A Review on the Durability of Recycled Asphalt Mixtures Embraced with Rejuvenators

Round 1

Reviewer 1 Report

General comment:

This paper focused on the durability of recycled asphalt pavement (RAP) with the introduction of rejuvenators. The durability of the RAP with rejuvenators was selected as the main topic in this paper. However, as a reviewer paper, the manuscript should be revised with more summary of current researches and more Figures/Tables should be provided to give us a more readable paper rather than lots of descriptions. The detailed comments are listed below for author's consideration.

Technique comments:

1. Line 107-116, as the authors mentioned that the rejuvenators could negatively affect the durability of recycled asphalt mixture, especially the aging and moisture damage resistance. However, the following discussions in section 3.2 are not consistent with the statement, the rejuvenators improved the durability of recycled asphalt. The author may consider revising the current problem of rejuvenators. In general, the introduction of rejuvenators will not significantly affect durability, which is not the main issue in the application of rejuvenators.

2. Line 420, Please correct the reference format.

3. Line 447-454, the authors firstly mentioned that the rejuvenators would reduce the moisture damage resistance, however, the authors then discussed that the other rejuvenator would improve the moisture damage resistance. What is the main purpose of this paragraph? Also, there is no detailed information or summary of the moisture damage effect caused by the rejuvenators, the authors did not discuss it in the previous paragraphs in this section.

4. There are different types of RAP, such as hot mixed, warm mixed, and cold mixed. Did the authors consider the combined effects of mixing temperature and warm-mixing additives in the recycling process of RAP with the addition of rejuvenators?

5. In the conclusion, the first sentence is not the main purpose of this study? Did you review the durability of rejuvenators?

6. Although there are lots of references had been cited for a review paper, the main purpose of this paper is not revealed by the authors. The authors should reorganize the paper to be considered for possible publication.

Author Response

REVIWER 1

General comment:

This paper focused on the durability of recycled asphalt pavement (RAP) with the introduction of rejuvenators. The durability of the RAP with rejuvenators was selected as the main topic in this paper. However, as a reviewer paper, the manuscript should be revised with more summary of current researches and more Figures/Tables should be provided to give us a more readable paper rather than lots of descriptions. The detailed comments are listed below for author's consideration.

Response: Thanks for the comment.

Thanks for the kind observation and suggestions for the improvement. Many figures and tables were added with more references (Please refer to the sentences which were written in red color)

Technique comments:

1. Line 107-116, as the authors mentioned that the rejuvenators could negatively affect the durability of recycled asphalt mixture, especially the aging and moisture damage resistance. However, the following discussions in section 3.2 are not consistent with the statement, the rejuvenators improved the durability of recycled asphalt. The author may consider revising the current problem of rejuvenators. In general, the introduction of rejuvenators will not significantly affect durability, which is not the main issue in the application of rejuvenators.

Response: Thanks for the comment.

The sentences were edited to be as follow: (Please refer to the line 107-108, Page 3)

“Despite the vast studies on the benefits of rejuvenating agents, only a handful of scholars have looked into impact of rejuvenators on pavement durability”.

2. Line 420, Please correct the reference format.

 Response: Thanks for the critical comments

The mistakes were corrected

Cavalli et al. [81] also portrays that the ageing indices of (RAP + B) and (RAP + C)

3. Line 447-454, the authors firstly mentioned that the rejuvenators would reduce the moisture damage resistance, however, the authors then discussed that the other rejuvenator would improve the moisture damage resistance. What is the main purpose of this paragraph? Also, there is no detailed information or summary of the moisture damage effect caused by the rejuvenators, the authors did not discuss it in the previous paragraphs in this section.

 Response: Thanks for the critical comments

Actually, not all rejuvenators reduce the moisture damage resistance. I edited the sentences. Nevertheless, this issue depends on several factors, such as properties of rejuvenator and its content in addition to the RAP characteristics and its percentage in the mixture. For this reason, I wrote in the instruction related to the selection of rejuvenator that the rejuvenating agent should adequate resistance to moisture damage before and after ageing

1. There are different types of RAP, such as hot mixed, warm mixed, and cold mixed. Did the authors consider the combined effects of mixing temperature and warm-mixing additives in the recycling process of RAP with the addition of rejuvenators?

Response: Thanks for the question

Actually, this article did not focus on the type of mixture. It deals with effect of rejuvenator on the durability of recycled asphalt.

1. In the conclusion, the first sentence is not the main purpose of this study? Did you review the durability of rejuvenators?

Response: Thanks for the question

The whole conclusion was edited and improved

1. Although there are lots of references had been cited for a review paper, the main purpose of this paper is not revealed by the authors. The authors should reorganize the paper to be considered for possible publication.

Response:

Thanks for the suggestions and critical comments.

The whole article was reorganised, where many sentences, figures and tables were added.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper discusses an interesting topic for the civil engineering community, namely the use of Rejuvenators for asphalt mixtures made with RAP.

The review of the state of the art is comprehensive and it has been discussed in details, with respect to a large numbers of literature papers. Suggestions for the proper selection of a rejuvenator are provided.

Reference source is not found at line 420.

