Manganese slag concrete admixture and preparation method thereof

Abstract

The invention relates to the technical field of admixtures, in particular to a manganese slag concrete admixture and a preparation method thereof.The manganese slag concrete admixture is prepared from, by weight, 65-75 parts of ground manganese slag, 10-15 parts of modified metakaolin, 5-8 parts of slag powder, 4-6 parts of gypsum, 3-5 parts of limestone powder, 2-4 parts of alkali activator, 0.3-0.6 part of water retention thickener and 0.5-1 part of polycarboxylate superplasticizer. A layer of itaconic anhydride-myrcene copolymer is grafted on the surface of the modified metakaolin through a covalent ester bond, so that performance guarantee is provided for large-dosage utilization of the manganese slag, and resource utilization of the manganese slag is realized on the premise of meeting the requirement of high-performance concrete.

Description

Technical Field

[0001] The present invention relates to the technical field of admixtures, in particular to a manganese slag concrete admixture and a preparation method thereof. Background Art

[0002] Manganese slag is one of the largest industrial waste streams generated by the manganese alloy industry. Its chemical composition primarily includes SiO2, CaO, Al2O3, MgO, and MnO. Glass is the primary mineral component, accounting for over 90%, with the remainder consisting of magnesia rhodonite and magnesia feldspar. Concrete admixtures refer to natural or artificial powdered minerals added during concrete mixing to improve concrete properties. Based on their chemical activity, concrete admixtures can be divided into two categories: active and inactive. Active admixtures do not harden themselves or harden very slowly, but they can set and harden when mixed with calcareous materials such as lime and slaked lime and water. They can also react with calcium hydroxide produced by cement hydration to form hydrated products with cementitious properties. Common active admixtures include fly ash, granulated blast furnace slag powder, zeolite powder, and silica fume. Inactive admixtures, such as limestone powder and ground quartz sand, primarily serve as fillers and do not impair cement properties. Active admixtures, when combined with water reducers, can increase the fluidity, cohesiveness, and water retention of fresh concrete, improve its pumpability, and enhance the strength and durability of hardened concrete. The use of admixtures can reduce cement usage, thereby lowering production costs. Furthermore, by optimizing the type and dosage of admixtures, concrete performance can be further enhanced to meet the construction requirements of different projects.

[0003] In the existing technology, although manganese slag contains potential active components, its own pozzolanic activity is far lower than that of mature active admixtures such as fly ash. Its activity requires a higher concentration of alkaline environment. The alkalinity provided by the hydration of ordinary cement may not be enough to fully stimulate its activity, resulting in slow and incomplete hydration reaction and little contribution to strength. In addition, manganese slag contains soluble Mn 2+ During the cement hydration process, ions may be adsorbed on the surface of C3S particles, hindering the hydration reaction of C3S, resulting in a significant extension of the setting time of concrete, seriously affecting the construction progress and the normal development of early strength. At the same time, in the late stage of hardening, the manganese slag particles that have not fully reacted may continue to react slowly, or the manganese-containing minerals in them may transform, resulting in micro-expansion, which will generate internal stress in the concrete and increase the risk of cracking. Mn dissolved in pore water 2+ , Ca 2+ 、SO4 2- Plasma migrates to the concrete surface along with moisture, reacts with CO2 or moisture in the air, and generates white MnCO3, CaCO3 or sulfur-containing precipitates, forming white spots or powdery substances on the surface, affecting the appearance quality. Summary of the Invention

[0004] In order to solve the problems mentioned in the above background technology, the present invention provides a manganese slag concrete admixture and a preparation method thereof.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A manganese slag concrete admixture comprises the following raw materials in parts by weight: 65-75 parts of ground manganese slag, 10-15 parts of modified metakaolin, 5-8 parts of slag powder, 4-6 parts of gypsum, 3-5 parts of limestone powder, 2-4 parts of alkali activator, 0.3-0.6 parts of water-retaining thickener and 0.5-1 parts of polycarboxylic acid water reducer.

