Anti-freezing concrete filled steel tube and preparation method thereof

Abstract

The invention relates to the technical field of concrete preparation, in particular to an anti-freezing concrete-filled steel tube and a preparation method thereof.The anti-freezing concrete-filled steel tube is prepared from, by weight, 650-670 parts of cement, 540-560 parts of machine-made sand, 540-560 parts of air-quenched aggregate, 3.8-4.12 parts of super absorbent resin, 3.0-3.2 parts of a water reducing agent, 10-15 parts of a composite anti-freezing agent, 1-2 parts of an air entraining agent and 290-304 parts of water; the composite antifreeze agent is composed of fumed silica, modified silica fume and calcium nitrite. According to the invention, the composite antifreeze agent, the super absorbent resin, the air entraining agent, the water reducing agent and the air-quenched aggregate are synergistically matched to construct a multi-scale and multi-mechanism antifreeze protection system, so that the problem of freeze-thaw damage when the concrete filled steel tube is applied in a cold region is effectively solved.

Description

Technical Field

[0001] This invention relates to the field of concrete preparation technology, and in particular to a frost-resistant steel pipe concrete and its preparation method. Background Technology

[0002] Concrete-steel tubular (SST) is a composite structural material formed by filling steel tubes with concrete. The steel tubes provide effective lateral restraint to the core concrete, placing it under triaxial compression, thus significantly improving its compressive strength and ductility. Simultaneously, the core concrete supports the steel tube, delaying or preventing local buckling and fully utilizing its tensile strength. This composite structure features high load-bearing capacity, good ductility, rapid construction, and excellent seismic performance, and has been widely used in major projects such as high-rise buildings, long-span bridges, and offshore platforms. With the expansion of infrastructure construction into cold regions, the long-term durability of SST structures in low-temperature environments is becoming increasingly prominent, with freeze-thaw cycles causing damage to the core concrete being a key factor affecting structural safety.

[0003] The frost resistance of concrete mainly depends on its internal pore structure and free water content. When the temperature drops below freezing, the free water in the concrete pores freezes and expands, generating internal stress. Repeated freeze-thaw cycles cause microcracks inside the concrete to gradually expand, eventually leading to strength loss and structural damage. To improve the frost resistance of concrete, current main technical measures include introducing air bubbles to buffer frost heave stress, reducing porosity to increase density, and reducing free water content. Commonly used techniques include adding air-entraining agents to form uniformly distributed microbubbles in the concrete, using high-performance water-reducing agents to lower the water-cement ratio, incorporating mineral admixtures to refine pore size distribution, and using water-absorbing materials for internal curing. In addition, considering the special working environment of steel-concrete composite pipes, corrosion protection of the steel pipes must also be considered. This is usually achieved by adding rust inhibitors to passivate the steel surface and prevent corrosion caused by chloride ions or other corrosive media.

[0004] Chinese patent CN113354368A discloses an antifreeze concrete. This patent adds an antifreeze agent made of calcium nitrate, triterpenoid saponins, hexadecyltrimethylammonium bromide, carboxymethyl cellulose, and hydroxypropyl distarch phosphate to the concrete. This creates numerous closed microbubbles within the concrete, facilitating the release of free water during freeze-thaw expansion and thus resisting damage to the internal structure of the concrete from freezing. Simultaneously, the patent uses sodium polyacrylate superabsorbent polymer particles to further reduce freeze-thaw expansion by lowering the proportion of free water in the early stages of concrete setting, and these particles fill pores after the concrete has solidified, thereby improving the compressive strength of the concrete. However, this patent technology primarily addresses the improvement of the freeze-thaw resistance of ordinary concrete and fails to adequately consider the special working conditions of steel-concrete composite structures in low-temperature environments and the long-term durability of the concrete-steel-pipe interface. Summary of the Invention

[0005] In view of this, the present invention proposes a frost-resistant steel-tube concrete and its preparation method to solve the problems of insufficient frost resistance, easy damage and deterioration of the internal structure of concrete under freeze-thaw cycles, and poor long-term durability of the interface between the steel tube and the core concrete in the prior art when steel-tube concrete is used in cold regions.

[0006] The technical solution of this invention is implemented as follows: This invention provides a frost-resistant steel-pipe concrete, which, by weight, comprises 650-670 parts of cement, 540-560 parts of manufactured sand, 540-560 parts of air-quenched aggregate, 3.8-4.12 parts of superabsorbent resin, 3.0-3.2 parts of water-reducing agent, 10-15 parts of composite antifreeze agent, 1-2 parts of air-entraining agent, and 290-304 parts of water; the composite antifreeze agent is composed of fumed silica, modified silica fume, and calcium nitrite.

[0007] Based on the above technical solutions, preferably, in the composite antifreeze agent, the mass ratio of fumed silica, modified silica fume and calcium nitrite is 1:(6~8):(2~4).

