Comparative Test on the Bond Damage of Steel and GFRP Bars Reinforcing Soft Rock Slopes
Round 1
Reviewer 1 Report
The reviewer has some comments for the authors to address in order to improve the merit of the manuscript as follows:
- In Abstract: the full term of GFRP should be provided as it is the first writing.
- Line 110: try to avoid the term "etc" as the details of the test divided can be sufficiently provided.
- Line 121: Please check the Error Reference.
- The details of the construction or setup of the steel and GRFP should be provided in addition to the test device.
- Figure 6 and Line 122-124: What were the reasons for using different patterns of cyclic loadings of steel bar and GRFP bar?
- Line 146-148: "(3) When the loading of ... under this load." It is hard to understand, please revise it.
- Results: Figure 7 versus Figure 8, The strain-load relationship curve of the steel bars and GRFP bars were presented under different conditions: load and anchorage depths. So, how its performance can be compared?
- Figure 9: The reason why the steel bar axial force decreased with time while the GRFP axial force increased and decreased with time should be well discussed rather than just reported the results.
- Line 183-184: what is "at a certain point trends upwards" mean? And what is the trigger and played a role refer to?
- Tables 6, 7, and Figures 10, 11: Please correct the term expensive soil to expansive soil.
Author Response
Response to Reviewer 1 Comments
Point 1: In Abstract: the full term of GFRP should be provided as it is the first writing.
Response 1: The full term of GFRP has been given in the abstract. Line 9.
Point 2: Line 110: try to avoid the term "etc" as the details of the test divided can be sufficiently provided.
Response 2: This has been modified in section 2.2.5. Line 177.
Point 3: Line 121: Please check the Error Reference.
Response 3: This has been checked in section 2.3. Line 195.
Point 4: The details of the construction or setup of the steel and GRFP should be provided in addition to the test device.
Response 4: The details of the construction or setup of the steel and GRFP have been provided in addition to the test device. Line 146-173.
Point 5: Figure 6 and Line 122-124: What were the reasons for using different patterns of cyclic loadings of steel bar and GRFP bar?
Response 5: This is a authors’ clerical error. GFRP bar is also multi cyclic loading, which has been corrected in the article. Line 197.
Point 6: Line 146-148: "(3) When the loading of ... under this load." It is hard to understand, please revise it.
Response 6: This has been modified in section 3.1. Line 217.
Point 7: Results: Figure 7 versus Figure 8, The strain-load relationship curve of the steel bars and GRFP bars were presented under different conditions: load and anchorage depths. So, how its performance can be compared?
Response 7: Although the load size is different, the load mode is the same, which reflects the same law that cyclic load aggravates the bond damage of bar body.
Point 8: Figure 9: The reason why the steel bar axial force decreased with time while the GRFP axial force increased and decreased with time should be well discussed rather than just reported the results.
Response 8: This is because the bond state and degradation, which is explained in the article. Line 275-294.
Point 9: Line 183-184: what is "at a certain point trends upwards" mean? And what is the trigger and played a role refer to?
Response 9: "at a certain point trends upwards" means that the axial force of the bar increases with time under constant load。“trigger and played a role” refer to Interfacial cohesion.
Point 10: Tables 6, 7, and Figures 10, 11: Please correct the term expensive soil to expansive soil.
Response 10: The relevant location has been modified. Tables 6, 7 and Figures 12, 13.
Please see the attachment—manuscript
Author Response File: 
Author Response.docx
Reviewer 2 Report
The work presents the results of the study on the behavior of two types of materials in the form of bars for the anchoring system in soft rock and in expansive soils. Soft rock slopes were anchored with still bars and GFRP composite bars. The difference in the performance of two types of anchorage elements was studied by an in situ test. It is certainly interesting to develop improved and more predictable anchorage systems for stabilizing landslide and unstable soils. As such, the study is important in the search for a better solutions and deserves to be published after the necessary modifications, corrections and clarification of unclear wordings, which is commented below.
