The Effect of Bayer Red Mud Blending on the Mechanical Properties of Alkali-Activated Slag-Red Mud and the Mechanism

Round 1

Reviewer 1 Report

The authors presented an experimental study on the effect of Bayer red mud content on the mechanical properties of AASR. And the influence mechanism of red mud content on the mechanical properties of AASR was revealed by the variation of micro-porosity, connected porosity, Isothermal calorimetry, XRD, FTIR, and BSE/EDS testing techniques. This study is well within the scope and interest of the journal. However, I would recommend some revision considering the following suggestions before accept:

1.RM means Red Mud? Please explain.

2.The corresponding units need to be added in Table 2.

3.Authors claim that the AASR specimens with a proper content of red mud is denser, and the RM content increases to more than 50%, the microstructure become loose. However, the image provided is only a fraction of the entire specimen. Hence, it is necessary to provide a wide range of images.

4.One of the primary problems with alkali activated material is its setting time. There is no information relating to the fresh properties of the alkali activated material in this study. It is necessary to include these information, especially the setting time with the varying slag content of the alkali activated material mix.

5.As the research progress in this field is constantly updated in recent years, it is necessary to add references in the recent three years to this paper.

6.As the content of RM reaches 70%, the connected porosity of AASR increased instead of decreasing until 14 days. However, the compressive strength of the specimens continued to increase. Please explain.

Author Response

Response 1: Thanks very much for pointing this out. The "RM" was used to represent red mud in this paper, ant the corresponding explanations are given in the revised paper.

Response 2: We have labeled the units in Table 2

Binder	GGBFS/g	RM/g	WG/g	NaOH/g	Water/g
AAS-Control	500	/	157.15	15.39	136.16
AAS-30%RM	350	150	157.15	15.39	136.16
AAS-50%RM	250	250	157.15	15.39	136.16
AAS-70%RM	150	350	157.15	15.39	136.16

 

Response 3: A wide range of images was added. See Figure 10 for details.

Response 4: Thanks for this suggestion. Relevant information about the condensation time has been added, and details are added in lines 197-201 in the manuscript and in Figure 4.

Response 5: Relevant references from the recent three years has been added in the introduction section.

Response 6: Thanks for this valuable comment. As the content of RM reaches 70%, the connected porosity of AASR increased before 14 days, which did seem contradictory to the continued increase of compressive strength. It should be noted that compressive strength of cementing materials depends not only on the porosity, but also on the degree of reaction, type of reaction products, and pore structure. As shown in the manuscript that the degree of reaction and phase compositions and the pore size distribution are changed by the incorporation of 70% red mud.

Author Response File: Author Response.docx

Reviewer 2 Report

This study focused on a promising topic. The aim of this study was to investigate the effect of Red-Mud replacement on mechanical properties of alkali-activated slag. Slag was replaced by the ratio of 30, 50, and 70% of red-mud .In experimental studies compressive strength, heat of hydration, XRD, FTIR, pore structure, and microstructural tests were carried out on paste specimens. Here are some minor observations and recommendations:

 

1.  The introduction is shallow and short. It should be strengthened by adding more information about using red mud in alkali-activated systems from literature with proper references.

2.   It is recommended to add line number in your manuscript for ease of referring during reviewing of your paper.

3.       In the introduction section, authors should add reference after the excerpt “Using Bayer red mud, Ground Granulated Blast Furnace Slag and a certain ratio of alkali activator to prepare a new clinker-free water-hardenable cementitious material, namely, alkali- activated slag-red mud (AASR), is a promising approach, which can offer high strength development, high resistance against chemical attacks, high resistance against chloride ingress and excellent durability.”

4.       The manuscript should be written consistently. The authors wrote “Figure” in some sentences and wrote “Fig.” in others. Please be consistent.

5.       Please, Figure2 is not presented properly. Please modify it as same as Figure6.

6.       All samples prepared in this paper are paste. However, the authors stated that “the AASR mortar specimens” while explaining the porosity test procedure in test procedure section. Confusing!!

7.       The SEM images and EDS are too small and not clear for readers. Please modify and attach very clear images. Also, all colors should be labeled clearly with representative chemical elements in the elemental maps images.

