A Review of Rubberised Asphalt for Flexible Pavement Applications: Production, Content, Performance, Motivations and Future Directions

Comments

Amendments

Location of the additional write up

The paper is good and relative to and interesting topic. It is well and clearly writing  .

Only some reviews like in some references about they are cited and certain parts of text. A version of paper with reviewer notes to be corrected was send back to authors consideration.

Thank you.

As the reviewer suggestion, we have fixed the manuscript and proofreading the paper to eliminate all such errors

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Comments

Amendments

Location of the additional write up

1. Moderate changes to the level of English would be beneficial, so editing of the draft by

someone with a good command of English would be quite beneficial. More specifically,

there are a number of items in the draft that need to be addressed as follows:

Your comments are appreciated.

As the reviewer suggestion, we have fixed the manuscript and proofreading the paper to eliminate all such errors.

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2. The link of overall text is missing

Thank you.

We hope after the reviewers comments the manuscript be more linked.

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3. The introduction section should be written better to highlight the study

Thanks for the kind observation.

The introduction was written in general way because specific explanation mentioned in the following sections (at the end of the introduction section add the aim of the study)

End of the introduction section 1.

4. Could you elaborate on the reasons behind this choice and the implications for the adoption

of CR asphalt in the industry?

Thanks again for the comment. Due to the excellent performance, reducing the greenhouse gases by using waste materials, increases the lifespan and durability of the pavement which leads to reduce the maintenance cost. The adoption of using CR asphalt in the industry is slow due to the high initial cost of CR asphalt production and in some cases not established a guidebook for industry fellows.

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5. How does the incorporation of Crumb Rubber (CR) recycled from waste tires contribute to

the realization of green pavement objectives and the attraction of global investors to a new

market?

Thanks for the comment.

The answer is can be found in section 3.4 in details.

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6. The last paragraph of introduction should be written properly to identify the objective of the

paper.

That was a useful comment from the reviewer. The objectives of the study have been added.

End of section 1

7. Explanation of figure is missing. The figure is not defined properly.

Thank you for your comment.

Which figure?

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8. How might these knowledge gaps impact the broader adoption of CR asphalt solutions?

Thank you for your valuable comment.

For example, in this paper, it can show that besides the high initial cost of CR asphalt, it has better durability and long lifespan than traditional asphalt which leads to a cost-effective asphalt besides the environmental benefits.

Also, show that the layer type and method used for CR asphalt could affect the performance and the cost.

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9. Check the reference style.

Thank you for your comment.

The references are adjusted as the journal format.

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10. There is lack of literature of covering material. Author should provide latest literature and

explain more briefly describe

Thank you for your comment.

The authors try to include the latest research and to achieve that 87 of 131 research were within the last ten years and other articles were between standard books and international websites to keep up with the latest industry achieving and problems faced during or before using the CR asphalt.

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11. Review's organizational structure is incorrect. To make the necessary corrections, look at the

most recent literature review.

Thank you for your comment. The authors try to summarize and identify the gap in using CR asphalt in the general concept. Our future plans will be more specific with the chosen topic and produce a systematic literature review.

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12. Based on conclusion How does the performance of asphalt with CR addition compare to that

of traditional asphalt mixtures in terms of service life and overall performance?

Thanks for your comment.

The comparison is based on lab testing and field result observations from the previous studies.

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Comments

Amendments

Location of the additional write up

1_ Please make more effort in the introduction to explain why is important to consider CR for recycling in pavement industry, i.e., motivation, availability, etc.

Thanks for the valuable comment.

More specific information is mention in the section 3.6

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2_ A brief comparison of dry and wet processing should be elaborated probably in a table. Also, which is most preferable and why? What limitations and effects on mix performance exist? Please elaborate.

Your comment is appreciated.

