Microscopic characterization and strength characteristics of cemented backfill under different humidity curing conditions

Under different exploitive conditions, the humidity levels of the backfill stopes are not the same. Humidity greatly affects the strength and microscopic characterization of the backfill. Cemented paste backfill (CPB) specimens were cured using 0, 30, 70% and standard curing (20°C, 99%) under four different humidity conditions. At 28 days, nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) techniques were used to obtain the microscopic features of the CPB specimens. The relationships between the permeability and uniaxial compressive strength (UCS) of the CPB specimens, and the microscopic characteristics of the CPB specimens, were established. The results showed the following: (i) The permeability of the CPB had an exponential functional relationship with its stone powder content. (ii) The stone powder content of CPB and the peak area of the T2 spectrum are negatively correlated with the UCS. However, there was a T2 peak area corresponding to the worst UCS with the same stone powder content. (iii) The peak area of the T2 spectrum showed that the proportion of area of a small pore size was more than 80%, indicating that the pore size was mainly small. The pore diameter of small pores was linearly and inversely proportional to the UCS of the specimens. It can be found that the factors affecting the strength characteristics of CPB include not only the stone powder content, but also the curing conditions of different humidity.


Introduction
There are lots of works already published in the literature which deal with the effect of internal and external factors on performance and quality of cemented paste backfill. Please consider the following works in this study: Xue et al., 2019a,b,c;Cao et al., 2018aCao et al., ,b, 2019Yilmaz 2011;2018;Yilmaz et al., 2013. Please rewrite the introduction section by focusing on problematic, suggested methods, and originality and specific objectives. Please use the present literature critically, not giving their whole details.
At the end of this section, please provide the originality and specific objectives of this study.

Materials and Methods
Please provide further information on tailings samples. Where the authors collect these samples in the mine? They come from tailings dams or paste plant filtering cakes or mineral processing discharge products. Please state it clearly.
What were the sample preparation and mixing conditions? Please mention about them shortly.
How is the manufacturing and curing process of CPB samples? Please make it simple in the revised paper.
Please explain the experimental test procedures in more detail. How were the working conditions of samples? Please state them clearly in the revised paper.
Please add the permeability tests in this section since the authors provide some results on this test later on.

Analysis results
Are there any threshold limits of NMR results? If yes, please discuss it in the body of the manuscript as well as in Figure 3 (as a dotted line).
What are the main reasons for observing this behavior in Figure 4 in terms of strength differences? Please discuss it thoroughly.
Results and discussion Which type of permeability tests were followed in this study? Please state it clearly.
In Figure 5; permeability tests were conducted on fresh or hardened samples? Please clear it in the revised paper.
In Figure 7; this figure is very nice. The authors need to present in a larger size for better resolution.

Conclusion
Please provide a short summary before highlighting the main findings of this research project.
What are the limitations and recommendations of this work which can give some inspirations to other researchers to be worked in the area of this research?
As a reviewer, I am pleased to suggest the paper to be accepted for publication in Construction and Building Materials through the aforementioned minor revisions.

Recommendation?
Accept with minor revision (please list in comments)

Comments to the Author(s)
(1) What is the chemical composition of cement？ and it would be better to explain the derivation process of Equation.
(2) what is the curing temperature of all samples? (3) which mine's UCS basic requirement is 1.4MPa, and what are the meanings of white areas and black areas in SEM binary images？ Decision letter (RSOS-191227.R0)

