Experimental Study on the Reinforcement of Prestressed Concrete Cylinder Pipes with External Prestressed Steel Strands
Round 1
Reviewer 1 Report
1) The format of the paper is not unique
2) Some spelling mistakes
3) The size of some pictures are not big enough
4) The text size of some pictures are not big enuogh
5) The abbreviation PCCPE is not explained
6) Line 43 a source is missing
7) Tab. 1: the units are not unique
8) Tab. 1: What was the young´s modulus of the mortar
9) Tab. 1: how was the strength of the mortar and concrete tested? Cubes (size)?
10) Fig. 5. is placed over 2 pages
11) Fig. 11. Dimensions are missing
12) Line 223: The value fcu,k is not explained
13) Line 227: Wrong figure number
14) Line 291: what was the reason for the load sound and why did it happen?
15) Conclusion: What is with long-term stresses?
Author Response
Response to Reviewer 1 Comments
We would like to extend our sincere appreciation to the editors’ effort and reviewers’ constructive comments toward improving our manuscript. We have studied the reviewers’ comments carefully and have made extensive modification to the previous manuscript which we hope to meet the requirements for publishing in Applied Sciences. The specific comments are addressed and explained in detail below and revised manuscript according to the comments of the reviewers is attached. All changes to the manuscript are all highlighted in red.
Point 1&2: The format of the paper is not unique & Some spelling mistakes.
Response 1&2: Thanks for your careful review and kind reminder. We feel really sorry for our carelessness. The manuscript has been thoroughly revised carefully. Some mistakes of format and spelling have been corrected. We also asked for native English speakers to polish the paper before it was submitted to the journal and this time. We wonder whether it has reached the standard for publishing in Applied Sciences.
Point 3&4: The size of some pictures are not big enough. & The text size of some pictures are not big enough.
Response 3&4: Thanks for your careful review and kind reminder. We really appreciate your thoughtfulness. The size and the text size of all pictures have been adjusted to reasonable sizes to make the pictures and text more clear.
Point 5: The abbreviation PCCPE is not explained
Response 5: Thanks for your careful review and kind reminder. Two types of PCCP are produced: lined prestressed concrete cylinder pipe and embedded prestressed concrete cylinder pipe. The abbreviation of lined prestressed concrete cylinder pipe and embedded prestressed concrete cylinder pipe in China is PCCPL and PCCPE according to the SL702-2015[1], respectively. Correspondingly, the abbreviation of these two types in the United States is LCP and ECP according to the ANSI/AWWA C304[2], respectively.
PCCP is a composite structure composed of a concrete core, a steel cylinder, prestressing wires, and a mortar coating. The differences between PCCPL and PCCPE are as follows:
In PCCPE, the steel cylinder is contained within the core. In PCCPL, the steel cylinder forms the outer element of the core. Attached to the steel cylinder are steel bell-and-spigot joint rings that, together with an elastomeric O-ring, provide a watertight and self-centering joint between sections of pipe. Concrete for PCCPE is vertically cast within steel molds. And concrete for PCCPL is centrifugally cast or placed within the steel cylinder by radial compaction.
The project of the South-to-North Water Transfer Project (Part of Beijing) is a significant project in China. The embedded prestressed concrete cylinder pipes were utilized in this project. SAs a result, the PCCPE was chosen to the research object.
We have re-written the sentence in Line 38 and Line72 according to the reviewer’s suggestion.
Line 38 (Line 39 in revised version): The 3D diagram of the embedded prestressed concrete cylinder pipe (PCCPE) with bell and spigot joint rings is shown in Fig. 1
Line72 (Line 82 in revised version): The structure of the embedded prestressed concrete cylinder pipe (PCCPE) adopted in this test is depicted in Fig. 2.
The structure of the PCCPE, adopted in this test is depicted in Fig. 2.
[1] GB/T 19685-2017, Prestressed concrete cylinder pipe[S], in Chinese.
[2] Standard for Design of Prestressed Concrete Cylinder Pipe[S], American Water Works Association, America, 2015.
