Dynamic and Quasi-Static Loading Behavior of Low-Strength Concrete Incorporating Rubber Aggregates and Polymer Fiber

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study systematically investigates the influence of rubber particles and polymer fibers on the mechanical properties of low-strength concrete under quasi-static and dynamic bending loads. The research objective is clear, and the experimental design is robust, effectively addressing a knowledge gap concerning the behavior of such materials under dynamic flexural loading. The data support is sufficient, and the discussion section provides reasonable interpretations in the context of existing literature. The work offers valuable experimental data and insights for developing safer and more sustainable roadside safety barriers.

1. The description of the specimen failure process during loading based on Fig 13and the presentation of the failure mode are not suitable for inclusion in Section 3.2.2.
2. Provide images illustrating the concrete mixing process.
3. Fig4-6(physical properties) and Fig7-9 (material properties) require more detailed descriptions; Fig10should be categorized under Section 3.2.1.
4. A new subsection should be added to compare the equations derived in Section 3.2.3 with measured data verifying the feasibility of the equations and providing the error margin.
5. The conclusion should specify the optimal mix proportion and discuss the potential for practical engineering application.

Author Response

Response to reviewer 1

Thank you for the time and effort you invested in revising our manuscript, “Dynamic and quasi-static loading behavior of low-strength concrete incorporating rubber aggregates and polymer fiber." We appreciate the valuable feedback you provided, which has significantly improved our work.

We have carefully considered all your comments and suggestions and made corresponding adjustments to the manuscript. Following, we provide detailed responses to each comment, addressing your concerns and outlining the changes made in response to your feedback.

1. Comment: The description of the specimen failure process during loading based on Fig 13and the presentation of the failure mode are not suitable for inclusion in Section 3.2.2.
   Response: We moved Figure 13 (now Figure 18) to section 3.2.3 after the paragraph discussing the possible causes for energy absorption differences between quasi-static and dynamic loads. We believe this change improves the logical flow between the discussion and the illustration of the failure process
2. Comment: Provide images illustrating the concrete mixing process.
   Response: We added Figure 1. to illustrate the concrete mixing process for clarity. This figure provides a clearer understanding of the specimen preparation procedure.
3. Comment: Fig 4-6 (physical properties) and Fig 7-9 (material properties) require more detailed descriptions;

Response: The following changes were applied (also the no. of the Figures):
Figure 5 illustrates the variation in air content with increasing percentages of rubber and fiber. The air content increased slightly from approximately 2.0% for the control mix to around 3.0–3.5% at a 20% rubber replacement. Overall, the changes remained within typical limits for a workable concrete mixture (lines 235-238)

Figure 6 presents the unit weight of the fresh concrete mixtures as a function of rubber and fiber contents. The unit weight decreased almost linearly with increasing rubber replacement—from approximately 2400 kg/m³ in the control mixture to about 2100 kg/m³ at 20% rubber. This reduction results directly from the significantly lower density of rubber aggregates (≈ approximately 1.1 g/cm³) compared to natural aggregates (≈ approximately 2.65 g/cm³). The addition of polypropylene fibers produced only negligible variations in density, confirming that the dominant factor controlling unit weight is the proportion of rubber substitution (lines 263-270)

Figure 7 illustrates the slump results for the tested mixtures. The slump value decreased consistently for any rubber addition above 5%, with the increase in rubber and fiber content, dropping by nearly 50% at a 15–20% rubber replacement. This reduction in workability is primarily due to the irregular shape and low surface energy of the rubber particles, which increase internal friction and decrease the mixture’s flowability. The inclusion of polypropylene fibers further decreased the slump due to the formation of a fiber network that restricts flow, although the difference between 0.6% and 1.2% fiber contents was not significant. These findings are in good agreement with previous studies on rubberized and fiber-reinforced concretes (lines 274-282)