18-Sep-2019
Dear Dr Zhao, The editors assigned to your paper ("Microscopic characterization and strength characteristics of cemented backfill under different humidity curing conditions") have now received comments from reviewers. We would like you to revise your paper in accordance with the referee and Associate Editor suggestions which can be found below (not including confidential reports to the Editor). Please note this decision does not guarantee eventual acceptance.
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If you wish to submit your supporting data or code to Dryad (http://datadryad.org/), or modify your current submission to dryad, please use the following link: http://datadryad.org/submit?journalID=RSOS&manu=RSOS-191227 • Competing interests Please declare any financial or non-financial competing interests, or state that you have no competing interests.
• Authors' contributions All submissions, other than those with a single author, must include an Authors' Contributions section which individually lists the specific contribution of each author. The list of Authors should meet all of the following criteria; 1) substantial contributions to conception and design, or acquisition of data, or analysis and interpretation of data; 2) drafting the article or revising it critically for important intellectual content; and 3) final approval of the version to be published.
All contributors who do not meet all of these criteria should be included in the acknowledgements.
We suggest the following format: AB carried out the molecular lab work, participated in data analysis, carried out sequence alignments, participated in the design of the study and drafted the manuscript; CD carried out the statistical analyses; EF collected field data; GH conceived of the study, designed the study, coordinated the study and helped draft the manuscript. All authors gave final approval for publication.
• Acknowledgements Please acknowledge anyone who contributed to the study but did not meet the authorship criteria.
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Once again, thank you for submitting your manuscript to Royal Society Open Science and I look forward to receiving your revision. If you have any questions at all, please do not hesitate to get in touch. Three reviewers have commented, with each providing at least some suggestions for improvement in the manuscript. Given the volume of the requested changes, we would like you revise the manuscript, and will invite the reviewers to look once again at the paper before a final decision is rendered.
Reviewers' Comments to Author: Review report for Royal Society Open Science (RSOS-191227): Microscopic characterization and strength characteristics of cemented backfill under different humidity curing conditions This paper presents the results of a comprehensive experimental work considered for investigating the effect of different humidity conditions on mechanical and microstructural properties of cemented paste tailings as a function of different curing times. The topic addressed in this work is interesting and within the scope of the journal. The experimental program is well designed and executed. The authors have obtained good results. The paper's structure and technical quality are fairly good. I strongly believe that the presented data are useful to other researchers. This reviewer has some minor corrections and/or comments which can improve the paper's quality. All comments/suggestions are as follows;

Introduction
There are lots of works already published in the literature which deal with the effect of internal and external factors on performance and quality of cemented paste backfill. Please consider the following works in this study: Xue et al., 2019a,b,c;Cao et al., 2018aCao et al., ,b, 2019Yilmaz 2011;2018;Yilmaz et al., 2013. Please rewrite the introduction section by focusing on problematic, suggested methods, and originality and specific objectives. Please use the present literature critically, not giving their whole details.
At the end of this section, please provide the originality and specific objectives of this study.

Materials and Methods
Please provide further information on tailings samples. Where the authors collect these samples in the mine? They come from tailings dams or paste plant filtering cakes or mineral processing discharge products. Please state it clearly.
What were the sample preparation and mixing conditions? Please mention about them shortly.
How is the manufacturing and curing process of CPB samples? Please make it simple in the revised paper.
Please explain the experimental test procedures in more detail. How were the working conditions of samples? Please state them clearly in the revised paper.
Please add the permeability tests in this section since the authors provide some results on this test later on.

Analysis results
Are there any threshold limits of NMR results? If yes, please discuss it in the body of the manuscript as well as in Figure 3 (as a dotted line).
What are the main reasons for observing this behavior in Figure 4 in terms of strength differences? Please discuss it thoroughly.
Results and discussion Which type of permeability tests were followed in this study? Please state it clearly.
In Figure 5; permeability tests were conducted on fresh or hardened samples? Please clear it in the revised paper.
In Figure 7; this figure is very nice. The authors need to present in a larger size for better resolution.

Conclusion
Please provide a short summary before highlighting the main findings of this research project.
What are the limitations and recommendations of this work which can give some inspirations to other researchers to be worked in the area of this research?
As a reviewer, I am pleased to suggest the paper to be accepted for publication in Construction and Building Materials through the aforementioned minor revisions.
Xue, G., Yilmaz, E., Song, W., Cao, S., 2019b. Analysis of internal structure behavior of fiberreinforced cement-tailings matrix composites through X-ray computed tomography. Composites Part B: Engineering, 175, 107091. Xue, G., Yilmaz, E., Song, W., Cao, S., 2019c The manuscript explored the characteristics of cemented backfill under different humidity curing conditions using NMR and SEM techniques, which contributes to the existing literatures. It is an interesting research that deserves to be published. However, some comments should be addressed as follows: 1 The introduction part needs to be extended. The Introduction should present the reasons why studying the effect of humidity in CPB is necessary, rather than just list previous publications in the related field. 2 The references should be updated. The authors are suggested to cite some latest literatures, as the CPB develops rapidly. 3 WAT2 is unclear, and it should be explained with a schematic diagram. 4 The sum of element contents isn't 100% In table2? 5 The NMR parameters are important in this manuscript and are not mentioned in the paper. The authors are suggested to provide the NMR parameters. 6 The authors claimed that "The distribution of the T2 value represents the pore size distribution", which is not suitable for some samples in this paper are not saturated. 7 Please specify the application conditions of Equation 2.
Reviewer: 3 (1) What is the chemical composition of cement？ and it would be better to explain the derivation process of Equation.
(2) what is the curing temperature of all samples?

