A green low-carbon UHPC formwork inner-casting recycled concrete gravity pier structure construction method

Abstract

The present application relates to the technical field of marine engineering structure design, and discloses a green low-carbon UHPC formwork inner-cast recycled concrete gravity pier structure construction method, which comprises the following steps: step one, LC-UHPC formwork factory prefabrication; step two, offshore transportation of the formwork; step three, construction foundation preparation; step four, on-site hoisting of the LC-UHPC formwork; step five, hoisting of a steel reinforcement cage inside the LC-UHPC formwork; step six, internal filling of recycled concrete; step seven, pouring of building solid waste and shock medium-coarse sand into the hollow part to form a pier body; and step eight, pouring of an upper closed layer and installation of an auxiliary structure; the present application saves a large amount of sand and stone resources and achieves the purpose of reducing carbon emissions by prefabricating LC-UHPC formwork and using a large amount of building solid waste and recycled aggregate, and greatly improves the durability of the structure by relying on the excellent performance of LC-UHPC, and has high construction efficiency and good construction benefits.

Description

Technical Field

[0001] This invention relates to the intersection of marine engineering technology and solid waste resource utilization, specifically to a berthing pier structure for use in marine anchorages, ports, waterways and other waterways, and particularly to a green, low-carbon, and highly durable berthing pier that combines an ultra-high performance concrete (UHPC) shell with a core of solid waste from building demolition. Background Technology

[0002] Offshore berths are critical infrastructure for ship berthing and mooring, constantly subjected to harsh environmental conditions such as ship impacts, seawater corrosion, wet-dry cycles, and freeze-thaw cycles. Traditional berths are mostly made of cast-in-place ordinary concrete or steel structures, which have the following drawbacks:

[0003] Insufficient durability: Ordinary concrete is prone to carbonization and steel corrosion in marine chloride environments, resulting in short structural service life and high maintenance costs.

[0004] High resource consumption: Concrete production consumes a large amount of natural resources such as cement and sand, which is not in line with the concept of green and low-carbon development.

[0005] Significant environmental pressure: The amount of solid waste generated from building demolition (such as waste concrete, bricks and tiles) is enormous, and it is currently mainly disposed of by landfill, which occupies land resources and pollutes the environment.

[0006] To address these issues, some existing technologies employ high-performance materials or utilize recycled aggregates in concrete structures. However, using recycled aggregates alone significantly reduces the strength and durability of concrete, making it difficult to meet the stringent requirements of marine engineering; while using UHPC across the entire cross-section is too costly and difficult to apply on a large scale.

[0007] Meanwhile, guided by the goals of energy conservation, emission reduction, and low-carbon development, this structure further integrates the technical path of preparing UHPC using recycled aggregates and recycled micro-powders, significantly reducing carbon emissions in the traditional UHPC production process and promoting the recycling of building materials resources. This innovative structure not only continues the mechanical and durability advantages of UHPC materials but also effectively improves the durability of berthing piers, providing a new technical path for my country's marine engineering, especially for the construction of berthing piers in harsh environments, and has broad prospects for promotion and application.

[0008] Therefore, there is an urgent need for a new type of berthing pier structure that can meet the stringent performance requirements of marine engineering, dispose of large quantities of construction waste, reduce costs, and is easy to construct. Summary of the Invention

[0009] The purpose of this invention is to address the shortcomings of existing technologies. This invention aims to provide a method for constructing a gravity pier structure using recycled concrete poured into a green and low-carbon UHPC (Low-Carbon Ultra-High Performance Concrete, LC-UHPC) mold shell. Specifically, it provides a combined marine berthing pier with a UHPC shell and an internally disposed solid waste core. This berthing pier achieves extremely high durability, excellent impact resistance, significant low-carbon environmental benefits, and good economic efficiency through an innovative "outer rigidity and inner flexibility" combination structure that utilizes superior materials.

[0010] To achieve the above objectives, the present invention provides the following solution:

[0011] A method for constructing a gravity pier structure using green, low-carbon UHPC (Ultra-High-Polymer) molded recycled concrete includes the following steps:

[0012] Step 1: Prefabricate the LC-UHPC mold shell; the LC-UHPC mold shell includes an outer shell and an inner shell, a recycled concrete filling cavity is formed between the inner wall of the outer shell and the outer wall of the inner shell, and the inner shell encloses to form a core cavity.

