Ultra-large-diameter steel pipe concrete additive for ultrahigh cable bent tower, concrete structure and construction method

Abstract

The invention belongs to the technical field of bridge construction, and particularly discloses an ultra-large-diameter concrete filled steel tube for an ultra-high cable bent tower, a concrete structure of the ultra-large-diameter concrete filled steel tube and a construction method. The super-large-diameter steel pipe concrete structure for the ultrahigh cable bent tower comprises a cable bent tower steel pipe structure and self-compacting concrete. The cable bent tower steel tube structure comprises a cable bent tower steel tube, an internal accessory structure and an external accessory structure; the internal accessory structure comprises shear nails, annular plates and stiffening ribs which are arranged on the inner wall of the cable bent tower steel pipe; the outer wrapping accessory structure comprises an outer wrapping steel shell wrapping the cable bent tower steel pipe. The strength grade of the self-compacting concrete is C60-C80, 100 kg-120 kg of the self-compacting concrete additive is doped in per cubic meter of concrete, and the self-compacting concrete additive comprises the following components in percentage by mass: 50%-60% of a calcium-magnesium composite expanding agent, 2.5%-4.5% of a hydration temperature rise inhibitor and 35.5%-47.5% of a rheology modifier. The super-large-diameter steel pipe concrete structure for the ultrahigh cable bent tower is compact in filling and free of cracking, and the concrete and the steel pipe cannot be disengaged in the whole life cycle of the early construction period and the long-term service period.

Description

Technical Field

[0001] The present invention belongs to the technical field of bridge construction. Specifically, it relates to a super-large diameter concrete-filled steel tube structure for a super-high pylon and a construction method thereof. Background Art

[0002] The pylon is the main load-bearing member of cable-supported bridges such as suspension bridges and cable-stayed bridges. With the increasing transportation demands of people, bridges are continuously developing towards the directions of super-large spans and super-wide decks, posing higher requirements for the height and cross-sectional dimensions of the pylon. Common types of pylons include reinforced concrete towers, steel towers, and concrete-filled steel tube towers. For steel bridge towers, due to the need to solve the problem of the stress stability of the steel wall panels, a large number of stiffening structures need to be designed. For reinforced concrete bridge towers, the amount of concrete used is large, the construction period of layered pouring is long, and the problem of concrete shrinkage and cracking is prominent, affecting the structural safety and service life. The amount of steel and concrete used in concrete-filled steel tube bridge towers is significantly lower than that of steel bridge towers and reinforced concrete bridge towers respectively, and the construction is convenient and the economy is good, showing significant advantages over steel bridge towers and reinforced concrete bridge towers. Therefore, more and more bridges choose concrete-filled steel tubes as the main towers of bridges. In order to meet the construction requirements of super-large spans and super-wide decks, the diameter of the steel tubes used is getting larger and the height of the pylon is getting higher.

[0003] Although China has accumulated a large amount of engineering practice in concrete-filled steel tube arch bridges, there are significant differences between the concrete-filled steel tube structures of the pylons of cable bridges and those of arch bridges, mainly including the following aspects. First, the structural types and dimensions are different. The concrete-filled steel tube structure of an arch bridge is arc-shaped, and the diameter of the steel tube is usually small, generally not exceeding 1.5 m. The concrete-filled steel tube structure of the pylon is overall vertical, and the diameter of the steel tube is generally large. For the steel tube of a super-high pylon, the diameter exceeds 3 m. Second, the construction methods are different. After all the steel tubes of the concrete-filled steel tube structure of an arch bridge are installed, concrete is usually poured by the jacking method, while the concrete-filled steel tube of the pylon is poured in vertical sections. Finally, the problems faced by the concrete-filled steel tube are different. The concrete-filled steel tube of an arch bridge mainly faces the problems of incomplete compaction and shrinkage and void formation, which can be solved by using self-compacting and non-shrinking concrete. In addition to incomplete compaction and shrinkage and void formation, the concrete-filled steel tube structure of the pylon also faces the difficult problem of shrinkage cracking for the super-large diameter concrete-filled steel tube used in super-high pylons.

[0004] It should be noted that for the concrete-filled steel tube structure of an arch bridge, it is equivalent to pouring concrete in a sealed space. The self-compacting and non-shrinking concrete adopted needs to solve the problems of concrete shrinkage and void formation in both the plastic stage and the hardening stage while ensuring self-compacting filling. For the concrete-filled steel tube structure of an ultra-high pylon, in addition to the need for self-compacting filling of concrete, it is also necessary to solve the problems of concrete shrinkage and void formation and cracking in the hardening stage. Due to the larger size of the concrete-filled steel tube structure of the pylon, the temperature history and shrinkage history of the concrete inside the tube are significantly different from those of the existing concrete-filled steel tube of an arch bridge. The temperature rise value is higher, the temperature drop shrinkage is greater, and the risk of concrete shrinkage and void formation during the early construction period and long-term service period is higher. At the same time, there are also differences in the requirements for the self-compacting performance of concrete for different structures. Therefore, the existing related technologies cannot solve the problems of incomplete pouring, shrinkage and void formation, and cracking faced by the concrete-filled steel tube with an ultra-large diameter for an ultra-high pylon. It is very necessary to propose targeted technical solutions to meet the needs of engineering construction. Summary of the Invention