[0007] Furthermore, the modified metakaolin is prepared by the following steps:

[0008] S1. Under nitrogen protection, itaconic anhydride and N-methylpyrrolidone are added to a reactor, and the mixture is in an oil bath for 15-25 minutes. Myrcene is added, and the stirrer is started. At the same time, the temperature is increased, and azobisisobutyronitrile is added. The mixture is stirred and reacted for 10-16 hours. The heating is stopped, and the mixture is cooled to room temperature. Anhydrous ethanol is added to dilute the viscous solution. Under vigorous stirring, the reaction solution is slowly added dropwise to an excess of ice-cold anhydrous ethanol. The mixture is allowed to stand and decompose. The supernatant is removed, and the precipitate is collected by filtration. The filter cake is washed with fresh anhydrous ethanol 2-3 times, and then washed with anhydrous ethyl acetate once, and dried at 60°C for 20-24 hours to obtain a white to light yellow polymer.

[0009] S2. Place the metakaolin in a constant temperature drying oven and dry it for 6-8 hours. Place it in a high-temperature furnace and keep it warm for 2-4 hours. Cool it to room temperature and add it to N-methylpyrrolidone. Under nitrogen protection, add the copolymer while stirring. Heat and stir to react for 6-8 hours. After the reaction is completed, cool it to room temperature and filter it. Wash the filter cake with N-methylpyrrolidone for 3 times and then with anhydrous ethanol for 3 times. Dry it at 40°C for 12-16 hours to obtain modified metakaolin.

[0010] Furthermore, the alkali activator includes one or more of sodium silicate, sodium hydroxide, potassium hydroxide, sodium carbonate and sodium sulfate.

[0011] Furthermore, the water-retaining thickener includes one or more of hydroxypropyl methylcellulose, methylcellulose, hydroxyethyl cellulose, weinlun gum, and polyacrylamide.

[0012] Furthermore, in step S1, the mass ratio of itaconic anhydride, N-methylpyrrolidone, myrcene and azobisisobutyronitrile is (10.5-11.5): (80-96): (13-13.8): (0.08-0.1).

[0013] Furthermore, in step S1, the temperature of the oil bath is 50-55° C., the temperature of the heating is 70-75° C., and the stirring speed is 300-400 rpm.

[0014] Furthermore, in step S2, the mass ratio of metakaolin, N-methylpyrrolidone and copolymer is 100:(10-15):(44-50).

[0015] Furthermore, in step S2, the insulation temperature in the high temperature furnace is 150-160°C, the heating rate is 5°C / min, the stirring speed is 800-1000 rpm, and the heating temperature is 88-92°C.

[0016] According to another aspect of the present invention, there is provided a method for preparing the above-mentioned manganese slag concrete admixture, comprising the following steps:

[0017] Weigh the raw material components by weight, add the ground manganese slag, slag powder and limestone powder into a mixer, the particle size of the ground manganese slag is D50 = 5-10μm, and the specific surface area is ≥420m² / kg, dry mix at a speed of 200-300rpm for 3-5min, add modified metakaolin and gypsum, continue mixing for 5-8min, dissolve the alkali activator in water 0.5-1 times its mass to form an activator solution, spray the activator solution into the mixer, add a water-retaining thickener at the same time, wet mix at a speed of 400-500rpm for 10-15min, add a polycarboxylate water reducer, continue mixing for 3-5min until the materials are uniform, dry at 40-50℃ after discharging to a moisture content of ≤0.8%, and sieve through 60-80 mesh to obtain the finished product.

