Anti-freezing steel pipe concrete and preparation method thereof

Abstract

The application relates to the technical field of concrete preparation, in particular to an anti-freezing steel pipe concrete and a preparation method thereof, which comprises the following components in parts by weight: cement 650-670 parts, machine-made sand 540-560 parts, air-quenched aggregate 540-560 parts, high water absorption resin 3.8-4.12 parts, water reducing agent 3.0-3.2 parts, composite anti-freezing agent 10-15 parts, air entraining agent 1-2 parts and water 290-304 parts; the composite anti-freezing agent is composed of fumed silica, modified silica ash and calcium nitrite. Through the synergistic cooperation of the composite anti-freezing agent, the high water absorption resin, the air entraining agent, the water reducing agent and the air-quenched aggregate, a multi-scale and multi-mechanism anti-freezing protection system is constructed, and the freeze-thaw damage problem of the steel pipe concrete when applied in cold regions is effectively solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of concrete preparation, and particularly relates to an anti-freezing steel pipe concrete and a preparation method thereof. BACKGROUND

[0002] Steel pipe concrete is a composite structural material formed by filling concrete in a steel pipe, wherein the steel pipe provides effective lateral restraint to the core concrete, making the concrete in a three-dimensional compression state, thereby significantly improving its compressive strength and ductility; at the same time, the core concrete provides support to the steel pipe, delaying or preventing local buckling of the steel pipe, and fully exerting the tensile strength of the steel pipe. This composite structure has the characteristics of high bearing capacity, good ductility, fast construction speed, excellent seismic performance, etc., and has been widely used in major projects such as high-rise buildings, large-span bridges, offshore platforms, etc. With the expansion of infrastructure construction to cold regions, the long-term durability of steel pipe concrete structures in low-temperature environments has become increasingly prominent, and the damage of freeze-thaw cycles to the core concrete is one of the key factors affecting the safety of the structure.

[0003] The anti-freezing performance of concrete mainly depends on its internal pore structure and free water content. When the temperature drops below the freezing point, the free water in the pores of the concrete freezes and expands, generating internal stress, and repeated freeze-thaw cycles will cause the internal micro-cracks of the concrete to gradually expand, eventually causing strength loss and structural damage. To improve the anti-freezing performance of concrete, current technical measures mainly include introducing air bubbles to buffer the frost heaving stress, reducing porosity to improve density, and reducing free water content. Common technical means include adding air entraining agents to form uniformly distributed micro-bubbles in the concrete, using high-performance water reducing agents to reduce the water-cement ratio, adding mineral admixtures to refine the pore size distribution, and using water-absorbing materials for internal curing. In addition, for the special working environment of steel pipe concrete, corrosion protection of the steel pipe also needs to be considered, usually by adding rust inhibitors to passivate the steel surface to prevent corrosion of the steel pipe caused by chloride ions or other corrosive media.

[0004] Chinese patent CN113354368A discloses an anti-freezing concrete, which adds a freeze-proofing agent made of calcium nitrate, triterpene saponin, cetyltrimethylammonium bromide, carboxymethyl cellulose, and hydroxypropyl distarch phosphate into the concrete, so that many closed small air bubbles are formed in the concrete, which is beneficial to the pressure relief when the free water in the concrete freezes and expands, thereby resisting the damage of ice to the internal structure of the concrete; at the same time, the patent also uses polyacrylic acid sodium superabsorbent resin particles to further reduce the degree of frost heaving by reducing the proportion of free water during the initial setting of the concrete, and to fill the pores after the concrete is solidified, thereby improving the compressive strength of the concrete. However, this patent technology mainly aims at improving the anti-freezing performance of ordinary concrete, and does not fully consider the special working conditions of steel pipe concrete in low-temperature environments and the long-term durability problems of the concrete-steel pipe interface. SUMMARY

[0005] Therefore, the application provides the anti-freezing steel pipe concrete and a preparation method thereof to solve the problems of insufficient anti-freezing performance of the steel pipe concrete in the prior art, easy damage and deterioration of the internal structure of the concrete under the freeze-thaw cycle, and poor long-term durability of the interface between the steel pipe and the core concrete.

[0006] The technical scheme of the application is as follows: the application provides an anti-freezing steel pipe concrete, which comprises, 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 superabsorbent resin, 3.0-3.2 parts of water reducing agent, 10-15 parts of composite anti-freezing agent, 1-2 parts of air entraining agent, and 290-304 parts of water; the composite anti-freezing agent is composed of fumed silica, modified silica fume, and calcium nitrite.

[0007] Preferably, in the composite anti-freezing agent, the mass ratio of the fumed silica, the modified silica fume, and the calcium nitrite is 1:(6-8):(2-4).

