A Review of Long-Term Skid Resistance of Asphalt Pavement
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe topic is interesting. However sometimes the writing is not very easy to follow.
I revision of the writing/language style is needed. This comment is applicable to the entire masnuscript.
The manuscript is quite long. I recommend reducing the length of the manuscript. Mostly that can be achieved through editing the text. For instance, in several occasions information is repeated in different sections. One example: in section 2.1 lines 89 to 95 repeat information already given in the section 1. Another example is in section 3.1 lines 248 to 256.
In summary, sections 1, 2 and 3 are highly repetitive, and also happens between section 4 and 5.
The distinction between section 5 and 6 is not very clear. I would suggest merging all the information in section 5. In any case, the text should be more clear and concise avoiding repeating the summary of the previous sections 2, 3 and 4.
On the side of the selected methods, for instance, it was considered the x-ray CT scanning. However possible, this method does not seem adequate at all. Thus, the authors are including solutions that likely will never be implemented, at least for skid resistance. This don’t bring added value and wastes the reader’s time. In this domain the article should be more concise.
Other minor remarks:
There is a typo in line 91? Where is written “the skid surface layer” shouldn’t be “the surface layer”?
The sentence in line 96-98 doesn’t make sense.
Figure 7 and respective caption are not entirely correct. And to be more logical for the reader, if there are 4 figures it must be a), b), c) and d).
Comments on the Quality of English LanguageThe manuscript would benefit from a strong revision of the English language.
Author Response
A Review of long-Term Skid Resistance of Asphalt Pavement
Yuanfeng Chen, Zhitang Li *, Yuankuo Wang, Guoxi Liang and Xiaolong Yang *
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Dear Editors and Reviewer:
Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “A Review of long-Term Skid Resistance of Asphalt Pavement. These comments are very valuable and very helpful for revising and improving our manuscript, as well as the important guiding significance to our researches. We have studied comments carefully and made corrections which we hope meet with approval. Revised portions are marked in red in the revised manuscript accordingly. Please keep the authors informed if there is any further action needed. The main corrections in the paper and the responds to the reviewer’s comments are as flowing:
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REVIEWER 1:
The topic is interesting. However sometimes the writing is not very easy to follow.
1) - I revision of the writing/language style is needed. This comment is applicable to the entire manuscript.
Response: Thank you for your comment. We have reviewed the article sentence by sentence to optimize the sentence structure and avoid piling up complex and lengthy sentences to make the expression more concise and clearer.
2) - The manuscript is quite long. I recommend reducing the length of the manuscript. Mostly that can be achieved through editing the text. For instance, in several occasions information is repeated in different sections. One example: in section 2.1 lines 89 to 95 repeat information already given in the section 1. Another example is in section 3.1 lines 248 to 256.
Response: Thank you for your comment. We have deleted section 2.1 lines 89 to 95 and section 3.1 lines 248 to 256. Furthermore, we’ve removed repetitive parts of the article and streamlined some of the statements to make the article shorter.
3) -In summary, sections 1, 2 and 3 are highly repetitive, and also happens between section 4 and 5.
Response: Thank you for your comment. We apologize for any inconvenience caused by our negligence. We've removed repetitive parts of the article. And reviewed the full text, to avoid the emergence of repeated statements.
4) -The distinction between section 5 and 6 is not very clear. I would suggest merging all the information in section 5. In any case, the text should be more clear and concise avoiding repeating the summary of the previous sections 2, 3 and 4.
Response: Thank you for your comment. According to your suggestion, we have adjusted the summary of section 2.3.4, and at the same time, according to the opinions of each reviewer, we have reconsidered the contents of summary 5 and summary 6, which not only avoids the repetition of the previous text, but also clarifies the future development direction. The details are as follows:
Conclusions:
This paper reviews and summarizes the research hotspots such as indoor and outdoor skid resistance testing methods of AP, skid resistance mechanism of AP, and the L-TSR decay law of AP, influencing factors, decay model, and predictive model, and the main conclusions are as follows:
(1) The digital image method can quickly and intuitively obtain information such as pavement texture. By analyzing the image data, the skid resistance of the pavement can be accurately evaluated. The intelligent sensor detection method can monitor the parameters related to the skid resistance of the pavement in real time and continuously, provide timely feedback on the changes of the pavement condition and ensure the traffic safety of the road.
(2) The indoor test can effectively evaluate the performance of skid resistance materials under different environmental conditions by simulating the actual road conditions, which can help to evaluate the effect of anti-skid materials and the performance of AP more accurately, and to verify the reliability and repeatability of the results, as well as to provide detailed data on the performance of the materials, including skid resistance coefficient of friction and so on.
(3) The coefficient of friction for skid resistance is provided by the adhesion com-ponent and deformation component. Improving asphalt viscosity, adopting aggregates with high quality aggregates, ensuring the content of fine aggregates on the surface (0.16-4.75) mm, and controlling the surface layer slurry can ensure that AP have sufficient skid resistance and improve the durability of the pavements. Preparation of AP by incorporating rubber, steel slag, slag or based on the principle of differential honing, which reduces the economic outlay, saves resources in terms of high-quality aggregates and improves the skid resistance of AP.
(4) For the L-TSR of AP, should consider the local pavement conditions, climatic conditions and environmental factors:①select the mineral composition of rich, matrix hardness difference between the aggregate;②select high-quality asphalt and asphalt dosage control;③choose a reasonable mineral grading;④set up the vehicle load and driving speed limit signs, and from time to time on the AP to clean up the asphalt;⑤Use high quality modified asphalt to improve the L-TSR of AP.
(5) The combined model synthesizes the advantages of various models and makes up for the shortcomings of a single model, which is the best choice for predicting the L-TSR of AP. In addition, the application of the combined model is not limited to the traditional prediction and analysis field, but also can be extended to many fields such as image processing and machine learning.
- Outlook
In recent years, a series of research have been conducted at home and abroad on the L-TSR performance of AP, and certain research results have been achieved. How-ever, domestic, and foreign research on L-TSR of AP has not been comprehensive, and subsequent research can be carried out from the following shortcomings in-depth re-search and discussion:
(1) With the rapid development of sensor technology, artificial intelligence and big data analysis, the future testing of the skid resistance of outdoor asphalt pavements will move towards intelligence and automation. Intelligent sensors will be able to collect various parameters of the pavement in real time, including texture, humidity, temperature and mechanical data during vehicle driving, and automatically transmit them to the back end for analysis and processing. The data analysis model based on artificial intelligence algorithms can quickly and accurately evaluate the skid resistance of the pavement, not only reducing human errors, but also enabling real-time monitoring and early warning of complex road conditions.
