Study on the Effects of Microwave Heating Time and Power on the Mechanical Properties of Cemented Tailings Backfill

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Review report for the manuscript titled:

Study on the Effects of Microwave Heating Time and Power on the Mechanical Properties of Cemented Tailings Backfill

In this article, the authors present their research on Study on the effects of microwave heating time and power on the mechanical properties of cemented tailings backfill. The paper is interesting and represents a promising future direction in the use of microwave in various mining applications.

v  General comments

Ø  I have a comment on the methodology: The research did not mention the calibration of the equipment used in the tests, nor did it mention any standard criteria that were followed during the experiments. Mentioning the calibration of the equipment is crucial to ensure the accuracy and validity of the measurements obtained. In addition, it is important to mention the approved standard criteria that were followed during the design and implementation of the tests. This will contribute to enhancing the reliability of the results and help assessment of these results with other studies in the same field.

Ø  It is also better to describe the model for each device used in this research, such as: mortar mixer, microwave heating device, compression machine, Scanning Electron Microscope device, and so on.

Ø  The paper lacks detail on the total number of mixtures used and the number of samples in each mixture. What procedures were followed in preparing samples to ensure consistency across them, how were samples selected, and whether there were samples that were excluded or their results excluded.

Ø  Accurately, the influence of one of the basic parameters, namely the water-to-binder ratio, has not been analyzed. Its value has not even been mentioned.

Ø  Examining the plagiarism of the manuscript, I found a 32% Similarity Index after excluding Bibliography and Quotes. This is a relatively high rate. I, therefore, suggest reducing direct citations and improving the original contribution of the paper by rewriting the relevant parts to reflect original analysis or innovation. For example, there is a source with a similarity index, according to the iThenticate Report, of 3%, and despite that, it was not referred to as a reference that was used. This source can be cited as follows: “Chao Zhu, Pan yang, Lang Liu, Yuanyuan Pu, Chongchong Qi, Qiusong Chen, Jie Chen. "Effect of ice addition on the properties and microstructure of cemented paste backfill at early-age", Journal of Building Engineering, 2023”. I kindly ask authors to add any references they are used or explain why they are not included if this is justified in some way.

v  Detailed Comments:

1. Introduction

1. Page 2. Line #53. Fall and others studied: Writing co-authorship with others in this way is less common in academic writing. It is better to write it as: Fall et al.

2. Page 2. Lines # 62-63. Compared to traditional heating methods, microwave heating offers advantages such as uniform heating. Microwave heating is referred to as providing uniform heating, but this is not always entirely accurate. Microwave heating relies on the absorption of microwave radiation by the material, which can result in uneven heating within the material. Therefore, although microwaves can provide faster and more efficient heating than conventional methods, it is not always “uniform.” Some applications may require additional techniques such as rotating the sample or using microwave diffusers to further improve heat distribution.

2. Experimental program and procedure

3. Page 3. Line #115. adopted from Ref. [34]. When I tried to look at reference [34], from which the chemical composition of the tailings was adopted., it is non-existent online in academic databases. Authors are requested to verify the validity of this reference or replace it with a reliable source.

4. Page 3. Line #116. Table 2. Physical properties of the tailings. Since the table title is general and does not accurately describe what it contains, I suggest that it be titled as follows: Grain size distribution analysis and gradation characteristics of tailings.

5. Page 4. Line #128. (Table 4). Here there is no need to mention Table 4 again, as it was referred to in the previous sentence and it is implicitly understood that the mix proportion are included in it.

6. Page 4. Line #128. Table 4. Mix proportion of each specimen. The name of Table 4 is somewhat misleading. It contains the variables that the researchers studied, and there is no relationship between the numbers written in the different columns of the table. Accordingly, if the columns represent independent variables, it may be better to rename the table to clarify this, such as "Variables for Mix Proportions" or provide separate tables for each set of related variables. If the columns do represent mixing proportions for a particular sample, you should ensure that the rows reflect the correct proportions for each sample, and that the relationships between the variables are clearly shown.