[0008] Specifically, in this invention, cement, manufactured sand, and air-quenched aggregate are blended to form the matrix structure of concrete. The air-quenched aggregate possesses porous characteristics and excellent interfacial bonding properties, enhancing the overall strength and durability of the concrete. A composite antifreeze agent is formed by blending fumed silica, modified silica fume, and calcium nitrite, establishing a robust antifreeze protection network. Fumed silica, as a nanoscale filler, effectively seals the nanoscale pore channels within the concrete, blocking moisture penetration at its source. Modified silica fume incorporates MOF structures on its surface, storing moisture and dynamically regulating the internal humidity environment during freeze-thaw cycles. Simultaneously, its surface-grafted flexible groups effectively alleviate the concentrated transmission of frost heave stress in the matrix and improve crack resistance. Calcium nitrite provides early strength while passivating the steel pipe surface to form a protective film against corrosion. These three components construct a multi-layered antifreeze protection system from the nanoscale, microscale, to the ionic scale. Superabsorbent polymers absorb and store moisture during the concrete hardening process, releasing it slowly later for internal curing. This synergistic effect with the water-storage function of modified silica fume reduces both early shrinkage and the content of free water that can freeze. Water-reducing agents enhance density by improving concrete fluidity and lowering the water-cement ratio, while air-entraining agents introduce uniformly distributed micro-bubbles into the concrete to provide a buffer against frost heave. Through the combined effects of these components—density filling, porosity control, bubble buffering, internal curing, and interface protection—the concrete maintains good mechanical properties and durability even under repeated freeze-thaw cycles, while ensuring the long-term stability of the interface between the steel pipe and the core concrete.

[0009] Based on the above technical solutions, preferably, the method for preparing the modified silica fume includes: S1. After the silica fume is activated by dilute hydrochloric acid, it is dispersed in an aqueous ethanol solution, aminopropyltriethoxysilane is added, and the mixture is stirred at 50~80℃ for 2~6 hours. After filtration, washing and drying, aminated silica fume is obtained. S2. Disperse aminated silica fume in DMF / water solution, then add zirconium tetrachloride and 2-aminoterephthalic acid, and hydrothermally react at 100~140℃ for 18~30h. After centrifugation, washing and drying, MOF modified silica fume is obtained. S3. Disperse MOF-modified silica fume in anhydrous toluene, add γ-methacryloyloxypropyltrimethoxysilane, stir and react at 60~80℃ for 3~6h, filter, wash and dry to obtain composite silica fume; S4. Disperse the composite silica fume in an ethanol aqueous solution, add butyl acrylate, hydroxyethyl acrylate and azobisisobutyronitrile, and stir the reaction at 50~70℃ for 4~8h under nitrogen protection. Filter, wash and dry to obtain modified silica fume.

[0010] Specifically, in step S1, impurities and the inert oxide layer on the surface of silica fume are removed by activation with dilute hydrochloric acid, fully exposing the surface silanol groups. The amino groups introduced on the silica fume surface by aminopropyltriethoxysilane not only improve the surface activity and hydrophilicity of the silica fume, but also provide coordination anchoring sites for the subsequent in-situ growth of the MOF structure. In step S2, a UiO-66-NH2 type metal-organic framework structure is formed in-situ by hydrothermal synthesis of zirconium tetrachloride and 2-aminoterephthalic acid on the aminated silica fume surface. This MOF structure can capture and store water molecules to slowly release moisture during the concrete curing period for continuous internal curing, and can also act as a buffer space to reduce frost heave pressure during freeze-thaw cycles. At the same time, the amino functional groups in the MOF framework form hydrogen bonds with the cement hydration products in the concrete matrix to enhance the interfacial bonding force. In step S3, γ-methacryloyloxypropyltrimethoxysilane provides polymerizable carbon-carbon double bond active sites on the MOF-modified silica fume surface. In step S4, butyl acrylate and hydroxyethyl acrylate are grafted onto the surface of the composite silica fume through a free radical-initiated copolymerization reaction to form a polymer coating layer. The butyl acrylate units, with their long alkyl side chains, impart excellent flexibility and hydrophobicity to the polymer layer, effectively buffering the brittle transmission of frost heave stress and bridging and inhibiting the initiation and propagation of microcracks through their elastic deformation capabilities, significantly improving the crack resistance of the concrete matrix. Simultaneously, it reduces excessive penetration of external moisture into the MOF layer. The hydroxyl groups of the hydroxyethyl acrylate units maintain the material's moderate hydrophilicity and can form a hydrogen bond network with the concrete matrix to enhance interfacial adhesion. Furthermore, this polymer layer forms a protective barrier for the inner MOF structure, preventing its degradation in the highly alkaline environment of concrete. In addition, the acrylate structure in the polymer layer has a similar chemical skeleton to the polycarboxylate superplasticizer, and the two produce a synergistic dispersion effect in the aqueous phase, effectively reducing the frictional resistance and agglomeration tendency between modified silica fume particles, thereby significantly improving the fluidity and dispersion uniformity of the composite antifreeze agent in the concrete mixture.

[0011] Based on the above technical solutions, preferably, in step S1, the mass ratio of activated silica fume to aminopropyltriethoxysilane is 100:(8~15).

[0012] Based on the above technical solution, preferably, in step S2, the mass ratio of the aminated silica fume, zirconium tetrachloride, and 2-aminoterephthalic acid is 100:(15~25):(12~20).

