Experimental Study of the Effectiveness of Strengthening Reinforced Concrete Slabs with Thermally Prestressed Reinforcement

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript titled "Strengthening of reinforced concrete slabs by means of thermally prestressed reinforcement - Experimental investigation of the effectiveness in the ultimate and serviceability limit states” presents the strengthening of reinforced concrete members with thermally prestressed reinforcement - a relatively new method developed to obtain the best possible performance from flexural strengthening facing the building's own weight. The manuscript is well-aligned with the aims and scope of CivilEng (ISSN 2673-4109). The topic is timely and current considering the renewed focus on sustainable and cost-efficient retrofits well adapted to aged infrastructure. The work is of interest to both researchers and practitioners working on innovative strengthening techniques for reinforced concrete members. The paper requires some corrections on the small flaws mentioned below before it is ready for publication.

• I suggest simplifying/shortening the abstract.
• I suggest enriching the introduction with a more extensive description of other modernization methods.
• Due to the significant number of symbols in the manuscript, it might be worthwhile to add a summary table of symbols with explanations.
• Reference formatting - the references section has duplicate numbering.

Author Response

Dear Reviewer,

We would like to sincerely thank you for your careful reading of our manuscript and for the many helpful and constructive remarks. We have carefully considered all comments and implemented the suggested changes in the revised version of the paper. To facilitate the review, all modifications have been highlighted in yellow in the manuscript.

Below, we provide our detailed responses to the individual comments and indicate how they have been addressed in the revised version.

Sincerely,
The Authors

 

I suggest simplifying/shortening the abstract.

• Thank you for the suggestion. We have simplified and shortened the abstract accordingly.

 

I suggest enriching the introduction with a more extensive description of other modernization methods.

• We have extended the introduction with a more detailed description of conventional modernization methods as recommended.

 

 

Reference formatting - the references section has duplicate numbering.

• We have corrected the reference formatting and removed the duplicate numbering.

 

Reviewer 2 Report

Comments and Suggestions for Authors

Manuscript presented interesting results and to enhance the final version, my minor comments are following:

1. It's suggested to revise the title and make it shorter and highlight the new of this study.
2. Too length abstract provided and authors must focus to highlight the important findings for this study. 
3. The obtained results must be compare to literature to highlight what this study add to this field.
4. Tables, affiliation, are not according to journal style. 
5. Conclusions not well written as well not follow the journal style. 

Comments on the Quality of English Language

English editing are required.

Author Response

Dear Reviewer,

We would like to sincerely thank you for your careful reading of our manuscript and for the many helpful and constructive remarks. We have carefully considered all comments and implemented the suggested changes in the revised version of the paper. To facilitate the review, all modifications have been highlighted in yellow in the manuscript.

Below, we provide our detailed responses to the individual comments and indicate how they have been addressed in the revised version.

Sincerely,
The Authors

 

It's suggested to revise the title and make it shorter and highlight the new of this study.

• Thank you. We have corrected the title.

 

 

Too length abstract provided and authors must focus to highlight the important findings for this study. 

• Thank you for the suggestion. We have simplified and shortened the abstract accordingly.

 

 

The obtained results must be compare to literature to highlight what this study add to this field.

• In our study, the obtained results are compared with reference beams, which serve as the benchmark. As there are no published results on thermal prestressing in the literature, the reference beams allow us to highlight the novelty and added value of this work.

 

 

Tables, affiliation, are not according to journal style. 

• Thank you for pointing this out. We have adjusted the style to match the journal style.

 

 

Conclusions not well written as well not follow the journal style

• Thank you. We have revised the conclusions.

 

Reviewer 3 Report

Comments and Suggestions for Authors

SUMMARY

The presented article is relevant for civil engineering. Reinforcement of reinforced concrete slabs with thermally prestressed reinforcement was performed.

The authors conducted a study of the efficiency in the limit states of strength of operational suitability.

The authors identified the problem - outdated, ineffective methods of strengthening existing structures. The reason is the self-weight of the structures.

The authors provide an effective alternative to solve the problem. They carried out thermal prestressing of additional reinforcement and performed large-scale experiments. Important data were obtained that will be useful for engineering practice and for science.

