Creating Mortars through the Alkaline Activation of Ceramic Waste from Construction: Case Studies on Their Applicability and Versatility in Conservation

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article is very interesting but a more detailed description of the geopolymer mix should be added. I did not find any amount of sand, fraction etc. I found just general information. Please also add physical-mechanical/chemical characterisation of resources.

Author Response

The authors thank the reviewer. The reason why a deep detailed description of the geopolymer mix is not added is because all the data related to precursors, synthesis parameters of the binders and geopolymeric binders are already exposed in the previous paper Fugazzotto et al., 2023 – Ceramics International. The present paper born as application study of the already investigated binders, improving from them new mortars, which content of aggregates or additives were empirically defined case by case, directly in situ or at the industry according to the required workability in that specific context. Therefore, it is not possible to specifically indicate their amount, as well as it is not possible to be more precise about the L/S ratio, indicated as range in the caption of Table 3. All the other data related to the new mortars (type of aggregates and waterglass used) are exposed in Table 3, that is now cited in the paragraph Materials and Methods. In order to make clearer also the synthesis conditions, some phrases explaining the mixture preparation, molding, and curing were added in the same paragraph. Regarding, instead, the resources characterization, the data on the raw materials employed are exposed in the previous paper, already cited, as well as the data to the original binders; while the data related to the aggregates are in this moment indicated in a further paper submitted to another journal. It would be interesting to characterize the new experimented products, but the available time for the reviews is not sufficient. We can plan them for future works focused on the characterization, while this paper will remain faithful to the original aim of applicability tests, to study the jump from laboratory to site/industry.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The article discusses an interesting way of geopolymer application in restoration of different historical products. However, there are numerous questions listed below:

- The title is debatable. I suppose that it should be reworked into an ordinary one, without questions.
- Abstract should be revised to highlight the main specific results of the work.
- I doubt that the "cultural heritage" keyword is suitable for this article, especially considering the journal's scope.
- Introduction should be revised to create a stronger connection between the article's aim and journal's aims.
- Chemical compositions of all raw materials should be added. And their other important properties and structure descriptions should also be added.
- What was the purpose of introducing natural hydraulic lime? 

- Despite the fact that “the starting binders are exposed in Table 1, further details are available in [15;27]”, the information on geopolymer mixture preparation, molding, and curing should be provided.
- It would also be helpful to explain the role of every mixture component and its content. - Results begin with the application of mortars for restoration of monuments. Meanwhile, there is no information
- Durability tests of the obtained materials should be provided to understand the applicability of developed materials for different types of renovation (especially outdoors).
- Processes occurring during geopolymer curing should be described (at least, briefly), and changes depending on mixture compositions should also be analyzed.
- The amount of amorphous phase should be considered for XRD analysis.
- Figure 16. There are no peaks at 17 and 18 ° that are shown by two corresponding yellow lines. And the "pss" term wasn't explained.
- Conclusions should be independent and should not contain tables and figures. Also, Conclusions should be more precise, describing specific results of the work.
- More than 30 % of references are self-citations. It should be revised.
- The English level should be strongly improved (as well as grammar and punctuation errors). Comments on the Quality of English Language

The English level should be strongly improved (as well as grammar and punctuation errors). It is hard-to-read, especially in the Introduction.

Author Response

Comment: The article discusses an interesting way of geopolymer application in restoration of different historical products. However, there are numerous questions listed below:

- The title is debatable. I suppose that it should be reworked into an ordinary one, without questions.

Response: We thank the reviewer for the suggestions, but we think that this is a subjective point. We believe that a title which exposes a question can provoke the interest of the reader, which will expect the answer to that question within the paper text.

Comment:- Abstract should be revised to highlight the main specific results of the work.

Response: We thank the reviewer for the suggestion. The abstract was implemented according to that.

Comment:- I doubt that the "cultural heritage" keyword is suitable for this article, especially considering the journal's scope.

Response: We thank the reviewer for his suggestion, but we not agree. The Special Issue on which the paper will be published talks about the passage between the lab and the applications. In this case it become important to specify the field of application, that means Cultural Heritage.

Comment:- Introduction should be revised to create a stronger connection between the article's aim and journal's aims.

Response: The authors thank the reviewer. The introduction is now implemented.

Comment:- Chemical compositions of all raw materials should be added. And their other important properties and structure descriptions should also be added.

