Construction method of cavity superimposed structure vacuum sand discharge and recyclable formwork

Abstract

The present application relates to a kind of cavity superimposed structure vacuum sand drainage and construction method of recyclable formwork, the method is embedded when lower plate construction sand drainage pipe and with water-soluble PVA capsule self-plugging, in the cavity of support frame top fills and compact sand layer and lays recyclable rigid thin plate formwork as upper plate bottom die after paving;After the upper plate concrete reaches preset strength, by vacuum suction cooperation high pressure airflow fluidization forms the fluidization sand drainage state of upper blowing and lower suction, sand layer is formed cavity by high-efficiency discharge, and sand drainage hole is pressure grouting from bottom to top and is blocked.The sand layer compaction parameters, sand drainage pipe arrangement spacing and support removal timing are optimized by PFC 3D, Fluent-EDEM and ABAQUS multiscale numerical simulation before construction.The sand drainage rate of the present application is more than 98%, formwork can be recycled 10-30 times, the upper plate bottom surface bubble rate is controlled to be within 1%, meets the fair-faced concrete finishing standard, realizes the efficient, green, high-quality construction of cavity superimposed structure.

Description

Technical Field

[0001] This invention relates to the field of building construction technology, specifically a method for constructing a cavity composite structure with vacuum sand removal and reusable formwork. Background Technology

[0002] A hollow composite structure (also known as a hollow double-layer floor slab or composite hollow floor slab) is a floor system with cavities formed by a lower slab, an upper slab, and surrounding structural beams. This type of structure reduces its self-weight and saves on concrete usage through its internal cavities. At the same time, the cavities can be used to achieve functions such as sound insulation, heat insulation, and pipeline passage. It is widely used in large-span public buildings, industrial plants, and buildings requiring fair-faced concrete finishes.

[0003] The construction challenges of hollow composite structures lie in the fact that supports and formwork must be installed within the confined cavities during the construction of the upper slab, and this support system must be either removed or retained after the concrete has hardened. Traditional construction methods suffer from the following technical discrepancies and drawbacks: Route 1: Internal support frame + formwork retention. For example, the "concrete hollow double-layer floor slab" disclosed in CN201710307967 (Guangdong Fourth Construction Engineering Co., Ltd.) uses a wooden support frame and the upper slab formwork permanently retained within the cavity. The drawbacks of this method are: the support frame occupies cavity space, limiting the weight reduction effect, and the internal support cannot be removed, affecting the subsequent use of the cavity.

[0004] Route Two: Infill Material + Simple Formwork. To overcome the shortcomings of Route One, subsequent techniques utilize removable infill material (such as sand) combined with a simple formwork (such as a waterproof membrane) as support for the upper slab construction. After the concrete hardens, the infill material is removed to form a cavity. This route is the technical starting point of this invention, but existing infill construction techniques still have significant deficiencies: (1) CN202111159148 (Shanghai Baoye Group Co., Ltd.) -- "A method for supporting templates for hollow composite structures" This technology is the closest existing technology to the present invention. Its technical solution is as follows: After the construction of the lower layer slab formwork of the composite structure is completed, construction sand is used to fill the composite cavity. A rigid waterproof membrane is laid on top of the sand as an outer formwork for supporting the upper layer slab. After the upper layer slab concrete is poured and reaches the specified strength, the formwork sealing box is broken to allow the sand to flow out naturally under its own weight. Then, a blower is used to clean up the residual sand.

[0005] This technology has the following drawbacks: First, the sand removal efficiency is low, relying entirely on the sand's own weight to flow out naturally. In areas such as the corners of cavities and low-lying curved surfaces, sand easily accumulates in dead zones, resulting in a high residue rate. Blower cleaning is highly dependent on worker skill, causing severe dust pollution and poor environmental performance. Second, the waterproof membrane is for single use only. Rigid waterproof membranes have poor puncture resistance, easily breaking during the binding of the upper slab's reinforcing steel, leading to grout leakage. Furthermore, it cannot be repaired or reused after damage, resulting in high construction costs. Third, there is a lack of quantitative optimization methods. Key parameters such as sand layer compaction and the timing of removing the sealing box are determined solely by experience without scientific calculation, leading to unstable construction quality.

