Additive for improving activity of concrete mineral admixture

Abstract

The invention provides an additive for improving the activity of a concrete mineral admixture, and belongs to the technical field of concrete.The additive is prepared from flue gas desulfurization gypsum, sodium metaaluminate, ferric oxide, calcium hydroxide, sodium methyl silicate, magnesium fluosilicate, sodium fluosilicate, an iron-aluminum bimetallic complex, nano-silica, calcium lignosulphonate and the like as raw materials. The components are compounded according to a specific ratio for use, and the additive prepared by a special preparation method has a very good active synergistic effect, effectively improves the activity of the components such as the fly ash and the slag powder, improves indexes such as material workability and strength, and can support mixing of the components such as the fly ash and the slag powder in a large ratio to prepare a high-performance concrete material.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology, specifically relating to an additive that improves the activity of mineral admixtures in concrete. Background Technology

[0002] Cement, as a crucial cementitious material in concrete, consumes a significant amount of energy and emits substantial amounts of carbon dioxide during its production. To mitigate the environmental impact of cement production while simultaneously improving the overall performance of concrete, mineral admixtures are widely used. Common mineral admixtures, such as fly ash, slag powder, and silica fume, possess potential reactivity and can undergo secondary reactions with cement hydration products within the concrete, thereby improving the concrete's microstructure and enhancing its strength, durability, and other properties.

[0003] However, the activity of these mineral admixtures presents some challenges in practical applications. Fly ash, a waste product from coal combustion in thermal power plants, has an activity primarily dependent on the type of coal, combustion conditions, and collection methods. Low-calcium fly ash, due to its high glass content and low active ingredient content, exhibits a slower hydration reaction in concrete, resulting in a lower contribution to early strength. Slag powder, a byproduct of blast furnace ironmaking, while possessing high potential activity, tends to agglomerate in concrete due to its fine particle size, hindering uniform mixing with cement paste and thus limiting its full potential activity. Although silica fume exhibits high activity, its large specific surface area and high water demand increase water consumption in concrete, leading to decreased workability.

[0004] To address these issues, enhancing the activity of mineral admixtures is crucial. Additives, as an effective means, can stimulate the potential activity of mineral admixtures, enabling them to perform better. Traditional activators, such as lime and gypsum, while able to improve the activity of mineral admixtures to some extent, suffer from limited activating effects and negative impacts on concrete durability. With the continuous development of materials science, new types of additives have emerged.

[0005] Some chemical admixtures, such as alkaline activators and sulfate activators, can disrupt the surface structure of mineral admixtures through chemical reactions, making their active components more easily soluble and thus accelerating the hydration reaction. Organic additives, such as some surfactants and polymers, can improve the dispersibility of mineral admixtures in concrete, enhance their compatibility with cement paste, and thus increase their activity. There are also composite additives that rationally combine multiple components to fully utilize their synergistic effects, improving not only the activity of mineral admixtures but also other properties of concrete, such as workability and durability.

[0006] However, there are many different kinds of additives on the market, and their effects vary. They also generally have the problem of limited activation effect: for some mineral admixtures with low activity, such as low-calcium fly ash, although some additives can activate their activity, it is difficult to make their activity fully exerted, and the strength improvement is still not obvious, which limits the large-scale use of admixtures. Summary of the Invention

[0007] To address the problem that existing additives have insufficient activation effects on some low-activity mineral admixtures, this invention provides an additive to improve the activity of mineral admixtures in concrete. It uses desulfurized gypsum, sodium aluminate, ferric oxide, calcium hydroxide, sodium methylsilicate, magnesium fluorosilicate, sodium fluorosilicate, iron-aluminum bimetallic complex, nano-silica, and calcium lignosulfonate as raw materials. These components are combined in a specific ratio and prepared using a special method. This additive exhibits excellent synergistic activity, effectively improving the activity of fly ash, slag powder, and other components, enhancing material workability and strength, and supporting the mixing of large proportions of fly ash, slag powder, and other components to prepare high-performance concrete materials. The specific technical solution is as follows: An additive for improving the activity of mineral admixtures in concrete comprises the following raw materials in parts by weight: 25-35 parts desulfurized gypsum, 2-5 parts sodium aluminate, 1-3 parts ferric oxide, 1-3 parts calcium hydroxide, 5-8 parts sodium methylsilicate, 3-5 parts magnesium fluorosilicate, 3-5 parts sodium fluorosilicate, 1-3 parts iron-aluminum bimetallic complex, 5-10 parts nano silica, and 3-5 parts calcium lignosulfonate.

