Effects of Rejuvenator Dosage, Temperature, RAP Content and Rejuvenation Process on the Road Performance of Recycled Asphalt Mixture
Round 1
Reviewer 1 Report
Effects of Rap Content and Regeneration Process on the Road Performance of Asphalt Mixture
For the construction and maintenance of sustainable pavements the mechanical behavior of recycled hot asphalt mixture is undoubtedly a very important issue.
In order to contribute to the authors for their research and paper, some suggestions are considered:
- The abstract should be rewritten because some ideas are not clear. Examples: Line 10: “three index tests” – which ones? Line 15 “the optimum rejuvenator dosage is 4% according to the three indexes” – which rates of rejuvenator are tested? Line 22 – “by using the regeneration process II and â…¢”- what processes?
- The authors chose a “permeable rejuvenator” - Please, clarify the nature and source, and provide rheological data of the rejuvenator.
- Please use international parameter designation. Examples: instead of the term “porosity”, you can use “air voids content”; instead of “water stability”, you can use “moisture-induced damage”, etc
- The authors tested three rates of rejuvenator for a RAP content and stated “Combined with the three index test results…. the optimum rejuvenator content is 4%”. How many samples were tested for each rejuvenator content? Without statistics it is very difficult to conclude whether the tests are reliable and repeatable, whether the results are really different. Why are the results obtained for 3 and 5% very similar and 4% very different from both, but similar to new asphalt? Please explain it.
- Clarify how deep into the asphalt layer is “the center temperature of structure layer” (Figure 3). What system is used for this measurement?
- According to the authors, Figure 6 shows the effect of pavement milling: “The damage of aggregate can be reduced by milling the pavement under high temperature and ensure the uniformity of the original pavement gradation. For every 10% increase in RAP content, the average mixing and compaction temperature of hot recycled asphalt mixture decreases by 2~6°C”. It is clear that the temperature (and the milling speed) interferes in the breakdown of the old asphalt layer and in the dimensions of the “black aggregates” obtained. Most important for the hot recycling process is the recovery rate of the old asphalt, quantifying the effective mobilized old asphalt content from “black aggregates”. This process is temperature dependent and a higher temperature increases the amount of old asphalt recovered. On the other hand, to further reduce the aging of old asphalt, a lower temperature can help the process. It is a very complex choice and depends on the RAP content and the total asphalt content (old and new binder) for each case. Increasing the RAP content should decrease the new binder content. The design parameters of the mixture are not mentioned, so it is really difficult to analyze the volumetric properties and results. How many samples are used in this experimental work?
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper "Effects of Rap Content and the Rejuvenation Process on the Road Performance of Asphalt Mixture" presents a relevant theme and is within the scope of this journal. It can be considered after some corrections suggested below:
1) The authors need to adequately revise the title to "Effects of Rap Content and the Rejuvenation Process on the Road Performance of Asphalt Mixture." In the introduction section, there are sections on background, literature review, motivation of the research, and finally, the suggestion is to address the objective at the end, making it easy to read for the reader.
2) Instead of regeneration, use in the whole manuscript "Rejuvenation" or "Rejuvenator"?
3) The literature review needs more enhancements. For example, one valuable reference
· https://doi.org/10.3390/ma14112781
· https://doi.org/10.3390/recycling7030035
4) The authors need to mention the optimum percentage of rejuvenator at 30% in the abstract section? (there has been several research about virgin asphalt binder as rejuvenator and any enhancement have been done in this study on the fatigue performance of rejuvenated asphalt.
5) As previously stated, in line 20, low-temperature crack resistance and moisture susceptibility are weakening, but how does it improve rutting?
6) The authors need to be credited for demonstrating the feasibility of rejuvenators using No. 90 virgin asphalt in RAP applications for solving diverse asphalt pavement problems.
7) In my opinion, the research articles still need to be enhanced since there are many researchers interested in the application of reclaimed asphalt pavement (RAP) by utilizing rejuvenators and the topic is hot for scientific credibility. However, it can be assessed as good, containing certain shortcomings that need to be eliminated. In terms of article quality, I am able to process a repeated review within 3 days in the case of the incorporation of comments or relevant justification for their non-incorporation.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The authors have adequately addressed my comments and observations on the present manuscript; thus, I suggest the manuscript can be accepted for publication in its current shape.
