Fly ash-based admixture and preparation method thereof

Abstract

The invention discloses a fly ash-based admixture and a preparation method thereof, and belongs to the technical field of building materials. The fly ash is used as a main body and cooperates with the slag, the steel slag and the volcanic rock powder, so that the utilization rate of industrial solid wastes is remarkably increased, the cement consumption is reduced, the hydration heat of the concrete is reduced, temperature cracks of mass concrete can be effectively inhibited, and meanwhile, the introduction of the volcanic rock powder further supplements active silicon-aluminum components, enhances the volcanic ash effect and improves the later strength; by introducing gypsum, the setting time can be adjusted, a sulfate excitation environment is provided, an early hydration reaction of a fly ash system is promoted, the problem that a traditional admixture is low in early strength is solved, concrete pores are filled through the micro-aggregate effect of the fly ash-based admixture, the structure is denser, and anti-permeability and mechanical properties are improved.

Description

Technical Field

[0001] The invention relates to the technical field of building materials, and in particular to a fly ash-based admixture and a preparation method thereof. Background Art

[0002] Fly ash, the fine particles collected from the flue gas of coal-fired power plant boilers, is the primary solid waste produced after coal combustion, with significant annual production. After pulverized coal is burned at high temperatures in boilers, it is discharged with the flue gas from the boiler exhaust and collected by dust collectors (such as electrostatic precipitators and bag filters). With increasingly stringent environmental protection requirements and the promotion of sustainable development concepts, the resource utilization of fly ash has become a key issue.

[0003] Engineering practice has proven that incorporating a certain amount of fly ash as a mineral admixture or supplementary cementitious material can improve concrete properties, reduce cement usage, enhance the quality of concrete components and projects, and reduce production and project costs. Fly ash has become an indispensable raw material for concrete. Numerous studies indicate that replacing part of the cement with fly ash in concrete can not only reduce the number of thermal cracks but also lower the heat of hydration of large-volume concrete, thereby enhancing concrete performance. Furthermore, combining two or more mineral admixtures with appropriate modifiers can achieve complementary advantages, potentially improving the overall properties of concrete more effectively than using a single mineral admixture alone.

[0004] Chinese patent document CN103435287A discloses a fly ash composite admixture for concrete and its preparation method. This invention primarily addresses the technical difficulties of existing mineral admixtures, such as excessive slump, large chemical and autogenous shrinkage, and high cost. The invention employs a technical solution: the fly ash composite admixture for concrete is prepared from slag, stone chips, fly ash, and desulfurized gypsum. The weight percentages of the raw materials are: 20-30% slag, 4-15% stone chips, 58-73% fly ash, and 1-4% desulfurized gypsum. The preparation method comprises the following steps: first, pulverizing the fly ash using ultrafine grinding equipment to produce ultrafine fly ash; then, mixing the slag, stone chips, and desulfurized gypsum uniformly and ball-milling them into a powder; and finally, mixing the ultrafine fly ash with the ball-milled powder and homogenizing it to produce the fly ash composite admixture for concrete. During the ball milling process, the solid particles in this patented preparation method are prone to secondary agglomeration, which can affect the dispersibility and activity of the admixture in concrete. Summary of the Invention

[0005] The main purpose of the present invention is to provide a fly ash-based admixture and a preparation method thereof.

[0006] To achieve the above objectives, the present invention proposes a fly ash-based admixture comprising the following components in parts 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, fluorinated gypsum and phosphogypsum.

[0009] Preferably, the preparation method of the functional additive is as follows: (1) Under a nitrogen atmosphere, 2-hydroxyethyl methacrylate phosphate and γ-glycidyloxypropyltrimethoxysilane are added to dimethyl sulfoxide and mixed evenly, trifluoroacetic acid as a catalyst is added, the temperature is raised to react, and after the reaction is completed, the phosphate-based silane modifier is obtained by distillation; (2) adding talc powder to a mixed solvent of deionized water and anhydrous ethanol, adding a phosphate silane modifier, heating to react, and then centrifuging, washing, and drying to obtain modified talc powder; (3) Add modified talc and azobisisobutyronitrile to N,N-dimethylformamide and mix evenly, add dimethyldiallylammonium chloride, react at a constant temperature, filter, collect the solid, wash and dry to obtain a functional additive.