[0006] (2) CN202110261652 (China Metallurgical Construction Group Co., Ltd.) -- "A construction method for hollow double-layer floor slabs" This technology, an improvement upon CN202111159148, involves pre-embedding multiple vertical sand-discharging pipes during the construction of the lower slab. Sand is discharged through these pipes to create cavities. However, this technology still has the following drawbacks: First, the sealing reliability of the sand-discharging pipes is poor. The upper end of the pipes is sealed with foam, which is lightweight and prone to floating or shifting during concrete pouring and vibration, leading to pipe seal failure. Concrete then enters the pipes, causing blockage and loss of sand discharge function. Second, sealing the sand discharge holes is difficult. After sand discharge, the holes need to be sealed from the bottom of the lower slab upwards. The limited operating space makes it difficult to guarantee sealing quality, easily leading to leakage risks. Furthermore, the location of the sand discharge holes leaves obvious repair marks on the bottom surface of the lower slab, failing to meet the aesthetic requirements of fair-faced concrete. Third, the sand discharge still relies on gravity, failing to solve the fundamental problem of incomplete sand discharge in curved surfaces and irregularly shaped cavities.

[0007] (3) Other related technologies CN202111196463 (Beijing Yihuida Qingshui Construction Engineering Co., Ltd.) discloses an assembly method for irregular hyperboloid fair-faced concrete walls, which involves a hyperboloid formwork system, but does not involve sand removal and formwork technology for cavity composite structures, which is different from the technical problem solved by this invention.

[0008] In summary, existing construction technologies for cavity composite structures have significant shortcomings in terms of sand removal efficiency, formwork turnover, fair-faced concrete quality, construction parameter optimization, and environmental performance. A new construction method is needed that can achieve efficient sand removal, reusable formwork, excellent fair-faced concrete quality, and scientifically controllable construction parameters. Summary of the Invention

[0009] This invention aims to overcome the shortcomings of existing technologies and provide a vacuum sand removal and reusable formwork construction method for cavity composite structures. Addressing the problems of low sand removal efficiency, one-time consumption of formwork materials, difficulty in guaranteeing the surface quality of fair-faced concrete, lack of quantitative optimization basis for construction parameters, and poor environmental performance in existing technologies, this invention achieves efficient, green, and high-quality construction of cavity composite structures through a vacuum negative pressure suction combined with a high-pressure airflow fluidization upward blowing and downward suction sand removal mechanism, a reusable rigid thin-plate formwork system, and multi-scale numerical simulation optimization.

[0010] To solve the above-mentioned technical problems, the present invention is implemented as follows: A method for constructing a cavity composite structure using vacuum sand removal and reusable formwork is disclosed. In the construction of the cavity composite structure, vacuum negative pressure suction combined with high-pressure airflow fluidization is used to remove the sand layer filling the cavity. A reusable rigid thin-plate formwork is used as the bottom formwork for the upper slab pouring. Construction parameters are optimized through numerical simulation. The method includes the following steps: During the construction of the lower slab, a sand removal pipe is pre-embedded. The upper end of the sand removal pipe is sealed with a water-soluble sealing material, and the lower end extends to the bottom surface of the lower slab. A support frame is erected above the lower slab, and a sand layer is filled and compacted in layers within the cavity formed at the top of the support frame. A reusable rigid thin-plate formwork is laid on the top surface of the sand layer as the bottom formwork for the upper slab pouring. After the upper slab concrete reaches a preset strength, the sand layer is removed through the sand removal pipe using vacuum negative pressure suction combined with high-pressure airflow fluidization, forming a cavity. The sand removal pipe is then pressure-sealed from bottom to top. Before construction, numerical simulation is used to determine the sand layer compaction parameters, the spacing of the sand removal pipes, and the timing of support removal.

[0011] Preferably, the sand discharge pipe is a PVC pipe with a diameter of 70mm-80mm, arranged in a quincunx pattern; the water-soluble sealing material is a water-soluble PVA capsule, the capsule being filled with micro-expansion cement mortar, which dissolves and releases the internal mortar upon contact with water to form a self-sealing seal; a rubber gasket is provided at the contact point between the lower end of the sand discharge pipe and the lower template, thereby reliably sealing the pipe opening during the pouring stage to prevent concrete from entering through the synergy of the pre-embedded sand discharge pipe and the self-dissolving seal, and automatically opening the sand discharge channel during the sand discharge stage, avoiding operational difficulties and pipe blockage caused by manual removal of the seal.

[0012] Preferably, the support frame adopts a socket-type disc-lock steel pipe support. Stability calculations are performed considering the equal volume load of sand filling the cavity and the live load from the construction of the upper slab. The total design load is not less than 12 kN / m. 2 This ensures the stability of the support system during the cavity sand filling and upper slab construction stages through scientific load calculations, thus meeting construction safety requirements.