More specific information’s add at end of section 2.4

End of section 2.4

3_ Subsection 3.3: I would suggest adding new input about the impact of CR on pavement functional performance, i.e., friction or else skid resistance. The issue is important, since it relates to road safety. On this context, the title of subsection 3.3 could slightly change to “impact of CR on pavement performance” to cover all aspects of pavement behavior. Limited studies exist about the impact of CR on surface condition, so this should be highlighted as a critical issue in a review paper for the sake of completeness, examples to see and probably cite: https://doi.org/10.3390/recycling7040047 , https://doi.org/10.3390/vehicles2010004

Your invaluable comments are appreciated. The authors will consider your valuable comment for the future work

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4_ Reference style is out of the requested format. Please fix it.

That was a useful comment from the reviewer. All references are adjusted as the journal format

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Comments

Amendments

Location of the additional write up

1. The written format needs check carefully, such as ‘larg’ in pp.1, ‘conventional asphalt. [12].’ in pp.2, the references, etc.

Thanks for the valuable comment.

we have fixed the manuscript and proofreading the paper to eliminate all such errors.

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2. From my point of view, the outline should be introduced in the introduction section.

Thank you for the suggestions.

The objectives of the study have been added.

End of the introduction section

3. This review contained many topics, each topic has very extensive research items. However, these descriptions and summaries are partial to conventional results, lack of sorting the latest results. So please emphasize some of them profoundly.

Thanks for the kind observation and suggestions for improvement. The authors try to add more explanations for the sections.

Section 2.4 and 3.6

(Last paragraph)

4. During the descriptions of the previous study, it was hard to find the focus of the authors, the main ideas or topics of the long statemen or comparations are missing.

Thank you for the suggestions.

The objectives of the study have been added in the introduction section.

End of the introduction section

5. In conclusion section, some of them can be merged and refined so that the conclusion can be the important items.

Thank you for your comments.

The conclusion was modified as the reviewer request.

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6. In ‘4.2 future research’ section, it mentioned the evaluation of the rubberized asphalt's life cycle costs, energy consumption, and environmental effects. From my view, these descriptions of the future research should be more powerful and the stronger correlation with the previous paragraphs so that it can be corresponding to the statement ‘However, the multiple criteria that in to produce CR asphalt led to a lack in the information related to greenhouse gas emissions, energy consumption, and life cycle cost.’ in abstract.

Thank you for your observation.

Acutely the authors forgot to add “during the recycling process “at the end of the sentence to be clearer to the readers.

Abstract

7. The quality figures in this manuscript were poor, which are not clear and low pixels. Please improve them.

Thank you for your valuable comment.

All figures in manuscript have been modified.

 All figures

8. There are lots of abbreviations in this manuscript, but some are not clear for the readers. Please explain them one by one in an appropriate site.

Thanks for the observation.

All abbreviations have been identified for the whole manuscript.

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Comments

Amendments

Location of the additional write up

1. Please review the English for typo and grammatical errors, the English writing of this manuscript is very poor, this manuscript needs to be polished.

Thanks for the valuable comment.

we have fixed the manuscript and proofreading the paper to eliminate all such errors.

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2. The title of the paper is too broad, it should reflect the work done in this article more specifically, please modify it.

Thank you for the suggestions. The authors modified the topic of the article as the reviewer suggestions.

Topic

3. The pictures in the article are not clear, and some pictures are compressed, such as Figure 2, Figure 5, Figure 9, please modify these pictures.

Thanks for the kind observation and suggestions for improvement.

Figures 2, 5, and 9

4. Table 5 and Table 6 should not be presented in table form, especially considering the different factors such as asphalt type, CR size and content in the table, it is not scientifically meaningful to present in such a way. The authors should classify and review them.

Thanks for the suggestions for improvement. The authors will consider your valuable comment for the future work.

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5. Two tables 5 appear in the article, please modify them.

Thanks for the kind observation. The table number have been corrected.

Table 7

6. What is the basis for the emission of gas produced by CR asphalt in Figure 7, the author must make the necessary explanation in the paper.

Thank you for your valuable comment.

As mentions in section 3.4, the “Greenhouse gases estimated during the production for the rubber and unmodified asphalt mixtures”. The asphalt production needs high mixing and compaction temperature during production of the asphalt pavement reach to 165, and 145 °C, respectively. The high production temperature leads to produce greenhouse gases. The authors do not mention it because it is basic information.