Response: The authors thank the reviewer. The reason why the chemical composition and the other characterization data of the raw materials used are not indicated is their exposition in previous papers, particularly on Fugazzotto et al., 2023 – Ceramics International; a part of them are instead presented in a further paper submitted to another journal. Authors can find the missing data on the paper cited within the text. Anyhow, the important properties which could affect the workability and the general behavior of the geopolymeric gel, interesting for understanding this research, were added within the text as suggested.

Comment:- What was the purpose of introducing natural hydraulic lime? 

Response: Natural hydraulic lime was added to the formulations due to its ability to modify the viscosity of the slurry. As a natural cement, it was expected to improve the workability of the slurry. This is due to the increase of Ca ions in the dissolved precursors, which are easily involved in the polycondensation reaction. This fact determines the evolution of a low-Ca geopolymeric gel (N-A-S-H), which is typical of systems as metakaolin-based geopolymers or highly sintered ceramic-based ones, into a high (C-A-S-H) or hybrid gel (N,C-A-S-H). The chemical difference between these gels is reflected in their microstructure, which is responsible for their technical properties. However, this research focuses solely on workability in practical contexts, which was investigated directly on-site using empirical method. Therefore, chemical and microstructural aspects are not investigated. A specific paper is in progress.

Comment:- Despite the fact that “the starting binders are exposed in Table 1, further details are available in [15;27]”, the information on geopolymer mixture preparation, molding, and curing should be provided.

Response: We thank the reviewer for the suggestions. The required data are now indicated within the text.

Comment:- It would also be helpful to explain the role of every mixture component and its content.

Response: We thank the reviewer for this suggestion. We decided to add briefly the role of the mixture components, even if already available in literature and in the previous paper. Also the role of Ca additive and of the marble and volcanic aggregates, not present in our previous papers, are now described. The content of all of the components is already present.

Comment:- Results begin with the application of mortars for restoration of monuments. Meanwhile, there is no information

Response: Maybe the reviewer means that there are not exposed the results of the products formulations? Or the synthesis step? We cannot actually understand the comment. However, all the apparently missing parts are exposed in previous works (Fugazzotto et al., 2023 published on Ceramics International and a new paper currently submitted to another journal), while here we focus on the application tests, as required by the Special Issue.

Comment:- Durability tests of the obtained materials should be provided to understand the applicability of developed materials for different types of renovation (especially outdoors).

Response: We kindly thank the reviewer for this suggestion, we totally agree. Indeed, we are planning a future work focused on the durability tests of this and further materials. In this context it is not possible to perform this kind of test, that require a lot of time of analysis.

Comment:- Processes occurring during geopolymer curing should be described (at least, briefly), and changes depending on mixture compositions should also be analyzed.

Response: The authors thank the reviewer for the suggestion. According to that, and to the successive comments, the observation of the variations linked to the geopolymerization process, and to different mixture compositions, are briefly described, also thanks to the quantitative analysis performed on XRD data, now added to the analytical results. No further study is presented, because it would be out of the aims of this paper.

Comment:- The amount of amorphous phase should be considered for XRD analysis.

Response: The authors thank the reviewer for the comment. According to his suggestion the quantitative analysis has been performed and it is now present and described within the manuscript.

Comment:- Figure 16. There are no peaks at 17 and 18 ° that are shown by two corresponding yellow lines. And the "pss" term wasn't explained

Response: The authors thank the reviewer for the comment. We are aware that the two peaks of pirssonite do not show a high intensity, thus it could result difficult to find them. With the yellow lines we tried to highlight them. They are not present everywhere, but only on the sample with 20P. Within the text we specifically said that the peaks are mostly visible in the sample without water. If looking carefully it is possible to individuate them on these sample. Its presence is now also confirmed by the quantitative analysis.

Comment:- Conclusions should be independent and should not contain tables and figures. Also, Conclusions should be more precise, describing specific results of the work.

Response: Conclusions are already independent and separately exposed with respect to the results and their discussion. Regarding tables and figures the authors guidelines do not indicate any limit for that. Furthermore, in this paper, where details of the products synthetized are only available after the synthesis themselves, put a summarizing table is, in our opinion, fundamental. Anyway, following the suggestion of the reviewer we decided to anticipate the Table in the previous paragraph, making the conclusions free from any link with tables and figures.

Comment:- More than 30 % of references are self-citations. It should be revised.

