Method for pouring concrete with abrupt change cross section

Abstract

The invention discloses an abrupt change section concrete pouring method which comprises the following steps: optimizing performance parameters of each layer of concrete according to a section abrupt change coefficient K through an integrated process of abrupt change section parameterization analysis, concrete mix proportion gradient design, adjustable template support, layered synchronous pouring and intelligent maintenance; the transition connection layer gives consideration to fluidity and bonding strength, the large-section main body layer optimizes compactness and heat dissipation performance, and the small-section main body layer improves strength and impermeability; in cooperation with flexible formwork supporting and ultrasonic-assisted vibration, seamless connection, uniformity and compactness of the abrupt change part are achieved; the intelligent maintenance system accurately controls the temperature and the humidity, and the crack risk is reduced. According to the invention, the bonding strength (greater than or equal to 1.5 MPa) and the compactness (the void ratio is less than or equal to 2%) of the concrete with the abrupt change cross section are obviously improved, the crack occurrence rate is reduced by 85% or more, the construction efficiency is improved by 40%, and the concrete is suitable for construction of structures such as industrial plant brackets, bridge pier stud variable cross sections and high-rise building transfer floors.

Description

Technical Field

[0001] This invention relates to the field of concrete pouring technology, and more specifically, to a method for pouring concrete with abrupt cross-sections. Background Technology

[0002] Concrete pouring is the construction process of pouring concrete into a mold until it is plasticized. It is widely used in civil engineering projects. It usually uses P.S42.5 slag silicate cement, combined with fine sand, 16-30mm aggregate, and FJ-1 pumping agent. Before construction, it is necessary to complete preparatory work such as operator training.

[0003] In construction engineering, abruptly changed cross-section concrete structures (such as corbels, piers with variable cross-sections, and transfer floors) often involve designs with sudden increases or decreases in cross-sectional dimensions due to stress requirements. Traditional casting methods often employ either monolithic, one-time casting or segmented casting followed by secondary connection, but these methods suffer from several technical drawbacks: First, the flowability and setting time of the concrete at the abrupt change are mismatched, resulting in insufficient bond strength at the interface and a tendency for cold joints and shrinkage cracks to form. Second, uneven compaction between large and small cross-sections leads to honeycomb-like pitting in small sections due to insufficient vibration, while large sections are prone to temperature cracks due to poor heat dissipation. Third, insufficient rigidity of formwork support causes stress concentration at the abrupt change, easily leading to formwork deformation and affecting the structural dimensional accuracy. Fourth, inadequate curing measures result in rapid moisture evaporation at the interface, further exacerbating crack formation. These problems severely impact the load-bearing capacity and durability of abruptly changed cross-section structures, limiting the application scope of traditional methods.

[0004] Therefore, there is an urgent need for a method for pouring concrete with abrupt cross-sections that can overcome the above-mentioned technical defects. Summary of the Invention

[0005] To address the problems existing in the prior art, the purpose of this invention is to provide a method for pouring concrete with abrupt cross-sections, thereby achieving seamless connection and uniform compaction of the concrete at the abrupt section and improving construction quality.

[0006] The present invention adopts the following technical solution:

[0007] A method for pouring concrete with abruptly changed cross-sections includes the following steps:

[0008] Step S1: Parametric analysis of abrupt change cross sections

[0009] A three-dimensional model of the abrupt cross section is established using BIM technology, the abrupt cross section coefficient K is calculated, and the transition layer, the large cross section main layer, and the small cross section main layer are divided.

[0010] Step S2: Concrete mix design with gradient

[0011] The transition layer has a water-cement ratio of 0.38-0.42 and a slump of 180-200 mm, with the addition of 0.05-0.1% polycarboxylate retarder. Its 28-day compressive strength is 5-10 MPa higher than that of the main layer with a large cross-section. The main layer with a large cross-section has a water-cement ratio of 0.43-0.47 and a slump of 160-180 mm, with the addition of 0.03-0.05% air-entraining agent. The main layer with a small cross-section has a water-cement ratio of 0.35-0.38 and a slump of 140-160 mm, with the addition of 5-8% silica fume.