Thus, this article contains scientific and practical value. However, the article has some shortcomings. They should be corrected.

 

COMMENTS

1. The title looks too long, it should be shortened. It can be called, for example, "Experimental study of the effectiveness of strengthening reinforced concrete slabs with thermally prestressed reinforcement."
2. The authors showed the engineering problems that arise when strengthening the structure at the beginning of the abstract. However, it should also be said that from a scientific point of view, the relationship between all the parameters of these processes has not been sufficiently studied. It would be nice if the scientific problem, the solution of which is necessary, was reflected.
3. The keywords should provide a full decoding of the HPC abbreviation. This should be done so that it is easier for readers to find this article. Also, the term "Experiments" in the keywords looks incorrect. This is not a keyword for this article, but simply a commonly used word. This is incorrect. It should be replaced with another term.
4. The Introduction section provides an overview of 30 literature sources on the topic of the study. However, many scientists have studied the issues of strengthening reinforced concrete slabs. Therefore, the authors are encouraged to expand the Introduction section and add an additional review of approximately 10-15 literature sources for the past 5 years. This is necessary to provide a more detailed analysis of the current state of the problem.
5. It would be nice if the scientific and applied problems, the purpose and objectives of the study were more clearly formulated.
6. It would be nice if the authors presented the methodology of their study in a flowchart format. It is necessary to show which parameters were varied, which samples were manufactured, and which characteristics of the reinforced slabs were determined. Such a flowchart would help to structure this article.
7. It would be nice if the authors not only presented the materials used in paragraph 2.2, but also justified the choice of these materials.
8. The photographs in the article seem uninformative. The authors need to add more high-quality photographs, research and testing processes. Is it possible to do this? This would be good for this article.
9. Unfortunately, some of the figures are of very low quality and the symbols on them are illegible. For example, this applies to Figure 7.
10. The discussion of the results obtained is a detailed analysis of the tests performed. However, it would be nice to have a comparative table or diagram with the results of other studies. It is necessary to clearly show the main advantages of the results obtained, their novelty and fundamental differences from other results.
11. It would be nice if the authors also showed the risks and limitations of the results obtained.
12. In the Conclusions section, it is proposed to number the conclusions and first arrange the scientific results obtained for the science of structures and buildings, and then provide the applied results.
13. It would be good to show at the end of the Conclusions section a recommendation for real implementation. Which organizations or objects are ready to apply the results obtained now?
14. In the References section, there are sources older than the last 5 years. It would be nice for the authors to show more recent scientific literature. That is why, as already mentioned, it is necessary to add about 15 sources of literature for the period 2020-2025.

Overall, this article seems interesting, important, and relevant. After correcting the comments, it should improve and become more ready for publication. Reviewer's overall conclusion – Major Revisions.

Author Response

Dear Reviewer,

We would like to sincerely thank you for your careful reading of our manuscript and for the many helpful and constructive remarks. We have carefully considered all comments and implemented the suggested changes in the revised version of the paper. To facilitate the review, all modifications have been highlighted in yellow in the manuscript.

Below, we provide our detailed responses to the individual comments and indicate how they have been addressed in the revised version.

Sincerely,
The Authors

 

The title looks too long, it should be shortened. It can be called, for example, "Experimental study of the effectiveness of strengthening reinforced concrete slabs with thermally prestressed reinforcement."

• Thank you for the helpful suggestion. We have adopted the proposed title.

 

 

The authors showed the engineering problems that arise when strengthening the structure at the beginning of the abstract. However, it should also be said that from a scientific point of view, the relationship between all the parameters of these processes has not been sufficiently studied. It would be nice if the scientific problem, the solution of which is necessary, was reflected.

• We thank the reviewer for this remark. The scientific problem of the bond behavior between filler material, reinforcement, and concrete has been addressed in detail in a separate publication by the authors (Schwarz, Y.; Sanio, D.; Mark, P. Influence of heat treatment on the bond creep of high-strength concrete. Beton- und Stahlbetonbau 2024, 119, 253–264, doi:10.1002/best.202300088). In the present paper, the focus is placed on the structural effectiveness of the strengthening method in serviceability and ultimate limit states. We have also added a corresponding note in the manuscript to guide the reader to this reference.