Specific comments:
The authors use ambiguous and sometimes unclear terms in many places of the MS, e.g. "bond body", "bar body", bar, what really the term “bond” mean? Is it a material of the bar or a bonding in the connection zone, interface ? what is the difference between "bond body" and "bar body"? Does “bond body” mean the material surrounding the bar, i.e. concrete? For readers of this work, this term may mean the interphase boundary between the bar and the concrete matrix.
e.g. “Because of the small difference in elastic modulus between the GFRP bar and the bond, the interface bonding around the GFRP bar can invoke more resistance of the bond efficiently which demonstrates its more effective anchorage performance than the steel bar under same conditions.”
Abstract- The authors state that they used new GFRP bars for anchoring, .. “rock slopes were anchored with new GFRP bars” .- how do these composites differ from the commonly used fiberglass- based composites? What is novelty of GFRP used by the authors? The authors do not explain this issue later in the manuscript.
Page 9, line 244, „The elastic modulus of the bond is close to the GFRP bar, leading to well-developed coordination between the bar and the bond. „ How was the "elastic modulus" of “bond body” determine? What does bond body mean?
Page 14, line 347 : the authors state „GFRP bars can withstand a higher ultimate load than steel bars, and the bonding strength of the interface between the bar and the bond is relatively high under the same condition”.
The materials used in the anchorage system in the form of bars significantly differ when comparing the sizes and shapes of flutes pitches and threads (Fig 3) as well as surface chemical states of both materials. These facts cannot be ignored in the discussion regarding the explanation of the differences in the behavior of both materials in anchorage. The authors explain the differences in “anchorage effectiveness” of two types of bars mainly the difference in the elastic modulus of both materials (steel, polymer composite). Such an explanation is not fully convincing. The cement-derived matrix surrounding the bars is ​​a brittle material and the cement/bar interfacial boundary can easily be damaged by shearing mechanism during stretching the steel bar. The inert surface of the steel bar in the grouting concrete matrix creates mainly a strong mechanical connection. In the case of a composite bar, chemical bonds may also be involved, in addition to the mechanical connection at the interface. The interface connection between the concrete matrix and the composite surface is probably weaker than the mechanical connection between the cement matrix and the surface of the steel bar; however during tensile test the composite bars may be more effective in a cement matrix due to the presence of frictional forces. Did the authors verify “bonding strength” of both types of connections by means of e.g. a pull-off test?
Section 2.1 page 3, line 84 „ Production of the test specimens”
The authors write: The bars used in this study were HRB400 threaded steel bars and GFRP bars.
The description of steel and composite specimens does not include information on their production. Did the bars were made by the authors or delivered from the market? The title of this section should be modified or additional information on the fabrication of specimens ( in particular ebars) should be added. There is no information on the type of fiberglass used to fabricate the GFRP. What kind of fiberglass was used to make the bars. The tensile strength of GFRP shown in table 4 is rather low, i.e. 450 MPa, with a relatively high fiber volume fraction in the composite (77%)? GFRP composites with such a high volume fraction should have a much higher tensile strength! The authors should comment this fact.
Figure 5 and in the Abstract: the authors use different wordings regarding the cement- based matrix for reinforcing bars, for example in Fig 5 "cement paste", in other places of the text "grouting concrete" - was it cement as mortar or concrete?
Page 6, line 122, „The cyclic test adopted the loading sequence shown in Figure 6(a), with multiple cyclic load levels of the steel bar and a single cyclic load level of the GFRP bar.” The authors do not explain why the loading conditions for the cyclic test differed for both types of bars?
Page 9, line 244, the authors state that „The elastic modulus of the bond is close to the GFRP bar, leading to well-developed coordination between the bar and the bond” . How was the elastic modulus of the bond determine?
Page 10, Tab 6 “average stress at bar interface” – what is the type of stress? shear stress or tensile stress at the interface of the bar/concrete ? How was the average stress determine at bar interface?