[0008] Specifically, in the application, the cement, the machine-made sand, and the air-quenched aggregate are compounded to form the matrix structure of the concrete, wherein the air-quenched aggregate has the porous characteristics and good interface bonding performance, and can enhance the overall strength and durability of the concrete. The fumed silica, the modified silica fume, and the calcium nitrite are compounded to form the composite anti-freezing agent, and a good anti-freezing protection network is established, wherein the fumed silica as the nanoscale filling material can effectively block the nanoscale pore channel in the concrete, and block the water penetration path from the source; the MOF structure is introduced into the modified silica fume by modifying the surface of the silica fume, and the water is stored and the internal humidity environment is dynamically adjusted during the freeze-thaw cycle; at the same time, the flexible groups grafted on the surface can effectively relieve the concentration transmission of the frost heaving stress in the matrix, and improve the anti-cracking performance; the calcium nitrite can provide early strength and passivate the steel pipe surface to form a protective film to prevent corrosion, and the three components construct a multi-level anti-freezing protection system from the nanoscale, the microscale, to the ionic scale. The superabsorbent resin absorbs and stores water during the hardening process of the concrete, and slowly releases the water in the later period to realize internal curing, and the water storage function of the modified silica fume forms a synergistic complement, which can not only reduce the early shrinkage but also reduce the content of the freezable water. The water reducing agent can enhance the compactness by improving the fluidity of the concrete, and the air entraining agent introduces the uniformly distributed micro-bubbles in the concrete to provide a buffer space for the frost heaving. The components cooperate with each other through multiple mechanisms such as dense filling, pore regulation, bubble buffering, internal curing, and interface protection, so that the concrete can still maintain good mechanical properties and durability when bearing repeated freeze-thaw cycles, and the long-term stability of the interface between the steel pipe and the core concrete is ensured.

[0009] Based on the above technical solutions, preferably, the preparation method of the modified silica ash comprises:

[0010] S1, after the silica ash is activated by dilute hydrochloric acid, it is dispersed in an ethanol aqueous solution, and aminopropyl triethoxysilane is added, and stirring reaction is carried out at 50-80℃ for 2-6h, and then filtration, washing and drying are carried out to obtain aminated silica ash;

[0011] S2, the aminated silica ash 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℃ for 18-30h, and then centrifugal washing and drying are carried out to obtain MOF modified silica ash;

[0012] S3, the MOF modified silica ash is dispersed in anhydrous toluene, and gamma-methacryloxypropyl trimethoxysilane is added, and stirring reaction is carried out at 60-80℃ for 3-6h, and then filtration, washing and drying are carried out to obtain composite silica ash;

[0013] S4, the composite silica ash is dispersed in an ethanol aqueous solution, and butyl acrylate, hydroxyethyl acrylate and azobisisobutyronitrile are added, and stirring reaction is carried out at 50-70℃ for 4-8h under nitrogen protection, and then filtration, washing and drying are carried out to obtain modified silica ash.

[0014] Specifically, in step S1, the impurities and inert oxide layers on the surface of the silica ash are removed by activation with dilute hydrochloric acid, so that the surface silicon hydroxyl is fully exposed, and the amino group introduced on the surface of the silica ash by the amino propyl triethoxysilane not only improves the surface activity and hydrophilicity of the silica ash, but also provides a coordination anchoring site for the subsequent in-situ growth of the MOF structure. In step S2, the UiO-66-NH2 type metal organic framework structure is formed by in-situ hydrothermal synthesis of zirconium tetrachloride and 2-amino terephthalic acid on the surface of the amino-functionalized silica ash, which can capture and store water molecules to slowly release water during the curing period of the concrete to achieve continuous internal curing, and can act as a buffer space to weaken the frost heaving pressure during freeze-thaw cycles, while 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, the MOF modified silica ash surface is provided with a polymerizable carbon-carbon double bond active site by gamma-methacryloxypropyl trimethoxysilane. In step S4, by free radical initiated copolymerization, butyl acrylate and hydroxyethyl acrylate are grafted on the composite silica ash surface to form a polymer coating layer, wherein the butyl acrylate unit has a long alkyl side chain to impart excellent flexibility and hydrophobicity to the polymer layer, which can effectively buffer the brittle transmission of frost heaving stress and bridge and inhibit the initiation and propagation of microcracks through its elastic deformation capacity, significantly improving the crack resistance of the concrete matrix, while reducing the excessive penetration of external moisture into the MOF layer, and the hydroxyl groups of the hydroxyethyl acrylate unit maintain the moderate hydrophilicity of the material and form a hydrogen bond network with the concrete matrix to enhance the interfacial adhesion, while the polymer layer forms a protective barrier for the inner MOF structure to avoid its degradation in the high alkalinity environment of the concrete. In addition, the acrylate structure in the polymer layer has a similar chemical backbone to polycarboxylic acid superplasticizer, and the two produce a synergistic dispersion effect in the aqueous phase, effectively reducing the frictional resistance and agglomeration tendency between the modified silica ash particles, thereby significantly improving the fluidity and dispersion uniformity of the composite anti-freezing agent in the concrete mixture.

[0015] On the basis of the above technical scheme, preferably, in step S1, the mass ratio of the activated silica ash to the amino propyl triethoxysilane is 100:(8-15).