[0013] Step 2: Transport the LC-UHPC formwork shell by sea to the construction area;

[0014] Step 3: Construction foundation preparation, including the construction of the riprap foundation;

[0015] Step 4: Hoist the LC-UHPC mold shell on site;

[0016] Step 5: Hoist the steel reinforcement cage between the inner wall of the LC-UHPC mold shell and the outer wall of the LC-UHPC mold shell.

[0017] Step 6: Fill the space between the inner wall of the LC-UHPC mold shell and the outer wall of the LC-UHPC mold shell with recycled concrete to form a recycled concrete layer;

[0018] Step 7: Contain construction waste and vibratory compacted medium-coarse sand into the core cavity formed by the inner shell of the LC-UHPC mold shell, and after compaction, form the core of the pier body composed of construction waste and vibratory compacted medium-coarse sand.

[0019] Step 8: Pour the upper sealing layer and install the auxiliary structures.

[0020] Furthermore, in step one, the LC-UHPC mold shell is a composite structure serving as an external protective layer, and the internal reinforcing bars of the LC-UHPC mold shell adopt an externally integrally welded reinforcing bar skeleton.

[0021] Furthermore, the thickness of the outer shell and the inner shell of the LC-UHPC mold are each independently 50mm to 120mm, and the thickness of the recycled concrete layer is 500mm.

[0022] Furthermore, a non-scraping stop strip is provided on the inner wall of the LC-UHPC mold shell and the outer wall of the LC-UHPC mold shell to form a scraping interface, eliminating the need for manual scraping.

[0023] Furthermore, in step three, the construction of the rubble bed involves first filling the original bearing layer with original rubble as the original rubble skeleton layer, and then laying a layer of recycled crushed stone composed of crushed construction waste concrete on top of the original rubble skeleton layer to construct a composite graded recycled bed.

[0024] Furthermore, in step five, a roller made of high-strength nylon is installed on the outermost vertical bar of the steel cage, and the roller plays a guiding role during the hoisting of the steel cage.

[0025] Furthermore, vertical conduits are arranged between the inner wall of the LC-UHPC outer shell and the outer wall of the LC-UHPC inner shell. Multiple vertical conduits are used to simultaneously pump the recycled concrete, maintaining a steady rise in the concrete level. Utilizing the fact that the density of the recycled concrete is greater than that of water, ballast water is squeezed out from the top, and over-pouring is performed. After the concrete has initially set, the over-pouring layer is removed. In this step, the method of arranging vertical conduits effectively avoids segregation caused by direct contact between the recycled concrete and the ballast water maintaining equilibrium within the original structure. The pouring method utilizes the principle that the density of concrete is greater than that of water to squeeze the ballast water out of the interior of the LC-UHPC outer shell.

[0026] Furthermore, in step eight, a precast LC-UHPC top slab is used for capping. The precast LC-UHPC top slab has pre-drilled grouting holes through which cement grout is injected. The precast LC-UHPC top slab is also connected to the extending reinforcing bars at the bottom via these pre-drilled holes, forming a wet joint. This step, injecting cement grout into the grouting holes in advance, enhances the overall strength of the grout injected into the core of the pier and reduces subsequent settlement.

[0027] Furthermore, in step four, the LC-UHPC mold shell is connected to the long-tailed high-strength sleeve pre-embedded on the top of the LC-UHPC mold shell by a spreader beam to ensure stability during the hoisting process.

[0028] The present invention discloses the following technical effects:

[0029] (1) Extremely high durability: LC-UHPC material has ultra-high strength (compressive strength ≥120 MPa), high toughness (tensile strength ≥8 MPa), low permeability and excellent corrosion resistance. As a permanent outer shell, it provides a physical and chemical barrier for the core recycled concrete layer and the core of building solid waste, completely blocking seawater erosion.