Point 6: Line 43 a source is missing
Response 6: Thanks for your careful review and kind reminder. We have confirmed the related references and added these references [3,4] in Line 43 (Line 46 in revised version).
X.Y. Du [3] mentioned that PCCP is widely used in China, and it has more than 150 water diversion projects (by the end of 2015). The typical projects include the Wanjiazhai Yellow River Diversion Project in Shanxi Province, the Beijing Zhangfang Emergency Water Conveyance Project, the Dahuofang Reservoir Water Delivery, the eastern water diversion project in Shenzhen, the Mopanshan diversion project in Harbin, etc. The largest one among these projects is the Beijing-Shijiazhuang section of the South-to-North Water Transfer Project. The total length of pipe is 112 km, and the inner diameter of these pipes is 4000 mm.
C. Zhang [4] pointed out that in recent years, PCCP has been widely used in electric power, water conservancy, municipal water supply and drainage and other related engineering fields. A large number of PCCP pipelines are used in the Wanjiazhai Yellow River Diversion Project, with a pipeline length of 43.5km. And the Xinjiang's Irtysh River Diversion to Karamay project uses a 15 km PCCP pipeline. In addition, PCCP is also used in dozens of water diversion projects, especially the vital projects in recent years in China, such as the South-to-North Water Transfer Project and the supporting water supply project. In terms of municipal water supply and drainage, the prestressed concrete cylinder pipes have been most utilized in Shanghai sewage treatment project, which accelerates the construction speed of the project and reduces the interference to the environment. The length, the diameter of a single pipe is 6.0 m and 3.6 m, respectively. And the total length of the pipeline is 3.9km.
Taken all projects mentioned above into consideration, we draw the conclusion that the amount of PCCP installed in China has accumulated to 18,000 km within the past two decades [3, 4](by the end of 2015).
[3] X.Y. Du, Study on key techniques for design of PCCP for long-distance diversion project, Water Resources and Hydropower Engineering, 46 (2015) 37-49.
[4] C. Zhang, Analysis on the Stress of Prestressed Concrete Cylinder Pipe during Wire Winded, Institute of Water Conservancy & Environment Zhengzhou University, Zhengzhou, 2015.
Point 7&8: (Tab. 1: the units are not unique) & (What was the young´s modulus of the mortar)
Response 7&8: Thanks for your careful check and valuable suggestions. We are really sorry for our carelessness. We have made the corrections to make the unit harmonized. The units of Tab.1 have been revised carefully. The Young´s modulus of the mortar has been added to the Tab.1 according to this comment. Moreover, we modified the names of ‘Compressive Strength’ to ‘Standard Compressive Strength’ to make it more precise. The revised version of Tab.1 is shown below. (Next page)
Tab. 1 Key parameters of the tested PCCP
Key Parameters | Values | Key Parameters | Values |
Inner Diameter of PCCP/mm | 2000 | Standard compressive strength of concrete / (N/mm2) | 55 |
Thickness of core concrete/mm | 140 | Modulus of concrete/(N/mm2) | 2.786×104 |
Inner Diameter of cylinder/mm | 2100 | Standard compressive strength of mortar / (N/mm2) | 45 |
Thickness of cylinder/mm | 1.5 | Modulus of mortar/(N/mm2) | 2.535×104 |
Diameter of wires/mm | 6 | Modulus of cylinder/(N/mm2) | 2.069×105 |
Spacing between each wire/mm | 22.1 | Modulus of wires/(N/mm2) | 1.93×105 |
Point 9: Tab. 1: how was the strength of the mortar and concrete tested? Cubes (size)?
Response 9: Thanks for your careful review and valuable suggestions. Cubes are tested to obtain the standard strength of concrete and mortar according to GB 50010-2010 ’Code for design of concrete structures’ in China. The side length of concrete and mortar cubes is 150 mm and 70.7 mm, respectively, which are produced and cured in standard methods. And the strength is tested by standard test methods in the specified age (usually 28 days). The basic data adopted in our manuscript was obtained from the pipeline manufacturer who is qualified to conduct a series of related test after the whole process of manufacture.
