Skid Resistance Attenuation of Asphalt Pavement Based on Multifactor Accelerated Wear Test

Round 1

Reviewer 1 Report

The paper was interesting, well-structured and meaningful. Laboratory testing and related discussion supported the presented findings. The reviewer suggests some revisions to be made in the paper according to the following remarks.

1_ Line 18 and 209-210: Do the authors imply that 24,000 polishing cycles correspond to the long-term skid resistance of a pavement surface. Please elaborate in the main text.

2_ Lines 41-43: Although profound, try to be more illustrative in your paper. You may add a figure/sketch explaining the frictional forces in the tire-road interaction. Please reconsider.  

3_ Lines 50-67: The introduction should more comprehensively deal with factors affecting skid resistance. The paragraph can be spitted if new material is to be added. Apart from textural components, traffic volumes and environmental conditions do affect the skid resistance of a pavement and this should be acknowledged. There are numerous studies and laboratory simulations aiming to demonstrate this impact on the frictional behavior. You may consult and cite https://doi.org/10.3390/vehicles2010004 , https://doi.org/10.3390/recycling7040047 etc. Please reconsider.

4_ Line 92: Please add the study’s outline and/or a flowchart.

5_ Table 3: How was the gradation of each mixture defined? Please elaborate and define any kind of aggregate specifications used.

6_ Lines 172-187: The discussion provided here is fine. The reviewer would like to also see a kind of BPN comparison between the central point of a slab and the other ones. The authors might recommend here a suitable area for BPN measures after performing a polishing tests, right? How many replicated BPN measures were performed at each locations (i.e., repeatability?). Please elaborate.

7_ Please comment on the inversion point between the attenuation curves of AC-16 and AC-13 in Figure 5 at the cycle No. 4000-6000. What is the physical explanation?

8_ What is the contribution of this study in the domain of GRA? Please provide discussion points.

9_ In the conclusions, please add any research limitations and future directions. Also, any practical recommendations that could help improving the mix design of surface courses? Please elaborate.

10_ Please renew the references list. The reviewer noticed only two references belonging to the last three years (from 2020 and on). The issue is timely and you should update the list.

11_ Please refine some typos and language issues (e.g., in line 84 you mean “although many studies…”).

Overall, the manuscript can be reconsidered if the authors improve their paper. Please remember to indicate the exact line numbering of comments and revisions in your replies to accelerate any re-review process.

Author Response

 Thanks very much for your comments. My replies are in the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

The present study extensively evaluates skid resistance decay with a number of load pass. It investigates the long-term impact of aggregate type, NMAS, and gradation on skid resistance attenuation. Although trends shown in the figure have been worked out and predicted in several other studies but it provides a quantitative measure to understand the rate of skid resistance decay. The paper is well written with clarity of thought; however, the reviewer has the following comments.

1.     It is not clear, how the life cycle of the pavement has been simulated with a number of abrasive cycles. Authors can explain the basis of number of abrasive cycles selected for the study. Does this maximum abrasion cycle correspond to the limiting friction value as represented by BPN?

2.     The decay rate used as an evaluation index is just reflecting the % change in skid resistance. If BPN can be checked at regular intervals of abrasion cycles, say per 1000 cycles, the decay rate can be better modelled with some fitting constants. It will give a better idea of skid resistance decay.

3.     Paper can be checked for grammatical mistakes (e.g., Line no – 110).

4.     The future scope of the study can be added to understand what authors think is missing in the study.

Author Response

 Thanks very much for your comments. My replies are in the attachment

Author Response File: Author Response.docx

Reviewer 3 Report

Thank you to the authors for submitting their work for consideration for publication. In this study, the authors evaluated different mixes including aggregate type, gradation, and NMAS to determine the optimal design for hot mix asphalt overlays based on BPN friction resistance after an accelerated surface loading program. The paper is overall well-written and easy to follow, although it is not so novel. It is worthy of publication with just a few minor comments. Please see these:

1. How many specimens for each were tested? It is also necessary to include error bars on figures to understand how meaningful results are.

2. The compaction process is not too clear. It is important to define what one "cycle" of compaction is.

3. Conclusion 1 is not really necessary. This is just dependent on your specific materials and cannot be generalized from the scope of this study.

Author Response

 Thanks very much for your comments. My replies are in the attachment

Author Response File: Author Response.docx

Reviewer 4 Report

1.      Line 84 to 94 is the core of the introduction, but the content is quite poor. It should be enriched. For examples, what analysis technique was used to qualitatively analyze the influence of aggregate types and gradation types on skid resistance?

2.      The materials and methods parts are insufficient. The author’s team should improve the content of the proposed materials. More aggregates and binder properties should be added into the manuscript.

3.      What factors were considered during the abrasion process that influence skid resistance? The author’s team should specify them.

4.      The results and discussions should be improved to clearly show how does skid resistance change with increasing abrasive cycles? The author’s team currently conduct some analysis and generate good results; however, they should be properly linked to the skid resistance. How do these factors relate to the skid resistance? The authors can write some statement regarding this.

5.      How does increasing nominal maximum aggregate size affect skid resistance? The explanation was not clear.

6.      The author’s team should quantify which sieve sizes were identified as critical for improving skid resistance?

7.      In the conclusion part, the author’s team should suggest which materials had the best skid resistance durability and stability for practical application.

8.      Based on the results presented in the manuscript, what recommendations could be made to improve the skid resistance of asphalt pavement, particularly in terms of material composition and mixture design? How might these recommendations be applied in practice, and what potential limitations or trade-offs should be considered when implementing them?

Comments for author File: Comments.docx

Author Response

 Thanks very much for your comments. My replies are in the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The paper was improved. Some extra revision remarks, please use units each time you refer to sieve opening (mm), like lines 23, 382 and 404. Please also replace the term "in a word" in line 381 with another phrase. Most importantly, in lines 88-90 the authors claim that most attempts about skid resistance rely on field studies. This is not absolutely true. Limitations like measurement equipment, sparse environmental conditions, uncontrolled traffic conditions (unlike laboratory abrasive tests) might force pavement researchers to mainly invest on laboratory controlled testing. The authors are asked to reconsider at this point. 

Author Response

Thanks very much for your comments. I very much agree with you , and some of my views are  arbitrary. I have changed it as follows:

      1)Units on sieves  have been added.

     2)The phrase “in a word” is changed to “It can be drawn that”

     3)Although the field research is the most direct and effective way to study skid resistance, there are many factors that affect the field skid resistance of asphalt pavement, including traffic volumes, environmental conditions, aggregate types, construction levels, and so on. It is difficult to grasp the long-term effects of materials on the skid resistance of pavement under the same external conditions.