[0013] Based on the above technical solutions, preferably, in step S3, the mass ratio of the MOF-modified silica fume to γ-methacryloyloxypropyltrimethoxysilane is 100:(3~8).

[0014] Based on the above technical solutions, preferably, in step S4, the mass ratio of the composite silica fume, butyl acrylate, and hydroxyethyl acrylate is 100:(25~40):(10~18); the amount of azobisisobutyronitrile is 0.3~1.0% of the total mass of the monomers.

[0015] Based on the above technical solutions, preferably, the air-quenched aggregate is a multi-stage compounded air-quenched titanium slag, wherein air-quenched titanium slag with a particle size <0.6 mm accounts for 40~50%, air-quenched titanium slag with a particle size of 0.6~1.18 mm accounts for 30~40%, and the remainder is air-quenched titanium slag with a particle size of 1.18~2.36 mm.

[0016] Air-quenched titanium slag is an industrial byproduct formed by rapidly cooling and quenching high-temperature molten titanium slag with high-speed airflow. The rapid cooling process causes a large number of glassy phases and microporous structures to form inside the slag, giving the aggregate good water absorption and release capabilities. It can work in conjunction with superabsorbent resin and modified silica fume to achieve multi-level internal curing during the concrete hardening process. At the same time, the nano- and micro-pores inside the aggregate can act as a dispersed buffer space to accommodate water frost swelling during freeze-thaw cycles, effectively dispersing and releasing frost swelling stress and preventing its concentrated transmission in the concrete matrix. In this invention, by multi-stage compounding of wind-quenched titanium slag, fine aggregate with a particle size <0.6 mm is used as the main filler phase, which can effectively fill the voids between coarse aggregates and provide sufficient specific surface area to enhance the contact area with cement paste; medium aggregate with a particle size of 0.6~1.18 mm plays a transitional role in the skeleton; and coarse aggregate with a particle size of 1.18~2.36 mm constitutes the main load-bearing skeleton of concrete. Through the interlocking and filling of aggregates with different particle sizes, the porosity inside the concrete is reduced to the maximum extent and the packing density is improved, forming a denser microstructure system, which further enhances the strength and frost resistance of steel-concrete composite.

[0017] Based on the above technical solutions, preferably, the cement is silicate cement, the superabsorbent resin is sodium polyacrylate, the water-reducing agent is at least one of polycarboxylic acid water-reducing agent, melamine water-reducing agent, fatty acid water-reducing agent, and aminosulfonate water-reducing agent; and the air-entraining agent is at least one of rosin thermal polymer, alkylbenzene sulfonate, fatty alcohol polyoxyethylene ether, and triterpenoid saponin.

[0018] This invention also provides a method for preparing frost-resistant steel-tube concrete, comprising the following steps: Air-quenched aggregate, manufactured sand, and cement are put into a mixer and dry-mixed for 1-2 minutes. Water-reducing agent and air-entraining agent are added to water to prepare an admixture aqueous solution. Then, the admixture aqueous solution, composite antifreeze agent, and super absorbent resin are added to the mixer and mixed for 3-5 minutes to obtain a concrete mixture. The concrete mixture is pumped into a steel pipe and continuously vibrated during the pouring process until the concrete surface is covered with slurry. After pouring, curing is carried out to obtain antifreeze steel pipe concrete.

[0019] The antifreeze steel pipe concrete and its preparation method of the present invention have the following advantages over the prior art: (1) Through the synergistic combination of composite antifreeze agent, superabsorbent resin, air-entraining agent, water-reducing agent and air-quenched aggregate, a multi-scale and multi-mechanism antifreeze protection system was constructed, which effectively solved the freeze-thaw damage problem of steel-concrete composite in cold regions. The fumed silica, modified silica fume and calcium nitrite in the composite antifreeze agent work synergistically in terms of nanofilling, pore control and interface protection, respectively. The superabsorbent resin and air-entraining agent reduce the content of freezeable water and release frost heave stress through internal curing and bubble buffering mechanism. The porous structure and optimized gradation of the air-quenched aggregate further improve the matrix density and stress dispersion ability, so that the concrete can still maintain good mechanical properties and durability after repeated freeze-thaw cycles, while ensuring the long-term stability of the interface between the steel pipe and the core concrete.

[0020] (2) The modified silica fume of the present invention forms a core-shell structure of silica fume core-MOF water storage layer-polymer flexible shell through modification. The high specific surface area and pore structure of the MOF layer can effectively store and slowly release water, providing a buffer space during freeze-thaw cycles. The outer polymer coating not only gives the material flexible crack resistance and hydrophobic protection, but also improves the fluidity and dispersion uniformity of the composite antifreeze agent in concrete through the synergistic dispersion effect with the water-reducing agent. Thus, the freeze-thaw cycle resistance and long-term durability of concrete are synergistically improved at multiple scales, including micro, meso and macro.