7. Page 4. Line #129. The produced CTB mixture was then poured into plastic molds. I noticed that the paper mentions using plastic molds to prepare the samples and then placing them in the microwave, but it doesn't specify what type of plastic was used. This is important because not all plastics are microwave safe, and can degrade or release harmful chemicals when heated in a microwave.

8. Page 5. Lines # 159. total of 567 CTB specimens were tested in this experiment.  Why was the number of mixtures prepared not explained in detail and the number of specimens in each mixture so that the reader can understand quickly instead of recalculating to confirm this number 567? Also clarify how many control specimens are used and what is the UCS value for them.

3. Results and discussion

9. The researchers observed that increasing the heating time has an effect on UCS of the samples. They clarified that microwave heating provides a certain amount of thermal energy, promoting the hydration reaction of the cementitious materials, resulting in a strength growth rate. However, prolonged microwave heating causes too high an internal temperature and severe moisture loss in CTB, leading to a decrease in UCS.

However, the specific temperature attained by the samples during each heating interval was not specified, which is a crucial aspect in comprehending the main reason behind the alteration in the samples' UCS.

It is essential to specify the temperatures reached by the samples during each microwave heating period. This will help in interpreting the results more accurately, and will allow for an assessment of the direct relationship between temperature, heating time, and their effect on UCS of the samples. If there are temperature measurements, they should be included in the text; if not, it may be useful to repeat the experiment or clarify this limitation in the discussion.

10. The same previous comment when studying the rest of the factors, the main reason was not measured.

References

11. Reference No. [34] is not available in the academic databases available online. You can replace it with another reference.

12. While reviewing the references list, I noticed that references [33] and [35] are exactly the same reference, with the same title, same authors, and same DOI. It is necessary to remove one of them to ensure the accuracy of the references and avoid unnecessary duplication in the references list.

v  Recommendation:

Based on the above comments, my recommendation is [accepted with major revisions].

Comments for author File: Comments.pdf

Author Response

General comments：

Comments 1：I have a comment on the methodology: The research did not mention the calibration of the equipment used in the tests, nor did it mention any standard criteria that were followed during the experiments. Mentioning the calibration of the equipment is crucial to ensure the accuracy and validity of the measurements obtained. In addition, it is important to mention the approved standard criteria that were followed during the design and implementation of the tests. This will contribute to enhancing the reliability of the results and help assessment of these results with other studies in the same field.

Response 1: The standard criteria that were followed during the experiments are explained in line 176.

Comments 2：It is also better to describe the model for each device used in this research, such as: mortar mixer, microwave heating device, compression machine, Scanning Electron Microscope device, and so on.

Response 2: Descriptions of the equipment used in the text have been added in lines 136, 176, and 192. It is important to note that the microwave device is a custom-made apparatus by us, and this device features adjustable output power, with a maximum capacity of 1000 W.

Comments 3：The paper lacks detail on the total number of mixtures used and the number of samples in each mixture. What procedures were followed in preparing samples to ensure consistency across them, how were samples selected, and whether there were samples that were excluded or their results excluded.

Response 3: The sample quantity and the procedures followed for sample preparation have been added in lines 179-183.

Comments 4：Accurately, the influence of one of the basic parameters, namely the water-to-binder ratio, has not been analyzed. Its value has not even been mentioned.

Response 4: In experimental design, descriptions of the mixture generally include common terms such as concentration, water-to-cement ratio, and cement-sand ratio. This article primarily studies the strength variations of different CTB concentrations and cement-sand ratio under microwave heating. Once the concentration and cement-sand ratio are determined, the water-to-cement ratio is a fixed value. However, since it is not a variable considered in this study, it is not mentioned in the paper.