Figure 8. the compressive strength results of the tested mixtures. The compressive strength decreased almost linearly with increasing rubber content, with a correlation coefficient of approximately, R, of −0.9 (Table 4). The control mixture reached approximately 28 MPa, while the mixture with 20% rubber exhibited a reduction to around 12–14 MPa… (lines 286-289)

Figure 9. shows the flexural strength of the concretes as a function of rubber and fiber content. Rubberized mixtures exhibited lower peak flexural strengths than the control. The flexural strength decreases with the rubber content. (lines 306-308)

Figure 10. illustrates the stress-strain curve of the concrete mixes in this investigation. The peak at the left is the flexural strength of the plain concrete, and the peak at the right is the flexural strength arises from the fiber bridging the fractured concrete. The second peak is lower than the first. This is the reason that the fiber content does not contribute to the flexural strength. The energy absorption capacity (toughness) calculated as the area under the load–deflection curve. It will be shown in subsection 3.2 that the absorbed energy increased markedly with fiber content and moderately with rubber replacement. This trend suggests that fibers play a significant role in enhancing the ductility and toughness of concrete. At a 1.2% fiber content, the total energy absorbed was nearly three times higher than that of the control mix. (lines 317-326)

1. Comment: These detailed descriptions have been incorporated into the revised manuscript to improve the interpretability of the experimental results and ensure alignment with the reviewer’s recommendation.Fig10 should be categorized under Section 3.2.1.
   Response: We appreciate the reviewer’s comment. Figure 12 presents the same dataset as Figure 11, reformatted for clarity to facilitate comparison between quasi-static and dynamic results. We intentionally retained both figures to maintain visual continuity and support reader comprehension. We believe this structure enhances readability without unnecessary duplication.  Therefore, Figure 11 was retained under Section 3.2.1 for clarity, while Figure 10 remains in the general results section for reference
2. Comment: A new subsection should be added to compare the equations derived in Section 3.2.3 with measured data, verifying the feasibility of the equations and providing the error margin.
   Response: We added a concluding paragraph at the end of the results and discussion section to answer this concern.

Since the results from the quasi-static tests can serve as an indicator of energy ab-sorption capacity, it is useful to compare them with values reported in the literature for plain concrete of strength class B-40, which is often used as a reference for fiber-reinforced concrete. For example, an energy absorption of approximately 4.2 J was reported for a cross-sectional area of 0.0255 m², corresponding to about 165 J/m². In contrast, the energy to failure of the specimen tested in this study (0.01 m² cross-section, containing 0.6 % fi-bers by volume) was approximately 90 J, or about 9,000 J/m²—more than an order of mag-nitude higher. Furthermore, the energy to failure of fiber-reinforced concrete under canti-lever loading is not directly correlated with compressive strength. Therefore, it can be con-cluded that any fiber-reinforced concrete mix will perform at least as well as B-40 grade concrete in terms of energy absorption. The remaining open question, not addressed in this study, concerns the minimum compressive strength required to ensure that a concrete barrier remains “forgiving” under impact loading.  (lines 496-508)

1. Comment: The conclusion should specify the optimal mix proportion and discuss the potential for practical engineering application.
   Response: We appreciate the reviewer’s valuable comment. Because the impact acceleration measurements could not be reliably obtained in this experimental setup, it was not possible to define a single “optimal” mix proportion quantitatively. Nevertheless, the results clearly indicate that incorporating rubber up to 10–15% combined with fiber contents of 0.6% or higher provides a substantial improvement in energy absorption and ductility compared to conventional concrete. We added the following paragraph to the conclusions:

7. Nevertheless, the energy absorbed by specimens containing 0.6 % or more fiber by volume was considerably higher than that expected for plain B-40 grade concrete, regardless of compressive strength. Importantly, the ability of such rubber- and fiber-modified concrete to absorb at least as much energy as the conventional concrete currently used in safety barriers suggests that its practical implementation is already feasible—even before the exact extent of its deceleration reduction upon impact is fully quantified. This finding indicates that fiber-reinforced concrete of this type can achieve superior energy absorption compared to conventional mixes. The remaining open question, which should be addressed in future research, concerns the acceleration at impact and the minimum compressive strength required for a truly “forgiving” concrete barrier. (lines 534-543)

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript explores low-strength concrete incorporating recycled rubber aggregates from waste tires and polymer fibers, with the aim of developing “forgiving” safety barriers that enhance road safety while supporting environmental sustainability. This manuscript provides a relatively rich set of experimental data but lacks sufficient scientific depth and rigorous analytical discussion, which limits the overall contribution and persuasiveness of the manuscript. Therefore, I recommend major revision and resubmission.

