PCCP (prestressed concrete cylinder pipe) with multi-layer protection and manufacturing method thereof

Abstract

The invention discloses a PCCP (prestressed concrete cylinder pipe) with multi-layer protection and a manufacturing method thereof, and particularly relates to the technical field of prestressed concrete cylinder pipes. The PCCP with the multi-layer protection comprises an inner concrete layer, a steel cylinder arranged on the outer ring of the inner concrete layer, an outer concrete layer arranged on the outer ring of the steel cylinder, a prestressed steel wire wound on the outer ring of the outer concrete layer, an inner protection layer coated on the outer side of the prestressed steel wire and used for wrapping the prestressed steel wire, and a middle protection layer coated on the outer side of the inner protection layer and used for wrapping the prestressed steel wire. And an outer protective layer is arranged on the outer side of the middle protective layer. According to the PCCP with the multi-layer protection, through multi-layer protection and strengthening measures, excellent performance and long-term durability are achieved, each structural layer plays a role independently and promotes other layers mutually to jointly form an efficient and stable system, and the overall performance and durability are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of prestressed concrete cylinder pipes, and in particular to a PCCP with multi-layer protection and a manufacturing method thereof. Background Art

[0002] PCCP refers to prestressed concrete cylinder pipe. This pipe is a composite structure, mainly made of thin steel plate, concrete, prestressed steel wire and cement mortar. It has the characteristics of high strength, high impermeability and high sealing, and is suitable for engineering environments with large diameters, high working pressure and high soil coverage.

[0003] However, the mortar protective layer of traditional PCCP is prone to cracking during use. There are two types of cracking in the PCCP mortar protective layer: "cracking first and then rusting" and "rusting first and then cracking". "Cracking first and then rusting" refers to cracks caused by mortar shrinkage, plasticity reduction, construction and other reasons. They usually become channels for harmful media such as air, moisture, chlorides, and sulfates to enter. Over time, the prestressed steel wire will rust and reduce the stress-bearing cross-sectional area of ​​the prestressed steel wire.

[0004] "Rust first, then crack" means that due to the carbonization of mortar or the effect of chloride salt, the volume of the corroded prestressed steel wire increases by 3 to 4 times that of the original prestressed steel wire, which produces a large tensile stress on the mortar around the prestressed steel wire, causing the mortar to split longitudinally along the length of the prestressed steel wire. Once the mortar protective layer splits, the prestressed steel wire will be in large-scale contact with harmful ions from the outside world, and the corrosion rate of the prestressed steel wire will be doubled.

[0005] In actual structures, these two situations interact with each other and occur simultaneously. The generation of cracks causes the prestressed steel wire to rust, and the development of prestressed steel wire corrosion promotes the expansion of cracks, thus forming a vicious cycle of "rust-crack-rust", which ultimately leads to the destruction of the pipeline structure and shortening the safe operation period of the pipeline.

[0006] The above situation mainly occurs because the protective layer of PCCP is too single, resulting in inadequate protection. Therefore, the present application proposes a PCCP with multi-layer protection and a manufacturing method thereof to solve the above problem. Summary of the invention

[0007] In view of the above situation, in order to overcome the defects of the prior art, the present invention provides a PCCP with multi-layer protection.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] A PCCP with multi-layer protection comprises: an inner concrete layer, a steel cylinder is arranged on the outer ring of the inner concrete layer, an outer concrete layer is arranged on the outer ring of the steel cylinder, a prestressed steel wire is wound around the outer ring of the outer concrete layer, an inner protective layer is coated on the outer side of the prestressed steel wire, the inner protective layer is filled in the axillary corners where the prestressed steel wire contacts the pipe core and wrapped on the outer side of the prestressed steel wire for protecting the prestressed steel wire, a middle protective layer is coated on the outer side of the inner protective layer, and an outer protective layer is arranged on the outer side of the middle protective layer.

[0010] Preferably, the inner protective layer is an epoxy coal tar coating.

[0011] Preferably, the middle protective layer is a CCCW coating.

[0012] Preferably, the outer protective layer is a mortar layer.

[0013] Preferably, the mortar protective layer contains CCCW.

[0014] Preferably, the mortar protective layer contains SAP.

[0015] A method for making a PCCP with multi-layer protection comprises the following steps:

[0016] S1: Prepare suitable steel cylinder: The production of steel cylinder is divided into the production of socket and spigot rings and the production of cylinder body. The socket and spigot rings are made by rolling the socket plate into a circle through a rolling device, and then welded by manual arc welding, and the size is fixed through the expansion and plate edge process; the cylinder body is made of thin steel plate automatically rolled and welded by a spiral welding machine. The finished steel cylinder includes a socket ring, a spigot ring and a cylinder body, and these parts are finally welded and fixed together by a spiral welding machine;

[0017] S2: Pipe core concrete pouring: hoist the steel cylinder into the pipe core forming position, assemble and accurately position it in the order of inner mold, steel cylinder, gland, and outer mold, and use a starting wrench to fix the inner and outer mold bolts synchronously and firmly to prevent the steel cylinder from shifting and slurry leakage; during the concrete construction process, start the vibrator at the same time to vibrate the concrete to make it dense. The surface of the concrete solidifies due to chemical changes, start the steam curing equipment, maintain a constant temperature of 50℃ for 6 hours, and heat up and cool down for 2 hours each, for a total of 10 hours. After the curing time is over, the strength of the test block reaches the design strength ≥30Mpa before the mold can be removed;

