Pavement Performance and Mechanism of Asphalt Mixtures Reinforced with Different Diameters of Basalt Fibers for the Surface Layer

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper is solid in experimental design and analysis. However, it needs improvements in clarity, statistical reporting, and contextualization to strengthen its international impact. With revisions, it will be a valuable contribution to the pavement engineering field.

1. The abstract effectively summarizes the findings, but it is quite dense. Consider simplifying it so that the key results and implications are more easily grasped by readers outside the field.
2. The introduction identifies that fiber diameter has been insufficiently studied, but it could emphasize more strongly why this knowledge gap matters in practical pavement engineering.
3. The literature review is broad, but some of the most recent international works on nano-additives and hybrid fiber reinforcement in asphalt could be briefly referenced to contextualize the contribution.
4. The introduction should close with a clear statement of what makes this study new compared to earlier works on basalt fiber in asphalt mixtures.
5. The binder, aggregates, and fiber characterization are clear, but the rationale for selecting a 0.3% fiber content and 6 mm length should be more explicitly justified.
6. The study follows Chinese standards, which is acceptable, but the authors should briefly discuss how these align with international standards (AASHTO, ASTM) to increase the global relevance.
7. The explanation based on equal cross-section theory is well done, but it remains somewhat abstract. A simple illustrative diagram would help readers visualize the concept.
8. Since the study focuses on basalt fiber, it would be helpful to briefly contrast these results with previous findings for lignin, polyester, or synthetic fibers.
9. The paper shows significant improvements at low temperatures with 7 μm fibers. The discussion could benefit from explaining the physical reason why smaller fibers improve flexibility.
10. The IDEAL-CT and IDEAL-RT results are convincing, but the authors could better connect these findings to real-world fatigue and cracking performance in pavements.
11. The authors conclude that 7 μm fibers are optimal, but it would be valuable to discuss whether such fibers are economically viable and widely available for pavement projects.
12. The study does not explicitly acknowledge limitations (e.g., only one fiber length tested, no field validation). A short paragraph on limitations would improve transparency.
13. The authors are encouraged to refer to the following related study: 10.3390/su17125472

 

Author Response

1.The abstract effectively summarizes the findings, but it is quite dense. Consider simplifying it so that the key results and implications are more easily grasped by readers outside the field.

Response: Thank you for your valuable comment. We fully agree with your view and reorganize the abstrat. Please find it below.

The diameter of basalt fiber influences the reinforcement of basalt fiber asphalt mixtures. However, the performance evaluation and mechanistic analysis of asphalt mixtures reinforced with varying fiber diameters have been insufficiently studied. AC-13 asphalt mixtures were designed and prepared with four different fiber diameters 7 μm, 16 μm, 25 μm, and an equal-mass mixture of these. The reinforcement mechanisms were analyzed using the equal cross-section theory. Results indicate that the incorporation of 7 μm and mixed-diameter basalt fibers significantly enhances the pavement performance of asphalt mixtures compared to the control group without fibers. Additionally, it is shown by triaxial shear tests that the cohesion of asphalt mixtures with the aforementioned two diameters of basalt fibers is strengthened by 61.5% and 55.5%. The dynamic modulus values in the high-frequency range are found to be positively correlated with fiber diameters. Since the fiber mass content and modulus were held constant, a decrease in diameter was observed to lead to an increase in fiber quantity. This is manifested by a multiple-fold increase in the total transformed cross-section (TTC_R) index for 7 μm fiber asphalt mixtures, as described by the equal cross-section theory. It is concluded that the performance improvement of asphalt mixtures can be further enhanced under the same fiber content and cost conditions by optimizing diameter parameters.

2.The introduction identifies that fiber diameter has been insufficiently studied, but it could emphasize more strongly why this knowledge gap matters in practical pavement engineering.

Response: Thank you for your valuable comment. In response to your comment, we have strengthened the explanation in the introduction section to highlight why insufficient research on fiber diameter is a knowledge gap in practical pavement engineering. Fiber diameter is crucial because, for a fixed mass of fiber added, it dictates the trade-off between the number of fibers and their surface area. Thinner fibers are far more numerous, creating a dense network that greatly increases the bonding surface area with the asphalt binder. This enhanced network more effectively inhibits crack propagation and strengthens the mix's internal cohesion. While thicker fibers may slightly increase stiffness, thinner fibers provide superior overall reinforcement and durability under the same cost and material constraints, making diameter a key design parameter for optimizing pavement performance.

3.The literature review is broad, but some of the most recent international works on nano-additives and hybrid fiber reinforcement in asphalt could be briefly referenced to contextualize the contribution.

Response: Thank you for your insightful comment. In the revised manuscript, we have added the brief references to the recent international research works focusing on hybrid fiber reinforcement in asphalt mixtures. These addary contents can help readers better understand the benefits of nano-additives and hybrid fiber reinforcement in improving the performance of asphalt mixtures.

