Post-tensioning method large pipe pile pipe joint composite forming method

Abstract

The invention provides a post-tensioning method large pipe pile pipe joint composite forming method, and belongs to the technical field of composite forming, hard concrete is matched with a centrifugation-vibration-rolling composite forming process, and strict material selection and performance parameter control are combined, so that the concrete section aggregate of the manufactured pipe joint is uniformly distributed, and the concrete section is uniform. And the concrete layering phenomenon caused by a traditional single centrifugal process is thoroughly eliminated. The concrete is high in strength, the compressive strength is not lower than a design label after static curing is finished, the electric flux is not larger than 800 coulomb, and the concrete is excellent in durability and can adapt to severe service environments such as hydraulic wharfs. By means of the design and application of the special duct forming device, it is guaranteed that the straightness of the reserved duct is high, good conditions are provided for subsequent penetrating and tensioning of the prestressed steel strand, the prestress loss of a pile finished product in the prestress tensioning and using process is effectively reduced, and the effective pre-compressive stress of the large pipe pile is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of composite molding technology, specifically relating to a post-tensioned composite molding method for large pipe pile sections. Background Technology

[0002] With the continuous advancement of hydraulic wharf construction, various projects are placing increasingly stringent requirements on the comprehensive performance of prestressed concrete pipe piles. Currently, PHC piles and long-section pipe piles widely used in projects generally employ a combination of plastic concrete and a single centrifugal process in their production. However, this production method has several inherent drawbacks: firstly, the concrete is prone to significant segregation during the molding process, leading to uneven internal structure of the pipe pile; secondly, the pipe piles have insufficient hammer impact resistance, making them susceptible to damage from external impacts during construction, installation, and subsequent use; and thirdly, the effective prestress is relatively low, affecting the bearing capacity and long-term stability of the pipe piles, making it difficult to meet the high standards required for the structural performance of pipe piles in large-scale hydraulic wharf projects.

[0003] Post-tensioned prestressed concrete large-diameter pipe piles (referred to as "large pipe piles") are a new type of prestressed concrete pipe pile produced using a composite process. The pipe sections are made of dry-hard concrete, formed through a centrifugal-vibration-roller pressing composite process, and undergo steam curing in four stages: static curing, heating, constant temperature, and cooling. The resulting concrete pipe sections exhibit excellent structural performance, providing a reliable performance foundation for the subsequent assembly of finished pipe piles and potentially overcoming the performance shortcomings of existing pipe piles. Summary of the Invention

[0004] This invention aims to provide a post-tensioned method for composite molding of large-diameter pipe pile segments, solving problems such as concrete segregation, insufficient hammer impact resistance, low effective prestress, non-straight pre-drilled ducts, and significant prestress loss in existing similar pipe piles. The final product is a pipe segment with high concrete strength, excellent durability, straight pre-drilled ducts, uniform aggregate distribution in the concrete cross-section, and no segregation. Large-diameter pipe piles assembled from these segments can significantly improve effective prestress and hammer impact resistance.

[0005] The present invention employs the following technical solution.

[0006] A post-tensioned composite molding method for large-diameter pipe pile sections includes: Step 1: Fabricate the steel reinforcement cage for the post-tensioned large-diameter pipe pile segments; Step 2: After fabricating the steel reinforcement cage for the pipe section, prepare the protective layer spacers; Step 3: After preparing the protective layer pads, select the steel mold for pipe section forming; Step 4: After selecting the steel mold for pipe section forming, configure the duct forming device; Step 5: After configuring the duct forming device, prepare dry-hard concrete; Step 6: After preparing the dry-hard concrete, install the reinforcing cage and duct forming device; Step 7: After the steel cage and duct forming device are installed, the composite process is used to form the pipe section; Step 8: After the composite process is used to form the pipe section, steam curing treatment is performed; Step 9: After performing steam curing, the duct forming device is removed; Step 10: Remove the duct forming device and demold the pipe section; Step 11: After demolding the pipe section, grind the end face of the pipe section; Step 12: After grinding the end face of the pipe section, perform the post-maintenance of the pipe section.

[0007] Preferably, in step 1, the steel reinforcement cage of the pipe section uses HPB300 steel bars, wherein the longitudinal stirrups and circumferential bars are cold-drawn from Φ8mm to Φ7mm, and the tensile strength of the steel bars after cold drawing must meet ≥550MPa.

