A cementing material based on fly ash and desulfurization gypsum, a preparation method and application thereof

Abstract

This invention belongs to the field of industrial solid waste resource utilization technology, specifically relating to a cementitious material prepared from fly ash and desulfurized gypsum, its preparation method, and its application. The raw materials for preparing this cementitious material, by weight, include 55-70 parts fly ash, 15-25 parts desulfurized gypsum, 8-15 parts sodium salt-modified calcined phosphogypsum, 5-12 parts cement, and 0.2-1.0 parts sodium thiocyanate. The sodium salt-modified calcined phosphogypsum is obtained by co-calcining phosphogypsum and sodium sulfate at 300-600℃. This invention achieves the preparation of a low-carbon cementitious material with a total solid waste content of over 78% under conditions where the cement content is less than 12%. It possesses good mechanical and construction properties and can be used in building materials such as concrete, mortar, road base courses, and slope protection.

Description

Technical Field

[0001] This invention belongs to the field of industrial solid waste resource utilization technology, specifically relating to a cementitious material prepared based on fly ash and desulfurized gypsum, its preparation method, and its application. Background Technology

[0002] Fly ash and desulfurization gypsum are the main solid wastes generated by coal-fired power plants. The large-scale stockpiling of industrial solid waste not only occupies valuable land resources, but also brings environmental risks such as soil salinization, groundwater pollution and heavy metal leakage. How to achieve large-scale and high-value utilization of these solid wastes has become an urgent problem to be solved.

[0003] Using fly ash and desulfurized gypsum to prepare cementitious materials is an important approach that balances environmental protection and economic benefits, as it can both dispose of solid waste, reduce cement clinker usage, and lower carbon emissions during building material production. Researchers have conducted extensive work on this topic. For example, patent CN121824077A discloses a solid waste-based cementitious material with high solid waste content and low alkali activation. It uses 30-55 parts of recycled construction waste powder, 20-40 parts of fly ash, 10-25 parts of steel slag powder, and 5-15 parts of desulfurized gypsum as raw materials, combined with a composite alkali activator, achieving a 28-day compressive strength of approximately 50 MPa. Patent CN120887698A discloses a desulfurized gypsum-based cementitious material, with 70-80 parts of desulfurized gypsum as the main component, compounded with 20-35 parts of steel slag, cement, and fly ash. However, the aforementioned technical solutions still rely on high amounts of cement clinker or alkaline activators to ensure the strength of cementitious materials. The actual effective utilization rate of solid waste has not achieved a fundamental breakthrough. Furthermore, the extensive use of chemical activators not only increases material costs but also raises concerns about alkali-aggregate reaction risks and long-term durability. Meanwhile, existing fly ash-desulfurized gypsum-based cementitious materials generally face the technical bottleneck of slow early strength development. The pozzolanic activity of fly ash requires an alkaline environment to be fully activated, and while sulfates in desulfurized gypsum can play a certain activating role, a single activation method often has unintended consequences—either insufficient early strength or weak later strength growth. In addition, most existing technologies are limited to simple compounding of the ternary system of cement, fly ash, and desulfurized gypsum, lacking methods for deep activation of the aluminosilicate mineral components in fly ash, and failing to fully explore the multiple functions of sulfate ions in desulfurized gypsum within the cementitious system.

[0004] Therefore, there is an urgent need for a low-carbon cementitious material and its preparation method that can achieve complementary advantages by utilizing the chemical characteristics of fly ash and desulfurized gypsum without relying on high-volume cement and strong alkaline activators, and effectively release the active components in fly ash through mild physicochemical means to participate in the cementation reaction, thereby obtaining a material with high solid waste content, excellent mechanical properties and good long-term durability. Summary of the Invention

[0005] The purpose of this invention is to provide a cementitious material based on fly ash and desulfurized gypsum, its preparation method and application, aiming to overcome the technical defects of existing fly ash-desulfurized gypsum-based cementitious materials, such as high dosage of cement clinker or alkaline activator, low actual utilization rate of solid waste and slow early strength development, and to provide a low-carbon cementitious material solution that can still obtain excellent mechanical properties under the condition of significantly reducing cement usage.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of this invention provides a cementitious material based on fly ash and desulfurized gypsum, wherein the raw materials for preparation include, by weight: 55-70 parts fly ash, 15-25 parts desulfurized gypsum, 8-15 parts sodium salt modified calcined phosphogypsum, 5-12 parts cement and 0.2-1.0 parts sodium thiocyanate. The sodium salt modified calcined phosphogypsum is a composite product obtained by calcining phosphogypsum and sodium sulfate together.