 

 

 

The keywords should provide a full decoding of the HPC abbreviation. This should be done so that it is easier for readers to find this article. Also, the term "Experiments" in the keywords looks incorrect. This is not a keyword for this article, but simply a commonly used word. This is incorrect. It should be replaced with another term.

• We thank the reviewer for the helpful remark. The abbreviation HPC has been fully written out as high-performance concrete in the keywords. In addition, the keyword Experiments has been removed.

 

 

 

 

 

The Introduction section provides an overview of 30 literature sources on the topic of the study. However, many scientists have studied the issues of strengthening reinforced concrete slabs. Therefore, the authors are encouraged to expand the Introduction section and add an additional review of approximately 10-15 literature sources for the past 5 years. This is necessary to provide a more detailed analysis of the current state of the problem.

• Thank you for this helpful suggestion. In the revised manuscript, we have expanded the Introduction by adding 12 recent publications (2019–2025) to provide a broader and more up-to-date overview.

It would be nice if the scientific and applied problems, the purpose and objectives of the study were more clearly formulated.

• We thank the reviewer for this valuable comment. In the revised version, the scientific and applied problems, as well as the purpose and objectives of the study, have been formulated more explicitly at the end of the Introduction.

 

 

It would be nice if the authors not only presented the materials used in paragraph 2.2, but also justified the choice of these materials.

• We have added a justification for the choice of materials in Section 2.2.

 

 

 

Unfortunately, some of the figures are of very low quality and the symbols on them are illegible. For example, this applies to Figure 7.

• We thank the reviewer for pointing this out. All figures were originally created as vector graphics to ensure high resolution and readability. During the conversion of the manuscript into Word, some figures were downscaled, which reduced their quality and made certain symbols less legible. In the final version, the figures will be provided in full resolution to guarantee high quality.

 

 

 

The discussion of the results obtained is a detailed analysis of the tests performed. However, it would be nice to have a comparative table or diagram with the results of other studies. It is necessary to clearly show the main advantages of the results obtained, their novelty and fundamental differences from other results.

 

 

It would be nice if the authors also showed the risks and limitations of the results obtained.

• We have added a paragraph on the limitations of the study as part of the discussion and the conclusions.

 

 

 

 

In the Conclusions section, it is proposed to number the conclusions and first arrange the scientific results obtained for the science of structures and buildings, and then provide the applied results.

• In the revised manuscript, the conclusions have been shortened and restructured. The results are now presented in numbered form, with the scientific findings listed first, followed by the applied findings.

 

It would be good to show at the end of the Conclusions section a recommendation for real implementation. Which organizations or objects are ready to apply the results obtained now?

• We have added this to the conclusions.

 

 

 

In the References section, there are sources older than the last 5 years. It would be nice for the authors to show more recent scientific literature. That is why, as already mentioned, it is necessary to add about 15 sources of literature for the period 2020-2025.

• We have added several recent sources (2020–2025).

 