Page 14, line 346 The authors state that in the GFRP bar ultimate stress (508 MPa) formed during tensile test of the anchorage system is higher than its ultimate strength (450 MPa.) How is it possible that the stress value in the composite bar is higher than its strength? In conclusion, the authors should respond to the above comments prior to publication.
Comments for author File: Comments.doc
Author Response
Response to Reviewer 2 Comments
Point 1: The authors use ambiguous and sometimes unclear terms in many places of the MS, e.g., "bond body", "bar body", bar, what really the term “bond” mean? Is it a material of the bar or a bonding in the connection zone, interface? what is the difference between "bond body" and "bar body"? Does “bond body” mean the material surrounding the bar, i.e., concrete? For readers of this work, this term may mean the interphase boundary between the bar and the concrete matrix.
e.g., “Because of the small difference in elastic modulus between the GFRP bar and the bond, the interface bonding around the GFRP bar can invoke more resistance of the bond efficiently which demonstrates its more effective anchorage performance than the steel bar under same conditions.”
Response 1: “bond body and bond” means “grouting body”. This has been revised in the manuscript. 2. “bar body” and “bar”both mean “bolt” or “anchor”.
Point 2: Abstract- The authors state that they used new GFRP bars for anchoring. “rock slopes were anchored with new GFRP bars”. - how do these composites differ from the commonly used fiberglass- based composites? What is novelty of GFRP used by the authors? The authors do not explain this issue later in the manuscript.
Response 2: GFRP bar and the commonly used fiberglass are the same. This has been explained in manuscript 2.2.1. Line 124-126.
Point 3: Page 9, line 244, The elastic modulus of the bond is close to the GFRP bar, leading to well-developed coordination between the bar and the bond. „ How was the "elastic modulus" of “bond body” determine? What does bond body mean?
Response 3: “bond body and bond” means “grouting body”. 2. The elastic modulus of grouting body is measured by pressure testing machine and deformation measuring instrument.
Point 4: Page 14, line 347: the authors state, GFRP bars can withstand a higher ultimate load than steel bars, and the bonding strength of the interface between the bar and the bond is relatively high under the same condition”.
The materials used in the anchorage system in the form of bars significantly differ when comparing the sizes and shapes of flutes pitches and threads (Fig 3) as well as surface chemical states of both materials. These facts cannot be ignored in the discussion regarding the explanation of the differences in the behavior of both materials in anchorage. The authors explain the differences in “anchorage effectiveness” of two types of bars mainly the difference in the elastic modulus of both materials (steel, polymer composite). Such an explanation is not fully convincing. The cement-derived matrix surrounding the bars is ​​a brittle material and the cement/bar interfacial boundary can easily be damaged by shearing mechanism during stretching the steel bar. The inert surface of the steel bar in the grouting concrete matrix creates mainly a strong mechanical connection. In the case of a composite bar, chemical bonds may also be involved, in addition to the mechanical connection at the interface. The interface connection between the concrete matrix and the composite surface is probably weaker than the mechanical connection between the cement matrix and the surface of the steel bar; however, during tensile test the composite bars may be more effective in a cement matrix due to the presence of frictional forces. Did the authors verify “bonding strength” of both types of connections by means of e.g., a pull-off test?
Response 4: The bond strength is calculated from the ultimate load, rod diameter and bond length. The differences in “anchorage effectiveness” of two types of bars may be related to the chemical action between the bar and the grouting body, which needs further research, but the difference of elastic modulus must be the main reason.
Point 5: Section 2.1 page 3, line 84 „ Production of the test specimens”
The authors write: The bars used in this study were HRB400 threaded steel bars and GFRP bars.
The description of steel and composite specimens does not include information on their production. Did the bars were made by the authors or delivered from the market? The title of this section should be modified or additional information on the fabrication of specimens (in particular ebars) should be added. There is no information on the type of fiberglass used to fabricate the GFRP. What kind of fiberglass was used to make the bars? The tensile strength of GFRP shown in table 4 is rather low, i.e., 450 MPa, with a relatively high fiber volume fraction in the composite (77%)? GFRP composites with such a high-volume fraction should have a much higher tensile strength! The authors should comment this fact.