Recommendation? Accept as is
Comments to the Author(s) All the comments have been addressed, and it can be plished.

Review form: Reviewer 3
Is the manuscript scientifically sound in its present form? Yes

Do you have any ethical concerns with this paper? No
Have you any concerns about statistical analyses in this paper? Yes

Recommendation?
Accept with minor revision (please list in comments)

Comments to the Author(s)
(1) please provide the original data of Fig.3, and explain that how to develop the fig.3 using the data.
(2)please add and explain that what is your research significance of the result for mine backfill application.

30-Oct-2019
Dear Dr Zhao: On behalf of the Editors, I am pleased to inform you that your Manuscript RSOS-191227.R1 entitled "Microscopic characterization and strength characteristics of cemented backfill under different humidity curing conditions" has been accepted for publication in Royal Society Open Science subject to minor revision in accordance with the referee suggestions. Please find the referees' comments at the end of this email.
The reviewers and Subject Editor have recommended publication, but also suggest some minor revisions to your manuscript. Therefore, I invite you to respond to the comments and revise your manuscript.
• Ethics statement If your study uses humans or animals please include details of the ethical approval received, including the name of the committee that granted approval. For human studies please also detail whether informed consent was obtained. For field studies on animals please include details of all permissions, licences and/or approvals granted to carry out the fieldwork.
• Data accessibility It is a condition of publication that all supporting data are made available either as supplementary information or preferably in a suitable permanent repository. The data accessibility section should state where the article's supporting data can be accessed. This section should also include details, where possible of where to access other relevant research materials such as statistical tools, protocols, software etc can be accessed. If the data has been deposited in an external repository this section should list the database, accession number and link to the DOI for all data from the article that has been made publicly available. Data sets that have been deposited in an external repository and have a DOI should also be appropriately cited in the manuscript and included in the reference list.
If you wish to submit your supporting data or code to Dryad (http://datadryad.org/), or modify your current submission to dryad, please use the following link: http://datadryad.org/submit?journalID=RSOS&manu=RSOS-191227.R1 • Competing interests Please declare any financial or non-financial competing interests, or state that you have no competing interests.
• Authors' contributions All submissions, other than those with a single author, must include an Authors' Contributions section which individually lists the specific contribution of each author. The list of Authors should meet all of the following criteria; 1) substantial contributions to conception and design, or acquisition of data, or analysis and interpretation of data; 2) drafting the article or revising it critically for important intellectual content; and 3) final approval of the version to be published.
All contributors who do not meet all of these criteria should be included in the acknowledgements.
We suggest the following format: AB carried out the molecular lab work, participated in data analysis, carried out sequence alignments, participated in the design of the study and drafted the manuscript; CD carried out the statistical analyses; EF collected field data; GH conceived of the study, designed the study, coordinated the study and helped draft the manuscript. All authors gave final approval for publication.
• Acknowledgements Please acknowledge anyone who contributed to the study but did not meet the authorship criteria.
• Funding statement Please list the source of funding for each author.
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Kind regards, Anita Kristiansen Editorial Coordinator Royal Society Open Science openscience@royalsociety.org on behalf of R. Kerry Rowe (Subject Editor) openscience@royalsociety.org Associate Editor Comments to Author: Comments to the Author: Please respond to the remaining queries of the reviewers -in particular, you have been asked to set your work in the wider context of existing research to demonstrate more effectively how your paper moves the field forwards.
Reviewer comments to Author: Reviewer: 3 Comments to the Author(s) (1) please provide the original data of Fig.3, and explain that how to develop the fig.3 using the data.
(2)please add and explain that what is your research significance of the result for mine backfill application.