[0013] Preferably, during the construction of the lower slab, an inflatable rubber sealing bladder is used instead of a traditional template caulking box for the gap between the two hanging slabs. The sealing bladder is a cylindrical hollow rubber product with an inflation pressure of 0.15MPa-0.20MPa. After inflation, it squeezes the pre-attached sponge strip to achieve a tight seal. Thus, through the elastic compression of the inflatable sealing bladder, a dynamic tight seal is formed in the gap between the hanging slabs, preventing grout leakage during pouring and accommodating minor displacements during concrete vibration.

[0014] Preferably, the reusable rigid thin-plate template is a fiber-reinforced cement board (GRC board) or an aluminum alloy honeycomb composite board. Before laying the GRC board, a release agent is applied to the bottom of the board, and the joints are sealed with self-adhesive butyl rubber waterproof tape. The board is temporarily fixed to the structural beam around its perimeter by angle steel strips. The aluminum alloy honeycomb composite boards are connected by mortise and tenon joints, with EPDM rubber sealing strips embedded at the joints. The board surface is treated with a fluorocarbon coating. Thus, through the high flatness of the rigid thin-plate template and the tight joints, the air bubble rate on the bottom surface of the upper board is controlled to within 1%, achieving the standard for fair-faced concrete finish. Moreover, the template can be reused, significantly reducing material consumption.

[0015] Preferably, the vacuum negative pressure suction uses an industrial-grade vacuum cleaner with a rated power of 2.5kW-3.5kW, a maximum vacuum degree of -0.07MPa to -0.09MPa, and an air volume of 160m³ / h. 3 / h-200m 3 / h; The high-pressure airflow fluidization uses a high-pressure air pipe to blow airflow into the sand layer at a pressure of 0.3MPa-0.4MPa, forming an upward blowing and downward suction fluidized sand discharge state. Thus, through the synergistic effect of vacuum negative pressure suction and high-pressure airflow fluidization, the sand layer is efficiently suctioned out in the fluidized state, with a sand discharge rate of over 98%, and it is suitable for standard rectangular and irregular hyperboloid complex cavities.

[0016] Preferably, after the sand is drained, the reusable rigid thin-plate template is removed for future use. The sand drainage holes are sealed by pressure injection of micro-expansion fine aggregate concrete from bottom to top. The expansion rate of the micro-expansion fine aggregate concrete is 0.03%-0.05%, and the strength grade is not lower than C35. Before injection, the hole wall is moistened with water. During injection, it is compacted in layers until the surface is flush with the bottom of the plate. Thus, by pressure injection from bottom to top, the sand drainage holes are densely filled in a narrow operating space. The sealing material is the same color as the base concrete, and there are no visible repair marks on the surface, meeting the appearance requirements of fair-faced concrete.

[0017] Preferably, the numerical simulation includes: using PFC 3D software to establish a cavity geometric model and a multi-spherical cluster particle model to simulate the sand layer filling and compaction process and determine the optimal sand layer compaction parameters; using the Fluent-EDEM coupling platform to establish a cavity flow field model to simulate the sand discharge process and optimize the sand discharge pipe arrangement spacing and adaptive quincunx arrangement scheme; using ABAQUS software to establish a composite structure model, using maturity-temperature coupled constitutive modeling to simulate the construction sequence and determine the timing of support removal, thereby replacing traditional experience-based judgment with multi-scale numerical simulation and realizing a technological leap from experience-based construction to quantitative construction.

[0018] Preferably, for the composite structure of irregular hyperboloid cavities, a geometric model of the hyperboloid cavity is established using PFC 3D software, with the radius of curvature of the surface varying from 5m to 15m. A multi-spherical cluster particle model is established to simulate actual sand particles, with a particle size distribution of 0.5mm-2mm and a normal stiffness kn=5×10. 7 N / m, tangential stiffness ks=2.5×10 7 N / m, friction coefficient μ=0.7; simulate different paving methods to determine the optimal process of layered paving combined with vibration compaction; establish a 1:1 hyperboloid cavity flow field model using the Fluent-EDEM coupling platform, with the inlet boundary at standard atmospheric pressure of 101325Pa and the outlet boundary at negative pressure of -0.05MPa, simulate the sand removal process and optimize the spacing of the sand removal pipes, densifying the spacing of the sand removal pipes to 600mm in areas with large curvature and widening it to 800mm in areas with gentle curvature, with an overall adaptive quincunx arrangement; establish a composite structure model using ABAQUS software, and use mature-temperature coupled constitutive simulation to simulate the construction sequence and determine the timing of support removal, thereby eliminating sand removal dead zones in low-lying areas of the curved surface through numerical simulation optimization for irregular hyperboloid cavities, ensuring the thoroughness of sand removal and construction safety in complex structures.

