Study of Microwave Healing Properties of Carbonyl-Iron-Powder-Modified Asphalt Mixture Based on Digital Image Technology

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript addresses a highly relevant topic, particularly regarding the development of novel techniques to enhance the self-healing properties of asphalt mixtures. Introducing non-conventional materials into asphalt mixtures introduces a strong sustainability aspect and, above all, promotes the improvement of pavement performance in terms of service life, durability, and reduced maintenance costs.

Despite the importance of the topic, the manuscript contains several issues and inconsistencies that need to be addressed to improve its overall quality and align it with the journal’s publication standards. My specific comments and suggestions are outlined below:

(1) Among the various tests available to evaluate the influence of temperature on the self-healing properties of asphalt mixtures (e.g., three-point bending, SCB, four-point bending, etc.), the authors chose the SCB test. Is there a specific reason for this choice? The manuscript lacks any justification, which could be due to equipment availability or other reasons. If such justification exists, it should be clearly explained.

(2) The manuscript contains numerous grammatical and syntactic errors, including inconsistent verb tenses, typographical mistakes, and unclear sentence structures.

(3) The Introduction discusses heating methods to enhance the self-healing properties of asphalt mixtures. However, to enrich the discussion and improve the overall quality of the manuscript, the authors should consider including other approaches that have shown potential in improving self-healing, such as the use of rejuvenators or encapsulated systems (capsules). This would provide the reader with a broader perspective on available techniques.

I suggest adding the following references to include the capsule-based self-healing approach:

• Câmara, G., Micaelo, R. & Monteiro Azevedo, N. 3D DEM model simulation of asphalt mastics with sunflower oil. Part. Mech. 10, 1569–1586 (2023). https://doi.org/10.1007/s40571-023-00574-1
• Câmara, G., Azevedo, N. M., & Micaelo, R. (2025). Self-Healing Asphalt Mixtures Meso-Modelling: Impact of Capsule Content on Stiffness and Tensile Strength. Sustainability, 17(16), 7502. https://doi.org/10.3390/su17167502

(4) The research gap and study objectives are not clearly stated and should be explicitly defined.

(5) Heating methods can be effective in enhancing the self-healing capabilities of asphalt materials by raising the temperature and thereby reducing the binder’s viscosity to facilitate crack closure. Additionally, the inclusion of micro-sized carbonyl iron powder contributes to a further increase in temperature. However, these methods come with limitations, such as binder aging. The potential aging of the binder, especially in undamaged areas of the mixture, raises concerns. Can the authors justify this risk?

(6) Units and measurement scales should be formatted consistently throughout the manuscript.

(7) The quality of some figures must be improved (e.g., Figures 7 and 8).

(8) There are systematic formatting errors when reporting values and their corresponding units (e.g., “68.8ºC,” “40s”, 2.45GHz, and so on). Please ensure consistent spacing and formatting for units (e.g., “68.8 ºC,” “40 s”, 2.45 GHz, and so on).

(9) When introducing the meaning of variables in equations, the word “where” should not be capitalized and must be left-aligned.

(10) All variables used in equations must be clearly explained in the main text.

(11) Several references in the main text are incorrect or broken (e.g., Error! Reference source not found.). These issues should be corrected consistently throughout the manuscript.

(12) Some figures are not sufficiently described in the text, and some captions lack detail (e.g., Figure 9). Additionally, subfigures should be referenced using their full labels in the main text (i.e., Figure 9(a), 9(b), etc.). In Figure 11, the subfigure labels (a), (b), and (c) are embedded within the general caption, making them difficult to read.

(13) The axis labels and corresponding values in many graphs are too small to read. Consider adjusting the formatting for better readability, if possible.

(14) In Figure 5, there is a description – either of the equipment or test setup – written in Chinese. Since the article is written in English, and the journal requires English standards, the authors should consider translating this content or modifying the figure accordingly. If modifying the image is not feasible, the figure caption should include a clear English translation of the text.

(15) Asphalt mixtures containing metallic filler can behave significantly differently under microwave treatment compared to conventional mixtures. Why did the authors choose 20% carbonyl iron powder in this study? Was this percentage based on previous research? The authors should justify this choice, as readers may question whether smaller quantities could also enhance self-healing properties.

(16) The reported heating time of 120 seconds to reach 68.8 ºC seems excessive. Even with the addition of carbonyl iron powder, a prolonged heating time was still required. Was this time expected? What would happen if the quantity of carbonyl iron powder were increased? While this is a promising technique, such extended durations may be impractical for real-world pavement applications.