(2) In the future, indoor accelerated loading equipment will be closely integrated with virtual models. By creating high-precision virtual models of asphalt pavements, different loading schemes and environmental conditions can be pre-simulated in a virtual environment to predict the changing trends of pavement performance, providing guidance for actual tests. Meanwhile, the data obtained from actual tests will be fed back into the virtual model to modify and optimize it, achieving mutual promotion between virtual simulation and actual testing, improving research efficiency and reducing testing costs.
(3) In the future, the analysis of the skid resistance mechanism of AP should in-clude multi-scale texture analysis, considering the influence of seasonal and long-term changes, exploring the application of new materials and technologies, studying the stability of base layer materials, and deeply understanding the influence of terrain on skid resistance. At the same time, the skid resistance of AP is quantitatively evaluated, and the results are compared with macro texture, microstructure and apparent morphology to fully verify the skid resistance of AP.
(4) when exploring the decay law of the long-term skid resistance of asphalt pavements, a comprehensive consideration of various complex factors will be carried out. From the micro level, such as the abrasion of aggregates and the aging of asphalt, to the macro level, including the cumulative annual traffic loads and the periodic cycles of seasons and climate, the gradual change trajectory of skid resistance under the individual and synergistic effects of each factor will be accurately sorted out. On the other hand, relying on big data and the Internet of Things, vast amounts of multisource and dynamic pavement information will be widely collected. By using advanced algorithms such as deep learning and reinforcement learning, the hidden com-plex relationships behind the data will be deeply explored to build a highly intelligent decay model of skid resistance.
(5) The combined prediction model of skid resistance of AP will make up for the deficiency of single model to a certain extent and improve the prediction accuracy. In the future, we should comprehensively consider various influencing factors, use ad-vanced calculation methods and algorithms, adopt probability and random models, make full use of experimental and field test data, and develop multivariate and high-precision combined prediction models. (line 734-814)
5) -On the side of the selected methods, for instance, it was considered the x-ray CT scanning. However possible, this method does not seem adequate at all. Thus, the authors are including solutions that likely will never be implemented, at least for skid resistance. This don’t bring added value and wastes the reader’s time. In this domain the article should be more concise.
Response: Thank you for your comment. We have deleted the detailed description of CT scanning. And we rethink the future development direction of asphalt pavement skid resistance detection method. The prospect of the modified detection method of skid resistance of asphalt pavement is as follows:
(1) With the rapid development of sensor technology, artificial intelligence and big data analysis, the future testing of the skid resistance of outdoor asphalt pavements will move towards intelligence and automation. Intelligent sensors will be able to collect various parameters of the pavement in real time, including texture, humidity, temperature and mechanical data during vehicle driving, and automatically transmit them to the back end for analysis and processing. The data analysis model based on artificial intelligence algorithms can quickly and accurately evaluate the skid resistance of the pavement, not only reducing human errors, but also enabling real-time monitoring and early warning of complex road conditions.
(2) In the future, indoor accelerated loading equipment will be closely integrated with virtual models. By creating high-precision virtual models of asphalt pavements, different loading schemes and environmental conditions can be pre-simulated in a virtual environment to predict the changing trends of pavement performance, providing guidance for actual tests. Meanwhile, the data obtained from actual tests will be fed back into the virtual model to modify and optimize it, achieving mutual promotion between virtual simulation and actual testing, improving research efficiency and reducing testing costs. (line 778-793)
6) - There is a typo in line 91? Where is written “the skid surface layer” shouldn’t be “the surface layer.
Response: Thank you for your comment. We apologize for any inconvenience caused by our negligence. We have already changed "the surface layer" to "the skid surface layer", and at the same time, we have carefully checked other sentences in the text to avoid similar problems.
7) - The sentence in line 96-98 doesn’t make sense.
Response: Thank you for your comment. We have deleted the sentences in lines 96 - 98 to stay focused.
8) - Figure 7 and respective caption are not entirely correct. And to be more logical for the reader, if there are 4 figures it must be a), b), c) and d).
Response: Thank you for your comment. According to your suggestion, we have already changed the icons of Figure 7 to a), b), c) and d). We also adjusted the sharpness of Figure 7 to make the image more presentable. (line 548-549)
9) - The manuscript would benefit from a strong revision of the English language.
Response: Thank you for your comment. We will meticulously review the content of the article sentence by sentence, optimize the sentence structure, avoid piling up complex and lengthy sentences, and make the expression more concise and clearer.
SUMMARY
According to the reviewers’ comments, we tried our best to revise the manuscript. And the revised portions are marked in red in the revised manuscript accordingly.
We appreciate the above advice of the reviewers very much. The advice will greatly benefit for the improvement of the paper and our future research. We appreciate for Editors/Reviewers’ warm work earnestly, and hope that the correction will meet with approvals of the journal.
Your good advice was very much appreciated.
Once again, thank you very much for your comments and suggestions.
Thank you and best regards.
Yours sincerely,
Yuanfeng Chen
Corresponding author:
Zhitang Li
Email: licareer@qq.com
Xiaolong Yang
Email: xiaolongyang@gxu.edu.cn
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe statements on lines 24-25, 145-153, and 731-733, "Digital image method, close-up photogrammetry method and intelligent sensor detection method, with higher accuracy and efficiency, less impact on road traffic, wide range of work and cheap cost, are the important methods for future AP skid resistance detection," cannot be fully agreed upon. While non-contact skid resistance evaluation is indeed the future and the focus of many researchers, accurately predicting skid resistance requires capturing pavement texture down to the microtexture level. Currently, this necessitates point-specific measurements on-site, with each measurement taking at least 15 seconds, which inevitably impacts traffic flow, especially when conducted on active road sections. Although the article referenced by the authors supports the hypothesis that texture parameters, such as MTD, are key for evaluating skid resistance, it does not provide evidence of a direct correlation between MTD and the friction coefficient.
Lines 48-53: I recommend rephrasing the discussion to clearly differentiate between the factors influencing the immediate skid resistance of asphalt pavement (e.g., aggregate morphology, gradation types, temperature, water film depth) and those affecting its long-term degradation (e.g., vehicle load, traveling speed, road pollution). This distinction would enhance the clarity and accuracy of the manuscript. The statement "the asphalt membrane and aggregate will be gradually worn out, resulting in a gradual decline in the skid-resistant ability of the pavement" is not entirely accurate. Initially, as the asphalt film is worn off and the aggregate's microtexture is exposed, skid resistance increases before eventually declining due to polishing of the aggregate over time. This phenomenon is supported by the results presented in Figure 7b, which show an initial increase in skid resistance before a long-term decrease. Additionally, while the immediate value of skid resistance is influenced by factors like aggregate morphology, gradation types, temperature, and water film depth, its long-term degradation is primarily determined by factors such as vehicle load, traveling speed, and road pollution, which should be clearly distinguished.
