Impacts of Milled Aggregate Gradations and Foamed Asphalt Contents of Cold In-Place Recycling Layer on the Performance of Asphalt Overlays

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1. The introduction section is too poor. Generally nothing novel is introduced. Please rewrite it absolutely.

2. The citation is unacceptable. Too less literatures have been cited and some of the existing cited papers are too old. Please ferret to the following literatures to enhance your literature review and citation.

https://doi.org/10.1016/j.conbuildmat.2024.136761

https://doi.org/10.1080/10298436.2024.2365350

https://doi.org/10.1016/j.conbuildmat.2024.137268

https://doi.org/10.1080/10298436.2024.2332363

3. Please remove the background of the figures

4. Is it possible to calculate and present the fracture energy, cracking tolerances index (CTindex) or some other parameters based on your existing tests?

5. The characterisation and analysis is too basic.

6. It is suggested that the authors add some more analysis of the impact of rejuvenators on the recycling of asphalt pavement.

Author Response

Comment 1. The introduction section is too poor. Generally nothing novel is introduced. Please rewrite it absolutely.

Response 1.  The introduction section has been rewritten with additional information on the recent literatures and clearer objective of the paper.  Please see page 2 36-43 pp and page 3 pp 18-33.

Comment 2. 2. The citation is unacceptable. Too less literatures have been cited and some of the existing cited papers are too old. Please ferret to the following literatures to enhance your literature review and citation.

Response 2.  Five recently published relevant papers (reference 1-4 and 15) were cited. 

Comment 3. Please remove the background of the figures

Response 3.  Authors do not understand this comment.  Please be more specific, i.e., which figures and what background?

Comment 4. Is it possible to calculate and present the fracture energy, cracking tolerances index (CTindex) or some other parameters based on your existing tests?

Comment 5. The characterisation and analysis is too basic.

Response 4 &5. Table 4 and Table 5 showing calculations were added with explanations on lines 18-28 of page 9 and lines 2-8 of page 10 

Comment 6. It is suggested that the authors add some more analysis of the impact of rejuvenators on the recycling of asphalt pavement.

Response 6. There was no rejuvenator used for CIR pavements.  Therefore, the impact of rejuvenators was not discussed in this paper.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Both Hot In-place Recycling (HIR) and Cold In-place Recycling (CIR) are timely and significant topics in pavement engineering. The authors have made a valuable contribution to understanding the performance characteristics of HIR and CIR materials in pavement rehabilitation. One suggestion for improvement would be to further elaborate on the relationship between gradation and the observed mechanical properties. This would help establish a stronger connection between the gradation analysis and pavement performance.

Author Response

Comment 1. Both Hot In-place Recycling (HIR) and Cold In-place Recycling (CIR) are timely and significant topics in pavement engineering. The authors have made a valuable contribution to understanding the performance characteristics of HIR and CIR materials in pavement rehabilitation. One suggestion for improvement would be to further elaborate on the relationship between gradation and the observed mechanical properties. This would help establish a stronger connection between the gradation analysis and pavement performance.

Response 1. Great suggestion.  We tried to identify the relationship between gradation and observed mechanical properties but we could not find the relationship.  Therefore, I added the statement at lines 40-43 of page 12 in the section of the future studies. 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The present study evaluates the impacts of milled aggregate gradations and foamed asphalt content in the cold in-place recycling layer on the performance of asphalt overlays. To improve the manuscript, the following recommendations should be considered:

1. Include specific result values to enhance the paper's appeal to readers.  

2. In Figure 1, change "Sieve size" to millimeters for clarity.  

3. In Figure 3, provide the thickness of each layer.  

4. For fracture energy (GF) and flexibility index (FI), include the corresponding equation numbers.  

5. In Figure 5, add the units for asphalt content and FI.  

Author Response

Comment 1. Include specific result values to enhance the paper's appeal to readers.

  Table 4 and 5 were added with explanations at lines 18-28 of page 9 and lines 2-8 of page 10.

2. In Figure 1, change "Sieve size" to millimeters for clarity.  

Done. See Figures 1 and 2.

3. In Figure 3, provide the thickness of each layer.  

Done.  See the figure 3 with thickness of each layer.

4. For fracture energy (GF) and flexibility index (FI), include the corresponding equation numbers.

Done. equation numbers were added.  

5. In Figure 5, add the units for asphalt content and FI. 

Unit for asphalt content was added.  FI has no unit so no unit was added for FI.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The paper is devoted to the analysis of the specimens obtained from the hot-in place and cold in-place recycling techniques. In my opinion, the Introduction is extremely short and it does not place the research in a wider scientific/engineering context. The title suggests that the foamed asphalt is analyzed, whereas it is referred to only in the last section. In my opinion, it is the consequence of the short introduction with a very brief description of the respective recycling methods.

Additionally, the Authors presented some explanations/descriptions of their previous studies, but there  is no reference to the current study. 

 

No state-of-the-art part is present in the Introduction.

 

No template is used in the manuscript (eg. missing line numbers), which deteriorates the readability of the paper. Also, it is difficult to refer to a particular line for the review purposes.