Response 5: The tensile strength reported in the research was provided by the manufacturers. The manufacturers did not indicate the type of fiberglass used to manufacture the GFRP bar.
Point 6: Figure 5 and in the Abstract: the authors use different wordings regarding the cement- based matrix for reinforcing bars, for example in Fig 5 "cement paste", in other places of the text "grouting concrete" - was it cement as mortar or concrete?
Response 6: The test used cement as mortar. The abstract has been modified.
Point 7: Page 6, line 122, The cyclic test adopted the loading sequence shown in Figure 6(a), with multiple cyclic load levels of the steel bar and a single cyclic load level of the GFRP bar.” The authors do not explain why the loading conditions for the cyclic test differed for both types of bars.
Response 7: This is a authors’ clerical error. GFRP bar is also multi cyclic loading, which has been corrected in the article. Line196-197.
Point 8: Page 9, line 244, the authors state that „The elastic modulus of the bond is close to the GFRP bar, leading to well-developed coordination between the bar and the bond”. How was the elastic modulus of the bond determine?
Response 8: The elastic modulus of grouting body is measured by pressure testing machine and deformation measuring instrument.
Point 9: Page 10, Tab 6 “average stress at bar interface” – what is the type of stress? shear stress or tensile stress at the interface of the bar/concrete? How was the average stress determine at bar interface?
Response 9: “average stress at bar interface” has been changed to “average stress”, which refers to the shear stress and tensile stress from the bar and grouting body. The average stress was measured by displacement of anchorage section, elastic modulus and effective anchorage depth. Table 6.
Point 10: Page 14, line 346 The authors state that in the GFRP bar ultimate stress (508 MPa) formed during tensile test of the anchorage system is higher than its ultimate strength (450 MPa.) How is it possible that the stress value in the composite bar is higher than its strength? In conclusion, the authors should respond to the above comments prior to publication.
Response 10: The ultimate stress of the GFRP provided by the manufacturer seems to have been under reported. The tests show that the ultimate stress is higher than the manufacturer suggests.
Please see the attachment-manuscript
Author Response File: Author Response.docx
Reviewer 3 Report
Dear Authors;
I have reviewed your paper, it can be interesting and useful. However, I have several major comments that you need to take care of all of them:
- You have a very brief introduction which is not suitable even for related civil engineering journals. You need to start with a big picture of history of this area, then the available techniques, then the problem with each category of them. So, flow in introduction is very important. You need to also explain your gap with more details.
- Section 2.2 is very important in this paper. The whole section should be revised focusing on more details on the tests, equipment and so on.
- Use a fully English map as Figure 1.
- Figures 7-9 should be colorful for better understanding.
- Try to include a practical suggestion for future similar projects.
- Limitations and future works should be included in conclusion section.
Author Response
Response to Reviewer 3 Comments
Point 1: You have a very brief introduction which is not suitable even for related civil engineering journals. You need to start with a big picture of history of this area, then the available techniques, then the problem with each category of them. So, flow in introduction is very important. You need to also explain your gap with more details.
Response 1: The introduction has been supplemented. Line 32-62.
Point 2: Section 2.2 is very important in this paper. The whole section should be revised focusing on more details on the tests, equipment and so on.
Response 2: The test process has been supplemented. Line 146-173.
Point 3: Use a fully English map as Figure 1.
Response 3: The Figure 1 has been modified.
Point 4: Figures 7-9 should be colorful for better understanding.
Response 4: Figures 9, 10 and 11 have been modified.
Point 5: Try to include a practical suggestion for future similar projects.
Response 5: Suggestions have been added. Line 516-526.
Point 6: Limitations and future works should be included in conclusion section.
Response 6: Limitations and future works have been added. Line 567-569.
Please see the attachment—manuscript
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The authors have responded to the reviewer's comments appropriately and could be considered for publication. Though English writing and grammar checked might be required.
