Self-compacting concrete for concrete filled steel tubular column and construction method

Abstract

The invention discloses self-compacting concrete for a concrete-filled steel tube column and a construction method, aims to solve the technical problems that the existing self-compacting concrete is easy to generate bubble retention under the constraint of a steel tube, the interface bonding strength is insufficient, and the construction process needs to depend on vibration assistance, and belongs to the technical field of building materials and structure construction. The self-compacting concrete for the concrete filled steel tubular column is prepared from the following components in parts by mass: 380 to 420 parts of cement, 80 to 120 parts of superfine slag powder, 30 to 50 parts of silica fume, 750 to 800 parts of washed river sand, 1050 to 1100 parts of gravel, 8 to 12 parts of polycarboxylic acid type high-efficiency water reducing agent, 5 to 8 parts of modified nano calcium carbonate, 0.8 to 1.2 parts of organic silane defoaming agent and 160 to 180 parts of tap water.

Description

A self-compacting concrete for steel-tube concrete columns and its construction method Technical Field

[0001] This invention belongs to the field of building materials and structural construction technology, and specifically relates to a self-compacting concrete for steel tube columns and its construction method. Background Technology

[0002] Concrete-filled steel tube (CFST) columns, combining the tensile strength of steel with the compressive strength of concrete, are widely used in super high-rise and long-span buildings. Self-compacting concrete (SCCC) is a preferred material for CFST columns because it can self-compact without vibration. However, existing technologies have two major problems: First, SCCC is prone to voids within the enclosed space of the steel tube due to air bubbles, resulting in insufficient interfacial bond strength (typically ≤3.5MPa) and affecting the overall load-bearing performance of the component. Second, relying solely on the fluidity of the concrete during construction can easily lead to segregation in long, slender steel tube columns exceeding 8m in height, requiring additional vibration, which contradicts the core advantage of SCCC: "vibration-free" compaction.

[0003] To address these issues, existing technologies often improve fluidity by increasing the dosage of water-reducing agents, but this can easily lead to concrete bleeding; or they may use a single defoamer, which can reduce air bubbles, but it will reduce the interfacial adhesion between the concrete and the steel pipe. Summary of the Invention

[0004] The purpose of this invention is to provide a self-compacting concrete for steel-tube concrete columns and a construction method thereof, in order to solve the technical problems of existing self-compacting concrete being prone to air bubble retention and insufficient interfacial bond strength under the constraint of steel tubes, and requiring vibration assistance during construction.

[0005] This invention is achieved using the following technical solution:

[0006] A self-compacting concrete for steel-concrete composite columns comprises, by weight, the following components: 380-420 parts cement, 80-120 parts ultrafine slag powder, 30-50 parts silica fume, 750-800 parts washed river sand, 1050-1100 parts crushed stone, 8-12 parts polycarboxylate-based high-efficiency water-reducing agent, 5-8 parts modified nano-calcium carbonate, 0.8-1.2 parts organosilane defoamer, and 160-180 parts tap water.

[0007] "Cement-Ultrafine Slag Powder-Silica Fume" is a ternary cementitious material. The ternary cementitious material consists of cement providing early strength, ultrafine slag powder optimizing the fluidity of the paste, and silica fume filling the micropores. The three work together to increase the 28-day axial compressive strength of concrete to over 85 MPa.

[0008] More preferably, the modified nano-calcium carbonate is nano-calcium carbonate with a particle size of 50-80 nm, which has been surface-modified with γ-aminopropyltriethoxysilane. Modified nano-calcium carbonate, after silane modification, not only fills the microscopic pores inside concrete and improves its density, but its surface amino groups can also chemically react with the epoxy groups in the interface treatment agent of the steel pipe inner wall, significantly improving the interfacial bonding strength.

[0009] Further preferably, the crushed stone is continuously graded basalt crushed stone with a particle size range of 5-20mm and a needle-like / flaky content of ≤5%. Organosilane defoamer: Utilizing a polyether-modified structure, it can efficiently eliminate air bubbles generated during concrete mixing and pouring (defoaming rate ≥90%), without reducing the adhesion between concrete and steel pipes like traditional mineral oil defoamers.

