An Experimental Study on Physical and Mechanical Properties of Fractured Sandstone Grouting Reinforcement Body Under Freeze–Thaw Cycle
and Jiahao Zhang 1,3Round 1
Reviewer 1 Report
Comments and Suggestions for Authors This study conducts a series of investigations into the physical and mechanical properties of fractured sandstone grouting reinforcement bodies under freeze-thaw cycles, showcasing a degree of innovation. The research findings hold certain reference value for the safe construction and long-term maintenance of grouting projects in cold regions. However, the article currently presents the following issues: --The introduction of the article provides a comprehensive review of previous studies, listing numerous research findings. This approach is not ideal. To improve readability, it is recommended to summarize the contributions of each study more concisely based on the research content or innovations. --What is the purpose of setting the crack dip angle in sandstone, and how does it correspond to practical engineering applications? --Section 2.1.1 uses XRD analysis to examine the composition of sandstone and cement. What is the purpose of this analysis, as it is not utilized in subsequent research? --During the drying process of the grouting reinforcement body, the drying temperature is set to 105°C. Could this temperature cause cracks at the slurry-rock interface? --The study employs NMR technology to test the pores in the grouting reinforcement body, which is a relatively novel approach. However, the paper mentions the transformation of micropores to mesopores and mesopores to macropores. From Figure 15, it can be observed that as the number of cycles increases, the three peaks shift to the right, but the magnitude of the shift is small, making it difficult to draw corresponding conclusions. --The study lacks a necessary discussion section. It is suggested to add a discussion chapter to elaborate on the differences between your findings and previous research results, as well as the potential applications of your findings in practical engineering.
Author Response
List of Responses
Dear Editors and Reviewers:
Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “Experimental Study on Physical and Mechanical Properties of Fractured Sandstone Grouting Reinforcement Body under Freeze-thaw Cycle” (applsci-3456796). Those comments are very helpful for revising and improving our paper, as well as the important guiding significance to our research. We have studied the comments carefully and have made corrections. Revised portions are marked in red in the paper. We appreciate the Editors/Reviewers’ work, and hope that the corrections will meet with approval.
The main corrections in the paper and the response to the reviewer’s comments are as follows:
Response to the reviewers’ comments:
Reviewer #1:
- Comment1: The introduction of the article provides a comprehensive review of previous studies, listing numerous research findings. This approach is not ideal. To improve readability, it is recommended to summarize the contributions of each study more concisely based on the research content or innovations.
Response1: Thank you very much for your valuable comments on the introduction section of our manuscript. We fully agree with your suggestion that the introduction should be more concise and focused on summarizing the key contributions and innovations of each study. To improve the readability and clarity of the introduction, we have thoroughly revised and streamlined this section.
- Comment2: What is the purpose of setting the crack dip angle in sandstone, and how does it correspond to practical engineering applications?
Response2: Thank you for your comment. The reasons for setting the fracture dip angle are as follows:
When grouting fractured or multiply-jointed rock masses, the complex spatial distribution of the primary fractures results in a correspondingly intricate spatial geometry of the grout stone body formed after grout filling, as shown in Figure 1. During the load-bearing process of the reinforcement body, the load direction and the grout vein will have different angles (β) at different locations. Moreover, during the load-bearing process, the rock blocks and the grout stones work together to bear the load. Clarifying the mechanical response of different locations within the reinforcement body under load, under various angles β, is fundamental to analyzing the overall mechanical performance of the reinforcement body.
Fig 1. Fracture dip angle diagram
Therefore, in this study, we set up through-going fractures with different dip angles in sandstone. After grouting reinforcement, a grout-rock composite is formed. This approach allows us to elucidate the mechanical properties of the local reinforcement body under different conditions, providing a reference for subsequent studies on the overall mechanical characteristics of grouting reinforcement bodies.
- Comment3: Section 2.1.1 uses XRD analysis to examine the composition of sandstone and cement. What is the purpose of this analysis, as it is not utilized in subsequent research?
Response3: Thank you for your comment. The XRD analysis here only provides more specific test material information. In the follow-up experiment, the phase composition of rock and cement did not change, so it was not mentioned in the follow-up study.
- Comment4: During the drying process of the grouting reinforcement body, the drying temperature is set to 105°C. Could this temperature cause cracks at the slurry-rock interface?
Response4: Thank you for your comment. The drying temperature of 105℃ will not cause cracks in the sample.
- Comment5: The study employs NMR technology to test the pores in the grouting reinforcement body, which is a relatively novel approach. However, the paper mentions the transformation of micropores to mesopores and mesopores to macropores. From Figure 15, it can be observed that as the number of cycles increases, the three peaks shift to the right, but the magnitude of the shift is small, making it difficult to draw corresponding conclusions.
