A fly ash-desulfurized gypsum composite activator, its preparation method, and its application in high salt-resistant and freeze-thaw resistant concrete.

Abstract

This application relates to the field of building materials, and in particular to a fly ash-desulfurized gypsum composite activator, its preparation method, and its application in high-salt-freeze concrete. The fly ash-desulfurized gypsum composite activator comprises fly ash, desulfurized gypsum, inorganic particles, organic salt additives, water glass, reinforcing agents, and water-reducing agents. The composite activator prepared in this application can significantly improve the durability of concrete under salt-freeze coupled environments, effectively resist the combined effects of de-icing salt erosion and freeze-thaw cycles, greatly inhibit surface spalling and the propagation of internal micro-cracks, and improve the workability of the cementitious system, facilitating construction operations. It can be widely applied in cold regions and in engineering fields such as airport runways, highway bridges, and seaports where de-icing salt is frequently used.

Description

Technical Field

[0001] This application relates to the field of building materials, and in particular to a fly ash-desulfurized gypsum composite activator, its preparation method, and its application in high salt-resistant and freeze-thaw-resistant concrete. Background Technology

[0002] In cold regions and engineering environments such as coastal areas, airports, and bridges where de-icing salt is widely used, concrete structures not only endure freeze-thaw cycles but also face the combined effects of corrosive media such as chlorides or sulfates. This salt-freezing damage manifests primarily as surface spalling, the propagation of internal microcracks, and accelerated steel reinforcement corrosion, leading to a significant decrease in the durability of concrete structures and a substantial reduction in their service life. Therefore, developing concrete materials with high salt-freezing resistance has become an important research direction in the field of civil engineering materials. Among mineral admixtures, fly ash is one of the most commonly used admixtures due to its wide availability, low cost, and pozzolanic activity. However, its early activity under normal temperature conditions is relatively low, and the addition of fly ash alone often results in slow early strength development of concrete and limited improvement in resistance to salt-freezing environments, making it difficult to meet the requirements for high salt-freezing resistance.

[0003] To enhance the potential activity of fly ash, existing technologies have developed chemical activators, including alkali metal hydroxides, alkali metal sulfates, silicates, and composite activating systems. Among these, strong alkali activators, such as sodium hydroxide and water glass, can significantly improve the dissolution rate and polymerization degree of fly ash. However, strong alkali activators suffer from difficulties in workability control, large shrinkage, and potential alkali-aggregate reaction risks, limiting their large-scale application in practical engineering. Meanwhile, desulfurization gypsum, a byproduct of wet flue gas desulfurization processes in coal-fired power plants, is mainly composed of calcium sulfate dihydrate. Its annual emissions are enormous, and its comprehensive utilization rate is low. Large-scale accumulation not only occupies land resources but also may cause secondary pollution to the environment.

[0004] To address the aforementioned issues, existing technologies have attempted to combine fly ash with desulfurized gypsum and add a small amount of alkaline substances or auxiliary activating components to synergistically enhance the activating effect. However, research on the adaptability of such composite activators in salt-freezing environments is still insufficient. Most solutions only focus on ordinary freeze-thaw cycles or single salt erosion conditions, failing to systematically consider the coupling mechanism between salt and freeze-thaw. Under actual service conditions, salt solutions lower the freezing point, thereby altering the damage mode of freeze-thaw cycles. On the other hand, salt crystallization pressure and ion erosion chemical action exacerbate the deterioration of the concrete pore structure, causing the hydration products formed by conventional activators to easily decompose or lose their bonding ability during salt-freezing cycles.

[0005] It is evident that existing composite activators based on fly ash and desulfurized gypsum suffer from several problems, including insufficient stability and microstructural density of hydration products under salt-freeze coupling, difficulty in resisting fatigue stress generated by salt solution penetration and freeze-thaw cycles over long periods, poor resistance to erosion in the later stages, and significant influence from environmental temperature and water-salt conditions. Summary of the Invention

[0006] Therefore, in summary, developing a novel composite activator that can fully leverage the synergistic activating effect of fly ash and desulfurized gypsum, form highly stable hydration products in a salt-freezing environment, and significantly improve the salt-freezing erosion resistance of concrete, to meet the performance requirements of existing high-salt-freezing concrete, has significant engineering application value and environmental benefits.

