A fly ash-based admixture and its preparation method

Abstract

This invention discloses a fly ash-based admixture and its preparation method, belonging to the field of building materials technology. This invention uses fly ash as the main component, in conjunction with slag, steel slag, and volcanic rock powder, significantly improving the utilization rate of industrial solid waste and reducing cement usage, lowering the heat of hydration in concrete, and effectively suppressing temperature cracks in large-volume concrete. Simultaneously, the introduction of volcanic rock powder further supplements the active silica-alumina components, enhancing the pozzolanic effect and improving later-stage strength. The introduction of gypsum can regulate setting time and provide a sulfate-activating environment, promoting the early hydration reaction of the fly ash system and solving the problem of low early-stage strength in traditional admixtures. The "micro-aggregate effect" of the fly ash-based admixture of this invention fills the pores of concrete, making the structure denser and improving impermeability and mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a fly ash-based admixture and its preparation method. Background Technology

[0002] Fly ash refers to the fine particles collected from the flue gas of coal-fired power plant boilers. It is a major solid waste product after coal combustion, with a huge annual output. It is the fine ash content collected by dust collectors (such as electrostatic precipitators and bag filters) after pulverized coal is burned at high temperatures in the boiler and discharged with the flue gas from the boiler tail end. With increasingly stringent environmental protection requirements and the promotion of sustainable development concepts, the resource utilization of fly ash has become an important issue.

[0003] Engineering practice has proven that incorporating a certain amount of fly ash as a mineral admixture or auxiliary cementitious material can improve concrete performance, save cement usage, enhance the quality of concrete components and projects, and reduce production costs and project costs. Fly ash has become an indispensable raw material for concrete. Numerous studies have indicated that replacing part of the cement with fly ash in concrete can not only reduce the number of temperature cracks but also lower the heat of hydration in large-volume concrete, enhance its workability, and, by using two or more mineral admixtures combined with appropriate modifiers, achieve complementary advantages, which is more beneficial for improving the overall performance of concrete than using a single type.

[0004] Chinese patent document CN103435287A discloses a fly ash composite admixture for concrete and its preparation method. This invention mainly addresses the technical difficulties of existing mineral admixtures, such as excessive slump, significant chemical shrinkage and autogenous shrinkage, and high usage costs. The technical solution adopted by this invention is: a fly ash composite admixture for concrete, prepared from slag, stone chips, fly ash, and desulfurized gypsum as raw materials, wherein the weight percentages of the raw materials are: slag 20-30%, stone chips 4-15%, fly ash 58-73%, and desulfurized gypsum 1-4%. The preparation method includes the following steps: first, fly ash is pulverized into ultrafine fly ash using an ultrafine pulverizing device; then, slag, stone chips, and desulfurized gypsum are mixed evenly and ball-milled into powder; finally, the ultrafine fly ash is mixed with the ball-milled powder and homogenized to produce the fly ash composite admixture for concrete. However, in this patent's preparation method, solid particles are prone to secondary agglomeration during ball milling, which affects the dispersibility and activity of the admixture in concrete. Summary of the Invention

[0005] The main objective of this invention is to propose a fly ash-based admixture and its preparation method.

[0006] To achieve the above objectives, the present invention proposes a fly ash-based admixture, comprising the following components by weight: 30-50 parts fly ash, 5-20 parts gypsum, 10-20 parts volcanic rock powder, 10-20 parts slag, 10-15 parts steel slag, and 1-5 parts functional additives.

[0007] Preferably, the fly ash is Class II fly ash.

[0008] Preferably, the gypsum is at least one of desulfurized gypsum, anhydrite, fluorogypsum, and phosphogypsum.

[0009] Preferably, the preparation method of the functional additive is as follows:

[0010] (1) Under a nitrogen atmosphere, 2-hydroxyethyl methacrylate phosphate and γ-glycidyl etheroxypropyltrimethoxysilane were added to dimethyl sulfoxide and mixed evenly. Trifluoroacetic acid was added as a catalyst and the mixture was heated to react. After the reaction was completed, the phosphate ester-based silane modifier was obtained by distillation.

[0011] (2) Add talc powder to a mixed solvent of deionized water and anhydrous ethanol, add phosphate ester-based silane modifier, heat to react, and then centrifuge, wash and dry to obtain modified talc powder;

[0012] (3) Add modified talc and azobisisobutyronitrile to N,N-dimethylformamide and mix evenly. Add dimethyl diallyl ammonium chloride, react at a constant temperature, filter, collect the solid, wash and dry to obtain the functional additive.