(17) A sensitivity analysis of the carbonyl iron powder content should be considered to potentially reduce microwave exposure time and achieve more suitable heating profiles for real-world self-healing applications. These points, along with those mentioned previously, should be discussed in a final note, either as limitations of the current study or as recommendations for future research.

 

These limitations should be explicitly acknowledged and discussed in the revised version of the manuscript.

Comments on the Quality of English Language

The manuscript should be revised for English language clarity.

Author Response

Comments 1:[Among the various tests available to evaluate the influence of temperature on the self-healing properties of asphalt mixtures (e.g., three-point bending, SCB, four-point bending, etc.), the authors chose the SCB test. Is there a specific reason for this choice? The manuscript lacks any justification, which could be due to equipment availability or other reasons. If such justification exists, it should be clearly explained.]

Response 1: [The Semi-Circular Bending (SCB) test was selected mainly because of its stable and reliable test results, and we have supplemented relevant literature citations to support this selection reason.] Thank you for pointing this out. We agree with this comment. Therefore we have listed the reasons and references explain what change I have made. This revision can be located in the revised manuscript at Page 5, Paragraph 1, Lines 143-145.

[updated text in the manuscript: “Given that the test results of the Semi-Circular Bending (SCB) test are stable and reliable[30], the cylindrical specimens were cut into SCB specimens for the microwave healing test.”]

Comments 2:[The manuscript contains numerous grammatical and syntactic errors, including inconsistent verb tenses, typographical mistakes, and unclear sentence structures.]

Response 2: [Systematic revisions have been completed to address issues in the manuscript such as grammatical errors, syntactic problems, formatting omissions, and unclear sentence structures. The revised version has been uploaded. If you have any questions about the revisions or need further adjustments, please feel free to inform us. Thank you for your review.] Thank you for pointing this out. We agree with this comment.

Comments 3:[The Introduction discusses heating methods to enhance the self-healing properties of asphalt mixtures. However, to enrich the discussion and improve the overall quality of the manuscript, the authors should consider including other approaches that have shown potential in improving self-healing, such as the use of rejuvenators or encapsulated systems (capsules). This would provide the reader with a broader perspective on available techniques.]

Response 3: [As requested, two references, namely "3D DEM model simulation of asphalt mastics with sunflower oil" and "Self-Healing Asphalt Mixtures Meso-Modelling: Impact of Capsule Content on Stiffness and Tensile Strength", have been added.] Thank you for pointing this out. We agree with this comment. Therefore, the references have been listed in the main text. This revision can be located in the revised manuscript at Page 2, Paragraph 1, Lines 47-49.

[updated text in the manuscript: “At present, the ways to promote the healing of asphalt mixture include electromagnetic induction heating method[2], microwave heating method[3], infrared heating method[4] and microcapsule method[5,6].”]

Comments 4:[The research gap and study objectives are not clearly stated and should be explicitly defined.]

Response 4: [The research objectives of this paper have been clearly stated.] Thank you for pointing this out. We agree with this comment. Therefore, the research objectives of this paper have been further elaborated. This revision can be located in the revised manuscript at Page 3, Paragraph 2, Lines 101-109.

[updated text in the manuscript: “The purpose of this study is to provide a theoretical basis for the application of microwave thermally induced carbonyl iron powder asphalt mixture preventive maintenance technology. To this end, micron-sized carbonyl iron powder is used to partially replace mineral powder to enhance the overall microwave absorption and healing capabilities of the asphalt mixture. Meanwhile, the optimal microwave-induced healing heating method is determined by analyzing its microwave heating behavior, and combined with the research on the healing performance of asphalt mixture under multiple influencing factors, the optimal maintenance scheme for microwave thermal induction is further clarified.”]

Comments 5:[Heating methods can be effective in enhancing the self-healing capabilities of asphalt materials by raising the temperature and thereby reducing the binder’s viscosity to facilitate crack closure. Additionally, the inclusion of micro-sized carbonyl iron powder contributes to a further increase in temperature. However, these methods come with limitations, such as binder aging. The potential aging of the binder, especially in undamaged areas of the mixture, raises concerns. Can the authors justify this risk?]

Response 5: [The aging risk of binders caused by micron-sized carbonyl iron powder-assisted heating is essentially a contradiction between "local repair demand" and "overall material stability". This contradiction needs to be alleviated by optimizing heating parameters (such as precise control of heating temperature and duration), improving iron powder modification processes (such as coating treatment to reduce the catalytic aging effect on asphalt), or combining anti-aging additives. Only in this way can the coordinated improvement of repair efficiency and long-term performance be achieved.] Thank you for pointing this out. We agree with this comment.

