Experimental Study on the Strength and Damage Characteristics of Cement–Fly Ash–Slag–Gangue Cemented Backfill
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors1- The authors need to state the novelty and objectives of the work
2- Details on the imaging parameters used during CT scanning (voltage, exposure time, current, etc.) should be included
3- Please discuss related papers about slag
· https://doi.org/10.21608/ejchem.2016.1439
· https://doi.org/10.21608/ejchem.2023.173658.7179
· https://doi.org/10.3390/ma16216876
https://doi.org/10.1007/s10163-023-01838-x
Author Response
1- The authors need to state the novelty and objectives of the work
Response: We want to thank you for your comments of this study. We have adopted your comments and revised our manuscript accordingly. As for the novelty and objectives of this work, we have emphasized it in the revised draft and made the following explanation.
Response：The novelty of this manuscript is mainly regarding the multi-scaled discussion on microscopic damage mechanism of backfill material, comparing with the published works. The objective of this investigation is to reveal the intrinsic relationship between fracture evolution and mechanical behavior of backfill under external loading through in-situ CT scanning tests.
2- Details on the imaging parameters used during CT scanning (voltage, exposure time, current, etc.) should be included
Response：Your suggestion has been adopted. We have added the information about CT scanning in the revised manuscript.
“In the study, the voltage and current for CT scanning are 120 kV and 0.5 mA. Each scanning needs an exposure time of 36 min. A total of 825 grayscale CT-slices with an image resolution of 20 μm were collected after each scan.”
3- Please discuss related papers about slag
https://doi.org/10.21608/ejchem.2016.1439
https://doi.org/10.21608/ejchem.2023.173658.7179
https://doi.org/10.3390/ma16216876
https://doi.org/10.1007/s10163-023-01838-x
Response：Your suggestion has been adopted. We have cited two of the above papers regarding the slag materials.
[4] Heikal, M.; Ali, M.A.;Ghernaout, D.; Elboughdiri, N.;Ghernaout, B.; Bendary, H.I.Prolonging the Durability ofMaritime Constructions through a Sustainable and Salt-Resistant Cement Composite. Materials 2023, 16, 6876. https://doi.org/10.3390/ma16216876
[6] Hem, Heikal, M.;·Ali, M. A;·Ibrahim, S. M.;·Bendary, H, I. Sustainable composite cement prepared by two different types of iron slag. J MATER CYCLES WASTE 2024, 26: 331-345.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe following parts of this article require revision
The x-axis in Figure 4 is strain, which is mainly composed of elastic strain and plastic strain. I suggest the author divide the measured strain into two parts: elastic strain and plastic strain, and compare the measured crack development with the plastic strain, so that the damage development process can be found more clearly.
The y-axis of Figure 4 is stress. Generally speaking, concrete is a three-phase material, consisting of a slurry part, an aggregate part, and an interface zone between aggregate and slurry. For different stress levels, follow Concrete
According to the textbook of Concrete Microstructure, Properties, and Materials （3rd ，Mehta and Monteiro, page 88, figure 4-3）, due to the different development of cracks in different phases, macroscopically, there are differences in the connection and expansion of cracks in different phases. I suggest that the author further subdivides the cracks when analyzing them to distinguish whether the cracks belong to the paste phase or the interface zone phase or aggregate phase.
I took a look at the references. In reference [27], the author has done similar research. The author needs to clearly explain what is the originality of this article compared with their previous work [27]?
Comments on the Quality of English LanguageModerate editing of English language required.
Author Response
- The x-axis in Figure 4 is strain, which is mainly composed of elastic strain and plastic strain. I suggest the author divide the measured strain into two parts: elastic strain and plastic strain, and compare the measured crack development with the plastic strain, so that the damage development process can be found more clearly.
Response：According to the requirements of reviewers, we divided the measured strain into elastic strain and plastic strain. The crack evolution was compared with the strain development. By comparing the fracture characteristics of elastic deformation and plastic deformation, the development process of damage is revealed.
“The initial two scanned samples displayed elastic deformation, while the subsequent two exhibited plastic deformation. During the process of elastic deformation, internal cracks in the specimen develop gradually. However, upon entering the stage of plastic deformation, there is a significant increase in the rate of crack expansion. This phenomenon suggests that structural damage in backfilling under uniaxial loading is predominantly concentrated during the plastic deformation stage. Understanding how materials behave under different stages of deformation can provide valuable insights for engineers and researchers working on projects involving backfilling or other construction activities. ”
- The y-axis of Figure 4 is stress. Generally speaking, concrete is a three-phase material, consisting of a slurry part, an aggregate part, and an interface zone between aggregate and slurry. For different stress levels, follow Concrete
Response: We have adopted this comment and revised our manuscript accordingly. In particular, we have added some details on the feature of backflling materials. We believe that the stress-strain relationship of backfilling and concrete is being investigated in the context of the current research paper.
“The stress is primarily supported by the paste consisting of hydration products and aggregates. This paste acts as a binding agent, holding together the various components of the backfilling material under pressure. The hydration products form a strong matrix that provides stability and resistance to loading, while the aggregates enhanced the loading durability to the structure.”
- According to the textbook of Concrete Microstructure, Properties, and Materials （3rd ，Mehta and Monteiro, page 88, figure 4-3）, due to the different development of cracks in different phases, macroscopically, there are differences in the connection and expansion of cracks in different phases. I suggest that the author further subdivides the cracks when analyzing them to distinguish whether the cracks belong to the paste phase or the interface zone phase or aggregate phase.