Response5: Thank you for your comment. Figure 15 shows that the three peaks of the T2 spectrum move to the right as the number of freeze-thaw cycles increases, but the movement is small. This indicates that the change of pore structure is gradual, and the change of pore size is not dramatic. However, this tiny movement still has important physical significance. According to the principle of NMR, the shift of T2 spectrum reflects the change of pore structure, especially the increase of pore size. Even if the movement range is small, it also shows that the pore structure is undergoing continuous evolution under the action of freeze-thaw cycles.
The quantitative analysis of the change of T2 spectrum area shows that the T2 spectrum area of micropores, mesopores and macropores increases with the increase of freeze-thaw cycles, which indicates that the number and size of pores are increasing. In particular, the T2 spectrum area of macropores increased more significantly in the later period, which was consistent with the transformation of pore structure from micropores to mesopores and from mesopores to macropores.
- Comment6: The study lacks a necessary discussion section. It is suggested to add a discussion chapter to elaborate on the differences between your findings and previous research results, as well as the potential applications of your findings in practical engineering.
Response6: Thank you very much for your suggestions on adding the discussion section. We added a separate ' discussion ' section (Section 3.4) between Sections 3 and 4 to provide a more in-depth analysis and evaluation of the experimental results. The following is the main content of the new discussion section :
3.4 Discussion
3.4.1 The influence mechanism of freeze-thaw cycle on grouting reinforcement body
In this study, the impact of freeze-thaw cycles on the physical and mechanical properties of grouting reinforcement body was investigated through a comprehensive series of experimental tests. Extensive freeze-thaw testing has demonstrated that the mass and wave velocity of grouting reinforcement exhibit significant declines as the number of freeze-thaw cycles increases. Correspondingly, the mass loss rate and wave velocity loss rate progressively rise. The macroscopic mechanical properties of grout-ing reinforcement body also deteriorate gradually, with notable reductions in peak strength, elastic modulus, and shear strength parameters. The peak strength and elas-tic modulus are found to have a negative exponential relationship with the number of freeze-thaw cycles, which is consistent with the experimental results obtained in this study.This phenomenon can be primarily attributed to the freezing of pore water within the grouting reinforcement body as ambient temperatures decrease. The ex-pansion of frozen water generates frost heave forces that act upon the rock and ce-ment particles. These forces exert a destructive influence on particles with weaker ce-mentation strength, leading to localized damage within the grouting reinforcement body. As temperatures rise, the water within the grouting reinforcement body thaws, resulting in the release of freezing stress and the migration of water. With increasing freeze-thaw cycles, these localized damage zones gradually coalesce into microcracks. The continuous propagation of these microcracks leads to a progressive reduction in the strength and stiffness of the grouting reinforcement body, ultimately causing par-ticle fracture and spalling.
During the freeze-thaw cycle, the freezing and thawing of water in the pores lead to the expansion of the original pores and fissures and the formation of new fissures. The evolution law of internal pores in grouting reinforcement body can be obtained by nuclear magnetic resonance T2 spectrum. In this study, with the increase of the number of freeze-thaw cycles, the T2 spectrum curve of the sample continued to grow upward, and the NMR signal intensities of the three peaks continued to increase. With the increase of the number of freeze-thaw cycles, the three peaks all showed a right-ward trend, which was manifested in the pore characteristics of micropores increasing and transitioning to mesopores, mesopores increasing and transitioning to macropores, and macropores increasing continuously. The change of the pore struc-ture directly leads to the decrease of the macroscopic mechanical properties of the grouting reinforcement body.
3.4.2 The influence of crack dip angle on grouting reinforcement body
This study also analyzes the influence of different crack dip angles on the perfor-mance of sandstone grouting reinforcement. The results show that when the crack dip angle is 0 °, 30 ° and 45 °, the grouting reinforcement has obvious plastic deformation and ductility after the peak strength. When the fracture dip angle is 60 °, the stress-strain relationship curve has no plastic deformation stage regardless of the con-fining pressure, and it decreases instantaneously after the axial stress reaches the peak value. The main reason is that the stress reaches the shear strength of the weak surface of the rock-slurry consolidation body, resulting in shear slip failure of the rock along the fracture surface. With the increase of crack dip angle, the failure mode of the grouting reinforcement body gradually changes from axial splitting failure to axial splitting-shear mixed failure, and finally to shear failure. This is relatively consistent with the research results of Rong Miren et al. The change of this failure mode further illustrates the importance of crack dip angle to the stability of the grouting reinforcement body.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments and Suggestions for AuthorsComments on the manuscript submitted for review:
Section 1: The authors presented a literature review pointing out many research results on the impact of body reinforcement. However, the authors do not highlight what new contributions they make to science. What is innovative about the authors' research? The authors also need to justify more extensively the use of their results in future research.