[0008] Preferably, in step 2, the protective layer thickness of the outermost circumferential reinforcement of the steel cage is 30mm, and the protective layer pad is made of high-density polyethylene plastic and has a standard card-type structure with concave and convex surfaces.

[0009] Preferably, in step 3, the steel mold for forming the pipe section adopts a single-opening mold design, and the maximum opening of the joint does not exceed 5cm, so as to avoid concrete leakage or insufficient forming accuracy due to excessively large joint opening. The steel mold is equipped with auxiliary devices, including a running wheel ring, a positioning ring, a vibration ring, a counterweight, lifting lugs, and end caps. The running wheel ring is used for rotational support of the steel mold. The positioning ring is on the outside of the steel mold and has a corresponding slot on the forming machine, which mainly ensures that the steel mold is accurately positioned on the forming machine. The vibration ring provides vibration force for vibration forming. The counterweight is used to adjust the rotational balance of the steel mold. The lifting lugs facilitate the lifting and handling of the steel mold. The end caps are used to seal both ends of the pipe section.

[0010] Preferably, in step 4, the channel forming device consists of two parts: a pull rod and a separating rubber tube; The tie rod adopts a three-section welded structure: ① The screw joint section is made of 45# steel and has a length L1=135mm; ② The middle section is made of 45# steel, using φ32 seamless steel pipe with a wall thickness δ=4.5mm and a length L2=5975mm; ③ The hole rod joint section is made of 40Cr round steel and has a length L3=140mm; The isolation hose is made of imported natural rubber, with the following parameters: inner diameter d1=34mm, outer diameter d2=44mm, and length L=6.2m.

[0011] Preferably, in step 5, the performance parameters of the dry-hard concrete are controlled as follows: Vebe consistency V = 25s-35s; cementitious material dosage G = 450-550 kg / m³; water-cement ratio λ < 0.30; apparent density ρ > 2500 kg / m³; concrete water content W ≤ 130 kg / m³; electrical flux Q ≤ 800 coulombs, ensuring that the concrete has high strength, high durability and good workability. The material requirements for preparing dry-hard concrete are as follows: Cement: Silicate or ordinary Silicate cement with a strength grade of 52.5 is selected; Admixture: A special steam-curing admixture is used, and its activity index is ≥100% after steam curing, at 3 days, and at 28 days. Fine aggregate: River sand with a mud content ωc≤1.0% and a gradation of Class I medium sand in Zone II; Coarse aggregate: Hard crushed stone is selected, and after two washing and screening processes, the particle size distribution is 5-20mm or 5-25mm (two-dimensional); the compressive strength of the stone is σ≥max, and the mud content is ωc≤0.5%; Admixture: Polycarboxylate superplasticizer is selected, with a water reduction rate η≥28%.

[0012] Preferably, step 6 specifically includes: The prepared protective layer spacers are evenly snapped onto the outer circumferential reinforcement bars of the fabricated steel cage to ensure that the spacers are firmly fixed and evenly distributed. The steel cage with the spacers installed is hoisted into the steel mold for forming the pipe section, and the position of the steel cage is adjusted to make it centrally located. According to the design requirements, the duct forming device is inserted into the steel cage and its two ends are fixed to the end caps of the steel mold.

[0013] Preferably, step 7 specifically includes: The steel mold containing the reinforcing cage and duct forming device is hoisted onto the forming machine. Concrete is fed into the steel mold via a belt conveyor, and the forming machine is started simultaneously. The pipe section is formed using a centrifugal-roller-vibration triple composite process. The specific steps are as follows: Phase 1: Initial feeding phase, motor speed n1=265 rpm, continuously feeding until the material thickness is about 8cm, centrifugation time t1=120s; then the motor speed is increased to n2=332 rpm, the vibrator is started, the vibration frequency f=60-75Hz, the belt conveyor continues to feed until the material thickness is flush with the inner ring of the end cap hole, at this time the pressure roller is lowered to limit the over-thickness replenishment, the over-thickness control amount Δh=6~10mm, the centrifugation time of this phase t2=270s; Phase 2: After the material feeding is completed, the vibrator continues to vibrate for t3=30s to further compact the concrete; after the vibration is completed, the pressure roller continues to apply pressure for t4=20s to compact the concrete surface. Phase 3: Increase the motor speed to n3=995 rpm, perform medium-speed centrifugation t5=180s, and remove excess water from the inside of the concrete. Stage 4: The motor speed is increased again to n4=1207 rpm, and high-speed centrifugation is carried out until the excess water in the concrete is fully squeezed to the inside and discharged. The centrifugation time is t6=120s. Phase 5: After high-speed centrifugation, the speed is gradually reduced until the steel mold stops rotating. The deceleration process takes t7 ≥ 60s.