Response: We know that it could seem self-referential, but the indicated self-citations are needed to present the previously studied binders, from which this work originates. Further self-citations are indicated as example of geopolymers obtained by recycling ceramic waste and of applications on Cultural Heritage, where no numerous further papers are available describing applications.

Comment: - The English level should be strongly improved (as well as grammar and punctuation errors).

Response: Thank you for the suggestion. The authors entirely revised the manuscript paying more attention to the English language.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

The authors report the use of geopolymer mortars manufactured with ceramic residues and alkaline activation that allow restorations and conservation of archaeological material, maintaining sustainability with the environment. The authors must improve the manuscript according to the following points.

Point 1. In the reintegration mortar section (lines 104-125), it is recommended to add the environmental conditions to which the material was exposed.

Point 2. The glazed tiles section (lines 130-141) refers to the manufacture of tiles; however, the operating conditions are not mentioned. Adding the conditions of firing, glazing, and drying, among others, of the tile is recommended.

Point 3. In line 194, it is mentioned that it is left to dry for approximately 10-15 minutes between each coat. It is suggested that the conditions of application be more specific. Was the setting time evaluated?

Point 4. It is suggested that the ideal formulations for each application used in this research and formulation conditions be reported.

Point 5. Lines 204-205 refer to the satisfactory application, but it is not justified that the good adhesion or lack of efflorescence or contraction in the material is due.

Point 6. Lines 224-225 refer to the strength of the material; however, in this work, no mechanical tests were performed on the specimens.

Point 7. Line 228 uses the phrase “by using kilos of materials” to which it refers.

Point 8. It is suggested that Figures 7 and 8 be homogenized into a diagram that adequately shows the process of making the material.

Point 9. Line 241 refers to curing; however, the curing time is not indicated.

Point 10. In the section on industrial scaling (lines 238-248), mechanical tests are suggested to corroborate the effectiveness of the material.

Point 11. Line 260 mentions the ideal thixotropic behavior of a geopolymer. Justify how this behavior is and how it affects the performance of the material.

Point 12. Line 274 refers to a plastic behavior; it is recommended to describe this behavior, as well as justify its importance in the handling of the material.

Point 13. Lines 309-311 mention that good results are obtained; however, what is due to these properties of adhesion efflorescence, among others, is not mentioned.

Point 14. Lines 361-364 refer to efflorescence, although these are not explained, or the reason for their presence in the material is justified. In addition to this, the climatological conditions in which the material was evaluated are not established.

Point 15. In the section on analytical results (X-rays), it is suggested to show and discuss the planes of the phases present, as well as the changes that occur due to the modification of the formulation, in the same way, to justify how this variation of phases affects the material. Finally, it is suggested that the planes of interest be placed in the diffractogram.

 

Comments on the Quality of English Language

Improve English vocabulary

 

Author Response

Comment: The authors report the use of geopolymer mortars manufactured with ceramic residues and alkaline activation that allow restorations and conservation of archaeological material, maintaining sustainability with the environment. The authors must improve the manuscript according to the following points.

Point 1. In the reintegration mortar section (lines 104-125), it is recommended to add the environmental conditions to which the material was exposed.

Response: The authors thank the reviewer. The manuscript was supplemented with the averages of temperature and relative humidity retrieved from the website of Catania Astrophysical Observatory. The related link is available in the bibliography.

Comment: Point 2. The glazed tiles section (lines 130-141) refers to the manufacture of tiles; however, the operating conditions are not mentioned. Adding the conditions of firing, glazing, and drying, among others, of the tile is recommended.

Response: We thank the reviewer for this suggestion. We added the required data within the text.

Comment: Point 3. In line 194, it is mentioned that it is left to dry for approximately 10-15 minutes between each coat. It is suggested that the conditions of application be more specific. Was the setting time evaluated?

Response: The indicated operative conditions were suggested by the restorer which was involved in the test.

Comment: Point 4. It is suggested that the ideal formulations for each application used in this research and formulation conditions be reported.

Response: The authors thank the reviewers for the suggestion. The ideal formulation for each application is now more evident within the discussions.

Comment: Point 5. Lines 204-205 refer to the satisfactory application, but it is not justified that the good adhesion or lack of efflorescence or contraction in the material is due.

Response: We thank the reviewer for the comment, but we would like to underline as the scope of the paper was the study of the applicability in different context, to understand criticalities or advantages in the applications themselves. The observations regarding the behavior over time of the applied mortars are only preliminary and do not claim to be a scientific monitoring. It should be interesting to study the durability over time of the presented products, in order to confirm their suitability and quality, but for the aims of this paper already the absence of salts, cracks or disintegrations could be, in our opinion and according to the suggestions of the restorers, sufficient to define the application satisfactory.

