Residual Mechanical Properties of Sandstone After Fire

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Comment 1
In my view, the true contribution of the paper lies in presenting the first systematic data set on the fire-induced behaviour of Božanov sandstone—a point that deserves greater emphasis. While the choice of uniaxial compression testing and DIC is entirely appropriate, the manuscript should explicitly acknowledge that these are well-established techniques. To substantiate the micro-mechanisms underlying the observed changes, I would encourage the authors to incorporate, or at least discuss, complementary microstructural methods such as SEM or XRD.

Comment 2
The relatively small number of specimens at each temperature level undermines the statistical robustness of the findings. This limitation ought to be stated more forthrightly. Although shape-factor corrections have been applied, basic statistics—standard deviations and a simple ANOVA, for example—would give the reader a clearer sense of data scatter. Future work should aim for larger sample sets to bolster confidence in the trends reported.

Comment 3
The literature survey is wide-ranging, yet the paper offers limited quantitative juxtaposition of its results with earlier studies. A concise table contrasting the present strength loss, strain and modulus data with those of Zhang et al. (2023) and Yu et al. (2015) would situate the work more convincingly within the existing body of knowledge.

Comment 4
All tests employ slow furnace cooling, even though rapid quenching is known to yield markedly different mechanical responses. The authors should clarify why a single cooling regime was selected and discuss how this choice constrains the generality of their conclusions.

Comment 5
The manuscript documents the mechanical degradation clearly, but gives only cursory attention to the underlying causes—microcracking, mineral decomposition or increased porosity. A brief, mechanism-oriented discussion (even if primarily conceptual) would deepen the reader’s understanding of the results.

Comment 6
Digital image correlation is a definite asset of the study; however, key technical details are missing. Camera resolution, illumination strategy and calibration procedures need to be reported so that others can reproduce the measurements.

Comment 7
Post-heating colour changes are described qualitatively, which inevitably invites subjective interpretation. Quantifying colour with a colourimeter and reporting CIE Lab* values would render this aspect of the work objective and readily comparable.

Comment 8
The conclusions gesture toward future work but remain rather general. Concrete suggestions—thermogravimetric analysis, Raman spectroscopy, or numerical modelling of thermal damage—would better convey the longer-term trajectory and potential impact of the present study.

 

 

To enrich the theoretical discussion on post-fire degradation and mechanical modeling, the following references are highly relevant:

Hacıefendioğlu, K., Genc, A.F., Nayır, S., Ayas, S., & Altunışık, A.C. (2022).
Automatic estimation of post-fire compressive strength reduction of masonry structures using deep convolutional neural network.
Fire Technology, 58(5), 2779–2809.
https://doi.org/10.1007/s10694-021-01220-z

 

 

Author Response

Dear Reviewer,

we would like to sincerely thank you for your thorough and thoughtful review of our manuscript. We greatly appreciate the time and effort you invested in evaluating our work and providing constructive feedback.

Your valuable suggestions and critical observations have helped us significantly improve the clarity, structure, and overall quality of the manuscript. We have carefully considered all comments and have incorporated the recommended changes into the revised version. We believe that these revisions have enhanced both the scientific rigor and the readability of the paper.

Comments 1: In my view, the true contribution of the paper lies in presenting the first systematic data set on the fire-induced behaviour of Božanov sandstone—a point that deserves greater emphasis. While the choice of uniaxial compression testing and DIC is entirely appropriate, the manuscript should explicitly acknowledge that these are well-established techniques. To substantiate the micro-mechanisms underlying the observed changes, I would encourage the authors to incorporate, or at least discuss, complementary microstructural methods such as SEM or XRD.
Response 1: Thank you for highlighting this important contribution. We have revised the introduction and conclusion to better emphasize the novelty of presenting the first systematic dataset on Božanov sandstone under high-temperature conditions. The text now explicitly acknowledges that both uniaxial compression testing and digital image correlation (DIC) are well-established and widely used methods for evaluating mechanical performance and strain behavior. In response to your suggestion, we have added a discussion on the potential of complementary microstructural techniques such as SEM and XRD to reveal underlying degradation mechanisms. In our future research we will incorporate these (and other) techniques.