[0007] To achieve the above objectives, this application provides the following technical solution: The first aspect of this application provides a fly ash-desulfurized gypsum composite activator, the raw material scheme of which, by mass, includes: 50-70 parts fly ash, 20-35 parts desulfurized gypsum, 4-10 parts inorganic particles, 0.8-3 parts organic salt additives, 2-5 parts water glass, 4-10 parts reinforcing agent, 0.5-1.5 parts water-reducing agent, and 0.3-1 parts cellulose ether.

[0008] Preferably, the fly ash is Grade I fly ash.

[0009] Preferably, the fineness of the fly ash is ≤10%.

[0010] Preferably, the 28-day activity index of the fly ash is 75-85%.

[0011] Preferably, the 28-day activity index of the fly ash is 80-85%.

[0012] Preferably, the SO3 content of the fly ash is ≤2.5%.

[0013] Preferably, the SO3 content of the fly ash is ≤2%.

[0014] Preferably, the desulfurization gypsum is wet flue gas desulfurization gypsum.

[0015] Preferably, the specific surface area of ​​the desulfurized gypsum is 280~350m². 2 / kg.

[0016] Preferably, the specific surface area of ​​the desulfurized gypsum is 300~330 m². 2 / kg.

[0017] Preferably, the desulfurized gypsum has a CaSO4·2H2O content of 92-98%.

[0018] Preferably, the inorganic particles are a combination of sodium hydroxide, sodium carbonate, and aluminum sulfate.

[0019] Preferably, the mass ratio of sodium hydroxide, sodium carbonate and aluminum sulfate is (1~3):(2~4):(1~3).

[0020] Preferably, the mass ratio of sodium hydroxide, sodium carbonate and aluminum sulfate is (1~2):(3~3.5):(1~2).

[0021] Preferably, the mass ratio of fly ash, desulfurized gypsum and inorganic particles is (6~7):(2.5~3.5):(0.5~0.9).

[0022] Preferably, the mass ratio of fly ash, desulfurized gypsum and inorganic particles is (6~6.5):(2.5~3):(0.6~0.8).

[0023] The compound raw material scheme adopted in this application constructs a complete system from particle deconstruction to hydration product regulation in the fly ash-desulfurized gypsum system through the combined action of alkali source, sulfur source, aluminum source and organic salt. The alkali composite system first gently destroys the surface network of fly ash glass, causing the internal active silica and aluminum to gradually dissolve. Then, the sulfate and aluminum ions provided by desulfurized gypsum and aluminum sulfate participate in the reaction, guiding the formation of a dense structure with gel as the main component. At the same time, the compounding of sodium citrate and sodium gluconate plays a dual regulatory role. The former appropriately slows down the crystallization rate of ettringite by complexing calcium ions, while the latter improves particle dispersion and slurry flow through adsorption. Thus, while avoiding excessively rapid setting and volume cracking, the hydration products are more evenly distributed and the microstructure is denser. Ultimately, while improving workability, it significantly enhances the concrete's ability to resist salt-freeze cycle damage, providing a good foundation for the excellent comprehensive performance of concrete.

[0024] Preferably, the organic salt additive is a combination of sodium citrate and sodium gluconate.

[0025] Preferably, the mass ratio of sodium citrate to sodium gluconate is (2~3):(0.8~1.5).

[0026] Preferably, the mass ratio of sodium citrate to sodium gluconate is (2.3~2.6):(1~1.2).

[0027] Preferably, the modulus of the water glass is 1 to 1.5.

[0028] Preferably, the modulus of the water glass is 1.2 to 1.5.

[0029] Preferably, the water glass has a Baumé degree of 40 to 60.

[0030] Preferably, the water glass has a Baumé degree of 40 to 50.

[0031] Preferably, the solid content of the water glass is 28-35%.

[0032] Preferably, the reinforcing agent is a combination of melamine, calcium formate and hydroxyethylidene diphosphonic acid.

[0033] Preferably, the mass ratio of melamine, calcium formate and hydroxyethylidene diphosphonic acid is (2~3):(4~6):(1~2).

[0034] Preferably, the mass ratio of melamine, calcium formate and hydroxyethylidene diphosphonic acid is (2.5~3):(5~5.5):(1~1.5).