8. All figures need to be improved (use proper size and font. etc..).

9. The results were not interpreted and discussed in details. Please add more convincing discussion in the revised manuscript.

10. Around 50% of references are old. Please update and cite more recent references.

11. The conclusion should be improved. Please make at least 5-6 bullet points in conclusion.

Author Response

Response to Reviewer 2 Comments

Dear reviewer：

The authors really appreciate time and efforts the reviewers and editor gave to this manuscript. The comments and suggestions are very valuable and helpful for us to improve the quality of this work. We believe that after addressing these suggestions in the revised draft, the findings of this study would become clearer and more interesting to the readers of “Applied Sciences”. The responses to the reviewer’s comments are summarized as flowing:

 

Point 1: The introduction is shallow and short. It should be strengthened by adding more information about using red mud in alkali-activated systems from literature with proper references.

 

Response 1: Thanks for pointing out this. According to this comment, the introduction of the manuscript has been improved and the references from the recent three years have been added.

 

Point 2: It is recommended to add line number in your manuscript for ease of referring during reviewing of your paper.

 

Response 2: The lines number has been added.

 

Point 3: In the introduction section, authors should add reference after the excerpt “Using Bayer red mud, Ground Granulated Blast Furnace Slag and a certain ratio of alkali activator to prepare a new clinker-free water-hardenable cementitious material, namely, alkali- activated slag-red mud (AASR), is a promising approach, which can offer high strength development, high resistance against chemical attacks, high resistance against chloride ingress and excellent durability.”

 

Response 3: Thanks for this suggestion.Related reference has been added.

 

Point 4: The manuscript should be written consistently. The authors wrote “Figure” in some sentences and wrote “Fig.” in others. Please be consistent.

 

Response 4: In the revised manuscript, the “Fig.” have been changed to "Figure".

 

Point 5: Please, Figure2 is not presented properly. Please modify it as same as Figure6.

 

Response 5: The format of Figure 2 has been corrected.

 

Point 6: All samples prepared in this paper are paste. However, the authors stated that “the AASR mortar specimens” while explaining the porosity test procedure in test procedure section. Confusing!!

 

Response 6: Thanks for noticing this error. The authors are very ashamed for this carelessness. All samples prepared in this paper are paste, and this error has been corrected in the manuscript.

 

Point 7: The SEM images and EDS are too small and not clear for readers. Please modify and attach very clear images. Also, all colors should be labeled clearly with representative chemical elements in the elemental maps images.

 

Response 7: The images have been changed to clearer images using ps. And, the chemical elements are also marked on the maps images.

 

Point 8: All figures need to be improved (use proper size and font. etc..).

 

Response 8: All figures are formatted in the template.

 

Point 9: The results were not interpreted and discussed in details. Please add more convincing discussion in the revised manuscript.

 

Response 9: We tried our best to improve the discussion of the results and made some changes in the manuscript. These changes will give a cleaner and more interesting information to the readers, and not influence the content and framework of the paper. And here we did not list the changes but marked in red in revised paper.

 

Point 10: Around 50% of references are old. Please update and cite more recent references.

 

Response 10: The references have been updated and marked in red in the new manuscript.

 

Point 11: The conclusion should be improved. Please make at least 5-6 bullet points in conclusion.

 

Response 11: Thanks. Two other valuable conclusions are drawn from the research results:

3. Due to the difficulty of red mud dissolution, it slows down the hydration process of the AASR system, which makes the initial and final setting time both longer.
4. The red mud content does not change the type of hydration products of the AASR cementitious material, but with the increase of red mud content, the amount of hy-dration generation decreases, which is one of the reasons for the reduction of the AASR system compressive strength.

 

We appreciate for reviewers’ warm work earnestly, and hope that the correction will meet with approval.

Once again, thank you very much for your comments and suggestions.

Author Response File: Author Response.docx

Reviewer 3 Report

The auothor investigates the Effect of Bayer Red Mud Blending on the Mechanical Properties of Alkali-Activated Slag-Red Mud. I think this manuscript has met the requirements for publication.

Author Response

Thank you for your approval of our manuscript!

Author Response File: Author Response.docx