[0014] Preferably, step 8 specifically includes: The formed pipe section, along with the steel mold, is hoisted into a steam curing tank for steam curing. The curing process is divided into four stages: Phase 1: Static curing phase, i.e., curing temperature T1=30℃, no steam supply, dry heat insulation method, static curing time t8=2 hours; Phase 2: Heating phase, which involves introducing steam to raise the temperature at a rate of v_rise = 15-20℃ / h, raising the temperature to the target temperature T2 = 65℃, and the heating time t9 = 2 hours. Phase 3: Constant temperature phase, i.e., maintaining the curing temperature T2=65℃ for continuous steam curing, and the constant temperature time t10=4 hours; Phase 4: Cooling phase, i.e., controlling the cooling rate v_drop = 15-20℃ / h, cooling down to temperature T3 = 30℃, cooling time t11 = 2 hours.

[0015] Preferably, step 9 specifically includes: After steam curing is completed, once the pipe section temperature drops to around 30°C, a special pre-drilled core-pulling machine is used to slowly pull out the tie rod and isolation hose from the concrete pipe section inside the steel mold using the duct forming device.

[0016] Preferably, step 10 specifically includes: Loosen the fixing bolts on one side of the steel mold, open the joint of the steel mold, and use a special U-shaped hook to smoothly pull the pipe section out of the steel mold.

[0017] Preferably, step 11 specifically includes: A specialized grinding robot is used to grind the two end faces of the demolded pipe section to a depth h ≥ 0.5 mm, ensuring that the pipe section cross-section is flat and vertical, providing good docking conditions for subsequent pipe section splicing and assembly.

[0018] Preferably, step 12 specifically includes: The polished pipe section is hoisted into the water curing tank for water curing, and the water curing time is t12=7d; After water curing, the pipe section will be hoisted to the designated storage yard for static curing, which will last for 7 days (t13).

[0019] The beneficial effects of the present invention are as follows, compared with the prior art: Significantly improved concrete performance: This invention employs a dry-hard concrete combined with a centrifugal-vibration-roller molding process, along with strict material selection and performance parameter control, resulting in uniform aggregate distribution across the concrete cross-section of the manufactured pipe sections. This completely eliminates the concrete segregation phenomenon caused by traditional single centrifugal processes. The concrete exhibits high strength; after curing, its compressive strength is no less than the design grade, and its electrical conductivity is no greater than 800 coulombs. It also demonstrates excellent durability, enabling it to withstand harsh service environments such as hydraulic engineering wharves.

[0020] Excellent quality of reserved ducts: Through the design and application of a special duct forming device, the straightness of the reserved ducts is ensured, which provides good conditions for the subsequent installation and tensioning of prestressed steel strands, effectively reduces the prestress loss of the finished pile during prestressing tensioning and use, and significantly improves the effective prestress of the large pipe pile.

[0021] Overall performance optimization of pipe piles: Post-tensioned large pipe piles made by splicing pipe sections based on the method of this invention have significantly better hammer impact resistance than existing PHC piles and long pipe section piles due to their high concrete density and large effective prestress. They can withstand greater impact loads during construction and installation, reducing the risk of damage, while improving the bearing capacity and long-term stability of the pipe piles. This effectively overcomes many defects of existing similar pipe piles and meets the needs of hydraulic wharf projects for high-performance prestressed concrete pipe piles.

[0022] High process stability: This invention has precisely set and strictly controlled the parameters of each production link. There are clear technical standards for each step, from steel cage fabrication and material preparation to molding, curing and post-processing, which ensures the stability and repeatability of the production process. It can mass-produce large pipe pile sections with consistent performance and reliable quality, and has good prospects for industrial application. Attached Figure Description

[0023] Figure 1 This is a flowchart of the post-tensioned large-diameter pipe pile composite molding method in this invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, other embodiments obtained by those skilled in the art without creative effort are all within the protection scope of this invention.