4.The introduction should close with a clear statement of what makes this study new compared to earlier works on basalt fiber in asphalt mixtures.

Response: Thank you for your valuable comment. We have revised the manuscript accordingly. At the end of the introduction, we have added a clear statement illustrating the novelty of this study in comparison with previous research on basalt fiber in asphalt mixtures.

5.The binder, aggregates, and fiber characterization are clear, but the rationale for selecting a 0.3% fiber content and 6 mm length should be more explicitly justified.

Response: We have enhanced the manuscript by incorporating a review of pertinent studies and their corresponding references in the introduction section. These additions provide detailed justification for selecting the specific parameter values of 0.3% fiber content and 6 mm fiber length.

6.The study follows Chinese standards, which is acceptable, but the authors should briefly discuss how these align with international standards (AASHTO, ASTM) to increase the global relevance.

Response: Thank you for your valuable comment. Regarding the alignment between the Chinese standards followed in this study and international standards, it should be noted that some of the Chinese standards adopted are consistent with the corresponding international standards. However, certain Chinese standards have been adjusted based on domestic practical conditions, including factors like local construction materials, regional temperature variations, and pavement load characteristics. Due to space constraints in the manuscript, it is not feasible to elaborate on the specific details of such alignment and adjustments. We appreciate your understanding in this regard.

7.The explanation based on equal cross-section theory is well done, but it remains somewhat abstract. A simple illustrative diagram would help readers visualize the concept.

Response: Thank you for your constructive comment. Regarding the visualization of the equal cross-section theory, please refer to Fig. 16 in the manuscript. This figure has already effectively illustrated the mechanism of the equal cross-section theory, which is expected to help readers better understand the related concept.

8.Since the study focuses on basalt fiber, it would be helpful to briefly contrast these results with previous findings for lignin, polyester, or synthetic fibers.

Response: Thank you for your valuable comment. It should be noted that basalt fiber is an inorganic mineral fiber, and its properties as well as the reinforcement mechanism it exerts on asphalt mixtures are completely different from those of lignin fibers, polyester fibers, and synthetic fibers. The authors have already conducted relevant discussions on this distinction during the performance analysis section of the manuscript.

9.The paper shows significant improvements at low temperatures with 7 μm fibers. The discussion could benefit from explaining the physical reason why smaller fibers improve flexibility.

Response: Thank you for your insightful comment. Regarding the physical reason why 7 μm fibers enhance the flexibility of asphalt mixtures at low temperatures, the analysis of Fig. 16 in the paper has already addressed this point. Specifically, as elaborated in the analysis: Basalt fibers interlace within the asphalt mixture and form bonds with the asphalt, which contributes to the toughening effect of the mixture. Furthermore, the overall deformation resulting from external loads counteracts displacement, thereby inhibiting crack propagation and effectively improving low temperature crack resistance of asphalt mixture.

10.The IDEAL-CT and IDEAL-RT results are convincing, but the authors could better connect these findings to real-world fatigue and cracking performance in pavements.

Response: Thank you for your valuable comment. First, it should be clarified that the IDEAL-CT and IDEAL-RT employed in this study are not the conventional indirect tensile tests. Notably, these two indicators have little correlation with the fatigue performance of pavements. Regarding the connection with cracking performance, we have added the relevant content about pavement cracking performance in the corresponding sections of the manuscript to better link the test results with practical pavement performance.

11.The authors conclude that 7 μm fibers are optimal, but it would be valuable to discuss whether such fibers are economically viable and widely available for pavement projects.

Response: Thank you for your valuable comment. Regarding the availability and economic viability of 7 μm fibers for pavement engineering projects, it should be clarified that all fibers with different diameters selected in this study can be produced in engineering practice and are commercially available in the market. As for the economic value of small-diameter fibers, their advantage lies in that, to achieve the same performance improvement effect on asphalt, the dosage of small-diameter fibers can be reduced. This reduction in fiber dosage effectively enhances the economic viability of using such fibers in pavement projects.

12.The study does not explicitly acknowledge limitations (e.g., only one fiber length tested, no field validation). A short paragraph on limitations would improve transparency.

Response: Thank you for your valuable comment. We fully agree that clarifying the study’s limitations is crucial for enhancing research transparency. In response, the authors have added a description of the study’s limitations at the end of the Conclusions section.

13.The authors are encouraged to refer to the following related study: 10.3390/su17125472

Response: Thank you for recommending the study Advancing Pavement Sustainability: Assessing Recycled Aggregates as Substitutes in Hot Mix Asphalt. After careful review, we note that this study mainly focuses on investigating the impact of using recycled concrete aggregates and reclaimed asphalt pavement aggregates as substitutes for natural aggregates on the performance of hot mix asphalt. However, the research object and core focus of this study differ from those of our manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

The reviewing paper presents a study on asphalt mixtures with basalt fibers of different diameters, focusing on how fiber size affects performance and reinforcement. Authors show that smaller (7 μm) and mixed-diameter fibers give clear improvements in strength and stiffness, pointing to the value of choosing the right fiber diameter for better pavement performance.