[0021] (3) The present invention uses wind-quenched titanium slag as aggregate and performs multi-level compounding, making full use of its porous structure and active glassy properties formed by rapid cooling and quenching. The nano-micro pores inside the aggregate can serve as a dispersed buffer space to accommodate frost heave stress. The rough surface morphology and active components enhance the bonding performance of the aggregate-slurry interface. Through multi-level gradation, aggregates of different particle sizes are interlocked and filled, maximizing the packing density and reducing permeability. Together with other components, a multi-level anti-freeze protection system is constructed from the inside of the aggregate, the interface zone to the matrix as a whole. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 These are morphological diagrams of the superabsorbent resin of the present invention after drying and after water saturation. Figure 2 This is a morphological diagram of the air-quenched titanium slag of the present invention; Figure 3 This is a curve showing the freeze-thaw mass loss rate of the antifreeze steel-concrete composite under different freeze-thaw cycles according to the present invention. Figure 4 The graph shows the freeze-thaw compressive strength loss rate of the antifreeze steel-concrete composite under different freeze-thaw cycles according to the present invention. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] It should be noted that the sodium polyacrylate used in this invention was purchased from Funa New Materials Co., Ltd., with a particle size D50 of 419.38 μm; the polycarboxylate superplasticizer was XCA-100, purchased from Beijing New Century Jingxi Waterproof Materials Co., Ltd.; and the air-entraining agent was sodium fatty alcohol polyoxyethylene ether sulfate.

[0026] Example 1 This embodiment provides a method for preparing antifreeze steel-tube concrete, comprising, by weight, 660 parts cement, 550 parts manufactured sand, 550 parts air-quenched aggregate, 3.96 parts sodium polyacrylate, 3.10 parts polycarboxylate superplasticizer, 13 parts composite antifreeze agent, 1.5 parts air-entraining agent, and 297 parts water. The composite antifreeze agent is composed of fumed silica, modified silica fume, and calcium nitrite in a mass ratio of 1:7:3. The air-quenched aggregate is a multi-grade compounded air-quenched titanium slag, wherein 45% has a particle size <0.6 mm, 35% has a particle size of 0.6~1.18 mm, and 20% has a particle size of 1.18~2.36 mm.

[0027] Methods for preparing modified silica fume include: S1. Add 100g of silica fume to a 5% dilute hydrochloric acid solution and stir to activate for 30min at room temperature. After filtration and washing with water until neutral, disperse the activated silica fume in 300mL of an ethanol-water solution with a volume ratio of 4:1 and sonicate for 30min. Add 11.5g of aminopropyltriethoxysilane and stir to react at 65℃ for 4h. After the reaction is complete, filter, wash and dry to obtain aminated silica fume. S2. 100g of aminated silica fume was dispersed in 400mL of DMF / water mixed solution with a volume ratio of 3:1 and ultrasonically dispersed for 30min. 20g of zirconium tetrachloride and 16g of 2-aminoterephthalic acid were added sequentially and stirred thoroughly for 30min. The mixture was then transferred to a reaction vessel and hydrothermally reacted at 120℃ for 24h. After the reaction was completed, the mixture was naturally cooled to room temperature, centrifuged, washed alternately with DMF and anhydrous ethanol, and vacuum dried to obtain MOF-modified silica fume. S3. Disperse 100g of MOF-modified silica fume in 400ml of anhydrous toluene, add 5.5g of γ-methacryloyloxypropyltrimethoxysilane under nitrogen protection, stir and react at 70℃ for 4.5h, filter after the reaction is completed, wash with anhydrous toluene, and vacuum dry to obtain composite silica fume. S4. Disperse 100g of composite silica fume in 500mL of ethanol-water solution with a volume ratio of 1:1, and sonicate for 20min. Then add 32.5g of butyl acrylate, 14g of hydroxyethyl acrylate and 0.35g of azobisisobutyronitrile in sequence. Under nitrogen protection, stir and react at 60℃ for 6h. After the reaction is completed, filter, wash with anhydrous ethanol to remove unreacted monomers, and vacuum dry to obtain modified silica fume.

[0028] The preparation method of frost-resistant steel pipe concrete includes: adding air-quenched aggregate, manufactured sand and cement into a mixer and dry mixing for 1-2 minutes; adding water-reducing agent and air-entraining agent into water to prepare an admixture aqueous solution, then adding the admixture aqueous solution, composite antifreeze agent and sodium polyacrylate together into the mixer and mixing for 3-5 minutes to obtain a concrete mixture; pumping the concrete mixture into the steel pipe, and continuously vibrating it with an attached vibrator during the pouring process until the concrete surface is covered with slurry and no obvious air bubbles emerge; after pouring, covering the end face with plastic film to prevent moisture evaporation, and curing in a standard curing room with a temperature of 20±2℃ and a relative humidity of ≥95% for 28 days to obtain frost-resistant steel pipe concrete.

[0029] Example 2 This embodiment provides a method for preparing antifreeze steel-tube concrete, comprising, by weight, 650 parts cement, 540 parts manufactured sand, 540 parts air-quenched aggregate, 3.8 parts sodium polyacrylate, 3.0 parts water-reducing agent, 10 parts composite antifreeze agent, 1 part air-entraining agent, and 290 parts water. The composite antifreeze agent is composed of fumed silica, modified silica fume, and calcium nitrite in a mass ratio of 1:6:2. The air-quenched aggregate is a multi-grade compounded air-quenched titanium slag, wherein 40% has a particle size <0.6 mm, 30% has a particle size of 0.6~1.18 mm, and 30% has a particle size of 1.18~2.36 mm.