[0025] like Figure 1As shown, this invention proposes a post-tensioned composite molding method for large-diameter pipe pile sections, comprising the following steps: Step 1: Fabricate the steel reinforcement cage for the post-tensioned large-diameter pipe pile segments; In a preferred but non-limiting embodiment of the present invention, in step 1, the steel reinforcement cage of the pipe section is made of HPB300 steel bars, wherein the longitudinal stirrups and circumferential bars are cold-drawn from Φ8mm to Φ7mm, and the tensile strength of the steel bars after cold drawing must meet ≥550MPa.

[0026] Taking the steel cage corresponding to the D1200 type large pipe pile as an example, its structural parameters are as follows: the relevant dimensions of the pile top section are 50mm×119=5950mm (pile top section length), the length range of non-standard sections is 1000~5000mm, and the length of standard sections is 6000mm; it is equipped with 48 strands of prestressed steel strands, with three strands per hole, and the ends of the sections are wrapped flat; the opening of the reserved hole is chamfered with 5mm, the outer diameter of the stirrups is 1140mm, and the outer diameter of the pipe pile is 1200mm.

[0027] Step 2: After fabricating the steel reinforcement cage for the pipe section, prepare the protective layer spacers; In a preferred but non-limiting embodiment of the present invention, in step 2, the protective layer thickness of the outermost circumferential reinforcement of the steel cage is 30mm, and the protective layer pad is made of high-density polyethylene plastic and its surface is designed as a standard card structure with concave and convex shapes.

[0028] The spacers must be securely fastened to the reinforcing cage and ensure that the protective layer thickness is uniform.

[0029] Step 3: After preparing the protective layer pads, select the steel mold for pipe section forming; In a preferred but non-limiting embodiment of the present invention, in step 3, the steel mold for forming the pipe section adopts a single-opening mold design, and the maximum opening of the joint does not exceed 5cm, so as to avoid concrete leakage or insufficient forming accuracy due to excessively large joint opening. The steel mold is equipped with a complete set of auxiliary devices, including running wheel rings, positioning rings, excitation rings, counterweights, lifting lugs, and end caps. The running wheel rings are used to support the rotation of the steel mold. The positioning rings are on the outside of the steel mold and have corresponding slots on the forming machine, mainly to ensure that the steel mold is accurately positioned on the forming machine. The excitation rings provide vibration force for vibration forming. The counterweights are used to adjust the rotational balance of the steel mold. The lifting lugs facilitate the lifting and handling of the steel mold. The end caps are used to seal both ends of the pipe section.

[0030] Step 4: After selecting the steel mold for pipe section forming, configure the duct forming device; In a preferred but non-limiting embodiment of the present invention, in step 4, the duct forming device consists of two parts: a pull rod and a separating rubber tube, to ensure that the reserved duct is straight and to provide good conditions for the subsequent installation of prestressed steel strands; The tie rod adopts a three-section welded structure: ① The screw joint section is made of 45# steel and has a length L1=135mm; ② The middle section is made of 45# steel, using φ32 seamless steel pipe with a wall thickness δ=4.5mm and a length L2=5975mm; ③ The hole rod joint section is made of 40Cr round steel and has a length L3=140mm; The isolation hose is made of imported natural rubber with the following parameters: inner diameter d1=34mm, outer diameter d2=44mm, and length L=6.2m. It has good elasticity and strength and can be easily extracted after concrete molding and steam curing, ensuring the quality of the duct formation.

