The Effect of Recycled Citrogypsum as a Supplementary Mineral Additive on the Physical and Mechanical Performance of Granulated Blast Furnace Slag-Based Alkali-Activated Binders

Round 1

Reviewer 1 Report

1) Abstract need to rewrite. add 1 or 2 lines for brief methodology adopted. Final outcome or conclusion in one line at the end of the abstract. also write only one paragraph.

2) Add more recent literature on that topic. why u need to add figure 1, it will not give any information. u can just write in one line regarding that. Add novelty and original contribution at the end of introduction section.

3) Do u have SEM images of figure 2. if yes then add them to know their micro-structural behavior.

4) Add pictures of conducted tests.

5) Fig. 6 need to redraw. use different patterns of bar chart to clear distinguish it. Also add variation bar in it. Same for figure 7 and 8.

6) Add separate section for Discussion. Compare your results with other people findings.

Author Response

Dear reviewer, thank you for your time and consideration. We truly value and all the comments and suggestions you have provided. The authors of this manuscript did their best to address your suggestions and made considerable text revision when it was required. For your convenience, all additions and corrections made in the manuscript have been marked with yellow.

 

• Abstract need to rewrite. add 1 or 2 lines for brief methodology adopted. Final outcome or conclusion in one line at the end of the abstract. also write only one paragraph.

Response. Thank you for this recommendation. The abstract of the manuscript was modified.

• Add more recent literature on that topic. why u need to add figure 1, it will not give any information. u can just write in one line regarding that. Add novelty and original contribution at the end of introduction section.

Response. Thank you for this recommendation. Figure 1 was deleted. Novelty and original contribution at the end of Conclusion section was added

• Do u have SEM images of figure 2. if yes then add them to know their micro-structural behavior.

Response. Thank you for this recommendation. The SEM images of the GBFS and citrogypsum products were incorporated as part of Figure 1.

• Add pictures of conducted tests.

Response. Unfortunately, the authors did not take any photographs of the conducted tests.

• 6 need to redraw. use different patterns of bar chart to clear distinguish it. Also add variation bar in it. Same for figure 7 and 8.

Response. All the mentioned Figures were redrawn and replaced in the manuscript.

6) Add separate section for Discussion. Compare your results with other people findings.

Response. Thank you for this recommendation.

This study focused on several parameters such as compressive strength, specific gravity and water resistance concurrently. For this reason, the discussion of the results was provided right after the experimental data were provided in text as well as in form of tables and graphs. Our understanding is that the information organized in such a way would be convenient for the reader to read and analyze.

As it is mentioned in the introduction section of the manuscript, due to very little published research studies focused on utilization of citrogypsum in GBFS-based alkali activated cements, the authors of the current manuscript unable to perform comparative analysis of the experimental results obtained in this study with the other people’s findings.

Reviewer 2 Report

The manuscript "The effect of citrogypsum as a recycling component on hardening process of alkali-activated binding systems at different temperature and humidity curing conditions" is interesting and gives some guide about the use and importance of different alkali-activators, the presence of gypsum and the curing conditions. Nevertheless,  some key points need to be reviewed as follows:

1) Figure 1. Please check it because it appears like properties of AAM and it must be AAC.

2) Table 2. Please amend the accumulative total residue percentage at 0.63 mesh, for citrogypsum.

3) In Table 4, appears a sample named M8, which has not be previously declared. The numbering of such table is wrong. Please amend it. 

4) Lines 298-300. The statement "..showed that the absence of any alkaline activator in AAC leads to the absence of a chemical interaction between water and GBFS, even in the presence of citrogypsum..." is not necessarily true, since the interaction between water and GBFS can take place even without an alkali activator, whose presence implies other chemical reactions. Otherwise, please give the fundamental reason for such statement.

5) Please explain in detail why the hydraulic curing improves the compressive strength for M3;i.e, what is the mechanism for it?

6) In general, the results are descriptive but most of them are not discussed  based on fundamental concepts, like the implied chemical reactions, which can give a deeper understanding of why/what is happening in the different systems (mixture). This need to be improved.

Author Response

Dear reviewer, thank you for your time and consideration. We truly value and all the comments and suggestions you have provided. The authors of this manuscript did their best to address your suggestions and made considerable text revision when it was required. For your convenience, all additions and corrections made in the manuscript have been marked with yellow.

 

• Figure 1. Please check it because it appears like properties of AAM and it must be AAC.

Response. It’s a very good catch. Indeed, there was a typo in Figure 1. The acronym AAC should be instead of «AAM».

• Table 2. Please amend the accumulative total residue percentage at 0.63 mesh, for citrogypsum.

Response. Thank you for this comment. Accumulative total residue percentage at 0.63 mesh, for citrogypsum was amended.

• In Table 4, appears a sample named M8, which has not be previously declared. The numbering of such table is wrong. Please amend it. 