Author Response

REVIWER 2

The paper discusses an interesting topic for the civil engineering community, namely the use of Rejuvenators for asphalt mixtures made with RAP.

The review of the state of the art is comprehensive and it has been discussed in details, with respect to a large numbers of literature papers. Suggestions for the proper selection of a rejuvenator are provided.

Response: The authors is grateful to the reviewer for his positive and encouraging comments

Reference source is not found at line 420.

Response: Thanks for the critical comments

The mistakes were corrected

Cavalli et al. [81] also portrays that the ageing indices of (RAP + B) and (RAP + C)

Author Response File: Author Response.pdf

Reviewer 3 Report

In general, paper gives overview of rejuvenators used for recycled asphalt mixtures.

I suggest acceptance of the paper after minor revision.

Specific comments:

Line 33 - asphaltic roads it is better to use term flexible pavement or asphalt pavement (flexible pavement is preferred)

Line 53 to 55 – two sentences “In fact, asphalt ageing is generally divided into short- term ageing (STA) and long-term ageing (LTA). Asphalt ageing is viewed in terms of long-term ageing (LTA) and short-term ageing (STA).” you are saying the same thing in slightly different manner. Omit one of the sentences (first one).

Line 56 – sentence “Asphalt becomes aged and hardened when its light 56 components turn volatile due to high temperature [13].” Given the content of the sentence it does not belong between explanations of STA and LTA. This sentence could be incorporated in sentence “The aromatic compounds in asphalt binders become oxidised and more polar carbonyl compounds are created; thus, increasing both elastic modulus and viscosity, as well as stiffening the binder [11].” - line 49-50

Line 76 – sentence “In any case, rejuvenating agents should satisfy both short- and long-term criteria.” And line 78 – sentence “Rejuvenators should be able to meet long- and short-term criteria.” – you are saying the same thing in slightly different manner. Omit one of the sentences (second one).

Line 81 - second part of the sentence “short-term criteria refer to rapid diffusion into RAP to promote asphalt mobilisation [22].” You are saying the same thing as in the sentence Short-term criteria denote the ability to diffuse quickly into the RAP and cause asphalt mobilisation [22].” - line 77. Omit one of the sentences.

Line 87-88 - explain how diffusion is affected by layer thickness!

Line 102 -103 – is water damage only climate-related factor that contributes to pavement failure in aggressive climatic conditions?

Line 103 – sentence “Meanwhile, some rejuvenating agents are susceptible to oxidation.” – is this sentence necessary?

Elaborate how were the papers, on which you based this review, selected; what was the criteria of inclusion of papers.

Consider changing title of subsections 3.1 to 3.5 by omitting part of the title:  Rejuvenation of recycled asphalt using…, and leaving the class of rejuvenator.

Line 420 – missing reference

One of the objectives of the paper is to address effect of rejuvenator on durability characteristics – consider elaborating more on this objective in subsections 3.1 to 3.5 since the title of the paper is “A Review on the Durability of Recycled Asphalt Mixtures Embraced with Rejuvenators”.

Section 4 is very general, consider elaborating more on selection of rejuvenator in light on its effect on durability.

Conclusions are very general, more specific conclusions can be drawn from literature review and the emphasis should be placed on effect of rejuvenator on durability.

Author Response

REVIWER 3

In general, paper gives overview of rejuvenators used for recycled asphalt mixtures.

I suggest acceptance of the paper after minor revision.

Response: The authors is grateful to the reviewer for his positive and encouraging comments

Specific comments:

Line 33 - asphaltic roads it is better to use term flexible pavement or asphalt pavement (flexible pavement is preferred)

Response: Your invaluable comments are appreciated;

The sentence was corrected (Please refer to the 34-35, Page 1).

The tremendous development witnessed in the Malaysian national infrastructure network since the past decade has led to an increase in road construction [1], where flexible pavement dominates the overall surfacing types across more than 87,626 km

Line 53 to 55 – two sentences “In fact, asphalt ageing is generally divided into short- term ageing (STA) and long-term ageing (LTA). Asphalt ageing is viewed in terms of long-term ageing (LTA) and short-term ageing (STA).” you are saying the same thing in slightly different manner. Omit one of the sentences (first one).

Response: Done and thanks for the suggestion

Line 56 – sentence “Asphalt becomes aged and hardened when its light 56 components turn volatile due to high temperature [13].” Given the content of the sentence it does not belong between explanations of STA and LTA. This sentence could be incorporated in sentence “The aromatic compounds in asphalt binders become oxidised and more polar carbonyl compounds are created; thus, increasing both elastic modulus and viscosity, as well as stiffening the binder [11].” - line 49-50

 Response: Done and thanks for the suggestion, (Please refer to the line 52-61, page 2)

The fractions of saturates, aromatics, resins, and asphaltenes (SARA) are modified when aromatics decrease and asphaltenes increase over time [12]. Upon being exposed to water, heat, and ultraviolet (UV) ray in its lifespan, the asphalt succumbs to ageing that affects its pavement performance [13]. In fact, asphalt ageing is generally divided into short-term ageing (STA) and long-term ageing (LTA). The STA process includes transporting, mixing, paving, and rolling of asphalt. Asphalt becomes aged and hardened when its light components turn volatile due to high temperature [13]. Asphalt ageing leads to poor workability, cohesiveness, fatigue resistance, as well as fatigue and thermal cracking. Hence, it is vital to restore and enhance the viscoelastic and engineering performance of aged asphalt [14].