[0007] Furthermore, the preparation method of the sodium salt modified calcined phosphogypsum includes the following steps: (a) Phosphogypsum and sodium sulfate are mixed in a certain proportion to obtain a mixture; (b) Calcine the mixture at 300℃~600℃ for 1~3 hours; (c) Cool the calcined product and grind it to an average particle size of 15-35 μm to obtain sodium salt modified calcined phosphogypsum.

[0008] Furthermore, the weight ratio of the phosphogypsum to sodium sulfate is 8:1 to 12:1.

[0009] Phosphogypsum is an industrial byproduct discharged during the wet-process phosphoric acid production. The fluoride ions and phosphate ions it contains are generally considered harmful impurities in existing technologies, not only delaying the hydration process of cement but also adversely affecting the later strength of the material. Therefore, most technical solutions remove it through methods such as water washing, lime neutralization, or high-temperature decomposition. However, this invention discovers that when phosphogypsum is mixed with sodium sulfate in a certain proportion and calcined at 300℃ to 600℃, sodium sulfate undergoes a crystal transformation at this temperature, changing its crystal lattice structure and enabling solid-phase diffusion with the surface of phosphogypsum particles to form a uniform sodium sulfate coating layer adhering to the particle surface. During calcination, some of the soluble fluoride in the phosphogypsum is converted into insoluble calcium fluoride, reducing the soluble fluoride content and mitigating the retarding effect on cement hydration. The sodium sulfate coating layer gradually releases sulfate and sodium ions into the cementitious system, working together with desulfurized gypsum to maintain a continuous supply of sulfate concentration within the system.

[0010] The second aspect of this invention provides a method for preparing the above-mentioned cementitious material based on fly ash and desulfurized gypsum, comprising the following steps: (1) Mix fly ash and desulfurized gypsum according to the formula ratio and grind them together to obtain grinding material; (2) Mix the grinding material with sodium salt modified calcined phosphogypsum and cement at a speed of 20-30 r / min for 2-4 minutes to obtain a mixture. Dissolve sodium thiocyanate in water to prepare a sodium thiocyanate solution. Spray the solution into the mixture by atomization spraying and continue mixing at a speed of 60-80 r / min for 3-5 minutes. (3) Place the mixture obtained in step (2) in a sealed container for aging; (4) Dry and grind the aged mixture to obtain the cementitious material prepared based on fly ash and desulfurized gypsum.

[0011] Furthermore, the specific surface area of ​​the abrasive material described in step (1) reaches 450–550 m². 2 / kg.

[0012] Furthermore, the mass concentration of the sodium thiocyanate solution in step (2) is 5% to 15%.

[0013] Furthermore, the aging temperature in step (3) is 40℃~60℃, the time is 12~24 hours, and the relative humidity inside the container is maintained at no less than 85% during the aging period.

[0014] Furthermore, the specific surface area of ​​the powder obtained after grinding in step (4) reaches 500-600 m². 2 / kg.

[0015] This invention first co-mills fly ash and desulfurized gypsum, allowing the sulfate ions in the desulfurized gypsum to act on the surface of the fly ash particles under mechanical force, inducing preliminary mechanochemical erosion of the fly ash vitreous structure. Subsequently, the fly ash-desulfurized gypsum abrasive is dry-mixed with sodium-modified calcined phosphogypsum and cement. Then, sodium thiocyanate is added via atomized spraying, causing the thiocyanate ions to uniformly adhere to the surface of the powder particles. During subsequent closed aging, these thiocyanate ions migrate along the particle interface and accumulate at active sites on the fly ash surface, coordinating with trace aluminum components dissolved from the fly ash surface during aging, thus weakening the aluminum-oxygen structure of the fly ash particle surface. After aging, a second milling process is performed, allowing the active components in the fly ash to be fully released and participate in the hydration reaction under relatively low cement dosage conditions.