[0010] Preferably, in step (1), the mass ratio of 2-hydroxyethyl methacrylate phosphate, γ-glycidyloxypropyltrimethoxysilane, and trifluoroacetic acid is 1.2-1.5:1:0.3-0.5; the temperature of the heating reaction is 40-60° C., and the reaction time is 4-6 h.

[0011] In this step, the reaction between 2-hydroxyethyl methacrylate phosphate and γ-glycidyloxypropyltrimethoxysilane retains the original silicon-oxygen bonding ability of the silane coupling agent while introducing carbon-carbon double bonds and phosphate groups. Compared with ordinary physical blending, the physically blended 2-hydroxyethyl methacrylate phosphate will be randomly dispersed in the mixing water and cannot be enriched on the surface of cement particles, and cannot function efficiently.

[0012] Preferably, in step (2), the mass ratio of talc powder to phosphate-based silane modifier is 5-8:3-6; the heating reaction temperature is 20-40° C., and the reaction time is 1-2 h.

[0013] Talc is a natural sheet-silicate mineral with excellent lubricating properties. In the admixture system, it can significantly reduce the frictional resistance between powder particles and reduce particle wear, thereby improving the flow efficiency of the powder. In this step, the phosphate-based silane modifier is grafted onto the talc. On the one hand, it can improve the dispersibility of the talc, better fill the tiny pores in the cement stone, optimize the pore structure of the concrete, and improve the density and durability of the concrete. In addition, the introduced phosphate functional groups are hydrolyzed in the alkaline environment of the concrete, continuously releasing active phosphate ions. These phosphate ions chemically react with the calcium ions in the cement hydration products to form a dense and insoluble phosphate thin layer in situ on the surface of the cement particles, forming a "chemical barrier" and further enhancing the concrete's anti-permeability and waterproofing capabilities.

[0014] Preferably, in step (3), the mass ratio of modified talc, azobisisobutyronitrile, and dimethyldiallylammonium chloride is 1:0.05-0.1:0.2-0.5; the constant temperature reaction temperature is 60-80° C., and the reaction time is 5-8 h.

[0015] In this step, dimethyldiallylammonium chloride is introduced into the modified talc powder, so that the modified talc powder can be firmly anchored on the surface of the powder particles and the interface of the newly formed cracks through the electrostatic adsorption mechanism, forming a charged adsorption layer. The charge layer generates an electrostatic repulsion barrier, which effectively hinders the close contact between the particles and inhibits the secondary agglomeration phenomenon caused by the van der Waals attraction between the particles. It significantly reduces the surface energy and interfacial friction resistance of the particles, making the particles more prone to brittle fracture under mechanical stress, greatly improving the grinding efficiency, ensuring that the grinding products remain in a good dispersed state, and can better stimulate the reaction activity inside the admixture, promote the hydration reaction of the material, and generate more hydration products, thereby improving the strength and durability of the concrete.

[0016] The present invention also provides a method for preparing the fly ash-based admixture, comprising the following steps: The slag, steel slag and gypsum are mixed, crushed and sieved, and then fly ash, volcanic rock powder and functional additives are added and ground to obtain the fly ash-based admixture.

[0017] Preferably, the grinding speed is 45-55 r / min, and the grinding time is 50-60 min.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1) The present 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 consumption, thereby reducing the hydration heat of concrete and effectively inhibiting temperature cracks in large-volume concrete. At the same time, the fly ash has high reactivity. Under alkaline conditions, its inert coating is destroyed, allowing it to participate in hydration reactions to generate hydration products such as CASH / CSH, thereby improving the strength and durability of concrete. The introduction of volcanic rock powder further supplements the active silicon and aluminum components, enhances the pozzolanic effect, and improves the later strength. The introduction of gypsum can adjust the setting time and provide a sulfate-stimulating environment, promoting the early hydration reaction of the fly ash system, thereby solving the problem of low early strength of traditional admixtures. The "micro-aggregate effect" of the fly ash-based admixture of the present invention fills the pores of the concrete, making the structure denser and achieving improved impermeability and mechanical properties. 2) The functional additive of the present invention is prepared by first reacting 2-hydroxyethyl methacrylate phosphate and γ-glycidyloxypropyltrimethoxysilane to obtain a phosphate-based silane modifier, which is then grafted onto the surface of talc powder. On the one hand, the dispersibility of talc powder can be improved, the tiny pores in cement stone can be better filled, the pore structure of concrete can be optimized, and the density and durability of concrete can be improved. Finally, dimethyldiallylammonium chloride is introduced into the modified talc powder, which significantly reduces the surface energy and interfacial friction resistance of the particles, inhibits the secondary agglomeration phenomenon caused by van der Waals attraction between particles, greatly improves the grinding efficiency, ensures that the grinding product remains in a good dispersed state, can better stimulate the reaction activity inside the admixture, promotes the hydration reaction of the material, and generates more hydration products, thereby improving the strength and durability of the concrete. DETAILED DESCRIPTION