[0035] Preferably, the mass ratio of fly ash, organic salt additives and reinforcing agents is (6~7):(0.15~0.25):(0.5~1).

[0036] Preferably, the mass ratio of fly ash, organic salt additives and reinforcing agents is (6~6.5):(0.2~0.25):(0.7~0.9).

[0037] The addition of the reinforcing agent further optimized the system's resistance to salt freezing. The three agents worked together to form flexible hydrogen bonds on the surface of the hydration products, improving the interfacial affinity between the gel and the particles, and assisting in the uniform dispersion of the powder. They also gently released calcium ions, providing a stable calcium source for the hydration reaction, avoiding structural looseness caused by local calcium deficiency, and ultimately achieving moderate chelation, inhibiting the explosive formation of ettringite, making the crystallization process smoother, thereby effectively alleviating volume stress concentration and improving the overall stability and erosion resistance of the hardened body in a salt freezing environment.

[0038] Preferably, the water-reducing agent is a polycarboxylate water-reducing agent.

[0039] Preferably, the cellulose ether is at least one selected from hydroxypropyl methylcellulose, methylcellulose, hydroxyethyl methylcellulose, sodium carboxymethylcellulose, and hydroxyethylcellulose.

[0040] Preferably, the cellulose ether is a combination of hydroxypropyl methylcellulose and sodium carboxymethyl cellulose.

[0041] Preferably, the mass ratio of hydroxypropyl methylcellulose to sodium carboxymethyl cellulose is (2~3):(1~1.5).

[0042] Preferably, the mass ratio of hydroxypropyl methylcellulose to sodium carboxymethyl cellulose is (2.5~3):(1.2~1.4).

[0043] The second aspect of this application provides a method for preparing the above-mentioned fly ash-desulfurized gypsum composite activator, specifically including the following steps: S1: sieving fly ash, desulfurized gypsum, inorganic particles and organic salt additives separately, and drying fly ash and desulfurized gypsum to a moisture content ≤1wt%; S2: adding inorganic particles and organic salt additives into a mixer and mixing to obtain a first premix, then adding reinforcing agent, water-reducing agent and cellulose ether into the mixer and mixing to obtain a second premix; S3: dry mixing fly ash and desulfurized gypsum in a double cone mixer to obtain a main material, adding the first and second premixes to the main material, and simultaneously adding the remaining raw materials to mix, ensuring that the material temperature is ≤50℃, and after completion, sieving the product, dispensing and sealing it to obtain the final product.

[0044] Preferably, the preparation method of the fly ash-desulfurized gypsum composite activator specifically includes the following steps: S1: passing fly ash, desulfurized gypsum, inorganic particles, and organic salt additives through a 0.15~0.2mm sieve, and drying the fly ash and desulfurized gypsum at 95~105℃ until the moisture content is ≤1wt%; S2: adding inorganic particles and organic salt additives into a mixer, mixing and stirring at 40~60rpm for 15~25min to obtain a first premix, and then adding reinforcing agent and water-reducing agent. S1: Add cellulose ether to a mixer and mix at 40-60 rpm for 10-15 min to obtain the second premix; S2: Add fly ash and desulfurized gypsum to a double cone mixer and dry mix at 20-30 rpm for 10-15 min to obtain the main material. Add the first and second premixes to the main material, along with the remaining raw materials, and mix at 25-35 rpm for 20-25 min, ensuring the material temperature is ≤50℃. After completion, pass the product through a 0.5-0.6 mm square hole sieve, and then package and seal it to obtain the final product.

[0045] The third aspect of this application defines the application of the aforementioned fly ash-desulfurized gypsum composite activator in high salt-resistant concrete.

[0046] The beneficial effects and application advantages of this application are as follows: 1. The composite activator prepared in this application can significantly improve the durability of concrete under salt-freeze coupled environment, effectively resist the combined effects of de-icing salt erosion and freeze-thaw cycle, greatly inhibit surface spalling and internal micro-crack propagation, and the activator improves the workability of cementitious system, so that the slurry maintains good fluidity and stability over time, which is convenient for construction operation. At the same time, the hardened concrete has excellent volume stability, small shrinkage deformation, and outstanding resistance to salt-freeze erosion. It makes full use of industrial by-product resources, reduces material costs and environmental impact, and can be widely used in cold regions and engineering fields such as airport runways, highway bridges, and seaports where de-icing salt is frequently used.