[0016] The third aspect of this invention provides the application of the above-mentioned cementitious material prepared based on fly ash and desulfurized gypsum in the preparation of building materials.

[0017] Furthermore, the building material is at least one of concrete, mortar, road base material, or slope protection material.

[0018] The cementitious material of this invention can be used in the preparation of concrete, mortar, or road base materials, significantly reducing cement usage and costs. Simultaneously, fly ash, desulfurized gypsum, and phosphogypsum, previously industrial wastes, are effectively utilized, reducing land occupation for storage and lowering carbon emissions from cement production. In practical applications, due to the early-strength effect of sodium thiocyanate and the continuous activation of fly ash activity by sodium-modified calcined phosphogypsum, the material's early strength is comparable to ordinary cement, and its later strength also shows stable growth. It can meet engineering requirements in scenarios with high durability requirements, such as road bases or slope protection.

[0019] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: This invention overcomes the limitations of existing fly ash-desulfurized gypsum-based cementitious materials that overly rely on cement or strong alkaline activators. By co-calcining phosphogypsum and sodium sulfate, harmful fluorine components are effectively converted, reducing their interference with hydration while retaining subsequent activation functions. Simultaneously, sodium sulfate is uniformly distributed on the particle surface as a coating layer, making the release of activating components more stable and sustained. Although the amount of sodium thiocyanate introduced in the formulation is extremely small, its combination with sodium salt-modified calcined phosphogypsum significantly improves the early hydration rate of the system, compensating for the low early strength of systems with high fly ash content. In terms of preparation method, fly ash and desulfurized gypsum are first co-milled to pre-act with sulfate on the fly ash surface. Sodium thiocyanate is added via atomized spraying and aged to ensure uniform dispersion and enrichment on the powder particle surface. A second milling process further homogenizes the components. This step-by-step activation method allows the activity of fly ash to be fully utilized under low cement content conditions. The total amount of phosphogypsum, desulfurized gypsum and fly ash in the entire scheme reaches more than 78%. The raw materials are widely available and inexpensive. The preparation process does not involve complex equipment or harsh conditions, making it easy to promote industrialization. It provides a practical and feasible technical path for the large-scale disposal of bulk industrial solid waste in the building materials field. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] The fly ash used in this invention is Class F low-calcium fly ash, with a total mass fraction of 82.5% for SiO2, Al2O3, and Fe2O3. Desulfurized gypsum is a byproduct of the wet desulfurization process in coal-fired power plants, with a calcium sulfate dihydrate mass fraction of 88.5%. Phosphogypsum is a byproduct of the wet-process phosphoric acid production process. It contains 85.2% calcium sulfate dihydrate, 1.2% water-soluble P2O5, and 0.3% water-soluble fluoride ions.

[0022] Example 1

[0023] This embodiment provides a cementitious material based on fly ash and desulfurized gypsum, the preparation method of which includes the following steps: (1) Take 620g of fly ash and 200g of desulfurized gypsum, place them in a planetary ball mill, and grind them together at a speed of 300r / min for 45 minutes to obtain the grinding material. The specific surface area of ​​the material was tested to be 502m². 2 / kg.

[0024] (2) Add the above-mentioned powdered material, 100g of sodium salt modified calcined phosphogypsum, and 80g of cement to a mixer and mix at a speed of 25r / min for 3 minutes to obtain a mixture. Dissolve 5g of sodium thiocyanate in 45g of deionized water to prepare a sodium thiocyanate solution with a mass concentration of 10%. Use an atomizing spray device to atomize the solution at a pressure of 0.5MPa and spray it into the above-mentioned mixture. After spraying, increase the speed of the mixer to 70r / min and continue mixing for 4 minutes.