[0005] In order to solve the problems of concrete shrinkage and void formation and cracking in the hardening stage of the concrete-filled steel tube structure of an ultra-high pylon in the prior art, the present invention provides a concrete-filled steel tube structure with an ultra-large diameter for an ultra-high pylon and a construction method. The concrete in the concrete-filled steel tube structure is filled densely and does not crack, and there will be no void formation between the concrete and the steel tube during the entire life cycle of the early construction period and long-term service period.

[0006] To achieve the above object, the present invention provides the following technical solutions: The present invention provides a self-compacting concrete additive, which comprises 50% - 60% calcium-magnesium composite expansion agent, 2.5% - 4.5% hydration temperature rise inhibitor, and 35.5% - 47.5% rheological modifier by mass percentage. This additive can effectively reduce the pumping resistance of concrete and at the same time can produce a sequential expansion effect to compensate for the shrinkage of concrete.

[0007] The calcium-magnesium composite expansion agent contains 40% - 60% calcium oxide and 20% - 40% magnesium oxide with an activity value of 100s - 140s.

[0008] The hydration temperature rise inhibitor is a starch-based hydration heat regulation material, which is a commercially available product, such as SBT ® -TRI concrete hydration temperature rise inhibitor.

[0009] The rheological modifier is composed of microspheres, silica fume and a dispersant, which is a commercially available product, such as SBT ® -HDC(III) high-performance concrete rheological modification material.

[0010] By using the self-compacting concrete additive in self-compacting concrete, it is particularly suitable for use as a concrete-filled steel tube with an ultra-large diameter and does not have void formation.

[0011] In order to ensure that the self-compacting concrete does not have voids in the ultra-large diameter steel pipes for the ultra-high cable tower, the self-compacting concrete additive regulates the long-term expansion process of the concrete at 60 days. Among them, the calcium-magnesium composite expansion agent has a restricted expansion rate in water at 7 days ≥ 0.050%, a restricted expansion rate after transferring to air at 21 days ≥ 0.015%, a restricted expansion rate after transferring to air at 53 days ≥ -0.015%, the difference between the restricted expansion rate at 28 days and 3 days in water at 60°C is 0.030% - 0.06%, and the difference between the restricted expansion rate at 60 days and 3 days in water at 60°C is 0.000% - 0.030%; the hydration temperature rise inhibitor has a 24-hour hydration heat reduction rate ≥ 30% and a 7-day hydration heat reduction rate ≤ 15%, and the time for the hydration heat to reach 30.0 J / g is 20 h - 30 h; the rheological modifier has a fluidity ratio ≥ 105% and a 28-day activity index ≥ 75%.

[0012] The present invention also provides a concrete structure with ultra-large diameter steel pipes for an ultra-high cable tower, which includes a cable tower steel pipe structure and self-compacting concrete in two parts; The cable tower steel pipe structure includes a cable tower steel pipe, an internal accessory structure, and an external accessory structure; the internal accessory structure includes shear studs, ring plates, and stiffening ribs arranged on the inner wall of the cable tower steel pipe; the external accessory structure includes an external steel shell covering the cable tower steel pipe; The strength grade of the self-compacting concrete is C60 - C80, and 100 kg - 120 kg of self-compacting concrete additive is incorporated per cubic meter of concrete. The self-compacting concrete additive includes 50% - 60% calcium-magnesium composite expansion agent, 2.5% - 4.5% hydration temperature rise inhibitor, and 35.5% - 47.5% rheological modifier by mass percentage.

[0013] Furthermore, the height of the cable tower steel pipe ≥ 300 m, and the diameter of the cable tower steel pipe is 3 m - 5 m.

[0014] Furthermore, the shear studs are arranged on the horizontal arc surface of the inner wall of the cable tower steel pipe at a spacing of 0.3 m - 0.6 m, and at a spacing of 0.5 m - 1.0 m in the height direction of the cable tower steel pipe; the stiffening ribs are arranged in the height direction of the cable tower steel pipe at a spacing of 3 m - 6 m, and the adjacent upper and lower rib plates are perpendicular to each other; the ring plates are arranged in the height direction of the cable tower steel pipe at a spacing of 1.5 m - 3.0 m.

[0015] Furthermore, the shear studs are 15 cm - 25 cm long and 10 mm - 25 mm in diameter; furthermore, the shear studs are one or two of cylinder head weld studs or threaded studs.