[0008] In the above-mentioned additives, the sodium aluminate has a particle size of nanometers.

[0009] In the above-mentioned additives, the desulfurized gypsum has a particle size in the micrometer range.

[0010] The preparation method of the iron-aluminum bimetallic complex in the above-mentioned additive includes the following steps: Ferrous sulfate (FeSO4·7H2O): sodium aluminate (NaAlO2): citric acid: water = (1.3~1.5): (0.8~0.9): (1.8~2.0): (3~5) by mass ratio; ferrous sulfate and sodium aluminate are added to water and mixed evenly; then citric acid is added and mixed evenly; the mixture is stirred at 200r / min~300r / min for 3h~4h at 60℃~70℃; and spray-dried to obtain a reddish-brown complex powder, i.e., the iron-aluminum bimetallic complex.

[0011] In the above-mentioned method for preparing iron-aluminum bimetallic complexes, the parameters for spray drying are: inlet air temperature of 150℃~180℃ and outlet air temperature of 80℃~100℃.

[0012] The preparation method of the above-mentioned additive for improving the activity of concrete mineral admixtures includes the following steps: S1: Calcine the desulfurized gypsum at 150℃~180℃ for 2h~3h to obtain β-type hemihydrate gypsum; mix the β-type hemihydrate gypsum with sodium methylsilicate; ball mill the β-type hemihydrate gypsum to obtain modified desulfurized gypsum powder. S2, Full Component Composite: Modified desulfurized gypsum powder, nano-sized sodium aluminate, ferric oxide, calcium hydroxide, magnesium fluorosilicate, sodium fluorosilicate, iron-aluminum bimetallic complex, nano-silica, and calcium lignosulfonate are added to a mixer and stirred at 150 r / min to 200 r / min for 10 min to 15 min; then stirred at 500 r / min to 800 r / min for 30 min to 60 min to obtain the additive.

[0013] In step S1 of the above preparation method, zirconia balls with a diameter of 5 mm to 10 mm are used as the grinding medium for ball milling, and the ball-to-material mass ratio is controlled at (5 to 10):1.

[0014] In step S1 of the above preparation method, the rotation speed of the ball mill is 150 r / min to 200 r / min; the ball milling time is 4 h to 5 h.

[0015] The additive of the present invention for improving the activity of mineral admixtures in concrete has the following beneficial effects: I. The additive raw materials of this invention include desulfurized gypsum, sodium aluminate, ferric oxide, calcium hydroxide, sodium methylsilicate, magnesium fluorosilicate, sodium fluorosilicate, iron-aluminum bimetallic complex, nano-silica, calcium lignosulfonate, etc. Specifically, desulfurized gypsum is calcined to prepare β-type hemihydrate gypsum, and then modified by ball milling with sodium methylsilicate. After calcination, the desulfurized gypsum transforms into β-type hemihydrate gypsum, its crystal structure changes, and its activity is improved. Sodium methylsilicate has a modifying effect on β-type hemihydrate gypsum, improving its surface properties and enhancing its affinity and synergistic effect with other components.

[0016] II. Sodium aluminate hydrolyzes in aqueous solution to produce aluminum hydroxide colloid. Aluminum hydroxide can react with other substances to form gelling agents, enhancing the bonding properties of materials and improving their water resistance and durability. Ferric oxide has certain oxidizing properties and can react with other reducing agents; it can also act as a catalyst for certain reactions, promoting some chemical reactions and contributing to the improvement of material properties. Calcium hydroxide provides hydroxide ions, which can neutralize acidic substances in the system, adjusting the pH value; it can also react with carbon dioxide to form calcium carbonate, increasing the strength and hardness of the material. Magnesium fluorosilicate can react with some metal ions in the system to form insoluble fluorides. These fluorides can fill the pores of the material, increasing its density and thus enhancing its strength and water resistance. The fluoride ions produced after the hydrolysis of sodium fluorosilicate can form stable complexes with other metal ions, helping to reduce the surface tension of the material, improving its flowability and workability, while also enhancing its corrosion resistance and workability. Iron-aluminum bimetallic complexes possess the properties of both iron and aluminum, forming complex chemical bonds and complex structures within the system. This enhances the material's cohesion and adhesion, improving its overall performance, weather resistance, anti-aging properties, and workability. Iron-aluminum bimetallic complexes also exhibit unique catalytic and synergistic effects as additives, promoting the dissolution and hydration of active components in mineral admixtures. Nano-silica has a large specific surface area and high activity, enabling it to undergo physical or chemical adsorption with other substances, filling the micropores of materials, improving density and uniformity, and enhancing mechanical properties and durability. Calcium lignosulfonate is a surfactant that adsorbs onto the surface of material particles, reducing surface tension between particles, resulting in uniform particle dispersion, improved flowability and workability, and a certain retarding effect, extending the material's construction time.