Comments 2: The relatively small number of specimens at each temperature level undermines the statistical robustness of the findings. This limitation ought to be stated more forthrightly. Although shape-factor corrections have been applied, basic statistics—standard deviations and a simple ANOVA, for example—would give the reader a clearer sense of data scatter. Future work should aim for larger sample sets to bolster confidence in the trends reported.
Response 2: We fully agree and have revised the manuscript to explicitly acknowledge the limitations imposed by the small sample size. In addition, we now include standard deviations, variation and variation coefficient for the key mechanical parameters and have conducted a one-way ANOVA and post hoc Tukey’s HSD test to assess statistical significance across temperature groups. These changes improve the transparency of data interpretation. We also agree that future research should include a larger number of specimens to enhance statistical robustness

Comments 3: The literature survey is wide-ranging, yet the paper offers limited quantitative juxtaposition of its results with earlier studies. A concise table contrasting the present strength loss, strain and modulus data with those of Zhang et al. (2023) and Yu et al. (2015) would situate the work more convincingly within the existing body of knowledge.
Response 3: Thank you for this constructive suggestion. We have added a new comparative Figure from our study alongside data reported by Zhang et al. (2023) and Yu et al. (2015). This addition helps to contextualize our results within the broader literature and highlights both similarities and differences among various sandstones under thermal loading.

Comments 4č: All tests employ slow furnace cooling, even though rapid quenching is known to yield markedly different mechanical responses. The authors should clarify why a single cooling regime was selected and discuss how this choice constrains the generality of their conclusions.
Response 4: We appreciate this observation. The manuscript has been revised to clarify that natural furnace cooling was selected to replicate moderate post-fire cooling conditions. A comparative investigation of cooling methods is planned for future work.

Comments 5: The manuscript documents the mechanical degradation clearly, but gives only cursory attention to the underlying causes—microcracking, mineral decomposition or increased porosity. A brief, mechanism-oriented discussion (even if primarily conceptual) would deepen the reader’s understanding of the results.
Response 5: We agree and have expanded the text to include a conceptual overview of potential degradation mechanisms. Although direct microstructural analysis was beyond the scope of the current study, we have highlighted these processes as plausible explanations for the observed trends and as targets for future microanalytical work.

Comments 6: Digital image correlation is a definite asset of the study; however, key technical details are missing. Camera resolution, illumination strategy and calibration procedures need to be reported so that others can reproduce the measurements.
Response 6: Thank you for this important observation. We have revised the Methods section to include detailed specifications of the DIC setup, including the 5 MPx resolution of the AOX-ONE camera (2448 × 2048 px), the use of a 50 mm lens, LED-based uniform illumination, and calibration procedures. The system complies with EN ISO 9513 Class 0.5 and ASTM E83 Class A, ensuring traceable and reproducible measurements.

Comments 7: Post-heating colour changes are described qualitatively, which inevitably invites subjective interpretation. Quantifying colour with a colourimeter and reporting CIE Lab* values would render this aspect of the work objective and readily comparable.
Response 7: We acknowledge this limitation and agree that objective color measurement would improve reproducibility and comparability. Although a colourimeter was not available for this study, we have added a note in the discussion section emphasizing the value of using CIE Lab* metrics in future research to quantitatively assess colour changes due to thermal exposure.

Comments 8: The conclusions gesture toward future work but remain rather general. Concrete suggestions—thermogravimetric analysis, Raman spectroscopy, or numerical modelling of thermal damage—would better convey the longer-term trajectory and potential impact of the present study.
Response 8: We appreciate this suggestion and have revised the conclusion to include specific directions for future research. This added detail clarifies the future trajectory and broader implications of our work.

Reviewer 2 Report

Comments and Suggestions for Authors

Dear authors,

I have reviewed the entitled manuscript buildings-3709429 “Residual mechanical properties of sandstone after fire”. Good and practical laboratory work has been done on the engineering properties of building materials. The literature review is well done and the references are relevant to the topic. Some comments are given below:

- The standard used for the dimensions of the experimental samples should be mentioned in the captions of Figures 3 and 4 and Table 1 (by adding a column).

- Why did the authors not discuss and review the shear strength test of the samples under the desired conditions. This is very important in the study of the engineering properties of building materials.

- Valid references from 2024 and 2025 should be used to support the article.

Comments on the Quality of English Language

The English could be improved to more clearly express the research.

Author Response

Dear Reviewer,

we would like to sincerely thank you for your thorough and thoughtful review of our manuscript. We greatly appreciate the time and effort you invested in evaluating our work and providing constructive feedback.