[0018] S3: Winding prestressed steel wire: After demoulding, the concrete pipe core is placed in the concentrated area of ​​the pipe core and watered for curing under self-heating conditions for 3 days. The wire winding operation can be carried out only when the strength of the test block reaches 70% of the design strength. The pipe core is hoisted and placed on the (vertical wire winding) prestressed wire winding table; according to the pre-selected stress parameters, the driving motors of the rotary table and the stress generating device are started at the same time, and run at a low speed. At this time, the steel wire is tightly wound at least three times at 1 / 2 times the predetermined stress, and the stress motor speed is changed to enter the predetermined full stress operation. At the same time, the driving device of the lifting system is started to make the lifting platform rise at a predetermined speed to achieve the purpose of winding at a certain pitch; during the operation, the speed is increased while ensuring the stability of the steel wire stress and the steel wire pitch;

[0019] S4: Spraying inner protective layer: The inner protective layer uses epoxy coal tar as raw material. When the tube core is wrapped with prestressed steel wire, epoxy coal tar is sprayed. During spraying, liquid epoxy coal tar is evenly sprayed on the outer side of the tube core through a spraying device to fill the axillary corner where the tube core contacts the prestressed steel wire and wrap the prestressed steel wire;

[0020] S5: Spraying the middle coating: After the epoxy coal tar spraying is completed, it is naturally dried for 4 hours. After the surface is dry, continue to spray the middle protective layer. The material of the middle coating is CCCW, and its thickness is 2-3mm. After the spraying is completed, let the CCCW dry naturally;

[0021] S6: Spraying mortar protective layer: After the CCCW is dried, the pipe core is hung on the spraying platform and the mortar is sprayed on the pipe core using the roller spraying mortar process; ensure that the net thickness of the mortar protective layer meets the requirements. After the spraying is completed, stop the spraying machine, lift the pipe away, and clean and tidy up the site.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention achieves excellent performance and long-term durability through multi-level protection and reinforcement measures. Each structural layer not only plays a role independently, but also promotes each other with other layers to form an efficient and stable system, improving the overall performance and durability;

[0024] (2) The mortar protective layer of the present invention contains CCCW. Once fine cracks appear in the mortar layer, water enters the cracks and the CCCW reacts with calcium ions in the mortar to form water-insoluble crystals, which promptly and effectively block the capillary pores and prevent water from penetrating, thereby protecting the internal structure from water vapor erosion;

[0025] (3) The SAP added to the mortar protective layer of the present invention can absorb excess water and slowly release it during the cement hydration process. This internal curing effect helps to maintain the humidity inside the mortar and promote a more complete hydration reaction of the cement. As the hydration reaction proceeds, the early strength of the mortar is effectively improved. Due to the water-releasing effect of SAP, even when the initial activity of CCCW is insufficient, it can ensure that there is enough water around the cement particles to participate in the reaction, thereby alleviating the problem of decreased hydration rate due to the addition of CCCW. At the same time, the micropores left by SAP after releasing water can serve as space for the formation of CCCW crystals, which helps to improve the density and later strength of the mortar. The presence of these micropores not only does not weaken the structure of the mortar, but provides more growth points for the crystallization of CCCW, thereby enhancing the overall performance of the mortar.

[0026] (4) In the present invention, the inner protective layer of epoxy coal tar is directly wrapped around the wound prestressed steel wire, providing a strong chemical and physical barrier for the metal, effectively preventing corrosion and wear of the steel wire; at the same time, it can fill the armpit corners when the prestressed steel wire is wound around the tube core, thereby improving the overall sealing and anti-seepage capabilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of the front view of the PCCP with multi-layer protection and a method for making the same provided by the present invention;

[0028] Figure 2 for Figure 1 A magnified view of part A;

[0029] Figure 3 This is a diagram of the crack self-repair test process;

[0030] Figure 4 are the compressive strength and strength growth test results;

[0031] Figure 5 It is the test results of water absorption and density;

[0032] Figure 6 is the result of the anti-seepage test;

[0033] Figure 7 are the experimental results of electric flux and electric flux ratio;

[0034] Figure 8 Diagram of the self-repair process at different ages;

[0035] Fig. 9 This is the electron microscope image of the mortar protective layer without CCCW added;

[0036] Fig.10 This is the electron microscope image of the product doped with 1.0% CCCW;

[0037] Fig.11 This is the electron microscope image of the product doped with 1.5% CCCW;

[0038] Fig.12 This is the electron microscope image of the alloy doped with 2.0% CCCW.

[0039] Among them, the names corresponding to the figure numbers are: 1-inner concrete layer, 2-steel cylinder, 3-outer concrete layer, 4-prestressed steel wire, 5-inner protective layer, 6-middle protective layer, 7-outer protective layer. DETAILED DESCRIPTION

[0040] The present invention is further described below in conjunction with the accompanying drawings and embodiments. The embodiments of the present invention include but are not limited to the following embodiments.