Response. Thank you for this comment. Information about M8 was added in Table 2. Numbering of this Table was adjusted accordingly.

• Lines 298-300. The statement "..showed that the absence of any alkaline activator in AAC leads to the absence of a chemical interaction between water and GBFS, even in the presence of citrogypsum..." is not necessarily true, since the interaction between water and GBFS can take place even without an alkali activator, whose presence implies other chemical reactions. Otherwise, please give the fundamental reason for such statement.

Response. Thank you for this comment. This sentence was modified as follows: «At the same time, the zero compressive strength values for reference mixes M1 and M2 showed that the absence of any alkaline activator in AAC leads to weak chemical interaction between water and GBFS, even in the presence of citrogypsum, which contains alkaline cations Ca²⁺.It can be associated with the low reactivity of the used GBFS».

• Please explain in detail why the hydraulic curing improves the compressive strength for M3;i.e, what is the mechanism for it?

Response. M3 consists of GBFS activated with Na₂CO₃. Na₂CO₃ is a source of Na⁺ cation. When dissolved in water, NaCO₃ creates alkaline media similar to what NaOH alkaline activator would do. In fact, alkaline media prompts mineral phases of GBFS such as akermanite, helenite, anorthite and others to react with Na⁺ cations resulting in formation of hydrates like C-S-H, N-C-S-H and N-A-S-H. These hydrates compose the structure of cementitious matrix.

6) In general, the results are descriptive but most of them are not discussed based on fundamental concepts, like the implied chemical reactions, which can give a deeper understanding of why/what is happening in the different systems (mixture). This need to be improved.

Response.

The fundamentals of the research study focus on a well-known binder, that is the “GBFS-alkaline activator” system. The alkaline activators NaOH, Na₂CO₃ and Na₂SiO₃ used in this work are well known and thoroughly studied in the past. The chemical reaction mechanism of these compounds in the system “GBFS-alkaline activator” was studied by a number of authors like Glukhovsky, Krivenko, Pudron, Davidovits etc. and currently well understood:

• DOI: 10.1016/j.conbuildmat.2007.10.0154;
• https://www.semanticscholar.org/paper/ALKALI-ACTIVATED-MATERIAL-–-GEOPOLYMER-Škvára/2fc55edc6c47eb9f3977d308528878a07582c9ac;
• https://www.researchgate.net/publication/265076752_Geopolymer_Chemistry_and_Applications/figures?lo=1;
• doi:10.1016/j.conbuildmat.2007.03.019.

For this reason, the authors consider redundant the information on principles of structure formation in the system “GBFS-alkaline activator” in the of this manuscript.

Besides, as a novelty of this work serves the study on response of citrogypsum in the system “GBFS-alkaline activator” in regard to structure formation as well as physical and mechanical characteristics. The study proposes to add citrogypsum as a supplementary source of alkaline elements, mainly Ca⁺ cations, which enable chemical activation and further hydration reaction of GBFS. This information was added to section «2.1. Materials».

Reviewer 3 Report

Abstract

1. the authors are required to explain briefly on the gypsum bearing waste. Is the gypsum bearing waste is one of the recycled gypsum? please clarify this in the abstract.

2. the authors should discuss a bit on the scenario work done by other on the citrogypsum. Also, the objective of the study should be clearly stated. 

3. A very well written on the methodology and summary of findings and also, easy to follow. However, the authors are required to include the a general conclusion for the study. 

 

Introduction

1. It is advisable for the authors to explain well on the gypsum bearing waste on how/where is the gypsum bearing waste in recycled gypsum research. 

2. A brief discussion on the research done on gypsum bearing waste is required. A justification on the potential of gypsum bearing waste as a binder component for ACC also needed. 

3. Objective of the study is not clear.

Methodology and methods

1. Line 157: what is RW? cannot find any RW explanation in introduction. Please check if this meant to be written. If yes, please clarify the classification for citrogypsum - is it RG, GW or RW?

2. Line 229-231: Please describe this with arrow (or etc) on the graph. 

3. it is not clear on % content of citrogypsum/GBFS. No clear mix design on the study is discussed. No clear parameter of ACC is explained. 

Result and discussion

1. in methodology, the authors stated curing condition as regime 1 and regime 2. However, difficult to follow the analysis. Line 274-277 did mentioned on the result based on the curing regime. However, the authors are suggested to restructure the discussion, as explained in the methodology.

 2. how the specific gravity is calculated. The determination of specific gravity is not clear for the mixes component.

3. the results discussion required a better structure of discussion. 

4. Need to revisit the methodology for a better/clear relation between methodology and result.

Conclusion.

This section need to be inline with the objective of the study.

 

Author Response

Dear reviewer, thank you for your time and consideration. We truly value and all the comments and suggestions you have provided. The authors of this manuscript did their best to address your suggestions and made considerable text revision when it was required. For your convenience, all additions and corrections made in the manuscript have been marked with yellow.