(1) This manuscript presents a large number of experimental results, but the analysis remains superficial. Most of the results are limited to data reporting and trend descriptions, with little integration of microstructural evidence or in-depth mechanistic discussion. As a result, the results section reads more like a data report than a research article with genuine scientific contribution.

(2) The conclusions are mainly qualitative and lack quantitative data to substantiate the key findings, which makes them appear overly general and limits their reference value for both research and engineering applications.

(3) The introduction is overly lengthy and covers a wide range of topics, but the content is fragmented and lacks a clear logical flow to highlight the research gap and objectives of the study. The linkage between the state of the art, the existing problems, and the research aims is not sufficiently tight, making it difficult for readers to quickly grasp the core innovation of the manuscript.

Author Response

Response to reviewer 2

Thank you for the time and effort you invested in revising our manuscript, “Dynamic and quasi-static loading behavior of low-strength concrete incorporating rubber aggregates and polymer fiber." We appreciate the valuable feedback you provided, which has significantly improved our work. We believe that these revisions have improved the clarity and scientific quality of the manuscript.

We have carefully considered all your comments and suggestions and made corresponding adjustments to the manuscript. Following, we provide detailed responses to each comment, addressing your concerns and outlining the changes made in response to your feedback.

1. Comment: This manuscript presents a large number of experimental results, but the analysis remains superficial. Most of the results are limited to data reporting and trend descriptions, with little integration of microstructural evidence or in-depth mechanistic discussion. As a result, the results section reads more like a data report than a research article with genuine scientific contribution.
   Response: The present work was designed primarily as an experimental and mechanical investigation aimed at quantifying the influence of rubber and fiber contents on the dynamic behavior of concrete. We fully acknowledge that a deeper microstructural analysis and mechanistic modeling would further strengthen the interpretation of the results; however, these aspects are beyond the scope of the current study and are planned for future work.
   The present findings nonetheless provide an important empirical foundation for subsequent studies, offering a comprehensive dataset that highlights consistent mechanical trends under quasi-static and dynamic loading. By publishing these results, we aim to contribute to the cumulative understanding of rubberized fiber-reinforced concrete behavior, on which future microstructural and theoretical research can build.
2. Comment: The conclusions are mainly qualitative and lack quantitative data to substantiate the key findings, which makes them appear overly general and limits their reference value for both research and engineering applications.
   Response: We appreciate the reviewer's helpful comment. In the revised version, we added a new concluding paragraph at the end of the Results and Discussion section and an additional statement in the Conclusions section to provide quantitative support for the main findings. These additions now specify the measured ranges and relative changes in key mechanical properties—for example, the 35–40 % reduction in compressive strength with 20 % rubber replacement and the approximately threefold increase in energy absorption at 1.2 % fiber content under dynamic loading.
   The revised conclusions now integrate these numerical trends to provide clearer guidance for both future research and practical engineering applications.
3. Comment: The introduction is overly lengthy and covers a wide range of topics, but the content is fragmented and lacks a clear logical flow to highlight the research gap and objectives of the study. The linkage between the state of the art, the existing problems, and the research aims is not sufficiently tight, making it difficult for readers to quickly grasp the core innovation of the manuscript.
   Response: We appreciate the reviewer's constructive comment. In the revised version, the Introduction has been reorganized to improve its logical flow and to clarify the link between the research problem, existing knowledge, and the objectives of this study. The section now follows a coherent structure:
4. Presentation of the engineering problem and the need for energy-dissipating (forgiving) barriers;
5. Discussion of the required material properties and the rationale for selecting rubber aggregates and polypropylene fibers as potential solutions;
6. Summary of previous studies on rubberized concrete and its mechanical limitations;
7. Review of surface treatments of rubber aggregates (as suggested by another reviewer);
8. Environmental motivation for using recycled rubber in cementitious composites.