Comments 5：Examining the plagiarism of the manuscript, I found a 32% Similarity Index after excluding Bibliography and Quotes. This is a relatively high rate. I, therefore, suggest reducing direct citations and improving the original contribution of the paper by rewriting the relevant parts to reflect original analysis or innovation. For example, there is a source with a similarity index, according to the iThenticate Report, of 3%, and despite that, it was not referred to as a reference that was used. This source can be cited as follows: “Chao Zhu, Pan yang, Lang Liu, Yuanyuan Pu, Chongchong Qi, Qiusong Chen, Jie Chen. "Effect of ice addition on the properties and microstructure of cemented paste backfill at early-age", Journal of Building Engineering, 2023”. I kindly ask authors to add any references they are used or explain why they are not included if this is justified in some way.

Response 5: The relevant sections of the paper have been revised to reduce Similarity Index, and reference "Effect of ice addition on the properties and microstructure of cemented paste backfill at early-age" has been cited at [37].

Detailed Comments:

Comments 1：Page 2. Line #53. Fall and others studied: Writing co-authorship with others in this way is less common in academic writing. It is better to write it as: Fall et al.

Response 1: Thank you for your suggestion. The phrase “Fall and others studied” has already been changed to “Fall et al. “in line 55.

Comments 2：Page 2. Lines # 62-63. Compared to traditional heating methods, microwave heating offers advantages such as uniform heating. Microwave heating is referred to as providing uniform heating, but this is not always entirely accurate. Microwave heating relies on the absorption of microwave radiation by the material, which can result in uneven heating within the material. Therefore, although microwaves can provide faster and more efficient heating than conventional methods, it is not always “uniform.” Some applications may require additional techniques such as rotating the sample or using microwave diffusers to further improve heat distribution.

Response 2: Thank you for your reminder. We also noted that the surface temperature and internal temperature of the sample after microwave heating are different. To express this more accurately, we have removed the phrase “uniform heating”.

Comments 3：Page 3. Line #115. adopted from Ref. [34]. When I tried to look at reference [34], from which the chemical composition of the tailings was adopted., it is non-existent online in academic databases. Authors are requested to verify the validity of this reference or replace it with a reliable source.

Response 3: Thank you for your suggestion. Due to the variation in chemical composition of tailings from the same mine at different time, X-ray fluorescence analysis of the tailings was conducted again to ensure the accuracy of the tests. The test results are presented in Table 1, and the source of the test data is explained in lines 117-118.

Comments 4：Page 3. Line #116. Table 2. Physical properties of the tailings. Since the table title is general and does not accurately describe what it contains, I suggest that it be titled as follows: Grain size distribution analysis and gradation characteristics of tailings.

Response 4: Thank you for your suggestion. The table title “Physical properties of the tailings” has already been changed to “Grain size distribution analysis and gradation characteristics of tailings “in line 123.

Comments 5：Page 4. Line #128. (Table 4). Here there is no need to mention Table 4 again, as it was referred to in the previous sentence and it is implicitly understood that the mix proportion are included in it.

Response 5: Thank you for your suggestion. (Table 4) has been deleted in line 136.

Comments 6：Page 4. Line #128. Table 4. Mix proportion of each specimen. The name of Table 4 is somewhat misleading. It contains the variables that the researchers studied, and there is no relationship between the numbers written in the different columns of the table. Accordingly, if the columns represent independent variables, it may be better to rename the table to clarify this, such as "Variables for Mix Proportions" or provide separate tables for each set of related variables. If the columns do represent mixing proportions for a particular sample, you should ensure that the rows reflect the correct proportions for each sample, and that the relationships between the variables are clearly shown.

Response 6: Thank you for your suggestion. The table title “Mix proportion of each specimen” has been changed to” Variables for mix proportions” in line 166. In order to describe the experimental process more accurately, a description of the control group was added in lines 134-135.

Comments 7：Page 4. Line #129. The produced CTB mixture was then poured into plastic molds. I noticed that the paper mentions using plastic molds to prepare the samples and then placing them in the microwave, but it doesn't specify what type of plastic was used. This is important because not all plastics are microwave safe, and can degrade or release harmful chemicals when heated in a microwave.