Your valuable suggestions and critical observations have helped us significantly improve the clarity, structure, and overall quality of the manuscript. We have carefully considered all comments and have incorporated the recommended changes into the revised version. We believe that these revisions have enhanced both the scientific rigor and the readability of the paper.

Comments 1: The standard used for the dimensions of the experimental samples should be mentioned in the captions of Figures 3 and 4 and Table 1 (by adding a column).
Response 1: Thank you for this helpful suggestion. We have revised the captions of Figures 3 and 4 and Note in Table 1 to include a reference to the standard used for sample dimensions (ČSN EN 772-1+A1). 

Comments 2: Why did the authors not discuss and review the shear strength test of the samples under the desired conditions. This is very important in the study of the engineering properties of building materials.
Response 2: We agree that shear strength is an important parameter in the characterization of natural stone. However, the present study focused on uniaxial compressive strength as a first step in evaluating the thermal degradation of Božanov sandstone. Due to limitations in sample material and testing capacity, shear tests were not included in this phase. We have now added a discussion in the manuscript highlighting the importance of shear strength and noting that it will be addressed in future studies to provide a more comprehensive understanding of the stone's post-fire mechanical behavior.

Comments 3: Valid references from 2024 and 2025 should be used to support the article.
Response 3: Thank you for this recommendation. We have updated the manuscript to include several relevant and peer-reviewed references from 2024 and 2025 where appropriate. These additions strengthen the currency and relevance of the literature review and provide a more up-to-date context for the findings presented.

Reviewer 3 Report

Comments and Suggestions for Authors

Residual mechanical properties of sandstone after fire are addressed in this manuscript, which is quite interesting for the readers in Journal. My comments are shown as follows:

1. More evidences should be provided to support the statement of "mineralogical transformations", which is essential for the analysis of the failure mechanism exposed by the high temperature treatment. Additionally, the advanced optical detection techniques such as the scanning electron microscope should be used to invest the microstructural changes.
2. Some data that are removed in Table 2 should be clarified. Those data cannot be presented in the manuscript?
3. Some stress-strain curves of sandstone samples under uniaxial compression in Figure 8 do not show the post-failure stage, and why?
4. For a high temperature of 900 °C, how to define the failure? Additionally, the sandstone failure under high temperature conditions commonly shows a static and progressive failure pattern, while the sandstone failure under room temperature conditions often shows a dynamic and violent failure pattern mimicking the rockburst in underground engineering. Authors are suggested to calculate and describe the brittleness of sandstone subjected to different temperature treatments and then link the results to the rockburst analysis in the light of the works in https://doi.org/10.1016/j.engfracmech.2025.111267.
5. This manuscript indicates the influence of high temperature on the mineralogical transformations, which is crucial for the macro mechanical properties and the failure behaviors. The resent contributions in the works entitled “An ordinary state-based peridynamic model for granular fracture in polycrystalline materials with arbitrary orientations in cubic crystals” highlighted the roles of microstructural features in materials’ failure behaviors and the resultant mechanical properties. Please combine this contribution to describe the limitation of the study.

Author Response

Dear Reviewer,

we would like to sincerely thank you for your thorough and thoughtful review of our manuscript. We greatly appreciate the time and effort you invested in evaluating our work and providing constructive feedback.

Your valuable suggestions and critical observations have helped us significantly improve the clarity, structure, and overall quality of the manuscript. We have carefully considered all comments and have incorporated the recommended changes into the revised version. We believe that these revisions have enhanced both the scientific rigor and the readability of the paper.

Comments 1: More evidences should be provided to support the statement of "mineralogical transformations", which is essential for the analysis of the failure mechanism exposed by the high temperature treatment. Additionally, the advanced optical detection techniques such as the scanning electron microscope should be used to invest the microstructural changes.
Response 1: We appreciate this important observation. We agree that direct evidence of mineralogical transformations would greatly enhance the understanding of failure mechanisms under high-temperature exposure. Although such analysis was beyond the scope of the present study, we have revised the text to acknowledge this limitation. We have also added that future research will include microstructural analysis using scanning electron microscopy (SEM), X-ray diffraction (XRD), and FTIR to characterize mineral changes and fracture patterns in greater detail.