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7. The review articles should refer to the latest research results published in the last five years as much as possible. The author cites a large number of literatures before 2015, which makes it difficult to convince people that this article summarizes the latest research results.

Thank you for your comment.

The authors try to include the latest research and to achieve that 87 of 131 research were within the last ten years and other articles were between standard books and international websites to keep up with the latest industry achieving and problems faced during or before using the CR asphalt.

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8. The conclusions of the article is too tedious, and the conclusions must be streamlined.

Thank you for your comments.

The conclusion was modified as the reviewer request.

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Comments

Amendments

The improvements are marginal. Please revise again and be more accurate. The conclusions need to be shortened. Identify your key findings.

-          The conclusion has been reduced to 8 importance point from 10 and made the others points specific and shorter as the reviewer suggestion.

-          This paper provides a comprehensive overview of incorporating crumb rubber (CR) into asphalt binder and mixtures, highlighting various aspects such as production methods, optimal rubber dosage, effects on asphalt properties, environmental impacts, and cost considerations. Key findings from previous research include:

1.       CR Sourcing: CR can be obtained through ambient mechanical grinding or cryogenic grinding. Ambient mechanical grinding is more cost-effective and widely used.

2.       Recommended Rubber Dosage: For the wet method, it's suggested to use 10% of the binder weight without additives and up to 30% with additives. In the dry method, 1.5% of the mixture weight without additives and up to 3% with additives is recommended.

3.       Binder Modification: Adding CR may slightly increase the optimal bitumen content due to CR particles absorbing some bitumen constituents.

4.       Viscosity Effects: CR increases asphalt viscosity, which can be mitigated with additives like warm mix asphalt (WMA) additives or rejuvenators.

5.       Physical Properties: CR improves physical properties such as lower penetration and viscosity and higher softening values. It enhances rheological properties by increasing stiffness and rutting resistance while reducing the phase angle.

6.       Environmental Impact: Rubberized asphalt production emits similar levels of O₂, N₂, CO₂, NOx, and SO₂ as unmodified asphalt but emits less CO and CH₄. Rubberized asphalt offers superior functional and structural performance during rehabilitation with fewer adverse environmental impacts.

7.       Energy Efficiency: Asphalt rubber has energy-saving benefits throughout its lifecycle, with lower energy consumption during construction and maintenance.

8.       Economic Considerations: Considering manufacturing costs for materials, construction, maintenance, and rehabilitation, CR asphalt pavement proves to be more economical than traditional pavement.

Comments

Amendments

1. The authors made some improvements for this manuscript. However, from my view, my opinions were not responded quite well, especially questions 3 and 4. Too many conclusions meant no important ones. Although the author added some explanations, the main points were still not very clear for me. So please pay attention to them seriously, as well as the figures, I don’t think that the improvements of them are efficient. So please revised more seriously.

-          The conclusion has been reduced to 8 importance points from 10 and made the others points specific and shorter as the reviewer suggestion.

-          This paper provides a comprehensive overview of incorporating crumb rubber (CR) into asphalt binder and mixtures, highlighting various aspects such as production methods, optimal rubber dosage, effects on asphalt properties, environmental impacts, and cost considerations. Key findings from previous research include:

1.       CR Sourcing: CR can be obtained through ambient mechanical grinding or cryogenic grinding. Ambient mechanical grinding is more cost-effective and widely used.

2.       Recommended Rubber Dosage: For the wet method, it's suggested to use 10% of the binder weight without additives and up to 30% with additives. In the dry method, 1.5% of the mixture weight without additives and up to 3% with additives is recommended.

3.       Binder Modification: Adding CR may slightly increase the optimal bitumen content due to CR particles absorbing some bitumen constituents.

4.       Viscosity Effects: CR increases asphalt viscosity, which can be mitigated with additives like warm mix asphalt (WMA) additives or rejuvenators.

5.       Physical Properties: CR improves physical properties such as lower penetration and viscosity and higher softening values. It enhances rheological properties by increasing stiffness and rutting resistance while reducing the phase angle.