[0019] The beneficial effects of this invention are as follows: As can be seen from the above technical solution, this application provides a method for vacuum sand removal and reusable template construction of cavity composite structure. In view of the problem of low sand removal efficiency in the present invention, the present invention adopts an active sand removal mechanism of upward blowing and downward suction combined with high-pressure airflow fluidization, replacing the traditional gravity natural flow and blower blowing, thereby increasing the sand removal rate to more than 98%, effectively eliminating the dead corners of sand accumulation in the four corners of the cavity and the low depressions of the curved surface, significantly shortening the sand removal operation time and reducing labor intensity.

[0020] To address the issue of disposable formwork materials, this invention uses fiber-reinforced cement board or aluminum alloy honeycomb composite board as a reusable rigid thin-plate formwork to replace disposable waterproof film. This allows the formwork to be reused 10 to 30 times due to its high puncture resistance and excellent demolding performance, significantly reducing formwork material consumption and construction costs.

[0021] To address the problem of difficulty in guaranteeing the surface quality of existing fair-faced concrete, this invention uses a high-flatness rigid thin-plate formwork and a special release agent. The air bubble rate on the bottom surface of the upper plate is controlled to within 1%, and the sand drainage holes are sealed by pressure injection of micro-expansion fine aggregate concrete from bottom to top. This ensures the standard of fair-faced concrete finish while eliminating visible repair marks on the bottom surface of the lower plate, thus improving the building's aesthetic quality.

[0022] To address the lack of quantitative optimization basis for existing construction parameters, this invention introduces PFC 3D, Fluent-EDEM and ABAQUS multi-scale numerical simulation technology to quantitatively optimize sand layer compaction process, sand discharge pipe spacing and support removal timing, thereby replacing traditional experience-based judgment and improving the stability and controllability of construction quality.

[0023] To address the problem of poor environmental performance of existing sand-discharging systems, this invention employs vacuum negative pressure sand removal. The sand is collected in a relatively closed pipeline system and can be directly screened and reused, thereby avoiding dust pollution caused by traditional blowers and improving the working environment at the construction site. Attached Figure Description

[0024] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments: Figure 1 These are schematic diagrams illustrating the structural forms of the various composite plates of the present invention; Figure 2 This is a schematic diagram of the construction process of the hollow composite plate of the present invention. Figure 1 ; Figure 3 This is a schematic diagram of the construction process of the hollow composite plate of the present invention. Figure 2 ; Figure 4 This is a schematic diagram showing the final construction effect of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection claimed in this application. Example 1 This embodiment provides a construction method for vacuum sand removal and reusable templates for cavity composite structures, applicable to the construction of standard rectangular cavity composite structures.

[0026] Step 1: Composite Slab Structure Analysis and Construction Sequence Determination like Figure 1As shown, based on the construction drawings, the structural form and geometric parameters of the composite slab are analyzed: lower slab thickness 120mm, upper slab thickness 150mm, cavity clear height 400mm, structural beam spacing 6000mm×8000mm. The construction sequence is determined as follows: lower slab construction → support frame erection → sand removal system pre-embedding → sand layer filling → reusable formwork installation → upper slab construction → vacuum negative pressure sand removal → sand removal hole sealing.

[0027] Step Two: Installation of Lower Hanging Panels and Sealing System like Figure 2 As shown, the lower hanging board template is made of 15mm thick film-coated clear water plywood with standardized processing, and the surface flatness deviation of the template is ≤1mm / 2m.

[0028] The gap between the two mounting plates is sealed with an inflatable rubber bladder instead of the traditional formwork caulking box. The bladder is a cylindrical hollow rubber product with an outer diameter of 50mm, and its length matches the gap width. During installation, the bladder is placed in the gap and inflated to a pressure of 0.15MPa~0.20MPa. After inflation, the pre-attached sponge strip (10mm thick and 30mm wide) is squeezed to achieve a tight seal. The two ends of the bladder are fixed to the surrounding formwork with L-shaped connecting pieces to prevent displacement during concrete pouring.