[0016] Furthermore, the thickness of the ring plate is 1.5 cm to 3 cm, and the width is 15 cm to 25 cm; further, circular holes are formed in the ring plate, the diameter of the circular holes is 5 cm to 10 cm, the distance from the center of the circular holes to the inner wall of the cable tower steel pipe is 5 cm to 10 cm, and the distance between the centers of adjacent circular holes is 0.2 m to 0.5 m.

[0017] Furthermore, the thickness of the rib plate is 1.5 cm to 3 cm, and the width is 20 cm to 50 cm; further, the stiffening rib is a straight rib plate.

[0018] Furthermore, the minimum distance between the outer steel shell and the cable tower steel pipe is 5 cm to 20 cm or not less than 80 cm; the outer attached structure adopts an outer steel shell with any shape and a thickness of 1.5 cm to 3.5 cm, and one or more cable tower steel pipes can be arranged in the outer steel shell.

[0019] In some embodiments, the raw materials for preparing the self-compacting concrete, per cubic meter, may include the following components: 260 - 330 kg of cement, 90 - 140 kg of fly ash, 0 - 60 kg of slag powder, 100 - 120 kg of self-compacting concrete additive, 650 - 900 kg of fine aggregate, 750 - 1000 kg of coarse aggregate, 6 - 9 kg of water reducer, and 135 - 155 kg of mixing water.

[0020] On the other hand, the present application provides a construction method for the super-large diameter concrete-filled steel tube structure for the above-mentioned ultra-high cable tower, including segmented concrete pouring, which needs to meet the following conditions: (1) The height of segmented pouring does not exceed 70 m; (2) Control the slump flow of the concrete to be 650 mm - 750 mm, T 500 ≤8 s, and the emptying time of the inverted slump cone ≤8 s; The adiabatic temperature rise of the concrete at 14 d ≤55 °C, the autogenous volume deformation at 7 d ≥+200 με, and the autogenous volume deformation at 60 d ≥+150 με.

[0021] In some embodiments, the concrete can be made to meet the above conditions (2) and (3) by adjusting the mix proportion of the concrete. For example, on the premise of meeting the strength requirements, the adiabatic temperature rise of the concrete can be made to meet the requirements by adjusting the cement dosage and the dosage of mineral admixtures. When the adiabatic temperature rise exceeds the control requirements, the cement and slag powder dosages can be reduced, and the fly ash dosage can be increased; by adjusting the dosage of the powder admixture, the T 500, inverted slump and autogenous volume deformation meet the requirements; by adjusting the amount of water reducer, the slump expansion of concrete meets the requirements. When the slump expansion is less than 650 mm, the amount of water reducer can be increased. When the slump expansion is greater than 750 mm, the amount of water reducer should be appropriately reduced.

[0022] Furthermore, in order to meet the actual needs of construction site, the initial setting time of concrete under the same conditions on site needs to be controlled to 35 h~45 h.

[0023] Furthermore, during concrete production, in order to control the maximum temperature of the cable tower steel tube concrete, measures should be taken to control the temperature of the concrete entering the mold, wherein when the average daily temperature is greater than 25 °C, the maximum temperature of the concrete is controlled to be ≤80 °C; when the average daily temperature is 10 °C to 25 °C, the maximum temperature of the concrete is controlled to be ≤75 °C; when the average daily temperature is less than 10 °C, the maximum temperature of the concrete is controlled to be ≤70 °C. Methods for controlling the temperature of concrete entering the mold include lowering the temperature of raw materials, replacing mixing water with flake ice, wrapping tank trucks, and construction during low temperature periods, which are all conventional technical means in the field and are not limited by this application.

[0024] Furthermore, after the steel tube concrete is poured, a 1.5 cm to 3.5 cm thick steel plate is used to seal the top surface of the cable tower steel tube and the outer steel shell; when the distance between the outer steel shell and each cable tower steel tube is 5 cm to 20 cm, the interlayer between the cable tower steel tube and the outer steel shell should be evacuated to a pressure not greater than -0.5 MPa.

[0025] In order to prevent ultra-large diameter steel tube concrete used in ultra-high cable towers from becoming hollow or cracked, the present invention pours concrete with specific properties into a steel tube structure with a specific structure.