[0030] (2) Green, low-carbon and resource recycling: The core of the pier is formed by the extensive use of recycled aggregates from construction solid waste and vibratory compacted medium-coarse sand, realizing the large-scale and high-value utilization of solid waste in marine engineering, directly reducing the mining of natural sand and gravel, and reducing the "hidden carbon" of the pier. At the same time, the high efficiency of LC-UHPC itself allows for a reduction in material usage, further reducing cement consumption and carbon footprint.

[0031] (3) Excellent structural performance and coordinated stress distribution:

[0032] Gravity stability: The recycled concrete filling provides most of the structure's self-weight, ensuring the anti-slip and anti-overturning stability of the pier as a gravity structure.

[0033] High impact resistance and toughness: The outer LC-UHPC mold shell has extremely high compressive and tensile strength, effectively resisting ship impacts and abrasion. Internal steel fibers enhance the material's toughness, making the structure less prone to brittle fracture upon impact.

[0034] Overall collaborative operation: Through pre-processed interface treatment, the LC-UHPC formwork is tightly integrated with the recycled concrete core to form a composite load-bearing body, ensuring the integrity of the structure when subjected to complex loads such as mooring forces and impact forces.

[0035] (4) Convenient construction and controllable quality: The LC-UHPC formwork is prefabricated in the factory, which can accurately control the size, the position of the embedded parts and the quality of the concrete. On-site, only hoisting and positioning are required before pouring the core recycled concrete. The construction speed is fast, less affected by the harsh sea conditions, and the quality is easy to guarantee. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the construction method of the present invention;

[0037] Figure 2 These are side and top views of the present invention;

[0038] Figure 3 This is a schematic cross-sectional view of the overall structure of the berth.

[0039] Figure 4 A schematic diagram of a steel cage structure with rollers;

[0040] Figure 5This is a schematic diagram of a composite graded regenerated substrate bed structure.

[0041] Reference numerals: 1. LC-UHPC formwork shell; 2. Recycled concrete layer; 3. Core of the pier body composed of construction solid waste and vibratory compacted medium-coarse sand; 4. Outer shell of LC-UHPC formwork shell; 5. Inner shell of LC-UHPC formwork shell; 6. Inner wall of the outer shell of LC-UHPC formwork shell; 7. Outer wall of the inner shell of LC-UHPC formwork shell; 8. Mooring bollard; 9. Fender; 10. Base; 11. High-strength nylon roller; 12. Connecting buckle; 13. Peripheral large stone bottom protection; 14. Flexible crushed stone buffer layer; 15. Recycled crushed stone transition layer; 16. Original stone skeleton layer; 17. Original bearing layer. Detailed Implementation

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Reference Figures 1-5 This invention discloses a method for constructing a gravity pier structure using recycled concrete poured into a green, low-carbon UHPC mold shell. A gravity-type berthing pier with a square base, designed according to the target ship type and sea conditions, is pre-built, with dimensions of 8m × 8m × 5m (height). The construction of the external LC-UHPC mold shell 1 includes the following steps:

[0044] Step 1: Factory prefabrication of LC-UHPC mold shell 1:

[0045] The LC-UHPC mold shell 1 is designed and prefabricated, comprising an outer shell 4 and an inner shell 5. A recycled concrete filling cavity is formed between the inner wall 6 of the outer shell and the outer wall 7 of the inner shell, which is used for subsequent filling with recycled concrete to form a recycled concrete layer 2. The inner shell 5 encloses a core cavity, which is used for subsequent input of construction waste and vibratory compacted medium-coarse sand to form the core 3 of the construction waste and vibratory compacted medium-coarse sand pier. A non-scratching grout-stopping strip is provided on the inner wall 6 of the outer shell and the outer wall 7 of the inner shell to form a roughened interface, enhancing interfacial adhesion; the interface roughness is not less than 4 mm.

[0046] Table 1 Results of oblique shear test

[0047]

[0048] Note: C represents the specimen treated with the interface of the fine grout stop strip, and B represents the specimen treated with the interface of the coarse grout stop strip.

[0049] For example, for the aforementioned 8m×8m×5m (height) mooring pier, a mold with dimensions of 8m×8m×5m (height) is designed. The thickness of the LC-UHPC outer shell 4 is 80mm, and the thickness of the LC-UHPC inner shell 5 is consistent with that of the LC-UHPC outer shell 4. The thickness of the recycled concrete layer 2 is 500mm. The outer mold material of the LC-UHPC shell 1 uses a shaped steel template, with mirror-polished contact surfaces and coated with a special UHPC release agent. Rubber waterstops are used at some joints to prevent grout leakage.