[0012] Step S3: Adjustable formwork support

[0013] The modular steel formwork is used, with a 5-8mm thick flexible rubber pad for the transition layer. The verticality deviation of the formwork is controlled to be ≤3mm / m through a hydraulic jacking system, and the splice joints are sealed with water-swellable waterstop strips.

[0014] Step S4: Layered synchronous pouring

[0015] First, pour the main layer with a small cross-section, then pour the transition and connection layer simultaneously, and finally pour the main layer with a large cross-section in layers.

[0016] Step S5, Intelligent Maintenance

[0017] Cover with a moisturizing film 4-6 hours after pouring, monitor the internal temperature with a temperature sensor, start spraying if the temperature difference between the inside and outside exceeds 25℃, and cure for ≥14 days. The transition layer requires additional steam curing.

[0018] Furthermore, in step S1, the thickness of the transition layer is 0.3-0.5 times the side length of the small cross section; in step S5, the curing conditions are: 40-50℃, humidity ≥90%, 3 days.

[0019] Furthermore, in step S2, the transition layer adopts a dual-blending technology, in which 2-3% fly ash is added in addition to the retarder.

[0020] Furthermore, in step S4, ultrasonic-assisted vibration is applied only to the interface between the transition layer and the main body layer with a large cross section, and each pouring layer is vibrated for 30-60 seconds.

[0021] Furthermore, in step S5, the temperature sensors are spaced 500-800mm apart, and the monitoring data is transmitted to the control system in real time to automatically adjust the spray frequency and steam supply.

[0022] Furthermore, in step S1, when the cross-sectional change coefficient K≥5, the thickness of the transition layer is 0.4-0.5 times the side length of the smaller cross-section, and a Φ6-8mm steel mesh is set in the transition layer with a spacing of 100-150mm.

[0023] Furthermore, in step S2, the silica fume of the small cross-section main layer is made of nano-sized silica fume with a specific surface area ≥20000m² / kg.

[0024] Furthermore, in step S3, the hydraulic jacking system is equipped with a pressure sensor to monitor the lateral pressure of the template in real time, and automatically initiates pressure relief regulation when the pressure exceeds 30kN / m².

[0025] Furthermore, in step S4, during the layered synchronous pouring, the pouring height difference between the small cross-section main layer and the transition connection layer is controlled to be ≤100mm.

[0026] Furthermore, in step S5, the steam curing adopts a segmented heating mode, with an initial heating rate of ≤10℃ / h for the first 2 hours, constant temperature curing after reaching 40-50℃, and a cooling rate of ≤8℃ / h at the end.

[0027] Beneficial effects

[0028] This invention integrates a process of cross-sectional gradient division, dynamic mix ratio adaptation, layered synchronous pouring, and intelligent vibration curing. It optimizes various performance parameters of concrete based on the dimensional change coefficient of abrupt cross sections. Combined with an adjustable flexible formwork support system and ultrasonic-assisted vibration technology, it achieves seamless connection and uniform compaction of concrete at abrupt sections, solving the problems of insufficient bonding and uneven compaction at the interface in traditional methods.

[0029] This invention proposes the principle of fluidity gradient matching. Through the special design of the transition layer, a good transition is formed between the upper and lower sections of concrete at the point of abrupt change, the bond strength is increased to ≥1.5MPa, the cracking rate is reduced by more than 85%, and the construction efficiency is increased by 40%. It is applicable to the construction of various abrupt cross-section concrete structures such as corbels of industrial plants, variable cross-section bridge piers, and transfer layers of high-rise buildings, and has significant practical and economic value.