[0030] Methods for preparing modified silica fume include: S1. Add 100g of silica fume to a 5% dilute hydrochloric acid solution and stir to activate for 30min at room temperature. After filtration and washing with water until neutral, disperse the activated silica fume in 300mL of an ethanol-water solution with a volume ratio of 4:1 and sonicate for 30min. Add 8g of aminopropyltriethoxysilane and stir to react at 50℃ for 6h. After the reaction is complete, filter, wash and dry to obtain aminated silica fume. S2. 100g of aminated silica fume was dispersed in 400mL of DMF / water mixed solution with a volume ratio of 3:1 and ultrasonically dispersed for 30min. 15g of zirconium tetrachloride and 12g of 2-aminoterephthalic acid were added sequentially and stirred thoroughly for 30min. The mixture was then transferred to a reaction vessel and hydrothermally reacted at 100℃ for 30h. After the reaction was completed, the mixture was naturally cooled to room temperature, centrifuged, washed alternately with DMF and anhydrous ethanol, and vacuum dried to obtain MOF-modified silica fume. S3. Disperse 100g of MOF-modified silica fume in 400ml of anhydrous toluene, add 3g of γ-methacryloyloxypropyltrimethoxysilane under nitrogen protection, stir and react at 60℃ for 6h, filter after the reaction is completed, wash with anhydrous toluene, and dry under vacuum to obtain composite silica fume. S4. Disperse 100g of composite silica fume in 500mL of ethanol-water solution with a volume ratio of 1:1, and sonicate for 20min. Then add 25g of butyl acrylate, 10g of hydroxyethyl acrylate and 0.11g of azobisisobutyronitrile in sequence. Under nitrogen protection, stir and react at 50℃ for 8h. After the reaction is completed, filter, wash with anhydrous ethanol to remove unreacted monomers, and vacuum dry to obtain modified silica fume.

[0031] The preparation method of frost-resistant steel pipe concrete includes: adding air-quenched aggregate, manufactured sand and cement into a mixer and dry mixing for 1-2 minutes; adding water-reducing agent and air-entraining agent into water to prepare an admixture aqueous solution, then adding the admixture aqueous solution, composite antifreeze agent and sodium polyacrylate together into the mixer and mixing for 3-5 minutes to obtain a concrete mixture; pumping the concrete mixture into the steel pipe, and continuously vibrating it with an attached vibrator during the pouring process until the concrete surface is covered with slurry and no obvious air bubbles emerge; after pouring, covering the end face with plastic film to prevent moisture evaporation, and curing in a standard curing room with a temperature of 20±2℃ and a relative humidity of ≥95% for 28 days to obtain frost-resistant steel pipe concrete.

[0032] Example 3 This embodiment provides a method for preparing antifreeze steel-tube concrete, comprising, by weight, 670 parts cement, 560 parts manufactured sand, 560 parts air-quenched aggregate, 4.12 parts sodium polyacrylate, 3.2 parts water-reducing agent, 15 parts composite antifreeze agent, 2 parts air-entraining agent, and 304 parts water. The composite antifreeze agent is composed of fumed silica, modified silica fume, and calcium nitrite in a mass ratio of 1:8:4. The air-quenched aggregate is a multi-grade compounded air-quenched titanium slag, wherein 50% has a particle size <0.6 mm, 40% has a particle size of 0.6~1.18 mm, and 10% has a particle size of 1.18~2.36 mm.

[0033] Methods for preparing modified silica fume include: S1. Add 100g of silica fume to a 5% dilute hydrochloric acid solution and stir to activate for 30min at room temperature. After filtration and washing with water until neutral, disperse the activated silica fume in 300mL of an ethanol-water solution with a volume ratio of 4:1 and sonicate for 30min. Add 15g of aminopropyltriethoxysilane and stir to react at 80℃ for 2h. After the reaction is complete, filter, wash and dry to obtain aminated silica fume. S2. 100g of aminated silica fume was dispersed in 400mL of DMF / water mixed solution with a volume ratio of 3:1 and ultrasonically dispersed for 30min. 25g of zirconium tetrachloride and 20g of 2-aminoterephthalic acid were added in sequence and stirred thoroughly for 30min. The mixture was then transferred to a reaction vessel and hydrothermally reacted at 140℃ for 18h. After the reaction was completed, the mixture was naturally cooled to room temperature, centrifuged, washed alternately with DMF and anhydrous ethanol, and vacuum dried to obtain MOF-modified silica fume. S3. Disperse 100g of MOF-modified silica fume in 400ml of anhydrous toluene, add 8g of γ-methacryloyloxypropyltrimethoxysilane under nitrogen protection, stir and react at 80℃ for 3h, filter after the reaction is completed, wash with anhydrous toluene, and dry under vacuum to obtain composite silica fume. S4. Disperse 100g of composite silica fume in 500mL of ethanol-water solution with a volume ratio of 1:1, and sonicate for 20min. Then add 40g of butyl acrylate, 18g of hydroxyethyl acrylate and 0.58g of azobisisobutyronitrile in sequence. Under nitrogen protection, stir and react at 70℃ for 4h. After the reaction is completed, filter, wash with anhydrous ethanol to remove unreacted monomers, and vacuum dry to obtain modified silica fume.