[0013] Preferably, in step (1), the mass ratio of 2-hydroxyethyl methacrylate phosphate, γ-glycidyl etheroxypropyltrimethoxysilane, and trifluoroacetic acid is 1.2-1.5:1:0.3-0.5; the heating reaction temperature is 40-60℃, and the reaction time is 4-6h.

[0014] In this step, the reaction between 2-hydroxyethyl methacrylate phosphate and γ-glycidyl etheroxypropyltrimethoxysilane retains the original silicon-oxygen bond linkage ability of the silane coupling agent, while introducing carbon-carbon double bonds and phosphate groups. Compared with ordinary physical blending, the 2-hydroxyethyl methacrylate phosphate in physical blending will be randomly dispersed in the mixing water and cannot be enriched on the surface of cement particles, thus failing to play an efficient role.

[0015] Preferably, in step (2), the mass ratio of talc powder to phosphate ester-based silane modifier is 5-8:3-6; the heating reaction temperature is 20-40℃, and the reaction time is 1-2h.

[0016] Talc is a natural flaky silicate mineral with excellent lubricating properties. In admixture systems, it can significantly reduce the frictional resistance between powder particles, reduce particle wear, and thus improve the flow efficiency of the powder. In this step, a phosphate ester-based silane modifier is grafted onto talc. On the one hand, this can improve the dispersibility of talc, better fill the tiny pores in cement paste, optimize the pore structure of concrete, and improve the density and durability of concrete. On the other hand, the introduced phosphate ester functional groups undergo hydrolysis in the alkaline environment of concrete, continuously releasing active phosphate ions. These phosphate ions react chemically with calcium ions in cement hydration products to form a dense, insoluble phosphate layer in situ on the surface of cement particles, forming a "chemical barrier" that further enhances the impermeability and waterproofing ability of concrete.

[0017] Preferably, in step (3), the mass ratio of modified talc, azobisisobutyronitrile, and dimethyl diallyl ammonium chloride is 1:0.05-0.1:0.2-0.5; the constant temperature reaction temperature is 60-80℃, and the reaction time is 5-8h.

[0018] In this step, dimethyl diallyl ammonium chloride is introduced onto the modified talc powder, enabling the modified talc powder to be firmly anchored to the surface of the powder particles and the interface of newly formed cracks through electrostatic adsorption, forming a charged adsorption layer. This charged layer generates an electrostatic repulsion barrier, effectively preventing close contact between particles and inhibiting secondary agglomeration caused by van der Waals forces between particles. This significantly reduces the surface energy of the particles and the interfacial frictional resistance, making the particles more prone to brittle fracture under mechanical stress, greatly improving grinding efficiency, ensuring that the grinding products maintain a good dispersion state, and better stimulating the internal reactivity of the admixture, promoting the hydration reaction of the material, generating more hydration products, thereby improving the strength and durability of concrete.

[0019] The present invention also provides a method for preparing the above-mentioned fly ash-based admixture, comprising the following steps:

[0020] Slag, steel slag, and gypsum are mixed, crushed, and screened. Then fly ash, volcanic rock powder, and functional additives are added and ground to obtain the fly ash-based admixture.

[0021] Preferably, the grinding speed is 45-55 r / min and the grinding time is 50-60 min.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1) This invention uses fly ash as the main component, in combination with slag, steel slag, and volcanic rock powder, to significantly improve the utilization rate of industrial solid waste and reduce cement usage, thereby lowering the heat of hydration in concrete and effectively inhibiting temperature cracks in large-volume concrete. Simultaneously, fly ash exhibits high reactivity; under alkaline conditions, its inert coating is destroyed, allowing it to participate in hydration reactions and generate hydration products such as CASH / CSH, improving the strength and durability of concrete. The introduction of volcanic rock powder further supplements the active silica-alumina components, enhancing the pozzolanic effect and improving later-stage strength. The introduction of gypsum can regulate setting time and provide a sulfate-activating environment, promoting early hydration reactions in the fly ash system and solving the problem of low early-stage strength in traditional admixtures. The "micro-aggregate effect" of the fly ash-based admixture in this invention fills concrete pores, making the structure denser and improving impermeability and mechanical properties.