[0016] On the basis of the above technical scheme, preferably, in step S2, the mass ratio of the amino-functionalized silica ash to the zirconium tetrachloride to the 2-amino terephthalic acid is 100:(15-25):(12-20).

[0017] On the basis of the above technical scheme, preferably, in step S3, the mass ratio of the MOF modified silica ash to the gamma-methacryloxypropyl trimethoxysilane is 100:(3-8).

[0018] Preferably, in step S4, the mass ratio of the composite silica fume, butyl acrylate and hydroxyethyl acrylate is 100:(25-40):(10-18); and the amount of the azobisisobutyronitrile is 0.3-1.0% of the total mass of the monomers.

[0019] Preferably, in the above technical solution, the air-quenching aggregate is a multi-stage compounded air-quenching titanomelte slag, wherein the air-quenching titanomelte slag with a particle size of less than 0.6 mm accounts for 40-50%, the air-quenching titanomelte slag with a particle size of 0.6-1.18 mm accounts for 30-40%, and the rest is the air-quenching titanomelte slag with a particle size of 1.18-2.36 mm.

[0020] The air-quenching titanomelte slag is an industrial byproduct formed by high-speed airflow quenching of high-temperature molten titanomelte slag, and the rapid cooling process forms a large number of glassy phases and micro-pore structures in the slag, which endow the aggregate with good water absorption and water release capacity, and can realize multi-level internal curing with the superabsorbent resin and modified silica fume during the hardening process of the concrete. Meanwhile, the nano-micropore in the aggregate can serve as a dispersed buffer space to accommodate water frost heaving during freeze-thaw cycles, effectively dispersing and releasing frost heaving stress to avoid its concentrated transmission in the concrete matrix. In the present application, the air-quenching titanomelte slag is compounded in multiple stages, wherein the fine aggregate with a particle size of less than 0.6 mm serves as the main filling phase, which can effectively fill the voids between the coarse aggregates and provide sufficient specific surface area to enhance the contact area with the cement paste; the medium aggregate with a particle size of 0.6-1.18 mm serves as a skeleton transition; and the coarse aggregate with a particle size of 1.18-2.36 mm constitutes the main bearing skeleton of the concrete. Through the mutual interlocking and filling of aggregates with different particle sizes, the porosity in the concrete is minimized and the packing density is improved, forming a more compact microstructure system, which further improves the strength and frost resistance of the steel pipe concrete.

[0021] Preferably, in the above technical solution, the cement is Portland cement, the superabsorbent resin is sodium polyacrylate, the water reducing agent is at least one of polycarboxylic acid type, melamine type, fatty acid type, and aminosulfonate type, and the air entraining agent is at least one of rosin hot polymer, alkyl benzene sulfonate, fatty alcohol polyoxyethylene ether, and triterpene saponin.

[0022] The present application also provides a preparation method of the anti-frost steel pipe concrete, comprising the following steps:

[0023] Put the air quenching aggregate, machine-made sand and cement into the mixer and dry mix for 1-2 minutes; prepare an admixture aqueous solution by adding water reducing agent and air entraining agent into water, and then add the admixture aqueous solution, composite anti-freezing agent and superabsorbent resin into the mixer and stir for 3-5 minutes to obtain a concrete mixture; pour the concrete mixture into the steel pipe by pumping and continuously vibrate the concrete surface to make it smooth during the pouring process; and then perform curing after the pouring is completed to obtain the anti-freezing steel pipe concrete.

[0024] The anti-freezing steel pipe concrete and the preparation method thereof have the following beneficial effects relative to the prior art:

[0025] (1) By synergistic cooperation of the composite anti-freezing agent, superabsorbent resin, air entraining agent, water reducing agent and air quenching aggregate, a multi-scale and multi-mechanism anti-freezing protection system is constructed, effectively solving the freeze-thaw damage problem of the steel pipe concrete when applied in cold regions. The air phase silicon dioxide, modified silica fume and calcium nitrite in the composite anti-freezing agent synergistically act from aspects of nano-filling, pore regulation and interface protection, the superabsorbent resin and air entraining agent reduce the freezable water content and release the frost heaving stress through internal curing and air bubble buffer mechanism, and the porous structure and optimized grading of the air quenching aggregate further improve the matrix density and stress dispersion capacity, so that the concrete can still maintain good mechanical properties and durability after repeated freeze-thaw cycles, and the long-term stability of the steel pipe and core concrete interface is ensured.

[0026] (2) The modified silica fume in the present application forms a core-shell structure of silica fume core-MOF water storage layer-polymer flexible shell layer, wherein the high specific surface area and pore structure of the MOF layer can effectively store and release water, providing a buffer space during freeze-thaw cycles, and the outer polymer coating not only endows the material with flexible anti-cracking properties and hydrophobic protection, but also improves the flowability and dispersion uniformity of the composite anti-freezing agent in the concrete through synergistic dispersion effect with the water reducing agent, thereby synergistically improving the freeze-thaw cycle resistance and long-term durability of the concrete at multiple scales of micro, meso and macro.