Response: Thank you for the comment. We have added the detail about the distributed area of cracks in the backfilling specimen.
“From the CT images, it is evident that cracks resulting from external loading are predominantly present in the matrix composed of hydration products. Additionally, localized stress appears to have caused damage to the aggregates. Upon further analysis, it was observed that these cracks were primarily concentrated in areas where there was a higher concentration of hydration products, indicating a correlation between the presence of these products and crack formation. Furthermore, the localized stress seemed to have led to microcracking within the aggregates, suggesting that they may have been subjected to significant mechanical strain. Overall, these findings highlight the importance of understanding how external loading and localized stress can impact the structural integrity of materials such as backfilling and concrete.”
- I took a look at the references. In reference [27], the author has done similar research. The author needs to clearly explain what is the originality of this article compared with their previous work [27]?
Response: We gratefully thank this constructive comment from the reviewer. We believe these detailed suggestions and valuable comments will greatly improve the paper quality.
This submitted manuscript not only elucidates the evolutionary pattern of various testing results, but also establishes the correlation of changes in mechanical properties of cemented backfill material. In comparison with previously published work, the manuscript's new contribution lies in exploring the damage mechanism of backfilling under loading effects that have not been fully understood in previous literature. The majority of prior studies in this field have primarily concentrated on crack development, without establishing a connection between cracks and structural damage as well as the stress-strain relationship. However, it is crucial to understand the interplay between crack propagation and its impact on the overall integrity of the structure. By investigating how cracks evolve under different loading conditions and their influence on the mechanical behavior of materials, we can gain valuable insights into predicting and preventing structural failure. Additionally, exploring the stress-strain relationship in conjunction with crack development can provide a more comprehensive understanding of material behavior under various environmental and operational conditions. Therefore, a comprehensive research approach is adopted to investigate alterations in compressive cracks and mechanical behavior, with a particular focus on discussing the stress-strain relationship between tested and data-fitting results. Additionally, relevant publications mentioned by reviewers are discussed in the Introduction section as per their suggestions.
Reviewer 3 Report
Comments and Suggestions for AuthorsThis study is devoted to investigate the damage characteristics of Cement-Flyash-Slag-Gangue cemented backfill under loading using X-ray computed tomography. Results of dynamic visualisation of crack distribution characteristics through two-dimensional slices and three-dimensional models are presented. This approach allows to obtain qualitative and quantitative insight into the behavior of crack development in the investigated materials.
Despite the fact that this article is focused solely on the study of fracture evolution in cement backfill mixed with solid waste using 2D and 3D models without physico-chemical explanation of crack formation, the following information should be added to the article.
- It is necessary to present the chemical composition of the initial materials, because the chemical composition is the main characteristic that determines the field and technology of application of technogenic raw materials in construction. Orientation only on XRD data is not correct.
- Type of cement used in the work? The physico-chemical interaction of aggregates with the cement dough in the contact zone depends significantly on both the type of aggregate and the type of cement.
- Figure 5. The designations CT-1, CT-2... need to be clarified.
Author Response
This study is devoted to investigate the damage characteristics of Cement-Flyash-Slag-Gangue cemented backfill under loading using X-ray computed tomography. Results of dynamic visualisation of crack distribution characteristics through two-dimensional slices and three-dimensional models are presented. This approach allows to obtain qualitative and quantitative insight into the behavior of crack development in the investigated materials. Despite the fact that this article is focused solely on the study of fracture evolution in cement backfill mixed with solid waste using 2D and 3D models without physico-chemical explanation of crack formation, the following information should be added to the article.
Response: Thank you very much for the recognition of the interest and novelty of this study. We have adopted all your comments and revised our manuscript accordingly. Special thanks are for the suggestions to physico-chemical explanation of crack formation.
1.It is necessary to present the chemical composition of the initial materials, because the chemical composition is the main characteristic that determines the field and technology of application of technogenic raw materials in construction. Orientation only on XRD data is not correct.
Response: We are grateful for this suggestion. We have added more details regarding the X-Ray Diffraction. The authors fully agree with the reviewer that the results will be more convincing by adding more XRD tests. According to the X-ray diffraction (XRD) experiments, the main minerals of coal gangue in the study area are quartz, illite and mica, followed by kaolinite, siderite and dolomite. The mineral composition analysis were was conducted to ascertain the chemical constituent of the gangue, revealing the presence of SiO2 (56.7%), Al2O3 (37.6%), CaO (2.1%), Fe2O3 (2.3%), and miscellaneous com-pounds (1.3%).
2. Type of cement used in the work? The physico-chemical interaction of aggregates with the cement dough in the contact zone depends significantly on both the type of aggregate and the type of cement.
Response: Thank you for your comment. We have adopted your comments and added the information of aggregate and the type of cement. Besides, we have added the testing data regarding shear strength in the “materials” section. The cement is ordinary Portland cement purchased in the market, with a strength grade of P.·O 42.5.
3. Figure 5. The designations CT-1, CT-2... need to be clarified.
Response: Thank you for the kind suggestion. We have added the explaination of “CT-1, CT-2…” in figure 5. CT-n indicates the n-th CT scanning.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors have adequately addressed the comments and concerns raised in the initial review.