[0019] To avoid redundancy, the items used in the following examples are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0020] The sources of some raw materials used in the present invention are as follows: Fly ash, grade II, comes from Huaneng Dalian Power Plant, and its chemical composition is 37.45% Al2O3, 32.27% SiO2, 20.7% Fe2O3, 3.9% TiO2, 2.4% CaO, 0.6% SO3, 0.45% MgO, and 2.23% other substances.

[0021] Volcanic rock powder comes from Jiajiang, Ya'an, Sichuan. Its chemical composition is 15.43% Al2O3, 61.09% SiO2, 5.3% Fe2O3, 0.77% SO3, 2.7% MgO, 2.37% K2O, 7.78% CaO, 3.30% Na2O, and 1.26% other substances.

[0022] The slag comes from Yongfeng Steel Co., Ltd., and its chemical composition is Al2O3 content of 15.26%, SiO2 content of 35.26%, Fe2O3 content of 0.81%, SO3 content of 1.27%, K2O content of 0.43%, CaO content of 36.03%, Na2O content of 0.10%, and other substances content of 10.84%.

[0023] Steel slag, from Anshan Iron and Steel Plant in Liaoning Province, has a chemical composition of 35.62% CaO, 26.13% Fe2O3, 8.72% SiO2, 6.14% MgO, 5.10% Al2O3, 0.52% SO3, 1.17% MnO, 1.34% P2O5, and 15.26% other substances.

[0024] Talc, talcum powder, 325 mesh, was purchased from Tianjin Yandong Haotian Mineral Products Co., Ltd. Example 1

[0025] A method for preparing a fly ash-based admixture comprises the following steps: 150g of slag, 128g of steel slag and 100g of desulfurized gypsum were mixed, crushed and sieved to a particle size of 2-10mm, and then 400g of fly ash, 150g of volcanic rock powder and 30g of functional additives were added and ground at 50r / min for 60min to obtain the fly ash-based admixture.

[0026] The preparation method of the functional additive is as follows: (1) Under nitrogen atmosphere, 13 g of 2-hydroxyethyl methacrylate phosphate and 10 g of γ-glycidyloxypropyltrimethoxysilane were added to 300 mL of dimethyl sulfoxide and mixed evenly. 4 g of trifluoroacetic acid was added as a catalyst, and the temperature was raised to 50 ° C for reaction for 5 h. After the reaction was completed, the phosphate-based silane modifier was obtained by distillation. (2) 36 g of talc was added to 200 mL of a mixed solvent of deionized water and anhydrous ethanol (the volume ratio of deionized water to anhydrous ethanol was 1:1), and 27 g of a phosphate silane modifier was added. The mixture was heated at 30 °C for 1.5 h. After the reaction was completed, the mixture was centrifuged, the solid matter was collected, washed, and dried to obtain modified talc. (3) Add 30 g of modified talc and 1.8 g of azobisisobutyronitrile to 200 mL of N,N-dimethylformamide and mix well. Add 10.5 g of dimethyldiallylammonium chloride and react at 70 °C for 6 h. Filter and collect the solids, wash and dry to obtain the functional additive. Example 2

[0027] A method for preparing a fly ash-based admixture comprises the following steps: 100g of slag, 100g of steel slag and 50g of desulfurized gypsum were mixed, crushed and sieved to a particle size of 2-10mm, and then 300g of fly ash, 100g of volcanic rock powder and 10g of functional additives were added and ground at 60r / min for 50min to obtain the fly ash-based admixture.