[0027] (3) The present application uses air quenching titanium slag as aggregate and performs multi-stage compounding, fully utilizing the porous structure and active glassy properties formed by the rapid cooling and quenching, the nanometer micropores inside the aggregate can be used as a dispersed buffer space to accommodate the frost heaving stress, the rough surface morphology and active ingredients enhance the bonding performance of the aggregate-slip interface, and through multi-stage grading, different particle size aggregates are interlocked and filled, thereby maximizing the packing density and reducing the permeability, and a multi-level anti-freezing protection system is constructed from the inside of the aggregate, the interface zone to the whole matrix. BRIEF DESCRIPTION OF DRAWINGS

[0028] 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.

[0029] Figure 1 These are morphological diagrams of the superabsorbent resin of the present invention after drying and after water saturation.

[0030] Figure 2 This is a morphological diagram of the air-quenched titanium slag of the present invention;

[0031] 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.

[0032] 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

[0033] 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.

[0034] 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.

[0035] Example 1

[0036] 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.

[0037] Methods for preparing modified silica fume include:

[0038] S1, 100 g of silica ash was added to a dilute hydrochloric acid solution with a mass concentration of 5%, stirred and activated at room temperature for 30 min, and after filtering and washing with water until neutral, the activated silica ash was dispersed in 300 mL of an ethanol aqueous solution with a volume ratio of 4:1, ultrasonic dispersed for 30 min, 11.5 g of aminopropyl triethoxysilane was added, and stirred and reacted at 65℃ for 4 h. After the reaction was completed, filtration, washing and drying were performed to obtain aminated silica ash;

[0039] S2, 100 g of aminated silica ash was dispersed in 400 mL of a DMF / water mixed solution with a volume ratio of 3:1, ultrasonic dispersed for 30 min, 20 g of zirconium tetrachloride and 16 g of 2-amino terephthalic acid were sequentially added, and after being fully stirred for 30 min, it was transferred to a reaction kettle, and hydrothermal reaction was performed at 120℃ for 24 h. After the reaction was completed, it was naturally cooled to room temperature, centrifugally separated, washed with DMF and anhydrous ethanol alternately, and vacuum dried to obtain MOF modified silica ash;

[0040] S3, 100 g of MOF modified silica ash was dispersed in 400 mL of anhydrous toluene, 5.5 g of γ-methacryloxypropyl trimethoxysilane was added under nitrogen protection, and stirred and reacted at 70℃ for 4.5 h. After the reaction was completed, filtration, washing with anhydrous toluene and vacuum drying were performed to obtain composite silica ash;

[0041] S4, 100 g of composite silica ash was dispersed in 500 mL of an ethanol aqueous solution with a volume ratio of 1:1, ultrasonic dispersed for 20 min, 32.5 g of butyl acrylate, 14 g of hydroxyethyl acrylate and 0.35 g of azobisisobutyronitrile were sequentially added, and stirred and reacted at 60℃ for 6 h under nitrogen protection. After the reaction was completed, filtration, washing with anhydrous ethanol to remove unreacted monomers and vacuum drying were performed to obtain modified silica ash.

[0042] The preparation method of the anti-freezing steel pipe concrete comprises the following steps: dry mixing air quenched aggregate, machine-made sand and cement in a mixer for 1-2 min; preparing an admixture aqueous solution by adding water reducing agent and air entraining agent into water, and then adding the admixture aqueous solution, a composite anti-freezing agent and sodium polyacrylate into the mixer and stirring for 3-5 min to obtain a concrete mixture; pouring the concrete mixture into a steel pipe in a pumping mode, continuously vibrating the concrete mixture by using an attached vibrator during the pouring process until the concrete surface is covered with paste and no obvious bubbles are generated; covering the end face of the concrete with a plastic film after the pouring is completed to prevent water evaporation, and curing the concrete in a standard curing room with a temperature of 20±2℃ and a relative humidity of ≥95% for 28 d to obtain the anti-freezing steel pipe concrete.

[0043] Example 2

[0044] The embodiment provides an anti-freezing steel pipe concrete and a preparation method thereof, and the anti-freezing steel pipe concrete comprises, in parts by weight, 650 parts of cement, 540 parts of machine-made sand, 540 parts of air-quenched aggregate, 3.8 parts of sodium polyacrylate, 3.0 parts of water reducing agent, 10 parts of composite anti-freezing agent, 1 part of air entraining agent and 290 parts of water, wherein the composite anti-freezing agent is composed of fumed silica, modified silica ash and calcium nitrite with a mass ratio of 1:6:2; and the air-quenched aggregate is a multi-stage compounded air-quenched ilmenite slag, wherein the particle size of 40% of the air-quenched aggregate is less than 0.6 mm, the particle size of 30% of the air-quenched aggregate is 0.6-1.18 mm, and the particle size of 30% of the air-quenched aggregate is 1.18-2.36 mm.