The design 28-days compressive strength of core concrete shall be tested in accordance with “Method of Sampling Freshly Mixed Concrete” (ASTM C 172), Building code requirements for structural concrete (ACI 318-05) and commentary (ACI 318R-05).
Moreover, the compressive strength of concrete tested in China is the standard compressive strength of core concrete, fcu,k. The standard compressive strength of core concrete,fcu,k, is equal to 1.25*fc' , in which fc' stands for the design 28-days compressive strength of core concrete in ASTM referring to the study of X.Z. Feng.
[5] X.Z. Feng. Comparison of ASTM concrete compressive strength and China's concrete strength grade, Northwest Hydropower 3 (2008), 65-67.
Point 10: Fig. 5. is placed over 2 pages
Response 10: Thanks for your careful review and kind reminder. The location of Fig.5 has been adjusted to one page in the attached manuscript.
Point 11: Fig. 11. Dimensions are missing
Response 11: Thanks for your careful review and kind reminder. We feel really sorry for our unclearness. Fig.11 has been changed to Fig.12 in the revised version. This figure shows the measuring arrangement of the strain gauges. The strain gauges were arranged on the surface of each strand wire at inverted (360°), crown (180°), and spring-line (90°, 270°) orientations of section 1 according to the order of clockwise or counterclockwise. The first measuring point was arranged on the surface of the strand wire, which in Number 1. The Number 1 is located near the side of the anchorage. And the Number 2 is located at the spring-line at a center angle of 90 degrees from Number 1. And so on. As a result, the number mentioned in the Fig.12 does not involve the dimension problem.
Point 12: Line 223: The value fcu,k is not explained
Response 12: Thanks for your careful review and valuable suggestions. We feel really sorry for our unclearness. As mentioned in Response 9, the compressive strength of concrete tested according to the criterions in China is the standard compressive strength of core concrete, fcu,k(N/mm2). The standard compressive strength of core concrete,fcu,k, is equal to 1.2*fc' , in which fc' stands for the design 28-days compressive strength of core concrete in ASTM referring to the study of X.Z. Feng.
We have re-written the sentence in Line 222-229 according to the reviewer’s suggestion.
To assess the state of PCCP, the onset of micro-cracking in the concrete core is when the strain of core concrete[13] reaches 1.5εt'=207*10-6, where εt' represents the elastic strain when the stress of the core concrete reaches the design value of tensile strength.
To assess the state of PCCP, the onset of micro-cracking in the concrete core is when the strain of core concrete[13] reaches 1.5εt'=207*10-6, where εt' and fcu,k represents the elastic strain when the stress of the core concrete reaches the design value of tensile strength, and the standard compressive strength of core concrete in N/mm2, respectively. Moreover, the standard compressive strength of core concrete, fuc,k, is equal to 1.25fc', in which fc' stands for the design 28-days compressive strength of core concrete in ASTM[19]. Once the strain reaches 11εt'=1522*10-6, visible cracks are likely to appear.
[5] X.Z. Feng. Comparison of ASTM concrete compressive strength and China's concrete strength grade, Northwest Hydropower 3 (2008), 65-67.
Point 13: Line 227: Wrong figure number
Response 13: Thanks for your careful review and kind reminder. We feel really sorry for our carelessness. The numbers of all figures have been rearranged based on your reminder in the revised version.
Point 14: Line 291: what was the reason for the load sound and why did it happen?
Response 14: Thanks for your careful review and valuable suggestions. Cracks propagated rapidly and new cracks occurred simultaneously when the percentage of broken wires was up to 20.18%. The cracking of concrete core induced the sound. And the appearance of these cracks intensified the damage of the pipe structure and made the pipe unable to sustain any tensile stress.
Point 15: Conclusion: What is with long-term stresses?
Response 15: Thanks for your careful review and valuable suggestions. Due to the constraints of test conditions and time, the test was only carried out for less than 48 hours. And the reinforcement effect of PCCP with external prestressed strands under long-term load was not studied in this experiment.