[0031] Step 5: After configuring the duct forming device, prepare dry-hard concrete; In a preferred but non-limiting embodiment of the present invention, in step 5, the performance parameters of the dry-hard concrete are controlled as follows: Vebe consistency V = 25s-35s; cementitious material dosage G = 450-550 kg / m³; water-cement ratio λ < 0.30; apparent density ρ > 2500 kg / m³; concrete water consumption W ≤ 130 kg / m³; electrical flux Q ≤ 800 coulombs, ensuring that the concrete has high strength, high durability and good workability. The material requirements for preparing dry-hard concrete are as follows: Cement: Use silicate or ordinary silicate cement with a strength grade of 52.5 to ensure the strength of the concrete foundation; Admixtures: Special steam-curing admixtures are used, with an activity index of ≥100% after steam curing, at 3 days, and at 28 days, which can improve the steam curing strength development and long-term performance of concrete. Fine aggregate: River sand with a mud content ωc≤1.0% is selected, and the gradation is Class I medium sand in Zone II to ensure the cleanliness and rationality of the fine aggregate and improve the workability of concrete; Coarse aggregate: Hard crushed stone is selected, and it is subjected to secondary washing and screening. The particle size distribution is 5-20mm or 5-25mm two-dimensional distribution. The compressive strength of the stone is σ≥max (max can be the standard value of concrete strength grade ×130%, or 120MPa), and the mud content is ωc≤0.5%, to ensure the strength and cleanliness of the coarse aggregate and improve the overall strength and durability of the concrete. Admixture: Polycarboxylate superplasticizer is selected, with a water reduction rate η≥28%, which can effectively reduce the water consumption of concrete, improve the workability of concrete, and enhance the strength and density of concrete.

[0032] Step 6: After preparing the dry-hard concrete, install the reinforcing cage and duct forming device; In a preferred but non-limiting embodiment of the present invention, step 6 specifically includes: The protective layer pads prepared in step 2 are evenly snapped onto the outer circumferential reinforcement bars of the steel cage made in step 1, ensuring that the pads are firmly fixed and evenly distributed; The steel cage with the pads installed is hoisted into the pipe section forming steel mold in step 3, and the position of the steel cage is adjusted to make it centrally positioned. According to the design requirements, insert the duct forming device from step 4 into the steel cage, ensuring that the duct forming device is accurately positioned and straight, and that both ends are reliably fixed to the steel mold end caps.

[0033] Step 7: After the steel cage and duct forming device are installed, the composite process is used to form the pipe section; In a preferred but non-limiting embodiment of the present invention, step 7 specifically includes: The steel mold containing the reinforcing cage and duct forming device is hoisted onto the forming machine. Concrete is fed into the steel mold via a belt conveyor, and the forming machine is started simultaneously. The pipe section is formed using a centrifugal-roller-vibration triple composite process. The specific steps are as follows: Phase 1: Initial feeding phase, motor speed n1 = 265 rpm, continuously feeding until the material thickness is about 8cm (the material thickness covers the pre-drilled hole hose), centrifugation time t1 = 120s; then the motor speed is increased to n2 = 332 rpm, the vibrator is started, the vibration frequency f = 60-75Hz, the belt conveyor continues to feed until the material thickness is flush with the inner ring of the end cap hole, at this time the pressure roller is lowered to limit the over-thickness replenishment, the over-thickness control amount Δh = 6~10mm, the centrifugation time of this phase t2 = 270s, through centrifugation, vibration combined with replenishment roller pressure, to ensure the concrete filling is dense; Phase 2: After the material feeding is completed, the vibrator continues to vibrate for t3=30s to further compact the concrete; after the vibration is completed, the pressure roller continues to apply pressure for t4=20s to compact the concrete surface and improve the flatness of the inner wall of the pipe section. Phase 3: Increase the motor speed to n3=995 rpm, perform medium-speed centrifugation t5=180s to remove excess water from the concrete and improve its density. Phase 4: The motor speed is increased again to n4=1207 rpm for high-speed centrifugation until the excess water in the concrete is fully squeezed out to the inside. The centrifugation time is t6=120s, which further improves the density and strength of the concrete. Phase 5: After the high-speed centrifugation is completed, the speed is slowly and steadily reduced until the steel mold stops rotating. The deceleration process time t7 ≥ 60s is to avoid damage to the concrete structure due to excessive speed reduction.