[0050] The reinforcement of the LC-UHPC mold shell 4 is externally welded, using a steel mesh for precise positioning. All steel bars, except for the embedded parts, are welded into a single steel skeleton, which is then hoisted into the precast LC-UHPC mold for pouring. A steel reinforcement jig similar to the LC-UHPC mold is designed, with steel positioning grooves. The LC-UHPC steel skeleton is welded onto the jig, and detachable triangular threaded steel supports are welded internally to form a truss structure. These supports are removed after placement in the mold and before pouring. A rectangular flat beam matching the skeleton's planar dimensions is used for hoisting into the mold, with a lifting point every 1.5-2m along the skeleton's perimeter to ensure its levelness. A flared guide made of smooth stainless steel is installed at the top of the outer mold to prevent the skeleton from hitting the mold edges during lowering. The steel skeleton is precisely fitted into the mold. LC-UHPC concrete is then poured into the mold, and steam curing completes the precasting of the entire LC-UHPC mold shell 4.

[0051] The embedded parts within the LC-UHPC steel mold are divided into four categories: hoisting components, interface connection components, construction auxiliary components, and operational facilities components. High-strength, long-tailed internally threaded sleeves are temporarily fixed to the steel mold using bolts at the thickened ribs or corners of the top of the LC-UHPC mold shell. Helical spring bars are tightly wrapped around the sleeves to form a confined concrete core. Two layers of fine wire mesh are added to the top surface of the sleeve (the tension zone of the concrete) to prevent surface cracking. Finally, the force-transfer reinforcing bars at the tail of the sleeve are spot-welded to the main reinforcing mesh of the mold shell to ensure no displacement during pouring.

[0052] Exposed embedded parts (such as connecting plates and cement-based sleeve openings) are made of 316L stainless steel or coated with Dacromet anti-corrosion coating on carbon steel surfaces. For connecting ribs extending deep into the interior, a penetrating crystallizing material is used for bottom sealing. Embedded short interface connecting ribs with a diameter of 10-15mm are left exposed 0-15cm from the inner wall, with the ends set as 90° hooks or welded small circles. Holes are pre-drilled in the steel mold to allow the ribs to pass through. A 10-12mm thick steel plate is selected, with 2-4 shear nails welded to the back. The surface of the steel plate should be completely flush with the inner wall of the LC-UHPC, and the edges should be chamfered to prevent stress concentration. The steel plate is then firmly fixed to the inner mold surface using bolts. Finally, a positioning compass and through-wall sleeves are pre-embedded in the template to facilitate the installation of subsequent auxiliary structures (such as mooring bollards 8 and fenders 9). To further improve local rigidity and prevent cracking that may occur during hoisting or precast demolding, longitudinal and transverse stiffening ribs (rib beams) are added to the inner wall.

[0053] The concrete used for casting LC-UHPC must have a 28-day compressive strength of not less than 120 MPa and a tensile strength of not less than 8 MPa. It must also incorporate steel fibers (2%-3% by volume) to significantly improve crack resistance and toughness. The formulation is shown in Table 2 below. The fibers used are copper-plated steel fibers with a diameter of 2 mm and a length of 10 mm, with a fiber volume content of 2%, and an appropriate amount of hydroxypropyl methylcellulose viscosity modifier is added.

[0054] Table 2 LC-UHPC mix proportions (unit: kg / m³) 3 )

[0055]

[0056] During the preparation of LC-UHPC, the dry LC-UHPC material and water-reducing agent are first poured into a mixer and dry-mixed for 5 minutes to ensure thorough mixing. Then, water mixed evenly with the defoamer is added and stirred for 3 minutes. Finally, steel fibers are slowly and evenly poured in while stirring, and then stirred for another 5 minutes. To ensure the mechanical properties and constructability of LC-UHPC, the dynamic yield stress of LC-UHPC is controlled at 1.0-2.0 kPa, the static yield stress is controlled at 1.5-2 kPa, the cubic compressive strength of LC-UHPC shall not be less than 120 MPa, the tensile strength shall not be less than 8 MPa, and the flexural strength shall not be less than 20 MPa (see Table 3).