[0017] Third, the iron-aluminum bimetallic complex is mainly responsible for adsorbing and complexing some organic impurities and some metal ions, while the fluorosilicate ions ionized from magnesium fluorosilicate and sodium fluorosilicate can form insoluble fluorosilicate precipitates with various metal ions, further removing metal impurities from the system. The combined effect of these three components significantly improves the purification level of the system. The iron-aluminum bimetallic complex can regulate the pH of the system, while magnesium fluorosilicate and sodium fluorosilicate can regulate the ionic strength. Their synergistic effect creates a chemical environment conducive to the formation of stable product structures and good performance, thereby improving the product's corrosion resistance, stability, and workability. Their synergistic effect can also promote some intermediate reactions, accelerate the entire reaction process, improve production efficiency, and result in a more superior final product. Detailed Implementation

[0018] The present invention will be further described below with reference to specific implementation examples, but the present invention is not limited to these embodiments.

[0019] Example 1 An additive for improving the activity of mineral admixtures in concrete comprises the following raw materials in parts by weight: 30 parts desulfurized gypsum, 4.5 parts sodium aluminate, 2 parts ferric oxide, 2 parts calcium hydroxide, 6.5 parts sodium methylsilicate, 4 parts magnesium fluorosilicate, 4 parts sodium fluorosilicate, 2 parts iron-aluminum bimetallic complex, 8 parts nano-silica, and 4 parts calcium lignosulfonate. The sodium aluminate has a particle size of nanometers, and the desulfurized gypsum has a particle size of micrometers.

[0020] The preparation method of the iron-aluminum bimetallic complex in the above-mentioned additive includes the following steps: Ferrous sulfate (FeSO4·7H2O): sodium aluminate (NaAlO2): citric acid: water = 1.4:0.85:1.9:4 by mass ratio; ferrous sulfate and sodium aluminate are added to water and mixed evenly; then citric acid is added and mixed evenly; the mixture is stirred at 250 r / min for 3.5 h at 65°C; spray drying is performed with the following parameters: inlet air temperature of 160°C and outlet air temperature of 90°C, to obtain a reddish-brown complex powder, i.e., the iron-aluminum bimetallic complex.

[0021] The preparation method of the above-mentioned additive for improving the activity of concrete mineral admixtures includes the following steps: S1: Calcine the desulfurized gypsum at 165℃ for 2.5h to obtain β-type hemihydrate gypsum; mix the β-type hemihydrate gypsum with sodium methylsilicate; ball mill the β-type hemihydrate gypsum using a ball mill with 8mm diameter zirconia balls as the grinding medium, controlling the ball-to-material mass ratio at 7.5:1, and ball milling at 180r / min for 4.5h to obtain modified desulfurized gypsum powder; S2, Full Component Composite: Modified desulfurized gypsum powder, nano-sized sodium aluminate, ferric oxide, calcium hydroxide, magnesium fluorosilicate, sodium fluorosilicate, iron-aluminum bimetallic complex, nano-silica, and calcium lignosulfonate are added to a mixer and stirred at 180 r / min for 12 min; then stirred at 650 r / min for 50 min to obtain the additive.

[0022] Example 2 An additive for improving the activity of mineral admixtures in concrete comprises the following raw materials in parts by weight: 25 parts desulfurized gypsum, 2 parts sodium aluminate, 1 part ferric oxide, 1 part calcium hydroxide, 5 parts sodium methylsilicate, 3 parts magnesium fluorosilicate, 3 parts sodium fluorosilicate, 1 part iron-aluminum bimetallic complex, 5 parts nano-silica, and 3 parts calcium lignosulfonate. The sodium aluminate has a particle size of nanometers, and the desulfurized gypsum has a particle size of micrometers.