[0010] More preferably, the polycarboxylate-based high-efficiency water-reducing agent has a water reduction rate of ≥35% and a solid content of 20-25%; the organosilane defoamer is a polyether-modified organosilane with a pH value of 6-8.

[0011] A construction method for steel-concrete composite columns, achieved by using self-compacting concrete, includes the following steps:

[0012] S1. Steel pipe pretreatment: The inner wall of the steel pipe is sandblasted to remove rust, and the rust removal grade reaches Sa2.5. Then, an interface treatment agent is applied by high-pressure airless spraying process. The interface treatment agent is a composite slurry of epoxy resin and cement. The coating thickness is 0.8-1.2mm. It is cured at room temperature for 24 hours until the surface is dry.

[0013] S2. Concrete preparation: First, put cement, ultrafine slag powder, silica fume, washed river sand and crushed stone into a mixer and dry mix for 2-3 minutes. Then, add tap water and polycarboxylate-based high-efficiency water-reducing agent and mix for 3-4 minutes. Finally, add modified nano-calcium carbonate and organosilane defoamer and mix at high speed for 1-1.5 minutes. The mixing speed is 1200-1500 r / min.

[0014] S3. Staged pouring: The prepared self-compacting concrete is introduced into the steel pipe through a chute and poured in stages. The height of each stage is 1.5-2.0m and the pouring interval is controlled at 15-20min. After each stage is poured, ultrasonic vibration of 20-30kHz is applied to the corresponding position on the outer wall of the steel pipe for 30-60s.

[0015] S4. Vacuum-assisted degassing: Set up a vacuum interface at the top of the steel pipe and connect a vacuum pump. When the concrete is poured to 90% of the height of the steel pipe, turn on the vacuum pump and maintain a vacuum of -0.08 to -0.09 MPa for 10-15 minutes. At the same time, continue to pour the remaining concrete to the top of the steel pipe.

[0016] S5. Curing and Monitoring: After pouring, the outer wall of the steel pipe is wrapped with plastic film for moisture retention and curing. The curing temperature is ≥15℃ and the curing time is ≥7 days. During the curing period, the shrinkage strain of the concrete is monitored in real time through the pre-embedded strain sensor to ensure that the shrinkage strain is ≤200με within 7 days.

[0017] More preferably, the epoxy resin to cement mass ratio of the interface treatment agent in S1 is 1:3, and 0.5% of the total mass of silane coupling agent KH-550 is added.

[0018] More preferably, the ultrasonic vibration described in S3 is performed using a portable ultrasonic vibrator, and the contact pressure between the vibration probe and the outer wall of the steel pipe is 0.3-0.5 MPa.

[0019] This invention provides a self-compacting concrete that combines high workability, high interfacial bond strength, and high density, along with corresponding construction techniques to meet the performance requirements of concrete-filled steel tube columns.

[0020] This invention achieves three major technological breakthroughs by optimizing the composition and construction process of self-compacting concrete: First, it solves the problem of air bubble retention in the concrete inside the steel tube, increasing the interfacial bond strength to over 4.2 MPa; second, it enables the casting of long and slender steel tube columns without vibration, improving construction efficiency by over 25%; and third, it significantly improves the seismic ductility and compressive strength of the steel tube concrete column, making it suitable for high-rise buildings, large spans, and other architectural scenarios with high structural performance requirements, and has broad engineering application prospects. Detailed Implementation

[0021] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0022] In this description, it should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. It should also be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joint" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0023] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0024] The specific embodiments of the present invention will be described in detail below.

[0025] Example 1

[0026] A self-compacting concrete for steel-concrete composite columns comprises the following components by weight: 380-420 parts cement, 80-120 parts ultrafine slag powder, 30-50 parts silica fume, 750-800 parts washed river sand, 1050-1100 parts crushed stone, 8-12 parts polycarboxylate-based high-efficiency water-reducing agent, 5-8 parts modified nano-calcium carbonate, 0.8-1.2 parts organosilane defoamer, and 160-180 parts tap water.

[0027] The modified nano-calcium carbonate is nano-calcium carbonate with a particle size of 50-80 nm, which has been surface-modified with γ-aminopropyltriethoxysilane.