[0047] 2. The compound raw material scheme adopted in this application, through the combined action of alkali source, sulfur source, aluminum source and organic salt, constructs a complete system from particle deconstruction to hydration product regulation in the fly ash-desulfurized gypsum system, guiding the formation of a dense structure with gel as the main component. At the same time, the compounding of sodium citrate and sodium gluconate plays a dual regulatory function. The former appropriately slows down the crystallization rate of ettringite by complexing calcium ions, while the latter improves particle dispersion and slurry flow through adsorption, making the hydration products more uniformly distributed and the microstructure more compact. Ultimately, while improving workability, it significantly enhances the concrete's ability to resist salt-freezing cycle damage, providing a good foundation for the concrete to achieve excellent comprehensive performance.

[0048] 3. The addition of the reinforcing agent in this application further optimizes the anti-salt freezing performance of the system. The reinforcing agent improves the interfacial affinity between the gel and the particles, gently releases calcium ions, provides a stable calcium source for the hydration reaction, avoids the structural looseness caused by local calcium deficiency, and ultimately carries out a moderate chelation effect, inhibits the explosive formation of ettringite, and makes the crystallization process smoother, thereby effectively alleviating the volume stress concentration and improving the overall stability and anti-erosion ability of the hardened body in the salt freezing environment. Detailed Implementation

[0049] In the following specific embodiments, unless otherwise specified, the sources / preparation methods of some raw materials are as follows: Example 1

[0050] A fly ash-desulfurized gypsum composite activator, by weight, comprises the following raw materials: 64 parts fly ash, 28.6 parts desulfurized gypsum, 7.5 parts inorganic particles, 2.2 parts organic salt additives, 3.8 parts water glass, 8.4 parts reinforcing agent, 0.8 parts water-reducing agent, and 0.9 parts cellulose ether.

[0051] The fly ash is grade I fly ash with a fineness of 10%, a 28-day activity index of 82%, and an SO3 content of 1.8%.

[0052] The desulfurization gypsum is a wet flue gas desulfurization gypsum with a specific surface area of ​​300 m². 2 / kg, with a CaSO4·2H2O content of 93%.

[0053] The inorganic particles are a combination of sodium hydroxide, sodium carbonate and aluminum sulfate in a mass ratio of 1.6:3.4:1.5.

[0054] The organic salt additive is a combination of sodium citrate and sodium gluconate in a mass ratio of 2.3:1.2.

[0055] The modulus of water glass is 1.3, the Baumé degree is 48, and the solid content is 30%.

[0056] The reinforcing agent is a combination of melamine, calcium formate and hydroxyethylidene diphosphonic acid in a mass ratio of 3:5:1.

[0057] The water-reducing agent is polycarboxylate superplasticizer PT-1230, manufactured by Foshan Nanhai Datian Chemical Co., Ltd.

[0058] The cellulose ether is a combination of hydroxypropyl methylcellulose and sodium carboxymethyl cellulose in a mass ratio of 3:1.2.

[0059] A method for preparing the above-mentioned fly ash-desulfurized gypsum composite activator specifically includes the following steps: S1: Fly ash, desulfurized gypsum, inorganic particles and organic salt additives are passed through a 0.15mm sieve, and the fly ash and desulfurized gypsum are dried at 100℃ until the moisture content is ≤1wt%; S2: Inorganic particles and organic salt additives are added to a mixer and mixed at 50rpm for 20min to obtain a first premix. Then, reinforcing agent, water-reducing agent and cellulose ether are added to the mixer and mixed at 50rpm for 15min to obtain a second premix; S3: Fly ash and desulfurized gypsum are added to a double cone mixer and dry-mixed at 30rpm for 15min to obtain the main material. The first and second premixes are added to the main material, along with the remaining raw materials. The mixture is mixed at 25rpm for 25min, ensuring that the material temperature is ≤50℃. After completion, the product is passed through a 0.6mm square hole sieve, packaged and sealed. Example 2

[0060] A fly ash-desulfurized gypsum composite activator, by weight, comprises the following raw materials: 70 parts fly ash, 30.6 parts desulfurized gypsum, 6.8 parts inorganic particles, 2.2 parts organic salt additives, 3.8 parts water glass, 8.4 parts reinforcing agent, 0.8 parts water-reducing agent, and 0.9 parts cellulose ether.