[0041] Embodiment 1:

[0042] like Figure 1-2As shown, the PCCP with multi-layer protection provided by the present invention includes: an inner concrete layer 1, which serves as the inner lining of the PCCP, provides basic structural and chemical stability, is tightly combined with the steel cylinder, and protects the steel cylinder from corrosion and wear. A steel cylinder 2 is arranged on the outer ring of the inner concrete layer 1. The steel cylinder 2 is the core component of the PCCP, which mainly plays the role of tensile resistance and impermeability. The presence of the steel cylinder significantly enhances the impermeability of the PCCP, enabling it to withstand higher internal pressure. An outer concrete layer 3 is arranged on the outer ring of the steel cylinder 2. The outer concrete layer is wrapped around the outside of the steel cylinder, further enhancing the rigidity and structural stability of the PCCP. It is tightly combined with the outside of the steel cylinder and protects the steel cylinder from corrosion by the external environment. The outer ring of the outer concrete layer 3 is wrapped with prestressed steel wire 4. The prestressed steel wire is the main force-bearing structure of the PCCP. The PCCP wrapped with the prestressed steel wire can safely resist internal water pressure and external loads. An inner protective layer 5 is coated on the outside of the prestressed steel wire 4. The inner protective layer 5 is an epoxy coal tar coating. The inner protective layer 5 is filled in the corners where the prestressed steel wire 4 contacts the tube core and is wrapped around the outside of the prestressed steel wire to protect the prestressed steel wire 4. The epoxy coal tar inner protective layer is directly wrapped around the wound steel wire, providing a solid chemical and physical barrier for the metal, effectively preventing corrosion and wear of the steel wire; at the same time, after filling the corners where the steel wire contacts the tube core when it is wound, the protective effect is further improved. The outer side of the inner protective layer 5 is coated with a middle protective layer 6, and the middle protective layer 6 is a CCCW coating (CCCW is a powdered waterproof material made of silicate cement, quartz sand and other basic materials, and then added with active chemical substances). The CCCW coating acts as a waterproof layer, which prevents the penetration of moisture and harmful substances and protects the internal concrete and metal structure from erosion; its unique chemical composition can react with calcium ions in concrete to form water-insoluble crystals, thereby blocking the capillary pores and enhancing the waterproof performance of the pipe. Here, it is used as a separate coating so that it can be used as a reserve layer to store more CCCW in case the cracks in the mortar layer are large and more CCCW is needed to participate in the reaction to block the cracks in the mortar layer. It is not recommended to set the CCCW coating on the outside of the mortar layer, because although the CCCW coating set on the outer layer of the mortar can react and seal the cracks in time, it is easy to be peeled off during construction, resulting in the failure of the coating protection. An outer protective layer 7 is provided on the outside of the CCCW coating. The outer protective layer 7 is a mortar protective layer. The mortar protective layer provides additional physical protection for the prestressed steel wire to prevent it from being damaged by external mechanical damage and corrosion by harmful ions. At the same time, the mortar protective layer cooperates with the CCCW coating to achieve self-healing of cracks.

[0043] Excellent performance and long-term durability are achieved through multiple levels of protection and reinforcement measures. Each structural level not only functions independently, but also promotes each other with other levels to form an efficient and stable system, improving overall performance and durability.

[0044] A method for making a PCCP with multi-layer protection comprises the following steps:

[0045] S1: Prepare suitable steel cylinder: The production of steel cylinder is divided into the production of socket and spigot rings and the production of cylinder body. The socket and spigot rings are made by rolling the socket plate into a circle through a rolling device, and then welded by manual arc welding, and the size is fixed through the expansion and plate edge process; the cylinder body is made of thin steel plate automatically rolled and welded by a spiral welding machine. The finished steel cylinder includes a socket ring, a spigot ring and a cylinder body, and these parts are finally welded and fixed together by a spiral welding machine;

[0046] S2: Pipe core concrete pouring: hoist the steel cylinder into the pipe core forming position, assemble and accurately position it in the order of inner mold, steel cylinder, gland, and outer mold, and use the starting wrench to fix the inner and outer mold bolts synchronously and firmly to prevent the steel cylinder from shifting and slurry leakage; during the concrete construction process, start the vibrator at the same time to vibrate the concrete to make it dense. The surface of the concrete solidifies due to chemical changes, start the steam curing equipment, maintain a constant temperature of 50℃ for 6 hours, and heat up and cool down for 2 hours each, a total of 10 hours, and the curing time is over. The test block strength ≥30Mpa can be removed before the mold.