[0018] Beneficial effects of the present invention:

[0019] 1. In this technical solution, a layer of itaconic anhydride-myrcene copolymer is grafted onto the surface of modified metakaolin via covalent ester bonds. The outer surface of this polymer layer is enriched with long-chain alkyl hydrophobic groups. When metakaolin particles approach each other in an aqueous phase, these extended hydrophobic chains generate strong mutual repulsion in the aqueous environment, resulting in particle dispersion stability far exceeding that of original metakaolin, effectively preventing agglomeration and maintaining a nearly monodisperse state of fine particles. This provides performance guarantees for the use of large amounts of manganese slag, enabling its resource utilization while meeting the requirements of high-performance concrete.

[0020] 2. In the technical solution of the present invention, the metakaolin particles themselves and the inherent steric hindrance they provide help improve the stability of the entire slurry system, reducing the tendency of particles to settle and segregate. The slight thickening effect produced by their large specific surface area and surface properties creates a synergistic effect with the water-retaining thickener in the system, enhancing the slurry's cohesiveness and reducing bleeding and laitance. Furthermore, the hydrophobic polymer layer on the metakaolin surface may reduce unnecessary adsorption of polycarboxylate superplasticizer molecules, allowing the polycarboxylate superplasticizer to more effectively act on other particles, such as cement, maintaining the slurry's good fluidity, encapsulation, and pumpability.

[0021] 3. In the technical solution of the present invention, the effective specific surface area of ​​the modified metakaolin is greatly increased, and the active silicon and aluminum sites (Si-OH, Al-OH) on all surfaces are highly exposed. In the alkaline environment of concrete paste, they are more easily exposed to OH - Erosion and dissolution (dissolution of SiO4 4- , AlO4 5- plasma), and Ca 2+ The dispersed modified metakaolin particles simultaneously serve as numerous, evenly distributed heterogeneous nucleation sites, guiding the preferential and uniform precipitation and growth of CSH and CASH gels on their surfaces. Consequently, the pozzolanic reaction of the metakaolin is significantly accelerated, significantly improving its efficiency and completeness. DETAILED DESCRIPTION

[0022] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0023] Preparation Example 1

[0024] The modified metakaolin is prepared by the following steps:

[0025] S1. Under nitrogen protection, 10.5 g of itaconic anhydride and 80 g of N-methylpyrrolidone were added to a reactor, and the mixture was placed in an oil bath at 50° C. for 15 min. 13 g of myrcene was added, and the agitator was started. The temperature was raised to 70° C., 0.08 g of azobisisobutyronitrile was added, and the reaction was stirred at 300 rpm for 10 h. After the reaction was completed, heating was stopped, the mixture was cooled to room temperature, and anhydrous ethanol was added to dilute the viscous solution. Under vigorous stirring, the reaction solution was slowly added dropwise to an excess of ice-cold anhydrous ethanol, and the mixture was allowed to stand for stratification. The supernatant was removed, and the precipitate was collected by filtration. The filter cake was washed twice with fresh anhydrous ethanol and once with anhydrous ethyl acetate, and dried at 60° C. for 20 h to obtain a polymer.

[0026] S2. Place 100g of metakaolin in a constant temperature drying oven at 50°C and dry for 6h, place it in a high-temperature furnace, heat it at a rate of 5°C / min, keep it at 150°C for 2h, cool it to room temperature, add 10g of N-methylpyrrolidone, and under nitrogen protection, add 44g of copolymer while stirring. Heat it to 88°C and stir it at 800rpm for 6h. After the reaction is completed, cool it to room temperature, filter it, wash the filter cake 3 times with N-methylpyrrolidone, and then wash the filter cake 3 times with anhydrous ethanol, and dry it at 40°C for 12h to obtain modified metakaolin.