There are lots of engineering practices in bridges and beams reinforced by prestressed strands[6,7]. And this method is also called post-tension. The feasibility and reliability of this method in long-term have been verified on the bridges and beams.
As to the PCCP, we will continue to conduct theoretical research and conduct supplementary experiments considering long-term stresses. Thank you very much for your constructive suggestion.
[6] Clayton A.Burningham, Repair of reinforced concrete deep beams using post-tensioned CFRP rods, Composite Structures[J], 125 (2015) 256–265.
[7] Shahawy M A, Beitelman T, Arockiasamy M, et al. Experimental investigation on structural repair and strengthening of damaged prestressed concrete slabs utilizing externally bonded carbon laminates[J]. Composites Part B: Engineering, 1996, 27(3-4): 217-224.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Find the comments in the attached file.
Comments for author File: 
Comments.pdf
Author Response
Response to Reviewer 2 Comments
We would like to extend our sincere appreciation to the editors’ effort and reviewers’ constructive comments toward improving our manuscript. We have studied the reviewers’ comments carefully and have made extensive modification to the previous manuscript which we hope to meet the requirements for publishing in Applied Sciences. The specific comments are addressed and explained in detail below and revised manuscript according to the comments of the reviewers is attached. All changes to the manuscript are all highlighted in red.
Point 1&2&3&4: (The abstract should be revised in order to transmit the message to the audience properly. A better organization is necessary. The utilization of long sentences should be avoided because keeps the consistency and the reader's interest at a low level.) & (The authors say: “Prestressed concrete cylinder pipe (PCCP) suffers from … environment and hydrogen embrittlement.” This sentence is evasive and generalist, because it highlights that the construction works are vulnerable to deteriorative processes. The focus, especially for the abstract, should be on the essence of the work reported.) & (The authors say: “The reinforcement with external prestressed strands is able to …, a high tensile strength and its ability to not decrease with an increase in the bending angle”. This sentence is not clear and present trivial statements. Consider the defragmentation.) & (The second part of the abstract describes the conducted experiments briefly, but it requires an in-depth review particularly for providing a better picture, highlighting the innovative part of the work.)
Response 1&2&3&4: Thanks for your careful review and valuable suggestions. We are very grateful for your comments regarding the manuscript since it can help to improve our work. Following your advice, we have re-organized the abstract and tried to avoid the utilization of long sentences. Evasive and ambiguous sentences have been revised according to your reminder. We also have added more details about the experiment.
The revised abstract is as follows.
The prestressed concrete cylinder pipe (PCCP) suffers from cracks and degrade due to the prestress loss which is induced by wires breakage. The reinforcement with external prestressed strands is an option to return the deteriorating pipe’s ability to withstand the internal pressures. This reinforcement contributes to actively compensate for the prestress loss caused by broken wires at an economic price. The crack propagation in the core is constrained by the strands. Moreover, the high tensile strength of strands does not decrease with an increase in the bending angle. It is also unnecessary to dewater the pipes during construction. To evaluate the reinforcement effect, a prototype test of PCCP was performed in an assembled apparatus. The apparatus was mainly constituted by two PCCPs whose internal diameter is 2000mm. The status of each component of the pipe was measured by resistance strain gauges in three sections along the axial direction at inverted (360°), crown (180°), and spring-line (90°, 270°) orientations. The maximum width of the cracks in the outer concrete core at spring-line reduced from 1.2 mm to 0.1 mm after strengthening. The cracks of the core concrete changed slightly when the internal water pressure increased to the design pressure of 0.9 MPa. The strengthened pipe was capable of sustaining the design internal water pressure and the water tightness property was in a good state. The strains of the steel strands were all below the tensile strain level. The reinforcement of PCCP with external prestressed steel strands is able to meet the strengthen requirement of the test.
Point 5: The same comments on the organization also stand for the introduction. The message that the authors want to present should be clear, straightforward and concise. The authors say: “It has several merits, such as a high capacity for withstanding loading, strong impermeability, strong durability, and cost-effectiveness”. What does it mean to withstand loads? The authors should clarify if they do refer to the water pressure or other loading conditions due to the schemes of the support of these systems.