Lines 64-66: The sentence is not grammatically correct; I recommend rephrasing it for clarity and proper structure.
Line 91: The term 'skid surface layer' is not commonly used in technical literature. I recommend using a more standard term, such as 'surface layer' or 'wearing course,' for better clarity and consistency.
Lines 93-95: The claim that skid resistance may have disadvantages in terms of ensuring driving safety is not accurate. Skid resistance inherently enhances vehicle safety by reducing the risk of skidding and improving braking performance. The authors may want to clarify whether they are referring to potential economic or maintenance challenges rather than safety issues.
Lines 138-144: The sentence highlights an important gap in the research on AP uniformity evaluation but is overly broad and lacks specific examples or evidence to support the claim. Additionally, the structure and grammar make it difficult to follow. I recommend rephrasing the sentence for clarity and providing concrete references or examples of existing methods and their limitations to strengthen the argument.
The reason why no unified method has yet been established is that no one has succeeded in capturing pavement texture at operational speeds with sufficient resolution to reliably predict the friction coefficient using non-contact measurements. Furthermore, universally applicable predictive models with high reliability are still lacking. Therefore, I agree with the authors that this area requires further research.
Lines 177-186: The sentence is overly long and lacks proper grammatical structure, making it difficult to follow. Key issues include the absence of a clear subject in the opening clause, improper use of phrases like 'the detection of time-consuming,' and redundancy in expressions. I recommend breaking the sentence into shorter, more concise statements and ensuring grammatical accuracy for better readability and clarity.
Lines 188-196: The phrase 'studies at home' is ambiguous and context-dependent. Readers cannot determine where 'home' refers to, particularly in an international publication. If the authors mean their own country, it would be more precise to explicitly state the country or region to avoid confusion, especially if the study is published for a global audience.
I disagree with the statement that MTD (Mean Texture Depth) is the most used or reliable indicator for characterizing the skid resistance of pavement. Numerous studies have demonstrated a weak correlation between MTD and the friction coefficient, with strong correlations observed only within specific ranges that cannot be considered universally applicable. Furthermore, it was proven many times that high values of individual texture characteristics, both on primary and micro and macrotexture surfaces, do not necessarily represent high friction coefficient values. It would be more accurate to acknowledge the limitations of MTD in predicting skid resistance and consider other parameters or combined indicators for a comprehensive evaluation.
The tables in the manuscript, including Table 1, are difficult to read due to misaligned rows and columns. I recommend aligning the rows and columns for better clarity and presentation. Additionally, methods such as the 'Sand spreading method' and 'Pendulum instrument method' have official names and corresponding standards that define their procedures. It would be more appropriate and precise to cite the relevant standards rather than referencing articles where these methods were applied.
Lines 262-263: The term 'skid friction' is not commonly used in technical literature and may be confusing. I recommend using a more standard term, such as 'friction coefficient' or 'skid resistance.' Additionally, the term 'deformation friction component' could be replaced with 'hysteresis component,' which is more commonly used and accurately reflects the energy loss mechanism associated with tire deformation on the pavement surface.
Lines 331-333: The explanation linking asphalt content to skid resistance is oversimplified and partially inaccurate. While low asphalt content may lead to aggregate loss, the relationship between asphalt content and skid resistance is more complex. Low asphalt content may initially expose more aggregate, increasing microtexture and skid resistance, while long-term aggregate polishing can reduce friction. Conversely, high asphalt content may lead to excessive coverage of aggregates, reducing microtexture. I recommend clarifying this relationship and addressing the multifactorial nature of skid resistance.
Lines 379-380: The sentence is grammatically incorrect and unclear. I recommend rephrasing it as: 'Aggregate is one of the most important materials in asphalt pavement (AP), and its physical and mechanical properties are key factors affecting the performance of AP.
Lines 383-385: The statement oversimplifies the relationship between aggregate size and skid resistance. While larger aggregates can contribute to improved macrotexture, skid resistance also depends on the microtexture of the aggregate, as well as its shape, hardness, and resistance to polishing. Several studies have shown that mixtures with the smallest maximum aggregate size exhibit the highest friction values, which are also maintained over a longer period. This can likely be attributed to the increased number of contact points between the pavement and the tire, enhancing microtexture. I recommend revising the statement to reflect these findings and considering the role of microtexture and aggregate size in influencing both initial and long-term skid resistance.
Lines 581-588: The explanation of the process in Figure 8a is partially correct but oversimplified and contains inaccuracies. While the initial spreading of asphalt and subsequent exposure of aggregate are plausible, the statement that 'deep asphalt continues to rise' is unlikely under normal conditions and should be clarified or supported by evidence. Additionally, the claim of a continuous decrease in skid resistance overlooks the intermediate phase where skid resistance may increase temporarily due to the activation of aggregate microtexture before it declines with polishing. I recommend revising this section to reflect the non-linear nature of skid resistance evolution.
Line 628: The reference to 'H et al' is unclear and likely incorrect, as a single letter cannot realistically represent a surname. I recommend verifying and providing the full surname of the referenced author to ensure proper citation.
The figures in the manuscript are generally difficult to read due to inconsistent font sizes and poor clarity. For instance, the text in Figure 5b appears mirrored, which reduces its interpretability. Additionally, I am uncertain whether the original source of this figure is correctly cited. I recommend ensuring that all figures are clear, consistently formatted, and properly sourced, with any mirrored or improperly oriented elements corrected.
The label 'Schematic diagram' in Figure 8a is misleading, as the figure does not depict a schematic diagram but rather a series of photographs or visual representations of the surface changes. I recommend revising the description to accurately reflect the content of the figure.
Comments on the Quality of English LanguageOverall, the quality of English in the manuscript needs improvement. Specific issues include grammatical errors, inconsistent sentence structures, unclear phrasing, and improper terminology usage. For example, terms like 'skid friction,' incorrect grammar in phrases such as 'Aggregate is composed of AP,' and ambiguous expressions like 'H et al' detract from the clarity and professionalism of the text. I recommend a thorough revision of the language, preferably with the assistance of a native English speaker or professional editor, to ensure accuracy and readability.