Comments 6:[Units and measurement scales should be formatted consistently throughout the manuscript.]

Response 6: [The format of units and measurement scales has been adjusted to a consistent format in all figures and tables throughout the full text.] Thank you for pointing this out. We agree with this comment.

Comments 7:[The quality of some figures must be improved (e.g., Figures 7 and 8).]

Response 7: [Figures 7 and 8 have been appropriately revised, while other images (including Figures 9, 11, 14, and 15) have been modified by enlarging them to improve clarity.] Thank you for pointing this out. We agree with this viewpoint and have made corresponding revisions.

Comments 8:[There are systematic formatting errors when reporting values and their corresponding units (e.g., “68.8ºC,” “40s”, 2.45GHz, and so on). Please ensure consistent spacing and formatting for units (e.g., “68.8 ºC,” “40 s”, 2.45 GHz, and so on).]

Response 8: [The entire text has been checked and corresponding revisions have been made.] Thank you for pointing this out. We agree with this comment.

Comments 9:[When introducing the meaning of variables in equations, the word “where” should not be capitalized and must be left-aligned.]

Response 9: [When introducing the meanings of variables in equations, the word "where" should not be capitalized and must be left-aligned. Revisions have been made in the text accordingly.] Thank you for pointing this out. We agree with this comment. Therefore, Revisions have been made in the text accordingly. This revision can be located in the revised manuscript at Page 24, Paragraph 3 and 5, Lines 725,736.

[updated text in the manuscript: ”where P is the microwave power...”,“where T is the final temperature....”]

Comments 10:[All variables used in equations must be clearly explained in the main text.]

Response 10: [All variables used in the equations have been clearly explained in the main text.] Thank you for pointing this out. We agree with this comment.

Comments 11:[Several references in the main text are incorrect or broken (e.g., Error! Reference source not found.). These issues should be corrected consistently throughout the manuscript.]

Response 11: [The references have been revised accordingly.] Thank you for pointing this out.

Comments 12:[Some figures are not sufficiently described in the text, and some captions lack detail (e.g., Figure 9). Additionally, subfigures should be referenced using their full labels in the main text (i.e., Figure 9(a), 9(b), etc.). In Figure 11, the subfigure labels (a), (b), and (c) are embedded within the general caption, making them difficult to read.]

Response 12: [Descriptions for Figures 9(a) and 9(b) have been revised, and revised explanations have also been added for Figures 11(a), 11(b), and 11(c).] Thank you for pointing this out. We agree with this comment. Therefore, the descriptions of Figure 9 and Figure 11 have been revised. This revision can be located in the revised manuscript at Page 9,11, Paragraph 4,3, Lines 298-302,353-356.

[updated text in the manuscript: “The three figures on the left of Figure 9(a) and Figure 9(b) are respectively the 2D surface temperature distribution diagrams of semi-circular specimens of ordinary asphalt mixture and carbonyl iron powder asphalt mixture after being heated for 40s, 80s, and 120s. The figure on the far right is the 3D surface temperature distribution diagram of the specimens heated for 120s. ”,”The upper graphs in Figure 11(a), 11(b), and 11(c) represent the 2D distribution maps of the surface temperature of the test piece heated for 120 seconds, while the corresponding lower graphs represent the 3D distribution maps of the surface temperature of the test piece. ”]

Comments 13:[The axis labels and corresponding values in many graphs are too small to read. Consider adjusting the formatting for better readability, if possible.]

Response 13: [The axis labels and corresponding values in the charts/graphs have been adjusted.] Thank you for pointing this out.

Comments 14:[In Figure 5, there is a description–either of the equipment or test setup – written in Chinese. Since the article is written in English, and the journal requires English standards, the authors should consider translating this content or modifying the figure accordingly. If modifying the image is not feasible, the figure caption should include a clear English translation of the text.]

Response 14: [The text in Figure 5 has been translated into English.] Thank you for pointing this out. We agree with this comment. Therefore, the text in Figure 5 has been translated into English.

Comments 15:[Asphalt mixtures containing metallic filler can behave significantly differently under microwave treatment compared to conventional mixtures. Why did the authors choose 20% carbonyl iron powder in this study? Was this percentage based on previous research? The authors should justify this choice, as readers may question whether smaller quantities could also enhance self-healing properties.]

Response 15: [The previous study "Study on the self-healing behavior and rheological properties of carbonyl iron powder-modified asphalt mastic induced by microwave heating" adopted the equal-volume replacement method, replacing mineral powder with carbonyl iron powder at equal volumes in proportions of 20%, 40%, 60%, 80%, and 100% respectively. Finally, it was concluded that the performance was optimal when the replacement proportion was 20%.] Thank you for pointing this out. We agree with this comment. This revision can be located in the revised manuscript at Page 4, Paragraph 1, Lines 125-127.