Response 5: Thanks for your careful review and valuable suggestions. We are really sorry for our unclearness. The PCCPs are usually subjected to the effects of working, transient, and internal pressure combinations according to ANSI/AWWA C304[1]. In detail, the working loads of long duration include pipe weight Wp, fluid weight Wf, external dead load We. Transient loads Wt contain highway live load, railway live load, aircraft live load and construction live load.
(1)Pipe weight Wp computed using nominal pipe dimensions and the following material unit weights:
Unit weight of concrete (shown in word)
Unit weight of mortar (shown in word)
Unit weight of steel (shown in word)
Fluid weight Wf computed using 62.4lb/ft3(1000kg/m3) as the unit weight of fresh water. If fluids other than fresh water are to be transported by the pipe, then the actual unit weight of those fluids shall be used.
External dead load We computed as the sum of earth load and surcharge load, if any. Earth load is computed in accordance with AWWA Manual M9; ACPA’s Concrete Pipe Design Manual; AASHTO’s Standard Specifications for Highway Bridges: 2002, 17th edition, division I, section 16.4. Surcharge load, resulting from the dead load of structures or other surface loads that are not transient loads as defined in transient loads, is computed in accordance with ACPA’s Concrete Pipe Design Manual.
(2)Highway live load shall be computed in accordance with, AASHTO’s Standard Specifications for Highway Bridges: 2002, 17th edition; AWWA Manual M9; and ACPA’s Concrete Pipe Design Manual.
Railroad live load shall be computed in accordance with AREMA’s Manual for Railway Engineering and ACPA’s Concrete Pipe Design Manual.
Aircraft live load shall be computed using appropriate aircraft wheel loads (see FAA AC150/5325-5C, Aircraft Data), in accordance with FAA AC150/5320-6C, Airport Pavement Design and Evaluation, and ACPA’s Concrete Pipe Design Manual.
Construction live load shall be computed using the specified load and earth cover in accordance with ACPA’s Concrete Pipe Design Manual procedure for highway live load.
(3) Internal pressure
Internal wording pressure Pw=max(Pg,Ps)
Pg-internal pressure established by the hydraulic gradient (psi[kPa])
Ps-internal pressure established by the static head (psi[kPa])
Internal transient pressure Pt, in excess of the internal working pressure, Pw, caused by rapid changes in pipeline flow velocity.
Pt=max(0.4Pw, 40psi[276kPa])
[1] Standard for Design of Prestressed Concrete Cylinder Pipe[S], American Water Works Association, America, 2015.
Point 6: Fig 1, is not completed and not sufficiently clear. It is a close view and should be referred to a section of the pipe. Moreover, the definition of the number 8 is not provided, either in the text or in the image.
Response 6: Thanks for your careful review and valuable suggestions. We feel really sorry for our carelessness. In the embedded prestressed concrete cylinder pipe (PCCPE), the steel cylinder is contained within the core. Attached to the steel cylinder are steel bell-and-spigot joint rings that provide a watertight and self-centering joint between sections of pipe. Figure 1 shows the specific section of the two pipes at the bell and spigot joint rings. The sentence in Line 38 has been re-written.
Line 38: The 3D diagram of the embedded prestressed concrete cylinder pipe (PCCPE) with is shown in Fig. 1.
Point 7: The authors say: “To return the deteriorating pipe to its original status…” the original status is not a correct term. Maybe the authors refer to a full capacity work of the system.
Response 7: Thanks for your careful review and valuable suggestions. The design status of a prestressed concrete cylinder pipe is determined by the magnitudes of design loads and internal pressures and the distributions of external loads on the pipe. As we mentioned in Response 5, the specific loads for the design of pipe contain working, transient and internal pressures. The types of loads and internal pressures are those normally required for the design of buried pressure pipe, which is explained in Response 5. The pipe weight , fluid weight, external dead load and the transient loads all keep the same before and after the field experiment. The vital index to evaluate the status of the pipe is to examine whether the pipe can withstand the internal pressures or not. We adopted the internal working pressure and the design value of internal pressure as the evaluation indexes to evaluate the status of the pipe with broken wires.
