Durability Evaluation Study for Crumb Rubber–Asphalt Pavement
Round 1
Reviewer 1 Report
The paper refers about a experimental study that investigated, by means of laboratory tests and procedures, the failure mechanism of crumb rubber-asphalt pavement under the combined effects of low temperature, water, and traffic load. The proposed method was designed by considering both mechanical and deformational properties of crumb rubber-asphalt mixture and the typical environmental and load conditions of road pavements that include this kind of material.
The topic is really interesting because currently the rubber powder is largely used to modify asphalt it allows to increase softening point and decrease ductility of asphalt. At the same time, due to the surface of the rubber powder that gradually softens, the "swelling effect" occurs and this significantly modifies the mechanical properties of binders. However, since rubber crumbs are incorporated as aggregates, when the temperature of the rubber crumbs is low the contact time with the asphalt is short, and the “swelling” effect is not obvious; in addition, in this case, also the adhesion of the asphalt to the rubber crumbs can be compromised.
The research investigated some mixtures obtained with various basic materials: SK-70 matrix asphalt, SBS modified asphalt, TPS modified (12%, 13.5% and 15% dosage) asphalt, basalt mineral aggregates, 0–3 mm mechanism sand, mineral powder, rubber-particles produced by the normal temperature mechanical shearing method; rubber particles belong to 0.6 mm-2.36 mm size range while the 1.18 mm particle size passing ratio is 25%. The main evaluation method was the Indirect Tensile Strength Test under freeze-thaw–boiling cycle; the Cantabro Abrasion Test under water-immersion was also adopted, as an auxiliary method.
The tests accomplishment and obtained results showed, first of all, the effectiveness of the proposed evaluation method; the different investigated mixtures have showed their specific properties, with regard both to mechanical performances and durability.
The presented research is well designed and correctly developed; the experimental study is quite innovative and widely referenced. The paper considers and discusses many previous studies and experiences in this field. The organization of the paper is good; the methodology is rigorous and the laboratory tests have been numerous and proper. The findings of the research are reliable and clearly presented.
In general, the paper can be considered as an interesting experimental research and a contribution to the better knowledge of the mechanical and durability characteristics of the materials that compose crumb rubber-asphalt pavement, as well as a proposal for the development of new test methods and standards.
Author Response
Thank you very much for your professional commentary and affirmation. In order to improve the quality of our manuscript, we have done minor revision for the original manuscript according to your review report. Lines 69-71 of Section 1.1 and lines 388-391 of Conclusion are further refined with reference to your elaboration.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper presents a new methodology for evaluating the durability of crumb rubber asphalt mixtures. Then, the results are compared with those obtained with the standard procedure. The paper is interesting and the proposal contributes to the knowledge about the behaviour of crumb rubber in asphalt pavements.
Some specific comments can help to improve the quality of the article:
Title: a different title could be clearer than the current one. I suggest something like “Evaluation of the durability of crumb rubber asphalt pavements”, although this is just an opinion.
Abstract: please explain the meaning of “aggregate asphalt mixtures”, is it SMA mixtures?
Section 2.1:
- Is a SK-70 matrix asphalt a conventional asphalt?
- Please add a brief explanation of what type of modifier TPS is.
- What does “mechanism sand” mean?
- What is 6.5% of “oil-stone ratio”? Is this ratio part of the design method (Course Aggregate Void filling method)?
- When authors speak about “The amount of TOR (rubber Vita-linker) was 4% of the rubber crumbs, that is 0.12%[41]”, please explain the values 4% and 0.12%. What are they percentages of?
Table 3: when authors write “Synthetic Grading”, it is assumed that they mean “Passing (%)”
Section 2.2.3: Cántabro Test was developed in Spain for the design of porous mixtures, which have more than 20% of air voids, to simulate the effect of traffic on wearing courses. For those who are not familiar with the procedure cited in the paper, it is somewhat strange to read that the test is used in other countries for evaluating properties of mixtures with 4 or 5% of air void contents. There must be a significant experience with the test if it was standardized. However, please confirm that the test procedure can be applied to dense mixtures (the standard is not free, so it is impossible to read it). It is not necessary to include any text in the paper.
Results: the results obtained with the water-boiling test are interesting. The proposed methodologies can be useful and even better ways for evaluating durability of this type of mixtures.