Section 2: On what basis did the authors establish a temperature range of -15°C and +15°C? Why are these not different ranges? For example, for rocks, EN 12371 gives other ranges, i.e. from -12°C to + 20°C.
Why was there a maximum of 30 freeze-thaw cycles? How is this reflected in practice? Long-term exposure to changing weather conditions gives a true view of the durability of the rock.
Additional section after section 3 and before section 4: The authors did not make a discussion of the results which is a critical assessment of the results obtained.
General comment: The literature cited in the article is mainly by Chinese authors which has a significant impact on the limitations of the article's impact on international science. The authors should perform the literature review more extensively using publications from around the world and not just Chinese authors.
General comment: What are the limitations of this research?
General comment: There are editing errors in the manuscript. This should be corrected.
Comments on the Quality of English Language
Sometimes the English language is difficult to understand. Authors should take the help of a native speaker.
Author Response
List of Responses
Dear Editors and Reviewers:
Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “Experimental Study on Physical and Mechanical Properties of Fractured Sandstone Grouting Reinforcement Body under Freeze-thaw Cycle” (applsci-3456796). Those comments are very helpful for revising and improving our paper, as well as the important guiding significance to our research. We have studied the comments carefully and have made corrections. Revised portions are marked in red in the paper. We appreciate the Editors/Reviewers’ work, and hope that the corrections will meet with approval.
The main corrections in the paper and the response to the reviewer’s comments are as follows:
Response to the reviewers’ comments:
- Comment1: Section 1: The authors presented a literature review pointing out many research results on the impact of body reinforcement. However, the authors do not highlight what new contributions they make to science. What is innovative about the authors' research? The authors also need to justify more extensively the use of their results in future research.
Response1: Thank you for your comments. We have refined the section 1 of manuscript to clearly highlight the novelty and practical significance of our research.
- Comment2: Section 2: On what basis did the authors establish a temperature range of -15°C and +15°C? Why are these not different ranges? For example, for rocks, EN 12371 gives other ranges, i.e. from -12°C to + 20°C.
Response2: Thank you for your comments. The background of this study is the grouting reinforcement body of the tunnel project in the Huzhu area of Qinghai, China. According to the climate data in this area, the minimum temperature in winter can reach about − 15 ° C, while the maximum temperature in summer is about 15 °C. Therefore, selecting the temperature range from-15 °C to + 15 °C can better simulate the actual seasonal temperature changes in the region.
- Comment3: Why was there a maximum of 30 freeze-thaw cycles? How is this reflected in practice? Long-term exposure to changing weather conditions gives a true view of the durability of the rock.
Response3: Thank you for your question about the number of freeze-thaw cycles. In this study, we chose a maximum of 30 freeze-thaw cycles based on the following considerations:
First of all, it can be seen from the experimental results that with the increase of the number of freeze-thaw cycles, the physical and mechanical properties of the grouting reinforcement body show a significant deterioration trend. After 30 cycles, we observed a significant decrease in performance, indicating that this number can reflect the destructive effect of freeze-thaw cycles on grouting reinforcement body.
Secondly, in this paper, we also consider the influence of four kinds of fracture dip angles on grouting reinforcement body. Considering the test cost and test period, we set up 30 freeze-thaw cycles.
Finally, although 30 freeze-thaw cycles cannot fully simulate all cases of long-term exposure to the natural environment, it provides an important reference for evaluating the durability of grouting reinforcement body in freeze-thaw environments. Our research can provide theoretical basis and experimental data support for subsequent long-term monitoring and more in-depth durability research.
In summary, 30 freeze-thaw cycles can better reflect the performance changes of grouting reinforcement body in freeze-thaw environment under limited experimental conditions, and consider the influence of crack angle on the durability of grouting reinforcement body. In future studies, we will further expand the experimental conditions to more comprehensively assess long-term durability.
- Comment4: Additional section after section 3 and before section 4: The authors did not make a discussion of the results which is a critical assessment of the results obtained.