[0029] The lower layer of slab reinforcement was tied according to conventional procedures. C30 fair-faced concrete with a slump of 160±20mm was used.

[0030] Step 3: Erection of support frame and pre-embedding of sand removal system like Figure 2 As shown, the support frame adopts a socket-type disc-lock steel pipe scaffold, with a column spacing of 900mm × 900mm and a step distance of 1500mm. Considering the equal volume load after filling the cavity with sand (sand density 18kN / m³), 3 The cavity height is 400mm, and the equivalent surface load is 7.2kN / m. 2 ) and the construction live load of the upper slab is 3kN / m 2 The total design load is taken as 12kN / m. 2 Stability calculations were performed to ensure compliance with the requirements of the "Safety Technical Specification for Socket-Type Disc-Type Steel Pipe Supports in Building Construction" (JGJ / T 231).

[0031] Pre-embedded sand drainage pipes: PVC sand drainage pipes with a diameter of 75mm and a wall thickness of 2.3mm are pre-embedded during the binding of the lower slab reinforcement. The sand drainage pipes are arranged in a quincunx pattern with a spacing of 800mm (determined through subsequent numerical simulation optimization). The lower end contacts the top surface of the lower formwork, and the upper end is flush with the top surface of the lower slab.

[0032] Sand discharge pipe sealing: The upper end of the sand discharge pipe is sealed with water-soluble PVA capsules. The capsules are cylindrical, 72mm in diameter and 30mm in height, and filled with micro-expansion cement mortar (expansion rate 0.05%). The capsules dissolve in water within 15-20 minutes, releasing the internal mortar to form a self-sealing seal. A rubber gasket is installed at the lower end of the sand discharge pipe where it contacts the lower formwork to prevent grout leakage during pouring.

[0033] The sand discharge pipe is fixed to the lower slab reinforcement by binding wire, with a verticality deviation of ≤5mm.

[0034] Step 4: Sand layer filling and compaction like Figure 2 As shown, after the lower slab concrete is poured and cured for 3 days, the strength reaches more than 30% of the design value, and then the sand layer is laid.

[0035] Dry medium-coarse sand (fineness modulus 2.3~3.0, moisture content <3%, mud content <1%) is used and laid in layers, with each layer being 200mm thick.

[0036] A plate vibratory compactor (1.5kW power, 2800 vibrations / min) was used for layered compaction, with each layer compacted at least three times. The compaction coefficient was tested on-site using the ring cutter method and controlled to be ≥0.95.

[0037] The top surface of the sand layer was leveled using a scraper, and the elevation was controlled to be the bottom elevation of the upper layer (allowable deviation ±5mm). The final sand layer thickness was 400mm, and the measured elastic modulus was calibrated to 105MPa through numerical simulation.

[0038] Step 5: Installation of reusable rigid thin-plate formwork like Figure 3 As shown, fiber-reinforced cement board (GRC board) was selected as the reusable bottom formwork, with dimensions of 1220mm×2440mm×8mm, flexural strength ≥15MPa, and impact strength ≥2.5kJ / m. 2 .

[0039] Before laying GRC slabs, apply a release agent (water-based release agent, application rate 0.15 kg / m²) to the bottom of the slabs. 2 ).

[0040] The joints of the GRC panels are sealed with self-adhesive butyl rubber waterproof tape (30mm wide and 1.5mm thick), with the center line of the tape aligned with the joint and rolled tightly.

[0041] The GRC panel is temporarily fixed to the structural beam around its perimeter using 30mm×30mm×3mm angle steel strips spaced 600mm apart, and is then fixed to the side of the structural beam using M6 expansion bolts.

[0042] When laying the upper layer of steel reinforcement on the GRC slab, mortar spacers (strength ≥ C30, thickness 15~20mm) should be placed between the steel reinforcement and the slab surface. The spacers should be arranged in a staggered pattern with a spacing of 800mm×800mm to prevent the steel reinforcement from piercing the GRC slab.

[0043] Step Six: Pouring and Curing of the Upper Slab Concrete like Figure 3 As shown, after the upper slab reinforcement is inspected and approved, C30 fair-faced concrete is poured with a slump of 160±20mm.

[0044] Concrete pouring is carried out using pumping, ensuring uniform material distribution and avoiding concentrated load impact on the GRC slabs.