[0023] The preparation method of the iron-aluminum bimetallic complex in the above-mentioned additive includes the following steps: Ferrous sulfate (FeSO4·7H2O): sodium aluminate (NaAlO2): citric acid: water = 1.3:0.8:1.8:3 by mass ratio; ferrous sulfate and sodium aluminate are added to water and mixed evenly; then citric acid is added and mixed evenly; the mixture is stirred at 200 r / min for 3 h at 60℃; spray drying is performed with the following parameters: inlet air temperature of 150℃ and outlet air temperature of 80℃, to obtain a reddish-brown complex powder, i.e., the iron-aluminum bimetallic complex.

[0024] The preparation method of the above-mentioned additive for improving the activity of concrete mineral admixtures includes the following steps: S1: Calcine the desulfurized gypsum at 150℃ for 2 hours to obtain β-type hemihydrate gypsum; mix the β-type hemihydrate gypsum with sodium methylsilicate; ball mill the β-type hemihydrate gypsum using a ball mill with 5mm diameter zirconia balls as the grinding medium, controlling the ball-to-material mass ratio at 5:1, and ball milling at 150r / min for 4 hours to obtain modified desulfurized gypsum powder; S2, Full Component Composite: Modified desulfurized gypsum powder, nano-sized sodium aluminate, ferric oxide, calcium hydroxide, magnesium fluorosilicate, sodium fluorosilicate, iron-aluminum bimetallic complex, nano-silica, and calcium lignosulfonate are added to a mixer and stirred at 150 r / min for 10 min; then stirred at 500 r / min for 30 min to obtain the additive.

[0025] Example 3 An additive for improving the activity of mineral admixtures in concrete comprises the following raw materials in parts by weight: 25 parts desulfurized gypsum, 5 parts sodium aluminate, 1 part ferric oxide, 3 parts calcium hydroxide, 5 parts sodium methylsilicate, 5 parts magnesium fluorosilicate, 3 parts sodium fluorosilicate, 3 parts iron-aluminum bimetallic complex, 5 parts nano-silica, and 5 parts calcium lignosulfonate. The sodium aluminate has a particle size of nanometers, and the desulfurized gypsum has a particle size of micrometers.

[0026] The preparation method of the iron-aluminum bimetallic complex in the above-mentioned additive includes the following steps: Ferrous sulfate (FeSO4·7H2O): sodium aluminate (NaAlO2): citric acid: water = 1.3:0.9:1.8:5 by mass ratio; ferrous sulfate and sodium aluminate are added to water and mixed evenly; then citric acid is added and mixed evenly; the mixture is stirred at 300 r / min for 3 h at 60℃; spray drying is performed with the following parameters: inlet air temperature of 180℃ and outlet air temperature of 80℃, to obtain a reddish-brown complex powder, i.e., the iron-aluminum bimetallic complex.

[0027] The preparation method of the above-mentioned additive for improving the activity of concrete mineral admixtures includes the following steps: S1: Calcine the desulfurized gypsum at 180℃ for 2 hours to obtain β-type hemihydrate gypsum; mix the β-type hemihydrate gypsum with sodium methylsilicate; ball mill the β-type hemihydrate gypsum using a ball mill with 10mm diameter zirconia balls as the grinding medium, controlling the ball-to-material mass ratio at 5:1, and ball milling at 200r / min for 4 hours to obtain modified desulfurized gypsum powder; S2, Full Component Composite: Modified desulfurized gypsum powder, nano-sized sodium aluminate, ferric oxide, calcium hydroxide, magnesium fluorosilicate, sodium fluorosilicate, iron-aluminum bimetallic complex, nano-silica, and calcium lignosulfonate are added to a mixer and stirred at 200 r / min for 10 min; then stirred at 800 r / min for 30 min to obtain the additive.

[0028] Example 4 An additive for improving the activity of mineral admixtures in concrete comprises the following raw materials in parts by weight: 35 parts desulfurized gypsum, 5 parts sodium aluminate, 3 parts ferric oxide, 3 parts calcium hydroxide, 8 parts sodium methylsilicate, 5 parts magnesium fluorosilicate, 5 parts sodium fluorosilicate, 3 parts iron-aluminum bimetallic complex, 10 parts nano-silica, and 5 parts calcium lignosulfonate. The sodium aluminate has a particle size of nanometers, and the desulfurized gypsum has a particle size of micrometers.