[0026] 1. Cable tower steel pipe structure design In order to ensure that the concrete is densely filled in the steel pipe and not empty, requirements are put forward for the steel pipe structure of the cable tower and the performance of the self-compacting concrete. In terms of the design of the steel pipe structure of the cable tower, it involves the internal auxiliary structure of the steel pipe and the external auxiliary structure of the steel pipe. The internal auxiliary structure of the steel pipe mainly plays two roles. One is to improve the rigidity and stability of the steel pipe structure of the cable tower, and the other is to improve the bonding effect between the concrete and the steel pipe to prevent emptying. However, the more and more complex the internal auxiliary structures are, the better. On the one hand, it will increase the difficulty and cost of steel pipe processing. On the other hand, it may hinder the flow of concrete in the steel pipe, resulting in defects between the concrete and the steel pipe. The external structure of the steel pipe mainly plays two roles. One is to provide insulation for the steel pipe concrete, reduce the influence of the steel pipe concrete structure on the ambient temperature and solar radiation, and ensure that the steel pipe and concrete will not be empty during long-term service. The second is to improve the bearing capacity and stability of the steel pipe concrete structure of the cable tower.

[0027] In each embodiment, to meet the requirements that the concrete-filled steel tower 1 has a height ≥ 300 m and a diameter of 3 m - 5 m, and ensure that the concrete-filled steel tower structure does not have voids or cracks, an auxiliary structure including shear studs 2, ring plates 3, and stiffening ribs 5 is designed inside the concrete-filled steel tower 1.

[0028] Among them, the shear studs 2 are one or both of cylinder head weld studs or threaded studs, with a length of 15 cm - 25 cm and a diameter of 10 mm - 25 mm; the horizontal arc distance between adjacent shear studs 2 along the inner wall of the concrete-filled steel tower 1 is 0.3 m - 0.6 m, and the distance along the height direction of the concrete-filled steel tower 1 is 0.5 m - 1.0 m. The ring plates 3 have a thickness of 1.5 cm - 3 cm and a width of 15 cm - 25 cm. The distance between adjacent ring plates 3 along the height direction of the concrete-filled steel tower 1 is 1.5 m - 3.0 m. Round holes 4 are opened on the ring plates 3, with a diameter of the round holes 4 being 5 cm - 10 cm. The distance from the center of the round holes 4 to the inner wall of the concrete-filled steel tower 1 is 5 cm - 10 cm, and the center distance between adjacent round holes 4 is 20 cm - 50 cm. The stiffening ribs 5 are I-shaped rib plates, with a rib plate thickness of 1.5 cm - 3 cm and a width of 20 cm - 50 cm. The spacing along the height direction of the concrete-filled steel tower 1 is 3 m - 6 m, and the upper and lower adjacent rib plates are perpendicular to each other.

[0029] The auxiliary structure outside the concrete-filled steel tower 1 is an outer steel shell with an arbitrary shape and a thickness of 1.5 cm - 3.5 cm. One or more concrete-filled steel towers 1 can be provided inside the outer steel shell, and the distance between the outer steel shell and each concrete-filled steel tower 1 is 5 cm - 20 cm or not less than 80 cm.

[0030] When the distance between the outer steel shell and each concrete-filled steel tower 1 is 5 cm - 20 cm, the space between the concrete-filled steel tower 1 and the outer steel shell should also be evacuated to a pressure not greater than -0.5 MPa.

[0031] (2) Concrete mix design.

[0032] Incompletely filled concrete in the pipe and voids caused by shrinkage of large-volume concrete in the pipe will both lead to quality defects in the concrete-filled steel pipe structure. This requires that the concrete must have self-compacting performance to meet the actual engineering needs. On the one hand, it can meet the requirements of ultra-high elevation pumping, and at the same time, it does not segregate during the pouring process and can densely fill the steel pipe. On the other hand, technical measures should be adopted to reduce and compensate for shrinkage deformations such as temperature shrinkage and autogenous shrinkage caused by the hydration of concrete. In addition, when the height of segmented pouring is relatively large and the one-time pouring volume of concrete is large, in addition to ensuring the dense filling of the concrete, the influence of the upper-layer poured concrete on the lower-layer concrete and the continuity of pouring should also be considered. This requires controlling both the self-compacting performance of the concrete and the setting time of the concrete poured into the steel pipe.

[0033] In order to ensure that the concrete is densely filled in the steel pipe without voids or cracks, combined with the specific working conditions of the super-large diameter concrete-filled steel tube structure for super-high pylons, the present invention proposes concrete performance control indexes, including adiabatic temperature rise at 14 d, autogenous volume deformation at 7 d and 60 d, slump flow, T 500 , the emptying time of the inverted slump cone, the initial setting time of on-site curing under the same conditions, etc.

[0034] In each embodiment, based on meeting the above performance, self-compacting, non-shrinking, and highly crack-resistant concrete-filled steel tubes with a strength grade of C60 - C80 are designed as shown in Table 1.