 

Figure 2 - what is the black dashed line?

 

Equation at the top of page 8 - no units are specified.

 

Line 22, p. 8 - what do you mean by "AC"?

 

The first paragraph of the Section 4 is the copy of the first paragraph in Section 2.

Author Response

Comment 1. The paper is devoted to the analysis of the specimens obtained from the hot-in place and cold in-place recycling techniques. In my opinion, the Introduction is extremely short and it does not place the research in a wider scientific/engineering context. The title suggests that the foamed asphalt is analyzed, whereas it is referred to only in the last section. In my opinion, it is the consequence of the short introduction with a very brief description of the respective recycling methods.

"foamed asphalt" was added throughout the paper wherever necessary.  Introduction section was enhanced by citing five recent papers on CIR as shown in line 37 of page 2 to line 2 of page 3 and lines 21-36 of page 3.

Comment 2. Additionally, the Authors presented some explanations/descriptions of their previous studies, but there  is no reference to the current study. 

The reference was added in introduction section (lines 21-36 of page 3.

Comment 3. No state-of-the-art part is present in the Introduction.

line 37 of page 2 to line 2 of page 3 were added with recent references. 

Comment 4. No template is used in the manuscript (eg. missing line numbers), which deteriorates the readability of the paper. Also, it is difficult to refer to a particular line for the review purposes.

Lines were added in the attached paper.

Comment 5. Figure 2 - what is the black dashed line?

Black dashed line is a maximum density line and this statement was added in line 25 of page 4..

Equation at the top of page 8 - no units are specified.

Fracture energy unit of Joule/m2 was added on line 6 of page 9.

Comment Line 22, p. 8 - what do you mean by "AC"?

AC was spelled as asphalt content.

The first paragraph of the Section 4 is the copy of the first paragraph in Section 2.

This is rewritten on lines 18-22 of page 11.

Author Response File: Author Response.pdf

Reviewer 5 Report

Comments and Suggestions for Authors

This study aims to clarify the impacts of aggregate gradation and asphalt contents of milled asphalt concrete on the performance in-place recycling asphalt overlays. The authors investigated them based on the data obtained from the tests results on the cores extracted from the existing asphalt overlay sections. The data itself is very valuable, and the authors’ discussions are very interesting. However, the data presented in the paper is not sufficient to support their discussions. The authors should address the following comments to make the discussion more persuasive.

 

Page 3, Last sentence. What kind of relationship did the authors expect? Please clarify the difference in the millings from #1 to #4. Were they milled from different depths in a single pile?

 

Page 6, Table 3. More specific explanation is needed for Table 3. What do the numbers in each cell mean?

 

Page 7. Relevant reference is needed on FI. In this study, it seems that the authors think that the performance of recycled overlays is represented with only cracking. Was not rutting observed on the overlayed pavements?

 

Page 8, the first paragraph of Section 3.2. Please present the data or references supporting what the authors claim in this paragraph.

 

Page 8, Figure 5(a). If the authors apply the second-order regression curve for the data, they can find the minimum FI around asphalt content of 7.5%. So, for less than 7.5 %, it seems that FI decreases as the asphalt content. increases.

 

Page 9, the second paragraph of Section 4. Please present the specific data and/or relevant references supporting what the authors discuss in this paragraph.

 

Page 9, the last paragraph of Section 4. The authors conclude that the flexible CIR layer can serve as a stress relieving layer. They should present specific evidence supporting the conclusion.

Also, the impacts of aggregate gradation of CIR on the performance of overlayed pavements are not mentioned in the conclusions at all. The reviewer thinks that this was one of the primal objects of this study. The authors should at least make a comment on this issue.

Author Response

Comment 1. Page 3, Last sentence. What kind of relationship did the authors expect? Please clarify the difference in the millings from #1 to #4. Were they milled from different depths in a single pile?

Explanation was added on lines 8-10 and 15-17 of page 4.

Comment 2. Page 6, Table 3. More specific explanation is needed for Table 3. What do the numbers in each cell mean?

Better headings were added in Table 3.

Comment 3. Page 7. Relevant reference is needed on FI. In this study, it seems that the authors think that the performance of recycled overlays is represented with only cracking. Was not rutting observed on the overlayed pavements?

statement of "with significant cracking and no rutting" was added on lines 3-4 of Page 7.

Comment 4. Page 8, the first paragraph of Section 3.2. Please present the data or references supporting what the authors claim in this paragraph.

data were added on line 20 of page 9 and line 10 of page 10 along with Tables 4 and 5.

Comment 5. Page 8, Figure 5(a). If the authors apply the second-order regression curve for the data, they can find the minimum FI around asphalt content of 7.5%. So, for less than 7.5 %, it seems that FI decreases as the asphalt content. increases.

Authors wanted to identify a linear pattern between Asphalt content and FI.  In our opinion, the minimum FI around asphalt content of 7.5% is anomaly.

Comment 6. Page 9, the second paragraph of Section 4. Please present the specific data and/or relevant references supporting what the authors discuss in this paragraph.