[0030] This invention is the first to combine BIM parametric analysis, ultrasonic-assisted vibration, and gradient mix design to form an integrated casting technology. The synergistic effect of each process step breaks through the technical bottleneck of traditional casting methods. Attached Figure Description

[0031] Figure 1 This is a flowchart of the preliminary preparation stage of an embodiment of the present invention;

[0032] Figure 2 This is a flowchart of the core construction stage of an embodiment of the present invention;

[0033] Figure 3 This is a flowchart illustrating the layered synchronous casting process according to an embodiment of the present invention;

[0034] Figure 4 This is a flowchart of the intelligent maintenance stage according to an embodiment of the present invention;

[0035] Figure 5 This is a flowchart of a quality inspection process according to an embodiment of the present invention;

[0036] Figure 6 This is a flowchart of a casting method according to an embodiment of the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0038] As shown in the figure, this invention discloses a method for pouring concrete with abrupt cross-sections, comprising the following steps:

[0039] Step S1: Parametric analysis of abrupt change cross sections

[0040] A 3D model of the abrupt section is established using BIM technology, and the abrupt change coefficient K (K = area of ​​the large section / area of ​​the small section) is calculated. This allows for the division into a transition layer, a main layer with a large section, and a main layer with a small section. The thickness of the transition layer is 0.3-0.5 times the side length of the small section. When the abrupt change coefficient K ≥ 5, the thickness of the transition layer is 0.4-0.5 times the side length of the small section. Φ6-8mm steel mesh is installed within the transition layer, with a spacing of 100-150mm, to strengthen the shear resistance of the interface. Parametric analysis clarifies the stress characteristics and construction requirements of each layer, providing a precise basis for subsequent mix design, formwork support, and pouring processes, avoiding the blindness of traditional division methods.

[0041] Step S2: Concrete mix design with gradient

[0042] The water-cement ratio of the transition layer is 0.38-0.42, the slump is 180-200mm, and 0.05-0.1% polycarboxylate retarder is added. In addition to the retarder, 2-3% fly ash is added. The 28-day compressive strength is 5-10MPa higher than that of the main layer with a large cross section, which balances fluidity and bonding strength and avoids cold joints at the bonding surface.

[0043] For large-section main layers, the water-cement ratio is 0.43-0.47, the slump is 160-180mm, and 0.03-0.05% air-entraining agent is added to optimize concrete density and heat dissipation, reducing the risk of temperature cracks.

[0044] The main layer of small cross-section concrete has a water-cement ratio of 0.35-0.38 and a slump of 140-160mm. It incorporates 5-8% of nano-sized silica fume with a specific surface area ≥20000m² / kg to generate dense hydrated calcium silicate gel, thereby improving the strength and impermeability of concrete. Other slump parameters can be selected, but the standard is ±180mm.

[0045] Step S3: Adjustable formwork support

[0046] Modular steel formwork is used, with 5-8mm thick flexible rubber pads installed at corresponding positions in the transition layer to absorb the lateral pressure of pouring. The formwork joints are sealed with water-swellable sealing strips to prevent grout leakage. A hydraulic jacking system and pressure sensors are provided to monitor the lateral pressure of the formwork in real time (threshold 30kN / ㎡). When the pressure exceeds the limit, the system automatically releases pressure and adjusts, while controlling the verticality deviation of the formwork to ≤3mm / m to ensure the accuracy of structural dimensions.

[0047] Step S4: Layered synchronous pouring

[0048] First, pour the main layer with a small cross-section (300-500mm high, vibrated with an immersion vibrator at 50-60Hz), then pour the transition layer simultaneously (using a concrete placing machine at a speed of 0.8-1.2m / h). Finally, pour the main layer with a large cross-section in layers, each layer being 200-300mm thick, using ultrasonic-assisted vibration at 300-500W, and vibrating each layer for 30-60 seconds to eliminate air bubbles and voids at the bonding surface.

[0049] During layered synchronous pouring, the pouring height difference between the main layer with small cross-section and the transition layer is controlled to be ≤100mm to ensure that the two layers of concrete fuse before initial setting.

[0050] Step S5, Intelligent Maintenance

[0051] Cover with a moisturizing film 4-6 hours after pouring, and install temperature sensors with a spacing of 500-800mm. The temperature sensors monitor the internal temperature. If the temperature difference between the inside and outside exceeds 25℃, start the spraying. Cure for ≥14 days, and provide additional steam curing for the transition layer.

[0052] In step S5, the curing conditions are: 40-50℃, humidity ≥90%, 3 days.

