Analysis of Factors Influencing the Modulus of Hot-Recycled Asphalt Mixture with High RAP

Round 1

Reviewer 1 Report

The study is aimed to examine the effect of regenerant content and curing time on performance of asphalt mixtures containing RAP. The study has a good contribution to science, however, it needs some revisions

- The authors have compared which factor has the most influenced portion on  mechanical parameters of recycled asphalt mixture. Also, it was sated "For its bending stiffness modulus, the influence of curing time is the greatest" I beleive the author should conduct a statistical analysis to determine the significance of each factor.

- The abstract needs to be revised as the methods were not included and also please include only the main findings

- The introduction needs to be revised as well. The authors should indicate the main gap of knowledge more clearly as some studies (especially in lines 47 to 67) used were outdated (published in 1980S- 1990S and 200S). please show the knowledge  gap for studies published in last two years only.

- The authors are advised to show how the hot asphalt mixtures were prepared i.e. Marshall or superpave. Also, pls include in Table main properties of mix design such as the bitumen content of virgin binder and volumetric properties.

- For section "2.1.3. Mix Design of Hot Recycled Asphalt Mixture, line 113" The authors are suggested to revise this section and show in detail the proportion of each component( the weight of virgin aggs and binder/ RAP agg and RAP binder)

- The authors are suggested to indicate the name of Regenerant and its physical and chemical properties.

- For all test methods, pls add the specification standards.

- For all figures, pls include colorful figures to show the lines clearly and also pls add label for stars, triangle and square lines.

- The discussions need to be improved. add more in-depth discussion and comapre this study's findings with previous ones.

- Pls revise all references. Delete the studies published before 2019.

 

- Authors should cite from 10 to 15 papers to improve the literature and quality of references, preferably papers published in MDPI journal published last two years.

- Line 31, pls change "diseases" to "distress"

- - Line 31, pls change "ruts" to "rutting"

-  Line 16. pls revise this "mixture; Overall," add full stop

- Line 55, pls revise this sentence's structure ", the asphalt mixture added with RAP is also"

- Line 71, add full stop instead of comma after " [20-22],"

- Line 115, pls clarify the content of RAP used " was 80

- The title needs some revision as it is quite general.

- pls revise all tenses as it is suggested to use past for literature review and results.

- avoid using instruction  like "draw" or "compare"

- The authors should avoid using long sentences. A longer sentence is harder to understand than a short one.

Author Response

Dear editors and reviewers,

 

Thank you very much for giving us the opportunity to provide clarifications and revise the manuscript.

 

According to your comments, we have explained and revised the manuscript as follows. The new texts have been highlighted in the main document using red color.

 

 

Reviewer 1:

Comments:

1. The authors have compared which factor has the most influenced portion on mechanical parameters of recycled asphalt mixture. Also, it was sated "For its bending stiffness modulus, the influence of curing time is the greatest" I believe the author should conduct a statistical analysis to determine the significance of each factor.

Response:

Thank you for your kind and valuable suggestion! We totally agree with your opinion. After consideration, a statistical analysis has been supplemented in “3.4.2 Quantitative Analysis of Modulus Changes”. We have calculated the grey correlation coefficients to evaluated the change among the data sequences. The dynamic modulus and bending stiffness modulus were taken as the reference sequences. And the regenerant dosage, curing temperature and curing time were settled as the comparative sequences. After comparison, the influence degree of influence factors of hot recycled asphalt mixture was clarified as follows. For dynamic modulus of the hot recycled asphalt mixture, the order was curing time > regenerant dosage > curing temperature. For Bending stiffness modulus, the order was regenerant dosage >curing time > curing temperature. We have corrected the wrong conclusion in the study. Thanks!

 

2. The abstract needs to be revised as the methods were not included and also please include only the main findings.

Response:

Thank you for your kind suggestion! We have already revised the abstract. The main research methods have been supplemented and the findings have been simplified. Thanks!

 

3. The introduction needs to be revised as well. The authors should indicate the main gap of knowledge more clearly as some studies (especially in lines 47 to 67) used were outdated (published in 1980S- 1990S and 200S). please show the knowledge gap for studies published in last two years only.

Response:

Thank you for your kind and valuable suggestion! We totally agree with your opinion. We have already deleted the outdated studies mostly. And we have supplemented some more representative references published in last two years, as depicts in Line 49 to 67. Thanks!

 

4. The authors are advised to show how the hot asphalt mixtures were prepared i.e. Marshall or superpave. Also, pls include in Table main properties of mix design such as the bitumen content of virgin binder and volumetric properties.