Although presented article may be interesting to the readers of Coatings journal, the paper may only be considered for publication after the following concerns have been addressed successfully in a revision:

1) I recommend adding a "Nomenclature" section to clearly define all abbreviations and symbols used in the text and equations. At present, some items, such as the names of test methods (standards) and certain subscripts, are not explained in enough detail, which may reduce clarity for readers. Furthermore, the unit symbols used in the equations are not always clearly indicated in the text. Please correct this and standardize it throughout the manuscript.

2) In my opinion, the introduction could be further strengthened to guide the reader more clearly. In particular, the concluding part would benefit from being more precise, highlighting the new research undertaken and its potential impact on the current state of knowledge. Including a clear thesis statement would also help frame the paper. One way to achieve this might be to begin the final paragraph with "The aim of this study..." and present the thesis in a concise and clear manner.

3) In my opinion, the quality of some images, such as Fig. 2, could be improved, as it is currently difficult to discern the differences clearly.

4) In the context of the presented results, I suggest considering a change to the title of Chapter 4 to simply "Results Discussion," with a subtitle "Mechanism Analysis Using the Equal Cross-Section Theory." This revision would likely present the reasoning behind the analysis of the observed mechanisms more coherently.

5) In the summary section, it could be helpful to include a discussion on how the presented results might be applied to future asphalt pavement design. Adding practical guidelines or recommendations—such as key points to consider and potential pitfalls to avoid—would make the section even more informative. Including some reference to the actual costs of implementing the proposed modifications could also provide valuable context for readers.

 

Author Response

1. I recommend adding a "Nomenclature" section to clearly define all abbreviations and symbols used in the text and equations. At present, some items, such as the names of test methods (standards) and certain subscripts, are not explained in enough detail, which may reduce clarity for readers. Furthermore, the unit symbols used in the equations are not always clearly indicated in the text. Please correct this and standardize it throughout the manuscript.

Response: Thank you for your constructive comment, which is of great significance for improving the readability and standardization of the manuscript. In response to your suggestion, we have added a summary section at the end of the manuscript, where all abbreviations and symbols appearing in the text are clearly defined and explained. This revision aims to address the issue of insufficient explanation of relevant items and ensure the standardization of symbols and units throughout the manuscript, thereby enhancing the clarity of the content for readers.

 

2. In my opinion, the introduction could be further strengthened to guide the reader more clearly. In particular, the concluding part would benefit from being more precise, highlighting the new research undertaken and its potential impact on the current state of knowledge. Including a clear thesis statement would also help frame the paper. One way to achieve this might be to begin the final paragraph with "The aim of this study..." and present the thesis in a concise and clear manner.

Response: Thank you for your valuable and constructive comment, which is instrumental in enhancing the clarity and guidance of the introduction. To address your suggestions, we have made targeted revisions to the introduction section. Specifically, we have added a clear thesis statement in the introduction. This revision makes the concluding part of the introduction more precise, clearly highlights the core content of the new research, and helps to frame the paper effectively, thereby better guiding readers to understand the research focus and its potential academic impact.

 

3. In my opinion, the quality of some images, such as Fig. 2, could be improved, as it is currently difficult to discern the differences clearly.

Response: Thank you for your valuable comment. We fully agree that improving image quality is crucial for readers to clearly discern relevant differences. To address this issue, we have replaced the low-quality images in the manuscript with higher-quality versions. The revised images are clearer and more detailed, which will help readers better understand the content presented in the figures.

 

4.In the context of the presented results, I suggest considering a change to the title of Chapter 4 to simply "Results Discussion," with a subtitle "Mechanism Analysis Using the Equal Cross-Section Theory." This revision would likely present the reasoning behind the analysis of the observed mechanisms more coherently.

Response: Thank you for your valuable suggestion. We have revised the title of Chapter 4 in accordance with your recommendation.

 

5. In the summary section, it could be helpful to include a discussion on how the presented results might be applied to future asphalt pavement design. Adding practical guidelines or recommendations—such as key points to consider and potential pitfalls to avoid—would make the section even more informative. Including some reference to the actual costs of implementing the proposed modifications could also provide valuable context for readers.

Response: Thank you for your valuable and constructive comment. We have revised the summary section of the manuscript. Specifically, regarding the application of the study results to future asphalt pavement design, we propose that in the future, fiber manufacturers may consider producing fiber products with a mixture of different diameters for direct use in pavement engineering projects. This proposal requires further verification through subsequent research and practical trials to ensure its feasibility and effectiveness in actual engineering scenarios.