Response 7: Thank you for your reminder and this suggestion is very important. The plastic mold is made of acrylic, which is non-toxic at room temperature, and the odor it emits is also non-toxic to humans. Harmful substances such as formaldehyde and carbon monoxide are only produced during incomplete combustion. Its melting point is 130-140 °C, and tests show that the maximum surface temperature of the test block during the experiment was 76.8 °C, which will not cause the plastic mold to melt and release toxic gases. To avoid controversy, an explanation was added in lines 138-141.

Comments 8：Page 5. Lines # 159. total of 567 CTB specimens were tested in this experiment.  Why was the number of mixtures prepared not explained in detail and the number of specimens in each mixture so that the reader can understand quickly instead of recalculating to confirm this number 567? Also clarify how many control specimens are used and what is the UCS value for them.

Response 8: Thank you for your question. In the UCS tests, there were a total of 12 experimental groups, each containing 20 samples, including 48 control samples. Due to the presence of crossover factors in the experiments, as described in lines 153-161, there are 48 duplicate samples, with each sample tested 3 times to obtain an average value, resulting in a total of 576 samples. The mention of 567 samples in the text was a typographical error, which has been clarified in lines 178-183, correcting the final sample count. Due to the large volume of data, and since this article focuses on the impact of microwave heating time and power on the growth rate of CTB strength, the specific measured strengths are not detailed in the paper, we will elaborate on the strengths of each sample in future research.

Comments 9：The researchers observed that increasing the heating time has an effect on UCS of the samples. They clarified that microwave heating provides a certain amount of thermal energy, promoting the hydration reaction of the cementitious materials, resulting in a strength growth rate. However, prolonged microwave heating causes too high an internal temperature and severe moisture loss in CTB, leading to a decrease in UCS.

However, the specific temperature attained by the samples during each heating interval was not specified, which is a crucial aspect in comprehending the main reason behind the alteration in the samples' UCS.

It is essential to specify the temperatures reached by the samples during each microwave heating period. This will help in interpreting the results more accurately, and will allow for an assessment of the direct relationship between temperature, heating time, and their effect on UCS of the samples. If there are temperature measurements, they should be included in the text; if not, it may be useful to repeat the experiment or clarify this limitation in the discussion.

Response 9: Thank you for your question and this is a very constructive suggestion. In fact, during the experiment, we used a ST8550 thermal imager to test the surface temperature of each microwave-heated sample. The temperatures mentioned in the paper have now been added in lines 209, 212, 214, 216-217, 232, 236, 268, 269, 270, 271, 318, 319, 320, 321, 363, 364, 365, 366. A description of the temperature measurement instrument has been added in lines 171-174.

Comments 10：The same previous comment when studying the rest of the factors, the main reason was not measured.

Response 10: Thank you for your question. The revisions regarding the temperature changes when studying the impact of microwave power on the UCS growth rate of CTB have been addressed in response 9.

Comments 11：Reference No. [34] is not available in the academic databases available online. You can replace it with another reference.

Response 11: Thank you for your reminder. X-ray fluorescence analysis of the tailings was conducted again to ensure the accuracy of the tests. There is no need to cite reference No. [34] again, and this reference has been removed.

Comments 12：While reviewing the references list, I noticed that references [33] and [35] are exactly the same reference, with the same title, same authors, and same DOI. It is necessary to remove one of them to ensure the accuracy of the references and avoid unnecessary duplication in the references list.

Response 12: Thank you for your reminder. Reference [35] has been removed, and the order in the paper has been adjusted accordingly.

Reviewer 2 Report

Comments and Suggestions for Authors

Comments on the manuscript minerals-3178872 are as follows.

 1. The chemical composition data of tailings used in Table 1 are extracted from other literatures, but the chemical composition of tailings from the same mine at different times is not exactly the same, so it is recommended to re-conduct XRF analysis of the chemical composition of tailings.

2. The article does not specify how many days after the completion of the test piece can the test piece be microwave heated.

3. Microwave heating mainly relies on the vibration of substances such as water in the test piece. Whether the lack of water in the test piece due to the evaporation of water in pores and cracks during microwave heating will lead to an increase in porosity or difficulty in hydration, and thus affect the strength, needs to be further explained.