Response:

Thank you for your kind suggestion! We have already supplemented the concerning information. The hot recycled asphalt mixture was designed to AC-16. Superpave Gyratory Compactor was employed to prepare the samples of dynamic Modulus test. And the samples were cored to obtain a φ 100 mm × 150 mm (high) cylindrical specimen. The plate-shaped specimen was prepared to obtain a 250 mm × 30 mm × 35 mm prism beams, being the samples of three-point bending test. Furthermore, the optimum asphalt content of recycled asphalt mixture was 4.9%. The volumetric properties have been listed in Table 3. Thanks!

 

5. For section "2.1.3. Mix Design of Hot Recycled Asphalt Mixture, line 113" The authors are suggested to revise this section and show in detail the proportion of each component (the weight of virgin aggs and binder/ RAP agg and RAP binder).

Response:

Thank you for your kind suggestion! We have stated the proportion of each component of hot recycled asphalt mixture in detail. Thanks!

Line 120

Hot recycled asphalt mixture contained 80% RAP; 14% fine aggregates with particle sizes of 0-3 mm and 6% coarse aggregates with particle sizes greater than 13.2.

Line 102

The asphalt content in RAP was calculated to be 4.2%.

Line 126

The optimum asphalt content of recycled asphalt mixture was determined to be 4.9%.

 

6. The authors are suggested to indicate the name of Regenerant and its physical and chemical properties.

Response:

Thank you for your kind suggestion! We have already supplemented the concerning information of regenerant in Section 2.1. The regenerant employed in this study was self-made. The related properties were recorded in Table 1. Thanks!

Table 1. Technical properties of regenerant

Testing Items	Indicators	Technical requirement
Flash Point (℃)	228	≥220
Saturates Content (%)	14.6	≤30
Viscosity Ratio Before and After Thin-Film Oven Test (%)	1.41	≤3
Mass Change After Thin-Film Oven Test (%)	1.4	≤4 ≥-4
Density 15℃ (g/cm3)	0.935	Measured Value

 

7. For all test methods, pls add the specification standards.

Response:

Thank you for your kind suggestion! We have already supplemented the specification standards for all test methods. Thanks!

Line 90

JTG/T F41-2017 for RAP performance evaluation

Line 123

JTG F40-2004 for Mix Design of Hot Recycled Asphalt Mixture

Line 127

JTG E20-2011 for Marshall test

Line 148 and Line 165

JTG E20-2011 for dynamic modulus test and three-point bending test

 

8. For all figures, pls include colorful figures to show the lines clearly and also pls add label for stars, triangle and square lines.

Response:

Thank you for your kind suggestion! We have already revised all the figures. All the figures have been colored. And the labels for stars, triangle and square lines have been added. Thanks!

 

9. The discussions need to be improved. add more in-depth discussion and comapre this study's findings with previous ones.

Response:

Thank you for your kind suggestion! The influence factors of the mechanical parameters of hot recycled asphalt mixture have been not only qualitatively but also quantitatively analyzed in this study. We have already supplemented a grey correlation analysis to further analyze the relevant degree of influence factors of modulus. The dynamic modulus and bending stiffness modulus were taken as the reference sequences respectively with the regenerant dosage, curing temperature and curing time being comparative sequences. The grey correlation coefficients were calculated. As a result, for dynamic modulus of the hot recycled asphalt mixture, the order was curing time > regenerant dosage > curing temperature. For Bending stiffness modulus, the order was regenerant dosage >curing time > curing temperature.

Previous studies mostly focused on the performance evaluation of hot recycled asphalt mixture with high RAP content[1-3]. When the proportion of RAP in the recycled mixture is high, it is necessary to add a regenerant. Under the circumstances, the factors influencing the mechanical performance have not been discussed systematically. Compared with the previous studies, this study focused on the mechanical performance of hot recycled asphalt mixture with the consideration of diffusion behavior of the rejuvenator, aiming at establishing the reference standard for the dosage and curing conditions of regenerant.

Thanks!

1. Hafeez, I.; Ozer, H.; Al-Qadi, I.L. Performance Characterization of Hot in-Place Recycled Asphalt Mixtures. J. Transp. Eng.2014, 140(8), 04014029.
2. Shao, H.; Sun, L.; Liu, L.; You, Z.; Yang, X. A Novel Double-Drum Mixing Technique for Plant Hot Mix Asphalt Recycling with High Reclaimed Asphalt Pavement Content and Rejuvenator. Constr. Build. Mater.2017, 134, 236-244.
3. Wu, J.; Sun, H.; Wan, L.; Yang, J.; Wang, S. Study on Low-Temperature and Fatigue Performance of High RAP Content Hot Recycled Asphalt Mixture Based on the Degree of Blending (Dob). Polymers-Basel2022, 14(21), 4520. 