[0035] Table 1 Concrete Mix Ratio Unit: kg / m 3 Cement Fly ash Ground granulated blast-furnace slag Self-compacting concrete additive Fine aggregate Coarse aggregate Water reducing agent Mixing water 260~330 90~140 0~60 100~120 650~900 750~1000 6~9 135~155 As for the selection of raw materials, the performance of cement should meet the requirements of "General Portland Cement" GB 175 and CCES01 in "Guide for Durability Design and Construction of Concrete Structures"; the performance of fly ash should meet the requirements of Class F Grade I specified in GB / T 1596 "Fly Ash Used in Cement and Concrete" and the requirements of GB / T 39701 "Limit and Test Method for Ammonium Ion Content in Fly Ash"; the performance of blast furnace slag powder should meet the requirements of Grade S95 and above specified in GB / T 18046 "Ground Granulated Blast Furnace Slag Used in Cement, Mortar and Concrete" and the requirements of CCES01 in "Guide for Durability Design and Construction of Concrete Structures"; the performance of fine aggregate should meet the requirements of natural medium sand in Zone 2 specified in "Sand for Construction" (GB / T 14684), with the mud content not exceeding 2.0%; the performance of coarse aggregate should meet the requirements of continuously graded gravel with a particle size of 5 mm - 20 mm specified in GB / T 14685 "Pebbles and Crushed Stones for Construction", and the loose bulk porosity should not exceed 43%; the performance of water reducer should meet the requirements of "Concrete Admixtures" (GB8076), and the shrinkage ratio should not exceed 100%.

[0036] The self-compacting concrete additive is composed of HME ® -II high-performance concrete magnesium oxide composite expansion agent, SBT ® -TRI concrete hydration temperature rise inhibitor and SBT ® -HDC(III) high-performance concrete rheology modifier compounded in a mass ratio of 50% - 60%, 2.5% - 4.5%, 35.5% - 47.5%.

[0037] It should be noted that the mixing water includes solid flake ice for cooling purposes, not limited to liquid water.

[0038] Thus, the performance index requirements of self-compacting concrete are shown in Table 2.

[0039] Table 2 Requirements for Concrete Performance Indexes

[0040] As understood by those skilled in the art, the adiabatic temperature rise of concrete is tested in accordance with the Standard Test Method for Properties of Ordinary Concrete Mixtures GB / T 50080, and the autogenous volume deformation is tested by the non-contact method in GB / T 50082 of the Standard Test Method for Long-Term Performance and Durability of Ordinary Concrete. The zero point selected is the initial setting of concrete. The autogenous volume deformation of 7 days ≥ +200 με means that "the autogenous volume expansion deformation of 7 days is not less than 200 με", and the autogenous volume deformation of 60 days ≥ +150 με means that "the autogenous volume expansion deformation of 60 days is not less than 150 με". The slump flow, T 500 , the inverted slump evacuation time, and the initial setting time of concrete are tested in accordance with the Standard Test Method for Properties of Ordinary Concrete Mixtures GB / T 50080.

[0041] (3) Construction of the concrete-filled steel tube structure of the pylon.

[0042] During the construction of the concrete-filled steel tube structure of the pylon, the following conditions shall be met: Firstly, control the maximum temperature of the concrete inside the pylon steel tube 1. When the construction is carried out with the average daily temperature > 25 °C, control the maximum temperature of the concrete ≤ 80 °C; when the construction is carried out with the average daily temperature of 10 °C - 25 °C, control the maximum temperature of the concrete ≤ 75 °C; when the construction is carried out with the average daily temperature < 10 °C, control the maximum temperature of the concrete ≤ 70 °C.

[0043] Due to the large structural size of the pylon steel tube 1 and the high temperature rise of the mass concrete inside the tube, in order to make the maximum temperature of the concrete meet the control requirements, one or more measures including controlling the pouring temperature and setting cooling water pipes shall also be taken. The specific measures can be determined through temperature control calculation. To control the pouring temperature of the concrete, measures such as reducing the temperature of raw materials, replacing mixing water with flake ice, wrapping the mixer truck, and constructing during low-temperature periods can be adopted.

[0044] Secondly, control the height of the segmented pouring of the concrete-filled steel tube of the pylon not exceeding 70 m.

[0045] Finally, after the concrete pouring is completed, seal the top surface of the pylon steel tube 1 and the outer steel shell with a steel plate with a thickness of 1.5 cm - 3.5 cm. When the distance between the outer steel shell and each pylon steel tube 1 is 5 cm - 20 cm, the space between the pylon steel tube 1 and the outer steel shell shall also be evacuated to a pressure not greater than -0.5 MPa.