[0028] The preparation method of the functional additive is as follows: (1) Under nitrogen atmosphere, 12 g of 2-hydroxyethyl methacrylate phosphate and 10 g of γ-glycidyloxypropyltrimethoxysilane were added to 300 mL of dimethyl sulfoxide and mixed evenly. 3 g of trifluoroacetic acid was added as a catalyst, and the temperature was raised to 40 ° C for 6 h. After the reaction was completed, the phosphate-based silane modifier was obtained by distillation. (2) 30 g of talc was added to 200 mL of a mixed solvent of deionized water and anhydrous ethanol (the volume ratio of deionized water to anhydrous ethanol was 1:1), and 18 g of a phosphate silane modifier was added. The mixture was heated at 20 °C for 2 h. After the reaction was completed, the mixture was centrifuged, the solid matter was collected, washed, and dried to obtain modified talc. (3) Add 30 g of modified talc and 1.5 g of azobisisobutyronitrile to 200 mL of N,N-dimethylformamide and mix well. Add 6 g of dimethyldiallylammonium chloride and react at 60 °C for 8 h. Filter and collect the solids, wash and dry to obtain the functional additive. Example 3

[0029] A method for preparing a fly ash-based admixture comprises the following steps: 200g of slag, 150g of steel slag and 200g of desulfurized gypsum were mixed, crushed and sieved to a particle size of 2-10mm, and then 500g of fly ash, 200g of volcanic rock powder and 50g of functional additives were added and ground at 50r / min for 60min to obtain the fly ash-based admixture.

[0030] The preparation method of the functional additive is as follows: (1) Under nitrogen atmosphere, 15 g of 2-hydroxyethyl methacrylate phosphate and 10 g of γ-glycidyloxypropyltrimethoxysilane were added to 300 mL of dimethyl sulfoxide and mixed evenly. 5 g of trifluoroacetic acid as a catalyst was added, and the temperature was raised to 60 ° C for 4 h. After the reaction was completed, the phosphate-based silane modifier was obtained by distillation. (2) 32 g of talc was added to 200 mL of a mixed solvent of deionized water and anhydrous ethanol (the volume ratio of deionized water to anhydrous ethanol was 1:1), and 24 g of a phosphate silane modifier was added. The mixture was heated at 40 °C for 1 h. After the reaction was completed, the mixture was centrifuged, the solid was collected, washed, and dried to obtain modified talc. (3) Add 30 g of modified talc and 3 g of azobisisobutyronitrile to 200 mL of N,N-dimethylformamide and mix well. Add 15 g of dimethyldiallylammonium chloride and react at 80 °C for 5 h. Filter and collect the solids, wash and dry to obtain the functional additive.

[0031] Comparative Example 1 A method for preparing a fly ash-based admixture comprises the following steps: 150g of slag, 128g of steel slag and 100g of desulfurized gypsum were mixed, crushed and sieved to a particle size of 2-10mm, and then 400g of fly ash, 150g of volcanic rock powder and 30g of functional additives were added and ground at 50r / min for 60min to obtain the fly ash-based admixture.

[0032] The preparation method of the functional additive is as follows: (1) Under nitrogen atmosphere, 13 g of 2-hydroxyethyl methacrylate phosphate and 10 g of γ-glycidyloxypropyltrimethoxysilane were added to 300 mL of dimethyl sulfoxide and mixed evenly. 4 g of trifluoroacetic acid was added as a catalyst, and the temperature was raised to 50 ° C for reaction for 5 h. After the reaction was completed, the phosphate-based silane modifier was obtained by distillation. (2) 36 g of talc was added to 200 mL of a mixed solvent of deionized water and anhydrous ethanol (the volume ratio of deionized water to anhydrous ethanol was 1:1), and 27 g of a phosphate silane modifier was added. The mixture was heated at 30 °C for 1.5 h. After the reaction was completed, the mixture was centrifuged, the solid matter was collected, washed, and dried to obtain a functional additive.

[0033] Comparative Example 2 A method for preparing a fly ash-based admixture comprises the following steps: 150g of slag, 128g of steel slag and 100g of desulfurized gypsum were mixed, crushed and sieved to a particle size of 2-10mm, and then 400g of fly ash, 150g of volcanic rock powder and 30g of functional additives were added and ground at 50r / min for 60min to obtain the fly ash-based admixture.

