Mechanical Characterization of Thin Asphalt Overlay Mixtures with 100% Recycled Aggregates
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
The paper is in general terms well written, and it is referred to an interesting subject as it is the use of recycled aggregates in the design of Thin Asphalt mixtures. Nonetheless, below are few comments that will help the authors in enhancing the quality of the same.
- Line 37. It would be suitable to include some more references as example of the use of these kinds of materials. Some examples can be found in:
Tauste-Martínez, R., Moreno-Navarro, F., Sol-Sánchez, M., & Rubio-Gámez, M. C. (2021). Multiscale evaluation of the effect of recycled polymers on the long-term performance of bituminous materials. Road Materials and Pavement Design, 22(sup1), S99-S116.
Hidalgo, A. E., Moreno-Navarro, F., Tauste, R., & Rubio-Gámez, M. C. (2020). The influence of reclaimed asphalt pavement on the mechanical performance of bituminous mixtures. An analysis at the mortar scale. Sustainability, 12(20), 8343.
- Line 112. Despite the design of the two proposed mixtures, it would be necessary to include a third mixture of reference so to fully assess the benefits of the new mixtures proposed when comparing to a solution that already is employed.
- Lines 122-123. Include the reference to these previous studies.
- Line 317. Although authors include a reference so to explain the higher values of wet group in relation to the dry one, a more extend explanation is required focusing on the reason behind this phenomenon does not occur in the mixture manufacture with modified bitumen.
Author Response
We would like to thank the reviewer for the comments and suggestions on our contribution ‘materials-2084323’ submitted for the Journal of Materials – Section: Construction and Building Materials – Special Issue: Recycling Pavements Materials. We have carefully taken the reviewer’s comments into consideration and addressing them all in the revised manuscript. Hereafter we provide a point-by-point response.
With best regards on behalf of all authors,
Giulia Tarsi.
The paper is in general terms well written, and it is referred to an interesting subject as it is the use of recycled aggregates in the design of Thin Asphalt mixtures. Nonetheless, below are few comments that will help the authors in enhancing the quality of the same.
Point 1: Line 37. It would be suitable to include some more references as example of the use of these kinds of materials. Some examples can be found in:
- Tauste-Martínez, R., Moreno-Navarro, F., Sol-Sánchez, M., & Rubio-Gámez, M. C. (2021). Multiscale evaluation of the effect of recycled polymers on the long-term performance of bituminous materials. Road Materials and Pavement Design, 22(sup1), S99-S116.
- Hidalgo, A. E., Moreno-Navarro, F., Tauste, R., & Rubio-Gámez, M. C. (2020). The influence of reclaimed asphalt pavement on the mechanical performance of bituminous mixtures. An analysis at the mortar scale. Sustainability, 12(20), 8343.
Response 1: The authors thank you for the suggestion. The literature has been improved according to the references recommended.
Point 2: Line 112. Despite the design of the two proposed mixtures, it would be necessary to include a third mixture of reference so to fully assess the benefits of the new mixtures proposed when comparing to a solution that already is employed.
Response 2: The authors have considered the European standard requirements as a reference to assess the feasibility of using an eco-friendly TAO mixture that contains recycled aggregates only. Since the study needs further investigations, the design and characterization of an additional TAO mix with virgin aggregates only will be also considered.
Point 3: Lines 122-123. Include the reference to these previous studies.
Response 3: Thanks to preliminary analysis on this specific study the optimum binder content has been defined for both TAO mixtures. In order to clarify this point, the word ‘previous’ was substituted with ‘preliminary’ and the performed tests were added to the description. Please, refer to lines 138-139.
Point 4: Line 317. Although authors include a reference so to explain the higher values of wet group in relation to the dry one, a more extend explanation is required focusing on the reason behind this phenomenon does not occur in the mixture manufacture with modified bitumen.
Response 4: Based on your comment the description of paragraph 3.4 has been improved accordingly. The almost unchanged ITSR value of TAO-PmB rather than the higher ITSR value of TAO-PEN 50/70 may be related to the different behaviour of the polymer-modified bitumen in combination of the cellulose fibres. PmBs are expected to be less prone to water/moisture susceptibility than standard bitumen, while cellulose fibres may speed up the diffusion process into the asphalt concrete. Please, refer to lines 368-372 for manuscript changes.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Authors
Thanks for your effort, it's a good article about the use of fibers and recycled asphalt in the flexible pavement, but some points of ambiguity and controversy will be raised in the following:
-The specifications of these two materials should be given in the text of the article.
a) cellulose fibers; b) synthetic fibers.
-What is the meaning of circular economy[Keywords]? In this article, in which part is it used specifically?
-Pictures of asphalt samples should be added to the article, how did you apply Thin Asphalt Overlay on the asphalt sample? Please give an explanation.