[0053] Steam curing adopts a segmented heating mode. The initial heating rate is ≤10℃ / h for the first 2 hours, and constant temperature curing is carried out after reaching 40-50℃. At the end, the cooling rate is ≤8℃ / h to avoid temperature stress cracking.

[0054] Example 1: Casting of corbel abrupt cross-section in industrial plant (K=4, high load scenario)

[0055] I. Engineering Parameters and Preliminary Preparations

[0056] 1. Cross-sectional parameters: The small cross-section of the corbel is 400mm×500mm (long side 500mm), and the large cross-section is 1000mm×800mm. The cross-sectional change coefficient K = (1000×800) / (400×500) = 4. The thickness of the transition layer is 0.4 times the long side of the small cross-section, i.e. 200mm. No additional steel mesh is required (K < 5).

[0057] 2. Material preparation:

[0058] Cement: P・O42.5 ordinary Portland cement;

[0059] Aggregates: crushed stone (16-30mm continuous gradation), medium sand (fineness modulus 2.6-2.8);

[0060] Admixtures: Polycarboxylate retarder (40% solids content), air-entraining agent (calcium lignosulfonate);

[0061] Admixtures: Grade II fly ash, nano-grade silica fume (specific surface area 22000 m2 / kg);

[0062] Template: Modular steel template (6mm thick), 5mm thick flexible rubber pad, water-swellable waterstop strip (20mm wide).

[0063] Equipment: BIM modeling software (Revit), hydraulic jacking system (with pressure sensor), immersion vibrator (55Hz), ultrasonic vibrator (400W), temperature sensor (accuracy ±0.5℃), spraying system, steam curing equipment.

[0064] II. Specific Construction Steps

[0065] 1. Parametric analysis of abrupt cross sections: A 3D model of the corbel is created using Revit, the boundaries of each layer and the location of the reinforcement are marked, the cross-sectional dimension data is exported, and the range of the transition connection layer is determined to be the area 200mm above the top of the small cross section.

[0066] 2. Concrete mix design (by mass):

[0067] Transition layer: Cement: Sand: Crushed stone: Water: Fly ash: Retarder = 1:1.8:3.2:0.40:0.03:0.0008, slump 190mm, 28d design compressive strength 45MPa;

[0068] Large cross-section main layer: cement: sand: crushed stone: water: air-entraining agent = 1:2.0:3.5:0.45:0.0004, slump 170mm, 28d design compressive strength 40MPa;

[0069] Small cross-section main layer: cement: sand: crushed stone: water: silica fume = 1:1.6:3.0:0.37:0.06, slump 150mm, 28d design compressive strength 50MPa.

[0070] 3. Template support installation:

[0071] The steel formwork is positioned and assembled according to the BIM model. Flexible rubber gaskets are pasted on the inside of the transition layer, and water-swellable waterstop strips are embedded in the splice joints to ensure a tight seal.

[0072] Install the hydraulic jacking system at 800mm intervals, start the pressure sensor calibration, set the lateral pressure threshold to 30kN / m², and adjust the verticality of the template to a deviation of ≤2mm / m.

[0073] 4. Layered synchronous pouring:

[0074] Before pouring, moisten the formwork and base layer. Start pouring the main layer with a small cross section first. Use a chute to place the concrete, with a pouring height of 400mm. Insert the immersion vibrator to a depth of 50mm into the lower layer of concrete, and vibrate for 20-30 seconds per point at a spacing of 300mm to avoid missing any vibration.

[0075] Simultaneously start the pouring of the transition layer, and the concrete placing machine evenly distributes the concrete along the transition layer. The pouring speed is maintained at 1.0m / h, and the height difference between the pouring and the small section is controlled at 80mm to ensure that the two layers of concrete are in a plastic state.

[0076] After the small section and the connecting layer are poured, the main layer of the large section is poured in layers, each layer is 250mm thick. The material is placed from the side away from the connecting layer toward the connecting layer. The ultrasonic vibrator is turned on in the joint area and each layer is vibrated for 45 seconds. After the vibration is completed, the surface is leveled with a scraper.

[0077] 5. Intelligent maintenance:

[0078] Five hours after pouring, cover with a moisturizing film and place three temperature sensors (600mm apart) at different heights of the corbel, transmitting the data to the control system in real time.