[0027] Preparation Example 2

[0028] The modified metakaolin is prepared by the following steps:

[0029] S1. Under nitrogen protection, 11.1 g of itaconic anhydride and 88 g of N-methylpyrrolidone were added to a reactor, and the mixture was placed in an oil bath at 52 ° C for 20 min. 13.5 g of myrcene was added, and the agitator was started. At the same time, the temperature was raised to 72 ° C. 0.09 g of azobisisobutyronitrile was added, and the reaction was stirred at a speed of 350 rpm for 13 h. After the reaction was completed, heating was stopped, and the mixture was cooled to room temperature. Anhydrous ethanol was added to dilute the viscous solution. Under vigorous stirring, the reaction solution was slowly added dropwise to an excess of ice-cold anhydrous ethanol, and the mixture was allowed to stand for stratification. The supernatant was removed and the precipitate was collected by filtration. The filter cake was washed twice with fresh anhydrous ethanol and once with anhydrous ethyl acetate, and dried at 60 ° C for 22 h to obtain a polymer.

[0030] S2. Place 100g of metakaolin in a constant temperature drying oven at 50°C and dry for 7h. Place it in a high-temperature furnace with a heating rate of 5°C / min and keep it at 155°C for 3h. Cool it to room temperature and add 12.5g of N-methylpyrrolidone. Under nitrogen protection, add 47g of copolymer while stirring. Heat it to 90°C and stir it at 900rpm for 7h. After the reaction is completed, cool it to room temperature, filter it, wash the filter cake 3 times with N-methylpyrrolidone, and then wash the filter cake 3 times with anhydrous ethanol. Dry it at 40°C for 14h to obtain modified metakaolin.

[0031] Preparation Example 3

[0032] The modified metakaolin is prepared by the following steps:

[0033] S1. Under nitrogen protection, 11.5 g of itaconic anhydride and 96 g of N-methylpyrrolidone were added to a reactor, and the mixture was oil bathed at 55 ° C for 25 min. 13.8 g of myrcene was added, and the agitator was started. At the same time, the temperature was raised to 75 ° C. 0.1 g of azobisisobutyronitrile was added, and the reaction was stirred at a speed of 400 rpm for 16 h. After the reaction was completed, heating was stopped, and the mixture was cooled to room temperature. Anhydrous ethanol was added to dilute the viscous solution. Under vigorous stirring, the reaction solution was slowly added dropwise to an excess of ice-cold anhydrous ethanol, and the mixture was allowed to stand for stratification. The supernatant was removed and the precipitate was collected by filtration. The filter cake was washed with fresh anhydrous ethanol 3 times and then with anhydrous ethyl acetate once, and dried at 60 ° C for 24 h to obtain a polymer.

[0034] S2. Place 100g of metakaolin in a constant temperature drying oven at 50°C and dry for 8h, place it in a high-temperature furnace, heat it at a rate of 5°C / min, keep it at 160°C for 4h, cool it to room temperature, add 15g of N-methylpyrrolidone, and under nitrogen protection, add 50g of copolymer while stirring. Heat it to 92°C and stir it at a speed of 1000rpm for 8h. After the reaction is completed, cool it to room temperature, filter it, wash the filter cake 3 times with N-methylpyrrolidone, and then wash the filter cake 3 times with anhydrous ethanol, and dry it at 40°C for 16h to obtain modified metakaolin.

[0035] Example 1

[0036] A method for preparing a manganese slag concrete admixture comprises the following steps:

[0037] Weigh the raw material components by weight, add 65 parts of ground manganese slag, 5 parts of slag powder, and 3 parts of limestone powder into a mixer, dry mix at a speed of 200 rpm for 3 minutes, add 10 parts of modified metakaolin obtained in Preparation Example 1 and 4 parts of gypsum, and continue mixing for 5 minutes. Dissolve 2 parts of sodium silicate in 0.5 times its mass of water to form an activator solution, spray the activator solution into the mixer, and add 0.3 parts of hydroxypropyl methylcellulose at the same time. Wet mix at a speed of 400 rpm for 10 minutes, add 0.5 parts of polycarboxylate water reducer, and continue mixing for 3 minutes until the materials are uniform. After discharging, dry at 40°C to a moisture content of 0.8%, and sieve through 60 mesh to obtain the finished product.