[0046] The present invention has the following beneficial effects: The super-large diameter concrete-filled steel tube structure for super-high pylons provided by the present invention starts from three aspects: the design of the steel tube structure, the regulation of the performance of the concrete inside the tube, and the technological measures. On the premise of ensuring the dense filling of the concrete inside the tube, it can effectively solve the problems of shrinkage voiding and cracking of the super-large diameter high-strength mass concrete in the super-high pylons with a height exceeding 300 m and a steel tube diameter exceeding 3 m. Especially through the design of the steel tube structure and the use of powder admixtures with viscosity regulation, shrinkage compensation, and hydration process regulation, it can avoid problems such as the voiding at the steel-concrete interface caused by heat of hydration and shrinkage during the early construction period of the concrete inside the tube and the steel tube structure, the shrinkage cracking of the concrete, and the voiding at the steel-concrete interface caused by the long-term temperature change in the surrounding environment and the temperature change caused by solar radiation during the long-term service period. Description of the Drawings

[0047] Figure 1 It is a schematic diagram of the shear studs of the internal accessory structure of the steel tube in Example 2; Figure 2 It is a schematic diagram of the ring plate of the internal accessory structure of the steel tube in Example 2; Figure 3 It is a schematic diagram of the stiffening ribs of the internal accessory structure of the steel tube in Example 2; Figure 4 It is a sectional view of the steel tube and its internal accessory structure in Example 2; Figure 5 It is a graph showing the change of the inner surface pressure of the pylon steel tube by the concrete in Example 1 over time; Figure 6 It is a graph showing the change of the inner surface pressure of the pylon steel tube by the concrete in Example 2 over time; In the figure: 1. Pylon steel tube; 2. Shear stud; 3. Ring plate; 4. Round hole; 5. Stiffening rib. Embodiment

[0048] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0049] The above-mentioned super-large diameter concrete-filled steel tube structure for super-high pylons provided by the present invention will be described below through specific construction cases and experimental data. Example

[0050] The full-scale model test of the super-large diameter concrete-filled steel tube structure for super-high pylons provided by the present invention was carried out in a certain highway project. The steel tube has a diameter of 4.5 m, a wall thickness of 4 cm, and a height of 10 m. The self-compacting concrete inside the steel tube has a strength grade of C80.

[0051] (I) Design of the steel tube auxiliary structure For the internal auxiliary structure of the pylon steel tube 1, threaded studs are used as shear studs 2, with a length of 25 cm and a diameter of 25 mm. The horizontal arc distance between adjacent shear studs 2 along the inner wall of the pylon steel tube 1 is 0.6 m, and the distance along the height direction of the pylon steel tube 1 is 1.0 m. The ring plate 3 has a thickness of 3 cm and a width of 25 cm. The distance between adjacent ring plates 3 along the height direction of the pylon steel tube 1 is 3 m. The ring plate 3 is provided with round holes 4 with a diameter of 10 cm. The center of the round hole 4 is 10 cm away from the inner wall of the pylon steel tube 1, and the center distance between adjacent round holes 4 is 50 cm. The I-shaped stiffening rib 5 has a plate thickness of 3 cm and a width of 50 cm, and the distance between the upper and lower adjacent rib plates is 6 m.

[0052] For the external auxiliary structure of the pylon steel tube 1, a steel tube with a thickness of 3.5 cm and a diameter of 4.7 m is used as the external auxiliary structure steel tube. The external auxiliary structure steel tube is concentric with the pylon steel tube 1, and the distance between the two is 20 cm.

[0053] (II) Design of the concrete mix ratio.

[0054] The selected concrete raw materials that meet the requirements include P·II 52.5 cement, class F I fly ash, slag powder of grade S105, medium sand in zone 2, continuous graded gravel of 5 mm - 20 mm, powder admixture, and PCA-I polycarboxylate water reducer. The admixtures added to the self-compacting concrete are the HME ® -II high-performance concrete magnesium oxide composite expansion agent and SBT ® -TRI concrete hydration temperature rise inhibitor and SBT ® -HDC(III) high-performance concrete rheology modification material, which are compounded in a mass ratio of 60%, 2.5%, and 37.5%. The self-compacting concrete is prepared by mixing according to the dosages shown in Table 3 below.

[0055] Table 3 Concrete mix ratio Unit: kg / m 3 Cement Fly ash Ground granulated blast-furnace slag Self-compacting concrete additive Fine aggregate Coarse aggregate Water reducing agent Mixing water 330 90 60 120 650 1000 8 135 The test results of the performance of the above-mentioned self-compacting concrete are shown in Table 4.

[0056] Table 4 Concrete performance

[0057] (3) Construction of the concrete-filled steel tubular structure of the pylon.

[0058] The full-scale model of the concrete-filled steel tubular structure of the pylon was cast under the condition of an average daily temperature of 20 °C. By taking measures such as shading the batching bin, storing cement, fly ash, slag powder and powder admixtures in advance to cool down, adding 60 kg of flake ice per cubic meter of concrete to replace the mixing water, etc., the temperature of the concrete entering the formwork was controlled at 19 °C, and the maximum temperature of the concrete was 74 °C.

[0059] The full-scale model was cast in one go with a height of 10 m. After the concrete was cast, the steel tube 1 of the pylon and the steel tube of the external package auxiliary structure were sealed with a 3.5 cm thick steel plate, and vacuum treatment was carried out until the pressure in the interlayer was -0.5 MPa. At the same time, heat and moisture preservation curing was carried out on the top surface of the concrete.