[0034] The preparation method of the functional additive is as follows: Under a nitrogen atmosphere, 13 g of 2-hydroxyethyl methacrylate phosphate and 10 g of γ-glycidyloxypropyltrimethoxysilane were added to 300 mL of dimethyl sulfoxide and mixed evenly. 4 g of trifluoroacetic acid as a catalyst was added, and the temperature was raised to 150° C. for reaction for 5 h. After the reaction was completed, the functional additive was obtained by distillation.

[0035] Comparative Example 3 A method for preparing a fly ash-based admixture comprises the following steps: 150g of slag, 128g of steel slag and 100g of desulfurized gypsum were mixed, crushed and sieved to a particle size of 2-10mm, and then 400g of fly ash, 150g of volcanic rock powder and 30g of talc were added and ground at 50r / min for 60min to obtain the fly ash-based admixture.

[0036] Performance Testing Compressive strength test: The fly ash-based admixtures prepared 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 Cement Mortar Strength". Standard test pieces of 40 mm × 40 mm × 160 mm were made and cured for 28 days under standard curing conditions. The compressive strength was tested using a universal testing machine. Water absorption test: refer to British Standard BS 1881, Part 122, 1983, and take the test piece after curing for 28 days; Anti-seepage pressure test: The test was conducted according to GB / T50082-2009 Standard Test Method for Long-term Performance and Durability of Ordinary Concrete. The test results are shown in Table 1: Table 1 Test results of fly ash-based admixture performance

[0037] It can be seen from the experimental results in Table 1 that the fly ash-based admixture of the present application can significantly improve the compressive strength and durability of concrete.

[0038] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of the present invention.

Claims

1. A fly ash-based admixture, characterized in that: The invention comprises the following components in parts by weight: 30-50 parts of fly ash, 5-20 parts of gypsum, 10-20 parts of volcanic rock powder, 10-20 parts of slag, 10-15 parts of steel slag and 1-5 parts of functional additives.

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

3. The fly ash-based admixture according to claim 1, characterized in that: The preparation method of the functional additive is as follows: (1) Under a nitrogen atmosphere, 2-hydroxyethyl methacrylate phosphate and γ-glycidyloxypropyltrimethoxysilane are added to dimethyl sulfoxide and mixed evenly, trifluoroacetic acid as a catalyst is added, the temperature is raised to react, and after the reaction is completed, the phosphate-based silane modifier is obtained by distillation; (2) adding talc powder to a mixed solvent of deionized water and anhydrous ethanol, adding a phosphate silane modifier, heating to react, and then centrifuging, washing, and drying to obtain modified talc powder; (3) Add modified talc and azobisisobutyronitrile to N,N-dimethylformamide and mix evenly, add dimethyldiallylammonium chloride, react at a constant temperature, filter, collect the solid, wash and dry to obtain a functional additive.

4. The fly ash-based admixture according to claim 3, characterized in that: In the step (1), the mass ratio of 2-hydroxyethyl methacrylate phosphate, γ-glycidyloxypropyltrimethoxysilane, and trifluoroacetic acid is 1.2-1.5:1:0.3-0.

5.

5. The fly ash-based admixture according to claim 3, characterized in that: The temperature of the reaction in step (1) is 40-60°C, and the reaction time is 4-6 hours.

6. The fly ash-based admixture according to claim 3, characterized in that: In the step (2), the mass ratio of talc powder to phosphate-based silane modifier is 5-8:3-6.

7. The fly ash-based admixture according to claim 3, characterized in that: The heating reaction temperature in step (2) is 20-40° C., and the reaction time is 1-2 h.

8. The fly ash-based admixture according to claim 3, characterized in that: In the step (3), the mass ratio of modified talc, azobisisobutyronitrile, and dimethyldiallylammonium chloride is 1:0.05-0.1:0.2-0.

5.

9. The fly ash-based admixture according to claim 3, characterized in that: In step (3), the constant temperature reaction temperature is 60-80° C., and the reaction time is 5-8 h.

10. A method for preparing a fly ash-based admixture, for preparing the fly ash-based admixture according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: mixing slag, steel slag and gypsum, crushing and screening the mixture, and then adding fly ash, volcanic rock powder and functional additives for grinding to obtain the fly ash-based admixture.

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