[0057] Table 3. Performance Comparison of LC-UHPC and Normal Concrete (NC)

[0058]

[0059] Note: NC is an abbreviation for Normal Concrete.

[0060] Step 2: Transport LC-UHPC formwork 1 by sea to the construction area:

[0061] The LC-UHPC formwork shell 1 is transported using a standard deck barge. A crane or large hoist lifts the LC-UHPC formwork shell 1 onto the barge using a spreader beam. Wooden sleepers are placed on the barge deck as a cushioning layer. L-shaped steel baffles are welded around the LC-UHPC formwork shell 1 on the barge deck, employing a triple safety system of "bottom limiting + lateral tightening + top lashing". A screw-type adjusting arm ensures the LC-UHPC formwork shell 1 is securely locked, while preventing hard impacts. All metal parts in contact with the LC-UHPC are wrapped with rubber or high-performance polymer gaskets to prevent electrochemical corrosion and hard point damage. The transport frame is welded and fixed to the deck, and tensioned in four directions with steel wire ropes to the hull tensioners to prevent any slippage. During sea transport, tilt sensors and GPS locators are installed on the transport frame to remotely monitor the attitude and position of the formwork shell for any abnormalities. Acceleration sensors are installed at some critical locations to monitor dynamic loads, allowing the tugboat to slow down or change course accordingly.

[0062] Step 3: Foundation Preparation for Construction

[0063] Measurements were taken and the excavation boundary was precisely defined using a positioning system combined with an underwater depth sounder. A grab dredger was then used to rapidly remove the surface silt. After excavation, a flat-bottomed grab bucket was used to remove excess silt from the bottom. Multibeam bathymetry and shallow seismic profiling were employed to ensure no backfilling at the bottom of the trench. During the excavation of the foundation bed, the excavation boundary was defined according to the geometry of the LC-UHPC formwork 1. Differential GPS positioning was used to control the dredger, keeping the excavation area within 1 meter of the design boundary. Backfilling monitoring was conducted to ensure the trench dimensions matched the LC-UHPC formwork 1, effectively reducing the amount of subsea earthwork.

[0064] For the construction of the riprap subgrade, first, larger-diameter original boulders are placed on the original bearing layer 17 to form the original boulder skeleton layer 16. Then, a recycled crushed stone transition layer 15, composed of recycled crushed stone formed from high-strength construction waste concrete, is laid on top of the original boulder skeleton layer 16 to construct a composite-graded recycled subgrade. A batch of unweathered stones is selected and placed using open-body barges or flat barges in conjunction with backhoes. Frequent measurement and placement are necessary during the placement process. Large-area placement is stopped when the stones reach approximately 30-50cm from the design top elevation; instead, localized patching is used to ensure sufficient settlement allowance for subsequent compaction.

[0065] Before the formal compaction, a section of the foundation bed is selected for trial compaction to determine a number of parameters such as the weight of the tamping hammer. The heavy hammer tamping boat is used to compact the foundation from the perimeter first, and then compact it towards the center. After compaction, it may be necessary to add stones.

[0066] Finally, divers were dispatched to level the gravel layer on the compacted stone surface, completing the entire foundation treatment.

[0067] On top of the compacted foundation bed, a layer of graded crushed stone with a thickness of 100-200mm is laid as a flexible crushed stone buffer layer 14. This flexible crushed stone buffer layer 14 is then finely leveled using an underwater leveling device to ensure a flatness error of ≤20mm. After leveling the foundation bed, large stones are placed around the perimeter to protect the bottom and prevent ocean currents from eroding the edges of the foundation bed during installation.

[0068] The aforementioned original bearing layer 17, original boulders skeleton layer 16, recycled crushed stone transition layer 15, and flexible crushed stone buffer pad layer 14 together constitute a stable base 10, providing a flat and solid support surface for the subsequent precise hoisting of the LC-UHPC mold shell 1.