[0029] The preparation method of the iron-aluminum bimetallic complex in the above-mentioned additive includes the following steps: Ferrous sulfate (FeSO4·7H2O): sodium aluminate (NaAlO2): citric acid: water = 1.5:0.9:2.0:5 by mass ratio; ferrous sulfate and sodium aluminate are added to water and mixed evenly; then citric acid is added and mixed evenly; the mixture is stirred at 300 r / min for 4 h at 70℃; spray drying is performed with the following parameters: inlet air temperature of 180℃ and outlet air temperature of 100℃, to obtain a reddish-brown complex powder, i.e., the iron-aluminum bimetallic complex.

[0030] The preparation method of the above-mentioned additive for improving the activity of concrete mineral admixtures includes the following steps: S1: Calcine the desulfurized gypsum at 180℃ for 3 hours to obtain β-type hemihydrate gypsum; mix the β-type hemihydrate gypsum with sodium methylsilicate; ball mill the β-type hemihydrate gypsum using a ball mill with 10mm diameter zirconia balls as the grinding medium, controlling the ball-to-material mass ratio at 10:1, and ball milling at 200r / min for 5 hours to obtain modified desulfurized gypsum powder; S2, Full Component Composite: Modified desulfurized gypsum powder, nano-sized sodium aluminate, ferric oxide, calcium hydroxide, magnesium fluorosilicate, sodium fluorosilicate, iron-aluminum bimetallic complex, nano-silica, and calcium lignosulfonate are added to a mixer and stirred at 200 r / min for 15 min; then stirred at 800 r / min for 60 min to obtain the additive.

[0031] Example 5 An additive for improving the activity of mineral admixtures in concrete comprises the following raw materials in parts by weight: 35 parts desulfurized gypsum, 2 parts sodium aluminate, 3 parts ferric oxide, 1 part calcium hydroxide, 8 parts sodium methylsilicate, 3 parts magnesium fluorosilicate, 5 parts sodium fluorosilicate, 1 part iron-aluminum bimetallic complex, 10 parts nano-silica, and 3 parts calcium lignosulfonate. The sodium aluminate has a particle size of nanometers, and the desulfurized gypsum has a particle size of micrometers.

[0032] The preparation method of the iron-aluminum bimetallic complex in the above-mentioned additive includes the following steps: Ferrous sulfate (FeSO4·7H2O): sodium aluminate (NaAlO2): citric acid: water = 1.5:0.8:2.0:3 by mass ratio; ferrous sulfate and sodium aluminate are added to water and mixed evenly; then citric acid is added and mixed evenly; the mixture is stirred at 70°C and 200 r / min for 4 h; spray drying is performed with the following parameters: inlet air temperature of 150°C and outlet air temperature of 100°C, to obtain a reddish-brown complex powder, i.e., the iron-aluminum bimetallic complex.

[0033] The preparation method of the above-mentioned additive for improving the activity of concrete mineral admixtures includes the following steps: S1: Calcine the desulfurized gypsum at 150℃ for 3 hours to obtain β-type hemihydrate gypsum; mix the β-type hemihydrate gypsum with sodium methylsilicate; ball mill the β-type hemihydrate gypsum using a ball mill with 5mm diameter zirconia balls as the grinding media, controlling the ball-to-material mass ratio at 10:1, and ball milling at 150r / min for 5 hours to obtain modified desulfurized gypsum powder; S2, Full Component Composite: Modified desulfurized gypsum powder, nano-sized sodium aluminate, ferric oxide, calcium hydroxide, magnesium fluorosilicate, sodium fluorosilicate, iron-aluminum bimetallic complex, nano-silica, and calcium lignosulfonate are added to a mixer and stirred at 150 r / min for 15 min; then stirred at 500 r / min for 60 min to obtain the additive.

[0034] In the above embodiments, the desulfurized gypsum was sourced from Lingshou County Chengjiang Mining Processing Plant; sodium aluminate from Shandong Jinwanhua Fine Chemical Co., Ltd.; ferric oxide from Shandong Yilai New Material Technology Development Co., Ltd.; calcium hydroxide from Anyang Qingyou Building Materials Co., Ltd.; sodium methylsilicate from Jinan Qingyuyuan New Material Co., Ltd.; magnesium fluorosilicate from Dezhou Fuyang Environmental Protection Technology Co., Ltd.; sodium fluorosilicate from Jinan Hongchuang Chemical Co., Ltd.; ferrous sulfate from Jinan Guocheng Chemical Co., Ltd.; citric acid from Henan Fengwei Biotechnology Co., Ltd.; and nano-silica from Hubei Huifu Nanomaterials Co., Ltd., model HL-450, with a specific surface area of ​​440 m². 2 / g; Calcium lignosulfonate is sourced from Jinan Sirui Chemical Co., Ltd.