[0034] The preparation method of frost-resistant steel pipe concrete includes: adding air-quenched aggregate, manufactured sand and cement into a mixer and dry mixing for 1-2 minutes; adding water-reducing agent and air-entraining agent into water to prepare an admixture aqueous solution, then adding the admixture aqueous solution, composite antifreeze agent and sodium polyacrylate together into the mixer and mixing for 3-5 minutes to obtain a concrete mixture; pumping the concrete mixture into the steel pipe, and continuously vibrating it with an attached vibrator during the pouring process until the concrete surface is covered with slurry and no obvious air bubbles emerge; after pouring, covering the end face with plastic film to prevent moisture evaporation, and curing in a standard curing room with a temperature of 20±2℃ and a relative humidity of ≥95% for 28 days to obtain frost-resistant steel pipe concrete.

[0035] Comparative Example 1 This comparative example provides a frost-resistant steel pipe concrete and its preparation method. The composition and preparation method are the same as in Example 1, except that the air-quenched aggregate is not graded and the air-quenched aggregate is air-quenched titanium slag with a particle size of <0.6 mm.

[0036] Comparative Example 2 This comparative example provides a frost-resistant steel-tube concrete and its preparation method. The composition and preparation method are the same as in Example 1, except that the modified silica fume is not grafted with MOF structure, and the preparation method of the modified silica fume includes: S1. Add 100g of silica fume to a 5% dilute hydrochloric acid solution and stir to activate for 30min at room temperature. After filtration and washing with water until neutral, disperse the activated silica fume in 400ml of anhydrous toluene. Add 5.5g of γ-methacryloyloxypropyltrimethoxysilane under nitrogen protection and stir to react at 70℃ for 4.5h. After the reaction is complete, filter, wash with anhydrous toluene, and vacuum dry to obtain composite silica fume. S2. Disperse 100g of composite silica fume in 500mL of ethanol-water solution with a volume ratio of 1:1, and sonicate for 20min. Then add 32.5g of butyl acrylate, 14g of hydroxyethyl acrylate and 0.35g of azobisisobutyronitrile in sequence. Under nitrogen protection, stir and react at 60℃ for 6h. After the reaction is completed, filter, wash with anhydrous ethanol to remove unreacted monomers, and vacuum dry to obtain modified silica fume.

[0037] Comparative Example 3 This comparative example provides a frost-resistant steel-tube concrete and its preparation method. The composition and preparation method are the same as in Example 1, except that the modified silica fume is not coated with a polymer layer, and the preparation method of the modified silica fume includes: S1. Add 100g of silica fume to a 5% dilute hydrochloric acid solution and stir to activate for 30min at room temperature. After filtration and washing with water until neutral, disperse the activated silica fume in 300mL of an ethanol-water solution with a volume ratio of 4:1 and sonicate for 30min. Add 11.5g of aminopropyltriethoxysilane and stir to react at 65℃ for 4h. After the reaction is complete, filter, wash and dry to obtain aminated silica fume. S2. 100g of aminated silica fume was dispersed in 400mL of DMF / water mixed solution with a volume ratio of 3:1 and ultrasonically dispersed for 30min. 20g of zirconium tetrachloride and 16g of 2-aminoterephthalic acid were added sequentially and stirred thoroughly for 30min. The mixture was then transferred to a reaction vessel and hydrothermally reacted at 120℃ for 24h. After the reaction was completed, the mixture was naturally cooled to room temperature, centrifuged, washed alternately with DMF and anhydrous ethanol, and vacuum dried to obtain MOF-modified silica fume. S3. Disperse 100g of MOF-modified silica fume in 400ml of anhydrous toluene, add 5.5g of γ-methacryloyloxypropyltrimethoxysilane under nitrogen protection, stir and react at 70℃ for 4.5h, filter after reaction, wash with anhydrous toluene, and dry under vacuum to obtain modified silica fume.

[0038] Comparative Example 4 This comparative example provides a frost-resistant steel-tube concrete and its preparation method. The composition and preparation method are the same as in Example 1, except that the modified silica fume is not subjected to amination treatment. The specific preparation method includes: S1. Add 100g of silica fume to a 5% dilute hydrochloric acid solution and stir to activate for 30min at room temperature. After filtration and washing with water until neutral, disperse the activated silica fume in 400mL of a 3:1 DMF / water mixed solution and sonicate for 30min. Then add 20g of zirconium tetrachloride and 16g of 2-aminoterephthalic acid in sequence, stir thoroughly for 30min, and transfer to a reaction vessel. Perform hydrothermal reaction at 120℃ for 24h. After the reaction is completed, allow it to cool to room temperature naturally, centrifuge, wash with DMF and anhydrous ethanol alternately, and vacuum dry to obtain MOF-modified silica fume. S2. Disperse 100g of MOF-modified silica fume in 400ml of anhydrous toluene, add 5.5g of γ-methacryloyloxypropyltrimethoxysilane under nitrogen protection, stir and react at 70℃ for 4.5h, filter after reaction, wash with anhydrous toluene, and vacuum dry to obtain composite silica fume. S3. Disperse 100g of composite silica fume in 500mL of ethanol-water solution with a volume ratio of 1:1, and sonicate for 20min. Then add 32.5g of butyl acrylate, 14g of hydroxyethyl acrylate and 0.35g of azobisisobutyronitrile in sequence. Under nitrogen protection, stir and react at 60℃ for 6h. After the reaction is completed, filter, wash with anhydrous ethanol to remove unreacted monomers, and vacuum dry to obtain modified silica fume.