Reviewer: 2
Comments to the Author(s) All the comments have been addressed, and it can be plished.

06-Nov-2019
Dear Dr Zhao, I am pleased to inform you that your manuscript entitled "Microscopic characterization and strength characteristics of cemented backfill under different humidity curing conditions" is now accepted for publication in Royal Society Open Science.
You can expect to receive a proof of your article in the near future. Please contact the editorial office (openscience_proofs@royalsociety.org and openscience@royalsociety.org) to let us know if you are likely to be away from e-mail contact --if you are going to be away, please nominate a coauthor (if available) to manage the proofing process, and ensure they are copied into your email to the journal.
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On behalf of the Editors of Royal Society Open Science, we look forward to your continued contributions to the Journal. 4. At the end of this section, please provide the originality and specific objectives of this study.
The originality and specific objectives of this study are "NMR technology and an uniaxial compression test were used to explore the effects of humidity on macroscopic and microscopic characteristics and mechanical laws of CPB." And I have provided the originality and specific objectives of this study in the revised paper.
in the mine? They come from tailings dams or paste plant filtering cakes or mineral processing discharge products. Please state it clearly.
The experimental tailings were taken from mineral processing discharge products from the concentrator. And I have stated it clearly in the revised paper.
6. What were the sample preparation and mixing conditions? Please mention about them shortly.
The sample preparation and mixing conditions were "Various raw materials were weighed according to the designed ratio and then place them in a mixing bowl and mix well by mixer." I have already described in the revised paper. 7. How is the manufacturing and curing process of CPB samples? Please make it simple in the revised paper.
I have simplified the manufacturing and curing process of CPB samples in the revised paper.
8. Please explain the experimental test procedures in more detail. How were the working conditions of samples? Please state them clearly in the revised paper.
the experimental test procedures has been changed to "① NMR test: An NMR analysis was conducted using MesoMR23-060H. Parameter settings were shown in Table 5. The cured specimens were tested by NMR. The NMR T2 spectrum was obtained using NMR analysis software, and the area of the T2 spectrum, the area of each peak, and its proportion were calculated. Of which the permeability parameter of samples subjected to saturation and centrifugation could be obtained by NMR.
② UCS test: The UCS test was carried out using a pressure tester No. 01000405. Its loading rate was 0.2 kN/s. And then the cured specimens were placed in the middle of the pressure plate to be tested by UCS test machine. The UCS value was obtained through a force measurement system analysis." I have stated it clearly in the revised paper.  Figure 3 (as a dotted line).
There are no threshold limits of NMR results.
11. What are the main reasons for observing this behavior in Figure 4 in terms of strength differences? Please discuss it thoroughly.
I added some discussion that when the stone powder content is the same, the UCS decreases obviously as the increase of humidity. It shows that the moist environment seriously affects the UCS. Although the moist environment could promote the hydration reaction, at this time, the moisture content is a decisive factor affecting the strength, which results in a decrease in the strength of CPB.
Results and discussion 12. Which type of permeability tests were followed in this study? Please state it clearly.
The type of permeability tests was Coates model. And I have stated it clearly in the revised paper.
13. In Figure 5; permeability tests were conducted on fresh or hardened samples? Please clear it in the revised paper.
Permeability tests were conducted on hardened samples. And I have stated it clearly in the revised paper.
14. In Figure 7; this figure is very nice. The authors need to present in a larger size for better resolution.
I have presented in a larger size figure in the revised paper.
Conclusion 15. Please provide a short summary before highlighting the main findings of this research project.
I have provided a short summary before highlighting the main findings of this research project.
16. What are the limitations and recommendations of this work which can give some inspirations to other researchers to be worked in the area of this research?
The limitations and recommendations of this work are various measurement errors and the co-effect of temperature and humidity changes on CPB. And I have already described it in the revised paper.
Special thanks to you for your good comments.
Reviewer #2: 1. The introduction part needs to be extended. The Introduction should present the reasons why studying the effect of humidity in CPB is necessary, rather than just list previous publications in the related field.