[0061] The inorganic particles are a combination of sodium hydroxide, sodium carbonate, and aluminum sulfate in a mass ratio of 2:3:2.

[0062] The above are the only differences between this embodiment and Embodiment 1; all other aspects are the same. Example 3

[0063] A fly ash-desulfurized gypsum composite activator, by weight, comprises the following raw materials: 60 parts fly ash, 28.6 parts desulfurized gypsum, 7.5 parts inorganic particles, 1.8 parts organic salt additives, 3.8 parts water glass, 6.9 parts reinforcing agent, 0.8 parts water-reducing agent, and 0.9 parts cellulose ether.

[0064] The organic salt additive is a combination of sodium citrate and sodium gluconate in a mass ratio of 3:1.

[0065] The above are the only differences between this embodiment and Embodiment 1; all other aspects are the same.

[0066] Comparative Example 1 A fly ash-desulfurized gypsum composite activator, by weight, comprises the following raw materials: 80 parts fly ash, 35.2 parts desulfurized gypsum, 10 parts inorganic particles, 3.5 parts organic salt additives, 4 parts water glass, 2.5 parts reinforcing agent, 1.2 parts water-reducing agent, and 1 part cellulose ether.

[0067] The above are the only differences between this comparative example and Example 1; all other aspects are the same.

[0068] Comparative Example 2 A fly ash-desulfurized gypsum composite activator, by weight, comprises the following raw materials: 75 parts fly ash, 20.5 parts desulfurized gypsum, 8.8 parts inorganic particles, 0.3 parts organic salt additives, 3.8 parts water glass, 9.5 parts reinforcing agent, 0.8 parts water-reducing agent, and 0.9 parts cellulose ether.

[0069] The above are the only differences between this comparative example and Example 1; all other aspects are the same.

[0070] Comparative Example 3 A fly ash-desulfurized gypsum composite activator, by weight, comprises the following raw materials: 64 parts fly ash, 28.6 parts desulfurized gypsum, 7.5 parts inorganic particles, 2.2 parts organic salt additives, 3.8 parts water glass, 8.4 parts reinforcing agent, 0.8 parts water-reducing agent, and 0.9 parts cellulose ether.

[0071] The inorganic particles are a combination of sodium hydroxide and sodium carbonate in a mass ratio of 1:3.

[0072] The organic salt additive is a combination of sodium citrate and sodium gluconate in a mass ratio of 3:0.5.

[0073] The above are the only differences between this comparative example and Example 1; all other aspects are the same.

[0074] Comparative Example 4 A fly ash-desulfurized gypsum composite activator, by weight, comprises the following raw materials: 64 parts fly ash, 28.6 parts desulfurized gypsum, 7.5 parts inorganic particles, 2.2 parts organic salt additives, 3.8 parts water glass, 8.4 parts reinforcing agent, 0.8 parts water-reducing agent, and 0.9 parts cellulose ether.

[0075] The inorganic particles are a combination of sodium hydroxide, sodium carbonate, and aluminum sulfate in a mass ratio of 4:0.5:2.

[0076] The organic salt additive is a combination of sodium citrate and sodium gluconate in a mass ratio of 1.5:2.5.

[0077] The above are the only differences between this comparative example and Example 1; all other aspects are the same.

[0078] Comparative Example 5 A fly ash-desulfurized gypsum composite activator, by weight, comprises the following raw materials: 64 parts fly ash, 28.6 parts desulfurized gypsum, 7.5 parts inorganic particles, 2.2 parts organic salt additives, 3.8 parts water glass, 8.4 parts reinforcing agent, 0.8 parts water-reducing agent, and 0.9 parts cellulose ether.

[0079] The reinforcing agent is a combination of melamine, calcium formate and hydroxyethylidene diphosphonic acid, with a mass ratio of 6:1:2.

[0080] The above are the only differences between this comparative example and Example 1; all other aspects are the same.

