The Development of Cement-Based, Intumescent and Geopolymer Fire-Retardation Coatings for Metal Structures: A Review

Round 1

Reviewer 1 Report

Review Report

This manuscript is well organized. The topic is interesting for readers and this review deals with potentially significant knowledge to the field.

1.       Keywords: “passive fireproofing system” is missing

2.       Line 39: Please provide definitions “extreme fire event” and “extremely high temperatures” ?

3.       Line 52 and 53 and 238 and 239– I suggest entering "toxic decomposition products" instead of "odours during fire event". Please add references in the field of flame retardants for epoxy resin (10.3390/ijerph19084828). Epoxy resins are highly toxic under fire conditions. Please complete the bibliography on epoxy toxicity and flame retardants for epoxy resin so that the visibility range can be really considered that the visibility is an important release or toxicity.

4.       Line 222  - Please provide definitions of "cellulosic fire conditions" What fire conditions have been assumed? Is this a fire class A? Please describe your answer in detail.

5.       Line 225  - Please provide definitions of "hydrocarbon fire conditions" What fire conditions have been assumed? Is this a fire class B or C? Please describe your answer in detail.

6.        Line 538 - In the LCA it is important to indicate the purpose and scope, functional unit, method (RECIPE, CML Baseline or other), impact category, damages category and system boundaries, e.g. production stage or post-consumer processing stage. These data are missing in the description. Please complete.

7.       The conclusions could be more comprehensive, and the discussions of the results could be more effective.

8.       The titles of references have a different format, the title of the article is written in capital letters at the beginning of words, others only in lower case. Also, the standardized format of presentation in the journal's name. Because names have been written in a different format, one is not abbreviated, others are not.

Page numbers are missing.

Overall, the manuscript calls for significant minor revisions in order to improve its quality.

Author Response

1. Keywords: “passive fireproofing system” is missing

Agree. This is important and is added.

2. Line 39: Please provide definitions “extreme fire event” and “extremely high temperatures” ?

This is added in Line 39-40

3. Line 52 and 53 and 238 and 239– I suggest entering "toxic decomposition products" instead of "odours during fire event". Please add references in the field of flame retardants for epoxy resin (10.3390/ijerph19084828). Epoxy resins are highly toxic under fire conditions. Please complete the bibliography on epoxy toxicity and flame retardants for epoxy resin so that the visibility range can be really considered that the visibility is an important release or toxicity.

Agree. This is changed and reference is added in line 60-61 and line 115

4. Line 222 - Please provide definitions of "cellulosic fire conditions" What fire conditions have been assumed? Is this a fire class A? Please describe your answer in detail.

Agree. This is added and in line in line 243-251 

5. Line 225  - Please provide definitions of "hydrocarbon fire conditions" What fire conditions have been assumed? Is this a fire class B or C? Please describe your answer in detail.-

Agree. This is added and in line in line 243-251 

6. Line 538 - In the LCA it is important to indicate the purpose and scope, functional unit, method (RECIPE, CML Baseline or other), impact category, damages category and system boundaries, e.g. production stage or post-consumer processing stage. These data are missing in the description. Please complete.

Agree. This is added in line 594-608

7. The conclusions could be more comprehensive, and the discussions of the results could be more effective.

Agree. This is amended.

8. The titles of references have a different format, the title of the article is written in capital letters at the beginning of words, others only in lower case. Also, the standardized format of presentation in the journal's name. Because names have been written in a different format, one is not abbreviated, others are not.

Agree. This is amended according to the suggestion and changed to MDPI style

Page numbers are missing.

This is shown at the top-right corner.

Reviewer 2 Report

The manuscript under the title: “The development of conventional and geopolymer fire-retardation coatings for metal structures: A review” is in line with the “Coatings” journal. The topic undertaken is up-to-date and important. Overall, the review is comprehensive and well-prepared, but it requires some revision. The following elements required to be improved:

·        Title: please, define what mean “conventional”

·        Introduction: line 47 “intumescent” is mentioned as examples for passive and active protection; please clarify (the same in lines 90, 146, 230…).

