Testing of Cationic Adhesion Promoters Derived from Rapeseed Oil in Bitumen and Asphalt Mixtures

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The study systematically synthesized a series of cationic adhesion promoters (APs) derived from rapeseed oil and evaluated their effects on the performance of bitumen and asphalt mixtures, particularly the improvement in moisture resistance and Indirect Tensile Strength Ratio (ITSR). The experimental design is relatively comprehensive, and the data presentation is clear. However, several shortcomings remain in the manuscript. The specific points requiring revision are as follows:

1. The chemical structure characterization of the APs is not described; it is recommended to supplement this information to enhance the credibility of the synthesis results.
2. Although commercial additives (Wetfix® BE and Carbazole AK-M) were used for comparison, their specific dosages are not provided.
3. The paper indicates that AP20 significantly improves adhesion and ITSR values, but the underlying mechanism is not explored in depth. It is suggested that the authors explain the mechanism from the perspective of the variations in polyethylene polyamine and rapeseed oil content.
4. The slight decrease in the strength of asphalt concrete after the addition of APs is attributed to the "thinning of the asphalt film," but no measurements of film thickness or microstructural evidence are provided.
5. Could the authors perform a quantitative analysis of the image processing in Figure 2, such as statistical proportions of each failure type ?

Author Response

Comments 1: The chemical structure characterization of the APs is not described; it is recommended to supplement this information to enhance the credibility of the synthesis results.

Response 1: Thank you for the valuable comment. The chemical structure of the synthesized adhesion promoters was studied in our previous works, particularly in “Sustainable Bitumen Modification Using Bio-Based Adhesion Promoters” (DOI: 10.3390/su17167187), where the reaction schemes of amidation and the FTIR spectra confirming the formation of amide groups were presented. Therefore, only a brief description was provided in this manuscript.

Comments 2: Although commercial additives (Wetfix® BE and Carbazole AK-M) were used for comparison, their specific dosages are not provided.

Response 2: Thank you for the comment. Their dosage has now been specified in the manuscript; the additives were applied at a concentration of 0.4 wt % with respect to the bitumen mass.

Comments 3: The paper indicates that AP20 significantly improves adhesion and ITSR values, but the underlying mechanism is not explored in depth. It is suggested that the authors explain the mechanism from the perspective of the variations in polyethylene polyamine and rapeseed oil content.

Response 3: We are grateful to the reviewer for this insightful comment. In the revised version of the manuscript, a detailed explanation of the adhesion improvement mechanism has been added. The new paragraphs (Section 3.1) discusses how the balance between polyethylene polyamine (PEPA) and rapeseed oil components determines the adhesion efficiency of AP20. It is also noted that increasing the PEPA content above 20 wt.% is not economically justified, as AP20 already provides a sufficient improvement in adhesion performance.

Comments 4: The slight decrease in the strength of asphalt concrete after the addition of APs is attributed to the "thinning of the asphalt film," but no measurements of film thickness or microstructural evidence are provided.

Response 4: We thank the reviewer for this constructive comment. In the revised version, we clarified the explanation of the “thinning of the asphalt film” phenomenon and its indirect confirmation through density and porosity measurements. Although direct microscopic determination of film thickness was not carried out in this study, the observed changes in bulk density, residual porosity, and water saturation indirectly support this conclusion. A corresponding paragraph has been added at the end of Section 3.2 (“Asphalt concretes”).

Comments 5: Could the authors perform a quantitative analysis of the image processing in Figure 2, such as statistical proportions of each failure type?

Response 5: Thank you for the comment. A quantitative analysis of the image in Figure 2 was not performed, as the assessment of failure types was carried out according to DSTU EN 12697-23:2024, which provides a standardized qualitative evaluation method rather than a statistical or quantitative analysis.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The paper infrastructures-3945407 investigates bio-based cationic adhesion promoters synthesized from rapeseed oil and evaluates their effects on bitumen and asphalt mixture performance. Among the tested formulations, AP20 demonstrated superior adhesion, strength, and moisture resistance compared to both unmodified bitumen and commercial additives. The results highlight AP20 as a sustainable and effective alternative for improving asphalt durability in road construction. 

I have some questions for the authors:

• Section numbering is inconsistent (e.g., there’s no “4. Discussion” heading; results and discussion are merged). Consider dividing into “3. Results” and “4. Discussion” for clarity. The patent and funding information should follow the MDPI journal format, but minor formatting inconsistencies (spacing, numbering, and alignment) need correction. Recheck for redundant repetitions—for example, Tables 9 and 10 are both introduced twice with slightly differing sentences.
• Simplify too long and wordy sentences. Fix typographical issues: missing or misplaced commas (e.g., “70/100 + 0.4 wt.% AP20” should be consistent); occasional inconsistent notation (e.g., “°С” vs “°C”; “wt.%” vs “wt. %”). Avoid repeated phrases such as “the influence of... is summarized in Table...”. Improve transitions between sections (e.g., between Results and Discussion)

• Although references are recent, there is some overreliance on the authors’ own prior work (multiple self-citations). Add a few independent studies for balance. Table 1 summarizes prior works well but lacks discussion on limitations or gaps in those studies—adding that would better justify the novelty of your work. Cite specific comparative studies on bio-based promoters beyond rapeseed oil (e.g., soy, tall oil) to broaden context.

• The chemical reaction scheme (Equation 1) is presented but lacks clarity on reaction yield or product confirmation (e.g., FTIR/NMR evidence). Consider adding or referencing analytical validation. Add a brief justification for the chosen dosage range (0.2–1.0 wt.%). Specify replication and statistical treatment (e.g., “All results represent the mean of three replicates ± standard deviation”). The Methods are very detailed but could benefit from subheadings (e.g., “Bitumen Testing”, “Asphalt Mix Design”, “Compaction Procedure”, “ITSR Determination”).