[0038] Example 2

[0039] A method for preparing a manganese slag concrete admixture comprises the following steps:

[0040] Weigh each raw material component by weight, add 70 parts of ground manganese slag, 7 parts of slag powder, and 4 parts of limestone powder into a mixer, dry mix at a speed of 250 rpm for 4 minutes, add 12 parts of modified metakaolin prepared in Preparation Example 2 and 5 parts of gypsum, and continue mixing for 7 minutes. Dissolve 3 parts of sodium hydroxide in 0.6 times its mass of water to form an activator solution, spray the activator solution into the mixer, and add 0.4 parts of methyl cellulose at the same time. Wet mix at a speed of 450 rpm for 12 minutes, add 0.7 parts of polycarboxylate water reducer, and continue mixing for 4 minutes until the materials are uniform. After discharging, dry at 45°C to a moisture content of 0.8%, and sieve through 70 mesh to obtain the finished product.

[0041] Example 3

[0042] A method for preparing a manganese slag concrete admixture comprises the following steps:

[0043] Weigh each raw material component by weight, add 75 parts of ground manganese slag, 8 parts of slag powder, and 5 parts of limestone powder into a mixer, dry mix at a speed of 300 rpm for 5 minutes, add 15 parts of modified metakaolin prepared in Preparation Example 3 and 6 parts of gypsum, and continue mixing for 8 minutes. Dissolve 4 parts of sodium carbonate in 1 times its mass of water to form an activator solution, spray the activator solution into the mixer, and add 0.6 parts of hydroxyethyl cellulose at the same time. Wet mix at a speed of 500 rpm for 15 minutes, add 1 part of polycarboxylate water reducer, and continue mixing for 5 minutes until the material is uniform. After discharging, dry at 50°C to a moisture content of 0.8%, and sieve through 80 mesh to obtain the finished product.

[0044] Comparative Example 1

[0045] The difference between this comparative example and Preparation Example 1 is that itaconic anhydride is not added, and the remaining steps are the same as those in Preparation Example 1.

[0046] Comparative Example 2

[0047] The difference between this comparative example and Preparation Example 2 is that myrcene is not added, and the remaining steps are the same as those in Preparation Example 2.

[0048] Comparative Example 3

[0049] The difference between this comparative example and Example 1 is that the metakaolin prepared in Comparative Example 1 is used instead of the modified metakaolin prepared in Preparation Example 1, and the remaining steps are the same as in Example 1.

[0050] Comparative Example 4

[0051] The difference between this comparative example and Example 2 is that the metakaolin prepared in Comparative Example 2 is used instead of the modified metakaolin prepared in Preparation Example 2, and the remaining steps are the same as in Example 2.

[0052] Comparative Example 5

[0053] The difference between this comparative example and Example 3 is that commercially available metakaolin is used instead of the modified metakaolin prepared in Preparation Example 3, and the remaining steps are the same as those in Example 3.

[0054] 300g of Portland cement, 150g of the admixtures prepared in Examples 1-3 and Comparative Examples 3-5, and 750g of standard sand were added to a mixing pot and stirred at 200rpm for 60s. 150g of water was added at a constant speed (completed within 60s), and the mixture was stirred at 200rpm for 90s. The mixture was covered with a wet cloth, and the stirring was stopped for 90s. The mixture was then stirred at 400rpm for 120s to obtain concrete. The following tests were performed:

[0055] (I) Fluidity: Refer to GB / T 8077-2023 "Test method for homogeneity of concrete admixtures". After mixing, immediately fill the concrete into a slump cone with a bottom diameter of 200 mm, a top diameter of 100 mm, and a height of 300 mm. Fill in three layers, and tamp each layer 25 times. Lift the slump cone vertically and measure the slump expansion diameter (D). Take the average value of the two vertical directions, accurate to 1 mm.