[0025] (3) Transfer the obtained mixture into a sealed plastic bag, remove the air from the bag, seal it tightly, and place it in a 50℃ constant temperature curing chamber for 18 hours. During the curing period, the relative humidity inside the bag should be maintained at 88% to 92%.

[0026] (4) Take out the aged mixture, spread it into a thin layer and place it in a forced-air drying oven. Dry it at 70°C until the moisture content is less than 2%. Then grind it with a vibratory mill for 10 minutes. The specific surface area was tested to be 546 m². 2 / kg, thus obtaining the cementitious material prepared based on fly ash and desulfurized gypsum.

[0027] The preparation method of the sodium salt modified calcined phosphogypsum is as follows: (a) Dry the phosphogypsum in an oven at 105°C until constant weight. Take 1000g of the dried phosphogypsum and mix it with 100g of sodium sulfate. Place the mixture in a planetary ball mill and mix at a speed of 200r / min for 15 minutes to obtain the mixture.

[0028] (b) Place the mixture in a muffle furnace and heat it to 450°C at a rate of 10°C / min, and calcine it at 450°C for 2 hours.

[0029] (c) After naturally cooling to room temperature, grind the powder with a vibratory mill until the average particle size is 25 μm to obtain sodium salt modified calcined phosphogypsum.

[0030] Example 2

[0031] This embodiment provides a cementitious material based on fly ash and desulfurized gypsum, the preparation method of which includes the following steps: (1) Take 580g of fly ash and 220g of desulfurized gypsum, place them in a planetary ball mill, and grind them together at a speed of 300r / min for 50 minutes to obtain the grinding material. The specific surface area of ​​the grinding material was tested to be 478m². 2 / kg.

[0032] (2) Add the above-mentioned powdered material, 120g of sodium salt modified calcined phosphogypsum, and 70g of cement to a mixer and mix at a speed of 22r / min for 2.5 minutes to obtain a mixture. Dissolve 6g of sodium thiocyanate in 44g of deionized water to prepare a sodium thiocyanate solution with a mass concentration of 12%. Use an atomizing spray device to atomize the solution at a pressure of 0.5MPa and spray it into the above-mentioned mixture. After spraying, increase the speed of the mixer to 75r / min and continue mixing for 3.5 minutes.

[0033] (3) Transfer the obtained mixture into a sealed plastic bag, remove the air from the bag, seal it tightly, and place it in a 45℃ constant temperature curing chamber for 20 hours. During the curing period, the relative humidity inside the bag should be maintained at 90% to 93%.

[0034] (4) Take out the aged mixture, spread it into a thin layer and place it in a forced-air drying oven. Dry it at 70°C until the moisture content is less than 2%. Then grind it with a vibratory mill for 8 minutes. The specific surface area was tested to be 522 m². 2 / kg, thus obtaining the cementitious material prepared based on fly ash and desulfurized gypsum.

[0035] The preparation method of the sodium salt modified calcined phosphogypsum is as follows: (a) Place the phosphogypsum in an oven at 105°C and dry it to constant weight. Take 1100g of the dried phosphogypsum and mix it with 100g of sodium sulfate. Place the mixture in a planetary ball mill and mix it at a speed of 200r / min for 15 minutes to obtain the mixture.

[0036] (b) Place the mixture in a muffle furnace and heat it to 380°C at a rate of 10°C / min, and calcine it at 380°C for 2.5 hours.

[0037] (c) After naturally cooling to room temperature, grind the powder with a vibratory mill until the average particle size is 20 μm to obtain sodium salt modified calcined phosphogypsum.

[0038] Example 3

[0039] This embodiment provides a cementitious material based on fly ash and desulfurized gypsum, the preparation method of which includes the following steps: (1) Take 660g of fly ash and 160g of desulfurized gypsum, place them in a planetary ball mill, and grind them together at a speed of 300r / min for 40 minutes to obtain the grinding material. The specific surface area of ​​the grinding material was tested to be 492m². 2 / kg.