[0047] S3: Winding prestressed steel wire: After demoulding, the concrete pipe core is placed in the concentrated area of ​​the pipe core and watered for curing under self-heating conditions for 3 days. The wire winding operation can be carried out only when the strength of the test block reaches 70% of the design strength. The pipe core is hoisted and placed on the (vertical wire winding) prestressed wire winding table; according to the pre-selected stress parameters, the drive motors of the rotary table and the stress generating device are started at the same time, and the synchronous speed control buttons of the rotary table and the lifting mechanism are slowly adjusted to evenly increase to the rated stress and enter the normal wire winding working state. During the wire winding process, the first circle of steel wire should be parallel to the end face of the socket ring, and the average stress is about half of the rated stress. After more than one circle, the tensile stress must reach the full stress. The steel wire shall not be pressed on the anchor block. The normal fluctuation of tensile stress shall not deviate from the average value (design stress) by more than 8%. When adjusting the knobs, the operator should pay close attention to the data displayed on the display instruments, torque display and recorder; when there is one turn left, reduce the tension to half of the rated tension, and after winding to the last position, move the wire to align it with the slot of the anchor block and hammer the wire into the anchor block, and then check whether it is firmly fixed. After anchoring, adjust the speed knob of the stress generating device to zero, and slowly rotate the rotary table in the opposite direction until the wire is loosened, cut the wire, and the winding is completed;

[0048] S4: Spraying inner protective layer: The inner protective layer uses epoxy coal tar as raw material. When the tube core is wrapped with prestressed steel wire, epoxy coal tar is sprayed. During spraying, liquid epoxy coal tar is evenly sprayed on the outer side of the tube core through a spraying device to fill the tube core and the prestressed steel wire axilla corner and wrap the prestressed steel wire;

[0049] S5: Spraying the middle coating: After the epoxy coal tar spraying is completed, it is naturally dried for 4 hours. After the surface is dry, continue to spray the middle protective layer. The material of the middle coating is CCCW, and its thickness is 2-3mm. After the spraying is completed, let the CCCW dry naturally;

[0050] S6: Spraying mortar protective layer: After the CCCW is dried, the pipe core is hung on the spraying platform and the mortar is sprayed on the pipe core using the roller spraying mortar process; ensure that the net thickness of the mortar protective layer meets the requirements. After the spraying is completed, stop the spraying machine, lift the pipe away, and clean and tidy up the site.

[0051] Embodiment 2:

[0052] Since in Example 1, large cracks appear in the mortar protective layer to allow the calcium ions inside to react with the CCCW coating and heal, which results in the mortar layer being unable to quickly achieve self-healing of small cracks. For this reason, the PCCP with multi-layer protection provided in this embodiment includes: an inner concrete layer 1, which serves as the inner lining of the PCCP, provides basic structural and chemical stability, is tightly combined with the steel cylinder, and protects the steel cylinder from corrosion and wear. A steel cylinder 2 is arranged on the outer ring of the inner concrete layer 1. The steel cylinder 2 is the core component of the PCCP, which mainly plays the role of tensile resistance and impermeability. The presence of the steel cylinder significantly enhances the impermeability of the PCCP, enabling it to withstand higher internal pressure. An outer concrete layer 3 is arranged on the outer ring of the steel cylinder 2. The outer concrete layer is wrapped around the outside of the steel cylinder, further enhancing the rigidity and structural stability of the PCCP. It is tightly combined with the outside of the steel cylinder and protects the steel cylinder from being corroded by the external environment. The outer ring of the outer concrete layer 3 is wrapped with prestressed steel wire 4. The prestressed steel wire is the main force-bearing structure of the PCCP. The PCCP wrapped with the prestressed steel wire can safely resist internal water pressure and external loads. An inner protective layer 5 is coated on the outside of the prestressed steel wire 4. The inner protective layer 5 is an epoxy coal tar coating. The inner protective layer 5 is filled in the corners where the prestressed steel wire 4 contacts the tube core and is wrapped around the outside of the prestressed steel wire to protect the outside of the prestressed steel wire and to wrap the prestressed steel wire 4. The epoxy coal tar inner protective layer is directly wrapped around the wound steel wire, providing a solid chemical and physical barrier for the metal, effectively preventing corrosion and wear of the steel wire; at the same time, after filling the corners where the steel wire contacts the tube core when it is wound, the protective effect is further improved. The outer side of the inner protective layer 5 is coated with a middle protective layer 6, and the middle protective layer 6 is a CCCW coating (CCCW is a powdered waterproof material made of silicate cement, quartz sand and other basic materials, and then added with active chemical substances). The CCCW coating acts as a waterproof layer, which prevents the penetration of moisture and harmful substances and protects the internal concrete and metal structure from erosion; its unique chemical composition can react with calcium ions in concrete to form water-insoluble crystals, thereby blocking the capillary pores and enhancing the waterproof performance of the pipe. Here, it is used as a separate coating so that it can be used as a reserve layer to store more CCCW in case the cracks in the mortar layer are large and more CCCW is needed to participate in the reaction to block the cracks in the mortar layer. It is not recommended to set the CCCW coating on the outside of the mortar layer, because although the CCCW coating set on the outer layer of the mortar can react and seal the cracks in time, it is easy to be peeled off during construction, resulting in the failure of the coating protection. An outer protective layer 7 is provided on the outside of the CCCW coating. The outer protective layer 7 is a mortar protective layer. The mortar protective layer provides additional physical protection for the prestressed steel wire to prevent it from being damaged by external mechanical damage and corrosion by harmful ions. At the same time, the mortar protective layer cooperates with the CCCW coating to achieve self-healing of cracks.The mortar protective layer contains CCCW. Once fine cracks appear in the mortar layer, water enters the cracks and the CCCW reacts with calcium ions in the mortar to form water-insoluble crystals, which promptly and effectively block the capillary pores and prevent water from penetrating, thereby protecting the internal structure from water vapor erosion.