Author Response
A Review of Long-Term Skid Resistance of Asphalt Pavement
Yuanfeng Chen, Zhitang Li *, Yuankuo Wang, Guoxi Liang and Xiaolong Yang *
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Dear Editors and Reviewer:
Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “A Review of Long-Term Skid Resistance of Asphalt Pavement. These comments are very valuable and very helpful for revising and improving our manuscript, as well as the important guiding significance to our researches. We have studied comments carefully and made corrections which we hope meet with approval. Revised portions are marked in red in the revised manuscript accordingly. Please keep the authors informed if there is any further action needed. The main corrections in the paper and the responds to the reviewer’s comments are as flowing:
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REVIEWER 2:
1) - The statements on lines 24-25, 145-153, and 731-733, "Digital image method, close-up photogrammetry method and intelligent sensor detection method, with higher accuracy and efficiency, less impact on road traffic, wide range of work and cheap cost, are the important methods for future AP skid resistance detection," cannot be fully agreed upon. While non-contact skid resistance evaluation is indeed the future and the focus of many researchers, accurately predicting skid resistance requires capturing pavement texture down to the microtexture level. Currently, this necessitates point-specific measurements on-site, with each measurement taking at least 15 seconds, which inevitably impacts traffic flow, especially when conducted on active road sections. Although the article referenced by the authors supports the hypothesis that texture parameters, such as MTD, are key for evaluating skid resistance, it does not provide evidence of a direct correlation between MTD and the friction coefficient.
Response: Thank you for your comment. We highly agree with your point of view. In response to your query, we have reconsidered the future detection methods for skid resistance in combination with the article. We believe that the digital image method and the intelligent sensor detection method will be important approaches in the future. Corresponding changes have been made in the relevant positions of the article. (line23-27，739-744)
Compared with traditional methods for testing pavement skid resistance, digital image method and intelligent sensor detection method have significantly improved in terms of efficiency and accuracy. However, it is indeed inevitable that they will affect traffic. If these methods can be improved to shorten the measurement time or serve as a carrier for other advanced testing methods, then the factors that interfere with traffic can be largely resolved.
Based on the principle of the digital image method, we can use unmanned aerial vehicles (UAVs) equipped with high-resolution cameras to conduct aerial photography of large areas of asphalt pavement to obtain macroscopic images of the pavement. Through image analysis technology, the texture features, wear conditions, and water accumulation situations of the pavement can be identified, and then the skid resistance performance of the pavement can be evaluated. Alternatively, laser scanners and cameras can be installed on vehicles. The laser scanners obtain the three-dimensional terrain data of the pavement, and the cameras capture the texture images of the pavement. After fusing the two sets of data, the micro and macro structures of the pavement can be analyzed more accurately, and skid resistance performance indicators such as the friction coefficient of the pavement can be calculated. This method can be carried out during the normal driving of vehicles, without affecting traffic, and has a relatively high detection accuracy.
Secondly, to solve the problem of identifying the micro-texture of the pavement, the non-destructive testing technology integration method will also be utilized in the future. For example, ground-penetrating radar can detect the internal structure and defects of the pavement, while infrared thermal imaging can detect the temperature distribution on the surface of the pavement. By combining the two, the skid resistance performance of the pavement can be comprehensively evaluated from both the internal structure and the surface state aspects.
Last, relevant literature has shown that the rougher the pavement, the greater the friction coefficient it provides. When we studied the skid and wear resistance of concrete pavements, we compared and fitted the texture parameters scanned by a 3D laser scanner with the friction coefficient. We found a positive correlation between the two. Based on this, we believe that there is a certain correlation between MTD and the friction coefficient.
We're truly grateful that you've raised this issue. In the subsequent exploration of the evolution laws of the long - term skid resistance and wear resistance of asphalt pavements using our independently developed indoor abrasion testing machine, we will focus on this aspect.
2) - Lines 48-53: I recommend rephrasing the discussion to clearly differentiate between the factors influencing the immediate skid resistance of asphalt pavement (e.g., aggregate morphology, gradation types, temperature, water film depth) and those affecting its long-term degradation (e.g., vehicle load, traveling speed, road pollution). This distinction would enhance the clarity and accuracy of the manuscript. The statement "the asphalt membrane and aggregate will be gradually worn out, resulting in a gradual decline in the skid-resistant ability of the pavement" is not entirely accurate. Initially, as the asphalt film is worn off and the aggregate's microtexture is exposed, skid resistance increases before eventually declining due to polishing of the aggregate over time. This phenomenon is supported by the results presented in Figure 7b, which show an initial increase in skid resistance before a long-term decrease. Additionally, while the immediate value of skid resistance is influenced by factors like aggregate morphology, gradation types, temperature, and water film depth, its long-term degradation is primarily determined by factors such as vehicle load, traveling speed, and road pollution, which should be clearly distinguished.
Response: Thank you for your comment. According to your suggestion, we have re-discussed lines 48 - 53. In addition, after asphalt pavements are worn, their skid resistance tends to increase. We have deleted the incorrect statements to ensure the accuracy of the article. The specific content is as follows:
The initial skid resistance of AP is mainly influenced by factors such as the type of asphalt [5–8], aggregate morphology, and gradation type [9,10]. However, during long - term service, the pavements are affected by factors like vehicle loads [11], traveling speed [12], road pollution [13–15], which reduces the skid resistance of the pavements. Therefore, the study of L-TSR of AP is particularly important. (line47-51)
3) -Lines 64-66: The sentence is not grammatically correct; I recommend rephrasing it for clarity and proper structure.
Response: Thank you for your comment. We have adjusted the grammar of lines 64-72. The details are as follows:
Therefore, the research on the L-TSR of AP mainly encompasses AP skid resistance testing methodologies, the mechanism and influencing factors of AP skid resistance, as well as the decay law and prediction model of the L-TSR of AP, among others [24,25]. Nevertheless, the current research on the L-TSR of AP has yet to be systematized and still exhibits certain deficiencies. For instance, there is a shortage of high-precision data acquisition equipment; reliable and comprehensive indoor acceleration loading devices capable of simulating real road conditions are lacking, and the evaluation systems of different equipment remain ununified; the optimal material composition parameters for different types of AP have not been precisely defined; and research on the decay law of the L-TSR of AP under the coupling effects of various factors is insufficient. These issues severely impede the improvement of the skid resistance of AP, necessitating further in-depth analysis and research. (line 61-72)
4) - Line 91: The term ' skid surface layer ' is not commonly used in technical literature. I recommend using a more standard term, such as 'surface layer' or 'wearing course,' for better clarity and consistency.
Response: Thank you for your comment. According to your suggestion, we have changed "skid surface layer" to "surface layer" or "wearing course" throughout the text.
5) -Lines 93-95: The claim that skid resistance may have disadvantages in terms of ensuring driving safety is not accurate. Skid resistance inherently enhances vehicle safety by reducing the risk of skidding and improving braking performance. The authors may want to clarify whether they are referring to potential economic or maintenance challenges rather than safety issues.
Response: Thank you for your comment. We have removed the incorrect understanding of the skid resistance of asphalt pavement. Skid resistance essentially enhances vehicle safety by reducing the risk of vehicle sideslip and improving braking performance. Therefore, good skid resistance of asphalt pavements can reduce the subsequent maintenance costs of the road surface and extend the service life of asphalt pavements.