[0024] 2) The preparation of the functional additive of the present invention first involves reacting 2-hydroxyethyl methacrylate phosphate and γ-glycidyl etheroxypropyltrimethoxysilane to obtain a phosphate ester-based silane modifier. Then, the phosphate ester-based silane modifier is grafted onto the surface of talc powder. On the one hand, this improves the dispersibility of talc powder, enabling it to better fill the micropores in cement paste, optimize the pore structure of concrete, and improve the density and durability of concrete. Finally, dimethyl diallyl ammonium chloride is introduced onto the modified talc powder, which significantly reduces the particle surface energy and interfacial friction resistance, inhibits the secondary agglomeration phenomenon caused by van der Waals attraction between particles, greatly improves grinding efficiency, ensures that the grinding product maintains a good dispersion state, and can better stimulate the internal reactivity of the admixture, promote the hydration reaction of the material, generate more hydration products, thereby improving the strength and durability of concrete. Detailed Implementation

[0025] To avoid unnecessary details, unless otherwise specified, all items used in the following examples are commercially available products, and all methods used are conventional methods unless otherwise specified.

[0026] The sources of some of the raw materials used in this invention are as follows:

[0027] The fly ash, grade II, comes from Huaneng Dalian Power Plant. Its chemical composition is as follows: Al2O3 content 37.45%, SiO2 content 32.27%, Fe2O3 content 20.7%, TiO2 content 3.9%, CaO content 2.4%, SO3 content 0.6%, MgO content 0.45%, and other substances content 2.23%.

[0028] The volcanic rock powder, sourced from Jiajiang County, Ya'an City, Sichuan Province, has the following chemical composition: Al2O3 content 15.43%, SiO2 content 61.09%, Fe2O3 content 5.3%, SO3 content 0.77%, MgO content 2.7%, K2O content 2.37%, CaO content 7.78%, Na2O content 3.30%, and other substances content 1.26%.

[0029] The slag, sourced from Yongfeng Steel Co., Ltd., has the following chemical composition: Al2O3 content 15.26%, SiO2 content 35.26%, Fe2O3 content 0.81%, SO3 content 1.27%, K2O content 0.43%, CaO content 36.03%, Na2O content 0.10%, and other substances content 10.84%.

[0030] The steel slag from Anshan Iron and Steel Plant in Liaoning Province has the following chemical composition: CaO content 35.62%, Fe2O3 content 26.13%, SiO2 content 8.72%, MgO content 6.14%, Al2O3 content 5.10%, SO3 content 0.52%, MnO content 1.17%, P2O5 content 1.34%, and other substances content 15.26%.

[0031] Talc powder, 325 mesh, purchased from Tianjin Yandong Haotian Mineral Products Co., Ltd. Example 1

[0032] A method for preparing a fly ash-based admixture includes the following steps:

[0033] Mix 150g of slag, 128g of steel slag, and 100g of desulfurized gypsum, crush and sieve to a particle size of 2-10mm, then add 400g of fly ash, 150g of volcanic rock powder, and 30g of functional additives, and grind at 50r / min for 60min to obtain the fly ash-based admixture.

[0034] The preparation method of the functional additive is as follows:

[0035] (1) Under a nitrogen atmosphere, 13g of 2-hydroxyethyl methacrylate phosphate and 10g of γ-glycidyl etheroxypropyltrimethoxysilane were added to 300mL of dimethyl sulfoxide and mixed evenly. 4g of trifluoroacetic acid catalyst was added and the temperature was raised to 50℃ for 5h. After the reaction was completed, the phosphate ester-based silane modifier was obtained by distillation.

[0036] (2) Add 36g of talc powder to a mixed solvent of 200mL of deionized water and anhydrous ethanol (the volume ratio of deionized water and anhydrous ethanol is 1:1), add 27g of phosphate ester-based silane modifier, heat at 30℃ for 1.5h, centrifuge after the reaction is complete, collect the solid, wash and dry to obtain modified talc powder.

[0037] (3) Add 30g of modified talc powder and 1.8g of azobisisobutyronitrile to 200mL of N,N-dimethylformamide and mix evenly. Add 10.5g of dimethyl diallyl ammonium chloride and react at 70℃ for 6h. Filter, collect the solid, wash and dry to obtain the functional additive. Example 2

[0038] A method for preparing a fly ash-based admixture includes the following steps:

[0039] Mix 100g of slag, 100g of steel slag, and 50g of desulfurized gypsum, crush and sieve to a particle size of 2-10mm, then add 300g of fly ash, 100g of volcanic rock powder, and 10g of functional additives, and grind at 60r / min for 50min to obtain the fly ash-based admixture.