[0053] A method for making a PCCP with multi-layer protection comprises the following steps:

[0054] S1: Prepare suitable steel cylinder: The production of steel cylinder is divided into the production of socket and spigot rings and the production of cylinder body. The socket and spigot rings are made by rolling the socket plate into a circle through a rolling device, and then welded by manual arc welding, and the size is fixed through the expansion and plate edge process; the cylinder body is made of thin steel plate automatically rolled and welded by a spiral welding machine. The finished steel cylinder includes a socket ring, a spigot ring and a cylinder body, and these parts are finally welded and fixed together by a spiral welding machine;

[0055] S2: Pipe core concrete pouring: hoist the steel cylinder into the pipe core forming position, assemble and accurately position it in the order of inner mold, steel cylinder, gland, and outer mold, and use a starting wrench to fix the inner and outer mold bolts synchronously and firmly to prevent the steel cylinder from shifting and slurry leakage; during the concrete construction process, start the vibrator at the same time to vibrate the concrete to make it dense. The surface of the concrete solidifies due to chemical changes, start the steam curing equipment, maintain a constant temperature of 50℃ for 6 hours, and heat up and cool down for 2 hours each, for a total of 10 hours. After the curing time is over, the strength of the test block reaches the design strength ≥30Mpa before the mold can be removed;

[0056] S3: Winding prestressed steel wire: After demoulding, the concrete pipe core is placed in the concentrated area of ​​the pipe core and watered for curing under self-heating conditions for 3 days. The wire winding operation can be carried out only when the strength of the test block reaches 70% of the design strength. The pipe core is hoisted and placed on the (vertical wire winding) prestressed wire winding table; according to the pre-selected stress parameters, the drive motors of the rotary table and the stress generating device are started at the same time, and the synchronous speed control buttons of the rotary table and the lifting mechanism are slowly adjusted to evenly increase to the rated stress and enter the normal wire winding working state. During the wire winding process, the first circle of steel wire should be parallel to the end face of the socket ring, and the average stress is about half of the rated stress. After more than one circle, the tensile stress must reach the full stress. The steel wire shall not be pressed on the anchor block. The normal fluctuation of tensile stress shall not deviate from the average value (design stress) by more than 8%. When adjusting the knobs, the operator should pay close attention to the data displayed on the display instruments, torque display and recorder; when there is one turn left, reduce the tension to half of the rated tension, and after winding to the last position, move the wire to align it with the slot of the anchor block and hammer the wire into the anchor block, and then check whether it is firmly fixed. After anchoring, adjust the speed knob of the stress generating device to zero, and slowly rotate the rotary table in the opposite direction until the wire is loosened, cut the wire, and the winding is completed;

[0057] S4: Spraying inner protective layer: The inner protective layer uses epoxy coal tar as raw material. When the tube core is wrapped with prestressed steel wire, epoxy coal tar is sprayed. During spraying, liquid epoxy coal tar is evenly sprayed on the outer side of the tube core through a spraying device to fill the tube core and the prestressed steel wire axilla corner and wrap the prestressed steel wire;

[0058] S5: Spraying the middle coating: After the epoxy coal tar spraying is completed, it is naturally dried for 4 hours. After the surface is dry, continue to spray the middle protective layer. The material of the middle coating is CCCW, and its thickness is 2-3mm. After the spraying is completed, let the CCCW dry naturally;

[0059] S6: Spraying mortar protective layer: After the CCCW is dried, the pipe core is hung on the spraying platform and the mortar is sprayed on the pipe core using the roller spraying mortar process; ensure that the net thickness of the mortar protective layer meets the requirements. After the spraying is completed, stop the spraying machine, lift the pipe away, and clean and tidy up the site.

[0060] Embodiment 3:

[0061] Since CCCW is added to the mortar protective layer in Example 2, this will have a certain weakening effect on the early strength of the mortar. The active chemical substances in CCCW need time to react with the calcium ions in the cement-based material to form water-insoluble crystals. In the early stage, these chemical reactions have not been fully carried out, so the contribution to the early strength of the concrete is limited; the addition of CCCW will affect the normal progress of the cement hydration reaction. Since the components of CCCW react with the cement components, the formation speed and structure of the hydration products will be changed to a certain extent, thereby affecting the early strength development of the mortar. To this end, the PCCP with multi-layer protection provided in this embodiment includes: an inner concrete layer 1, which serves as the inner lining of the PCCP, provides basic structure and chemical stability, is closely combined with the steel cylinder, and jointly bears the pressure of the internal fluid, while protecting the steel cylinder from corrosion and wear. A steel cylinder 2 is arranged on the outer ring of the inner concrete layer 1. The steel cylinder 2 is the core component of the PCCP, which mainly plays the role of tensile resistance and impermeability. The presence of the steel cylinder significantly enhances the impermeability of the PCCP, enabling it to withstand higher internal pressures. The outer ring of the steel cylinder 2 is provided with an outer concrete layer 3, which is wrapped around the outer side of the steel cylinder, further enhancing the rigidity and structural stability of the PCCP. It is tightly combined with the outer side of the steel cylinder, and at the same time protects the steel cylinder from being corroded by the external environment. The outer ring of the outer concrete layer 3 is wrapped with a prestressed steel wire 4, which is the main force-bearing structure of the PCCP. After being wrapped with the prestressed steel wire, the PCCP can safely resist the internal water pressure and external load. An inner protective layer 5 is coated on the outer side of the prestressed steel wire 4, and the inner protective layer 5 is an epoxy coal tar coating. The inner protective layer 5 is filled in the axillary corners where the prestressed steel wire 4 contacts the tube core and is wrapped around the outer side of the prestressed steel wire to protect the prestressed steel wire 4. The epoxy coal tar inner protective layer is directly wrapped around the wrapped steel wire, providing a solid chemical and physical barrier for the metal, effectively preventing the corrosion and wear of the steel wire; at the same time, after filling the axillary corners where the steel wire contacts the tube core when it is wrapped, the protective effect is further improved. The outer side of the inner protective layer 5 is coated with a middle protective layer 6, and the middle protective layer 6 is a CCCW coating (CCCW is a powdered waterproof material made of silicate cement, quartz sand and other basic materials, and then added with active chemical substances). The CCCW coating acts as a waterproof layer, which prevents the penetration of moisture and harmful substances and protects the internal concrete and metal structure from erosion; its unique chemical composition can react with calcium ions in concrete to form water-insoluble crystals, thereby blocking the capillary pores and enhancing the waterproof performance of the pipe. Here, it is used as a separate coating so that it can be used as a reserve layer to store more CCCW in case the cracks in the mortar layer are large and more CCCW is needed to participate in the reaction to block the cracks in the mortar layer. It is not recommended to set the CCCW coating on the outside of the mortar layer, because although the CCCW coating set on the outer layer of the mortar can react and seal the cracks in time, it is easy to be peeled off during construction, resulting in the failure of the coating protection.An outer protective layer 7 is provided on the outside of the CCCW coating. The outer protective layer 7 is a mortar protective layer. The mortar protective layer provides additional physical protection for the prestressed steel wire, preventing mechanical damage and the influence of external environmental factors. At the same time, the mortar protective layer cooperates with the CCCW coating to achieve self-healing of cracks. The mortar protective layer contains CCCW. Once fine cracks appear in the mortar layer, water enters the cracks. The CCCW reacts with the calcium ions in the mortar to form water-insoluble crystals, which timely and effectively block the capillary pores and prevent water from penetrating, thereby protecting the internal structure from water vapor erosion. The mortar protective layer also contains SAP (super absorbent resin). SAP can absorb excess water and slowly release it during the cement hydration process. This internal curing effect helps to maintain the humidity inside the mortar and promote a more complete hydration reaction of the cement. As the hydration reaction proceeds, the early The initial strength of the mortar has been effectively improved, and due to the water-releasing effect of SAP, even when the initial activity of CCCW is insufficient, it can ensure that there is enough water around the cement particles to participate in the reaction, thereby slowing down the problem of decreased hydration rate due to the addition of CCCW; at the same time, the micropores left by SAP after releasing water can be used as space for the formation of CCCW crystals, which helps to improve the density and later strength of the mortar. The existence of these micropores not only does not weaken the structure of the mortar, but provides more growth points for the crystallization of CCCW, thereby enhancing the overall performance of the mortar.

[0062] A method for making a PCCP with multi-layer protection comprises the following steps:

[0063] S1: Prepare suitable steel cylinder: The production of steel cylinder is divided into the production of socket and spigot rings and the production of cylinder body. The socket and spigot rings are made by rolling the socket plate into a circle through a rolling device, and then welded by manual arc welding, and the size is fixed through the expansion and plate edge process; the cylinder body is made of thin steel plate automatically rolled and welded by a spiral welding machine. The finished steel cylinder includes a socket ring, a spigot ring and a cylinder body, and these parts are finally welded and fixed together by a spiral welding machine;

[0064] S2: Pipe core concrete pouring: hoist the steel cylinder into the pipe core forming position, assemble and accurately position it in the order of inner mold, steel cylinder, gland, and outer mold, and use a starting wrench to fix the inner and outer mold bolts synchronously and firmly to prevent the steel cylinder from shifting and slurry leakage; during the concrete construction process, start the vibrator at the same time to vibrate the concrete to make it dense. The surface of the concrete solidifies due to chemical changes, start the steam curing equipment, maintain a constant temperature of 50℃ for 6 hours, and heat up and cool down for 2 hours each, for a total of 10 hours. After the curing time is over, the strength of the test block reaches the design strength ≥30Mpa before the mold can be removed;

