Fly ash gel system composite early strength agent dry powder as well as preparation method and application thereof
By optimizing spray drying parameters, a composite early-strength agent dry powder for fly ash cementitious systems was prepared, solving the problem of difficult separation of CSH@PCE nanocrystals and realizing its stable application and early strength improvement in cement-based building materials.
Patent Information
- Application Number
- CN202511810383.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-03
- Publication Date
- 2026-02-24
AI Technical Summary
CSH@PCE nanocrystal seed particles are difficult to separate directly from the solution, resulting in high storage and transportation costs. They are also difficult to use in dry powder premixes or commercial production, which affects their promotion in large-scale engineering applications.
By optimizing the drying temperature, spray pressure, and liquid flow rate during the spray drying process, a composite early-strength agent dry powder for fly ash cementitious systems was prepared, forming uniform spherical particles and improving its application performance in cement-based building materials.
It reduces storage and transportation costs, enables stable preservation of CSH@PCE early strength agent, facilitates large-scale engineering applications, and significantly improves the early mechanical and rheological properties of fly ash cementitious materials.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of cement-based building material admixtures, and in particular to a dry powder of a composite early-strength agent for fly ash cementitious systems, its preparation method, and its application. Background Technology
[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.
[0003] To achieve the resource utilization of solid waste, auxiliary cementitious materials such as high-volume fly ash and slag have been widely used in civil engineering. Effectively addressing the issue of low early strength due to reduced cement usage has become a key focus of industry research. CSH@PCE nanocrystalline seed early-strength agent can significantly accelerate the hydration process of cement, thereby greatly improving the early mechanical properties of cementitious materials. However, CSH seed particles, with a particle size ranging from tens to hundreds of nanometers, are stably dispersed in PCE aqueous solution, making it difficult to directly separate solid nanoparticles from the solution, thus facing significant limitations in practical applications. This increases storage and transportation costs and makes direct use in dry powder premixes or commercial production difficult, severely restricting its promotion in large-scale engineering applications.
[0004] Traditional drying methods suffer from drawbacks such as long drying times, inability to operate continuously, and the resulting solids often being in block or flake form, significantly impacting the performance and commercial application of CSH@PCE nanocrystalline seed early-strength agents. Spray drying is a process that uses an atomizing device to disperse liquid raw materials into fine droplets, which then rapidly contact the droplets with a drying medium such as hot air in a drying chamber to obtain solid powder. However, during spray drying, CSH seed crystals may undergo partial structural damage due to dehydration, resulting in reduced activity; simultaneously, nanoparticles are prone to agglomeration, leading to increased particle size and decreased dispersibility, thus affecting their effectiveness in cementitious materials. Summary of the Invention
[0005] In view of this, the present invention provides a dry powder of composite early-strength agent for fly ash cementitious systems, its preparation method, and its application. This invention solves the problem that CSH@PCE solid particles are difficult to separate directly from solution and that their large-scale engineering application is limited. By optimizing the drying temperature, spray pressure, and liquid inlet volume during the drying process, a dry powder of composite early-strength agent for fly ash cementitious systems is prepared, which has significant practical implications for promoting the efficient application of low-carbon cementitious materials.
[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a method for preparing dry powder of composite early strength agent (CSH@PCE) for fly ash cementitious system, comprising the following steps: Polycarboxylate superplasticizer (PCE) was dissolved in water and the pH was adjusted to 11-13 to prepare the reaction base solution; Ca- and Si-source precursor solutions were added to the reaction substrate, stirred and reacted, and purified by dialysis to obtain a composite early strength agent for fly ash cementitious system. The prepared fly ash cementitious system composite early strength agent was spray-dried to obtain fly ash cementitious system composite early strength agent dry powder.
[0007] Furthermore, the operating parameters for spray drying are as follows: liquid inlet rate of 200 mL / h-400 mL / h, inlet temperature of 150 ℃-180 ℃, and spray pressure of 0.1 MPa-0.15 MPa.
[0008] Furthermore, the method also includes: placing the spray-dried early strength agent product in a forced-air drying oven at 50-60℃ to dry, weighing it periodically until the mass remains unchanged.
[0009] Furthermore, the stirring reaction time is 20-24 h; the stirring is magnetic stirring at a speed of 1000-2000 rpm.
[0010] Furthermore, the Ca source is a calcium nitrate solution; the Si source is a sodium metasilicate solution.
[0011] Furthermore, the concentrations of the calcium nitrate solution and the sodium metasilicate solution are 1-2 M.
[0012] Furthermore, the volume ratio of the Ca and Si source precursor solutions to the reaction substrate is 0.1-0.15.
[0013] Furthermore, the pH adjuster is either NaOH or HNO3, which can be selected according to the pH of the solution being tested. The mass fraction of the NaOH solution is 30-50%, and the molar concentration of the HNO3 solution is 1-3 mol / L.
[0014] Furthermore, the concentration of the PCE solution is 3%-6%.
[0015] Furthermore, the preparation method of PCE is as follows: acrylic acid, methyl allyl polyoxyethylene ether-2400 (HPEG2400), initiator and chain transfer agent are added to a container in a preset ratio, and then water is added and stirred until completely dissolved to obtain a mixed solution; The mixed solution was subjected to a polymerization reaction, and solid PCE was obtained by dialysis to remove impurities and freeze-drying.