[0040] (2) Add the above-mentioned powdered material, 90g of sodium salt modified calcined phosphogypsum, and 100g of cement to a mixer and mix at a speed of 28r / min for 3.5 minutes to obtain a mixture. Dissolve 4g of sodium thiocyanate in 46g of deionized water to prepare a sodium thiocyanate solution with a mass concentration of 8%. Use an atomizing spray device to atomize the solution at a pressure of 0.5MPa and spray it into the above-mentioned mixture. After spraying, increase the speed of the mixer to 65r / min and continue mixing for 4.5 minutes.

[0041] (3) Transfer the obtained mixture into a sealed plastic bag, remove the air from the bag, seal it tightly, and place it in a 55℃ constant temperature curing chamber for 15 hours. During the curing period, the relative humidity inside the bag should be maintained at 85% to 88%.

[0042] (4) Take out the aged mixture, spread it into a thin layer and place it in a forced-air drying oven. Dry it at 70°C until the moisture content is less than 2%. Then grind it with a vibratory mill for 12 minutes. The specific surface area was tested to be 551 m². 2 / kg, thus obtaining the cementitious material prepared based on fly ash and desulfurized gypsum.

[0043] The preparation method of the sodium salt modified calcined phosphogypsum is as follows: (a) Dry the phosphogypsum in an oven at 105°C until constant weight. Take 900g of the dried phosphogypsum and mix it with 100g of sodium sulfate. Place the mixture in a planetary ball mill and mix at 200r / min for 15 minutes to obtain the mixture.

[0044] (b) Place the mixture in a muffle furnace and heat it to 520°C at a rate of 10°C / min, and calcine it at 520°C for 1.5 hours.

[0045] (c) After naturally cooling to room temperature, grind the powder with a vibratory mill until the average particle size is 30 μm to obtain sodium salt modified calcined phosphogypsum.

[0046] Comparative Example 1 The difference between this comparative example and Example 1 is that sodium salt modified calcined phosphogypsum is not prepared in advance, but unmodified phosphogypsum and sodium sulfate are directly added to the formula as raw materials.

[0047] The preparation method of the cementitious material in this comparative example includes the following steps: (1) Take 620g of fly ash and 200g of desulfurized gypsum, put them in a planetary ball mill, and grind them together at a speed of 300r / min for 45 minutes to obtain the grinding material.

[0048] (2) Add the above-mentioned powdered material, 100g of phosphogypsum, 10g of sodium sulfate, and 80g of cement to a mixer and mix at a speed of 25r / min for 3 minutes to obtain a mixture. Dissolve 5g of sodium thiocyanate in 45g of deionized water to prepare a sodium thiocyanate solution with a mass concentration of 10%. Use an atomizing spray device to atomize the solution at a pressure of 0.5MPa and spray it into the above-mentioned mixture. After spraying, increase the speed of the mixer to 70r / min and continue mixing for 4 minutes.

[0049] (3) Transfer the obtained mixture into a sealed plastic bag, remove the air from the bag, seal it tightly, and place it in a 50℃ constant temperature curing chamber for 18 hours. During the curing period, the relative humidity inside the bag should be maintained at 88% to 92%.

[0050] (4) Take out the aged mixture, spread it into a thin layer and place it in a forced-air drying oven. Dry it at 70°C until the moisture content is less than 2%. Then grind it with a vibratory mill for 10 minutes. The specific surface area was tested to be 518 m². 2 / kg yields the cementitious material.

[0051] Comparative Example 2 The difference between this comparative example and Example 1 is that sodium thiocyanate is not added in step (2).

[0052] Comparative Example 3 The difference between this comparative example and Example 1 is that sodium thiocyanate in step (2) is replaced with an equal amount of triethanolamine.

[0053] Comparative Example 4 This comparative example provides a cementitious material based on fly ash and desulfurized gypsum, the preparation method of which includes the following steps: (1) Take 620g of fly ash, 200g of desulfurized gypsum, 100g of sodium salt modified calcined phosphogypsum and 80g of cement, put them in a planetary ball mill and grind them together at a speed of 300r / min for 45 minutes to obtain the grinding material.