6) -Lines 138-144: The sentence highlights an important gap in the research on AP uniformity evaluation but is overly broad and lacks specific examples or evidence to support the claim. Additionally, the structure and grammar make it difficult to follow. I recommend rephrasing the sentence for clarity and providing concrete references or examples of existing methods and their limitations to strengthen the argument.
Response: Thank you for your comment. We have cited relevant references to demonstrate the limitations of the digital image method, and adjusted the structure and grammar of the paragraphs to facilitate understanding. The details are as follows:
In recent years, researchers have proposed various noise reduction methods for the digital image method [28,29], including algorithms based on non - local means [30], sparse representation[31], wavelet transform, deep learning[32], etc. These methods are usually targeted at specific types of noise or specific scenarios, and no unified evaluation standard has been formed. Regarding the image threshold segmentation technology, existing research has shown that threshold segmentation methods can be divided into hard thresholding and soft thresholding and are further optimized by combining with technologies such as wavelet transform and neural networks [32]. However, due to the differences in segmentation accuracy and computational complexity among different algorithms, there is currently no unified evaluation standard to measure their performance. Regarding the evaluation of image uniformity, it mainly relies on the meth-od of manually selecting uniform regions and calculating their mean and standard deviation [33]. Although this method is simple and intuitive, it has significant limitations. For example, it requires manual intervention and is difficult to automate. (line 116-128)
7) -The reason why no unified method has yet been established is that no one has succeeded in capturing pavement texture at operational speeds with sufficient resolution to reliably predict the friction coefficient using non-contact measurements. Furthermore, universally applicable predictive models with high reliability are still lacking. Therefore, I agree with the authors that this area requires further research.
Response: Thank you for your comment. At present, the common prediction models for pavement skid resistance are affected by many factors. Most of them only focus on the change of the friction coefficient, without in - depth consideration of the pavement texture. Therefore, exploring a high - precision prediction model by combining the changes of the friction coefficient and the pavement texture is one of the important future directions. Meanwhile, we are also making efforts in this regard.
8) –Lines 177-186: The sentence is overly long and lacks proper grammatical structure, making it difficult to follow. Key issues include the absence of a clear subject in the opening clause, improper use of phrases like 'the detection of time-consuming,' and redundancy in expressions. I recommend breaking the sentence into shorter, more concise statements and ensuring grammatical accuracy for better readability and clarity.
Response: Thank you for your comment. Based on your suggestion, we have restructured the statement and replaced time-consuming. the changes are as follows:
AP skid resistance testing methods and characteristics are shown in Table 1. Through analyzing different AP skid resistance testing methods, we found that the outdoor testing has the merit that the measured skid data can vividly reflect the actual changes of AP skid resistance [36]. However, its demerit is that the detection is rather lengthy, labor-intensive and necessitates traffic closure. Generally, to stabilize the pavement's skid resistance, it usually takes 3 - 5 years of vehicle loading. Thus, regarding the detection cycle, there are drawbacks like a prolonged cycle, disruption to normal traffic, high cost, unobvious data patterns and numerous uncontrollable elements [37]. (line 163-170)
9) –Lines 188-196: The phrase 'studies at home' is ambiguous and context-dependent. Readers cannot determine where 'home' refers to, particularly in an international publication. If the authors mean their own country, it would be more precise to explicitly state the country or region to avoid confusion, especially if the study is published for a global audience.
Response: Thank you for your comment. Most of the domestic and foreign studies only calculate the Mean Texture Depth (MTD) indicator after obtaining the pavement texture information. The MTD is the most commonly used indicator for characterizing the skid resistance of the pavement after non-contact acquisition of the AP texture information. This point can be demonstrated by citing relevant reference literature.
Khasawneh, M.; Shbeeb, N.; Al-Omari, A. Analytical Tool to Shorten Polishing Time Based on Mean Texture Depth (MTD) of Flexible Pavements. ROAD MATERIALS AND PAVEMENT DESIGN 2020, 21, 737–756, doi:10.1080/14680629.2018.1527717.
Pranjić, I.; Deluka-Tibljaš, A. Pavement Texture–Friction Relationship Establishment via Image Analysis Methods. Materials 2022, 15, doi:10.3390/ma15030846.
Ban, I.; Deluka-Tibljaš, A.; Ružić, I. Skid Resistance Performance Assessment by a PLS Regression-Based Predictive Model with Non-Standard Texture Parameters. Lubricants 2024, 12, doi:10.3390/lubricants12010023.
9) –I disagree with the statement that MTD (Mean Texture Depth) is the most used or reliable indicator for characterizing the skid resistance of pavement. Numerous studies have demonstrated a weak correlation between MTD and the friction coefficient, with strong correlations observed only within specific ranges that cannot be considered universally applicable. Furthermore, it was proven many times that high values of individual texture characteristics, both on primary and micro and macrotexture surfaces, do not necessarily represent high friction coefficient values. It would be more accurate to acknowledge the limitations of MTD in predicting skid resistance and consider other parameters or combined indicators for a comprehensive evaluation.
Response: Thank you for your comment. We very much agree with your point of view. Compared with the sand paving method, the Mean Texture Depth (MTD) has higher credibility and reliability in characterizing the skid resistance of the pavement. However, it cannot be denied that the correlation between MTD and the friction coefficient is rather weak, and a strong correlation can only be observed within a specific range. Based on this, when exploring the correlation between MTD and the pavement skid resistance, we acknowledged the limitations of MTD in predicting skid resistance and called for the use of other parameters or comprehensive indicators for a comprehensive evaluation. Meanwhile, we have emphasized this point at the corresponding position in the article. The specific content is as follows:
Compared with the sand spreading method, the MTD has higher credibility and reliability in characterizing the skid resistance of the pavement. However, it cannot be denied that the correlation between MTD and the friction coefficient is rather weak, and a strong correlation can only be observed within a specific range, the texture structure and distribution of the pavement are more complex, only one MTD indicator fails to comprehensively reflect the pavement texture information and skid resistance, so the subsequent study should use multiple indicators to characterize the texture and skid resistance of the AP in multiple dimensions. (line 171-182)
10) –The tables in the manuscript, including Table 1, are difficult to read due to misaligned rows and columns. I recommend aligning the rows and columns for better clarity and presentation. Additionally, methods such as the 'Sand spreading method' and 'Pendulum instrument method' have official names and corresponding standards that define their procedures. It would be more appropriate and precise to cite the relevant standards rather than referencing articles where these methods were applied.
Response: Thank you for your comment. Based on your suggestions, we have aligned the rows and columns of Table 1 to enhance clarity and expressiveness. Additionally, while citing the articles that apply these methods, we have also referenced the official names of some methods and relevant standards, making the article more appropriate and accurate.