6.       Environmental Impact: Rubberized asphalt production emits similar levels of O₂, N₂, CO₂, NOx, and SO₂ as unmodified asphalt but emits less CO and CH₄. Rubberized asphalt offers superior functional and structural performance during rehabilitation with fewer adverse environmental impacts.

7.       Energy Efficiency: Asphalt rubber has energy-saving benefits throughout its lifecycle, with lower energy consumption during construction and maintenance.

8.       Economic Considerations: Considering manufacturing costs for materials, construction, maintenance, and rehabilitation, CR asphalt pavement proves to be more economical than traditional pavement.

-          Al figures have been improved.

Comments

Amendments

1. Headings are too long

Thank you for your suggestion.

The authors modified three sub-headings 2.3, 2.4, and 2.5.

2. The conclusions of the article is still too tedious, and the conclusions must be streamlined.

-          The conclusion has been reduced to 8 importance points from 10 and made the others points specific and shorter as the reviewer suggestion.

-          This paper provides a comprehensive overview of incorporating crumb rubber (CR) into asphalt binder and mixtures, highlighting various aspects such as production methods, optimal rubber dosage, effects on asphalt properties, environmental impacts, and cost considerations. Key findings from previous research include:

1.       CR Sourcing: CR can be obtained through ambient mechanical grinding or cryogenic grinding. Ambient mechanical grinding is more cost-effective and widely used.

2.       Recommended Rubber Dosage: For the wet method, it's suggested to use 10% of the binder weight without additives and up to 30% with additives. In the dry method, 1.5% of the mixture weight without additives and up to 3% with additives is recommended.

3.       Binder Modification: Adding CR may slightly increase the optimal bitumen content due to CR particles absorbing some bitumen constituents.

4.       Viscosity Effects: CR increases asphalt viscosity, which can be mitigated with additives like warm mix asphalt (WMA) additives or rejuvenators.

5.       Physical Properties: CR improves physical properties such as lower penetration and viscosity and higher softening values. It enhances rheological properties by increasing stiffness and rutting resistance while reducing the phase angle.

6.       Environmental Impact: Rubberized asphalt production emits similar levels of O₂, N₂, CO₂, NOx, and SO₂ as unmodified asphalt but emits less CO and CH₄. Rubberized asphalt offers superior functional and structural performance during rehabilitation with fewer adverse environmental impacts.

7.       Energy Efficiency: Asphalt rubber has energy-saving benefits throughout its lifecycle, with lower energy consumption during construction and maintenance.

8.       Economic Considerations: Considering manufacturing costs for materials, construction, maintenance, and rehabilitation, CR asphalt pavement proves to be more economical than traditional pavement.

3. Tables 5 and 6 should not be presented in tabular form, and there is no scientific significance in presenting them in such a way.

Thank you for your suggestion.

As the authors discussed, we agree to let the tables and not present them in paragraph form for the following reasons:

- It can easily show the trends in all test result

- It can show more details

- Readers can get a quickly overview

- Table gives the ability to show more studies.

Thank you for your understanding.

Comments

Amendments

Still some editing is needed. 

Thank you.

As the reviewer's suggestion, we have sent the manuscript for a second round of proofreading to eliminate all such errors

Comments

Amendments

The author is very perfunctory to the reviewer's opinions, and has not made serious modifications and replies to the reviewer's opinions.

-          We want to express our sincere gratitude for taking the time to thoroughly review our manuscript and for providing us with invaluable feedback. Your insightful comments have significantly contributed to the refinement of our work. The whole paper has been improved, and our dedication to advancing knowledge in this field remains unwavering. We are fully committed to addressing the concerns you have raised. If you have any other specific comments, please let us know and we will be pleased to take them into consideration.

-          As the reviewer's suggestion, we have sent the manuscript for a second round of proofreading to eliminate all such errors.

Comments

Amendments

-          The author has settled all the comments and recommends acceptance.

-          Minor editing of English language required.

Thank you.

As the reviewer's suggestion, we have sent the manuscript for a second round of proofreading to eliminate all such errors.