Reviewer 4 Report

Comments and Suggestions for Authors    

1. Clarity of Introduction and Objectives: The introduction effectively outlines the need for strengthening reinforced concrete slabs using thermally prestressed reinforcement, highlighting applications in bridges and slabs. However, the objectives could be more explicitly stated with measurable hypotheses. For instance, quantifying the expected increase in load-bearing capacity or deflection reduction would strengthen the scientific rigor. This would help readers better understand the scope and anticipated outcomes.
2. Methodology Description: The experimental setup is detailed, including beam dimensions, insulation with polystyrene panels, and the use of triangular slots for reinforcement. Yet, the description of the heating process lacks specifics on temperature control mechanisms, such as the exact heating duration, power input, or monitoring equipment. Providing these details would enhance reproducibility and allow for better comparison with numerical models.
3. Material Properties: The paper mentions high-performance concrete (HPC) and reinforcement bars, but material characterizations (e.g., compressive strength, tensile properties, thermal expansion coefficients) are insufficiently tabulated. A comprehensive table summarizing tested material properties, including standard deviations from multiple samples, is recommended to validate the experimental results and support the thermal prestressing claims.
4. Data Presentation: Figures such as load-deflection diagrams (Fig. 8) and strain distributions (Fig. 6, 7, 9) are informative, but some lack clear labels or legends. For example, distinguishing between prestressed and reference beams in all plots with consistent color coding would improve readability. Additionally, error bars on experimental data points are missing, which is crucial for assessing variability and reliability.
5. Numerical Modeling: The comparison between experimental and numerical results (e.g., temperature distributions and strains in Fig. 7 and 12) is a strong aspect, demonstrating good agreement. However, the modeling assumptions (e.g., finite element software used, boundary conditions, mesh size) are not fully disclosed. Elaborating on validation metrics, such as root mean square error between simulated and measured strains, would bolster the credibility of the predictions.
6. Effectiveness in ULS and SLS: The discussion on ultimate limit state (ULS) and serviceability limit state (SLS) effectiveness is supported by load increases and reduced deflections. Nevertheless, the paper could benefit from a quantitative analysis, such as calculating efficiency ratios (e.g., prestress contribution to total capacity) and comparing them to traditional strengthening methods like external steel plates or FRP. This would contextualize the novelty of thermal prestressing.
7. Limitations and Assumptions: The study assumes symmetric thermal boundary conditions via insulation, which mimics continuous slabs well. However, potential limitations, such as edge effects in real-world applications or long-term creep under sustained loads, are not addressed. Acknowledging these and suggesting future studies on durability (e.g., corrosion in heated reinforcement) would provide a more balanced view.
8. References and Literature Review: The reference list is extensive, covering related works on retrofitting techniques (e.g., FRP, steel plates). Still, it could include more recent studies (post-2020) on thermal prestressing in concrete, as the field evolves rapidly. Cross-referencing with cited works in the discussion section would also strengthen arguments, particularly when claiming advantages over conventional methods.
9. Conclusions and Implications: Conclusions succinctly summarize the increased effectiveness in ULS (e.g., higher failure loads) and SLS (e.g., reduced cracks). However, practical implications for bridge engineering, such as cost-benefit analysis or scalability to full-scale slabs, are underdeveloped. Expanding this section with recommendations for design codes or field trials would enhance the paper's impact.
10. Overall Structure and Language: The paper is well-structured with logical flow from theory to experiments and analysis. Language is technical and precise, but minor grammatical issues (e.g., inconsistent use of abbreviations like "SG" for strain gauge) and repetitive phrasing in descriptions could be refined. Proofreading for clarity and ensuring all equations (e.g., Eq. 1 for strains) are clearly derived would polish the manuscript.

 

Author Response

Dear Reviewer,

We would like to sincerely thank you for your careful reading of our manuscript and for the many helpful and constructive remarks. We have carefully considered all comments and implemented the suggested changes in the revised version of the paper. To facilitate the review, all modifications have been highlighted in yellow in the manuscript.

Below, we provide our detailed responses to the individual comments and indicate how they have been addressed in the revised version.

Sincerely,
The Authors

 

 

Clarity of Introduction and Objectives: The introduction effectively outlines the need for strengthening reinforced concrete slabs using thermally prestressed reinforcement, highlighting applications in bridges and slabs. However, the objectives could be more explicitly stated with measurable hypotheses. For instance, quantifying the expected increase in load-bearing capacity or deflection reduction would strengthen the scientific rigor. This would help readers better understand the scope and anticipated outcomes.

• Thank you. We have added this to the introduction.

 

Methodology Description: The experimental setup is detailed, including beam dimensions, insulation with polystyrene panels, and the use of triangular slots for reinforcement. Yet, the description of the heating process lacks specifics on temperature control mechanisms, such as the exact heating duration, power input, or monitoring equipment. Providing these details would enhance reproducibility and allow for better comparison with numerical models.

• Thank you. We have added information on the heating system.”

 

 

 

Material Properties: The paper mentions high-performance concrete (HPC) and reinforcement bars, but material characterizations (e.g., compressive strength, tensile properties, thermal expansion coefficients) are insufficiently tabulated. A comprehensive table summarizing tested material properties, including standard deviations from multiple samples, is recommended to validate the experimental results and support the thermal prestressing claims.