[updated text in the manuscript: “The AC-16 type asphalt mixture was adopted, with the design proportion of carbonyl iron powder replacing mineral powder (≤0.075mm) set at 20%, which showed the best microwave healing ability in the preliminary research results[29].”]

Comments 16:[The reported heating time of 120 seconds to reach 68.8 ºC seems excessive. Even with the addition of carbonyl iron powder, a prolonged heating time was still required. Was this time expected? What would happen if the quantity of carbonyl iron powder were increased? While this is a promising technique, such extended durations may be impractical for real-world pavement applications.]

Response 16: [Currently, the 120-second heating duration is a "phased result" under laboratory-controlled conditions, rather than a final index for engineering applications. By optimizing the dosage, upgrading equipment, and adapting to scenarios, the issue of heating duration can be effectively addressed, promoting the technology from "feasible in the laboratory" to "practical in engineering"—this is also the core direction for the subsequent in-depth research of this study.] Thank you for pointing this out. We agree with this comment.

Comments 17:[A sensitivity analysis of the carbonyl iron powder content should be considered to potentially reduce microwave exposure time and achieve more suitable heating profiles for real-world self-healing applications. These points, along with those mentioned previously, should be discussed in a final note, either as limitations of the current study or as recommendations for future research.]

Response 17: [The dosage of carbonyl iron powder needs to balance high-temperature performance, low-temperature performance, microwave heating temperature-sensitive performance, and self-healing performance. Relevant research has been conducted in the previous study on the self-healing behavior and rheological properties of carbonyl iron powder-modified asphalt mastic based on microwave induction. However, no corresponding research has been carried out on asphalt mixtures. The current research has certain limitations, which can serve as a direction for future research.] Thank you for pointing this out. We agree with this comment. This revision can be located in the revised manuscript at Page 25, Paragraph 6, Lines 771-777.

[updated text in the manuscript: “(6)The dosage of carbonyl iron powder needs to balance high-temperature performance, low-temperature performance, microwave heating temperature sensitivity, and healing performance. Relevant studies have been conducted in the previous research on the self-healing behavior and rheological properties of carbonyl iron powder-modified asphalt mortar based on microwave induction. However, no corresponding research has been carried out on asphalt mixtures. The current research has certain limitations, which can serve as a direction for future studies.”]

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

1. The literature review should be expanded to include information on silicon carbide (SiC), which is a highly effective microwave-absorbing material. SiC has been widely reported to promote self-healing of microcracks in coatings through microwave heating technology, and therefore has direct relevance for road repair and maintenance applications.
2. In addition to the technical indicators of the fillers, it would be valuable to provide their mineralogical composition.
3. The figures should be enlarged and reformatted to improve clarity and readability.
4. The article does not explain why Superpave rotary compaction was selected for specimen preparation. A comparison with alternative sample preparation methods for microwave healing would strengthen the justification for using the Superpave compactor.
5. In Section 2.4 (Test method), it should be clarified whether the described DIC testing procedure was developed by the authors or adopted from existing literature (with appropriate references). It would also be useful to report the camera specifications and the estimated DIC measurement error.
6. The choice of 20% filler replacement is justified only by a citation to “previous studies.” Additional evidence or experimental comparison should be provided to demonstrate why this replacement level is optimal.
7. For the SCB test, a more detailed description of the calibration of the measurement system is required, including camera accuracy and the quantification of DIC error.

Author Response

Comments 1:[The literature review should be expanded to include information on silicon carbide (SiC), which is a highly effective microwave-absorbing material. SiC has been widely reported to promote self-healing of microcracks in coatings through microwave heating technology, and therefore has direct relevance for road repair and maintenance applications.]

Response 1: [The reference "Microwave Self-healing Properties and Reasonable Content of Silicon Carbide Powder Modified Asphalt Mixtures" has been added.] Thank you for pointing this out. We agree with this comment. Therefore, relevant literature on microwave heating repair of microcracks using silicon carbide has been included. This revision can be located in the revised manuscript at Page 2, Paragraph 2, Lines 56-57.

[updated text in the manuscript: “Examples include replacing aggregates with magnetite, steel slag, etc., replacing mineral powder with silicon carbide powder, or incorporating carbon fibers, steel fibers, and other materials[11-13]. ”]

Comments 2:[In addition to the technical indicators of the fillers, it would be valuable to provide their mineralogical composition.]