[0039] Comparative Example 5 This comparative example provides a frost-resistant steel-tube concrete and its preparation method. The composition and preparation method are the same as in Example 1, except that the composite antifreeze agent is modified silica fume.

[0040] Performance testing The antifreeze-resistant concrete prepared in the examples and comparative examples was subjected to performance testing. The performance test indicators included 28-day compressive strength, freeze-thaw mass loss rate, and freeze-thaw compressive strength loss rate. Among them, the 28-day compressive strength was tested according to the "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" GB / T 50081. The test method was as follows: take out the concrete specimen, wipe the surface dry, place it in the center of the pressure plate of the compression testing machine, and slowly load it (loading rate 0.5 MPa / s) until the specimen breaks. Record the maximum pressure value and calculate the compressive strength. Freeze-thaw mass loss rate and freeze-thaw compressive strength loss rate were tested according to GB / T 50082, "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete". Concrete specimens were saturated with water for 7 days before undergoing freeze-thaw tests. One freeze-thaw cycle consisted of freezing at ~30℃ for 4 hours, followed by thawing in water at 20℃ for 4 hours. A total of 300 cycles were performed. The mass loss rate was calculated after 300 cycles by weighing the dried specimens: Mass loss rate % = (Initial mass - Mass after cycle) / Initial mass × 100%; Compressive strength loss rate % = (Initial 28-day compressive strength - Compressive strength after freeze-thaw) / Initial 28-day compressive strength × 100%. The test results are shown in Table 1.

[0041] Table 1 28-day compressive strength (MPa) Freeze-thaw quality loss rate (%) Freeze-thaw compressive strength loss rate (%) Example 1 67 1.2 7.8 Example 2 65 1.3 8.0 Example 3 68 1.2 7.7 Comparative Example 1 58 3.1 14.2 Comparative Example 2 62 2.4 12.1 Comparative Example 3 61 2.2 11.5 Comparative Example 4 60 2.7 13.3 Comparative Example 5 62 2.0 10.6 Figure 1 Figure (a) shows the morphology of superabsorbent resin in its dry state, and Figure (b) shows the morphology of superabsorbent resin after it has absorbed water to saturation. Figure 2 Figure (a) shows air-quenched titanium slag with a particle size <0.6 mm, Figure (b) shows air-quenched titanium slag with a particle size of 0.6~1.18 mm, and Figure (a) shows air-quenched titanium slag with a particle size of 1.18~2.36 mm. (From...) Figure 3 and 4 It can be seen that, due to the complete multi-layered antifreeze protection system, the damage accumulation in Example 1 is relatively slow and uniform; the comparative example, due to the lack of some key functional structures, has a faster initial damage rate, and as the number of cycles increases, the microcracks continue to expand and connect, resulting in a more obvious acceleration of damage in the later stages.

[0042] As shown in Table 1, the frost-resistant steel-tube concrete prepared in the embodiments of the present invention has good frost and crack resistance. In Comparative Example 1, the wind-quenched aggregate was not graded and consisted entirely of fine particles, resulting in poor aggregate packing density, increased internal porosity of the concrete, weakened the overall strength and density of the matrix, and lacked the interlocking and filling of coarse and fine aggregates, failing to form a tight skeleton structure. This made it easier for water to penetrate and the frost heave stress could not be effectively dispersed and transferred. Therefore, the 28-day compressive strength decreased significantly, and the freeze-thaw mass loss rate and compressive strength loss rate increased substantially. In Comparative Example 2, the modified silica fume was not incorporated. The branched MOF structure, lacking the high specific surface area nanoporous network provided by the metal-organic framework, cannot effectively store and slowly release moisture to achieve dynamic humidity regulation. It also lacks the function of the pores as a moisture buffer space to mitigate frost heave pressure during freeze-thaw cycles. Although the outer polymer layer still provides flexible protection, the absence of MOF water storage and regulation results in a high content of free water that can be frozen inside the concrete, leading to a significant decrease in freeze-thaw performance. In Comparative Example 3, the modified silica fume without a polymer coating layer loses the flexible crack resistance and stress buffering function provided by the acrylate copolymer, and also lacks the hydrophobic polymer layer. The protective inner MOF structure makes the MOF susceptible to partial degradation in the high-alkali environment of concrete. Furthermore, the loss of the synergistic dispersion effect between the polymer layer and the water-reducing agent leads to poor dispersibility of the modified silica fume in the mixture, affecting the density and uniformity of the concrete. Consequently, both compressive strength and freeze-thaw resistance decrease. In Comparative Example 4, the modified silica fume was not pretreated with amination, resulting in a lack of coordination anchoring points on the silica fume surface. MOF crystals could not grow uniformly and firmly in situ on the silica fume surface, instead tending to form freely in solution, significantly reducing the MOF's water storage, humidity regulation, and pore buffering capabilities. The effectiveness of the free MOF is also affected by its tendency to agglomerate, which affects dispersion. Therefore, the freeze-thaw resistance is significantly worse than that of Example 1. In Comparative Example 5, the composite antifreeze agent only uses modified silica fume, which lacks the synergistic effect of fumed silica and calcium nitrite. The nanoscale filling of fumed silica cannot effectively seal the nanopore channels inside the concrete, thus reducing the water penetration resistance. The lack of calcium nitrite causes the steel pipe surface to be unable to form a passivation protective film and loses its early strength contribution. The multi-level antifreeze protection system constructed by the three components from the nano, micro and ionic scales is destroyed, thus reducing the freeze-thaw resistance.