[0045] Concrete vibration is performed using a Φ50mm immersion vibrator with a vibration spacing of 400mm. The vibrator should be inserted quickly and withdrawn slowly to avoid touching the GRC slab.

[0046] After the concrete is poured, cover it with plastic film to keep it moist and cure it for no less than 7 days.

[0047] Step 7: Vacuum negative pressure sand removal like Figure 3 As shown, sand removal operations will begin once the concrete strength of the upper slab reaches more than 75% of the design value (approximately 7 days, verified by numerical simulation).

[0048] Remove the lower formwork to expose the lower end of the sand discharge pipe.

[0049] The lower end of the sand discharge pipe is connected to an industrial-grade vacuum cleaner (rated power 3kW, maximum vacuum degree -0.08MPa, air volume 180m³ / h). 3 / h), the dust suction pipe and the sand discharge pipe are connected by a reducing joint (75mm→50mm) for sealing.

[0050] At the same time, a high-pressure air pipe (0.3MPa~0.4MPa) is inserted through the pre-drilled hole at the top of the cavity (or intermittently through the sand discharge pipe) to blow airflow into the sand layer, causing the sand to fluidize.

[0051] A fluidized sand discharge state of "blowing from above and sucking from below" is formed. The sand is collected into a sand collection bag by a vacuum cleaner and can be screened and reused.

[0052] The single-point sand removal time is approximately 8-12 minutes, and the total sand removal area of ​​the cavity is approximately 48m². 2 The total sand removal time was approximately 2.5 hours, and the actual sand removal rate was 98.6%.

[0053] Step 8: Sealing and Surface Treatment of Sand Drainage Holes like Figure 4 As shown, after the sand is drained, the GRC panels are removed (for future reuse, with an estimated reuse count of ≥10 times).

[0054] Inspect the bottom surface of the lower shelf; remove any remaining sand particles with a soft brush.

[0055] The sand drainage holes were sealed by pressure injection from bottom to top using micro-expansion fine aggregate concrete (expansion rate 0.04%, strength C35). Before injection, the hole walls were moistened with water, and during injection, the concrete was compacted in layers until the surface was flush with the bottom of the slab.

[0056] After sealing, allow it to cure for 3 days, then perform minor repairs on the bottom surface of the lower slab (using cement putty of the same color), and apply two coats of fair-faced concrete protective agent to the entire surface.

[0057] Numerical simulation optimization Key parameters were determined through numerical simulation before construction: PFC 3D software was used to establish a cavity geometric model and a multi-spherical cluster particle model to simulate the sand layer filling and compaction process and determine the optimal sand layer compaction parameters.

[0058] A cavity flow field model was established using the Fluent-EDEM coupling platform to simulate the sand discharge process and optimize the spacing of the sand discharge pipes and the adaptive quincunx arrangement scheme.

[0059] An ABAQUS software was used to establish a composite structure model. The mature-temperature coupled constitutive model (CEB-FIP model) was used to simulate the construction sequence. The hydration heat parameter Q∞=330kJ / kg and the activation energy Ea=33.5kJ / mol were used. The step-by-step activation unit simulated the activation of the lower slab, sand layer, upper slab pouring and upper slab activation stages to determine the timing of support removal.

[0060] Example 2 In this embodiment, the construction scenario is a project with a tight schedule and high requirements for turnover. Therefore, the reusable rigid thin-plate formwork is replaced with an aluminum alloy honeycomb composite panel, with dimensions of 1200mm × 2400mm × 10mm. The panel is made of 0.8mm thick 3003-H14 aluminum alloy, and the core layer is aluminum honeycomb (honeycomb side length 6mm, foil thickness 0.06mm), with a bending stiffness ≥500kN·mm. 2 / m; The aluminum alloy panels are connected by mortise and tenon joints, with EPDM rubber sealing strips embedded at the joints, and the surface is treated with fluorocarbon coating; assembly and disassembly are carried out using special clamps and fixed to the structural beams, with an expected turnover rate of ≥30 times. The above adjustments only changed the material and connection and fixing method of the reusable template, while the core construction logic of vacuum negative pressure suction combined with high-pressure airflow fluidization sand removal, water-soluble PVA capsule self-sealing, bottom-up pressure injection sealing, and numerical simulation optimization of construction parameters remains unchanged. Thus, in projects with higher turnover requirements, aluminum alloy honeycomb composite panels can achieve the same molding quality and sand removal effect as fair-faced concrete, and the turnover rate is significantly improved.