[0054] (2) Add the above-mentioned powder to the mixer and mix at a speed of 25 r / min for 3 minutes to obtain a mixture. Dissolve 5 g of sodium thiocyanate in 45 g of deionized water to prepare a sodium thiocyanate solution with a mass concentration of 10%. Use an atomizing spray device to atomize the solution at a pressure of 0.5 MPa and spray it into the above-mentioned mixture. After spraying, increase the speed of the mixer to 70 r / min and continue mixing for 4 minutes.

[0055] (3) Transfer the obtained mixture into a sealed plastic bag, remove the air from the bag, seal it tightly, and place it in a 50℃ constant temperature curing chamber for 18 hours. During the curing period, the relative humidity inside the bag should be maintained at 88% to 92%.

[0056] (4) Take out the aged mixture, spread it into a thin layer and place it in a forced-air drying oven. Dry it at 70°C until the moisture content is less than 2%. Then grind it with a vibratory mill for 10 minutes. The specific surface area was tested to be 563 m². 2 / kg yields the cementitious material.

[0057] Comparative Example 5 The difference between this comparative example and Example 1 is that the sodium salt modified calcined phosphogypsum is replaced with an equal amount of quartz sand.

[0058] Performance testing 1. Flexural strength and compressive strength tests The test was performed in accordance with GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)". The cementitious material of this invention was mixed with ISO standard sand at a mass ratio of 1:3, with a fixed water-cement ratio of 0.5. The mixture was thoroughly mixed using a planetary mortar mixer, and then molded into 40mm × 40mm × 160mm prism specimens using a vibratory compaction table. After 24 hours of molding, the specimens were demolded and cured in water at 20±1℃ until the specified age. The flexural strength and compressive strength of the specimens were tested at 3d, 7d, and 28d.

[0059] 2. Setting time test The setting time test was performed according to GB / T 1346-2011 "Test Methods for Standard Consistency Water Requirement, Setting Time and Soundness of Cement". First, the water required for the cementitious material to reach standard consistency was determined using the standard method. Standard consistency neat cement paste was prepared using this water and placed in a circular mold. The moment when all the cement was added to the water was recorded as the starting time. The mold containing the neat cement paste was placed in a humidity curing chamber at a temperature of 20℃±1℃ and a relative humidity of not less than 90% for curing. The first measurement was performed 30 minutes after water addition. The mold was removed and placed under the Vicat apparatus needle. After the needle made contact with the surface of the neat cement paste, it was suddenly released, allowing the paste to sink vertically and freely into the paste. The reading when the needle stopped sinking was observed. Subsequent measurements were repeated at regular intervals. Near the initial setting point, measurements were taken every 5 minutes. The time when the needle sank to 4mm±1mm from the bottom plate was the initial setting time. After the initial setting time was measured, the mold was rotated 180° so that the bottom surface was facing upwards for continued curing. Measurements were taken every 15 minutes as the final setting time approached, with the final setting needle replaced for each measurement. The final setting time was defined as the time when the final setting needle sank to a depth of no more than 0.5 mm into the neat cement paste and the annular attachment left no trace on the paste surface. The entire test environment was controlled at a temperature of 20℃±2℃ and a relative humidity of no less than 50%.

[0060] 3. Mortar Flowability Test The test was conducted in accordance with GB / T 2419-2005, "Determination of Flowability of Cement Mortar". The cementitious material and ISO standard sand were mixed at a mass ratio of 1:3, with a fixed water-cement ratio of 0.5, to obtain a uniform mortar. The mortar was then placed in two layers into a truncated conical mold fitted with a test bench. After each layer was tamped and smoothed, the mold was lifted vertically, and the test bench was immediately started to complete 25 jumps within 25s ± 1s. After the jumps, the two mutually perpendicular diffusion diameters on the bottom surface of the mortar were measured with calipers, and the arithmetic mean was taken as the flowability of that group of mortars. The total time for the entire test, from adding water and mixing to the completion of the measurement, was controlled within 6 minutes.

[0061] The test results are shown in Table 1.