[0081] Comparative Example 6 A fly ash-desulfurized gypsum composite activator, by weight, comprises the following raw materials: 64 parts fly ash, 28.6 parts desulfurized gypsum, 7.5 parts inorganic particles, 2.2 parts organic salt additives, 3.8 parts water glass, 8.4 parts reinforcing agent, 0.8 parts water-reducing agent, and 0.9 parts cellulose ether.

[0082] The reinforcing agent is a combination of melamine, calcium formate and hydroxyethylidene diphosphonic acid, with a mass ratio of 1:5:3.

[0083] The above are the only differences between this comparative example and Example 1; all other aspects are the same.

[0084] Performance testing 1. Slump and slump loss: (1) The products prepared in the examples and comparative examples were added to the concrete at a content of 10 wt%. The concrete mix design was based on C40 grade, with a water-cement ratio of 0.38. The test environment temperature was 23±2℃ and the relative humidity was 52±3%. The test was started within 15 minutes after the concrete mixture was prepared.

[0085] (2) First, wet the inner wall and bottom plate of the slump cone with a damp cloth. Place the slump cone on a horizontal rigid base plate and fix it by stepping on the foot pedal. Fill the cone with the concrete mixture in three layers, each layer being about 1 / 3 of the cone height. Use a tamping rod to tamp each layer 25 times evenly from the edge to the center in a spiral direction. Tamp the bottom layer to the bottom and the top layer to about 10mm below the surface of the bottom layer. After tamping, smooth the cone opening and remove the scattered concrete around the cone. Lift the slump cone vertically and steadily within 5 to 10 seconds. Measure the height difference between the top of the cone and the highest point of the slumped concrete mixture, which is the slump value. Round the result to 5mm. When testing the slump loss over 1 hour, let the mixture stand in a sealed container for 1 hour and then measure the slump again according to the above steps. Calculate the difference between the slump and the initial slump. Record the initial slump and the 1-hour slump loss value in Table 1.

[0086] 2. Compressive strength: (1) Concrete is prepared by the same method as described above. Five cubic specimens of size 150mm×150mm×150mm are used in each group. The specimens are tested as soon as possible after being taken out of the curing room. The specimens are placed in the center of the lower platen of the press, and the upper platen is in uniform contact with the top surface of the specimen.

[0087] (2) When testing, start the press and continuously and uniformly load the specimen at the specified loading rate until the specimen fails. Record the failure load. The compressive strength is calculated by dividing the failure load by the bearing area. The result is the arithmetic mean of the 7-day compressive strength of 5 specimens and recorded in Table 1, accurate to 0.1 MPa.

[0088] 3. Salt-freezing cycle test: (1) Concrete was prepared by the same method as described above. Five prism specimens with dimensions of 100mm×100mm×400mm were used in each group. The freeze-thaw medium was 3% NaCl solution. Each freeze-thaw cycle was completed within 3 hours. During the freezing period, the temperature of the specimen center dropped to -18±2℃ and during the thawing period, it rose to 5±2℃. The number of cycles was set to 300.

[0089] (2) After the cycle is completed, weigh the specimen mass, calculate the mass loss rate, and record the arithmetic mean of the 5 specimens in Table 1.

[0090] 4. Chloride ion penetration resistance test: (1) Concrete was prepared by the same method as described above. Cylindrical specimens with a diameter of 100±1mm and a height of 50±2mm were used, with 5 specimens per group. The specimens were cured for 28 days. The test solutions were 10% NaCl solution (cathode side) and 0.3mol / L NaOH solution (anode side). The test voltage was 30V and the duration was 72h.

[0091] (2) Contact the NaCl solution with the top surface in contact with the NaOH solution; apply the specified voltage and record the initial current and solution temperature; after the specified energizing time is reached, remove the specimen, split it axially, spray silver nitrate solution as a colorimetric agent on the split surface, and measure the chloride ion penetration depth; calculate the chloride ion unsteady-state migration coefficient DRCM according to the standard formula, accurate to 0.01×10⁻⁶. -12 m 2 / s, and the result is the arithmetic mean of 5 times, which is recorded in Table 1.