11) –Lines 262-263: The term 'skid friction' is not commonly used in technical literature and may be confusing. I recommend using a more standard term, such as 'friction coefficient' or 'skid resistance.' Additionally, the term 'deformation friction component' could be replaced with 'hysteresis component,' which is more commonly used and accurately reflects the energy loss mechanism associated with tire deformation on the pavement surface.
Response: Thank you for your comment. According to your suggestions, we have changed “skid friction” to “friction coefficient” and “deformation friction component” to “hysteresis component” to accurately reflect the energy loss mechanism with tire deformation on the pavement surface. (line 240-241)
12) –Lines 331-333: The explanation linking asphalt content to skid resistance is oversimplified and partially inaccurate. While low asphalt content may lead to aggregate loss, the relationship between asphalt content and skid resistance is more complex. Low asphalt content may initially expose more aggregate, increasing microtexture and skid resistance, while long-term aggregate polishing can reduce friction. Conversely, high asphalt content may lead to excessive coverage of aggregates, reducing microtexture. I recommend clarifying this relationship and addressing the multifactorial nature of skid resistance.
Response: Thank you for your comment. Our explanation that linked the asphalt content to skid resistance through the research of other scholars was oversimplified. Although there is a certain connection between asphalt content and pavement skid resistance, the relationship between them is rather complex. Therefore, after citing the conclusions of previous scholars, we also clarified this relationship and addressing the multifactorial nature of skid resistance later to ensure the rigor of the article. (line 318-323)
13) –Lines 379-380: The sentence is grammatically incorrect and unclear. I recommend rephrasing it as: 'Aggregate is one of the most important materials in asphalt pavement (AP), and its physical and mechanical properties are key factors affecting the performance of AP.
Response: Thank you for your comment. In accordance with your suggestion, we have revised the original text to: "Aggregate is among the most crucial materials in AP, and its physical and mechanical properties represent key factors influencing the performance of AP." (line 363-364)
14) –Lines 383-385: The statement oversimplifies the relationship between aggregate size and skid resistance. While larger aggregates can contribute to improved macrotexture, skid resistance also depends on the microtexture of the aggregate, as well as its shape, hardness, and resistance to polishing. Several studies have shown that mixtures with the smallest maximum aggregate size exhibit the highest friction values, which are also maintained over a longer period. This can likely be attributed to the increased number of contact points between the pavement and the tire, enhancing microtexture. I recommend revising the statement to reflect these findings and considering the role of microtexture and aggregate size in influencing both initial and long-term skid resistance.
Response: Thank you for your comment. Our previous description oversimplified the relationship between aggregate size and skid resistance. Therefore, we have revised the statement to reflect these findings and considering the roles of microtexture and aggregate size in influencing the initial and long-term skid resistance. The specific content is as follows:
Microtexture and aggregate size play significant roles in affecting the initial and long-term skid resistance of asphalt pavements. Microtexture can provide additional frictional surfaces. When vehicle tires meet the pavement, the micro-texture can embed into the grooves on the tire surface, enhancing the mechanical interlocking between them and thereby improving the initial skid resistance of the pavement. During long-term use, although the microtexture will gradually wear away, if the pavement material possesses a certain self-healing ability or can continuously expose new microtexture under traffic loads, the skid resistance can be maintained to some extent. Larger-sized aggregates can make the pavement surface rougher, increasing the contact area and friction force between the tires and the pavement, thus enhancing the initial skid resistance. Moreover, under the long-term action of vehicle loads, they can more effectively resist wear, preserving the roughness and skid resistance of the pavement. Meanwhile, appropriately sized aggregates can interlock with each other in the pavement, forming a stable structure that can withstand the repeated action of vehicle loads, making it less likely for aggregates to become loose or fall off, which is conducive to maintaining long-term skid resistance. (line 367-382)
15) –Lines 581-588: The explanation of the process in Figure 8a is partially correct but oversimplified and contains inaccuracies. While the initial spreading of asphalt and subsequent exposure of aggregate are plausible, the statement that 'deep asphalt continues to rise' is unlikely under normal conditions and should be clarified or supported by evidence. Additionally, the claim of a continuous decrease in skid resistance overlooks the intermediate phase where skid resistance may increase temporarily due to the activation of aggregate microtexture before it declines with polishing. I recommend revising this section to reflect the non-linear nature of skid resistance evolution.
Response: Thank you for your comment. We have reinterpreted Figure 8a-8d and cited relevant literature. At the same time, we have also revised the wrong statement that the skid resistance continues to decline. The modified content is as follows:
Figure 8(a) shows that, from the surface changes in the AP in the early loading stage, the asphalt mortar on the mixture’s surface spreads around under wheel load, and the asphalt mortar in the deep layer keeps rising. Thus, the surface texture constantly re-duces, and the number of oil spots constantly increases. When loading to a certain ex-tent, the asphalt film on the surface of the mixture is worn and consumed under the action of wheel load, and the aggregate wrapped underneath is gradually exposed [69]; It can be seen from Figure 8 (b) that the asphalt mixture has a relatively rich section texture before loading. With the increase in loading times, the small texture wears out, and the large texture structures lose most of the time. The texture structure of the section as a whole is worn out [69]; It can be seen from Figure 8 (c) that in see that under the action of the vehicular loading, the macro-texture of AP gradually becomes smooth, and the dense aggregate is gradually worn out. texture gradually becomes smooth, dense spikes gradually disappear, and the proportion of protruding agglomerates is significantly reduced, indicating that the agglomerates are worn and compacted [151]; Figure 8(d) shows that, in the role of the vehicle load, the texture of the AP by the initial sharp, rough gradually become smooth and rounded [59].
At the initial stage of wear, the original loose aggregate is further embedded and compacted, and some micro-textures and macro-textures are gradually formed and highlighted, which increases the roughness of the pavement surface, so that the skid resistance may be improved. And under the friction of the vehicle, the asphalt film will gradually be worn thin, and the edges and textures of the aggregate will gradually be exposed. This running-in process makes the road surface gradually become rough from the initial smooth state, and the skid resistance may also be improved [59,152,153]. As the service life continues to increase, the repeated action of the vehicle load and the continuous friction between the tire and the road surface will gradually flatten the aggregate surface, the edges and corners of the aggregate will be worn out, and the micro and macro textures of the road surface will be continuously weakened, resulting in a decline in skid resistance [153,154]. Thus, the skid resistance may temporarily increase due to the activation of the aggregate micro-texture and then decrease with polishing. (line 578-611)
16) –Line 628: The reference to 'H et al' is unclear and likely incorrect, as a single letter cannot realistically represent a surname. I recommend verifying and providing the full surname of the referenced author to ensure proper citation.