[0056] (II) Setting time: With reference to GB / T 50080-2016 “Standard test method for properties of ordinary concrete mixtures”, concrete is placed in a penetration resistance test mold and the penetration resistance is tested every 30 minutes. When the penetration resistance reaches 3.5 MPa, it is the initial setting time, and when it reaches 28.0 MPa, it is the final setting time.

[0057] (III) Compressive strength: Refer to GB / T 17671-2021 "Test method for strength of cement mortar (ISO method)". Take concrete and load it into the mold in two layers. Ram each layer 40 times. Vibrate the vibrating table for 60 seconds at a frequency of 50Hz to produce a 40×40×160mm prism specimen. Cover with plastic film and let it stand for 24 hours before removing the mold. Curing in a standard curing room for 28 days. Use a universal testing machine to load at a rate of 2400±200 N / s, record the failure load, and calculate the compressive strength f c , the formula is as follows:

[0058]

[0059] Where, F is the failure load, A=1600mm².

[0060] The results are shown in Table 1:

[0061] Table 1. Concrete performance test results

[0062] Group Flowability (mm) Initial setting time (h) 28d compressive strength (MPa) Example 1 540±15 4.2±0.2 55.8±1.5 Example 2 550±12 4.5±0.2 57.3±1.3 Example 3 560±10 4.8±0.2 59.5±1.2 Comparative Example 3 485±20 3.5±0.3 49.2±1.8 Comparative Example 4 495±18 3.6±0.3 50.1±1.7 Comparative Example 5 510±15 3.2±0.4 46.5±2.0

[0063] As shown in Table 1, the concretes produced in Examples 1-3 exhibited excellent performance in terms of fluidity, initial setting time, and 28-day compressive strength. As the number of examples increases, the concrete's fluidity gradually increases, the initial setting time gradually lengthens, and the 28-day compressive strength gradually improves. Conversely, the concretes produced in Comparative Examples 3-5 performed relatively poorly, with lower fluidity, shorter initial setting times, and lower 28-day compressive strength than the examples.

[0064] The modified metakaolin used in the examples was prepared by modifying metakaolin with a polymer obtained by copolymerizing itaconic anhydride and myrcene. This polymer has a long-chain structure, which may act as a lubricant in concrete, reducing friction between particles, thereby making the concrete more fluid and improving its fluidity. Comparative Example 3 lacked itaconic anhydride, and Comparative Example 4 lacked myrcene, resulting in an incomplete copolymer structure or poor performance. The metakaolin modification effect was not as good as in the examples, resulting in relatively high friction between concrete particles and reduced fluidity. Comparative Example 5 used commercially available unmodified metakaolin, which did not lubricate concrete as well as the modified metakaolin and had relatively low fluidity.

[0065] The polymer on the surface of the modified metakaolin can be adsorbed on the surface of cement particles, forming a thin film that hinders the contact between cement and water, thereby slowing the hydration reaction of cement and extending the initial setting time of concrete. In Comparative Examples 3 and 4, due to the lack of raw materials during the preparation of the modified metakaolin, the modification effect was poor, the inhibitory effect on the cement hydration reaction was weakened, and the initial setting time was shortened. In Comparative Example 5, the commercially available metakaolin does not have the effect of this modified polymer, and the inhibitory effect on the cement hydration reaction is even smaller, and the initial setting time is further shortened. The modified metakaolin may exert a volcanic ash effect in concrete, reacting with the calcium hydroxide produced by cement hydration to form gel substances such as hydrated calcium silicate, which fills the pores in the concrete, increases the density of the concrete, and thus enhances the compressive strength of the concrete. At the same time, the polymer on the surface of the modified metakaolin can improve the interfacial bonding between concrete particles and improve the mechanical properties of the concrete.

[0066] In Comparative Examples 3 and 4, the modified metakaolin had poor performance, weakened its pozzolanic effect and improved interfacial bonding, resulting in reduced density and mechanical properties of the concrete, and decreased 28-day compressive strength. Comparative Example 5, based on unmodified commercially available metakaolin, had limited pozzolanic effect and improved interfacial bonding, resulting in the lowest 28-day compressive strength.