The introduction part has been extended. I have presented the reasons why studying the effect of humidity in CPB. And I have rewritten the introduction section in the revised paper. The reasons are "The hydration of cement is affected by the level of humidity. In different stopes of underground mines, the environment humidity is not the same. Humidity affects the hydration of CPB, which affects the strength characteristics of the CPB. There are some scholars who have studied the concrete curing humidity, but there are few studies on curing humidity of CPB. And the hydration reaction of cement in CPB under different humidity conditions, particularly the backfill in the replacement using stone powder cement, must have its own law." 2. The references should be updated. The authors are suggested to cite some latest literatures, as the CPB develops rapidly.
I have already cited some latest literatures in the revised paper.
3. WAT2 is unclear, and it should be explained with a schematic diagram.
I have explained it with a schematic diagram in the revised paper.
4. The sum of element contents isn't 100% In table2?
There are other elements that are not listed in Table 2, so the sum of element contents isn't 100%.
5. The NMR parameters are important in this manuscript and are not mentioned in the paper. The authors are suggested to provide the NMR parameters.
I have provided the NMR parameters in the revised paper. The NMR Parameters are as follows: 6. The authors claimed that "The distribution of the T2 value represents the pore size distribution", which is not suitable for some samples in this paper are not saturated.
"The distribution of the T2 value represents the pore size distribution" changed to "The distribution of the T 2 value represents the pore size distribution for samples which are saturated".
And I also changed this sentence in the revised paper.
7. Please specify the application conditions of Equation 2.
For the pores of spherical model and tube bundle model, this equation 2 can be used. And I have stated in the revised paper.
Special thanks to you for your good comments.
Reviewer #3: 1. What is the chemical composition of cement？ and it would be better to explain the derivation process of Equation.
I have provided the chemical composition of cement in the revised paper. the chemical composition of cement are as follows: 2. what is the curing temperature of all samples?
The curing temperature of all samples is 20℃. And I have stated in the revised paper.
3. which mine's UCS basic requirement is 1.4MPa, and what are the meanings of white areas and black areas in SEM binary images？ Gaofeng mine's UCS basic requirement is 1.4MPa. white represents pores and black represents solids in the binarization diagram. And I have stated in the revised paper. The content added in the original paper is "The binarization image can well reflect the distribution of pores. Binarization mainly uses threshold grayscale segmentation to transform the solid phase and pores in the image into black and white regions. The principle is: ( , ) = { 0, ( , )＜ 1, ( , ) ≥ Where: T is the threshold gray scale. By the binarization function, the pixel points whose gray value are lower than T are set to 0, that is, the black point (solid phase), and the pixel points whose gray value are higher than or equal to T are set to 1, that is, white point (porosity)." Special thanks to you for your good comments.
Dear Editor and Reviewers: Thank you for your letter and for the editor' comments and reviewer' comments concerning our manuscript entitled "Microscopic characterization and strength characteristics of cemented backfill under different humidity curing conditions" (ID: RSOS-191227). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the paper. The main corrections in the paper and the responds to the reviewers and editor comments are as flowing: (Red indicates the respond.) Reviewer: 3 (1) please provide the original data of Fig.3, and explain that how to develop the fig.3 using the data. I have provided the original data of Fig.3 in the attachment. I used the Origin software to analyze the data to get fig.3.
(2)please add and explain that what is your research significance of the result for mine backfill application. The use of stone powder instead of cement can effectively reduce the filling cost. The research on the influence of curing humidity on CPB can provide guidance for CPB in different stopes to meet the requirements of mines. And I have already added this section in the revised paper. Editor: Please respond to the remaining queries of the reviewers -in particular, you have been asked to set your work in the wider context of existing research to demonstrate more effectively how your paper moves the field forwards. I have responded to the remaining queries of the reviewers. Although there have been some researches on curing conditions of CPB, they did not study in detail the influence of curing humidity on CPB. In this paper, the influence of curing humidity on strength characteristics and microscopic characterization of CPB is studied in detail, and the existing research in this field is supplemented to make the research in this field more perfect.