposition RAP, but there has been little research into the characteristics of refined decomposition RAP.

3. Please add more in-depth discussions for all findings.

According to reviewer' opinions, some contents were supplemented in the discussion part.

4. The Conclusions section should be written in a discussion concept. Instead of directly giving the increase and decrease obtained as a result, some more controversial and evaluative comments should be made. Accordingly, the conclusions section should be expanded.

According to the comments of reviewers, some more controversial and evaluative comments were supplemented.

5. The authors have stated in methods that the asphalt mixtures are evaluated at high and low temperatures, however, I could not find any results showing the evaluation of high and low temperatures in whole text

According to the comments of reviewers, relevant contents were supplemented in Figure 11.

 

Figure 11. Road performance of recycled asphalt mixture.

6. The authors uses the phrase "significantly" in describing the increase of decrease the values, however, there was no statistical analysis to show whether the increase or decrease was significant.

According to the reviewers' opinions, the authors added relevant data analysis to show the control of refined decomposition on RAP gradation variability.

As seen from Figure 4, the gradation CV of RAP-O (A-1, A-2, A-3) is significantly greater than that of refined decomposition RAP (D-1, D-2, D-3). For the key size (4.75mm), the CV of accumulated passing percentage of A-1 is 13.5%, and that of D-1 is 3.88%. Compared with A-1, the CV of accumulated passing percentage of D-1 decreased by 67.5%. This is mainly due to the existence of many "false particles" in RAP-O, which causes great fluctuation in the gradation. The refined decomposition makes the RAP to collide and rub repeatedly in the centrifugal impact crusher. The "false particles" of RAP are broken along the asphalt interface between aggregate, and most of the asphalt enters the fine RAP to realize the separation of asphalt and coarse aggregate. Refined de-composition reduces the agglomeration phenomenon in the RAP and stabilizing the gradation. The refined decomposition improves RAP gradation stability and the raw material quality of the recycled asphalt mixture.

7. Pls add table to show the composition of samples from 1 to 4 or add them in Table 1.

According to the reviewer's requirements, the number of samples have been added to Table 1 and explanations for the relevant content have been added.

The RAP used in the experiment was divided into two types, original RAP without refined decomposition (RAP-O) and refined decomposition RAP (RAP-RD). The number of RAP samples used in the test is shown in Table 1. “0Hz” represents that RAP has not undergone refined decomposition. The "30Hz", "40Hz" and "50Hz" are frequency parameters used by refined decomposition equipment to control the speed of centrifugal impact crushers, which are linearly related to the rotor speed. In addition, in order to ensure the representativeness of the sample, RAP-O and RAP-RD remove the part within the depth range of 15-20cm from the surface of the stockpile before sampling, and take the material from the quartered position of the stockpile, which are respectively represented by ①②③④.

Table 1. RAP sample number in the test.

Size /mm	RAP-O （0Hz）	RAP-RD （30Hz）	RAP-RD （40Hz）	RAP-RD （50Hz）
9.5-19	A-1	B-1	C-1	D-1
	①②③④	①②③④	①②③④	①②③④
4.75-9.5	A-2	B-2	C-2	D-2
	①②③④	①②③④	①②③④	①②③④
0-4.75	A-3	B-3	C-3	D-3
	①②③④	①②③④	①②③④	①②③④

8. Pls add the properties of aged asphalt in section 2.2.

The reviewer's review is very meticulous. Aging asphalt is an analytical material used in experiments. Aging asphalt was extracted by RAP. Strictly speaking, RAP is the only material used in the test.

9.Figure 7 (b), pls add more easily understood chart.

The ordinate of the Figure 7 (b) was modified according to the comments of the reviewer.

 

10. The number of references is not sufficient, Pls add more updated references (published last two years)

According to the reviewers, the references were sorted out and the latest references were added.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors have responded appropriately to some comments, however, some others need to addressed more specifically

- First, the objectives need to be revised as what authors stated are still not specific. objectives describe what you intend your research project to accomplish in specific and measurable manners

- Also, for limitation of the study is not specified , this can be added at the end of the conclusion with adding the future studies.

- The discussions need to be improved.

- the authors were asked to add more references, however, only 2 references was added!.  Here are my suggestions

https://doi.org/10.3390/coatings13081318

https://doi.org/10.3390/buildings13071787

https://doi.org/10.3390/su15043807

https://doi.org/10.3390/buildings13071578

 

Author Response

Dear Editor and Reviewer:

Thank you very much to the editors and reviewers for hard work in this article. We consider and discuss the valuable suggestions put forward by the reviewers. We have carefully revised the manuscript according to the reviewer's comments. The revised content of the manuscript is shown below.

1. First, the objectives need to be revised as what authors stated are still not specific. objectives describe what you intend your research project to accomplish in specific and measurable manners.

The authors revised the last paragraph of "Introduction" again according to the suggestions of the reviewers. The research objectives are divided into general objectives and specific objectives. The specific research objectives are divided into three parts, and the research objectives of the article are introduced in detail. The revised paragraph is as follows.