Comments 2: Some data that are removed in Table 2 should be clarified. Those data cannot be presented in the manuscript?
Response 2: Thank you for pointing this out. The values that were excluded from the statistical analysis in Table 2 were identified as outliers using Grubbs’s test. However, for transparency, all raw data—including outliers—are presented in the table, with the omitted values clearly marked and noted in the caption. We have also clarified this procedure in the methodology section.

Comments 3: Some stress-strain curves of sandstone samples under uniaxial compression in Figure 8 do not show the post-failure stage, and why?
Response 3: We acknowledge this observation and appreciate your attention to detail. In some cases, the post-failure stage is not fully captured due to rapid specimen fragmentation or limitations in displacement measurement after peak load. We have unified the curves to not include the post peak portions of the curves. We acknowledge this limitation and will aim to improve it in future tests.

Comments 4: For a high temperature of 900 °C, how to define the failure? Additionally, the sandstone failure under high temperature conditions commonly shows a static and progressive failure pattern, while the sandstone failure under room temperature conditions often shows a dynamic and violent failure pattern mimicking the rockburst in underground engineering. Authors are suggested to calculate and describe the brittleness of sandstone subjected to different temperature treatments and then link the results to the rockburst analysis in the light of the works in https://doi.org/10.1016/j.engfracmech.2025.111267.
Response 4: Thank you for this valuable suggestion. In our experiments, failure was defined based on the peak stress in the stress–strain curve, consistent with standard uniaxial compression test procedures. We agree that analyzing brittleness could offer additional insight into temperature-dependent failure behavior. Although brittleness was not calculated in this study, we have now added a discussion acknowledging this omission and highlighting its importance in the context of rockburst analysis. The referenced work has also been cited, and we plan to include brittleness analysis in future studies.

Comments 5: This manuscript indicates the influence of high temperature on the mineralogical transformations, which is crucial for the macro mechanical properties and the failure behaviors. The resent contributions in the works entitled “An ordinary state-based peridynamic model for granular fracture in polycrystalline materials with arbitrary orientations in cubic crystals” highlighted the roles of microstructural features in materials’ failure behaviors and the resultant mechanical properties. Please combine this contribution to describe the limitation of the study.
Response 5: We thank the reviewer for this insightful reference. We agree that microstructural features, including grain orientation and intergranular bonding, play a critical role in failure processes. We have revised the discussion to include a note on the relevance of microstructural modeling approaches, such as peridynamic simulations, which could help predict fracture propagation in thermally degraded sandstone. The referenced work has been cited to illustrate the limitation of our current approach and to suggest a potential pathway for future modeling efforts that account for the internal heterogeneity of natural stones. Also these elements will be addressed in future studies to enhance understanding of sandstone degradation and failure after fire exposure.

Reviewer 4 Report

Comments and Suggestions for Authors

This paper presents a well-structured experimental study examining the mechanical degradation of Božanov sandstone after high-temperature exposure. The authors expose sandstone samples to controlled heating regimes up to 900 °C and assess residual properties through uniaxial compression tests, with additional discussion on stress-strain behaviour, colour change, and elastic modulus. However, the manuscript would benefit from methodological detail, deeper interpretation, and improvements in presentation.

 

1. Only three samples were tested per temperature group. While this is common in materials testing due to availability, it limits statistical reliability. For clarity, the authors should comment more directly on this limitation and consider including confidence intervals or error bars in the figures.
2. While colour change is noted and attributed to iron oxidation, this remains speculative without mineralogical evidence. Even basic post-test visual microscopy or petrography would strengthen the conclusion and could be added in future work or discussed more explicitly as a limitation.
3. Although the manuscript acknowledges the role of cooling in stone degradation, the experiment uses only natural furnace cooling. A comparative discussion with other cooling regimes (e.g. quenching) from the literature would provide context and enhance the practical relevance of the findings.
4. The tables and text often show relative values as percentages of “original” or “reference,” but this is not always consistent or easy to track (e.g., 87–109% of what baseline?). Consider unifying how residual strength, strain, and modulus are presented, and ensure figures include these benchmarks visually.
5. Figures 8–12 show important trends, but the legends, axes, and labels could be clearer. Additionally, referencing figures more precisely within the discussion sections (e.g., “see Figure 10 for axial strain increase”) would guide the reader more effectively.
6. The conclusion could be expanded with more applied recommendations. For example, what does a 43% drop in UCS mean for post-fire structural assessment of heritage buildings? Even if speculative, a paragraph offering such context would enhance impact.