Conclusions: it is clear that the main objective of the paper is to propose a new methodology but the procedures were applied to a limited type of asphalts and a specific size of rubber-particles. Conclusions could be improved with some specific comments about the comparison of the asphalts and rubber-particles studied and evaluated in the paper.
Author Response
Thank you very much for your extremely professional commentary and affirmation. We have done minor revisions for the original manuscript according to your specific comments and suggestions. And the details as shown in the Word file of response.
Author Response File: Author Response.pdf
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
Dear Editor,
the Authors have revised the manuscript according to my comments.
I just noticed that ref 17 in the reference list is not cited in the manuscript. Probably it is an oversight that can be corrected in the proof correction stage.
So, I believe that the manucript can be accepted.
Best regards.
Author Response
Dear Reviewer,we have correct the ref,it is cited as ref 18 corresponding to the second paragraph marked in the revised manuscript. Best wishes,Thank you very much.
Reviewer 2 Report
Please find attached a PDF file with my comments and suggestions for authors.
Comments for author File: Comments.pdf
Author Response
Dear Reviewer 2, we have completed the major revisions according your cements.At the same time, we have study and disscuss your suggestions carefully.For details of the modification, please refer to the revised manuscript. For the reply to your comments, please refer to the corresponding response letter for you.
Thank you very much.
Wish everything goes well with your work!
Author Response File: Author Response.pdf
Reviewer 3 Report
Generally, the authors should have more contribution in this study. The verification of suggested method is not done properly, and the methodology should be explained clearly (it’s confusing). The durability of crumb rubber asphalt pavement is supposed to be evaluated in this study and a new method has been suggested. In section 4, the testing results of authors method is given, but they didn’t compare their method with the previous ones (NET absorption, …).
- Is figure 1 taken by the authors in the lab? If not, please add reference.
- Page 10, line 352, table number is not correct.
Author Response
Dear Reviewer 3, We have done considerable revision for the original manuscript according to your comments and suggestions.For details of the modification, please refer to the revised manuscript and the corresponding response letter.
Thank you very much for your review!
Wish everything goes well with your work!
Author Response File: Author Response.pdf
Reviewer 4 Report
Dear Authors!
Thank you very much for the interesting paper!
Please find the detailed comments in the attached document - please consider the notes.
Additionally:
- Clarity and Structuring could be improved (for example sometimes jump back and forth from detail to overall view - makes it sometimes difficult to follow/understand); please mind to operate from the general to the specific; sometimes there are repetitions that were already said elsewhere
- Referrals in text could help for a greater clarity (see chapter XX)
- Comparison of the results (values) to standard asphalt pavement would be nice, not just the values of 1 tested mixture - comparison and interpretation of the findings; not everything in the text is conclusive; description of the variables could be improved
- Conclusion could be worked out more significantly
Thanks and best regards
Comments for author File: Comments.pdf
Author Response
Dear Reviewer 4, We have done considerable revision for the original manuscript according to your comments and suggestions.For details of the modification, please refer to the revised manuscript. For the reply to your comments, please refer to the corresponding response letter for you.
Thank you very much for your careful and meticulous review!
Wish everything goes well with your work!
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
As I told in my previous reviews of this manuscript, this is a well-known topic, so the novelty of the manuscript is very low. The relevance of the research is still very low and the authors have not made anything to improve that.
The majority of the comments of my previous reviews of the manuscript have not been addressed in this new version of the manuscript, and the responses of authors are vague and imprecise. Some of the comments which has not been addressed are comments 3, 4, 5, 6, 7, 8 and 9.
Finally, it is important to emphasize that some of the responses of the authors show a total lack of respect to the reviewer suggestions, such as the answer to comments 8 and 9, in which my comments are qualified as rancorous, subjective and arbitrary. I only want that authors improve their manuscript in order to reach the good quality that Applied Sciences journal deserves. Instead of preparing a better paper, the authors only try to discredit me.
In view of that, in my opinion this article does not still reach the high quality standards required for being published in Applied Sciences journal, so my recommendation is to reject it.
Reviewer 3 Report
The comments are properly addressed by the authors. There are some editorial mistakes like spaces and commas that need to be corrected.