• Thank you. We have added some more details on the materials used. The material properties of the HPC directly depend on the duration of tempering and the specimen geometry. Therefore, accompanying tests at this point do not provide significant insights. However, this relationship has been examined in detail in a separate publication. We have added a corresponding note in the manuscript at the relevant section.

 

 

 

Data Presentation: Figures such as load-deflection diagrams (Fig. 8) and strain distributions (Fig. 6, 7, 9) are informative, but some lack clear labels or legends. For example, distinguishing between prestressed and reference beams in all plots with consistent color coding would improve readability. Additionally, error bars on experimental data points are missing, which is crucial for assessing variability and reliability.

• We thank the reviewer for this remark. Since the presented results are from large-scale tests, only one experiment was conducted for each configuration, and therefore error bars cannot be provided. The color coding and labeling of the individual tests are defined in Table 1 and applied consistently throughout the figures.

 

Numerical Modeling: The comparison between experimental and numerical results (e.g., temperature distributions and strains in Fig. 7 and 12) is a strong aspect, demonstrating good agreement. However, the modeling assumptions (e.g., finite element software used, boundary conditions, mesh size) are not fully disclosed. Elaborating on validation metrics, such as root mean square error between simulated and measured strains, would bolster the credibility of the predictions.

• We thank the reviewer for this valuable remark. We have added further information on the numerical model in the manuscript. Additional details can be found in [Sanio, D.; Mark, P.; Ahrens, M.A. Computation of temperature fields on bridges. Implementation by means of spread­sheets. Beton- und Stahlbetonbau 2017, 112, 85–95, doi:10.1002/best.201600068.]. Moreover, we have included the absolute strain values from both the experiment and the model to support the comparison.

 

 

Effectiveness in ULS and SLS: The discussion on ultimate limit state (ULS) and serviceability limit state (SLS) effectiveness is supported by load increases and reduced deflections. Nevertheless, the paper could benefit from a quantitative analysis, such as calculating efficiency ratios (e.g., prestress contribution to total capacity) and comparing them to traditional strengthening methods like external steel plates or FRP. This would contextualize the novelty of thermal prestressing.

• We thank the reviewer for this remark. For this purpose, the reference tests are included, as no other studies on thermal prestressing are yet available in the literature. These serve as the benchmark for quantifying the effectiveness and highlighting the novelty of the method.

 

 

Limitations and Assumptions: The study assumes symmetric thermal boundary conditions via insulation, which mimics continuous slabs well. However, potential limitations, such as edge effects in real-world applications or long-term creep under sustained loads, are not addressed. Acknowledging these and suggesting future studies on durability (e.g., corrosion in heated reinforcement) would provide a more balanced view.

• We have investigated the influence of heat treatment on the durability of the HPC in a separate publication and found no significant damaging effects. We have added a corresponding note in the manuscript at the relevant section. Likewise, we do not consider corrosion of the reinforcement to be critical, since it is only heated once to 80 °C.

 

References and Literature Review: The reference list is extensive, covering related works on retrofitting techniques (e.g., FRP, steel plates). Still, it could include more recent studies (post-2020) on thermal prestressing in concrete, as the field evolves rapidly. Cross-referencing with cited works in the discussion section would also strengthen arguments, particularly when claiming advantages over conventional methods.

• Thank you. We have added some more recent references.

 

Conclusions and Implications: Conclusions succinctly summarize the increased effectiveness in ULS (e.g., higher failure loads) and SLS (e.g., reduced cracks). However, practical implications for bridge engineering, such as cost-benefit analysis or scalability to full-scale slabs, are underdeveloped. Expanding this section with recommendations for design codes or field trials would enhance the paper's impact.

• In the revised version, we have expanded the Conclusions by adding an outlook on practical implications.

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have revised the manuscript in accordance with the review comments. I have also reviewed the other revisions marked in yellow and, in my opinion, the manuscript is suitable for publication in its current form.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have taken into account all the reviewer's comments. The article has been significantly improved. The article can now be published. The reviewer has no more comments.

Reviewer 4 Report

Comments and Suggestions for Authors

The authors revised the manuscript.