[0069] Step 4: On-site hoisting of LC-UHPC mold shell 1:

[0070] Before lifting, check that the internal rigid frame connections of LC-UHPC mold shell 1 are secure. Connect the rigid top long-tail high-strength sleeve to the mold shell via a spreader beam. Slowly raise the main hook of the crane to vertically lift LC-UHPC mold shell 1 off the transport barge. Move it horizontally above the installation point and lower it slowly. When the bottom plate of the mold shell touches the water surface, pause for 1-2 minutes to observe whether the mold shell leaks water and whether its posture is tilted.

[0071] Initial lowering is performed, utilizing the formwork's own weight. When buoyancy equals its weight, the formwork suspends. Water is then injected into the LC-UHPC formwork shell 4, with the injection rate controlled to maintain the crane hook bearing approximately 10%-20% of the formwork's weight. When the bottom of the LC-UHPC formwork shell 4 is 30-50cm from the top surface of the foundation bed, lowering is paused for a period, then water injection resumes, allowing the shell to slowly settle onto the flexible gravel buffer layer 14 of the foundation bed. After landing, while maintaining structural balance, excess seawater is drained from the shell using pumps or other pumping equipment. After pumping, the lifting equipment is retrieved, completing the offshore lifting operation.

[0072] Before the hoisting operation, digital technologies such as BIM are used to simulate the entire hoisting process, simulating the movement of the ship and components under different sea conditions, and optimizing the hoisting point positions, rigging lengths, and ship positioning.

[0073] Step 5: Hoist the reinforcing cage into the LC-UHPC formwork 1:

[0074] The reinforcing cage is fabricated on-site. The intersections of the main reinforcement bars and stirrups are spot-welded to improve overall rigidity. Its outer contour should be 30-50mm smaller than the dimensions of the LC-UHPC formwork shell 4. High-strength nylon rollers 11 are installed on the outermost vertical reinforcement bars. Double-layered reinforcing stirrups are installed at the top and bottom of the cage as lifting and landing points. The fabricated reinforcing cage is lifted by a crane above the LC-UHPC formwork shell 1 and slowly lowered, guided into place by the high-strength nylon rollers 11. The reinforcing cage is then tied or welded to the interface connecting short bars pre-embedded on the inner wall 6 of the LC-UHPC formwork shell 4 and secured with connecting clips 12, forming a unified whole between the inner core reinforcement bars and the LC-UHPC formwork shell 4.

[0075] Step 6: Fill the interior of LC-UHPC mold shell 1 with recycled concrete:

[0076] Recycled concrete is filled between the inner wall 6 of the LC-UHPC outer shell and the outer wall 7 of the LC-UHPC inner shell (i.e., the recycled concrete filling cavity) to form a recycled concrete layer 2. A set of vertical conduits is arranged between the inner wall 6 and the outer wall 7 of the LC-UHPC outer shell. Multiple vertical conduits are used for synchronous pumping to deliver the required recycled concrete to the bottom of the structure, maintaining a steady rise in the concrete level. As the recycled concrete accumulates at the bottom, taking advantage of the fact that the density of recycled concrete is greater than that of water, all the ballast water remaining inside the LC-UHPC outer shell 4 is gradually discharged through the top. Furthermore, due to the contact between the bottom concrete and seawater, a certain degree of over-pouring is required. After the concrete initially sets, the inferior over-pouring layer is removed by manual chiseling. Then, it is cured.

[0077] Step 7: Fill the core cavity formed by the inner shell 5 of the LC-UHPC mold with construction solid waste and vibratory compaction medium-coarse sand:

[0078] Construction solid waste and vibratory compacted medium-coarse sand are placed into the core cavity formed by the inner shell 5 of the LC-UHPC mold as the main material source for the pier body. A vibratory compactor is used for compaction, forming the core 3 of the pier body composed of construction solid waste and vibratory compacted medium-coarse sand. This core serves as the main part of the pier body and forms a gravity-type berthing pier under its own weight. Alternatively, the construction solid waste can be crushed, mixed with fluidized solidified soil (cement + fly ash slurry), and pumped into the hollow part. After compaction, it forms a gravity-type berthing pier body under its own weight.