[0062] Table 1 Performance Test Results

[0063] The performance test results above show that the cementitious materials of Examples 1-3 of this invention exhibit good strength development at all ages, moderate setting time, and fluidity that meets construction requirements under conditions of significantly reduced cement content. In Comparative Example 1, because the phosphogypsum was not calcined and modified, the soluble fluorine in it significantly retarded cement hydration, resulting in a significantly prolonged setting time, inhibited hydration reaction, and a significant decrease in strength at all ages. Comparative Example 2 lacked the early strength and coordination activation effects of sodium thiocyanate, resulting in a significant decrease in early strength and a significantly slower setting time, indicating that sodium thiocyanate is indispensable for promoting early hydration of the system. In Comparative Example 3, after replacing sodium thiocyanate with triethanolamine, the performance was inferior to that of Example 1, indicating that triethanolamine cannot replace the role of sodium thiocyanate in the system of this invention. In Comparative Example 4, after grinding all raw materials in one step, the strength was lower than that of Example 1, indicating that the pre-activation step of co-grinding fly ash and desulfurized gypsum was indeed effective. In Comparative Example 5, after replacing sodium salt-modified calcined phosphogypsum with inert quartz sand, the strength at all ages was significantly reduced and the setting was the slowest, indicating that the activation effect of sodium salt-modified calcined phosphogypsum is irreplaceable.

[0064] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A cementitious material prepared based on fly ash and desulfurized gypsum, characterized in that, The raw materials for its preparation include, by weight: 55-70 parts fly ash, 15-25 parts desulfurized gypsum, 8-15 parts sodium salt modified calcined phosphogypsum, 5-12 parts cement and 0.2-1.0 parts sodium thiocyanate; The sodium salt modified calcined phosphogypsum is a composite product obtained by calcining phosphogypsum and sodium sulfate together.

2. The cementitious material prepared based on fly ash and desulfurized gypsum according to claim 1, characterized in that, The preparation method of the sodium salt modified calcined phosphogypsum includes the following steps: (a) Phosphogypsum and sodium sulfate are mixed in a certain proportion to obtain a mixture; (b) Calcine the mixture at 300℃~600℃ for 1~3 hours; (c) Cool the calcined product and grind it to an average particle size of 15-35 μm to obtain sodium salt modified calcined phosphogypsum.

3. The cementitious material prepared based on fly ash and desulfurized gypsum according to claim 1, characterized in that, The weight ratio of phosphogypsum to sodium sulfate is 8:1 to 12:

1.

4. The method for preparing the cementitious material based on fly ash and desulfurized gypsum according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Mix fly ash and desulfurized gypsum according to the formula ratio and grind them together to obtain grinding material; (2) Mix the grinding material with sodium salt modified calcined phosphogypsum and cement at a speed of 20-30 r / min for 2-4 minutes to obtain a mixture. Dissolve sodium thiocyanate in water to prepare a sodium thiocyanate solution. Spray the solution into the mixture by atomization spraying and continue mixing at a speed of 60-80 r / min for 3-5 minutes. (3) Place the mixture obtained in step (2) in a sealed container for aging; (4) Dry and grind the aged mixture to obtain the cementitious material prepared based on fly ash and desulfurized gypsum.

5. The preparation method according to claim 4, characterized in that, The specific surface area of ​​the grinding material in step (1) reaches 450-550 m². 2 / kg.

6. The preparation method according to claim 4, characterized in that, The mass concentration of the sodium thiocyanate solution in step (2) is 5% to 15%.

7. The preparation method according to claim 4, characterized in that, The aging temperature in step (3) is 40℃~60℃, and the time is 12~24 hours. During the aging period, the relative humidity inside the container is maintained at no less than 85%.

8. The preparation method according to claim 4, characterized in that, The specific surface area of ​​the powder obtained after grinding in step (4) reaches 500-600 m². 2 / kg.

9. The application of the cementitious material according to any one of claims 1-3 or the cementitious material prepared by the method according to any one of claims 4-8 in the preparation of building materials.

10. The application according to claim 9, characterized in that, The building material is at least one of concrete, mortar, road base material, or slope protection material.

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