The final paragraph of the Introduction now explicitly identifies the research gap and clearly states the objectives and novelty of this work—namely, the combined evaluation of rubber and fiber effects

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The paper presents research on cementitious composites incorporating rubber aggregates and polymer fibers, focusing on their application in energy-absorbing road barriers. The objective is to enhance passive transport safety while simultaneously managing waste materials. Although the properties of concrete with rubber and fibers are widely documented, the unique combination of these additives in the context of "forgiving" barriers and the innovative methodology for dynamic testing contribute to the originality of the work.

 

After a thorough analysis of the article, the following comments have been formulated:

1. Introduction: The literature review is incomplete - it omits key recent studies concerning the effects of rubber surface treatment and advanced dynamic tests (SHPB), which weakens the scientific context of the paper.

2. Research Methodology: The test employing a pendulum hammer does not allow for a precise dynamic characterization of the material; calibration data and an analysis of the actual strain rate are missing. The key formulas (1) and (2) are presented without citing their source, which constitutes a serious methodological flaw.

3. Analysis of Results: The presented results exhibit high variability, which, in the absence of a defined level of statistical significance, undermines the statistical power of the conclusions. The analysis of the rubber's impact on energy absorption is marginalized by the effect of the fibers, and this should be reflected in the discussion.

4. Interpretation and Conclusions: The conclusions regarding the poor adhesion of rubber are not supported by microstructural analysis (e.g., SEM). The final conclusions are too general and lack specific numerical data, thus failing to provide a robust quantitative summary.

5. Editing and Structure: The article requires careful editorial revision. The results and discussion sections must be more clearly separated, and redundant figures should be removed (Figs. 10 and 11 present the same dataset, which is a duplication). The quality of the graphical material is low: data point markers in the graphs are too large, the dimensions in Fig. 1 are disproportionate, and the photographs in Fig. 3 lack explanatory labels. It is also necessary to standardize the units (according to the SI system) and verify the completeness of bibliographic citations.

Author Response

Response to reviewer 3

Thank you for the time and effort you invested in revising our manuscript, “Dynamic and quasi-static loading behavior of low-strength concrete incorporating rubber aggregates and polymer fiber." We appreciate the valuable feedback you provided, which has significantly improved our work.

We have carefully considered all your comments and suggestions and made corresponding adjustments to the manuscript. Following, we provide detailed responses to each comment, addressing your concerns and outlining the changes made in response to your feedback.

1. Comment: Introduction: The literature review is incomplete - it omits key recent studies concerning the effects of rubber surface treatment and advanced dynamic tests (SHPB), which weakens the scientific context of the paper.
   Response: We added a new paragraph (lines 85-90) addressing this issue. While we were unable to identify any published studies reporting SHPB tests on surface-treated recycled rubber aggregates, we would greatly appreciate the reviewer’s guidance or specific DOI reference to include in the next revision.,
2. Comment: Research Methodology: The test employing a pendulum hammer does not allow for a precise dynamic characterization of the material; calibration data and an analysis of the actual strain rate are missing. The key formulas (1) and (2) are presented without citing their source, which constitutes a serious methodological flaw.
   Response: We thank the reviewer for this important observation. In the revised version, Equations (1)–(3) and (5)–(6) have been expanded and properly referenced to clarify their derivation and to address the lack of citation in the initial submission. We fully acknowledge the limitations of the pendulum hammer setup in providing a precise dynamic characterization and in determining the actual strain rate. This limitation is now explicitly stated and discussed in the revised manuscript.