Response: Thank you for your comment. We have provided the full surname of the referenced author to ensure proper citation. (line 639-641)
17) –The figures in the manuscript are generally difficult to read due to inconsistent font sizes and poor clarity. For instance, the text in Figure 5b appears mirrored, which reduces its interpretability. Additionally, I am uncertain whether the original source of this figure is correctly cited. I recommend ensuring that all figures are clear, consistently formatted, and properly sourced, with any mirrored or improperly oriented elements corrected.
Response: Thank you for your comment. We have adjusted the format of all the pictures in the full text to ensure that all the charts are clear, consistent in format, and with correct sources. （Figure 1，Figure 2，Figure 4a，Figure 5b，Figure 7，Figure 8）
18) –The label 'Schematic diagram' in Figure 8a is misleading, as the figure does not depict a schematic diagram but rather a series of photographs or visual representations of the surface changes. I recommend revising the description to accurately reflect the content of the figure.
Response: Thank you for your comment. Following your suggestion, we have changed the label of Figure 8a to “Change in the surface condition of asphalt mixture under different loading conditions”. (line 578-579)
19) –Overall, the quality of English in the manuscript needs improvement. Specific issues include grammatical errors, inconsistent sentence structures, unclear phrasing, and improper terminology usage. For example, terms like 'skid friction,' incorrect grammar in phrases such as 'Aggregate is composed of AP,' and ambiguous expressions like 'H et al' detract from the clarity and professionalism of the text. I recommend a thorough revision of the language, preferably with the assistance of a native English speaker or professional editor, to ensure accuracy and readability.
Response: Thank you for your comment. We will meticulously review the content of the article sentence by sentence, optimize the sentence structure, avoid piling up complex and lengthy sentences, and make the expression more concise and clearer.
SUMMARY
According to the reviewers’ comments, we tried our best to revise the manuscript. And the revised portions are marked in red in the revised manuscript accordingly.
We appreciate the above advice of the reviewers very much. The advice will greatly benefit for the improvement of the paper and our future research. We appreciate for Editors/Reviewers’ warm work earnestly, and hope that the correction will meet with approvals of the journal.
Your good advice was very much appreciated.
Once again, thank you very much for your comments and suggestions.
Thank you and best regards.
Yours sincerely,
Yuanfeng Chen
Corresponding author:
Zhitang Li
Email: licareer@qq.com
Xiaolong Yang
Email: xiaolongyang@gxu.edu.cn
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe reviewed article concerns the problems of long-term skid resistance of asphalt pavement. This is a very important problem from an engineering and road safety point of view. The mathematical analysis of the problems considered is difficult and interesting from a scientific point of view. The topics addressed are in the scope of the journal Applied Sciences. The authors have reviewed an impressive number of scientific papers in this field (191!). The literature review is clear, comprehensive and of relevance to the field. The items cited are up-to-date.
The authors have described in detail methods for testing the skid resistance of asphalt road pavements. They have included methods that can be applied in the laboratory and in the field. They clearly presented their advantages and disadvantages. They then addressed a theoretical model describing the mechanism of the skid resistance of a road pavement. In this description, they considered the quality of the asphalt and the properties of the aggregate. They identified the factors that have a significant effect on improving skid resistance.
Authors then presented the problems of road surface degradation over time and how this affects skid resistance. They indicated the influence of various factors on changes in this resistance over time. Authors presented models for predicting the long-term skid resistance of asphalt pavements. They highlighted the big differences between deterministic and probabilistic models and pointed out the great advantages and possibilities of modern models based on neural networks.
In the conclusions, the authors summarised the previous considerations. An interesting and valuable element is the final chapter presenting recommended directions for further research work.
The article is relatively well written and edited. Figures and tables are correctly prepared, well described, correctly present the data, and are easy to interpret and understand. Nevertheless, the article needs editorial improvements, e.g. the literature numbering is not separated by a space from the enclosing words. Some of the tables are very large and do not fit on one page which makes them difficult to use. Several figures are not of the best quality. They look like scans from other literature items. They are not very sharp and their background is not very clean. In particular, these remarks apply to Figures 1 and 2. Several figures show characters of the Chinese alphabet, which should be removed or replaced by English subtitles.
The final assessment of the article is very difficult. The authors have not presented the results of their research but have made a very extensive and in-depth review of the literature and presented conclusions on the possibilities for further research work. Such a review and conclusions may be of great interest to other researchers in the field of road pavements. I do not know what the position of the journal editors is towards review articles in which the authors do not present the results of their own research? If there is a possibility to publish such articles then this peer-reviewed one, after the corrections described above, could be a valuable and interesting article.
Author Response
A Review of long-Term Skid Resistance of Asphalt Pavement
Yuanfeng Chen, Zhitang Li *, Yuankuo Wang, Guoxi Liang and Xiaolong Yang *
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Dear Editors and Reviewer:
Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “A Review of long-Term Skid Resistance of Asphalt Pavement. These comments are very valuable and very helpful for revising and improving our manuscript, as well as the important guiding significance to our researches. We have studied comments carefully and made corrections which we hope meet with approval. Revised portions are marked in red in the revised manuscript accordingly. Please keep the authors informed if there is any further action needed. The main corrections in the paper and the responds to the reviewer’s comments are as flowing:
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REVIEWER 3:
The reviewed article concerns the problems of long-term skid resistance of asphalt pavement. This is a very important problem from an engineering and road safety point of view. The mathematical analysis of the problems considered is difficult and interesting from a scientific point of view. The topics addressed are in the scope of the journal Applied Sciences. The authors have reviewed an impressive number of scientific papers in this field (191!). The literature review is clear, comprehensive and of relevance to the field. The items cited are up-to-date.
1) -The authors have described in detail methods for testing the skid resistance of asphalt road pavements. They have included methods that can be applied in the laboratory and in the field. They clearly presented their advantages and disadvantages. They then addressed a theoretical model describing the mechanism of the skid resistance of a road pavement. In this description, they considered the quality of the asphalt and the properties of the aggregate. They identified the factors that have a significant effect on improving skid resistance.
Response: Thank you for your comment. We have also taken the reviewer's suggestion to go deeper into the article about the factors affecting the skid resistance of asphalt pavements.
2) -Authors then presented the problems of road surface degradation over time and how this affects skid resistance. They indicated the influence of various factors on changes in this resistance over time. Authors presented models for predicting the long-term skid resistance of asphalt pavements. They highlighted the big differences between deterministic and probabilistic models and pointed out the great advantages and possibilities of modern models based on neural networks.
Response: Thank you for your comment. We also rethink the future direction of skid resistance prediction modeling. We hope to further investigate the long-term skid resistance of asphalt pavements in terms of testing, simulation, modeling, and big data.