-In the abstract, the numerical results of this study should also be mentioned.
-Give the specifications of the recycled asphalt used in this article. Were these materials uniform in terms of granulation and the amount of bitumen available? Were the characteristics of the aged bitumen determined in this recycled material? please explain.
-The adhesion of the Thin Asphalt Overlay and the asphalt in the bottom layer changes when the fiber is used (it acts as a barrier), how is this function considered in this study?
Thanks
Author Response
We would like to thank the reviewer for the comments and suggestions on our contribution ‘materials-2084323’ submitted for the Journal of Materials – Section: Construction and Building Materials – Special Issue: Recycling Pavements Materials. We have carefully taken the reviewer’s comments into consideration and addressing them all in the revised manuscript. Hereafter we provide a point-by-point response.
With best regards on behalf of all authors,
Giulia Tarsi.
Dear Authors, thanks for your effort, it's a good article about the use of fibers and recycled asphalt in the flexible pavement, but some points of ambiguity and controversy will be raised in the following:
Point 1: The specifications of these two materials should be given in the text of the article.
- cellulose fibers; b) synthetic fibers.
Response 1: The main specifications of the two fibres used were reported in paragraph 2.2, where additional information was provided to the readers while revising the manuscript. In detail, please, refer to lines 163-164 and 170-171.
Point 2: What is the meaning of circular economy [Keywords]? In this article, in which part is it used specifically?
Response 2: The keyword ‘circular economy’ has been added to highlight the use of recycled aggregates. In the present study, recycled aggregates from wastes and/or by-products of different industrial chains have been used to improve the sustainability of the final asphalt mixes. The authors have changed the order of keywords in order to better connect the terms ‘circular economy’ and ‘recycled aggregates’.
Point 3: Pictures of asphalt samples should be added to the article, how did you apply Thin Asphalt Overlay on the asphalt sample? Please give an explanation.
Response 3: Unfortunately, the authors did not take pictures of samples unless they were under testing devices. However, the TAO mixes were not overlayed on a bottom asphalt sample. This study wanted to represent a preliminary investigation on the characteristics of recycled TAO mixtures producing samples 3.8 mm approx. thick. The considered thickness allows the performance of the planned volumetric and mechanical tests. The authors referred to the document of the Federal Highway Administration, FHWA-HIF-19-053, entitled ‘The use of Thin Asphalt Overlay for Pavement Preservation’ to consider the thickness of the asphalt mixtures’ samples. The authors thank you for the comment and in order to clarify this aspect some changes have been introduced in the description of ‘Methods’ section, please see lines 247-251.
Point 4: In the abstract, the numerical results of this study should also be mentioned.
Response 4: The abstract has been improved trying to better highlight the results and conclusions obtained from the experimental analysis.
Point 5: Give the specifications of the recycled asphalt used in this article. Were these materials uniform in terms of granulation and the amount of bitumen available? Were the characteristics of the aged bitumen determined in this recycled material? please explain.
Response 5: The authors evaluated the grading distribution and the bitumen content of the used RAP aggregates. In order to clarify this aspect, lines 184-187 of the manuscript were changed accordingly. The cohesive property of the aged bitumen present in RAP aggregates was investigated following the RILEM recommendation as explained in lines 189-197; while, the physico-rheological properties of the extracted bitumen from RAP were not analysed. The characteristics of aged bitumen and the interaction between this binder and the virgin ones can be further investigated.
Point 6: The adhesion of the Thin Asphalt Overlay and the asphalt in the bottom layer changes when the fiber is used (it acts as a barrier), how is this function considered in this study?
Response 6: This study did not evaluate the adhesion of the Thin Asphalt Overlay mixtures and the bottom layer as it wanted to represent a preliminary study on the characterisation of recycled TAO mixtures. In detail, all asphalt samples were produced and tested without overlayed them on a bottom sample since the maximum thickness of the TAO mix is 3.8 cm approximately. The considered thickness allows the performance of all planned volumetric and mechanical tests. The authors referred to the document of the Federal Highway Administration, FHWA-HIF-19-053, entitled ‘The use of Thin Asphalt Overlay for Pavement Preservation’ to consider the thickness of the asphalt mixtures’ samples. The effect of fibres on the final adhesion of the asphalt layer on a bottom one will be further investigated following your suggestion. In order to clarify this aspect, some changes have been introduced in the description of ‘Methods’ and in the ‘Conclusions’ section, please refer to lines 247-251 and 441-444, respectively.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThis review report has been removed from the review record as it did not meet MDPI’s review report standards (https://www.mdpi.com/reviewers#_bookmark11).
Author Response
NA
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsThis review report has been removed from the review record as it did not meet MDPI’s review report standards (https://www.mdpi.com/reviewers#_bookmark11).