[0034] Step 8: After the composite process is used to form the pipe section, steam curing treatment is performed; In a preferred but non-limiting embodiment of the present invention, step 8 specifically includes: The formed pipe section, along with the steel mold, is hoisted into a steam curing tank for steam curing. The curing process is divided into four stages, with strict control of temperature and time parameters to ensure stable development of concrete strength. Phase 1: Static curing phase, i.e., curing temperature T1=30℃, no steam supply, dry heat insulation method, static curing time t8=2 hours, to allow the concrete surface to initially set and avoid cracks during subsequent heating. Phase 2: Heating phase, which involves introducing steam to raise the temperature at a rate of 15-20℃ / h, raising the temperature to the target temperature T2=65℃, and taking t9=2 hours. The heating is done slowly to avoid excessive temperature difference between the inside and outside of the concrete, which could cause cracks. Phase 3: Constant temperature phase, which involves maintaining the curing temperature at T2=65℃ for continuous steam curing and a constant temperature time of t10=4 hours to ensure the full development of concrete strength; Phase 4: Cooling phase, i.e., controlling the cooling rate v_drop = 15-20℃ / h, cooling down to temperature T3 = 30℃, cooling time t11 = 2 hours, slow cooling to avoid shrinkage cracks in concrete due to sudden temperature drop.

[0035] Step 9: After performing steam curing, the duct forming device is removed; In a preferred but non-limiting embodiment of the present invention, step 9 specifically includes: After steam curing is completed, once the pipe section temperature drops to around 30°C, a special pre-drilled hole core-pulling machine is used to slowly pull out the tie rod and isolation hose from the concrete pipe section inside the steel mold, ensuring that the pre-drilled hole is intact and straight.

[0036] Step 10: Remove the duct forming device and demold the pipe section; In a preferred but non-limiting embodiment of the present invention, step 10 specifically includes: Loosen the fixing bolts on one side of the steel mold, open the joint of the steel mold, and use a special U-shaped hook to smoothly pull the pipe section out of the steel mold to complete the demolding operation, avoiding collision damage to the pipe section during the demolding process.

[0037] Step 11: After demolding the pipe section, grind the end face of the pipe section; In a preferred but non-limiting embodiment of the present invention, step 11 specifically includes: A specialized grinding robot is used to grind the two end faces of the demolded pipe section to a depth h ≥ 0.5 mm, ensuring that the pipe section cross-section is flat and vertical, providing good docking conditions for subsequent pipe section splicing and assembly.

[0038] Step 12: After grinding the end face of the pipe section, perform the post-maintenance of the pipe section.

[0039] In a preferred but non-limiting embodiment of the present invention, step 12 specifically includes: The polished pipe section is then hoisted into a water curing tank for water curing. The water curing time is t12=7 days. The water quality is kept clean to ensure that the concrete is fully hydrated. After water curing, the pipe section will be hoisted to the designated storage yard for static curing. The static curing time is t13=7 days to avoid the pipe section being affected by external loads and environmental factors. After static curing, the compressive strength of the pipe section will be ≥ the design grade to ensure that the performance of the pipe section meets the standards.

[0040] The beneficial effects of the present invention are as follows, compared with the prior art: Significantly improved concrete performance: This invention employs a dry-hard concrete combined with a centrifugal-vibration-roller molding process, along with strict material selection and performance parameter control, resulting in uniform aggregate distribution across the concrete cross-section of the manufactured pipe sections. This completely eliminates the concrete segregation phenomenon caused by traditional single centrifugal processes. The concrete exhibits high strength; after curing, its compressive strength is no less than the design grade, and its electrical conductivity is no greater than 800 coulombs. It also demonstrates excellent durability, enabling it to withstand harsh service environments such as hydraulic engineering wharves.

[0041] Excellent quality of reserved ducts: Through the design and application of a special duct forming device, the straightness of the reserved ducts is ensured, which provides good conditions for the subsequent installation and tensioning of prestressed steel strands, effectively reduces the prestress loss of the finished pile during prestressing tensioning and use, and significantly improves the effective prestress of the large pipe pile.

[0042] Overall performance optimization of pipe piles: Post-tensioned large pipe piles made by splicing pipe sections based on the method of this invention have significantly better hammer impact resistance than existing PHC piles and long pipe section piles due to their high concrete density and large effective prestress. They can withstand greater impact loads during construction and installation, reducing the risk of damage, while improving the bearing capacity and long-term stability of the pipe piles. This effectively overcomes many defects of existing similar pipe piles and meets the needs of hydraulic wharf projects for high-performance prestressed concrete pipe piles.