 

10. Pls revise all references. Delete the studies published before 2019.

Response:

Thank you for your kind suggestion! We have already deleted the most of references published before 2019. But some previous studies have still remained because their research is of great significance for the development of asphalt mixture regeneration. Thanks!

 

11. Authors should cite from 10 to 15 papers to improve the literature and quality of references, preferably papers published in MDPI journal published last two years.

Response:

Thank you for your kind suggestion! We have updated the reference list in the manuscript. And also, some papers published in MDPI were employed. Thanks!

 

12. Line 31, pls change "diseases" to "distress".

Response:

Thank you for your kind suggestion! We have changed "diseases" to "distress" on Line 33. Thanks!

 

13. Line 31, pls change "ruts" to "rutting".

Response:

Thank you for your kind suggestion! We have changed "ruts" to "rutting" on Line 33. Thanks!

 

14. Line 16. pls revise this "mixture; Overall," add full stop.

Response:

Thank you for your kind suggestion! We have already revised this part of text descriptions. Thanks!

 

15. Line 55, pls revise this sentence's structure ", the asphalt mixture added with RAP is also".

Response:

Thank you for your kind suggestion! We have already revised this part of text descriptions. Thanks!

 

16. Line 71, add full stop instead of comma after " [20-22],".

Response:

Thank you for your kind suggestion! We have already revised this mistake. Thanks!

 

17. Line 115, pls clarify the content of RAP used " was 80.

Response:

Thank you for your kind suggestion! We have revised this sentence as shown on Line 120. The hot recycled asphalt mixture of AC-16 in this study is designed to contain 80% RAP, 14% fine aggregates and 6% coarse aggregates. Thanks!

 

18. The title needs some revision as it is quite general.

Response:

Thank you for your kind suggestion! We have revised the title of this manuscript. It’s called “Analysis of Factors Influencing the Modulus of Hot Recycled Asphalt Mixture with High RAP” to make clearer of this study. Thanks!

 

19. Comments on the Quality of English Language.
20. pls revise all tenses as it is suggested to use past for literature review and results.
21. avoid using instruction like "draw" or "compare".
22. The authors should avoid using long sentences. A longer sentence is harder to understand than a short one.

Response:

Thank you for your kind suggestion! Following your suggestions, we have revised the inappropriate words and the sentence. Moreover, the English language of the manuscript had been edited by a professional team. Thanks!

In addition to above revisions, we also have the language polished and add some related references. We appreciate it very much for the editors and the reviewers’ comments and suggestions. Please do not hesitate to contact us if you have more questions regarding this response and the revised paper.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Asphalt concrete recycling is a top topic because there are many unsolved questions that need to be solved by research. This article focuses on the effect of curing time and curing temperature on the mechanical properties. This is a practically important factor in the production and laying of asphalt concrete containing RAP

There is a lack of information about the rejuvenation agent, not as a commercial product, but as it renews the properties of aged bitumen/asphalt. Regenerating/rejuvenating substance plays a decisive role. It is necessary to understand how the properties of bitumen/asphalt changes due to short-term aging (RTFOT method).

For asphalconcrete with lagest fraction 16 mm, to show the properties of the constructive layer, the desired thickness is usually 3x the largest fraction. However, for research purposes with such a large sample, this factor can be ignored.

A large number of reference sources are over 5 even 10 years old. However, there are some for 2022 and even 2023. A very important factor influencing the mechanical properties is the RAP content and the type of bitumen (modified or unmodified), for example, referring to the DOI:10.1080/10298436.2020.1850721. RAP bitumen is aged and hard, but this factor can be made positive, i.e. by using high quanity of RAP in asphalt concrete types that require high stiffness. This is HMAC (high modulus asphalt concrete)

Author Response

Dear editors and reviewers,

 

Thank you very much for giving us the opportunity to provide clarifications and revise the manuscript.

 

According to your comments, we have explained and revised the manuscript as follows. The new texts have been highlighted in the main document using red color.

Reviewer 2:

Comments:

1. There is a lack of information about the rejuvenation agent, not as a commercial product, but as it renews the properties of aged bitumen/asphalt. Regenerating/rejuvenating substance plays a decisive role. It is necessary to understand how the properties of bitumen/asphalt changes due to short-term aging (RTFOT method).