[0079] For the first 7 days, spray three times a day (30 minutes each time). When the temperature difference between inside and outside reaches 26℃, the spraying frequency will be automatically increased to once every 2 hours.

[0080] Steam curing of the transition layer: initially raise the temperature to 30℃ in 2 hours (heating rate 8℃ / h), then raise the temperature to 45℃ at 5℃ / h, maintain the temperature for 3 days (humidity 95%), and finally cool down to ambient temperature at 6℃ / h.

[0081] The total maintenance cycle is 14 days. During this period, the integrity of the moisturizing film should be checked regularly to prevent moisture loss.

[0082] III. Testing and Verification Results

[0083] Dimensional deviations: Measured using a laser rangefinder, the cross-sectional dimensional deviation of the bracket is ≤4mm, and the perpendicularity deviation is 2mm / m, which meets the design requirements;

[0084] Mechanical properties: Core samples were taken after 28 days. The bond strength between the transition layer and the small section interface was 1.8 MPa, the compressive strength of the concrete in the small section was 52.3 MPa, and that in the large section was 41.7 MPa.

[0085] Density and cracks: The porosity is 1.5% as determined by ultrasonic testing, and no visible cracks are observed by the naked eye. The impermeability grade is P10, and the frost resistance grade is F250, meeting the high load and high durability requirements of industrial plants.

[0086] Example 2: Variable cross-section casting of bridge piers (K=4, large volume scenario)

[0087] I. Engineering Parameters and Preliminary Preparations

[0088] 1. Section parameters: The small section diameter of the pier column is 800mm, the large section diameter is 1600mm, and the section change coefficient K = (π×800² / 4) / (π×400² / 4) = 4; the thickness of the transition layer is 0.375 times the small section diameter, i.e. 300mm (K<5, no need to add steel mesh).

[0089] 2. Materials and equipment: Same as in Example 1, except that the template is changed to an arc-shaped steel template, the steam curing constant temperature is 48℃, and the curing cycle is extended to 21 days.

[0090] II. Specific Construction Steps

[0091] 1. Parametric Analysis and Mix Proportion Adjustment: BIM modeling determined the transition layer to be a 300mm annular area upwards from the top of the small section. The concrete mix proportion was adjusted as follows:

[0092] Transition layer: water-cement ratio 0.41, slump 185mm, 28-day design compressive strength 44MPa;

[0093] Large cross-section main layer: water-cement ratio 0.46, slump 165mm, 28d design compressive strength 39MPa;

[0094] Small cross-section main layer: water-cement ratio 0.36, slump 145mm, 28-day design compressive strength 51MPa.

[0095] 2. Formwork and pouring process:

[0096] A 6mm flexible rubber pad is pasted on the inside of the arc-shaped steel formwork, and the hydraulic jacking system is evenly arranged along the circumference (600mm spacing), with verticality deviation controlled to ≤3mm / m;

[0097] Small cross-sections and transition layers are poured simultaneously, using guide pipes for material placement (to avoid segregation), with a pouring speed of 0.9 m / h and a height difference of ≤90 mm; large cross-sections are layered with a thickness of 280 mm, using an ultrasonic vibrator with a power of 450 W, and each layer is vibrated for 50 seconds.

[0098] 3. Intelligent maintenance:

[0099] Temperature sensors are arranged radially along the pier (700mm spacing), with a total of 4 monitoring points;

[0100] Steam curing was performed at a constant temperature of 48°C and a humidity of 92%, with the same segmented heating / cooling rates as in Example 1, and a total curing cycle of 21 days.

[0101] III. Testing and Verification Results

[0102] Dimensional deviations: Pier diameter deviation ≤ 5mm, verticality deviation 2.5mm / m;

[0103] Mechanical properties: Bond strength at the interface is 1.7 MPa, compressive strength of small section is 53.1 MPa, and compressive strength of large section is 40.2 MPa;

[0104] Durability: Porosity 1.8%, no temperature cracks, impermeability grade P8, freeze-thaw resistance grade F200, meeting the durability requirements for outdoor service in bridge engineering.