[0061] Example 3 In this embodiment, the construction scenario is a standard rectangular cavity stacked structure, eliminating the need for hyperboloid adaptive layout considerations. Therefore, the spacing of the sand discharge pipes is uniformly adjusted to a standard 800mm quincunx pattern, and the adaptive densification scheme for changes in surface curvature is eliminated. In the numerical simulation, only PFC 3D and ABAQUS are used to analyze the compaction parameters and construction sequence of the standard rectangular cavity; Fluent-EDEM hyperboloid flow field optimization is not enabled. These adjustments only change the adaptation strategy for the sand discharge pipe layout and the enabled modules for numerical simulation. The core construction logic—pre-embedded sand discharge pipes combined with water-soluble PVA capsules for self-sealing, vacuum negative pressure combined with high-pressure airflow for fluidized sand discharge, reusable rigid thin-plate templates, and bottom-up pressure injection sealing—remains unchanged. This simplifies the numerical simulation process in the construction of the standard rectangular cavity, achieving the same sand discharge efficiency and construction quality with a conventional layout.

[0062] Example 4 In this embodiment, the construction scenario involves the alternative application of sealing materials for sand drainage pipes. Instead of the water-soluble PVA capsules used for sealing the upper end of the sand drainage pipe, other water-soluble sealing materials (such as polyvinyl alcohol film-wrapped micro-expansion mortar clumps) are used. These materials automatically dissolve and release upon contact with water, forming a self-sealing seal. This adjustment only changes the specific form of the water-soluble sealing material; the core construction logic remains unchanged: pre-embedded sand drainage pipes, vacuum negative pressure suction combined with high-pressure airflow fluidization for sand drainage, reusable rigid thin-plate formwork as the upper slab bottom mold, and pressure injection sealing from bottom to top. Thus, under different material supply conditions, an equivalent water-soluble self-sealing mechanism achieves the same pipe opening sealing and automatic opening effect for the sand drainage channel.

[0063] The above are merely embodiments provided in this application and are not intended to limit this application. Although this application has been described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. However, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A construction method for a cavity-overlapping structure with vacuum sand removal and reusable formwork, characterized in that, In the construction of cavity composite structures, vacuum negative pressure suction combined with high-pressure airflow fluidization is used to remove the sand layer filling the cavity. A reusable rigid thin plate formwork is used as the bottom formwork for the upper slab pouring. The construction parameters are optimized through numerical simulation, including the following steps: During the construction of the lower slab, a sand discharge pipe is pre-embedded. The upper end of the sand discharge pipe is sealed with a water-soluble sealing material, and the lower end extends to the bottom surface of the lower slab. A support frame is erected above the lower plate, and sand is filled into the cavity formed at the top of the support frame and compacted in layers. A reusable rigid thin plate formwork is laid on the top surface of the sand layer as the bottom formwork for the pouring of the upper slab; After the upper concrete slab reaches the preset strength, the sand layer is discharged through the sand discharge pipe by vacuum negative pressure suction combined with high-pressure airflow fluidization, forming a cavity; The sand discharge pipe was sealed by pressure injection from bottom to top; Before construction, numerical simulation was used to determine the compaction parameters of the sand layer, the spacing of the sand discharge pipes, and the timing of the support removal.

2. The construction method for vacuum sand removal and reusable formwork of the cavity composite structure according to claim 1, characterized in that: The sand discharge pipe is a PVC pipe with a diameter of 70mm-80mm, arranged in a quincunx pattern; the water-soluble sealing material is a water-soluble PVA capsule, the capsule is filled with micro-expansion cement mortar, which dissolves and releases the internal mortar upon contact with water to form a self-sealing seal; a rubber gasket is installed at the contact point between the lower end of the sand discharge pipe and the lower template.

3. The construction method for vacuum sand removal and reusable formwork of the cavity composite structure according to claim 1, characterized in that: The support frame adopts a socket-type disc-lock steel pipe support. Stability calculations are performed considering the equal volume load of sand filling the cavity and the live load from the construction of the upper slab. The total design load is not less than 12kN / m. 2 .

4. The method for constructing a cavity composite structure with vacuum sand removal and reusable formwork according to claim 1, characterized in that: During the construction of the lower slab, an inflatable rubber sealing bladder is used to replace the traditional template caulking box in the gap between the two hanging boards. The sealing bladder is a cylindrical hollow rubber product with an inflation pressure of 0.15MPa-0.20MPa. After inflation, the pre-attached sponge strip is squeezed to achieve a tight seal.