Response:

Thank you for your kind and valuable suggestion! We totally agree with your opinion. The regenerant employed in this study was self-made. Related information about the technical properties of regenerant has been supplemented in Section 2.1. What’s more, the research concerning properties of asphalt changes due to short-term aging is indeed important for the employment of hot recycled asphalt mixture. Actually, we have taken the modulus of recycled asphalt (RTFOT/ PAV mixed with regenerant) as the main study subject to clarify the change trend of modulus (complex modulus/ bending stiffness modulus). They will be sorted into a systematic series of papers in the next step, some findings depict as follows.

The addition of regenerant could significantly reduce the complex modulus of aged asphalt. The curing temperature of 100℃ could restore the complex modulus of recycled asphalt so that it is comparable to that of virgin asphalt. However, the complex modulus of recycled asphalt cured at 135℃ was closer to that of aged asphalt than the modulus cured at 60℃, so the complex modulus of recycled asphalt was not inversely proportional to the curing temperature. It was assumed that within a certain temperature range, the complex modulus of recycled asphalt decreased first and then increased with increasing curing temperature.

The research findings mentioned above have not been added in the revised manuscript due to the page limit and different research topic with this article. The results of the research will be further completed and submitted soon. We are looking forward to your comments and suggestions again. Thanks!

 

2. For asphalconcrete with lagest fraction 16 mm, to show the properties of the constructive layer, the desired thickness is usually 3x the largest fraction. However, for research purposes with such a large sample, this factor can be ignored.

Response:

Thank you for your kind suggestion! The hot recycled asphalt mixture of AC-16 in this study is designed to conduct the dynamic modulus test and three-point bending test. The laboratory experiments were conducted in accordance with JTG E20-2011. Based on the guidelines, the size effect of samples can be ignored. The size effect will be considered on the site in the future. Thanks!

 

3. A large number of reference sources are over 5 even 10 years old. However, there are some for 2022 and even 2023. A very important factor influencing the mechanical properties is the RAP content and the type of bitumen (modified or unmodified), for example, referring to the DOI:10.1080/10298436.2020.1850721. RAP bitumen is aged and hard, but this factor can be made positive, i.e. by using high quanity of RAP in asphalt concrete types that require high stiffness. This is HMAC (high modulus asphalt concrete)

Response:

Thank you for your kind suggestion! We have deleted some studies over 5 even 10 years old to update the reference list. In this study, we analyzed the influence factors of the modulus of hot recycled asphalt mixture containing high RAP with consideration of the diffusion behavior of the rejuvenator. And we totally agree with your opinion. As mentioned above, the RAP content and the type of bitumen will also influence the mechanical properties of hot recycled asphalt mixture. In the future, we will continue to study the modulus influence laws of the RAP content and the type of bitumen combined with regenerant diffusion behavior. Thanks!

In addition to above revisions, we also have the language polished and add some related references. We appreciate it very much for the editors and the reviewers’ comments and suggestions. Please do not hesitate to contact us if you have more questions regarding this response and the revised paper.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear authors,

you have done a decent work, but I have some comments:

- please add more references to better describe the state of the art.

- please describe the used equipment and methods.

- please develop the conclusions, highlights the arguments

 

 

Author Response

Dear editors and reviewers,

 

Thank you very much for giving us the opportunity to provide clarifications and revise the manuscript.

 

According to your comments, we have explained and revised the manuscript as follows. The new texts have been highlighted in the main document using red color.

Reviewer 3:

Comments:

1. Please add more references to better describe the state of the art.

Response:

Thank you for your kind and valuable suggestion! We totally agree with your opinion. We have updated the reference list in the manuscript. Thanks!

 

2. Please describe the used equipment and methods.

Response:

Thank you for your kind suggestion! In this study, the hot recycled asphalt mixture was prepared to conduct dynamic modulus test and three-point bending test. The employed equipment and method have been supplemented in Section 2.5.1. Thanks!

 

3. Please develop the conclusions, highlights the arguments

Response:

Thank you for your kind suggestion! We have further revised the conclusions in this manuscript to highlight the arguments. Thanks!

In addition to above revisions, we also have the language polished and add some related references. We appreciate it very much for the editors and the reviewers’ comments and suggestions. Please do not hesitate to contact us if you have more questions regarding this response and the revised paper.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

All comments were addressed by the authors. The manuscript can be accepted now for publication 

Reviewer 3 Report

Dear authors,

thank you for the answers