[0092] Table 1 Performance Test Results Analysis of Test Results: Performance testing comparisons show that Examples 1-3 achieved superior overall performance compared to Comparative Examples 1-6. The compound raw material schemes used in Examples 1-3, through the combined action of alkali, sulfur, aluminum, and organic salts, constructed a complete system in the fly ash-desulfurized gypsum system, from particle destructive processes to hydration product regulation. This guided the formation of a dense structure dominated by gel. Simultaneously, the combination of sodium citrate and sodium gluconate played a dual regulatory role, and the reinforcing agent improved the interfacial affinity between the gel and particles, gently releasing calcium ions to provide a stable calcium source for the hydration reaction. This prevented structural loosening due to localized calcium deficiency and ultimately achieved moderate chelation, inhibiting the explosive formation of ettringite and making the crystallization process smoother. This effectively alleviated volumetric stress concentration and improved the overall stability and erosion resistance of the hardened body under salt-freezing conditions. In contrast, Comparative Examples 1-6, because they employed different technical solutions than those specified in this application, showed a significant decrease in the effectiveness of their respective raw materials in the system, resulting in a decline in the overall performance.

[0093] The above description is the preferred embodiment of this application. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principles described in this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A fly ash-desulfurization gypsum composite activator, characterized in that: The raw material formula, by weight, includes: 50-70 parts fly ash, 20-35 parts desulfurized gypsum, 4-10 parts inorganic particles, 0.8-3 parts organic salt additives, 2-5 parts water glass, 4-10 parts reinforcing agent, 0.5-1.5 parts water reducing agent, and 0.3-1 parts cellulose ether. The fly ash has an activity index of 75-85% after 28 days; the desulfurized gypsum has a specific surface area of ​​280-350 m². 2 / kg; The inorganic particles are a combination of sodium hydroxide, sodium carbonate and aluminum sulfate, with a mass ratio of (1~3):(2~4):(1~3). The organic salt additive is a combination of sodium citrate and sodium gluconate in a mass ratio of (2~3):(0.8~1.5). The reinforcing agent is a combination of melamine, calcium formate and hydroxyethylidene diphosphonic acid, in a mass ratio of (2~3):(4~6):(1~2).

2. The fly ash-desulfurization gypsum composite activator according to claim 1, characterized in that: The fly ash is Grade I fly ash with a fineness of ≤10%.

3. The fly ash-desulfurization gypsum composite activator according to claim 2, characterized in that: The desulfurization gypsum is wet flue gas desulfurization gypsum with a CaSO4·2H2O content of 92-98%.

4. The fly ash-desulfurization gypsum composite activator according to claim 3, characterized in that: The mass ratio of fly ash, desulfurized gypsum, and inorganic particles is (6~7):(2.5~3.5):(0.5~0.9).

5. The fly ash-desulfurization gypsum composite activator according to claim 4, characterized in that: The water glass has a modulus of 1 to 1.5 and a Baume degree of 40 to 60.

6. The fly ash-desulfurization gypsum composite activator according to claim 5, characterized in that: The water-reducing agent is a polycarboxylate water-reducing agent.

7. The fly ash-desulfurization gypsum composite activator according to claim 6, characterized in that: The cellulose ether is at least one of hydroxypropyl methylcellulose, methylcellulose, hydroxyethyl methylcellulose, sodium carboxymethylcellulose, and hydroxyethylcellulose.

8. The fly ash-desulfurization gypsum composite activator according to claim 7, characterized in that: The mass ratio of fly ash, organic salt additives and reinforcing agents is (6~7):(0.15~0.25):(0.5~1).

9. A method for preparing the fly ash-desulfurization gypsum composite activator according to any one of claims 1 to 8, characterized in that: Specifically, the following steps are included: S1: Sieve fly ash, desulfurized gypsum, inorganic particles, and organic salt additives separately, and dry fly ash and desulfurized gypsum to a moisture content ≤1wt%; S2: Add inorganic particles and organic salt additives to a mixer and mix to obtain the first premix; then add reinforcing agent, water-reducing agent, and cellulose ether to the mixer and mix to obtain the second premix; S3: Add fly ash and desulfurized gypsum to a double cone mixer and dry mix to obtain the main material; add the first and second premixes to the main material, and add the remaining raw materials at the same time to mix, ensuring that the material temperature is ≤50℃. After completion, sieve the product, package and seal it to obtain the final product.

10. The application of the fly ash-desulfurized gypsum composite activator according to any one of claims 1 to 8 in high salt-resistant concrete.

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