·        Introduction - last paragraph of the Introduction part should explain the main aim of the article and stress the novelty aspect given by review; why this review is needed?

·        Introduction or additional part - lack of information on methodology and research methods. In the review article short information about used keywords, databased or general methodology for the literature review should be presented.

·        Introduction or chapter 2. Please mention that the geopolymer were developed as fire-resistant materials; moreover, some short information about this material for passive fire protection is required, including some new research that allows one to compare the behavoiur of these materials in fire, please compare: https://0-doi-org.brum.beds.ac.uk/10.3390/en15093363 and https://0-doi-org.brum.beds.ac.uk/10.1051/matecconf/201824700031

·        Chapter 2.2. Geopolymers are also used for protection of polymer material against fire, please see: https://0-doi-org.brum.beds.ac.uk/10.3390/polym14101945

·        Chapter 3.1.: Line 328 “et al.” is missing.

·        Chapter 3.3. (lines 423-424), the upper index is missing. Please correct upper / down index in whole text.

·        Chapter 4. There is only a few comparisons for fire behaviour, so be more focused on this aspect given in the title.

·        Also, give also some outlook on perspectives in this area, including multifunctional coatings. Consider also some new solutions as foam coatings: https://0-doi-org.brum.beds.ac.uk/10.3390/app122111205 or coatings with photocatalytic properties: https://0-doi-org.brum.beds.ac.uk/10.3390/coatings12091348

·        References: please use the journal template for the references

·        References: Taking into account the character of the article there are a small number of gicven references, the topic should be analysed more in-depth.

Author Response

Title: please, define what mean “conventional”

Not too sure about this, but this was defined in the main text (line 11)

Introduction: line 47 “intumescent” is mentioned as examples for passive and active protection; please clarify (the same in lines 90, 146, 230…).

Agree. This is modified in line 48-52

Introduction - last paragraph of the Introduction part should explain the main aim of the article and stress the novelty aspect given by review; why this review is needed?

Agree. This is shown in line 92-102

Introduction or additional part - lack of information on methodology and research methods. In the review article short information about used keywords, databased or general methodology for the literature review should be presented.

Agree. This is added in Line 67-72 and line 80-82

Introduction or chapter 2. Please mention that the geopolymer were developed as fire-resistant materials; moreover, some short information about this material for passive fire protection is required, including some new research that allows one to compare the behavoiur of these materials in fire, please compare: https://0-doi-org.brum.beds.ac.uk/10.3390/en15093363 and https://0-doi-org.brum.beds.ac.uk/10.1051/matecconf/201824700031

Agree. This is added in line 76-79

Chapter 2.2. Geopolymers are also used for protection of polymer material against fire, please see: https://0-doi-org.brum.beds.ac.uk/10.3390/polym14101945

Agree. This is added in line 79-80

Chapter 3.1.: Line 328 “et al.” is missing.

Agree. This is modified.

Chapter 3.3. (lines 423-424), the upper index is missing. Please correct upper / down index in whole text.

Agree. This is amended.

Chapter 4. There is only a few comparisons for fire behaviour, so be more focused on this aspect given in the title.

Agree. This is added in line 572-594

Also, give also some outlook on perspectives in this area, including multifunctional coatings. Consider also some new solutions as foam coatings: https://0-doi-org.brum.beds.ac.uk/10.3390/app122111205 or coatings with photocatalytic properties: https://0-doi-org.brum.beds.ac.uk/10.3390/coatings12091348

Agree. This is added in line 677-679

References: please use the journal template for the references

Agree. This is amended according to the suggestion and changed to MDPI style

References: Taking into account the character of the article there are a small number of gicven references, the topic should be analysed more in-depth.