3) -In the conclusions, the authors summarised the previous considerations. An interesting and valuable element is the final chapter presenting recommended directions for further research work.
Response: Thank you for your comment. We revisited future research directions carefully, as described below:
(1) With the rapid development of sensor technology, artificial intelligence and big data analysis, the future testing of the skid resistance of outdoor asphalt pavements will move towards intelligence and automation. Intelligent sensors will be able to collect various parameters of the pavement in real time, including texture, humidity, tempeature and mechanical data during vehicle driving, and automatically transmit them to the back end for analysis and processing. The data analysis model based on artificial intelligence algorithms can quickly and accurately evaluate the skid resistance of the pavement, not only reducing human errors, but also enabling real-time monitoring and early warning of complex road conditions.
(2) In the future, indoor accelerated loading equipment will be closely integrated with virtual models. By creating high-precision virtual models of asphalt pavements, different loading schemes and environmental conditions can be pre-simulated in a virtual environment to predict the changing trends of pavement performance, providing guidance for actual tests. Meanwhile, the data obtained from actual tests will be fed back into the virtual model to modify and optimize it, achieving mutual promotion between virtual simulation and actual testing, improving research efficiency and reducing testing costs.
(3) In the future, the analysis of the skid resistance mechanism of AP should include multi-scale texture analysis, considering the influence of seasonal and long-term changes, exploring the application of new materials and technologies, studying the stability of base layer materials, and deeply understanding the influence of terrain on skid resistance. At the same time, the skid resistance of AP is quantitatively evaluated, and the results are compared with macro texture, microstructure and apparent morphology to fully verify the skid resistance of AP.
(4) when exploring the decay law of the long-term skid resistance of asphalt pavements, a comprehensive consideration of various complex factors will be carried out. From the micro level, such as the abrasion of aggregates and the aging of asphalt, to the macro level, including the cumulative annual traffic loads and the periodic cycles of seasons and climate, the gradual change trajectory of skid resistance under the individual and synergistic effects of each factor will be accurately sorted out. On the other hand, relying on big data and the Internet of Things, vast amounts of multi-source and dynamic pavement information will be widely collected. By using advanced algorithms such as deep learning and reinforcement learning, the hidden complex relationships behind the data will be deeply explored to build a highly intelligent decay model of skid resistance.
(5) The combined prediction model of skid resistance of AP will make up for the deficiency of single model to a certain extent and improve the prediction accuracy. In the future, we should comprehensively consider various influencing factors, use advanced calculation methods and algorithms, adopt probability and random models, make full use of experimental and field test data, and develop multivariate and high-precision combined prediction models.（line 776-814）
4) -The article is relatively well written and edited. Figures and tables are correctly prepared, well described, correctly present the data, and are easy to interpret and understand. Nevertheless, the article needs editorial improvements, e.g. the literature numbering is not separated by a space from the enclosing words. Some of the tables are very large and do not fit on one page which makes them difficult to use. Several figures are not of the best quality. They look like scans from other literature items. They are not very sharp and their background is not very clean. In particular, these remarks apply to Figures 1 and 2. Several figures show characters of the Chinese alphabet, which should be removed or replaced by English subtitles.
Response: Thank you for your comment. According to your suggestions, we have separated the literature from the text in the article with spaces, and adjusted the formatting of the tables and pictures in the article to make them clearer and more viewable, as well as modified the Chinese characters in the pictures.（Figure 1，Figure 2，Figure 4a，Figure 5b，Figure 7，Figure 8）
5) -The final assessment of the article is very difficult. The authors have not presented the results of their research but have made a very extensive and in-depth review of the literature and presented conclusions on the possibilities for further research work. Such a review and conclusions may be of great interest to other researchers in the field of road pavements. I do not know what the position of the journal editors is towards review articles in which the authors do not present the results of their own research? If there is a possibility to publish such articles then this peer-reviewed one, after the corrections described above, could be a valuable and interesting article
Response: Thank you for your comment. The purpose is to systematically sort out the knowledge system in this field. It integrates the achievements scattered in numerous research literatures in the past, covering from basic theories, such as the mechanical principles related to skid resistance and the microscopic mechanisms of material properties, to the application technology level, including the research progress of various indoor and outdoor testing methods and accelerated loading equipment, as well as the quantitative analysis of the influence of different factors on the skid resistance of asphalt pavements. This provides subsequent researchers with a comprehensive and well-organized theoretical reference, helping them identify new research entry points and promoting the in-depth development of the discipline. Secondly, through the review, the current research gaps and deficiencies can be discovered. For example, the limitations of existing testing methods in simulating complex environmental conditions and the need to improve the accuracy of long-term skid resistance prediction models. These issues can guide the direction of scientific research funding, inspire more innovative research to overcome difficulties, and promote the formation of a virtuous cycle in the research field of asphalt pavement skid resistance, continuously improving the overall technical level of the industry.
In addition, we have made careful revisions according to the comments of each reviewer. Meanwhile, we have also rethought the future research directions in depth. We have deleted some old references and cited those published within the recent three years. Finally, apart from summarizing the current research status of the long-term skid resistance of asphalt pavements, we have independently developed two indoor abrasion testing devices and actively carried out experiments on the skid resistance and abrasion resistance of granite manufactured sand pavement concrete as well as the long-term skid resistance and abrasion resistance of asphalt pavements.
（1）The long-term skid resistance and abrasion resistance of asphalt pavements
（2）The skid resistance and abrasion resistance of granite manufactured sand pavement concrete.
SUMMARY
According to the reviewers’ comments, we tried our best to revise the manuscript. And the revised portions are marked in red in the revised manuscript accordingly.
We appreciate the above advice of the reviewers very much. The advice will greatly benefit for the improvement of the paper and our future research. We appreciate for Editors/Reviewers’ warm work earnestly, and hope that the correction will meet with approvals of the journal.
Your good advice was very much appreciated.
Once again, thank you very much for your comments and suggestions.
Thank you and best regards.
Yours sincerely,
Yuanfeng Chen
Corresponding author:
Zhitang Li
Email: licareer@qq.com
Xiaolong Yang
Email: xiaolongyang@gxu.edu.cn
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsLet's agree to disagree on some things. But that's probably fine, I guess. Some figures are still not sufficiently readable, but I'll leave the final decision on publication to the editor.
Author Response
- Let's agree to disagree on some things. But that's probably fine, I guess. Some figures are still not sufficiently readable, but I'll leave the final decision on publication to the editor.
Response: Thank you for your comment. According to your question, we have reviewed all the pictures in the text and re-adjusted the clarity of Figure 3, Figure 6, Figure 7 (c) to make it more legible.
Author Response File: Author Response.pdf