• The discussion is largely descriptive; strengthen the analytical interpretation—e.g., link changes in adhesion or strength to possible molecular interactions. Include replication details and indicate statistical variability or error margins. Avoid repeating data explanations (the same trends are re-explained twice in Tables 9 and 10).
• Indicate future work or application potential (e.g., “field trials or aging resistance testing”).
• Add quantitative comparisons in the Conclusions (e.g., % improvement in ITSR).

•  
• Remove placeholder text (e.g., “Article 1,” “to be added by editorial staff”).

Author Response

Comments 1: Section numbering is inconsistent (e.g., there’s no “4. Discussion” heading; results and discussion are merged). Consider dividing into “3. Results” and “4. Discussion” for clarity. The patent and funding information should follow the MDPI journal format, but minor formatting inconsistencies (spacing, numbering, and alignment) need correction. Recheck for redundant repetitions—for example, Tables 9 and 10 are both introduced twice with slightly differing sentences.

Response 1: Thank you for the comment. All formatting inconsistencies, redundancies, and minor errors have been corrected. Regarding the division into “3. Results” and “4. Discussion,” we have maintained a combined Results and Discussion section, as this structure is acceptable and allows for a more integrated presentation of findings.

Comments 2: Simplify too long and wordy sentences. Fix typographical issues: missing or misplaced commas (e.g., “70/100 + 0.4 wt.% AP20” should be consistent); occasional inconsistent notation (e.g., “°С” vs “°C”; “wt.%” vs “wt. %”). Avoid repeated phrases such as “the influence of... is summarized in Table...”. Improve transitions between sections (e.g., between Results and Discussion)

Response 2: 

Thank you for your valuable comments. All typographical issues and inconsistencies have been corrected. Long and wordy sentences were simplified, and notation was unified (e.g., “°C”, “wt.%”). Repetitions such as “the influence of... is summarized in Table...” were removed. Transitions between sections, particularly between Results and Discussion, were improved for better flow. All suggested corrections have been implemented in the revised manuscript.

Comments 3: Although references are recent, there is some overreliance on the authors’ own prior work (multiple self-citations). Add a few independent studies for balance. Table 1 summarizes prior works well but lacks discussion on limitations or gaps in those studies—adding that would better justify the novelty of your work. Cite specific comparative studies on bio-based promoters beyond rapeseed oil (e.g., soy, tall oil) to broaden context.

Response 3: Thank you for the comment. Changes have been made to the article.

Comments 4: The chemical reaction scheme (Equation 1) is presented but lacks clarity on reaction yield or product confirmation (e.g., FTIR/NMR evidence). Consider adding or referencing analytical validation. Add a brief justification for the chosen dosage range (0.2–1.0 wt.%). Specify replication and statistical treatment (e.g., “All results represent the mean of three replicates ± standard deviation”). The Methods are very detailed but could benefit from subheadings (e.g., “Bitumen Testing”, “Asphalt Mix Design”, “Compaction Procedure”, “ITSR Determination”).

Response 4: 

Thank you for the valuable suggestions. The chemical reaction scheme and structural characterization of the adhesion promoters have been studied in our previous works, where FTIR and NMR analyses were used to confirm product formation (see, e.g., Sustainable Bitumen Modification Using Bio-Based Adhesion Promoters, DOI: 10.3390/su17167187).

The chosen dosage range of 0.2–1.0 wt % is a commonly used range in the literature for bitumen modification and has been selected to ensure effective performance without compromising workability. All experimental results represent the mean of three replicates ± standard deviation. Regarding the suggested subheadings for the Methods section, we appreciate the recommendation; however, we believe the current structure provides a clear and logical flow of the procedures.

Comments 5: The discussion is largely descriptive; strengthen the analytical interpretation—e.g., link changes in adhesion or strength to possible molecular interactions. Include replication details and indicate statistical variability or error margins. Avoid repeating data explanations (the same trends are re-explained twice in Tables 9 and 10).

Response 5: All tests of the physical and mechanical properties of bitumens were carried out on a series of three independent samples (n=3) for each composition studied in accordance with the requirements of DSTU/EN, except for Adhesion to glass (n=5) and adhesion to crushed stone (n=6).

Comments 6: Indicate future work or application potential (e.g., “field trials or aging resistance testing”).

Response 6: We appreciate the reviewer’s valuable suggestion. In the revised version of the manuscript, the Conclusions section has been expanded to include a statement on future work and practical application potential. Specifically, we now emphasize the need for field trials to validate laboratory results, as well as further studies on long-term aging resistance, storage stability, and environmental performance of AP20-modified bitumen. These additions highlight the relevance of the research for real-world implementation and future development of bio-based adhesion promoters.

Comments 7: Add quantitative comparisons in the Conclusions (e.g., % improvement in ITSR).

Response 7: We thank the reviewer for this helpful suggestion. In the revised version of the manuscript, the Conclusions section has been updated to include quantitative comparisons illustrating the performance improvement achieved with AP20. The revised text now specifies the percentage increase in ITSR, density, and reduction in water saturation relative to the virgin mix.

Comments 8: Remove placeholder text (e.g., “Article 1,” “to be added by editorial staff”).

Response 8: Thank you for the comment. The manuscript has been formatted according to the MDPI template.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

accept

Reviewer 2 Report

Comments and Suggestions for Authors

The paper can be accepted.