[0065] S3: Winding prestressed steel wire: After demoulding, the concrete pipe core is placed in the concentrated area of ​​the pipe core and watered for curing under self-heating conditions for 3 days. The wire winding operation can be carried out only when the strength of the test block reaches 70% of the design strength. The pipe core is hoisted and placed on the (vertical wire winding) prestressed wire winding table; according to the pre-selected stress parameters, the drive motors of the rotary table and the stress generating device are started at the same time, and the synchronous speed control buttons of the rotary table and the lifting mechanism are slowly adjusted to evenly increase to the rated stress and enter the normal wire winding working state. During the wire winding process, the first circle of steel wire should be parallel to the end face of the socket ring, and the average stress is about half of the rated stress. After more than one circle, the tensile stress must reach the full stress. The steel wire shall not be pressed on the anchor block. The normal fluctuation of tensile stress shall not deviate from the average value (design stress) by more than 8%. When adjusting the knobs, the operator should pay close attention to the data displayed on the display instruments, torque display and recorder; when there is one turn left, reduce the tension to half of the rated tension, and after winding to the last position, move the wire to align it with the slot of the anchor block and hammer the wire into the anchor block, and then check whether it is firmly fixed. After anchoring, adjust the speed knob of the stress generating device to zero, and slowly rotate the rotary table in the opposite direction until the wire is loosened, cut the wire, and the winding is completed;

[0066] S4: Spraying inner protective layer: The inner protective layer uses epoxy coal tar as raw material. When the tube core is wrapped with prestressed steel wire, epoxy coal tar is sprayed. During spraying, liquid epoxy coal tar is evenly sprayed on the outer side of the tube core through a spraying device to fill the tube core and the prestressed steel wire axilla corner and wrap the prestressed steel wire;

[0067] S5: Spraying the middle coating: After the epoxy coal tar spraying is completed, it is naturally dried for 4 hours. After the surface is dry, continue to spray the middle protective layer. The material of the middle coating is CCCW, and its thickness is 2-3mm. After the spraying is completed, let the CCCW dry naturally;

[0068] S6: Spraying mortar protective layer: After the CCCW is dried, the pipe core is hung on the spraying platform and the mortar is sprayed on the pipe core using the roller spraying mortar process; ensure that the net thickness of the mortar protective layer meets the requirements. After the spraying is completed, stop the spraying machine, lift the pipe away, and clean and tidy up the site.

[0069] Experimental study on external mortar protective layer

[0070] 1. Experimental Materials

[0071] The experimental materials used for the mortar protective layer are as follows:

[0072] Table 1 Experimental materials

[0073]

[0074] 2. Experimental mix ratio

[0075] This experiment is based on the mix ratio of PCCP mortar protective layer in Guangdong Huanbei Project (lime-sand ratio 1:2.5), and relevant experiments are carried out by adding CCCW with cement mass fractions of 0, 1%, 1.5%, and 2.0%. The specific mix ratios are as follows.

[0076] Table 7.1 Test proportion table

[0077]

[0078] 3. Test piece preparation

[0079] The production of PCCP mortar protective layer is different from other concrete structures. It is produced by roller spraying. The protective layer produced by this method is dense and uniform, and has strong adhesion. All experiments in this invention are comparative experiments. In order to ensure the consistency of the quality of the test blocks in each experimental group, all test blocks are obtained by cutting the mortar test board that is roller sprayed at the production site.

[0080] In order to cut and obtain the required test blocks (such as chloride ion penetration and impermeability), the roller thickness of the mortar test plate was 65mm, which far exceeds the PCCP mortar protective layer thickness ≥ 25mm stipulated in GB / T19685-2017. Therefore, the density of the test blocks obtained by cutting will be lower than the mortar protective layer of the PCCP finished pipe. However, as a comparative experiment, the influence of different CCCW dosages on the various properties of PCCP mortar protection can still be judged through experimental data.

[0081] Experimental arrangement

[0082] (1) Strength test

[0083] The strength test was carried out according to the test method in Appendix C of GB / T15345-2017, and the specimen size was 40×40×40mm.

[0084] (2) Water absorption test

[0085] The water absorption test is also carried out according to the test method in Appendix D of GB / T15345-2017, and the specimen size is 40×40×40mm.

[0086] (3) Impermeability test

[0087] The anti-seepage test was carried out according to JGJ / T70-2009 anti-seepage performance test, and the specimen size was φ70×φ80×30mm. The instrument used was SS-15 mortar anti-seepage instrument.

[0088] (4) Chloride ion penetration resistance test

[0089] The chloride ion penetration resistance test was carried out according to the electric flux method of GB / T50082-2009, and the specimen size was φ100×50mm.

[0090] (5) Crack self-repair test

[0091] The specimen size is 40×40×40mm. After placing the specimens of each test group on a pressure testing machine to artificially create fine visible cracks, the crack width is measured, and then the specimens are placed in water for curing, and the crack healing is regularly observed and the crack repair rate is calculated.

[0092] Test results analysis

[0093] (1) Strength test

[0094] Compressive strength and strength growth test results

[0095]

[0096] Results: The test results show that the 28d compressive strength of mortars with CCCW content of 0, 1%, 1.5% and 2% are 20.2MPa, 20.6MPa, 23.5MPa and 36.5MPa respectively. Compared with the undoped CCCW, the 28d strength growth rate after adding CCCW is 1.9%, 16.3% and 80.7% respectively. The 90d compressive strength of mortars with CCCW content of 0, 1%, 1.5% and 2% are 22.9MPa, 26MPa, 346MPa and 38MPa respectively. Compared with the undoped CCCW, the 90d strength growth rate after adding CCCW is 13.5%, 51.1% and 65.9% respectively. Therefore, CCCW has a significant effect on improving the compressive strength of mortar.