Agree. This is amended according to the suggestion

Reviewer 3 Report

Revision for Coatings (ISSN 2079-6412)

Manuscript ID: coatings-2218119

Title: The development of conventional and geopolymer fire-retardation

coatings for metal structures: A review

List of authors: Kaibao Wang, Huirong Le*

The authors present a comprehensive review on conventional geopolymer-based passive coatings used for metal substrate in the prevention of fire-induced structural collapses, also considering more recent and sustainable approaches. Overall, I find the paper well written and full of useful information. I do have some suggestions that would further improve the review paper.  As the subject is interesting, I am willing to recommend major revisions with pending manuscript decision. I will gladly be able to review the modified manuscript once the following points have been fully addressed:

1) Page 1, lines 41-44 – Could the authors provide more statistical data regarding fire-induced structural collapse events?

2) Page 2, lines 45-49 – The authors should mention the use of waste-derived compounds in the development of more recent coatings and polymer based systems. The authors could cite some relevant references in the field:

- Beh, J. H., Yew, M. K., Yew, M. C., & Saw, L. H. (2021). Characterization and fire protection properties of rubberwood biomass ash formulated intumescent coatings for steel. Journal of Materials Research and Technology, 14, 2096-2106.

- Beh, J. H., Yew, M. C., Saw, L. H., & Yew, M. K. (2020). Fire resistance and mechanical properties of intumescent coating using novel bioash for steel. Coatings, 10(11), 1117.

- Wang, C., Huo, S., Liu, S., Hu, Q., Zhang, Q., & Liu, Z. (2021). Recycle of magnesium alloy scrap for improving fire resistance, thermal stability, and water tolerance of intumescent fire-retardant coatings. Journal of Coatings Technology and Research, 18, 447-458.

- Venezia, V., Matta, S., Lehner, S., Vitiello, G., Costantini, A., Gaan, S., ... & Bifulco, A. (2021). Detailed thermal, fire, and mechanical study of silicon-modified epoxy resin containing humic acid and other additives. ACS Applied Polymer Materials, 3(11), 5969-5981.

3) Page 2, lines 50-54 – Epoxy resin based materials show some water absorption phenomena. The influence of that on the protection of building materials should be mentioned in this introduction.

4) Page 2, lines 54-57 – Could the authors provide an histogram representation showing the rising interest for coatings in the last years?

5) Page 2, lines 71-80 – Some advantages highlighting the effectiveness of geopolymers in the manufacturing of coating for building materials should be reported, also mentioning and referring to Lyon, R. E., Balaguru, P. N., Foden, A., Sorathia, U., Davidovits, J., & Davidovics, M. (1997). Fire‐resistant aluminosilicate composites. Fire and materials, 21(2), 67-73.

6) Page 3, lines 102-106 – Could the authors provide a figure summarizing the use of different fillers for a specific application and advantage? This would make an easier identification for the reader.

7) Page 3, lines 108-111 – I would suggest to mention some sentences explaining how the encapsulation process is performed.

8) Page 3, lines 118-125 – The use of PVA fibres may result in the occurrence of water absorption phenomena. The authors should mention the drawbacks related to this choose.

9) Page 3, lines 128-132 – Which mechanical properties? Could the authors provide some relevant examples?

10) Page 3, lines 133-144 – The authors should mention how the chemical pre-treatment of fibres could help to improve the interphases. Please, provide some examples.

11) Page 4, line 150 – I would suggest to add more recent references to support these statements.

12) Page 5, lines 181-188 – Could the author add some sentences reporting an example about the effectiveness of APP and melamine phosphate combination?

13) Page 5, lines 208-2019 – The flame retardant mechanisms related to the use of inorganic fillers or their hydroxides should be mentioned, highlighting both the shielding effect and “sinken effect”.

14) Page 6, lines 236-240 – The authors should mention how the amount of released smoke is usually reduced or limited in the case of epoxy systems.