[0045] The preparation method of the modified silica ash comprises the following steps:

[0046] S1, 100g of silica ash is added to a dilute hydrochloric acid solution with a mass concentration of 5%, stirred and activated at room temperature for 30min, and then filtered and washed with water until neutral; after that, the activated silica ash is dispersed in 300mL of an ethanol water solution with a volume ratio of 4:1, ultrasonic dispersed for 30min, 8g of aminopropyl triethoxysilane is added, and stirred and reacted at 50℃ for 6h; after the reaction is completed, the aminopropyl triethoxysilane is filtered, washed and dried to obtain aminated silica ash;

[0047] S2, 100g of the aminated silica ash is dispersed in 400mL of a DMF / water mixed solution with a volume ratio of 3:1, ultrasonic dispersed for 30min, 15g of zirconium tetrachloride and 12g of 2-amino terephthalic acid are added in sequence, stirred for 30min, and then transferred to a reaction kettle to be hydrothermally reacted at 100℃ for 30h; after the reaction is completed, the reaction kettle is naturally cooled to room temperature, centrifugally separated, washed with DMF and anhydrous ethanol in sequence, and vacuum dried to obtain MOF modified silica ash;

[0048] S3, 100g of the MOF modified silica ash is dispersed in 400ml of anhydrous toluene, 3g of gamma-methacryloxypropyl trimethoxysilane is added under the protection of nitrogen, stirred and reacted at 60℃ for 6h; after the reaction is completed, the product is extracted by filtration, washed with anhydrous toluene, and vacuum dried to obtain composite silica ash;

[0049] S4, 100g of the composite silica ash is dispersed in 500mL of an ethanol water solution with a volume ratio of 1:1, ultrasonic dispersed for 20min, 25g of butyl acrylate, 10g of hydroxyethyl acrylate and 0.11g of azobisisobutyronitrile are added in sequence, stirred and reacted at 50℃ for 8h under the protection of nitrogen; after the reaction is completed, the product is extracted by filtration, washed with anhydrous ethanol to remove unreacted monomers, and vacuum dried to obtain modified silica ash.

[0050] The preparation method of the anti-freezing steel pipe concrete comprises the following steps: dry mixing wind-quenched aggregate, machine-made sand and cement in a mixer for 1-2 minutes; preparing an admixture aqueous solution by adding water reducing agent and air entraining agent into water, and then adding the admixture aqueous solution, a composite anti-freezing agent and sodium polyacrylate into the mixer for stirring for 3-5 minutes to obtain a concrete mixture; pouring the concrete mixture into a steel pipe by using a pumping mode, continuously vibrating by using an attached vibrator during the pouring process until the concrete surface is covered with paste and no obvious bubbles are generated; covering the end face with a plastic film after the pouring is completed to prevent water evaporation, and curing in a standard curing room with a temperature of 20±2 DEG C and a relative humidity of 95% or more for 28 days to obtain the anti-freezing steel pipe concrete.

[0051] Example 3

[0052] The embodiment provides an anti-freezing steel pipe concrete and a preparation method thereof, and the anti-freezing steel pipe concrete comprises, in parts by weight, 670 parts of cement, 560 parts of machine-made sand, 560 parts of wind-quenched aggregate, 4.12 parts of sodium polyacrylate, 3.2 parts of water reducing agent, 15 parts of a composite anti-freezing agent, 2 parts of air entraining agent and 304 parts of water, wherein the composite anti-freezing agent is composed of fumed silica, modified silica ash and calcium nitrite with a mass ratio of 1:8:4; and the wind-quenched aggregate is a multi-stage compounded wind-quenched ilmenite slag, wherein the content of the wind-quenched ilmenite slag with a particle size of less than 0.6 mm is 50%, the content of the wind-quenched ilmenite slag with a particle size of 0.6-1.18 mm is 40%, and the content of the wind-quenched ilmenite slag with a particle size of 1.18-2.36 mm is 10%.

[0053] The preparation method of the modified silica ash comprises the following steps:

[0054] S1, 100g of silica ash is added into a dilute hydrochloric acid solution with a mass concentration of 5%, stirred and activated at room temperature for 30 minutes, filtered and washed with water until neutral, and then the activated silica ash is dispersed in 300mL of an ethanol aqueous solution with a volume ratio of 4:1, ultrasonic dispersed for 30 minutes, 15g of aminopropyl triethoxysilane is added, and stirred and reacted at 80 DEG C for 2 hours; after the reaction is completed, the aminopropyl triethoxysilane is filtered, washed and dried to obtain aminated silica ash;

[0055] S2, 100g of the aminated silica ash is dispersed in 400mL of a DMF / water mixed solution with a volume ratio of 3:1, ultrasonic dispersed for 30 minutes, 25g of zirconium tetrachloride and 20g of 2-amino terephthalic acid are sequentially added, stirred for 30 minutes, and then transferred into a reaction kettle, and hydrothermal reaction is carried out at 140 DEG C for 18 hours; after the reaction is completed, the reaction kettle is naturally cooled to room temperature, centrifugally separated, washed with DMF and anhydrous ethanol alternately, and vacuum dried to obtain MOF modified silica ash.