Author Response

Dear Reviewer,

we would like to sincerely thank you for your thorough and thoughtful review of our manuscript. We greatly appreciate the time and effort you invested in evaluating our work and providing constructive feedback.

Your valuable suggestions and critical observations have helped us significantly improve the clarity, structure, and overall quality of the manuscript. We have carefully considered all comments and have incorporated the recommended changes into the revised version. We believe that these revisions have enhanced both the scientific rigor and the readability of the paper.

Comments 1: Only three samples were tested per temperature group. While this is common in materials testing due to availability, it limits statistical reliability. For clarity, the authors should comment more directly on this limitation and consider including confidence intervals or error bars in the figures.
Response : We agree with this observation. The manuscript has been amended to explicitly state the limitations of statistical evaluation due to the small sample size..

Comments 2: While colour change is noted and attributed to iron oxidation, this remains speculative without mineralogical evidence. Even basic post-test visual microscopy or petrography would strengthen the conclusion and could be added in future work or discussed more explicitly as a limitation.
Response : We fully agree. The text has been revised to discuss this limitation more explicitly and to emphasize the potential benefits of complementary mineralogical analyses such as petrography or microscopy. We also note that such methods are planned as part of our future research.

Comments 3: Although the manuscript acknowledges the role of cooling in stone degradation, the experiment uses only natural furnace cooling. A comparative discussion with other cooling regimes (e.g. quenching) from the literature would provide context and enhance the practical relevance of the findings.
Response : Thank you for this helpful suggestion. We have made changes to the text stating the benefits of such analysis. Comparative experimental evaluation, including quenching, will be addressed in future research currently in preparation.

Comments 4: The tables and text often show relative values as percentages of “original” or “reference,” but this is not always consistent or easy to track (e.g., 87–109% of what baseline?). Consider unifying how residual strength, strain, and modulus are presented, and ensure figures include these benchmarks visually.
Response : We agree. The text and tables have been substantially revised to ensure consistency and clarity in how relative values are presented. Reference baselines are now clearly defined, and percentages are expressed uniformly throughout the manuscript.

Comments 5: Figures 8–12 show important trends, but the legends, axes, and labels could be clearer. Additionally, referencing figures more precisely within the discussion sections (e.g., “see Figure 10 for axial strain increase”) would guide the reader more effectively.
Response : We agree with this recommendation. Figure captions and labels have been improved for clarity, and more specific references to relevant figures have been added throughout the discussion to better guide the reader.

Comments 6: The conclusion could be expanded with more applied recommendations. For example, what does a 43% drop in UCS mean for post-fire structural assessment of heritage buildings? Even if speculative, a paragraph offering such context would enhance impact.
Response : We agree and have expanded the conclusion to address the implications of residual mechanical degradation for post-fire assessment of historical stone structures. The added text discusses the relevance of these findings for decision-making in conservation, including structural retention, strengthening, or repair strategies.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

General Impression

Scientific Contribution: The revision has clarified the original contribution of the study and has strengthened its position within the existing body of literature.

Methodological Transparency: The test setup, statistical analyses, and study limitations have been described in detail, improving reproducibility and clarity.

Reviewer Concerns: All eight major comments from the reviewer have been addressed through structural revisions or expanded discussions.

Remaining Limitations: The sample size remains relatively small, and microstructural analyses are still at the conceptual stage. However, both limitations have been transparently acknowledged and are directed toward future research.

Conclusion and Recommendation

The major revision has satisfactorily addressed the core criticisms raised by the reviewer and has substantially improved the scientific rigor of the manuscript. Remaining issues are minor in nature (e.g., editorial polishing, figure quality, and future microstructural validation) and do not compromise the validity of the findings or their interpretation.

Therefore, the manuscript has reached an acceptable level and may be recommended for acceptance after minor editorial corrections.

Reviewer 2 Report

Comments and Suggestions for Authors

The current format of the revised manuscript can be published at the journal.

Reviewer 3 Report

Comments and Suggestions for Authors

The revised manuscript has addressed the reviewers' comments and is now of high-quality, which can be accepted in current version. 

Reviewer 4 Report

Comments and Suggestions for Authors

All comments addressed