Nevertheless, we believe that reporting these findings is valuable, as the results still provide comparative insights into the influence of rubber and fiber content under impact conditions. Moreover, documenting the methodological challenges encountered with the pendulum test can help guide future researchers and prevent similar pitfalls in experimental design. We believe that these revisions and clarifications significantly improve the methodological transparency of the paper.

3. Comment: Analysis of Results: The presented results exhibit high variability, which, in the absence of a defined level of statistical significance, undermines the statistical power of the conclusions. The analysis of the rubber's impact on energy absorption is marginalized by the effect of the fibers, and this should be reflected in the discussion.
   Response: We thank the reviewer for this important observation. The variability of the results was acknowledged in the revised manuscript lines 374-376 "…indicating that the rubber content does not significantly affect the dynamic energy absorption, particularly when fibers are included in the concrete mix." and lines 386-387 "3) The energy absorbance of the fiber makes the rubber contribution insignificant." An additional note was added to clarify that statistical significance was not evaluated due to the limited number of specimens per configuration (6 specimens per configuration). However, the standard deviation is clearly reported on the graphs, and the consistent trends observed across tests with calculated p-value confirm the reliability of the reported conclusions. The discussion was expanded to explicitly note that the fibers’ contribution dominates the energy absorption response, as suggested by the reviewer.
4. Comment: Interpretation and Conclusions: The conclusions regarding the poor adhesion of rubber are not supported by microstructural analysis (e.g., SEM). The final conclusions are too general and lack specific numerical data, thus failing to provide a robust quantitative summary.
   Response: We appreciate the reviewer’s insightful comment. Indeed, microstructural analysis such as SEM imaging was beyond the scope of the present study, which focused on the macroscopic mechanical behavior of rubberized fiber-reinforced concrete. The discussion regarding the poor adhesion between rubber particles and the cement matrix is therefore presented as an inferred mechanism, supported by relevant literature (lines 293–298 in the revised manuscript).
   In the updated version, this limitation is now clearly stated in the Discussion section, and the Conclusions have been refined to emphasize the observed quantitative results—particularly the measured reductions in compressive and flexural strength and the corresponding increases in energy absorption—while avoiding overgeneralization of the microstructural interpretation.
5. Comment: Editing and Structure: The article requires careful editorial revision. The results and discussion sections must be more clearly separated

Response: We thank the reviewer for the thorough editorial feedback. All the issues mentioned have been carefully reviewed and addressed as follows:

(a) Redundant figures: We acknowledge the reviewer’s concern. Figures 10 and 11 (11 and 12 in the revised version) indeed present the same dataset but organized differently — by fiber content and by rubber content, respectively. This presentation was intentionally chosen to emphasize two complementary trends, improving readability and comparison. However, should the editorial board prefer, we are willing to merge or remove Figure 11 (12 in the revised version) in the final version.

(b) Graphical quality: The graphical materials were revised. Marker size was reduced from 10 pt to 6 pt, and line thickness from 2 pt to 1 pt, to improve clarity and visual balance.

(c) Figure 1 proportions: Figure 1 (2 in the revised version) is a schematic perspective intended to illustrate the experimental setup; therefore, the spatial dimensions are not to scale. The actual geometric dimensions are explicitly provided within the figure and in the text for accuracy.

(d) Figure 3 (4 in the revised version) labels: Explanatory labels and annotations were added to clarify the figure content.

(e) Standardization of units: All dimensional data were checked and standardized to SI units (mm, MPa, kg/m³, etc.) throughout the manuscript and figures.

(f) Bibliographic completeness: All references were verified for accuracy and completeness. Missing citation details were added where needed, and formatting was standardized according to the Applied Sciences reference style

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

accept

Author Response

Thank you for accepting our manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have made partial revisions to the manuscript based on the previous review comments, and the overall structure and readability have slightly improved. However, several key issues remain insufficiently addressed, particularly in the introduction and conclusion sections, where the logical coherence and scientific rigor are still inadequate. The manuscript as a whole requires further improvement.