[0056] S3, 100 g of the MOF-modified silica fume was dispersed in 400 ml of anhydrous toluene, 8 g of γ-methacryloxypropyltrimethoxysilane was added under nitrogen protection, and the reaction was stirred at 80℃ for 3 h. After the reaction was completed, it was filtered, washed with anhydrous toluene, and vacuum dried to obtain a composite silica fume;

[0057] S4, 100 g of the composite silica fume was dispersed in 500 mL of an ethanol-water solution with a volume ratio of 1:1, ultrasonic dispersion was performed for 20 min, 40 g of butyl acrylate, 18 g of hydroxyethyl acrylate, and 0.58 g of azobisisobutyronitrile were sequentially added, and the reaction was stirred at 70℃ for 4 h under nitrogen protection. After the reaction was completed, it was filtered, washed with anhydrous ethanol to remove unreacted monomers, and vacuum dried to obtain the modified silica fume.

[0058] The preparation method of the anti-freezing steel pipe concrete comprises the following steps: dry mixing air-quenched aggregates, machine-made sand, and cement in a mixer for 1-2 min; preparing an admixture aqueous solution by adding a water reducing agent and an air entraining agent into water, and then adding the admixture aqueous solution, a composite anti-freezing agent, and sodium polyacrylate into the mixer to stir for 3-5 min to obtain a concrete mixture; pouring the concrete mixture into a steel pipe in a pumping mode, continuously vibrating the concrete surface with an attached vibrator until the concrete surface is covered with a paste and no obvious bubbles are generated during the pouring process; covering the end face with a plastic film after pouring to prevent water evaporation, and curing in a standard curing room with a temperature of 20±2℃ and a relative humidity of ≥95% for 28 d to obtain the anti-freezing steel pipe concrete.

[0059] Comparative Example 1

[0060] The present comparative example provides an anti-freezing steel pipe concrete and a preparation method thereof, which have the same composition and preparation method as those of Example 1, except that the air-quenched aggregates are not graded, and the air-quenched aggregates are air-quenched ilmenite slag with a particle size of <0.6 mm.

[0061] Comparative Example 2

[0062] The present comparative example provides an anti-freezing steel pipe concrete and a preparation method thereof, which have the same composition and preparation method as those of Example 1, except that the modified silica fume is not grafted with a MOF structure, and the preparation method of the modified silica fume comprises the following steps:

[0063] S1, 100 g of silica fume was added to a 5% dilute hydrochloric acid solution, stirred at room temperature for 30 min, and then filtered and washed with water until neutral. The activated silica fume was dispersed in 400 ml of anhydrous toluene, 5.5 g of γ-methacryloxypropyltrimethoxysilane was added under nitrogen protection, and the reaction was stirred at 70℃ for 4.5 h. After the reaction was completed, it was filtered, washed with anhydrous toluene, and vacuum dried to obtain a composite silica fume;

[0064] S2, 100 g of the composite silica fume was dispersed in 500 mL of an ethanol aqueous solution with a volume ratio of 1:1, and ultrasonic dispersion was performed for 20 min. Then, 32.5 g of butyl acrylate, 14 g of hydroxyethyl acrylate, and 0.35 g of azobisisobutyronitrile were sequentially added, and reaction was performed under stirring at 60°C for 6 h under nitrogen protection. After the reaction was completed, unreacted monomers were removed by filtration and washing with anhydrous ethanol, and vacuum drying was performed to obtain the modified silica fume.

[0065] Comparative Example 3

[0066] The present comparative example provides an anti-frozen steel pipe concrete and a preparation method thereof. The composition and the preparation method are the same as those in Example 1, and the difference lies in that the modified silica fume is not coated with a polymer layer, and the preparation method of the modified silica fume comprises:

[0067] S1, 100 g of the silica fume was added to a dilute hydrochloric acid solution with a mass concentration of 5%, and stirring activation was performed at room temperature for 30 min. After filtration and washing to neutral, the activated silica fume was dispersed in 300 mL of an ethanol aqueous solution with a volume ratio of 4:1, ultrasonic dispersion was performed for 30 min, 11.5 g of aminopropyl triethoxysilane was added, and reaction was performed under stirring at 65°C for 4 h. After the reaction was completed, filtration, washing, and drying were performed to obtain the aminated silica fume;

[0068] S2, 100 g of the aminated silica fume was dispersed in 400 mL of a DMF / water mixed solution with a volume ratio of 3:1, ultrasonic dispersion was performed for 30 min, 20 g of zirconium tetrachloride and 16 g of 2-amino terephthalic acid were sequentially added, stirring was performed for 30 min, and then the mixture was transferred to a reaction kettle, hydrothermal reaction was performed at 120°C for 24 h, the reaction was naturally cooled to room temperature after being completed, centrifugal separation was performed, washing was performed with DMF and anhydrous ethanol alternately, and vacuum drying was performed to obtain the MOF-modified silica fume;

[0069] S3, 100 g of the MOF-modified silica fume was dispersed in 400 mL of anhydrous toluene, 5.5 g of γ-methacryloxypropyl trimethoxysilane was added under nitrogen protection, reaction was performed under stirring at 70°C for 4.5 h, filtration was performed after the reaction was completed, washing was performed with anhydrous toluene, and vacuum drying was performed to obtain the modified silica fume.