[0035] Comparative Example 1 In the additives, sodium methylsilicate is not added, that is, sodium methylsilicate is not added in S1 for ball milling modification; in S2, β-type hemihydrate gypsum is used instead of modified desulfurized gypsum powder; other parameters and methods are the same as in Example 1.

[0036] Comparative Example 2 In step S1, the desulfurized gypsum is not calcined, but directly mixed and ball-milled with sodium methylsilicate; other parameters and methods are the same as in Example 1.

[0037] Comparative Example 3 No iron-aluminum bimetallic complex was added to the additive; other parameters and methods were the same as in Example 1.

[0038] Comparative Example 4 Magnesium fluorosilicate is not added to the additives; other parameters and methods are the same as in Example 1.

[0039] Comparative Example 5 Sodium fluorosilicate was not added to the additives; other parameters and methods were the same as in Example 1.

[0040] Comparative Example 6 The additive does not contain iron-aluminum bimetallic complex, magnesium fluorosilicate, or sodium fluorosilicate; other parameters and methods are the same as in Example 1.

[0041] The additives in the above embodiments and comparative examples were tested and evaluated using the additives.

[0042] 1. Strength improvement rate: Prepare standard cement (ordinary Portland cement), standard sand (particle size less than 4.75mm), water, and additives for different examples and comparative proportions. Accurately weigh 350g of cement, 150g of low-calcium fly ash (CaO content 7.5%), 100g of slag powder, and 1300g of standard sand. Calculate the required water volume based on a water-cement ratio of 0.5, and control the additive dosage to 10% of the cement mass. Mix the weighed cement, standard sand, water, and additives together. First, mix at 20 rpm for 5 minutes to initially mix the materials; then mix at 40 rpm for 5 minutes; stop mixing for 90 seconds; and finally mix at 40 rpm for 10 minutes to obtain the sample. Pour the sample into a 40mm×40mm×160mm triple mold to form the specimen. Place the formed specimen in a standard curing chamber under the curing conditions of 20℃ and 95% relative humidity; cure for the specified age of 14 days. Strength Testing: First, the flexural strength of the specimens was tested using a flexural testing machine, and the failure load was recorded. The flexural strength improvement rate was calculated as follows: (Flexural strength of the specimen with additives / Flexural strength of the reference specimen) × 100%. The reference specimen was a concrete specimen without additives. Then, the compressive strength was tested using a compressive testing machine, and the failure load was recorded. The compressive strength improvement rate was calculated as follows: (Compressive strength of the specimen with additives / Compressive strength of the reference specimen) × 100%. The reference specimen was a concrete specimen without additives. The results are shown in Table 1 below.

[0043] 2. Flowability testing: Referring to the test method in GB / T 2419 "Determination of Flowability of Cement Samples", the sample from Experiment 1 was used. Preparation of the test table and mold: Place the truncated cone mold in the center of the test table. Wipe the inner wall of the mold, the tamping rod, and the test table surface with a damp cloth to keep them moist and prevent sample sticking. Filling and tamping: Quickly fill the mold in two layers. The first layer is filled to about 2 / 3 of the mold's height. Use a knife to make 5 cuts in each of two perpendicular directions to remove air bubbles. Then, use the tamping rod to evenly tamp the sample 15 times from the edge to the center, ensuring even pressure to make the sample dense. The second layer is filled to about 20mm above the mold. Again, make 5 cuts with a knife and then tamp 10 times. Smoothing and tamping: After tamping, use a knife to scrape off any sample above the mold and smooth the surface to make it flat. Gently lift the circular mold vertically upwards and immediately start the oscillation table, performing 30 oscillations at a frequency of once per second within 30 seconds. Measure the flowability: After the oscillations, use calipers to measure the diameter of the sample's bottom surface in two mutually perpendicular directions. Take the average value as the flowability of the sample with that ratio, in mm. The results are shown in Table 1 below.