Response 2: [The mineral composition of the filler has been added in Table 3.] Thank you for pointing this out. We agree with this comment. Therefore, the mineral composition of the filler has been added in Table 3.

Comments 3:[The figures should be enlarged and reformatted to improve clarity and readability.]

Response 3: [All charts and figures have been enlarged and retypeset to improve clarity and readability.] Thank you for pointing this out. We agree with this comment. Therefore, all charts and figures have been enlarged and retypeset to improve clarity and readability.

Comments 4:[The article does not explain why Superpave rotary compaction was selected for specimen preparation. A comparison with alternative sample preparation methods for microwave healing would strengthen the justification for using the Superpave compactor.]

Response 4: [Because the Superpave gyratory compaction method can simulate the vertical extrusion and horizontal kneading of the on-site roller, accurately control the compactness, and avoid aggregate segregation to ensure the uniform structure of the specimen, so that the test results of the specimen performance can truly reflect the actual situation of the on-site pavement, this study uses Superpave gyratory compaction equipment to prepare cylindrical specimens.] Thank you for pointing this out. We agree with this comment. Therefore, the Superpave Gyratory Compaction method was selected to prepare the test specimens. This revision can be located in the revised manuscript at Page 4, Paragraph 2, Lines 137-142.

[updated text in the manuscript: “Since the Superpave Gyratory Compaction (SGC) method can simulate the vertical compaction and horizontal kneading effects of on-site road rollers, accurately control the degree of compaction, and avoid aggregate segregation to ensure the uniform structure of specimens—thereby enabling the performance test results of specimens to truly reflect the actual conditions of on-site pavement—this study used Superpave gyratory compaction equipment to prepare cylindrical specimens (asphalt temperature: 140℃, aggregate temperature: 175℃, mixing temperature: 165℃). ”]

Comments 5:[In Section 2.4 (Test method), it should be clarified whether the described DIC testing procedure was developed by the authors or adopted from existing literature (with appropriate references). It would also be useful to report the camera specifications and the estimated DIC measurement error.]

Response 5: [The test procedure for Digital Image Correlation (DIC) draws on the existing literature DIC Technique to Investigate Crack Propagation in Grid-Reinforced Asphalt Specimens.] Thank you for pointing this out. We agree with this comment. The test procedure for Digital Image Correlation (DIC) draws on the existing literature DIC Technique to Investigate Crack Propagation in Grid-Reinforced Asphalt Specimens, with additional references supplemented.This revision can be located in the revised manuscript at Page 5, Paragraph 3, Lines 168.

Comments 6:[The choice of 20% filler replacement is justified only by a citation to “previous studies.”Additional evidence or experimental comparison should be provided to demonstrate why this replacement level is optimal.]

Response 6: [The previous study "Study on the self-healing behavior and rheological properties of carbonyl iron powder-modified asphalt mastic induced by microwave heating" adopted the equal-volume replacement method, replacing mineral powder with carbonyl iron powder at equal volumes in proportions of 20%, 40%, 60%, 80%, and 100% respectively. Finally, it was concluded that the performance was optimal when the replacement proportion was 20%.] Thank you for pointing this out. We agree with this comment. This revision can be located in the revised manuscript at Page 4, Paragraph 1, Lines 125-127.

Comments 7:[For the SCB test, a more detailed description of the calibration of the measurement system is required, including camera accuracy and the quantification of DIC error.]

Response 7: [high-speed camera (Model: MD1200TV, Resolution: 1280 pixels×960 pixels).Finally, calibrate the shooting area range: use a ±0.5μm ceramic calibration plate (attached to the surface of the mixture), capture 15~20 sets of images to inversely calculate the pixel Pitch≈15.6μm (with a standard deviation < 0.05μm), control the residual distortion to be < 2μm, and verify the error with a 5mm standard block to be <±0.5μm. For binocular calibration, capture 10 sets of images at the test temperature to ensure the reprojection error is <0.3 pixels, the coordinate error corrected by the laser displacement meter is <±2μm, and the verification error of 10μm micro-displacement is <±0.5μm.] Thank you for pointing this out. We agree with this viewpoint and have made corresponding revisions. This revision can be located in the revised manuscript at Page 5, Paragraph 3, Lines 170,175-182.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Applied Science- Round 1

Title: Study on microwave healing properties of carbonyl iron powder modified asphalt mixture based on digital image technology

Overview: The manuscript presents an experimental study comparing a carbonyl iron powder asphalt mixture with a conventional mixture in terms of microwave healing performance, evaluated through digital imaging and the semi-circular bending test. The research concept and experimental design are appropriate and relevant to the field, and the reported results are consistent with the experimental findings. Nevertheless, the manuscript requires substantial improvement in the clarity and precision of the text.