[0060] During the casting process, the concrete was visibly filled and compacted. Side pressure sensors were arranged at the pores on the inner wall of the steel tube 1 of the pylon. The long-term monitoring results in the past nearly 2 years showed that the pressure on the inner side surface of the steel tube 1 by the concrete was always above 0.2 MPa, that is, the steel tube was always in a compressed state. As Figure 5 shown, continuous tracking of the concrete also did not show any cracking phenomenon. Example

[0061] The super-large diameter concrete-filled steel tubular structure for ultra-high pylons provided by the present invention was applied to a suspension bridge project of a highway. The pylon was 350 m high, the diameter of the steel tube was 3.6 m, the wall thickness of the steel tube was 2.5 cm, and the strength grade of the concrete in the steel tube was C60.

[0062] (1) Design of the steel tube auxiliary structure For the internal auxiliary structure of the steel tube 1 of the pylon, stud welding nails were used as shear studs 2, with a length of 15 cm and a diameter of 10 cm; the horizontal arc distance between adjacent shear studs 2 along the inner wall of the steel tube 1 of the pylon was 0.3 m, and the distance along the height direction of the steel tube 1 of the pylon was 0.5 m. The thickness of the ring plate 3 was 1.5 cm and the width was 15 cm. The distance between adjacent ring plates 3 along the height direction of the steel tube 1 of the pylon was 1.5 m. There were round holes 4 with a diameter of 5 cm on the ring plate 3, and the distance from the center of the round hole 4 to the inner wall of the steel tube 1 of the pylon was 5 cm. The distance between the centers of adjacent round holes 4 was 20 cm. The thickness of the I-shaped stiffening rib 5 was 1.5 cm and the width was 20 cm. The distance between the upper and lower adjacent rib plates was 3 m.

[0063] For the external package auxiliary structure of the steel tube 1 of the pylon, a square steel box with a thickness of 1.5 cm and a side length of 5.2 m was used. The distance between the steel box and the steel tube 1 of the pylon was 80 cm. According to the structural bearing capacity requirements, there were 4 steel tubes 1 of the pylon in the steel box.

[0064] (2) Design of the concrete mix ratio.

[0065] Select concrete raw materials with qualified quality, including P·II 52.5 cement, Class F I fly ash, medium sand in Zone 2, continuously graded gravel with a size of 5 mm - 20 mm, self-compacting concrete additive, PCA-I polycarboxylate water reducer, and powder admixtures including HME produced by Jiangsu Sobute New Materials Co., Ltd., ® -II high-performance concrete magnesium oxide composite expansion agent, SBT ® -TRI concrete hydration temperature rise inhibitor, SBT ® -HDC(III) high-performance concrete rheology modifier, which are compounded in a mass ratio of 50%, 3.5%, and 46.5%. Prepare self-compacting concrete according to the dosage shown in Table 5 below.

[0066] Table 5 Concrete Mix Ratio Unit: kg / m 3 Cement Fly ash Self-compacting concrete additive Fine aggregate Coarse aggregate Water reducing agent Mixing water 260 140 100 842 949 7 148 The test results of the above-mentioned self-compacting concrete are shown in Table 6.

[0067] Table 6 Concrete Properties

[0068] (3) Construction of the concrete-filled steel tube structure of the pylon.

[0069] The concrete-filled steel tube structure of the pylon is constructed in a hot climate with an average daily temperature of 28 - 32 °C. By taking measures such as shading the bunker, storing cement, fly ash, and powder admixtures in advance to cool them down, starting construction during the low-temperature period at night, and adding 60 - 80 kg of flake ice per cubic meter of concrete to replace mixing water, the concrete pouring temperature is controlled at 28 °C - 30 °C, and the maximum concrete temperature is 78 °C - 80 °C.

[0070] The one-time pouring height of the concrete is 30 m - 70 m. After the concrete pouring is completed, seal the steel tube 1 of the pylon and the outer steel shell with a 1.5 cm thick steel plate. At the same time, carry out heat and moisture preservation maintenance on the concrete surface.

[0071] During the pouring process, the concrete is visibly filled and compacted. Side pressure sensors are arranged at the pores on the inner wall of the steel tube 1 of the pylon. The long-term monitoring results in the past nearly 2 years show that the inner surface pressure of the steel tube 1 by the concrete is always above 0.3 MPa, that is, the steel tube is always in a compressed state. As Figure 6 shown.

[0072] In summary, the super-large diameter concrete-filled steel tube structure for ultra-high pylons provided by the present invention is improved and innovated in terms of the steel tube structure of the pylon, the concrete material inside the tube, and the process measures, which can effectively solve the problems of incomplete compaction of the concrete filling in the super-large diameter concrete-filled steel tube for ultra-high pylons, shrinkage voids and cracking caused by concrete hydration heat release and shrinkage, and the voiding problems caused by environmental temperature changes and solar radiation during long-term service.