The internal working pressure Pw=0.6N/mm2
The design value of internal pressure P=Pw+Pt=0.876N/mm2
And the sentence has been re-written as follows.
To return the deteriorating pipe to its original status…
To return the deteriorating pipe’s ability to withstand the internal pressures….
Point 8: “Compared with replacement and internal reinforcement, …, which is especially suitable for pipes that cannot be dewatered”. This sentence needs a review and a better organization.
Response 8: Thanks for your careful review and valuable suggestions. This sentence has been re-written in the revised version.
Compared with replacement and internal reinforcement, the significant advantage of the external reinforcement is that it actively compensating for the prestress loss caused by the broken prestressing wires[7] and it is unnecessary to take the deteriorating pipes out of service, which is especially suitable for pipes that cannot be dewatered.
The significant advantage of the external reinforcement is that it is unnecessary to take the deteriorating pipes out of service. Moreover, it is able to actively compensate for the prestress loss caused by the broken prestressing wires[7].
Point 9: “The well-known large-scale application of the external prestressed strands is the Great Man-Made River pipelines in Libya”. The authors should specify the context of the application and the efficiency of this application, and any consideration of the cost-effective would be worthy to be brought out through real applications.
Response 9: Thanks for your careful review and valuable suggestions. The context of the application and the efficiency of this application have been added in the revised version.
The well-known large-scale application of the external prestressed strands is the Great Man-Made River pipelines in Libya[14].
The well-known large-scale application of the external prestressed strands is the Great Man-Made River pipelines (GMR) in Libya[14]. The GMR represents around 4000 km of pipes and most of them are 4.20m internal diameter. In 1999, GMR has faced some pipe bursts due to a high corrosive environment. The authority immediately organized to proceed with repair of critical pipes with additional external post tensioning. The typical cycle for one pipe repair is 6 days (plus 2 days for a special pipe) in this project. And some operations can be fulfilled simultaneously to shorten the time cycle during peak period. The significant advantage of this reinforcement is that it is unnecessary to take the deteriorating pipes out of service. This is significant to water supply and other associated social issues. This reinforcement technology is a cost-effective way to give a long term service of the pipes with broken wires.
Point 10: “However, little progress has been made in the strengthening effect of the external prestressed strands on PCCP”. From this statement may be derived that this strengthening system with prestressed strands on PCCP has not a significant effect? A review of the statement is probably necessary.
Response 10: Thanks for your careful review and kind reminder. There are some misunderstandings in our expression. We have re-written this sentence in the revised version.
However, little progress has been made in the strengthening effect of the external prestressed strands on PCCP.
However, few experimental studies have been carried out in the strengthening effect of the external prestressed strands on PCCP.
Point 11: Figure 2, should have a higher quality to be readable.
Response 11: Thanks for your careful review and kind reminder. Figure 2 has been changed to a higher quality in the revised version. Thanks so much for this suggestion again.
Point 12: Table 1 may be reviewed. N/mm2=MPa so why both units are used? The elastic modulus of wire is lower than the elastic modulus of the concrete! Why?
Response 12: Thanks for your careful check and kind reminder. We are really sorry for our carelessness. We have made the corrections to make the unit harmonized. The units of Tab.1 have been revised according to this comment. Moreover, the modulus of concrete has been corrected based on your reminder.
Tab. 1 Key parameters of the tested PCCP
Key Parameters | Values | Key Parameters | Values |
Inner Diameter of PCCP/mm | 2000 | Compressive Strength of concrete / (N/mm2) | 55 |
Thickness of core concrete/mm | 140 | Modulus of concrete/(N/mm2) | 2.786×104 |
Inner Diameter of cylinder/mm | 2100 | Compressive Strength of mortar / (N/mm2) | 45 |
Thickness of cylinder/mm | 1.5 | Modulus of mortar/(N/mm2) | 2.535×104 |
Diameter of wires/mm | 6 | Modulus of cylinder/(N/mm2) | 2.069×105 |
Spacing between each wire/mm | 22.1 | Modulus of wires/(N/mm2) | 1.93×105 |
Point 13: Section 3.1 provides with a notation of the real strain. The authors should explain in detail this concept and what is the difference with the measured strain. How is calculated or measured in this case the initial prestrain caused by the prestressing?