Response4: Thank you very much for your suggestions on adding the discussion section. We added a separate ' discussion ' section (Section 3.4) between Sections 3 and 4 to provide a more in-depth analysis and evaluation of the experimental results. The following is the main content of the new discussion section :
3.4 Discussion
3.4.1 The influence mechanism of freeze-thaw cycle on grouting reinforcement body
In this study, the impact of freeze-thaw cycles on the physical and mechanical properties of grouting reinforcement body was investigated through a comprehensive series of experimental tests. Extensive freeze-thaw testing has demonstrated that the mass and wave velocity of grouting reinforcement exhibit significant declines as the number of freeze-thaw cycles increases. Correspondingly, the mass loss rate and wave velocity loss rate progressively rise. The macroscopic mechanical properties of grout-ing reinforcement body also deteriorate gradually, with notable reductions in peak strength, elastic modulus, and shear strength parameters. The peak strength and elas-tic modulus are found to have a negative exponential relationship with the number of freeze-thaw cycles, which is consistent with the experimental results obtained in this study.This phenomenon can be primarily attributed to the freezing of pore water within the grouting reinforcement body as ambient temperatures decrease. The ex-pansion of frozen water generates frost heave forces that act upon the rock and ce-ment particles. These forces exert a destructive influence on particles with weaker ce-mentation strength, leading to localized damage within the grouting reinforcement body. As temperatures rise, the water within the grouting reinforcement body thaws, resulting in the release of freezing stress and the migration of water. With increasing freeze-thaw cycles, these localized damage zones gradually coalesce into microcracks. The continuous propagation of these microcracks leads to a progressive reduction in the strength and stiffness of the grouting reinforcement body, ultimately causing par-ticle fracture and spalling.
During the freeze-thaw cycle, the freezing and thawing of water in the pores lead to the expansion of the original pores and fissures and the formation of new fissures. The evolution law of internal pores in grouting reinforcement body can be obtained by nuclear magnetic resonance T2 spectrum. In this study, with the increase of the number of freeze-thaw cycles, the T2 spectrum curve of the sample continued to grow upward, and the NMR signal intensities of the three peaks continued to increase. With the increase of the number of freeze-thaw cycles, the three peaks all showed a right-ward trend, which was manifested in the pore characteristics of micropores increasing and transitioning to mesopores, mesopores increasing and transitioning to macropores, and macropores increasing continuously. The change of the pore struc-ture directly leads to the decrease of the macroscopic mechanical properties of the grouting reinforcement body.
3.4.2 The influence of crack dip angle on grouting reinforcement body
This study also analyzes the influence of different crack dip angles on the perfor-mance of sandstone grouting reinforcement. The results show that when the crack dip angle is 0 °, 30 ° and 45 °, the grouting reinforcement has obvious plastic deformation and ductility after the peak strength. When the fracture dip angle is 60 °, the stress-strain relationship curve has no plastic deformation stage regardless of the con-fining pressure, and it decreases instantaneously after the axial stress reaches the peak value. The main reason is that the stress reaches the shear strength of the weak surface of the rock-slurry consolidation body, resulting in shear slip failure of the rock along the fracture surface. With the increase of crack dip angle, the failure mode of the grouting reinforcement body gradually changes from axial splitting failure to axial splitting-shear mixed failure, and finally to shear failure. This is relatively consistent with the research results of Rong Miren et al. The change of this failure mode further illustrates the importance of crack dip angle to the stability of the grouting reinforcement body.
- Comment5: The literature cited in the article is mainly by Chinese authors which has a significant impact on the limitations of the article's impact on international science. The authors should perform the literature review more extensively using publications from around the world and not just Chinese authors.
Response5: Thank you very much for your valuable comments on the literature cited in our article. We fully agree with your views and have fully revised and supplemented the literature review section to ensure that the cited literature is more representative and international.
- Comment6: What are the limitations of this research?
Response6: Thank you for your questions about the limitations of this study. The following are some of the main limitations we realized during the study:
The number of freeze-thaw cycles is limited. In this study, the maximum number of freeze-thaw cycles was 30 times. Although this setting can better reflect the effect of freeze-thaw cycles on rock reinforcement in the short term, it is still insufficient compared with the long-term and repeated freeze-thaw cycles that rocks may experience in practical engineering.
The unity of reinforcement materials. The reinforcement material used in this study is 800 mesh ultra-fine cement. Although ultrafine cement shows good reinforcement effect in the experiment, other types of reinforcement materials, such as epoxy resin and polymer cement, may be used in practical engineering.
Simplification of fracture morphology. In this study, it is assumed that the cracks are regular and smooth through cracks, while the cracks in the actual rock may have complex shapes, such as bending and branching. These complex fracture morphology may have different effects on the mechanical properties under freeze-thaw cycles, so the hypothesis of fracture morphology in this study may limit the universality of the conclusion.
- Comment7: There are editing errors in the manuscript. This should be corrected.
Response7: Thank you very much for pointing out that there are editing errors in the manuscript. We have conducted a comprehensive proofreading and editing of the manuscript to ensure the accuracy, consistency and professionalism of the language.
Author Response File: 
Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsAll comments have been addressed.
Reviewer 2 Report
Comments and Suggestions for AuthorsPolecam manuskrypt do publikacji.