[0044] Table 1 Test Results Sample Flexural strength improvement rate (%) Compressive strength improvement rate (%) Flowability (mm) Example 1 65 75 190 Example 2 60 70 185 Example 3 63 73 188 Example 4 70 80 195 Example 5 62 72 186 Comparative Example 1 45 55 170 Comparative Example 2 50 60 175 Comparative Example 3 55 65 180 Comparative Example 4 58 68 182 Comparative Example 5 57 67 181 Comparative Example 6 42 52 168 The results above show that the additives in Examples 1 to 5 can effectively improve mixing workability, activity and fluidity, and enhance strength.

[0045] Comparative Example 1 (without sodium methylsilicate): Sodium methylsilicate modifies β-type hemihydrate gypsum, improving its surface properties and enhancing its affinity and synergistic effect with other components. Without sodium methylsilicate, β-type hemihydrate gypsum cannot be effectively modified, resulting in reduced dispersibility and reactivity in the additive system. This significantly diminishes the activation effect of the additive on mineral admixtures such as low-calcium fly ash, weakens the hydration reaction of the specimens, reduces the quantity of hydration products, and results in a less dense structure, thus reducing the improvement rate of flexural and compressive strength. Because the performance of desulfurized gypsum is not fully utilized, the internal structure and interparticle lubrication of the sample are affected, increasing interparticle friction and worsening the fluidity and flowability of the sample.

[0046] Comparative Example 2 (Uncalcined Desulfurized Gypsum): After calcination, the desulfurized gypsum transforms into β-type hemihydrate gypsum, resulting in a change in its crystal structure. The uncalcined desulfurized gypsum primarily exists as dihydrate gypsum, participating in the hydration reaction in the additive system at a slower rate and to a lower extent. This leads to a reduction in the amount of early and late hydration products generated, failing to form a sufficient strength-supporting structure, thus limiting strength development. The increase in flexural and compressive strength is lower than in the calcined example. The particle morphology and surface properties of the uncalcined desulfurized gypsum are unfavorable for sample flow; its surface is relatively rough, resulting in greater friction with other particles, hindering sample expansion in the jump table test and leading to decreased flowability.

[0047] Comparative Example 3 (without iron-aluminum bimetallic complex): The iron-aluminum bimetallic complex exhibits unique catalytic and synergistic effects in additives, promoting the dissolution and hydration reactions of active components in the mineral admixtures. Without the addition of the iron-aluminum bimetallic complex, the hydration reaction of the mineral admixtures lacks this crucial promoting factor, resulting in a slower reaction rate. The amount of hydration products generated in the early stages is reduced, failing to promptly fill the pores inside the sample and form an effective strength framework. Although the later hydration reaction continues, the weaker foundation from the earlier reactions affects the final flexural and compressive strength, leading to a decrease in the strength improvement rate. Because the changes in the hydration reaction affect the internal structure and interparticle interactions of the sample, altering the cohesive force and frictional force, this influences the flowability to some extent, resulting in a decrease in flowability compared to the examples.

[0048] Comparative Example 4 (without magnesium fluorosilicate): Magnesium fluorosilicate in the additive system can interact with other components to promote the early hydration reaction of mineral admixtures. It can chemically react with certain components in cement to generate products that are beneficial to strength development, while accelerating the dissolution of active components in mineral admixtures. Without magnesium fluorosilicate, the kinetics and reaction pathways of the early hydration reaction are affected, and the amount of hydration products generated is reduced, especially in the early stages, resulting in insufficient contribution to strength. With increasing age, although the later hydration reaction can compensate for some of the strength increase, the overall strength improvement is still inhibited to some extent due to insufficient early reaction, and the rate of increase in flexural and compressive strength decreases. Due to the change in the early hydration reaction, the viscosity and cohesion of the sample change, resulting in a slight increase in the flow resistance of the sample in the jump table test, leading to a slight decrease in fluidity.

[0049] Comparative Example 5 (without sodium fluorosilicate): Sodium fluorosilicate also plays an important role in the activation reaction of mineral admixtures by additives. It can participate in the hydration reaction and promote the structural formation and strength development of cement paste. Without sodium fluorosilicate, some strength-beneficial products formed during the hydration reaction are missing, resulting in a less dense and stable cement paste structure and inhibited strength development. Especially in the early stage, the impact on strength growth is more significant, leading to a decrease in the rate of increase in flexural and compressive strength. At 14 days, it is also affected to some extent due to the change in the overall reaction process. The absence of sodium fluorosilicate affects the formation of the internal structure of the sample, causing changes in the arrangement and interaction between particles, resulting in a slight decrease in flowability and fluidity in the jump table test.