[0043] High process stability: This invention has precisely set and strictly controlled the parameters of each production link. There are clear technical standards for each step, from steel cage fabrication and material preparation to molding, curing and post-processing, which ensures the stability and repeatability of the production process. It can mass-produce large pipe pile sections with consistent performance and reliable quality, and has good prospects for industrial application.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention without departing from the spirit and scope of the present invention. Any modifications or equivalent substitutions should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for composite molding of post-tensioned large-diameter pipe pile sections, characterized in that, include: Step 1: Fabricate the steel reinforcement cage for the post-tensioned large-diameter pipe pile segments; Step 2: After fabricating the steel reinforcement cage for the pipe section, prepare the protective layer spacers; Step 3: After preparing the protective layer pads, select the steel mold for pipe section forming; Step 4: After selecting the steel mold for pipe section forming, configure the duct forming device; Step 5: After configuring the duct forming device, prepare dry-hard concrete; Step 6: After preparing the dry-hard concrete, install the reinforcing cage and duct forming device; Step 7: After the steel cage and duct forming device are installed, the composite process is used to form the pipe section; Step 8: After the composite process is used to form the pipe section, steam curing treatment is performed; Step 9: After performing steam curing, the duct forming device is removed; Step 10: Remove the duct forming device and demold the pipe section; Step 11: After demolding the pipe section, grind the end face of the pipe section; Step 12: After grinding the end face of the pipe section, perform the post-maintenance of the pipe section.

2. The post-tensioned large-diameter pipe pile composite forming method according to claim 1, characterized in that, In step 1, the steel reinforcement cage of the pipe section uses HPB300 steel bars, wherein the longitudinal stirrups and circumferential bars are cold-drawn from straight Φ8mm to Φ7mm, and the tensile strength of the steel bars after cold drawing must meet ≥550MPa; In step 2, the protective layer thickness of the outermost circumferential reinforcement of the steel cage is 30mm, and the protective layer pad is made of high-density polyethylene plastic and its surface is a standard card structure with concave and convex shapes. In step 3, the steel mold for forming the pipe section adopts a single mold design, and the maximum opening of the joint does not exceed 5cm, so as to avoid concrete leakage or insufficient forming accuracy due to excessive joint opening. The steel mold is equipped with auxiliary devices, including a running wheel ring, a positioning ring, a vibration ring, a counterweight, lifting lugs, and end caps. The running wheel ring is used for rotational support of the steel mold. The positioning ring is on the outside of the steel mold and has a corresponding slot on the forming machine. The vibration ring provides vibration force for vibration forming. The counterweight is used to adjust the rotational balance of the steel mold. The lifting lugs facilitate the lifting and handling of the steel mold. The end caps are used to seal both ends of the pipe section.

3. The post-tensioned large-diameter pipe pile composite forming method according to claim 2, characterized in that, In step 4, the channel forming device consists of two parts: a pull rod and a separating rubber tube. The tie rod adopts a three-section welded structure: ① The screw joint section is made of 45# steel and has a length L1=135mm; ② The middle section is made of 45# steel, using φ32 seamless steel pipe with a wall thickness δ=4.5mm and a length L2=5975mm; ③ The hole rod joint section is made of 40Cr round steel and has a length L3=140mm; The isolation hose is made of imported natural rubber, with the following parameters: inner diameter d1=34mm, outer diameter d2=44mm, and length L=6.2m.

4. The post-tensioned large-diameter pipe pile composite forming method according to claim 3, characterized in that, In step 5, the performance parameters of the dry-hard concrete are controlled as follows: Vebe consistency V = 25s-35s; cementitious material content G = 450-550 kg / m³; water-cement ratio λ < 0.30; apparent density ρ > 2500 kg / m³; concrete water content W ≤ 130 kg / m³; electrical flux Q ≤ 800 coulombs, to ensure that the concrete has high strength, high durability and good workability. The material requirements for preparing dry-hard concrete are as follows: Cement: Silicate or ordinary Silicate cement with a strength grade of 52.5 is selected; Admixture: A special steam-curing admixture is used, and its activity index is ≥100% after steam curing, at 3 days, and at 28 days. Fine aggregate: River sand with a mud content ωc≤1.0% and a gradation of Class I medium sand in Zone II; Coarse aggregate: Hard crushed stone is selected, and after two washing and screening processes, the particle size distribution is 5-20mm or 5-25mm (two-dimensional); the compressive strength of the stone is σ≥max, and the mud content is ωc≤0.5%; Admixture: Polycarboxylate superplasticizer is selected, with a water reduction rate η≥28%; Step 6 specifically includes: The prepared protective layer spacers are evenly snapped onto the outer circumferential reinforcement bars of the fabricated steel cage to ensure that the spacers are firmly fixed and evenly distributed. The steel cage with the spacers installed is hoisted into the steel mold for forming the pipe section, and the position of the steel cage is adjusted to make it centrally located. According to the design requirements, the duct forming device is inserted into the steel cage and its two ends are fixed to the end caps of the steel mold.