Claims

1. A self-compacting concrete additive, characterized in that, It includes 50% - 60% calcium-magnesium composite expansive agent, 2.5% - 4.5% hydration temperature rise inhibitor and 35.5% - 47.5% rheological modifier by mass percentage; The calcium-magnesium composite expansive agent contains 40% - 60% calcium oxide and 20% - 40% magnesium oxide with an activity value of 100s - 140s.

2. A special concrete for super-large diameter steel pipes, characterized in that, The special concrete for super-large diameter steel pipes is composed of self-compacting concrete and the self-compacting concrete additive described in Claim 1. The strength grade of the self-compacting concrete is C60 - C80, and 100 kg - 120 kg of the self-compacting concrete additive is incorporated into each cubic meter of the self-compacting concrete.

3. The super-large diameter concrete-filled steel tube structure for super-high pylons according to claim 2, characterized in that, The raw materials for preparing the self-compacting concrete, per cubic meter, include the following components: 260 - 330 kg of cement, 90 - 140 kg of fly ash, 0 - 60 kg of slag powder, 100 - 120 kg of self-compacting concrete additive, 650 - 900 kg of fine aggregate, 750 - 1000 kg of coarse aggregate, 6 - 9 kg of water reducer, and 135 - 155 kg of mixing water.

4. A super-large diameter concrete-filled steel tube structure for a super-high cable tower, characterized in that, It is composed of a super-large diameter steel pipe for an ultra-high pylon and the special concrete for super-large diameter steel pipes described in Claim 2 or 3. The super-large diameter steel pipe for the ultra-high pylon has a structure including a pylon steel pipe, an internal accessory structure, and an external accessory structure. The internal accessory structure includes shear studs, ring plates, and stiffening ribs arranged on the inner wall of the pylon steel pipe. The shear studs are arranged along the horizontal arc surface of the inner wall of the pylon steel pipe with a spacing of 0.3 m - 0.6 m and along the height direction of the pylon steel pipe with a spacing of 0.5 m - 1.0 m. The stiffening ribs are arranged along the height direction of the pylon steel pipe with a spacing of 3 m - 6 m, and the adjacent rib plates are perpendicular to each other. The ring plates are arranged along the height direction of the pylon steel pipe with a spacing of 1.5 m - 3.0 m. The external accessory structure includes an external steel shell covering the pylon steel pipe.

5. The super-large diameter concrete-filled steel tube structure for super-high pylons according to claim 4, characterized in that, The height of the pylon steel pipe is ≥300 m, and the diameter of the pylon steel pipe is 3 m - 5 m.

6. The super-large diameter concrete-filled steel tubular structure for super-high pylons according to claim 4, characterized in that, The shear studs are 15 cm - 25 cm long and 10 mm - 25 mm in diameter. The ring plates are 1.5 cm - 3 cm thick and 15 cm - 25 cm wide. The rib plates are 1.5 cm - 3 cm thick and 20 cm - 50 cm wide.

7. The super-large diameter concrete-filled steel tube structure for super-high pylons according to claim 6, characterized in that, The ring plates are provided with round holes. The diameter of the round holes is 5 cm - 10 cm, the distance from the center of the round holes to the inner wall of the pylon steel pipe is 5 cm - 10 cm, and the distance between the centers of adjacent round holes is 0.2 m - 0.5 m.

8. The super-large diameter concrete-filled steel tubular structure for super-high cable towers according to claim 4, characterized in that, The minimum distance between the external steel shell and the pylon steel pipe is 5 cm - 20 cm or not less than 80 cm.

9. The construction method of the super-large diameter concrete-filled steel tubular structure for super-high pylons according to any one of claims 4-8, characterized in that, It includes segmented concrete pouring, which needs to meet the following conditions: The height of segmented pouring does not exceed 70 m. Control the slump flow of concrete to be 650 mm to 750 mm, and T 500 ≤8 s, and the emptying time of the inverted slump cone ≤8 s; (3) The adiabatic temperature rise of the concrete at 14 d ≤ 55 °C, the autogenous volume deformation at 7 d ≥ +200 με, and the autogenous volume deformation at 60 d ≥ +150 με.

10. The construction method according to claim 9, characterized in that, Control the initial setting time of the concrete at 35 h - 45 h under the same conditions on site.

11. The construction method according to claim 9, characterized in that, When the average daily temperature > 25 °C during construction, control the maximum concrete temperature ≤ 80 °C; when the average daily temperature is 10 °C - 25 °C during construction, control the maximum concrete temperature ≤ 75 °C, and when the average daily temperature < 10 °C during construction, control the maximum concrete temperature ≤ 70 °C.

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