[0040] The preparation method of the functional additive is as follows:

[0041] (1) Under a nitrogen atmosphere, 12g of 2-hydroxyethyl methacrylate phosphate and 10g of γ-glycidyl etheroxypropyltrimethoxysilane were added to 300mL of dimethyl sulfoxide and mixed evenly. 3g of trifluoroacetic acid catalyst was added and the temperature was raised to 40℃ for 6h. After the reaction was completed, the phosphate ester-based silane modifier was obtained by distillation.

[0042] (2) Add 30g of talc powder to a mixed solvent of 200mL of deionized water and anhydrous ethanol (the volume ratio of deionized water and anhydrous ethanol is 1:1), add 18g of phosphate ester-based silane modifier, heat at 20℃ for 2h, centrifuge after the reaction is completed, collect the solid, wash and dry to obtain modified talc powder.

[0043] (3) Add 30g of modified talc powder and 1.5g of azobisisobutyronitrile to 200mL of N,N-dimethylformamide and mix evenly. Add 6g of dimethyl diallyl ammonium chloride and react at 60℃ for 8h. Filter, collect the solid, wash and dry to obtain the functional additive. Example 3

[0044] A method for preparing a fly ash-based admixture includes the following steps:

[0045] Mix 200g of slag, 150g of steel slag, and 200g of desulfurized gypsum, crush and sieve to a particle size of 2-10mm, then add 500g of fly ash, 200g of volcanic rock powder, and 50g of functional additives, and grind at 50r / min for 60min to obtain the fly ash-based admixture.

[0046] The preparation method of the functional additive is as follows:

[0047] (1) Under a nitrogen atmosphere, 15g of 2-hydroxyethyl methacrylate phosphate and 10g of γ-glycidyl etheroxypropyltrimethoxysilane were added to 300mL of dimethyl sulfoxide and mixed evenly. 5g of trifluoroacetic acid catalyst was added and the temperature was raised to 60℃ for 4h. After the reaction was completed, the phosphate ester-based silane modifier was obtained by distillation.

[0048] (2) Add 32g of talc powder to a mixed solvent of 200mL of deionized water and anhydrous ethanol (the volume ratio of deionized water and anhydrous ethanol is 1:1), add 24g of phosphate ester-based silane modifier, heat at 40℃ for 1h, centrifuge after the reaction is complete, collect the solid, wash and dry to obtain modified talc powder.

[0049] (3) Add 30g of modified talc powder and 3g of azobisisobutyronitrile to 200mL of N,N-dimethylformamide and mix evenly. Add 15g of dimethyl diallyl ammonium chloride and react at 80℃ for 5h. Filter, collect the solid, wash and dry to obtain the functional additive.

[0050] Comparative Example 1

[0051] A method for preparing a fly ash-based admixture includes the following steps:

[0052] Mix 150g of slag, 128g of steel slag, and 100g of desulfurized gypsum, crush and sieve to a particle size of 2-10mm, then add 400g of fly ash, 150g of volcanic rock powder, and 30g of functional additives, and grind at 50r / min for 60min to obtain the fly ash-based admixture.

[0053] The preparation method of the functional additive is as follows:

[0054] (1) Under a nitrogen atmosphere, 13g of 2-hydroxyethyl methacrylate phosphate and 10g of γ-glycidyl etheroxypropyltrimethoxysilane were added to 300mL of dimethyl sulfoxide and mixed evenly. 4g of trifluoroacetic acid catalyst was added and the temperature was raised to 50℃ for 5h. After the reaction was completed, the phosphate ester-based silane modifier was obtained by distillation.

[0055] (2) Add 36g of talc powder to a mixed solvent of 200mL of deionized water and anhydrous ethanol (the volume ratio of deionized water and anhydrous ethanol is 1:1), add 27g of phosphate ester-based silane modifier, heat at 30℃ for 1.5h, centrifuge after the reaction is complete, collect the solid, wash and dry to obtain the functional additive.

[0056] Comparative Example 2

[0057] A method for preparing a fly ash-based admixture includes the following steps:

[0058] Mix 150g of slag, 128g of steel slag, and 100g of desulfurized gypsum, crush and sieve to a particle size of 2-10mm, then add 400g of fly ash, 150g of volcanic rock powder, and 30g of functional additives, and grind at 50r / min for 60min to obtain the fly ash-based admixture.