4. It is recommended to add a test piece without microwave treatment when analyzing the UCS strength growth rate, so that readers can better understand the advantages of microwave heating.

5. It needs to be explained whether heavy metal ions in the tailings will be released due to heating during microwave treatment, thereby polluting the filling environment.

6.The increase in UCS strength should also be explained with respect to which control group is being compared to. For example, if the strength increases by 25% when the power is increased from 100W to 200W, it needs to be specified what the control group is.

7. SEM analysis is relatively limited, and further discussion is needed on the impact of factors such as hydration reaction and pores on the overall strength, as well as the microstructure contribution to the enhanced strength after microwave heating. 

 

In conclusion, this study has certain innovation and practicality, but further optimization and improvement are needed in terms of experimental design and conclusion analysis. Accept after minor revisions.

Comments on the Quality of English Language

 Minor editing of English language required.

Author Response

Comments 1：The chemical composition data of tailings used in Table 1 are extracted from other literatures, but the chemical composition of tailings from the same mine at different times is not exactly the same, so it is recommended to re-conduct XRF analysis of the chemical composition of tailings.

Response 1: Thank you for your suggestion. Due to the variation in chemical composition of tailings from the same mine at different time, X-ray fluorescence analysis of the tailings was conducted again to ensure the accuracy of the tests. The test results are presented in Table 1, and the source of the test data is explained in lines 117-118.

Comments 2：The article does not specify how many days after the completion of the test piece can the test piece be microwave heated.

Response 2: Thank you for your suggestion. We added a sentence " underwent microwave heating after the slurry was added to the mold" in lines 142-143to accurately describe the duration and process of the experiment.

Comments 3：Microwave heating mainly relies on the vibration of substances such as water in the test piece. Whether the lack of water in the test piece due to the evaporation of water in pores and cracks during microwave heating will lead to an increase in porosity or difficulty in hydration, and thus affect the strength, needs to be further explained.

Response 3: Thank you for your suggestion. To better illustrate the experimental results, we added a description of the experiment in lines 222-226. “Conversely, extended heating durations may elevate the internal temperature of the CTB excessively, causing significant moisture evaporation from the specimen within a short timeframe. This not only disrupts the normal hydration progression but also induces the formation of numerous voids within the specimen, ultimately diminishing the UCS growth rate.”

Comments 4：It is recommended to add a test piece without microwave treatment when analyzing the UCS strength growth rate, so that readers can better understand the advantages of microwave heating.

Response 4: Thank you for your suggestion. In the paper, the strength growth rate of CTB refers to the microwave-heated specimens compared to the unheated specimens of the same curing age. In lines 141-143, it has been clarified that the prepared specimens are divided into two parts: one of which was not subjected to microwave heating, while the other part, with the same mix proportion, underwent microwave heating after the slurry was added to the mold. To describe the experimental process accurately, " In the evaluation of the experimental outcomes, the UCS growth rate is defined as the comparative strength of the microwave-treated specimens versus the control specimens that were not exposed to microwave heating at the same age." has been added in lines 143-146 for clarification.

Comments 5：It needs to be explained whether heavy metal ions in the tailings will be released due to heating during microwave treatment, thereby polluting the filling environment.

Response 5: Thank you for your question and this is a very constructive suggestion. This paper investigates the effects of microwave heating time and power on the UCS growth rate of CTB. We did not focus on the release of heavy metal ions during this process; however, we will emphasize this topic in our future research.

Comments 6：The increase in UCS strength should also be explained with respect to which control group is being compared to. For example, if the strength increases by 25% when the power is increased from 100W to 200W, it needs to be specified what the control group is.

Response 6: Thank you for your suggestion. To express the analysis of the experimental results more precisely, we added a description of the experiment in lines 143-146: “In the evaluation of the experimental outcomes, the UCS growth rate is defined as the comparative strength of the microwave-treated specimens versus the control specimens that were not exposed to microwave heating at the same age”.

Comments 7：SEM analysis is relatively limited, and further discussion is needed on the impact of factors such as hydration reaction and pores on the overall strength, as well as the microstructure contribution to the enhanced strength after microwave heating. 