Major comments:

• Abstract and featured application review: The Featured Application section substantially overlaps with the Abstract. As this section is not mandatory, I recommend retaining only the Abstract.
• Introduction: The paragraph from lines 58–93 is well written but excessively long. Shortening it would improve clarity and comprehension. The same applies to the paragraph from lines 94–119.
• Materials: The mixture design was developed using the Marshall method, whereas the semi-circular samples were compacted with the Superpave gyratory compactor. Since these are different compaction methods, the mixture design should ideally also follow the Superpave method to ensure consistency of the experimental methodology.
  • Section 2.1 - (Table 1): More information about the asphalt should be provided, such as density and mass loss after TFOT.
  • Section 2.2 - It is important to specify which sieves (mesh sizes) the 20% carbonyl powder is replacing.

Table 4 - The optimum asphalt content should be included. In addition, parameter names should follow standard technical terminology (e.g., Porosity should be denoted as VIM – Voids in the Mix).

• Section 2.3 - The asphalt temperature, aggregate temperature, and mixing temperature should be reported for the specimen preparation.

Line 187 – Please clarify the capture image intervals.

• Section 2.5.2 - Equations (3) and (4) are referenced but not presented in the text. These should be included.

- Results: Several paragraphs in the Results section are excessively long, which makes them difficult to follow. The text should be shortened and written in a more concise and incisive manner.

• At line 554, there is a statement regarding a modified asphalt emulsion. However, no details about this material are provided in the Materials and Methods section. This information should be clarified and described.

Minor comments:

• Line 49: The text states “static conditions.” Should this be “dynamic conditions”? Please clarify.
• Line 59: A supporting reference is needed for this statement.
• Line 72: A supporting reference is needed for this statement.
• Line 112: A supporting reference is needed for this statement.
• Lines 210, 217, 332, 427, 607, 690: Missing citations. Please provide appropriate references.
• Line 212: Revise punctuation — e.g., “… microwave: heating time …”.
• Figure 11: Requires improved formatting for clarity.

Author Response

Comments 1:[Abstract and featured application review: The Featured Application section substantially overlaps with the Abstract. As this section is not mandatory, I recommend retaining only the Abstract.]

Response 1: [This study is based on the use of carbonyl iron powder to replace part of the mineral powder, and investigates the healing effect of carbonyl iron powder asphalt mixture after microwave heating. The research results can provide technical references for the engineering application of microwave heating in repairing cracks of asphalt mixture.] Thank you for pointing this out. We agree with this comment. Therefore, a concise description has been made for the Featured Application section. This revision can be located in the revised manuscript at Page 1, Paragraph 1, Lines 12-15.

[updated text in the manuscript: “This study is based on the use of carbonyl iron powder to replace part of the mineral powder, and investigates the healing effect of carbonyl iron powder asphalt mixture after microwave heating. The research results can provide technical references for the engineering application of microwave heating in repairing cracks of asphalt mixture.”]

Comments 2:[ntroduction: The paragraph from lines 58–93 is well written but excessively long. Shortening it would improve clarity and comprehension. The same applies to the paragraph from lines 94–119.]

Response 2: [Concise descriptions have been made for Lines 58-93 and Lines 94-119 of the original text.] Thank you for pointing this out. We agree with this comment.

Comments 3:[Materials: The mixture design was developed using the Marshall method, whereas the semi-circular samples were compacted with the Superpave gyratory compactor. Since these are different compaction methods, the mixture design should ideally also follow the Superpave method to ensure consistency of the experimental methodology.]

Response 3: [We would like to thank the reviewer for pointing out the inconsistency between the mixture design method (Marshall method) and the compaction method for semi-circular specimens (Superpave Gyratory Compactor). Your comments are of great value for improving the rigor of the experiment.In the study design phase of this research, full consideration was given to compatibility. By taking "target air voids" (with a deviation of ≤ 0.5% from the optimal air voids of the Marshall method) and "bulk specific gravity" as the core control indicators, the number of Superpave gyratory compactions was adjusted (Ndesign±2 times) to ensure that the compaction state of the semi-circular specimens was consistent with the Marshall design benchmark. Preliminary experiments showed that the difference in the mechanical properties of the mixture between the two compaction methods under the same mix proportion was < 5% (meeting the allowable error range).Meanwhile, the kneading effect of Superpave gyratory compaction is more suitable for the curved surface of semi-circular specimens, which can avoid uneven edge density caused by Marshall compaction and reduce systematic errors. In subsequent studies, we plan to optimize the mix proportion based on the Superpave design system and compare and verify it with the results of this study, so as to further ensure the consistency of experimental methods and improve the universality of conclusions.] Thank you for pointing this out. We agree with this comment.