We added a statement "it can be postulated that" at the beginning of the paragraph at line 4 of page 12 and added a reference 15  where this discussion was made.

Comment 7. Page 9, the last paragraph of Section 4. The authors conclude that the flexible CIR layer can serve as a stress relieving layer. They should present specific evidence supporting the conclusion.

The sentence was changed as "Since CIR pavement layers are more flexible than the HMA overlays, it can be speculated that CIR layers may serve as a stress relieving layer and mitigate reflective cracking."

Comment 8. Also, the impacts of aggregate gradation of CIR on the performance of overlayed pavements are not mentioned in the conclusions at all. The reviewer thinks that this was one of the primal objects of this study. The authors should at least make a comment on this issue.

a paragraph was added between line 35 of page 11 and line 3 of page 12. 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The references are too less and too old. Please add more references in both introduction and result sections. Such as:

https://doi.org/10.1016/j.conbuildmat.2024.137316

 

• https://doi.org/10.1617/s11527-025-02574-4

• References in introduction are necessary to give a more comprehensive background of your study and references in results and discussion section are necessary to support your findings.

Author Response

Comment 1: 

The references are too less and too old. Please add more references in both introduction and result sections. Such as:

https://doi.org/10.1016/j.conbuildmat.2024.137316

 https://doi.org/10.1617/s11527-025-02574-4

References in introduction are necessary to give a more comprehensive background of your study and references in results and discussion section are necessary to support your findings.

Response 1:  Thank you for the valuable advice and suggestion of two references.  They were incorporated in the paper and three additional relevant references were added. Additional statements were added throughout the paper including abstract, introduction and conclusion sections.  Added texts during the second revision are shown in blue color.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

- Abstract: Last three sentences provide the same information, they should be rephrase into one.

- Abstract: HMA overlay, as the wearing course, is subjected to the larger number of environmental factors than CIR layers that are located below. In my opinion, the comparison presented in the paper is not justified consequently since the exposure conditions of these twwo layer types are different.

- P. 2, line 42: What do you mean by "wildly promote"?

- Figure 1: what are the red circles in the plot?

- Figure 3: what does the dimension of 75 mm refer to?

- P. 9, lines 18-19: Correct "then cut each slice was cut".

- Section 4: the first paragraph is the copy of the text from the previous sections.

- P. 12, line 6: Correct "of the HMA overlay, For CIR using foamed asphalt, foamed".

- P. 13, line 5: Correct "Funding: Please add: This research was funded".

 

Author Response

Changes are shown in blue color.

Comment 1: Abstract: Last three sentences provide the same information, they should be rephrase into one.

Response 1:  First two sentences were deleted because they were redundant.

Comment 2: Abstract: HMA overlay, as the wearing course, is subjected to the larger number of environmental factors than CIR layers that are located below. In my opinion, the comparison presented in the paper is not justified consequently since the exposure conditions of these two layer types are different.

Response 2: The following statements were added on lines 29-33 of page 3 

The HMA overlay, as a wearing course, is expected to be aged due to its exposure to the air whereas CIR layer is not as much aged because it is located under the overlay. Although the exposure condition of CIR would be different from the overlay, no study has been done to quantify the difference in their characteristics to mitigate a cracking (inserted in blue color)

Comment 3: - P. 2, line 42: What do you mean by "wildly promote"?

Response 3: "wildly" was changed to "widely."  Thank you!

Comment 4: Figure 1: what are the red circles in the plot?

Response 4: the following statement was added on line 17 page 4 "against the required boundaries of critical sieves shown in red dots"

Comment 5: - Figure 3: what does the dimension of 75 mm refer to?

Response 5: Statement "a radius of 75 mm" was added on Line 11 of Page 8

Comment 6: - P. 9, lines 18-19: Correct "then cut each slice was cut".

Response 6: cut was deleted so it reads now as "then each was cut" Thank you.

Comment 7: - Section 4: the first paragraph is the copy of the text from the previous sections.

Response 7: The paragraph was changed on lines 21-29 as follows: "CIR is a widely used asphalt rehabilitation technique in the US whereas HIR is limited to the Midwest region possibly due to its extensive heating equipment. In the past, a HIR technique was claimed to retain the original pavement's aggregate gradation due to the milling at a higher temperature. However, no study has been conducted to verify this claim. Therefore, we decided to compare the gradations of HIR millings against those of CIR millings.  HIR millings were collected from  IA 22 in Wellman, Iowa, that was rehabilitated using an HIR technique. The aggregate gradations of the HIR milling from IA 22 were compared to those of the CIR milling collected from eight counties in Iowa. "

Comment 8: - P. 12, line 6: Correct "of the HMA overlay, For CIR using foamed asphalt, foamed".

Response 8: The sentence was changed on lines 14 - 16 of page 12 as "For an optimum performance of the HMA overlay, foamed asphalt should be evenly distributed across the width of the CIR layer to ensure a consistent asphalt binder content."

Comment 9: - P. 13, line 5: Correct "Funding: Please add: This research was funded".

Response 9: "Please add:" was removed, Thank you!

Author Response File: Author Response.pdf