Response 7: Thank you for your suggestion. To conduct a more in-depth analysis of these issues, we have added " These findings indicate that microwave irradiation expedites the hydration process, facilitating rapid ettringite crystal growth, thereby effectively occluding pores and enhancing the CTB's structural coherence." in lines 412-414. Added" This observation implies that microwave treatment not only hastens the initial hydration but also alters the long-term microstructural evolution of CTB. The formation of C-S-H crystals is pivotal for the mechanical strength development in cementitious materials. Therefore, the interaction between Ca²⁺ and Al₂O₃ under microwave conditions may result in a more rapid and uniform distribution of these strength-enhancing phases." in lines 422-427.

Reviewer 3 Report

Comments and Suggestions for Authors

This study investigates the application of microwave heating technology in Cement Tailings Backfill (CTB), focusing on the effects of heating time and power on CTB's mechanical properties. While the study falls within the journal’s scope, there are ambiguities regarding the application of microwave heating. Specifically, it is unclear how the microwaves were applied to the samples, the number of samples used, and their positioning within the microwave cavity. Additionally, at what stage or time (while fresh or hardened) were the samples exposed to microwave heating? The water content, which is crucial for absorbing microwave energy, is not discussed. Moreover, the temperature of the specimens during microwave heating—a key parameter affecting their long-term durability—has been overlooked in this study.

 

 

 

Author Response

Comments：This study investigates the application of microwave heating technology in Cement Tailings Backfill (CTB), focusing on the effects of heating time and power on CTB's mechanical properties. While the study falls within the journal’s scope, there are ambiguities regarding the application of microwave heating. Specifically, it is unclear how the microwaves were applied to the samples, the number of samples used, and their positioning within the microwave cavity. Additionally, at what stage or time (while fresh or hardened) were the samples exposed to microwave heating? The water content, which is crucial for absorbing microwave energy, is not discussed. Moreover, the temperature of the specimens during microwave heating—a key parameter affecting their long-term durability—has been overlooked in this study.

Response: Thank you for your question and they are very constructive suggestions. The following paragraph has been added to the paper to explain the method of applying microwaves to the samples and their positioning within the microwave cavity. It clarifies that the samples were subjected to microwave heating immediately after being placed in the mold, specifies the grouping and quantity of the samples, and indicates the control group to express the analysis of the experimental results more precisely.

”underwent microwave heating after the slurry was added to the mold. In the evaluation of the experimental outcomes, the UCS growth rate is defined as the comparative strength of the microwave-treated specimens versus the control specimens that were not exposed to microwave heating at the same age.” in lines 142-146.

“During the implementation of microwave heating, the microwave device is placed above the mold containing the specimen for a specified duration, followed by surface temperature measurement of the specimens.” in lines 141-144

“This experiment consists of a total of 16 groups, with 20 type samples in each group, including 48 duplicate samples, for each type of CTB, three identical samples were tested, and their average UCS value was calculated as the final strength [35, 36], resulting in a total of 576 samples tested.” in lines179-183

the temperature of the specimens during microwave heating is a key parameter affecting their long-term durability, in fact, during the experiment, we used a ST8550 thermal imager to test the surface temperature of each microwave-heated sample. The temperatures mentioned in the paper have now been added in lines 209, 212, 214, 216-217, 232, 236, 268, 269, 270, 271, 318, 319, 320, 321, 363, 364, 365, 366. A description of the temperature measurement instrument has been added in lines 171-174.

Moisture content is a critical factor, and the different mineral compositions of cement particles and tailings also affect the absorption of microwave energy. We will focus on this issue in future research.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I would like to thank you for your comprehensive response to my comments and for the edits you have made. After reviewing the revised version, I believe that you have addressed all my comments appropriately and that the edits made have improved the quality of the paper.

I believe that the current version reflects significant progress and is now suitable for publication.

I wish you the best in your next steps.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have addressed the comments appropriately. In my opinion, the paper is ready for publication, but I leave the final decision to the editor.