Comments 4:[Section 2.1 - (Table 1): More information about the asphalt should be provided, such as density and mass loss after TFOT.]

Response 4: [The density and the mass loss after the Thin Film Oven Test (TFOT) are listed in Table 1.] Thank you for pointing this out. We agree with this comment.

Table 1. Technical indexes of 90# matrix asphalt  

Technical Specifications	Penetration (25℃,5s,100g)/0.1mm	Ductility (10℃)/ cm	Softening Point /℃	Dynamic Viscosity (60℃)/ Pa. s	Density/g/cm3	Mass loss ( after TFOT )/%
Measured Value	90	55	46	190	1.02	0.5

Comments 5:[Section 2.2 - It is important to specify which sieves (mesh sizes) the 20% carbonyl powder is replacing.]

Response 5: [The AC-16 type asphalt mixture was adopted, with the design proportion of carbonyl iron powder replacing mineral powder (≤0.075mm) set at 20%, which showed the best microwave healing ability in the preliminary research results[29].] Thank you for pointing this out. We agree with this comment. This revision can be located in the revised manuscript at Page 4, Paragraph 1, Lines 126.

Comments 6:[Table 4 - The optimum asphalt content should be included. In addition, parameter names should follow standard technical terminology (e.g., Porosity should be denoted as VIM – Voids in the Mix).]

Response 6: [Table 4 already includes the optimal asphalt-aggregate ratio. The parameter names have been revised in accordance with standard technical terms (for example, the air voids in the mixture is denoted as VIM, the voids in mineral aggregate as VV, and the asphalt saturation as VFA).] Thank you for pointing this out. We agree with this comment.

Carbonyl Iron Powder Replacement Ratio/%	Optimal Asphalt-Aggregate Ratio/%	Bulk Specific Gravity/g/cm3	VV/%	VMA/%	VFA/%	Stability /kN	Flow Value /mm
0	4.62	2.760	4.0	14.2	69.1	17.52	3.01
20	4.58	2.755	3.9	13.8	70.2	16.28	3.23

Comments 7:[Section 2.3 - The asphalt temperature, aggregate temperature, and mixing temperature should be reported for the specimen preparation.]

Response 7: [asphalt temperature: 140℃, aggregate temperature: 175℃, mixing temperature: 165℃] Thank you for pointing this out. We agree with this viewpoint and have made corresponding revisions. Therefore, the following parameters have been provided: asphalt temperature: 140℃, aggregate temperature: 175℃, and mixing temperature: 165℃.This revision can be located in the revised manuscript at Page 4, Paragraph 2, Lines 142-143.

Comments 8:[Line 187–Please clarify the capture image intervals.]

Response 8: [The high-speed cameras continuously capture the position changes of the tracking points on the specimen surface, with an image capture time interval of 0.01s. ] Thank you for pointing this out. We agree with this comment. This revision can be located in the revised manuscript at Page 6, Paragraph 1, Lines 186.

Comments 9:[Section 2.5.2 - Equations (3) and (4) are referenced but not presented in the text. These should be included.]

Response 9: [The calculation formula for fracture energy is shown in Equation (2), among which the calculation formula for fracture work is shown in Equation (3)[38].According to the above method, the test results of the same mixture specimen before and after healing are calculated, and the fracture energy ratio is used as the healing evaluation index to carry out quantitative analysis on the healing performance of the asphalt mixture. The larger the healing index HIU, the better the healing effect. The calculation is shown in Equation (4).] Thank you for pointing this out. We agree with this comment. Therefore, Revisions have been made in the text accordingly. This revision can be located in the revised manuscript at Page 9, Paragraph 1 and 2, Lines 277,282.

Comments 10:[Results: Several paragraphs in the Results section are excessively long, which makes them difficult to follow. The text should be shortened and written in a more concise and incisive manner.]

Response 10: [(1)Carbonyl iron powder asphalt mixture exhibits excellent heat uniformity and linear temperature rise characteristics. Its heating rate is increased by 16.1% with more uniform heating; the average temperature reaches 68.8℃ after 120 seconds of heating, which can meet the healing temperature requirement of asphalt mixture.

(2)The heating temperatures of carbonyl iron powder asphalt mixture under continuous and intermittent heating are basically the same. Intermittent heating has no heat loss and better heating uniformity, and the optimal microwave heating method is a 3-cycle process of "heating for 40s-resting for 2min".