Response 13: Thanks for your careful review and valuable suggestions. Hoop compressive strains were produced by prestressing wires. The concrete core of PCCP is in compression after manufacture. The initial stress of core concrete fic in PCCP is governed by the prestress caused by prestressing wires. The final prestress in the core concrete fcr after creep and shrinkage of the concrete and mortar and relaxation of the wire is calculated according to the equations given in ANSI/AWWA C304.
The internal water pressure exerts a tensile stress on the pipe, which is opposite to the effect of the prestressing wires. Therefore, the hoop tensile strain caused by internal water pressure in each component of the PCCP will be balanced by the compressive prestrain. In other words, only when the tensile strain is larger than the compressive prestrain will the real tensile strain be measured. Therefore, the real strain state of the core concrete and prestressing wires should be revised by the following equation:
εr=εi+εm
where εr is the real strain of the component, εi is the initial prestrain caused by prestress,εm is the strain measured by strain gauges. Moreover, positive values represent the tensile strain and negative values represent the compressive strain.
Moreover, the initial prestrain in the prestressing wire is calculated as follows.
εis=fis/Es
where fis is the initial prestress in the prestressing wire and Es is the design modulus of elasticity of prestressing wires.
Point 14: What is the role of the analytical equation of section 3.1 in this research? Are any comparisons with the empiric values and those obtained experimentally?
Response 14: Thanks for your careful review and valuable suggestions. As mentioned in Response 13, the initial stress of core concrete fic in PCCP is governed by the wrapping stress in prestressing wires. The final prestress in the core concrete fcr is calculated considering creep and shrinkage of the concrete and mortar and relaxation of the wire. All equations are defined in ANSI/AWWA C304. All of these equations are used to calculate the final prestress. The final prestrain in the concrete is a significant index to evaluate the situation of the pipe.
Point 15: The units should be the same throughout the text, i.e. the figures have the format strain(s)(10-6), while in the text is με.
Response 15: Thanks for your careful check and kind reminder. We are really sorry for our carelessness. We have changed με to 10-6 to make the unit harmonized.
Point 16: In section 3.2. it is discussed the propagation of the cracks in respect to the water pressure, broken wires and the prestress. It is not clear by the text, the required (even analytical or from other experiments) reinforcing material. Thence it is unable to confront the role of the wires, and the retrofitting, regarding the limit states.
Response 16: Thanks for your careful review and valuable suggestions. Hoop compressive strains were produced by prestressing wires. The wires cannot supply the design prestress for the pipe after their breakage. So PCCP suffers from cracks and degrades due to the prestress loss which is induced by wires breakage. The reinforcing material, the prestressed strand, plays the same role of prestressing wires and compensates the prestress loss due to the wire breakage. The strains and contribution of strands have been described in section 3.4.
Point 17: The denoted nominal strain of the strands is more than 50% higher compared to the maximum measured strain. How do the authors justify that? Does it match a case of over strengthening? Such comment should be addressed at comment 4 of the conclusions.
Response 17: Thanks for your careful review and valuable suggestions. The nominal tensile strength of strands is 1860MPa. The tensile strength of strands is the maximum amount of tensile stress that it can take before failure. Once the strain of strain meet the level of the nominal tensile strain, which is equal to 9538.46*10-6, the strand is likely to break.
And the design of tensile strength factor for strands is 0.63, indicating that the target tensile strength is equal to 1171.8 MPa. The target tensile strain is 6009.23*10-6 corresponding to the target tensile strength.
The real situation of strains in prestressed strands was measured by resistance strain gauges, as shown in figure below. All strains measured were below the tensile strain level. This means that there is no situation of over strengthening.