(1) Although the conclusion section has been revised, it remains largely qualitative. The key findings are still presented in a descriptive manner without sufficient quantitative evidence or numerical comparisons to support them. As a result, the conclusions appear overly general.

(2) Although the introduction has been revised, it remains overly lengthy and only superficially reorganized. The logical linkage between the background, state of the art, research gap, and study objectives is still weak, making it difficult for readers to clearly follow the rationale of the study or identify its core innovation. Furthermore, the cited literature is relatively outdated, with limited inclusion of recent studies from the past three years. As a result, the introduction does not sufficiently reflect the current state of research in this field.

Author Response

Comment (1) Although the conclusion section has been revised, it remains largely qualitative. The key findings are still presented in a descriptive manner without sufficient quantitative evidence or numerical comparisons to support them. As a result, the conclusions appear overly general.

We thank the reviewer for this valuable observation. The Conclusions section has been further revised to include specific quantitative comparisons and numerical evidence supporting the main findings. In particular, the revised version now reports:

The approximate reduction in compressive strength (≈40%) due to the incorporation of recycled rubber.

The significant increase in energy absorption (up to about 9,000 J/m²) compared with plain B-40 grade concrete (≈165 J/m²);

The estimated tensile strength range of approximately 3 MPa is required for a “forgiving” concrete element.

These additions provide a more solid quantitative basis for the conclusions and clarify the engineering implications of the results. Furthermore, the final paragraph emphasizes the practical feasibility of using rubber- and fiber-modified concrete in safety barriers, even before full quantification of the deceleration effect is achieved. We believe these revisions have strengthened the scientific rigor and clarity of the conclusions

Comment (2) Although the introduction has been revised, it remains overly lengthy and only superficially reorganized. The logical linkage between the background, state of the art, research gap, and study objectives is still weak, making it difficult for readers to clearly follow the rationale of the study or identify its core innovation. Furthermore, the cited literature is relatively outdated, with limited inclusion of recent studies from the past three years. As a result, the introduction does not sufficiently reflect the current state of research in this field.

We appreciate this constructive feedback and have made extensive revisions to the Introduction and Discussion sections to address these concerns.

The Introduction has been restructured for clearer logical flow, now progressing from the general problem statement (the need for forgiving, energy-absorbing concrete) to the state of the art, the identified research gap, and the specific objectives of this study.

A new paragraph was added summarizing recent work (2022–2025) on the dynamic behavior of rubber-containing concrete and Dynamic Increase Factor (DIF) modeling, citing fourteen up-to-date references [62,73–85]. This paragraph explicitly identifies the current limitations of empirical models—particularly their inaccuracy at low strain rates and large variability for similar mix compositions.

In the Discussion section, an additional paragraph (including Table 7) compares calculated dynamic strengths based on five representative DIF models from recent literature (Lan et al. 2023; Huang et al. 2023; Ye et al. 2024; Elzeadani et al. 2023, etc.). This analysis demonstrates the shortcomings of existing predictive models and highlights how the present experimental results provide a benchmark for refining future formulations.

Together, these additions ensure that the introduction now reflects the current state of research and that the discussion effectively connects the new experimental results to recent developments in the field. We believe these substantial updates fully address the reviewer’s concerns regarding the structure, timeliness, and relevance of the manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

The article looks much better after the corrections than in its original version. Basically, all the changes, corrections and additions expected by the reviewer have been made. However, the disproportionately large descriptions of the dimensions in Fig. 2 still look very unfavourable and must be corrected without fail.

Author Response

Figure 2 was replaced with a 4-viewport image to better communicate the specimen's dimensions. 

Round 3

Reviewer 2 Report

Comments and Suggestions for Authors

Although the authors have made partial revisions to the manuscript, they have not provided targeted responses to the core issues raised previously. The Introduction section still suffers from unclear logic, excessive citation of literature, and unnecessary verbosity. In addition, the Conclusion section remains qualitative, lacking quantitative analysis and data support for the experimental results. These issues indicate that the manuscript has not yet reached the level of scientific rigor and standardization required for a research-type academic paper. Therefore, I recommend major revision and resubmission for further review. If the revised version does not show substantial improvement in methodology, analysis, and presentation, rejection should be considered.