5. The post-tensioned large-diameter pipe pile composite forming method according to claim 4, characterized in that, Step 7 specifically includes: The steel mold containing the reinforcing cage and duct forming device is hoisted onto the forming machine. Concrete is fed into the steel mold via a belt conveyor, and the forming machine is started simultaneously. The pipe section is formed using a centrifugal-roller-vibration triple composite process. The specific steps are as follows: Phase 1: Initial feeding phase, motor speed n1=265 rpm, continuously feeding until the material thickness is about 8cm, centrifugation time t1=120s; then the motor speed is increased to n2=332 rpm, the vibrator is started, the vibration frequency f=60-75Hz, the belt conveyor continues to feed until the material thickness is flush with the inner ring of the end cap hole, at this time the pressure roller is lowered to limit the over-thickness replenishment, the over-thickness control amount Δh=6~10mm, the centrifugation time of this phase t2=270s; Phase 2: After the material feeding is completed, the vibrator continues to vibrate for t3=30s to further compact the concrete; after the vibration is completed, the pressure roller continues to apply pressure for t4=20s to compact the concrete surface. Phase 3: Increase the motor speed to n3=995 rpm, perform medium-speed centrifugation t5=180s, and remove excess water from the inside of the concrete. Stage 4: The motor speed is increased again to n4=1207 rpm, and high-speed centrifugation is carried out until the excess water in the concrete is fully squeezed to the inside and discharged. The centrifugation time is t6=120s. Phase 5: After high-speed centrifugation, the speed is gradually reduced until the steel mold stops rotating. The deceleration process takes t7 ≥ 60s.

6. The post-tensioned large-diameter pipe pile composite forming method according to claim 5, characterized in that, Step 8 specifically includes: The formed pipe section, along with the steel mold, is hoisted into a steam curing tank for steam curing. The curing process is divided into four stages: Phase 1: Static curing phase, i.e., curing temperature T1=30℃, no steam supply, dry heat insulation method, static curing time t8=2 hours; Phase 2: Heating phase, which involves introducing steam to raise the temperature at a rate of v_rise = 15-20℃ / h, raising the temperature to the target temperature T2 = 65℃, and the heating time t9 = 2 hours. Phase 3: Constant temperature phase, i.e., maintaining the curing temperature T2=65℃ for continuous steam curing, and the constant temperature time t10=4 hours; Phase 4: Cooling phase, i.e., controlling the cooling rate v_drop = 15-20℃ / h, cooling down to temperature T3 = 30℃, cooling time t11 = 2 hours.

7. The post-tensioned large-diameter pipe pile composite forming method according to claim 6, characterized in that, Step 9 specifically includes: After steam curing is completed, once the pipe section temperature drops to around 30°C, a special pre-drilled core-pulling machine is used to slowly pull out the tie rod and isolation hose from the concrete pipe section inside the steel mold using the duct forming device.

8. The post-tensioned large-diameter pipe pile composite forming method according to claim 7, characterized in that, Step 10 specifically includes: Loosen the fixing bolts on one side of the steel mold, open the joint of the steel mold, and use a special U-shaped hook to smoothly pull the pipe section out of the steel mold.

9. The post-tensioned large-diameter pipe pile composite forming method according to claim 8, characterized in that, Step 11 specifically includes: A specialized grinding robot is used to grind the two end faces of the demolded pipe section to a depth h ≥ 0.5 mm, ensuring that the pipe section cross-section is flat and vertical, providing good docking conditions for subsequent pipe section splicing and assembly.

10. The post-tensioned large-diameter pipe pile composite forming method according to claim 9, characterized in that, Step 12 specifically includes: The polished pipe section is hoisted into the water curing tank for water curing, and the water curing time is t12=7d; After water curing, the pipe section will be hoisted to the designated storage yard for static curing, which will last for 7 days (t13).

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