Point 18: “The location of the inner concrete pipe … the broken point”. The structure of this sentence may not be correct, consider modifying.
Response 18: Thanks for your careful review and valuable suggestions. We feel really sorry for our limitation of expression. This sentence has been re-written in revise version according to your comment.
The location of the inner concrete pipe at crown was most affected by the operation of wires breakage, while the wires breakage significantly influenced the outer concrete core at spring-line near the broken point.
The operation of breaking wires most affected the strains of the inner concrete at crown. And it significantly influenced the outer concrete core at spring-line which is near the broken point.
Point 19: The authors says: “The debonding between… observation”. The authors are asked to clarify to which field observation do they refer. It is trivial that the debonding (as shown), occurs close to the break of the wires.
Response 19: Thanks for your careful review and valuable suggestions. We have added a specific explanation on the pictures of field observation according to your comment.(shown in word)
Point 20: “The strands can not only constrain the crack propagation in the concrete core, but also compensate the prestress loss due to the wire breakage”. The conclusion is trivial but even not properly expressed.
Response 20: Thanks for your careful review and valuable suggestions. We feel really sorry for our limitation of expression. PCCP is a composite structure composed of a concrete core, a steel cylinder, prestressing wires and a mortar coating. High-tensile steel wires, helically wrapped around the core under controlled tension, produce uniform compressive prestress in the core that offsets tensile stresses from internal pressure and external loads. PCCP can be designed to provide the optimum amount of prestress needed for the required operating conditions. PCCP suffers from cracks and degrade due to the prestress loss which is induced by wires breakage as the service period increases. In our experiment, the maximum width of cracks in the outer concrete core at the spring-line was 2.2 mm when the operation of breaking wires stopped.
The prestressed strands play the same role of prestressing wires and compensate the prestress loss due to the wire breakage. And after the tensioning operation of strands, most visible cracks show closure property and are eventually difficult to found. The maximum width of cracks in the outer concrete core at spring-line was reduced from the former 1.2 mm to 0.1 mm. This phenomenon verified the compensation contribution of strands on prestress.
We have re-organized this sentence in revised version based on your comment.
The strands can not only constrain the crack propagation in the concrete core, but also compensate the prestress loss due to the wire breakage.
After the tensioning operation of strands, the strands contribute to compensate the prestress loss induced by the wires breakage. The crack propagation in the core is also be constrained by the strands simultaneously.
Point 21: What is the comment of the authors according to a remaining crack of 0.1 mm. Does it involve additional intervention to the prestressed steel strands, to decrease the corrosion risk of the steel pipe?
Response 21: Thanks for your careful review and valuable suggestions. We haven’t mentioned the additional intervention to the prestressed strands in our manuscript considering the number of words.
Our experiment mainly focuses on the reinforcement effect of prestressed strands. So we only described the methods and results related to the reinforcement effect. In fact, the additional intervention for reinforced structure must be conducted in engineering practice. The intervention mainly contains two aspects.
One is the protection of anchorages. We have conducted the corrosion protection of anchorages at the end of our experiment, which is shown in the picture below. The specific steps are as follows, (1) Remove the excess length steel strand at the anchor end, (2) install the anchor protection cover, and (3) infuse the anchor with anti-corrosion grease.
And the other aspect is the protection of pipe and strands. The epoxy coating is applied to the base material of the strand at the fabrication stage, which provides a layer of protection against corrosion. There are double polyethylene cables (PE) outside the strand to ensure the strand’s corrosion resistance property. In addition, the double polyethylene cables are filled with anti-corrosive grease of ≥50g/m to achieve the free sliding between PE1 and PE2 with low friction. In general, each strand is protected by three anti-corrosion barriers. A concrete protective layer with a thickness of 10 mm will be sprayed on the surface of the pipe and the steel strand once the reinforcement completes in engineering practices. The purpose of this operation is to prevent the steel cylinder and strands from physical damage and external corrosion.
Author Response File: Author Response.docx