5. The method for constructing a cavity composite structure with vacuum sand removal and reusable formwork according to claim 1, characterized in that: The reusable rigid thin-plate template is a fiber-reinforced cement board, i.e., GRC board, or an aluminum alloy honeycomb composite board; before laying the GRC board, a release agent is applied to the bottom of the board, and the joints of the board are sealed with self-adhesive butyl rubber water-stop tape. The board is temporarily fixed to the structural beam around the perimeter by angle steel strips; the aluminum alloy honeycomb composite boards are connected by mortise and tenon joints, and EPDM rubber sealing strips are embedded at the joints. The surface of the board is treated with fluorocarbon coating.

6. The construction method for vacuum sand removal and reusable formwork of the cavity composite structure according to claim 1, characterized in that: The vacuum negative pressure suction uses an industrial-grade vacuum cleaner with a rated power of 2.5kW-3.5kW, a maximum vacuum degree of -0.07MPa to -0.09MPa, and an air volume of 160m³ / h. 3 / h-200m 3 / h; The high-pressure airflow fluidization adopts the method of blowing airflow into the sand layer through a high-pressure air pipe, with an air pressure of 0.3MPa-0.4MPa, to form an upward blowing and downward suction fluidized sand discharge state.

7. The method for constructing a cavity composite structure with vacuum sand removal and reusable formwork according to claim 1, characterized in that: After the sand is drained, the reusable rigid thin plate template is removed for future use. The sand drain hole is sealed by pressure injection of micro-expansion fine stone concrete from bottom to top. The expansion rate of the micro-expansion fine stone concrete is 0.03%-0.05%, and the strength grade is not lower than C35. The hole wall is moistened with water before injection, and compacted in layers during injection, with the surface flush with the bottom of the plate.

8. The construction method for vacuum sand removal and reusable formwork of the cavity composite structure according to claim 1, characterized in that: The numerical simulation includes: using PFC 3D software to establish a cavity geometric model and a multi-spherical cluster particle model to simulate the sand layer filling and compaction process and determine the optimal sand layer compaction parameters; using the Fluent-EDEM coupling platform to establish a cavity flow field model to simulate the sand discharge process and optimize the sand discharge pipe arrangement spacing and adaptive quincunx arrangement scheme; using ABAQUS software to establish a composite structure model and using maturity-temperature coupled constitutive model to simulate the construction sequence and determine the timing of support removal.

9. The method for constructing a cavity composite structure with vacuum sand removal and reusable formwork according to claim 8, characterized in that: For the composite structure of irregular hyperboloid cavities, a geometric model of the hyperboloid cavity was established using PFC 3D software. The radius of curvature of the surface varied from 5m to 15m. A multi-spherical cluster particle model was established to simulate actual sand particles with a particle size distribution of 0.5mm-2mm and a normal stiffness kn=5×10. 7 N / m, tangential stiffness ks=2.5×10 7 N / m, friction coefficient μ=0.7; simulate different paving methods to determine the optimal process of layered paving combined with vibration compaction, and control porosity and angle of repose; use the Fluent-EDEM coupling platform to establish a 1:1 hyperboloid cavity flow field model, with the inlet boundary at standard atmospheric pressure of 101325Pa and the outlet boundary at negative pressure of -0.05MPa, to simulate the sand discharge process and optimize the spacing of the sand discharge pipes. The spacing of the sand discharge pipes is increased to 600mm in areas with large curvature and increased to 800mm in areas with gentle curvature, with an overall adaptive quincunx arrangement; use ABAQUS software to establish a composite structure model, and use maturity-temperature coupled constitutive model to simulate the construction sequence and determine the timing of support removal.

10. A cavity-composite structure vacuum sand removal and reusable formwork construction system, characterized in that, include: The sand discharge pipe is embedded in the lower slab, with its lower end extending to the bottom surface of the lower slab and its upper end flush with the top surface of the lower slab. A water-soluble sealing material is applied to the upper end of the sand discharge pipe; Support frame, erected above the lower slab; Reusable rigid thin plate formwork is laid on the top surface of the sand layer as the bottom formwork for the pouring of the upper slab; A vacuum suction device is used to connect to the lower end of the sand discharge pipe and provide a vacuum negative pressure; High-pressure air source, used to blow high-pressure airflow into the sand layer from the top of the cavity; A rubber gasket is provided at the contact point between the lower end of the sand discharge pipe and the lower template.

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