[0050] Comparative Example 6 (without the addition of iron-aluminum bimetallic complex, magnesium fluorosilicate, and sodium fluorosilicate): Due to the simultaneous absence of several components that play an important role in activating the activity of the mineral admixture, the hydration reaction of the mineral admixture was severely hindered. The absence of the iron-aluminum bimetallic complex resulted in a lack of catalytic and synergistic effects on the hydration reaction, while the absence of magnesium fluorosilicate and sodium fluorosilicate affected the early hydration reaction and the formation of strength-related products. This led to the specimen failing to undergo normal hydration reactions in both the early and late stages, resulting in extremely slow strength growth and a significant reduction in the rate of increase in flexural and compressive strength, reaching a low level similar to Comparative Example 1. The absence of multiple key components had a significant impact on the internal structure and interparticle interactions of the specimen, altering the cohesion, friction, and interparticle lubricity of the specimen in a way that was detrimental to flow, resulting in a flowability significantly lower than that of Example 1.

Claims

1. An additive for improving the activity of mineral admixtures in concrete, characterized in that, The additives include the following raw materials in parts by weight: 25-35 parts desulfurized gypsum, 2-5 parts sodium aluminate, 1-3 parts ferric oxide, 1-3 parts calcium hydroxide, 5-8 parts sodium methylsilicate, 3-5 parts magnesium fluorosilicate, 3-5 parts sodium fluorosilicate, 1-3 parts iron-aluminum bimetallic complex, 5-10 parts nano silica, and 3-5 parts calcium lignosulfonate.

2. The additive for improving the activity of mineral admixtures in concrete according to claim 1, characterized in that, The sodium aluminate has a particle size in the nanometer range.

3. The additive for improving the activity of mineral admixtures in concrete according to claim 1, characterized in that, The desulfurized gypsum has a particle size in the micrometer range.

4. The additive for improving the activity of mineral admixtures in concrete according to claim 1, characterized in that, The preparation method of the iron-aluminum bimetallic complex includes the following steps: Ferrous sulfate: sodium aluminate: citric acid: water are mixed in a mass ratio of (1.3-1.5): (0.8-0.9): (1.8-2.0): (3-5). Ferrous sulfate and sodium aluminate are added to water and mixed evenly. Then citric acid is added and mixed evenly. The mixture is stirred at 60℃-70℃ and 200-300 r / min for 3-4 hours. The mixture is then spray-dried to obtain a reddish-brown complex powder, i.e., the iron-aluminum bimetallic complex.

5. The additive for improving the activity of mineral admixtures in concrete according to claim 4, characterized in that, The parameters for the spray drying are: inlet air temperature of 150℃~180℃ and outlet air temperature of 80℃~100℃.

6. The additive for improving the activity of mineral admixtures in concrete according to claim 1, characterized in that, The preparation method of the additive includes the following steps: S1: Calcine the desulfurized gypsum at 150℃~180℃ for 2h~3h to obtain β-type hemihydrate gypsum; mix the β-type hemihydrate gypsum with sodium methylsilicate; ball mill the β-type hemihydrate gypsum to obtain modified desulfurized gypsum powder. S2, Full Component Composite: Modified desulfurized gypsum powder, nano-sized sodium aluminate, ferric oxide, calcium hydroxide, magnesium fluorosilicate, sodium fluorosilicate, iron-aluminum bimetallic complex, nano-silica, and calcium lignosulfonate are added to a mixer and stirred at 150 r / min to 200 r / min for 10 min to 15 min; then stirred at 500 r / min to 800 r / min for 30 min to 60 min to obtain the additive.

7. The additive for improving the activity of mineral admixtures in concrete according to claim 6, characterized in that, In S1, zirconia balls with a diameter of 5mm to 10mm are used as grinding media in the ball mill, and the ball-to-material mass ratio is controlled at (5 to 10):

1.

8. The additive for improving the activity of mineral admixtures in concrete according to claim 6, characterized in that, In S1, the ball mill speed is 150 r / min to 200 r / min; the ball milling time is 4 h to 5 h.