This study focuses on the properties of RAP after refined decomposition and the impact of refined decomposition RAP on recycled asphalt mixtures. The specific re-search objectives are divided into three parts. Firstly, the influence of refined decom-position process was studied on the variation of gradation, asphalt content, aged asphalt properties and aggregate (extracted) properties for RAP. Second, the maximum addition proportion of coarse RAP to recycled asphalt mixture was analyzed based on refined decomposition. Thirdly, the influence of refined decomposition on the road performance of recycled asphalt mixture was studied, including high-temperature performance, low-temperature performance, and water stability. The research results provide a technical basis for the high addition proportion of RAP in recycled asphalt mixture and the quality improvement of recycled asphalt mixture. The research is conducive to im-proving the utilization level of highway solid waste and providing technical support for the construction of low-carbon and sustainable highway.

2. Also, for limitation of the study is not specified, this can be added at the end of the conclusion with adding the future studies.

The research shows that the coarse RAP (≥4.75mm) surface contains little asphalt, which is close to the ordinary aggregate. Coarse RAP can be 100% used for recycled asphalt mixture. However, there is no specific description for the application of the fine RAP(≤4.75mm). This part of the research is being carried out in the laboratory, and the relevant data are not sufficient.

Future research will focus on the application of fine RAP (≤4.75mm) after refined decomposition to further improve the high-value utilization level of RAP.

3. The discussions need to be improved.

Relevant discussion contents were modified according to the requirements of reviewers. Some of the contents are as follows.

As shown in Figure 3, for the coarse RAP (>4.75mm), the aggregate gradation curves of original RAP (A-1 and A-2) samples have obvious differences. The aggregate gradation curves of RAP-RD (D-1 and D-2) are basically the same. The consistency of aggregate gradation curves of refined decomposition RAP-RD (D-1 and D-2) is significantly better than that of original RAP (A-1 and A-2). The result shows that the stability of RAP aggregate gradation with refined decomposition is very good. Refined decom-position is beneficial to improve the stability of coarse RAP aggregate gradation. For the fine RAP (0-4.75mm), the consistency of refined decomposition RAP (D-3) aggregate gradation curve is slightly better than that of original RAP (A-3), and the influence of refined decomposition on the consistency of the coarser RAP aggregate gradation curve is greater than that of the fine RAP. In order to express the variability of the aggregate gradation more clearly, the coefficient of variation (CV) of RAP aggregate gradation passing percentage was calculated, and the results are shown in Figure 4.

As seen from Figure 4, the aggregate gradation CV of RAP-O (A-1, A-2, A-3) is significantly greater than that of refined decomposition RAP (D-1, D-2, D-3). For the key size (4.75mm), the CV of accumulated passing percentage of A-1 is 13.5%, and that of D-1 is 3.88%. Compared with A-1, the CV of accumulated passing percentage of D-1 decreased by 67.5%. The refined decomposition process is beneficial to improve the stability of RAP aggregate gradation. This is mainly due to the existence of many "false particles" in RAP-O, which causes great fluctuation in the aggregate gradation. The re-fined decomposition makes the RAP to collide and rub repeatedly in the centrifugal impact crusher. The "false particles" of RAP are broken along the asphalt interface be-tween aggregate, and most of the asphalt enters the fine RAP to realize the separation of asphalt and coarse aggregate. Refined decomposition reduces the agglomeration phenomenon in the RAP and stabilizing the aggregate gradation. The refined decomposition improves RAP aggregate gradation stability and the raw material quality of the recycled asphalt mixture.

As shown in Figure 7, the change of aged asphalt properties (penetration, softening point, ductility) is not obvious with the increase of frequency. However, the variability of aged asphalt properties (penetration, softening point, ductility) gradually decreases with the increase of frequency. The results show that the refined decomposition process can not change the properties of aging asphalt, but can improve the stability of asphalt properties. This is mainly due to the further mixing of RAP during collision and friction in refined decomposition process, which reduces the variability of RAP asphalt properties. In addition, the refined decomposition is a physical process (collision and friction between the RAP), which has a relatively little influence on the asphalt properties.

As shown in Figure 9, based on the gradation variability control method and the asphalt content variability control method, the maximum addition proportion of RAP-RD (D-1 and D-2) is much higher than that of RAP-O (A-1 and A-2). According to the gradation and the asphalt content variability control method, the maximum addition proportion of A-1 (RAP-O) shall not exceed 33% and 29% respectively. When the addition proportion exceeds calculated value, the mixture gradation or asphalt content of the recycled asphalt mixture may easily exceed the control range. This calculation result meets the requirement that RAP addition proportion should not exceed 30% in the current specification. For RAP-RD (D-1 and D-2), the maximum addition proportion calculated by the gradation and the asphalt content variability control method has significantly exceeded 100%. This calculation result shows the addition proportion of D-1 and D-2 (≥4.75mm) can achieve 100% replacement of new coarse aggregate. The results prove that the refined decomposition can improve the addition proportion of coarse RAP. The refined decomposition process provides a reference for achieving large addition proportion of RAP.

 

4. the authors were asked to add more references, however, only 2 references was added.  Here are my suggestions

https://doi.org/10.3390/coatings13081318

https://doi.org/10.3390/buildings13071787

https://doi.org/10.3390/su15043807

https://doi.org/10.3390/buildings13071578

According to the reviewers' opinions, some references have been added.

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

No further comments as all my comments were addressed by the authors.  The manuscript can be accepted now for publication