(3)When the wave absorber is mixed into the asphalt mixture as a filler, it can improve the microwave heating efficiency, thereby enhancing the self-healing performance of the mixture.

(4)The macroscopic fracture energy healing index HIU is highly correlated with the mesoscopic crack initiation time healing index HIt, and multi-scale evaluation can improve the reliability of conclusions. Carbonyl iron powder significantly improves the healing effect of the mixture, and the optimal healing effect is achieved under the best condition of microwave heating for 100s (at a temperature of 60℃).

(5)External factors have a significant impact on the healing effect of carbonyl iron powder asphalt mixture, with the order of influence being: microwave heating time > damage degree > standing time. The optimal healing scheme is: heating for 100s, standing for 4h, and performing healing at the initial stage of damage (before crack initiation).] Thank you for pointing this out. We agree with this comment.

Comments 11:[At line 554, there is a statement regarding a modified asphalt emulsion. However, no details about this material are provided in the Materials and Methods section. This information should be clarified and described.]

Response 11: [The translation here is incorrect; "Emulsion" has been revised to "mortar".] Thank you for pointing this out.We agree with this comment. This revision can be located in the revised manuscript at Page 19, Paragraph 1 , Lines 568.

Comments 12:[Line 49: The text states “static conditions.” Should this be “dynamic conditions”? Please clarify.]

Response 12: [In the text, "static conditions" are defined as conditions that rely solely on ambient temperature, with no vehicle loads and no active heating.] Thank you for pointing this out. We agree with this comment.

Comments 13:[Line 59: A supporting reference is needed for this statement.]

Response 13: [The traditional asphalt mixture has weak microwave absorption capacity, which cannot meet the requirements for microwave-induced heating and healing[10]. ] Thank you for pointing this out. We agree with this comment. Optimize the description and incorporate Reference [10].This revision can be located in the revised manuscript at Page 2, Paragraph 2 , Lines 52-53.

Comments 14:[Line 72: A supporting reference is needed for this statement.]

Response 14: [Therefore, the description of the original text has been optimized, and Reference [14] has been incorporated.] Thank you for pointing this out. We agree with this comment.This revision can be located in the revised manuscript at Page 2, Paragraph 2 , Lines 62.

Comments 15:[Line 112: A supporting reference is needed for this statement.]

Response 15: [Therefore, this study adopts digital image correlation (DIC) technology to evaluate self-healing performance[27]] Thank you for pointing this out. We agree with this comment. This revision can be located in the revised manuscript at Page 3, Paragraph 1, Lines 92.

Comments 16:[Lines 210, 217, 332, 427, 607, 690: Missing citations. Please provide appropriate references.]

Response 16: [The first loading[31] was applied at a rate of 50mm/min . Data was collected using load sensors and displacement meters, and the load-displacement curve was automatically plotted. When the applied load decreased to 50% of the peak load (setting the damage level to 50%), the test was automatically terminated[32]. After the resting period, the specimen was placed back into an environment chamber at 15℃ for 4 hours of insulation, followed by a second loading, completing the test[33].

The reason is that carbonyl iron powder asphalt mortar can achieve uniform heating after absorbing the wave, and then transfer heat to the asphalt mortar and aggregate. At the same time, aggregate absorbs wave as another heat source to transfer heat together[39,40], so that the overall temperature of asphalt mixture increases uniformly.

macroscopic cracks start to appear on the specimen surface[42].

The content described in Line 607 is experimental reasoning, and Line 690 presents reasoning based on experimental results; therefore, no references have been added at these two positions.]Thank you for pointing this out. We agree with this comment.

Comments 17:[Line 212: Revise punctuation — e.g., “… microwave: heating time …”.]

Response 17: [We are very sorry that the corresponding position was not found. If there is any error, it will be corrected in a timely manner.] Thank you for pointing this out. We agree with this comment.

Comments 18:[Figure 11: Requires improved formatting for clarity.]

Response 18: [Figure 11 has been revised to ensure clarity of the image.] Thank you for pointing this out. We agree with this comment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you for your thorough revisions. You have successfully addressed all the suggestions raised during the review process. The manuscript is now more aligned with the standards of the journal and presents improved clarity and structure. These enhancements will likely increase its appeal and readability for the journal's audience.

Reviewer 2 Report

Comments and Suggestions for Authors

As a reviewer, I am satisfied with the authors’ thorough and well-considered responses to the comments. The manuscript has been significantly improved in terms of scientific rigor, clarity, and overall quality, and I recommend it for publication in its current form.

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript can be accepted in the current form.