[0028] The crushed stone is continuously graded basalt crushed stone with a particle size range of 5-20 mm and a needle-like and flaky content of ≤5%.

[0029] The polycarboxylate-based high-efficiency water-reducing agent has a water reduction rate of ≥35% and a solid content of 20-25%; the organosilane defoamer is a polyether-modified organosilane with a pH value of 6-8.

[0030] Example 2

[0031] A construction method for steel-concrete composite columns, implemented using self-compacting concrete as described in Example 1, includes the following steps:

[0032] S1. Steel pipe pretreatment: The inner wall of the steel pipe is sandblasted to remove rust, and the rust removal grade reaches Sa2.5. Then, an interface treatment agent is applied by high-pressure airless spraying process. The interface treatment agent is a composite slurry of epoxy resin and cement. The coating thickness is 0.8-1.2mm. It is cured at room temperature for 24 hours until the surface is dry.

[0033] S2. Concrete preparation: First, put cement, ultrafine slag powder, silica fume, washed river sand and crushed stone into a mixer and dry mix for 2-3 minutes. Then, add tap water and polycarboxylate-based high-efficiency water-reducing agent and mix for 3-4 minutes. Finally, add modified nano-calcium carbonate and organosilane defoamer and mix at high speed for 1-1.5 minutes. The mixing speed is 1200-1500 r / min.

[0034] S3. Staged pouring: The prepared self-compacting concrete is introduced into the steel pipe through a chute and poured in stages. The height of each stage is 1.5-2.0m and the pouring interval is controlled at 15-20min. After each stage is poured, ultrasonic vibration of 20-30kHz is applied to the corresponding position on the outer wall of the steel pipe for 30-60s.

[0035] S4. Vacuum-assisted degassing: Set up a vacuum interface at the top of the steel pipe and connect a vacuum pump. When the concrete is poured to 90% of the height of the steel pipe, turn on the vacuum pump and maintain a vacuum of -0.08 to -0.09 MPa for 10-15 minutes. At the same time, continue to pour the remaining concrete to the top of the steel pipe.

[0036] S5. Curing and Monitoring: After pouring, the outer wall of the steel pipe is wrapped with plastic film for moisture retention and curing. The curing temperature is ≥15℃ and the curing time is ≥7 days. During the curing period, the shrinkage strain of the concrete is monitored in real time through the pre-embedded strain sensor to ensure that the shrinkage strain is ≤200με within 7 days.

[0037] The epoxy resin to cement mass ratio of the interface treatment agent described in S1 is 1:3, and 0.5% of the total mass of silane coupling agent KH-550 is added.

[0038] The ultrasonic vibration described in S3 uses a portable ultrasonic vibrator, and the contact pressure between the vibration probe and the outer wall of the steel pipe is 0.3-0.5 MPa.

[0039] Example 3

[0040] 1. Preparation of self-compacting concrete: Weigh out 400 parts cement, 100 parts ultrafine slag powder, 40 parts silica fume, 780 parts washed river sand, 1080 parts basalt crushed stone (5-20mm continuous gradation), 10 parts polycarboxylate-based high-efficiency water-reducing agent (water reduction rate 38%), 6 parts modified nano calcium carbonate (50-80nm, γ-aminopropyltriethoxysilane modified), 1.0 part organosilane defoamer (polyether modified), and 170 parts tap water according to the following weight proportions: First, dry mix the solid powder for 2.5 min, add water and water-reducing agent and stir for 3.5 min, and finally add modified nano calcium carbonate and defoamer, and stir at high speed of 1300 r / min for 1.2 min to obtain self-compacting concrete.

[0041] 2. Steel pipe pretreatment: The steel pipe specifications are Φ800×20mm. The inner wall is sandblasted to remove rust to Sa2.5 grade. Epoxy resin-cement composite interface treatment agent (epoxy resin:cement = 1:3, with 0.5% KH-550 added) is applied with a thickness of 1.0mm and cured at room temperature for 24 hours.