[0059] The preparation method of the functional additive is as follows:

[0060] Under a nitrogen atmosphere, 13g of 2-hydroxyethyl methacrylate phosphate and 10g of γ-glycidyl etheroxypropyltrimethoxysilane were added to 300mL of dimethyl sulfoxide and mixed thoroughly. 4g of trifluoroacetic acid catalyst was added, and the mixture was heated to 150℃ and reacted for 5h. After the reaction was completed, the functional additive was obtained by distillation.

[0061] Comparative Example 3

[0062] A method for preparing a fly ash-based admixture includes the following steps:

[0063] Mix 150g of slag, 128g of steel slag, and 100g of desulfurized gypsum, crush and sieve to a particle size of 2-10mm, then add 400g of fly ash, 150g of volcanic rock powder, and 30g of talc powder and grind at 50r / min for 60min to obtain the fly ash-based admixture.

[0064] Performance testing

[0065] Compressive strength test: The fly ash-based admixtures obtained in Examples 1-3 and Comparative Examples 1-3 were prepared into mortar test blocks at a water-cement ratio of 0.32. The mortar mixing process was carried out in accordance with GB / T17671-2021 "Test Method for Strength of Cement Mortar". Standard specimens of 40mm×40mm×160mm were prepared and cured under standard curing conditions for 28 days. The compressive strength was tested using a universal testing machine.

[0066] Water absorption test: Refer to British Standard BS 1881, Part 122, 1983, and take test blocks that have been cured for 28 days for testing;

[0067] Permeability pressure test: The test was conducted according to GB / T50082-2009 standard for test methods of long-term performance and durability of ordinary concrete. The test results are shown in Table 1.

[0068] Table 1 Performance test results of fly ash-based admixtures

[0069]

[0070] As can be seen from the experimental results in Table 1, the fly ash-based admixture of this application can significantly improve the compressive strength and durability of concrete.

[0071] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A fly ash-based admixture, characterized in that, It includes the following components by weight: 30-50 parts fly ash, 5-20 parts gypsum, 10-20 parts volcanic rock powder, 10-20 parts slag, 10-15 parts steel slag, and 1-5 parts functional additives. The preparation method of the functional additive is as follows: (1) Under a nitrogen atmosphere, 2-hydroxyethyl methacrylate phosphate and γ-glycidyl etheroxypropyltrimethoxysilane were added to dimethyl sulfoxide and mixed evenly. Trifluoroacetic acid was added as a catalyst and the mixture was heated to react. After the reaction was completed, the phosphate ester-based silane modifier was obtained by distillation. (2) Add talc powder to a mixed solvent of deionized water and anhydrous ethanol, add phosphate ester-based silane modifier, heat to react, and then centrifuge, wash and dry to obtain modified talc powder; (3) Add modified talc and azobisisobutyronitrile to N,N-dimethylformamide and mix evenly. Add dimethyl diallyl ammonium chloride, react at a constant temperature, filter, collect the solid, wash and dry to obtain the functional additive. In step (1), the mass ratio of 2-hydroxyethyl methacrylate phosphate, γ-glycidyl etheroxypropyltrimethoxysilane, and trifluoroacetic acid is 1.2-1.5:1:0.3-0.

5. In step (1), the temperature for heating the reaction is 40-60℃ and the reaction time is 4-6h. In step (2), the mass ratio of talc powder to phosphate ester-based silane modifier is 5-8:3-6. In step (2), the heating reaction temperature is 20-40℃ and the reaction time is 1-2h; In step (3), the mass ratio of modified talc, azobisisobutyronitrile, and dimethyl diallyl ammonium chloride is 1:0.05-0.1:0.2-0.

5. In step (3), the constant temperature reaction temperature is 60-80℃ and the reaction time is 5-8h.

2. The fly ash-based admixture according to claim 1, characterized in that: The gypsum is at least one of desulfurized gypsum, anhydrite, fluorogypsum, and phosphogypsum.

3. A method for preparing the fly ash-based admixture according to any one of claims 1-2, characterized in that, The process includes the following steps: mixing slag, steel slag, and gypsum, crushing and screening them, then adding fly ash, volcanic rock powder, and functional additives for grinding to obtain the fly ash-based admixture.

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