[0070] Comparative Example 4

[0071] The present comparative example provides an anti-frozen steel pipe concrete and a preparation method thereof. The composition and the preparation method are the same as those in Example 1, and the difference lies in that the modified silica fume is not subjected to amination treatment, and the specific preparation method comprises:

[0072] S1, 100 g of silica ash was added to a dilute hydrochloric acid solution with a mass concentration of 5%, stirred and activated at room temperature for 30 min, and after filtering and washing with water until neutral, the activated silica ash was dispersed in a 400 mL mixed solution of DMF / water with a volume ratio of 3:1, ultrasonic dispersed for 30 min, 20 g of zirconium tetrachloride and 16 g of 2-amino terephthalic acid were added in turn, stirred for 30 min, then transferred to a reaction kettle, and hydrothermally reacted at 120°C for 24 h. After the reaction was completed, it was naturally cooled to room temperature, centrifuged, washed with DMF and anhydrous ethanol alternately, and vacuum dried to obtain MOF modified silica ash;

[0073] S2, 100 g of MOF modified silica ash was dispersed in 400 ml of anhydrous toluene, 5.5 g of γ-methacryloxypropyltrimethoxysilane was added under nitrogen protection, and stirred at 70°C for 4.5 h. After the reaction was completed, it was suction filtered, washed with anhydrous toluene, and vacuum dried to obtain composite silica ash.

[0074] S3, 100 g of composite silica ash was dispersed in 500 mL of an ethanol aqueous solution with a volume ratio of 1:1, ultrasonic dispersed for 20 min, 32.5 g of butyl acrylate, 14 g of hydroxyethyl acrylate, and 0.35 g of azobisisobutyronitrile were added in turn, and stirred at 60°C for 6 h under nitrogen protection. After the reaction was completed, it was suction filtered, washed with anhydrous ethanol to remove unreacted monomers, and vacuum dried to obtain modified silica ash.

[0075] Comparative Example 5

[0076] This comparative example provides an anti-freezing steel pipe concrete and a preparation method thereof. The composition and preparation method are the same as those of Example 1, and the difference lies in that the composite anti-freezing agent is modified silica ash.

[0077] Performance detection

[0078] The anti-freezing concrete prepared from the examples and comparative examples is subjected to performance detection, and the performance detection indexes include 28d compressive strength, freeze-thaw mass loss rate and freeze-thaw compressive strength loss rate. Among them, the 28d compressive strength is detected according to the Standard for Testing Methods of Mechanical Properties of Ordinary Concrete GB / T 50081, and the detection method is as follows: the concrete test block is taken out, the surface is wiped dry, and placed in the center of the pressure test machine bearing plate, slowly loaded (loading rate 0.5 MPa / s), until the test block is damaged, the maximum pressure value is recorded, and the compressive strength is calculated. The freeze-thaw mass loss rate and the freeze-thaw compressive strength loss rate are detected according to the Standard for Testing Methods of Long-term Performance and Durability of Ordinary Concrete GB / T 50082, and the concrete test block is saturated with water for 7d, then subjected to freeze-thaw test, freeze-thaw cycle: frozen at ~30℃ for 4h, then thawed in water at 20℃ for 4h, as one cycle, a total of 300 cycles; mass loss rate: after 300 cycles, dry the test block and weigh, calculate the mass loss rate, mass loss rate%= (initial mass-cycle mass) / initial mass ×100%; compressive strength loss rate%= (initial 28d compressive strength-freeze-thaw compressive strength) / initial 28d compressive strength ×100%. The detection results are shown in Table 1.

[0079] Table 1

[0080] 28d Compressive strength (MPa) Freeze-thaw mass loss (%) Freeze-thaw compressive strength loss (%) 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

[0081] Figure 1 Fig. (a) in the figure is the morphology of the superabsorbent resin in dry state, and Fig. (b) is the morphology of the superabsorbent resin after being saturated with water; Figure 2 Fig. (a) in the figure is air-quenched titaniferous slag with particle size <0.6mm, Fig. (b) is air-quenched titaniferous slag with particle size of 0.6-1.18mm, and Fig. (a) is air-quenched titaniferous slag with particle size of 1.18-2.36mm. From Figure 3 and 4 It can be seen that, in Example 1, the damage accumulation is relatively slow and uniform due to the complete multi-level anti-freezing protection system; in the comparative example, the initial damage rate is fast due to the absence of some key functional structures, and with the increase of cycle number, the microcracks continuously expand and connect, and the damage accelerates more obviously in the later stage.