Author Response

We have carefully revised the manuscript in accordance with your feedback, focusing on the key issues you raised regarding the Introduction, scientific rigor, quantitative analysis, and overall structure.
Below, we summarize the major revisions and explain how each addresses your concern directly.

1. Introduction – Improved Logic, Focus, and Conciseness

Reviewer’s comment:

The Introduction still suffers from unclear logic, excessive citation of literature, and unnecessary verbosity. It is too long and should focus more on motivation and novelty.

Response:

We have substantially rewritten and condensed the Introduction to improve its logical flow and focus. The revised version now starts with a clear problem definition, followed by the research motivation and novelty of our study. We reorganized the literature review into a concise, thematic structure, highlighting only the most relevant works. Redundant or tangential references have been removed. A new “knowledge gap” paragraph and Table 1 were added to clearly demonstrate the lack of quantitative studies on dynamic tensile and flexural behavior of rubberized fiber concretes. The Introduction was reduced by approximately 30% in length and now provides a direct transition to the study's objectives. These changes make the Introduction clearer, shorter, and better aligned with the scientific motivation and innovation of our work.

2. Methodology – Strengthened Experimental and Analytical Rigor

Reviewer’s comment:

The manuscript needs substantial improvement in methodology and standardization.

Response:

We carefully revised the methodology section to ensure scientific rigor and reproducibility:

• Section 2 now includes detailed descriptions of material composition, specimen preparation, curing process, and testing setup according to relevant EN standards.
• Subsection 2.4 provides a full justification for the choice of the pendulum impact test and its suitability for simulating vehicle–barrier collisions.
• We introduced explicit formulas (Eqs. 1–7) for calculating impact energy and stress–strain relations, showing both analytical and numerical approaches.
• All measurements were repeated, and statistical consistency (mean values ± standard deviations) is now reported.

This revision ensures that the experimental procedures are well-defined, standardized, and transparent.

3. Results and Discussion – Quantitative and Statistical Analysis Added

Reviewer’s comment:

The Conclusion remains qualitative, lacking quantitative analysis and data support for the experimental results.

Response:

The entire Results and Discussion section has been strengthened with quantitative evidence:

 

• We added regression analyses (Table 4) including correlation coefficients (R²) and significance levels (p-values).
• Figures 5–17 now include numerical data trends (e.g., 0.74 MPa decrease per 1 % rubber addition).
• Comparisons with literature values (e.g., 9000 J/m² vs. 187 J/m² for reference concrete) are now provided to contextualize the results.
• A clear link between material composition and mechanical performance is now demonstrated quantitatively.

These improvements transform the manuscript from a qualitative description into a data-driven scientific study.

4. 4. Conclusions – Quantitative, Structured, and Practical

Reviewer’s comment:

The Conclusion section remains qualitative and lacks data support.

Response:

The Conclusions were completely rewritten:

• They now summarize the main findings numerically (e.g., tenfold improvement in absorbed energy, 25–35 % increase under dynamic loading).
• The optimal composition ranges (10–20 % rubber, 0.6 % fibers) are provided as practical design recommendations.
• A new “Future Work” paragraph outlines next research steps to further validate the findings.

The revised Conclusions now provide measurable outcomes and real engineering implications.

We believe that the revised version now fully addresses all major concerns and meets the standards required for publication.

Round 4

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have made extensive and targeted revisions in response to the previous comments. The overall structure, logic, and readability of the manuscript have been significantly improved. The Introduction is now more concise and logically clearer. In addition, the revised Conclusion provides more explicit quantitative support for the main research findings, enhancing the scientific rigor of the work. Overall, the manuscript has now reached the publication standard. Therefore, I recommend acceptance.