15) Page 6, lines 254-266 – I would suggest to add a table summarizing main advantages and limitations elated to each deposition method.

16) Page 6, Figure 3 – The resolution of Figure 3 should be improved together with related captions.

13) Page 7, lines 314-320 – I would suggest to mention the importance related to use fly ash as filler for geopolymer coatings. The authors could explain the origin of fly ash and the most significant sustainable approaches.

14) Page 8, Figure 4 – The resolution of bars in Figure 4 should be improved to make them clearer for the reader.

15) Page 9, lines 391-401 - The used foaming agent contains halogen species, I would suggest to mention also an example based on a greener additive.

16) Page 10, lines 416-420 - I would suggest to briefly mention some explanation about corrosion phenomena and related issues in the field of building materials.

17) Page 10, lines 427-439 - Phosphate groups are also responsible for an improved fire behaviour. The authors should mention the possibility of such effect in addition to the beneficial effect on corrosion phenomena.

18) Page 14, Conclusions section - Could the authors add some quantitative data and comparisons, with different materials, to highlight the beneficial effects resulting from the use of geopolymer based coatings?

Author Response

Page 1, lines 41-44 – Could the authors provide more statistical data regarding fire-induced structural collapse events?

Agree. This is added in line 40-42 and line 47 (Table 1)

Page 2, lines 45-49 – The authors should mention the use of waste-derived compounds in the development of more recent coatings and polymer based systems. The authors could cite some relevant references in the field:

- Beh, J. H., Yew, M. K., Yew, M. C., & Saw, L. H. (2021). Characterization and fire protection properties of rubberwood biomass ash formulated intumescent coatings for steel. Journal of Materials Research and Technology, 14, 2096-2106.

- Beh, J. H., Yew, M. C., Saw, L. H., & Yew, M. K. (2020). Fire resistance and mechanical properties of intumescent coating using novel bioash for steel. Coatings, 10(11), 1117.

- Wang, C., Huo, S., Liu, S., Hu, Q., Zhang, Q., & Liu, Z. (2021). Recycle of magnesium alloy scrap for improving fire resistance, thermal stability, and water tolerance of intumescent fire-retardant coatings. Journal of Coatings Technology and Research, 18, 447-458.

- Venezia, V., Matta, S., Lehner, S., Vitiello, G., Costantini, A., Gaan, S., ... & Bifulco, A. (2021). Detailed thermal, fire, and mechanical study of silicon-modified epoxy resin containing humic acid and other additives. ACS Applied Polymer Materials, 3(11), 5969-5981.

Agree. This is added in line 54-55

Page 2, lines 50-54 – Epoxy resin based materials show some water absorption phenomena. The influence of that on the protection of building materials should be mentioned in this introduction.

Agree. This is added in line 61-62

4) Page 2, lines 54-57 – Could the authors provide an histogram representation showing the rising interest for coatings in the last years?

Agree. This is added in line 81-83

5) Page 2, lines 71-80 – Some advantages highlighting the effectiveness of geopolymers in the manufacturing of coating for building materials should be reported, also mentioning and referring to Lyon, R. E., Balaguru, P. N., Foden, A., Sorathia, U., Davidovits, J., & Davidovics, M. (1997). Fire‐resistant aluminosilicate composites. Fire and materials, 21(2), 67-73.

Agree. This is added in line 96

6) Page 3, lines 102-106 – Could the authors provide a figure summarizing the use of different fillers for a specific application and advantage? This would make an easier identification for the reader.

Agree. This is added in line 135

7) Page 3, lines 108-111 – I would suggest to mention some sentences explaining how the encapsulation process is performed.

Agree. This is amended in line 130-134

8) Page 3, lines 118-125 – The use of PVA fibres may result in the occurrence of water absorption phenomena. The authors should mention the drawbacks related to this choose.

Agree. This is added in line 143-146

9) Page 3, lines 128-132 – Which mechanical properties? Could the authors provide some relevant examples?

