Using Molecular Dynamics Simulation to Analyze the Feasibility of Using Waste Cooking Oil as an Alternative Rejuvenator for Aged Asphalt

Round 1

Reviewer 1 Report

This paper investigates the effects of rejuvenator in the aged asphalt using the MD simulation. Multiple parameters/performance indicators such as density, viscosity, and various moduli were computed to compare the binder samples. However, I recommend that revisions are warranted due to the two issues present in the paper.

The first one is regarding the grammar mistakes and composition issues shown in the draft. Such as in the Line 44, 51, 68, 99, 122, 188, 194, 211, 244, 270, 284, 296, and so on. To that end, I suggest seeking the assistance of a professional editor to proofread the draft and fix the errors.

The second issue is related to the paper objective. The paper can be improved by improving the MD simulation method (as mentioned in the context that gaps exist between the simulation and the lab test results). Alternatively, compare the simulation results with the authors' or other researchers' tested results in Section 3.

Moreover, some comments are listed below.

• Page 2, Line 56: "all rejuvenators…improved rutting resistance". This is not true, and in general, rutting resistance is reduced when the rejuvenator is added.
• Page 4, Line 146: please add any reference or basis for the values listed in Table 1.
• Page 5, Line 179: "following" should be "above"?
• Page 7, Line 195: "…than the reported experiment data…" please add references here.
• Page 8, Line 229: "the anti-deformation ability" may not be accurate here. You are introducing molecular attraction property, which may be correlated more to the recovery ability under external force (crack resistance). Suggest doublechecking the term.

Author Response

Please see the Response to Reviewer 1 Comments

Author Response File: Author Response.pdf

Reviewer 2 Report

The subject of this paper is very interesting, contemporary and environmentally friendly as it studies the use of a waste material (used cooking oil) to help the use of another waste material (old asphalt). It is without any doubt in the scope of the journal. The authors perform a molecular dynamics simulation and made comparisons with a commercial rejuvenator and with some laboratory results from the references.

With respect to English writing, it is too easy to find grammatical mistakes in the body of the manuscript and therefore a good revision should be carried out. This is a very important task to do. Examples: line 37: “ls and provide … “ ; line 44:  “… the crack was rapidly generation …”; line 83: “Due to WCO is rich in unsaturated …” this is not a sentence! and line 98: “Only a few studies the …” this is not a sentence neither!; line 239: “… the anti-deformation ability worse …” or shall it be “ … the anti-deformation ability gets worse …”? line 251: “Mechanical properties are the important properties to judge …” or should it be  “are the most important”? “are also important”? “are important”?

- line 53 “For instance, Zau-manis et al. studied the … rejuvenators [7].” Should be “For instance, Zau-manis et al. [7] studied the … rejuvenators.”; the same for other similar situations (lines 58, 60, 89, 104, and more)

- lines 171 to 175:  the reason why these values were chosen (298 K, 1 fs, 100 ps) should be added; the meaning of NPT and NVE should be added

- lines 195 to 196: “… slightly smaller than the reported experiment data from …” experimental data published by who? A reference should be added

- the authors must confirm the values given along the paper. As an example, the last paragraph on page 9 shows the same exactly values for both the WCO and the rejuvenator and that is not shown in the respective figure; furthermore, line 211 on page 7 “From the results, 6% rejuvenator decreased the viscosity by 15.4%, WCO reduced viscosity by 17.4%”. From the figure we can see that is not true, for 6% the rejuvenator shows a higher decrease than the WCO.

- legend of figure 7: should be “Elastic modulus (E)”, “Bulk modulus (K)” and Shear modulus (G)”, therefore add (E), (K) and (G) to the legend

- line 271 “However, its ductility was decreased …” where in the figure it can be seen the changes in ductility with age for WCO and for rejuvenator?

- line 316 “… three modulus of asphalt were recovered to a better level.” What do you mean by a better level, is it considered an acceptable level? Why?

- conclusions must be revised according

Author Response

Please see the Response to Reviewer 2 Comments

Author Response File: Author Response.pdf

Reviewer 3 Report

This is a well-written and carefully structured paper that uses the concept of the new molecular dynamics simulation to analyse the behavior of aged bitumen mixed with waste cooking oil as an alternative rejuvenator.

I have a few comments that might be usefully addressed to improve the overall quality of the paper:

My suggestion to the author is to present more detailed the relation between the different three type of asphalt modulus (lines 258-262) for a better understanding of the relations between them.

Also, in the simulation it is mandatory to take care about the dispersion rate of the new rejuvenator on the entire mass of the asphalt, knowing that this is one of a major concern related to this topic.

The physical-mechanical characteristics of the binder should have been briefly verified, through laboratory studies, to validate the method.

Author Response

Please see the Response to Reviewer 3 Comments

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Thank you for your thorough revisions to the manuscript. I have no further comments, so I recommend this work being published. One more thing I want to mention is about a small grammar mistake. When listing three or more items in a series or combining two complete sentences, you missed an "AND" before the final item/sentence in a few places (please check). I hope it can be corrected before publishing.