Comment: Point 6. Lines 224-225 refer to the strength of the material; however, in this work, no mechanical tests were performed on the specimens.

Response: We thank the reviewer, but we underline that the resistance to which the phrase refers is thermal resistance. We modified the phrase in order to make it clearer.

Comment: Point 7. Line 228 uses the phrase “by using kilos of materials” to which it refers. 

Response: We modified the phrase in order to make it clearer.

Comment: Point 8. It is suggested that Figures 7 and 8 be homogenized into a diagram that adequately shows the process of making the material.

Response: Thanks to the reviewers for the suggestion. We put the two figures together, in order to have a more precise idea of the process of making the product. The single steps shown in the photos are also now described in the caption.

Comment: Point 9. Line 241 refers to curing; however, the curing time is not indicated.

Response: We thank the reviewer for the comment. According to that, we added the indication of the curing time (28 days) within the text, in the Materials and Methods paragraph, valid for all the formulations. We also explained the curing differences among the mortars applied on site and those used for pre-casted prototype.

Comment: Point 10. In the section on industrial scaling (lines 238-248), mechanical tests are suggested to corroborate the effectiveness of the material.

Response: We thank the reviewer for the suggestion. For sure data related to mechanical tests would be useful to support the effectiveness of the materials, but it would require more time than the time we have available for the revisions. Notwithstanding this study will be performed in a future work. At this step, compressive strength is available for the original binders from which the mortars are here improved (available in Fugazzotto et al., 2023 – Ceramics International). Further indications that could give positive results translated on the mortars here synthetized and applied come from the data currently submitted to another journal. 

Comment: Point 11. Line 260 mentions the ideal thixotropic behavior of a geopolymer. Justify how this behavior is and how it affects the performance of the material.

Response: We thank the reviewer for the suggestion. His suggestion is appreciated and we will consider it for future articles, but considering the objective of this work the thixotropic behavior was not investigated. We just cited the tendency of geopolymers to behave according to thixotropy, which has a practical consequence in the workability. The thixotropic behavior makes the slurry too viscous and difficult to shape. Therefore, although the thixotropic behavior would give complementary information, the authors of this work consider that it is not necessary to carry out specific test for the purpose of this work.

Comment: Point 12. Line 274 refers to a plastic behavior; it is recommended to describe this behavior, as well as justify its importance in the handling of the material.

Response: We thank the reviewer for the suggestion. In this study the plastic behavior was visually monitored during the process by adding additive to the mixture. In particular, to achieve the desired plasticity for application of the obtained geopolymer in various restouration scenarios and prevent rapid hardening, calcium-based additive was used. It allows to control the plasticity of the mixture by reducing the liquid limit and increasing the plastic limit. We briefly explained this point within the text.

Comment: Point 13. Lines 309-311 mention that good results are obtained; however, what is due to these properties of adhesion efflorescence, among others, is not mentioned.

Response: The authors do not understand this comment. Probably the reviewer would like to know why the good adhesion to the substrate, the lack of efflorescence or cracks, etc, are good results of applicability? If so, we consider unnecessary this explanation, that would be didactic.

Comment: Point 14. Lines 361-364 refer to efflorescence, although these are not explained, or the reason for their presence in the material is justified. In addition to this, the climatological conditions in which the material was evaluated are not established.

Response: We thank the reviewer for the comment. We added to bibliographic reference, to point out the climate of Catania, which belong to a Mediterranean climatic area (Beck et al., 2018). The problem of efflorescence formation is a typical problem of geopolymers, however we briefly described the point.

Comment: Point 15. In the section on analytical results (X-rays), it is suggested to show and discuss the planes of the phases present, as well as the changes that occur due to the modification of the formulation, in the same way, to justify how this variation of phases affects the material. Finally, it is suggested that the planes of interest be placed in the diffractogram.

Response: We consider that suggestion out of the aims of the present paper and of the special issue itself.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The article became much better. There are still some minor weak points in English level. And I still believe that the amount of self-citing can be reduced.

Comments on the Quality of English Language

The English is better now. But there are still some minor weak points in English level. 

Reviewer 3 Report

Comments and Suggestions for Authors

The authors made all suggestions and/or comments