[0042] 3. Staged pouring: Pour in stages using chutes, with each stage being 1.8m high and spaced 18min apart. After each stage, vibrate with a 25kHz ultrasonic vibrator (contact pressure 0.4MPa) for 45s. When the pouring reaches 90% of the height, turn on the vacuum pump to maintain a vacuum of -0.085MPa for 12min, and continue pouring to the top.

[0043] 4. Curing and monitoring: The plastic film is kept moist at 20℃ for 7 days; the pre-embedded strain sensor monitors the shrinkage strain after 7 days, which is 182με, meeting the design requirements.

[0044] Example 4

[0045] 1. Preparation of self-compacting concrete: 390 parts cement, 90 parts ultrafine slag powder, 35 parts silica fume, 760 parts washed river sand, 1060 parts basalt crushed stone, 9 parts polycarboxylate-based high-efficiency water-reducing agent, 5.5 parts modified nano calcium carbonate, 0.9 parts organosilane defoamer, and 165 parts tap water; the mixing process is the same as in Example 1. The self-compacting concrete prepared has a spread of 770 mm and a collapse time of 4.5 s.

[0046] 2. Construction process: Steel pipe specifications Φ600×16mm, interface treatment agent thickness 0.9mm, staged pouring height 1.5m, interval 15min, ultrasonic vibration frequency 22kHz, vacuum degree -0.08MPa, vacuuming for 10min; after curing for 28 days, the axial compressive strength is 86.3MPa, and the interface bond strength is 4.4MPa.

[0047] To verify the performance advantages of this invention, the following comparative experiments were conducted. The experimental subjects included: the self-compacting concrete of this invention (experimental group), commercially available ordinary self-compacting concrete (control group 1), and self-compacting concrete with added single defoamer (control group 2). The experimental results are shown in the table below:

[0048] Performance Indicators Experimental Group Control Group 1 Control Group 2 Spread (mm) 780±15 720±20 735±18 Collapse Time (s) 4.2±0.3 5.8±0.5 5.5±0.4 28d Axial Compressive Strength (MPa) 88.6±2.1 75.3±1.8 78.5±2.0 Interfacial Bond Strength (MPa) 4.5±0.2 3.2±0.3 3.6±0.2 7d Shrinkage Strain (με) 185±12 258±15 232±14 Seismic Ductility Coefficient of Concrete-Concrete Composite Steel Tube Column 5.8±0.3 4.3±0.2 4.6±0.3 surface

[0049] The experimental data show that the experimental group has better workability indicators such as expansion and collapse time than the control group, and the 28-day axial compressive strength and interfacial bond strength are increased by 17.7% and 40.6% respectively compared with the control group. The steel-concrete composite column constructed using the method of this invention has a seismic ductility coefficient that is 34.9% higher than that of the traditional process, which fully demonstrates the technical advantages of this invention.

[0050] This invention relates to self-compacting concrete. By optimizing the cementitious material system and aggregate gradation, and introducing a compound component of modified nano-calcium carbonate and organosilane defoamer, it achieves high workability while meeting the requirements of a spread ≥750mm and a collapse time ≤5s. Simultaneously, it achieves an interfacial bond strength ≥4.2MPa with the inner wall of the steel tube and a 28-day axial compressive strength ≥85MPa. Its construction method utilizes a synergistic process of "graded material placement - vacuum assistance - ultrasonic monitoring" to eliminate internal voids in the concrete, ensuring the density and mechanical performance stability of the steel tube concrete column. Experimental verification shows that the seismic ductility coefficient of the steel tube concrete column using this invention is improved by more than 35% compared to traditional methods, making it suitable for the construction of steel tube concrete columns in large-span spatial structures and super high-rise steel structures.

[0051] The construction method of this invention adopts a synergistic process of "graded material placement - ultrasonic assistance - vacuum degassing" to specifically solve the casting problem of long and slender steel pipe columns:

[0052] Graded pouring: Control the pouring height and interval of each stage to avoid segregation of concrete due to gravity, and allow time for air bubbles to escape.

[0053] Ultrasonic assistance: High-frequency ultrasound is applied after each stage of pouring to use vibration energy to make tiny air bubbles inside the concrete float to the surface, and the ultrasonic frequency (20-30kHz) will not damage the cohesive structure of the concrete.