Agree. This is added in line152-154

10) Page 3, lines 133-144 – The authors should mention how the chemical pre-treatment of fibres could help to improve the interphases. Please, provide some examples.

Agree. This is added in line 165-168

11) Page 4, line 150 – I would suggest to add more recent references to support these statements.

Agree. This is modified in line 174

12) Page 5, lines 181-188 – Could the author add some sentences reporting an example about the effectiveness of APP and melamine phosphate combination?

Agree. This is added in line 208-210

13) Page 5, lines 208-2019 – The flame retardant mechanisms related to the use of inorganic fillers or their hydroxides should be mentioned, highlighting both the shielding effect and “sinken effect”.

Agree. This is added in line 226-228

14) Page 6, lines 236-240 – The authors should mention how the amount of released smoke is usually reduced or limited in the case of epoxy systems.

Agree. This is added in line 266-269

15) Page 6, lines 254-266 – I would suggest to add a table summarizing main advantages and limitations elated to each deposition method.

Agree. This is added in line 295

16) Page 6, Figure 3 – The resolution of Figure 3 should be improved together with related captions.

Agree. This is modified.

13) Page 7, lines 314-320 – I would suggest to mention the importance related to use fly ash as filler for geopolymer coatings. The authors could explain the origin of fly ash and the most significant sustainable approaches.

Agree. This is added in line 349-351

14) Page 8, Figure 4 – The resolution of bars in Figure 4 should be improved to make them clearer for the reader.

Agree. This is modified

15) Page 9, lines 391-401 - The used foaming agent contains halogen species, I would suggest to mention also an example based on a greener additive.

Agree. This is added in line 432-433

16) Page 10, lines 416-420 - I would suggest to briefly mention some explanation about corrosion phenomena and related issues in the field of building materials.

Agree. This is added in line 448-454

17) Page 10, lines 427-439 - Phosphate groups are also responsible for an improved fire behaviour. The authors should mention the possibility of such effect in addition to the beneficial effect on corrosion phenomena.

Agree. This is added in line 480-482

18) Page 14, Conclusions section - Could the authors add some quantitative data and comparisons, with different materials, to highlight the beneficial effects resulting from the use of geopolymer based coatings?

Agree. This is amended.

Round 2

Reviewer 2 Report

The manuscript entitle: “The development of conventional and geopolymer fire-retardation coatings for metal structures: A review” was significantly improved, however some issues still required some clarifications, including:

1) Title: please, define what mean “conventional” - the given explanation is not clear, "definition" in the text is connected with fire systems not coatings, please consider change in the title.

2)  Introduction - the novelty aspect given by review are not explained enough.

Author Response

The manuscript entitle: “The development of conventional and geopolymer fire-retardation coatings for metal structures: A review” was significantly improved, however some issues still required some clarifications, including:

• Title: please, define what mean “conventional” - the given explanation is not clear, "definition" in the text is connected with fire systems not coatings, please consider change in the title.

Agree. This is amended in the title

• Introduction - the novelty aspect given by review are not explained enough.

Agree. The main challenge of geopolymer coating is stated in the abstract, while the novelty and significance of this article is explained in the last paragraph of introduction.

Reviewer 3 Report

Revision for Coatings (ISSN 2079-6412)

Manuscript ID: coatings-2218119

Title: The development of conventional and geopolymer fire-retardation coatings for metal structures: A review

List of authors: Kaibao Wang, Huirong Le*

Recommendation

Accepted for publication in the present form.

1.     Overview and general recommendation

The authors have largely addressed all the comments and question that I raised in my previous review. In particular, the description of the different sections and systems, including some exemplificative figures, the supporting references and the text concerning results already present in the literature are much more improved in the revised manuscript. Overall, I think this is a commendable advancement and therefore I recommend the manuscript for publication on Coatings.

Author Response

Thank you very much for providing such helpful suggestions. It provides a useful guide for future articles.