[0079] Step 8: Pour the upper sealing layer and install auxiliary structures:

[0080] First, the upper part of the slag is washed away with high-pressure water. Vertical reinforcing bars are inserted by drilling holes on the inner side of the top of the LC-UHPC formwork shell 4. Anti-pull-out anchor bars are then inserted by drilling holes in the roughened recycled concrete surface. The main and distribution bars of the sealing layer are tied, and the deeply embedded anchor bolt groups for the mooring bollards 8 and fenders 9 are installed. A precast LC-UHPC top slab is used for capping. Grouting holes are pre-drilled in the precast LC-UHPC top slab, through which cement grout is injected to enhance the overall strength of the core of the pier and reduce later settlement. The precast LC-UHPC top slab is connected to the protruding reinforcing bars at the bottom through the pre-drilled holes via grouting (wet joint), achieving modular capping. Then, LC-UHPC concrete of the same type as the inner and outer shells of the LC-UHPC formwork is poured on top. After pouring, a waterproof cloth is used for curing.

Claims

1. A method for constructing a gravity pier structure using green, low-carbon UHPC (Ultra-High-Pressure Polymer) molded recycled concrete, characterized in that... Includes the following steps: Step 1: Prefabricate the LC-UHPC mold shell; the LC-UHPC mold shell includes an outer shell and an inner shell. A recycled concrete filling cavity is formed between the inner wall of the outer shell and the outer wall of the inner shell. The inner shell encloses and forms a core cavity. The internal reinforcing bars of the outer shell are made of an externally integrally welded reinforcing steel skeleton. Step 2: Transport the LC-UHPC formwork shell by sea to the construction area; Step 3: Construction foundation preparation, including the construction of the riprap foundation; Step 4: Hoist the LC-UHPC mold shell on site; Step 5: Hoist the steel reinforcement cage between the inner wall of the LC-UHPC mold shell and the outer wall of the LC-UHPC mold shell. Step 6: Fill the space between the inner wall of the LC-UHPC mold shell and the outer wall of the LC-UHPC mold shell with recycled concrete to form a recycled concrete layer; Step 7: Contain construction waste and vibratory compacted medium-coarse sand into the core cavity formed by the inner shell of the LC-UHPC mold shell, and after compaction, form the core of the pier body composed of construction waste and vibratory compacted medium-coarse sand. Step 8: Pour the upper sealing layer and install the auxiliary structure; use a precast LC-UHPC top slab for sealing, the precast LC-UHPC top slab has reserved grouting holes, and cement slurry is injected through the grouting holes.

2. The method for constructing a gravity pier structure using recycled concrete poured into a green, low-carbon UHPC mold according to claim 1, characterized in that: The thickness of the outer shell and the inner shell of the LC-UHPC mold are each independently 50mm to 120mm, and the thickness of the recycled concrete layer is 500mm.

3. The method for constructing a gravity pier structure using recycled concrete poured into a green, low-carbon UHPC mold according to claim 1, characterized in that: The inner wall of the LC-UHPC mold shell and the outer wall of the LC-UHPC mold shell are provided with a non-scraping stop strip to form a scraping interface, eliminating the need for manual scraping.

4. The method for constructing a gravity pier structure using recycled concrete poured into a green, low-carbon UHPC mold according to claim 1, characterized in that: In step three, the construction of the rubble bed involves first filling the original bearing layer with original rubble as the original rubble skeleton layer, and then laying a layer of recycled crushed stone composed of crushed construction waste concrete on top of the original rubble skeleton layer to construct a composite graded recycled bed.

5. The method for constructing a gravity pier structure using green, low-carbon UHPC molded recycled concrete as described in claim 1, characterized in that: In step five, rollers made of high-strength nylon are installed on the outermost vertical bars of the steel cage. These rollers serve as guides during the hoisting of the steel cage.

6. The method for constructing a gravity pier structure using recycled concrete poured into a green, low-carbon UHPC mold according to claim 1, characterized in that: Vertical guide pipes are arranged between the inner wall of the LC-UHPC mold shell and the outer wall of the LC-UHPC mold shell. Multiple vertical guide pipes are used to pump the recycled concrete synchronously to keep the concrete liquid level rising steadily. Taking advantage of the fact that the density of the recycled concrete is greater than that of water, the ballast water is squeezed out from the top and over-filling is performed. After the concrete has initially set, the over-filled layer is removed.

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