 

Abstract

The authors are required to explain briefly on the gypsum bearing waste. Is the gypsum bearing waste is one of the recycled gypsum? please clarify this in the abstract.

Response. Thank you for this recommendation. Gypsum-bearing waste materials is one of the common globally produced ones among industrial and domestic wastes that are currently recycled and further utilized. This remark was added to the introduction section of the manuscript.

2. the authors should discuss a bit on the scenario work done by other on the citrogypsum. Also, the objective of the study should be clearly stated. 

Response. Thank you for this comment. Indeed, the information of areas of application of citrogypsum was not provided.  In the modified version of the manuscript attached the overview of some studies on application of citrogypsum was provided in the Introduction section.

The statement of the objective of the study is now provided in Introduction section of the manuscript.

3. A very well written on the methodology and summary of findings and also, easy to follow. However, the authors are required to include the a general conclusion for the study. 

It was observed, that the type alkali activator and curing regime are crucial factors that govern  the response of citrogypsum as a supplementary materials in the mix of AAC in regard to such performance as compressive strength, specific gravity and water resistance. This statement was added to the conclusion.

Introduction

1. It is advisable for the authors to explain well on the gypsum bearing waste on how/where is the gypsum bearing waste in recycled gypsum research. 

Response. Thank you for your comment. The information of the recyclability of the gypsum bearing waste products was provided in the Introduction section.

2. A brief discussion on the research done on gypsum bearing waste is required. A justification on the potential of gypsum bearing waste as a binder component for ACC also needed. 

Response. In the Introduction section was added a brief discussion on the research done for gypsum bearing wastes.

Dear reviewer, thank you so much for the comment. The highlighted information on the potential use of gypsum bearing waste products in AAC binder system as well as previous research done of gypsum bearing waste was provided in the modified version of the manuscript as part of Introduction.

3. Objective of the study is not clear.

Response. Thank you for this recommendation. Objective of the study was added at the end of the Introduction section.

Methodology and methods

1. Line 157: what is RW? cannot find any RW explanation in introduction. Please check if this meant to be written. If yes, please clarify the classification for citrogypsum - is it RG, GW or RW?

Response. Thank you for pointing this out. Indeed, this is a typo. The correct acronym is RG that stands for recycled gypsum.

2. Line 229-231: Please describe this with arrow (or etc) on the graph. 

Response. Particle distribution of GBFS and citrogypsum was describes with arrows on Figure 3.

3. it is not clear on % content of citrogypsum/GBFS. No clear mix design on the study is discussed. No clear parameter of ACC is explained. 

Response.  content of citrogypsum/GBFS (in %) and details on the mix designs of the AAC were added to the manuscript. Table 3 was modified, as well.

Result and discussion

1. in methodology, the authors stated curing condition as regime 1 and regime 2. However, difficult to follow the analysis. Line 274-277 did mentioned on the result based on the curing regime. However, the authors are suggested to restructure the discussion, as explained in the methodology.

Response. Thank you for this comment. Results and Discussion section was restructured according to the Methodology section.

2. how the specific gravity is calculated. The determination of specific gravity is not clear for the mixes component.

Response. Thank you for this comment. Calculation mode of Specific gravity and its values for mixes component: citrogypsum and GBFS was added in the section «2.2. Methods»

3. the results discussion required a better structure of discussion. 

Response.

4. Need to revisit the methodology for a better/clear relation between methodology and result.

Response. The section Result and discussion was rewritten in accordance with the Methodology section.

 

Conclusion.

This section need to be inline with the objective of the study.

Response. Conclusions section was modified according with the objective of the study

Round 2

Reviewer 2 Report

Dear authors,

Thank you for addressing most of the observations. I suggest to add your response (included in the next lines) to my observation number 5 in line 372 of the revised version.

"M3 consists of GBFS activated with Na2CO3. Na2CO3 is a source of Na+ cation. When dissolved in water, NaCO3 creates alkaline media similar to what NaOH alkaline activator would do. In fact, alkaline media prompts mineral phases of GBFS such as akermanite, helenite, anorthite and others to react with Na+ cations resulting in formation of hydrates like C-S-H, N-C-S-H and N-A-S-H. These hydrates compose the structure of cementitious matrix"

Author Response

Dear Reviewer,

Thank you for your recommendation. The sentences: "M3 consists of GBFS activated with Na₂CO₃. Na₂CO₃ is a source of Na⁺ cation. When dissolved in water, Na₂CO₃ creates alkaline media similar to what NaOH alkaline activator would do. In fact, alkaline media prompts mineral phases of GBFS such as akermanite, helenite, anorthite and others to react with Na⁺ cations resulting in formation of hydrates like C-S-H, N-C-S-H and N-A-S-H. These hydrates compose the structure of cementitious matrix" were added to the manuscript (Lines 368–373) and highlighted by blue marker.