Line 76 – sentence “In any case, rejuvenating agents should satisfy both short- and long-term criteria.” And line 78 – sentence “Rejuvenators should be able to meet long- and short-term criteria.” – you are saying the same thing in slightly different manner. Omit one of the sentences (second one).

Response: Done and thanks for the suggestion

Line 81 - second part of the sentence “short-term criteria refer to rapid diffusion into RAP to promote asphalt mobilisation [22].” You are saying the same thing as in the sentence Short-term criteria denote the ability to diffuse quickly into the RAP and cause asphalt mobilisation [22].” - line 77. Omit one of the sentences.

Response: Done and thanks for the suggestion

Line 87-88 - explain how diffusion is affected by layer thickness!

Response: Thanks for the suggestion

The main factor related to the thickness is the time required to blend the rejuvenator with the RAP. Actually, I did not explain this factor in details. The reason is that the introduction contains more than 1000 words. If I explain in detail, the reader may be confused. But if you want to add more sentences, I will do.

Line 102 -103 – is water damage only climate-related factor that contributes to pavement failure in aggressive climatic conditions?

Response: Thanks for the question

Actually, water damage represents the biggest problem associated with the climatic condition.

Line 103 – sentence “Meanwhile, some rejuvenating agents are susceptible to oxidation.” – is this sentence necessary?

Response: Thanks for the question

I think, yes. The reason is that if the rejuvenator was susceptible to the oxidation, the rejuvenated asphalt properties will be negatively affected.

Elaborate how were the papers, on which you based this review, selected; what was the criteria of inclusion of papers.

Response: Thanks again for the question

I always depend on the articles from famous publishers such as ELSEVIER, SPRINGER, MDPI. Moreover, I try always to focus on Q1 and Q2 journal.

Consider changing title of subsections 3.1 to 3.5 by omitting part of the title:  Rejuvenation of recycled asphalt using…, and leaving the class of rejuvenator.

Response: Done and thanks for the suggestion

Line 420 – missing reference

Response: Thanks for the critical comments

The mistakes were corrected

Cavalli et al. [81] also portrays that the ageing indices of (RAP + B) and (RAP + C)

One of the objectives of the paper is to address effect of rejuvenator on durability characteristics – consider elaborating more on this objective in subsections 3.1 to 3.5 since the title of the paper is “A Review on the Durability of Recycled Asphalt Mixtures Embraced with Rejuvenators”.

Response: Thanks for the critical comments, many sentences, tables and figures were added to explain objectives of the article. Please refer to the sentences which were written in red color

Section 4 is very general, consider elaborating more on selection of rejuvenator in light on its effect on durability.

Response: Your invaluable comments are appreciated; section 4 was edited and improved

Conclusions are very general, more specific conclusions can be drawn from literature review and the emphasis should be placed on effect of rejuvenator on durability.

Response: Your invaluable comments are appreciated; the conclusion was edited and improved based on your request.

Author Response File: Author Response.pdf

Reviewer 4 Report

(1) In most cases, the authors summarized literatures one by one, whereas the commons and differences among varied publications were not compared well. 

(2) The information in Table 3 was sort of old and can be updated. Especially in addition to the product name, more details can be provided on its performance both in laboratory and in the field. 

(3) In section 4, seems like the authors provided more about the research target of rejuvenator (i.e. restore viscosty, penetration), whereas not sufficient information was provided on how appropriate rejuvenator can be selected. 

(4) In section 4, the effect of asphalt aging seveirty on the selection of rejuvenator was very generalized and more quantatitive effect details are expected.  

(5) In the conclusions, the authors indicate that "..offers crucial econmical and environmental benefits", whereas no relavent data was provided in the article to support the above conclusion. 

Author Response

REVIWER 4

(1) In most cases, the authors summarized literatures one by one, whereas the commons and differences among varied publications were not compared well. 

Response: Your invaluable comments are appreciated;

Several tables were added in order to obtain acceptable comparison among the rejuvenators.

(2) The information in Table 3 was sort of old and can be updated. Especially in addition to the product name, more details can be provided on its performance both in laboratory and in the field. 

Response: Thanks for the suggestion

Table 3 was deleted from the article

(3) In section 4, seems like the authors provided more about the research target of rejuvenator (i.e. restore viscosty, penetration), whereas not sufficient information was provided on how appropriate rejuvenator can be selected. 

(4) In section 4, the effect of asphalt aging seveirty on the selection of rejuvenator was very generalized and more quantatitive effect details are expected.  

Response: Thanks for the suggestion, section 4 was edited and improved based on your request.

(5) In the conclusions, the authors indicate that "..offers crucial econmical and environmental benefits", whereas no relavent data was provided in the article to support the above conclusion. 

Response: Your invaluable comments are appreciated; section 4 was edited and improved based on your request.

Author Response File: Author Response.pdf