[0054] Vacuum degassing: In the later stage of pouring, residual air bubbles are actively extracted by vacuum negative pressure to ensure that the concrete density is ≥99.5% and to avoid shrinkage cracks at the top.

[0055] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the present invention. Although detailed descriptions have been provided with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments, and they should all be covered within the protection scope of the claims.

Claims

1. A self-compacting concrete for steel-concrete composite columns, characterized in that: By weight, it includes the following components: 380-420 parts cement, 80-120 parts ultrafine slag powder, 30-50 parts silica fume, 750-800 parts washed river sand, 1050-1100 parts crushed stone, 8-12 parts polycarboxylate-based high-efficiency water-reducing agent, 5-8 parts modified nano calcium carbonate, 0.8-1.2 parts organosilane defoamer, and 160-180 parts tap water.

2. The self-compacting concrete for steel-tube concrete columns according to claim 1, characterized in that: The modified nano-calcium carbonate is nano-calcium carbonate with a particle size of 50-80 nm, which has been surface-modified with γ-aminopropyltriethoxysilane.

3. The self-compacting concrete for steel-tube concrete columns according to claim 2, characterized in that: The crushed stone is continuously graded basalt crushed stone with a particle size range of 5-20 mm and a needle-like and flaky content of ≤5%.

4. The self-compacting concrete for steel-tube concrete columns according to claim 3, characterized in that: The polycarboxylate-based high-efficiency water-reducing agent has a water reduction rate of ≥35% and a solid content of 20-25%; the organosilane defoamer is a polyether-modified organosilane with a pH value of 6-8.

5. A construction method for steel-concrete composite columns, characterized in that, The self-compacting concrete for steel-concrete composite columns as described in any one of claims 1-4 is achieved by the following steps: S1, Steel pipe pretreatment: The inner wall of the steel pipe is sandblasted to remove rust, achieving a rust removal grade of Sa2.

5. Then, a high-pressure airless spraying process is used to apply an interface treatment agent, which is a composite slurry of epoxy resin and cement, with a coating thickness of 0.8-1.2 mm. The mixture is cured at room temperature for 24 hours until the surface is dry. S2, Concrete preparation: Cement, ultrafine slag powder, silica fume, washed river sand, and crushed stone are first added to a mixer and dry-mixed for 2-3 minutes. Then, tap water and a polycarboxylate-based high-efficiency water-reducing agent are added and mixed for 3-4 minutes. Finally, modified nano-calcium carbonate and an organosilane defoamer are added and mixed at high speed for 1-1.5 minutes at a mixing speed of 1200-1500 r / min. S3, Staged pouring: The prepared self-compacting concrete is poured into the steel pipe through a chute, using a staged pouring method, with each stage having a pouring height of 1.5 mm. -2.0m, the pouring interval is controlled at 15-20min, and after each pouring, ultrasonic vibration of 20-30kHz is applied to the corresponding position on the outer wall of the steel pipe for 30-60s; S4, vacuum-assisted degassing: a vacuum interface is set at the top of the steel pipe and connected to a vacuum pump. When the self-compacted concrete is poured to 90% of the height of the steel pipe, the vacuum pump is turned on and the vacuum degree is maintained at -0.08 to -0.09MPa for 10-15min. At the same time, the remaining concrete is poured to the top of the steel pipe; S5, curing and monitoring: after pouring, the outer wall of the steel pipe is wrapped with plastic film for moisture curing. The curing temperature is ≥15℃ and the curing time is ≥7d. During the curing period, the shrinkage strain of the concrete is monitored in real time through the pre-embedded strain sensor to ensure that the shrinkage strain is ≤200με within 7d.

6. A construction method for a steel-concrete composite column according to claim 5, characterized in that: The epoxy resin to cement mass ratio of the interface treatment agent described in S1 is 1:3, and 0.5% of the total mass of silane coupling agent KH-550 is added.

7. A construction method for a steel-concrete composite column according to claim 6, characterized in that: The ultrasonic vibration described in S3 uses a portable ultrasonic vibrator, and the contact pressure between the vibration probe and the outer wall of the steel pipe is 0.3-0.5 MPa.