[0067] In summary, manganese slag concrete admixture prepared by modifying metakaolin with polymer obtained by copolymerization of itaconic anhydride and myrcene can significantly improve the comprehensive properties of concrete, including fluidity, setting time and compressive strength.

[0068] Throughout the specification, reference to terms such as "Preparation," "Example," or "Examples" indicates that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or preparation are included in at least one embodiment or preparation of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or preparation. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or preparations.

[0069] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A manganese slag concrete admixture, characterized in that: The raw materials include the following by weight: 65-75 parts of ground manganese slag, 10-15 parts of modified metakaolin, 5-8 parts of slag powder, 4-6 parts of gypsum, 3-5 parts of limestone powder, 2-4 parts of alkali activator, 0.3-0.6 parts of water-retaining thickener and 0.5-1 parts of polycarboxylic acid water reducer.

2. A manganese slag concrete admixture according to claim 1, characterized in that: The modified metakaolin is prepared by the following steps: S1. Under nitrogen protection, add itaconic anhydride and N-methylpyrrolidone to a reactor, oil bath for 15-25 minutes, add myrcene and azobisisobutyronitrile, heat and stir to react for 10-16 hours, stop heating, cool to room temperature, stand and separate, collect the precipitate by filtration, wash, and dry to obtain a polymer; S2. Dry the metakaolin for 6-8 hours, put it into a high-temperature furnace, keep it warm for 2-4 hours, cool it to room temperature, add it to N-methylpyrrolidone, and under nitrogen protection, add the copolymer while stirring. Heat and stir to react for 6-8 hours. After the reaction is completed, cool it to room temperature, filter, wash, and dry it for 12-16 hours to obtain modified metakaolin.

3. A manganese slag concrete admixture according to claim 1, characterized in that: The alkali activator includes one or more of sodium silicate, sodium hydroxide, potassium hydroxide, sodium carbonate and sodium sulfate.

4. A manganese slag concrete admixture according to claim 1, characterized in that: The water-retaining thickener includes one or more of hydroxypropyl methylcellulose, methylcellulose, hydroxyethyl cellulose, Wenlun gum, and polyacrylamide.

5. A manganese slag concrete admixture according to claim 2, characterized in that: The mass ratio of itaconic anhydride, N-methylpyrrolidone, myrcene and azobisisobutyronitrile in step S1 is (10.5-11.5):(80-96):(13-13.8):(0.08-0.1).

6. A manganese slag concrete admixture according to claim 2, characterized in that: In step S1, the temperature of the oil bath is 50-55° C., the temperature of the heating is 70-75° C., and the stirring speed is 300-400 rpm.

7. A manganese slag concrete admixture according to claim 2, characterized in that: In step S2, the mass ratio of metakaolin, N-methylpyrrolidone and copolymer is 100:(10-15):(44-50).

8. A manganese slag concrete admixture according to claim 2, characterized in that: In step S2, the temperature of the high-temperature furnace is kept at 150-160°C, the heating rate is 5°C / min, the stirring speed is 800-1000 rpm, and the heating temperature is 88-92°C.

9. A method for preparing a manganese slag concrete admixture according to any one of claims 1 to 8, characterized in that: The following steps are involved: Weigh the raw material components by weight, add the ground manganese slag, slag powder and limestone powder into a mixer, dry mix for 3-5 minutes, add modified metakaolin and gypsum, continue mixing for 5-8 minutes, dissolve the alkali activator in water 0.5-1 times its mass to form an activator solution, spray the activator solution into the mixer, add a water-retaining thickener at the same time, wet mix for 10-15 minutes, add a polycarboxylate water reducer, continue mixing for 3-5 minutes until the materials are uniform, dry at 40-50°C after discharge to a moisture content of ≤0.8%, and sieve through 60-80 mesh to obtain the finished product.

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