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A frost-resistant steel pipe concrete, characterized by: The cement is 650-670 parts by weight, the machine-made sand is 540-560 parts by weight, the air-quenching aggregate is 540-560 parts by weight, the superabsorbent resin is 3.8-4.12 parts by weight, the water reducing agent is 3.0-3.2 parts by weight, the composite anti-freezing agent is 10-15 parts by weight, the air entraining agent is 1-2 parts by weight, and the water is 290-304 parts by weight; the composite anti-freezing agent is composed of fumed silica, modified silica fume and calcium nitrite.

2. A frost-resistant steel pipe concrete according to claim 1, characterized in that: In the composite anti-freezing agent, the mass ratio of fumed silica, modified silica fume and calcium nitrite is 1:(6-8):(2-4).

3. The frost-resistant steel pipe concrete according to claim 1, wherein: The preparation method of the modified silica fume comprises: S1, after the silica fume is activated by dilute hydrochloric acid, it is dispersed in an ethanol aqueous solution, and aminopropyl triethoxysilane is added, and stirred at 50-80 DEG C for 2-6 hours, filtered, washed and dried to obtain aminated silica fume; S2, the aminated silica fume is dispersed in a DMF / water solution, then zirconium tetrachloride and 2-amino terephthalic acid are added, and hydrothermal reaction is carried out at 100-140 DEG C for 18-30 hours, centrifuged, washed and dried to obtain MOF modified silica fume; S3, the MOF modified silica fume is dispersed in anhydrous toluene, gamma-methacryloxypropyl trimethoxysilane is added, and stirred at 60-80 DEG C for 3-6 hours, filtered, washed and dried to obtain composite silica fume; S4, the composite silica fume is dispersed in an ethanol aqueous solution, butyl acrylate, hydroxyethyl acrylate and azobisisobutyronitrile are added, and stirred at 50-70 DEG C for 4-8 hours under nitrogen protection, filtered, washed and dried to obtain modified silica fume.

4. A frost-resistant steel tube concrete according to claim 3, wherein: In step S1, the mass ratio of the activated silica fume and aminopropyl triethoxysilane is 100:(8-15).

5. A frost-resistant steel tube concrete according to claim 3, wherein: In step S2, the mass ratio of the aminated silica fume, zirconium tetrachloride and 2-amino terephthalic acid is 100:(15-25):(12-20).

6. An anti-freeze steel tube concrete according to claim 3, wherein: In step S3, the mass ratio of the MOF modified silica fume and gamma-methacryloxypropyl trimethoxysilane is 100:(3-8).

7. A frost-resistant steel pipe concrete according to claim 3, wherein: In step S4, the mass ratio of the composite silica fume, butyl acrylate and hydroxyethyl acrylate is 100:(25-40):(10-18); the amount of azobisisobutyronitrile is 0.3-1.0% of the total mass of monomers.

8. The frost-resistant steel pipe concrete according to claim 1, wherein: The air-quenching aggregate is a multi-stage compounded air-quenching ilmenite slag, wherein the air-quenching ilmenite slag with a particle size of less than 0.6 mm accounts for 40-50%, the air-quenching ilmenite slag with a particle size of 0.6-1.18 mm accounts for 30-40%, and the rest is the air-quenching ilmenite slag with a particle size of 1.18-2.36 mm.

9. The frost-resistant steel pipe concrete according to claim 1, wherein: The cement is Portland cement, the superabsorbent resin is sodium polyacrylate, and the water reducing agent is at least one of polycarboxylic acid type, melamine type, fatty acid type, and aminosulfonate type; the air entraining agent is at least one of rosin hot polymer, alkyl benzene sulfonate, fatty alcohol polyoxyethylene ether, and triterpene saponin.

10. A method of producing a frost-resistant steel tube concrete according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: The wind quenching aggregate, the machine-made sand and the cement are put into a mixer for dry mixing for 1-2 minutes; the water reducing agent and the air entraining agent are added into water to prepare an admixture aqueous solution, and then the admixture aqueous solution, the composite anti-freezing agent and the superabsorbent resin are added into the mixer for stirring for 3-5 minutes to obtain a concrete mixture; the concrete mixture is poured into the steel pipe in a pumping mode, and the concrete is continuously vibrated until the surface of the concrete is covered with a layer of paste during the pouring process; and after the pouring is completed, curing is carried out to obtain the anti-freezing steel pipe concrete.

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