[0105] The above description is merely a preferred embodiment of the present invention; however, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concepts, should be covered within the scope of protection of the present invention.

Claims

1. A method for pouring concrete with abruptly changed cross-sections, characterized in that, Includes the following steps: Step S1: Parametric analysis of abrupt change cross sections A three-dimensional model of the abrupt cross section is established using BIM technology, the abrupt cross section coefficient K is calculated, and the transition layer, the large cross section main layer, and the small cross section main layer are divided. Step S2: Concrete mix design with gradient The transition layer has a water-cement ratio of 0.38-0.42 and a slump of 180-200 mm, with the addition of 0.05-0.1% polycarboxylate retarder. Its 28-day compressive strength is 5-10 MPa higher than that of the main layer with a large cross-section. The main layer with a large cross-section has a water-cement ratio of 0.43-0.47 and a slump of 160-180 mm, with the addition of 0.03-0.05% air-entraining agent. The main layer with a small cross-section has a water-cement ratio of 0.35-0.38 and a slump of 140-160 mm, with the addition of 5-8% silica fume. Step S3: Adjustable formwork support The modular steel formwork is used, with a 5-8mm thick flexible rubber pad for the transition layer. The verticality deviation of the formwork is controlled to be ≤3mm / m through a hydraulic jacking system, and the splice joints are sealed with water-swellable waterstop strips. Step S4: Layered synchronous pouring First, pour the main layer with a small cross-section, then pour the transition and connection layer simultaneously, and finally pour the main layer with a large cross-section in layers. Step S5, Intelligent Maintenance Cover with a moisturizing film 4-6 hours after pouring, monitor the internal temperature with a temperature sensor, start spraying if the temperature difference between the inside and outside exceeds 25℃, and cure for ≥14 days. The transition layer requires additional steam curing.

2. The method for pouring concrete with abruptly changed cross-section according to claim 1, characterized in that, In step S1, the thickness of the transition layer is 0.3-0.5 times the side length of the small cross section; in step S5, the curing conditions are: 40-50℃, humidity ≥90%, 3 days.

3. The method for pouring concrete with abrupt cross-section according to claim 1, characterized in that, In step S2, the transition layer adopts a dual-blending technology, which incorporates 2-3% fly ash in addition to the retarder.

4. The method for pouring concrete with abrupt cross-section according to claim 1, characterized in that, In step S4, ultrasonic-assisted vibration is applied only to the interface between the transition layer and the main body layer with a large cross section, and each pouring layer is vibrated for 30-60 seconds.

5. The method for pouring concrete with abrupt cross-section according to claim 1, characterized in that, In step S5, the temperature sensors are spaced 500-800mm apart, and the monitoring data is transmitted to the control system in real time to automatically adjust the spray frequency and steam supply.

6. The method for pouring concrete with abruptly changed cross-section according to claim 1, characterized in that, In step S1, when the cross-sectional change coefficient K≥5, the thickness of the transition layer is 0.4-0.5 times the side length of the smaller cross-section, and a Φ6-8mm steel mesh is set in the transition layer with a spacing of 100-150mm.

7. The method for pouring concrete with abrupt cross-section according to claim 1, characterized in that, In step S2, the silica fume of the small cross-section main layer is made of nano-sized silica fume with a specific surface area ≥20000m² / kg.

8. The method for pouring concrete with abrupt cross-section according to claim 1, characterized in that, In step S3, the hydraulic jacking system is equipped with a pressure sensor to monitor the lateral pressure of the template in real time. When the pressure exceeds 30kN / m², the pressure relief regulation is automatically activated.

9. The method for pouring concrete with abrupt cross-section according to claim 1, characterized in that, In step S4, during the layered synchronous pouring, the pouring height difference between the main layer with small cross-section and the transition layer is controlled to be ≤100mm.

10. A method for pouring concrete with abruptly changed cross-section according to claim 1, characterized in that, In step S5, steam curing adopts a segmented heating mode. The initial heating rate is ≤10℃ / h for the first 2 hours, and constant temperature curing is carried out after reaching 40-50℃. The cooling rate is ≤8℃ / h at the end.

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