[0082] As can be seen from Table 1, the anti-freezing and anti-cracking performance of the anti-freezing steel pipe concrete prepared in the embodiment of the present application is good. In the comparative example 1, the wind-quenched aggregate is not graded, and all of them are fine particles, which leads to poor aggregate packing density, increased internal porosity of the concrete, weakened overall strength and density of the matrix, and lack of mutual interlocking and filling of coarse and fine aggregates, so that a tight skeleton structure cannot be formed, water permeation is easier, and frost heaving stress cannot be effectively dispersed and transmitted, thus the 28d compressive strength is significantly reduced, and the frost-melting mass loss rate and the compressive strength loss rate are greatly increased. In the comparative example 2, the modified silica ash is not grafted with MOF structure, which loses the high specific surface area nanochannel network provided by the metal organic framework, cannot effectively store and release water to achieve dynamic humidity control, and also lacks the function of the pore cavity as a water buffer space to weaken the frost heaving pressure during the freeze-thaw cycle. Although the outer polymer still has a flexible protective effect, in the absence of MOF water storage and regulation, the internal freezable water content of the concrete is high, leading to a significant decrease in freeze-thaw performance. In the comparative example 3, the modified silica ash is not coated with a polymer layer, which loses the flexible anti-cracking and stress buffering function provided by the acrylate copolymer, and also lacks the protection of the polymer hydrophobic layer to the inner MOF structure, so that the MOF is prone to partial degradation in the high-alkali environment of the concrete, and the synergistic dispersion effect of the polymer layer and the water reducing agent disappears, leading to poor dispersibility of the modified silica ash in the mixture, affecting the density and uniformity of the concrete, and thus the compressive strength and freeze-thaw resistance are both decreased. In the comparative example 4, the modified silica ash is not pretreated by amination, which leads to a lack of coordination anchoring sites on the surface of the silica ash, and the MOF crystals cannot grow uniformly and firmly in situ on the surface of the silica ash, but tend to be generated freely in the solution, which greatly reduces the effectiveness of MOF water storage and humidity control and pore buffering, and the free MOF is prone to aggregation, thus the freeze-thaw resistance is significantly worse than that of the embodiment 1. In the comparative example 5, the composite anti-freezing agent only uses modified silica ash, lacking the synergistic effect of fumed silica and calcium nitrite, in which the nanoscale filling of fumed silica cannot effectively block the nanopore channel in the concrete, leading to a decrease in water permeation resistance, and the absence of calcium nitrite leads to the failure to form a passivation protective film on the surface of the steel pipe and the loss of early strength contribution, thus the multi-level anti-freezing protection system constructed from nanoscale, microscale to ionic scale is destroyed, and the freeze-thaw resistance is decreased.

[0083] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A type of frost-resistant steel-pipe concrete, characterized in that: By weight, it comprises 650-670 parts cement, 540-560 parts manufactured sand, 540-560 parts air-quenched aggregate, 3.8-4.12 parts superabsorbent resin, 3.0-3.2 parts water-reducing agent, 10-15 parts composite antifreeze agent, 1-2 parts air-entraining agent, and 290-304 parts water; the composite antifreeze agent is composed of fumed silica, modified silica fume, and calcium nitrite. The modified silica fume is prepared by the following method steps: 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.

2. The antifreeze steel-tube concrete as described in claim 1, characterized in that: In the composite antifreeze agent, the mass ratio of fumed silica, modified silica fume and calcium nitrite is 1:(6~8):(2~4).

3. The antifreeze steel-tube concrete as described in claim 1, characterized in that: In step S1, the mass ratio of activated silica fume to aminopropyltriethoxysilane is 100:(8~15).

4. The antifreeze steel-pipe concrete as described in claim 1, characterized in that: In step S2, the mass ratio of the aminated silica fume, zirconium tetrachloride, and 2-aminoterephthalic acid is 100:(15~25):(12~20).

5. The antifreeze steel-pipe concrete as described in claim 1, characterized in that: In step S3, the mass ratio of the MOF-modified silica fume to γ-methacryloyloxypropyltrimethoxysilane is 100:(3~8).

6. The antifreeze steel-tube concrete as described in claim 1, characterized in that: 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.

7. The antifreeze steel-tube concrete as described in claim 1, characterized in that: The air-quenched aggregate is a multi-grade 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.

8. The antifreeze steel-tube concrete as described in claim 1, characterized in that: The cement is silicate cement, the superabsorbent resin is sodium polyacrylate, and 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; the air-entraining agent is at least one of rosin thermal polymer, alkylbenzene sulfonate, fatty alcohol polyoxyethylene ether, and triterpenoid saponin.

9. A method for preparing frost-resistant steel-tube concrete as described in any one of claims 1 to 8, characterized in that: Includes 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.

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