[0097] (2) Water absorption test

[0098] Water absorption and density test results

[0099]

[0100] Result analysis: The test results show that after adding 1%, 1.5% and 2% CCCW, the water absorption of the mortar decreased by 10.8%, 20% and 21.5% respectively. CCCW reduced the water absorption of the mortar and improved the waterproof performance of the mortar. After adding 1%, 1.5% and 2% CCCW, the dry density of the mortar increased by 2.5%, 4.2% and 6.1% respectively, and the wet density increased by 1.7%, 2.7% and 4.4% respectively. Therefore, the addition of CCCW increased the internal density of the protective layer mortar specimen.

[0101] (3) Impermeability test

[0102] Results of anti-seepage test

[0103]

[0104] Result analysis: The test results show that the anti-seepage pressure values ​​of mortars with CCCW content of 0, 1%, 1.5% and 2% are 0.3MPa, 0.7MPa, 1.2MPa and 1.4MPa, respectively. Compared with the C1 specimen, the anti-seepage pressure ratios of C2, C3 and C4 are 233%, 400% and 466%, respectively. The secondary anti-seepage pressure values ​​of mortars with CCCW content of 0, 1%, 1.5% and 2% are 0.3MPa, 0.8MPa, 1.2MPa and 1.5MPa, respectively. Compared with the C1 specimen, the secondary anti-seepage pressure ratios of C2, C3 and C4 are 266%, 400% and 500%, respectively. Therefore, the addition of CCCW can greatly improve the anti-seepage ability of mortar.

[0105] (4) Chloride ion penetration resistance test

[0106] Chloride ion penetration resistance test results

[0107]

[0108] Result analysis: The test results show that the 28d electric flux ratios of mortars with CCCW content of 1%, 15% and 2% are 94%, 72% and 62% respectively, the 90d electric flux ratios are 81%, 67% and 46% respectively, and the 120d electric flux ratios are 80%, 52% and 47% respectively.

[0109] Compared with the 28-day age, the electric flux of the C1 group at the 90-day age and the 120-day age decreased by 19% and 28%, respectively, the electric flux of the C2 group decreased by 31% and 39%, respectively, the electric flux of the C3 group decreased by 25% and 47%, respectively, and the electric flux of the C4 group decreased by 40% and 45%, respectively. Therefore, CCCW has a significant effect on improving the chloride ion penetration resistance of the mortar.

[0110] (5) Self-repair test Figure 8 shown.

[0111] Result analysis: From the test pictures, it can be seen intuitively that the repair rate of each test group with CCCW added is significantly higher than that of the blank group at each age, and the repair rate increases with the increase of the dosage. Therefore, adding CCCW to the mortar protective layer can significantly improve the crack repair rate of the mortar and shorten the crack repair cycle.

[0112] (6) Scanning electron microscopy test Figure 9-12 shown.

[0113] Results analysis: According to the microscopic morphology analysis of the outer layer test block samples, the internal structure of the test block without CCCW is loose and cracked, and the hydration products are mainly composed of CSH, CH, At and other products: petal-shaped hydration products appear in the test block after CCCW is added, and as the CCCW dosage increases, the number of such petal-shaped products increases accordingly. In the test block with 2% CCCW added, such hydration products can be seen stacked. It can be seen that CCCW increases the number of hydration products to a certain extent.

Claims

1. A PCCP with multi-layer protection, characterized in that: include: An inner concrete layer (1), a steel cylinder (2) is arranged on the outer ring of the inner concrete layer (1), an outer concrete layer (3) is arranged on the outer ring of the steel cylinder (2), a prestressed steel wire (4) is wound around the outer ring of the outer concrete layer (3), an inner protective layer (5) is coated on the outer side of the prestressed steel wire (4), the inner protective layer (5) is filled in the axillary corner where the prestressed steel wire (4) contacts the tube core and is wrapped on the outer side of the prestressed steel wire (4) for protecting the prestressed steel wire (4), a middle protective layer (6) is coated on the outer side of the inner protective layer (5), and an outer protective layer (7) is arranged on the outer side of the middle protective layer (6).

2. A PCCP with multi-layer protection according to claim 1, characterized in that: The inner protective layer (5) is an epoxy coal tar coating.

3. A PCCP with multi-layer protection according to claim 2, characterized in that: The middle protective layer (6) is a CCCW coating.

4. The PCCP with multi-layer protection according to claim 3, characterized in that: The outer protective layer (7) is a mortar layer.

5. The PCCP with multi-layer protection according to claim 4, characterized in that: The mortar protective layer contains CCCW.

6. The PCCP with multi-layer protection according to claim 5, characterized in that: The mortar protective layer contains SAP.

7. A method for preparing a PCCP with multi-layer protection applicable to any one of 1-6, characterized in that: The steps include: S1: Prepare a suitable steel cylinder; S2: pouring of core concrete; S3: winding prestressing steel wire; S4: spraying inner protective layer; S5: spraying middle coating; S6: Spray mortar protective layer.

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