[0016] Furthermore, the initiator is I2959.
[0017] Furthermore, the chain transfer agent is mercaptoacetic acid.
[0018] Furthermore, the ratio of acrylic acid, HPEG 2400, initiator and chain transfer agent is (100-110): (14-16): (1-1.2): 1.
[0019] Furthermore, the polymerization reaction temperature is 20-25 ℃, and the time is 4-6 h.
[0020] Furthermore, ultraviolet (UV) lamps are used for irradiation during the polymerization process. The power of the UV lamps is 15-20 W and the wavelength is 360-370 nm.
[0021] Secondly, the present invention provides a dry powder of composite early strength agent for fly ash cementitious system prepared by the preparation method described in the first aspect.
[0022] Thirdly, the present invention provides the application of the dry powder of the composite early strength agent of the fly ash cementitious system described in the second aspect in fly ash-based cementitious materials.
[0023] Fourthly, the present invention provides a fly ash-based cementitious material, which, by mass fraction, is composed of the following components: 50-70% fly ash, 30-50% cement clinker, wherein the dry powder of the composite early strength agent of the fly ash cementitious system described in the second aspect accounts for 0.1-0.3% of the total mass of the cementitious components (fly ash and clinker), and the water-cement ratio is 0.5-0.7.
[0024] Furthermore, the composition is 60% fly ash, 40% cement clinker, and the dry powder of the composite early-strength agent in the fly ash cementitious system described in the second aspect accounts for 0.2% of the total mass of the cementitious components (fly ash and clinker), with a water-cement ratio of 0.6.
[0025] When using, first add the dry powder of the fly ash cementitious system composite early strength agent to water and stir evenly. Then add fly ash and cement clinker and stir evenly. Pour the mixture into a mold. The water-cement ratio is the ratio of water to the sum of fly ash and clinker.
[0026] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) The method for preparing dry powder of composite early strength agent for fly ash cementitious system provided by the present invention can convert CSH@PCE nano-dispersion into dry powder early strength agent that is easy to store, transport and use. On the one hand, it reduces storage and transportation costs, and on the other hand, it can be added to the fly ash cementitious system in the form of dry powder premix, which is convenient for large-scale application in actual engineering. After the CSH@PCE early strength agent solution is prepared, it is prone to agglomeration as the storage time increases, and the ultrasonic dispersion performance will also be greatly reduced. CSH@PCE early strength agent dry powder is more stable and easier to store than liquid.
[0027] (2) The drying technology used in this invention is spray drying. The optimal process conditions for spray drying were determined based on the influence of three key process parameters—drying temperature, spray pressure, and liquid feed rate—on the product performance. Under these process conditions, the moisture content and yield of the dry powder are optimal, and the redispersed particle size is smallest. For CSH@PCE early-strength agent, the smaller the particle size, the greater the specific surface area and the more active nucleation sites, resulting in a stronger nucleation effect and coagulation promotion. Therefore, the redispersed particle size determines the product performance. This invention proposes the relationship between the three process parameters—drying temperature, spray pressure, and liquid feed rate—and the moisture content, yield, and redispersed particle size of the dry powder. The yield and performance of the product can be adjusted according to different production requirements, effectively meeting the requirements of actual production.
[0028] (3) The method for preparing CSH@PCE early strength agent dry powder provided by the present invention has the advantages of fast drying speed, adjustable performance of dried product and continuous process flow. The dried product obtained is uniform spherical particles. Compared with other drying methods such as freeze drying and baking, the dried product has a more regular shape and better redispersibility, and has good engineering application performance.
[0029] (4) This invention provides a method for applying the dry powder of composite early strength agent in fly ash cementitious system. The dry powder of CSH@PCE composite early strength agent can significantly improve the rheological properties of fly ash clinker slurry, reduce the setting time of slurry, and has a certain accelerating effect. After adding the early strength agent, the early mechanical properties of fly ash cementitious materials can be significantly improved. Detailed Implementation
[0030] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.
[0031] The technical solution of the present invention will be further described below with reference to specific embodiments.
[0032] Example 1 Polycarboxylate superplasticizer (PCE) was synthesized using the following steps: 22.4 mmol of acrylic acid, 3.2 mmol of HPEG 2400, 0.214 mmol of I2959, and 0.214 mmol of mercaptoacetic acid were added to a container, followed by 50 mL of deionized water and stirring until completely dissolved. The polymerization reaction was initiated at room temperature by irradiation with a 365 nm wavelength, 18 W UV lamp for 5 h. After polymerization, unreacted monomers were removed by dialysis, and the PCE solid was finally obtained by freeze-drying.
[0033] A certain mass of solid PCE was dissolved in deionized water to prepare a 4% PCE solution. The pH was adjusted to 12 using NaOH and HNO3. Precursor solutions of 1.5 M sodium nitrate and calcium silicate were prepared separately, with a volume ratio of 0.12 between the precursor solution and the PCE solution. Both precursor solutions were simultaneously added dropwise to the prepared 4% PCE solution using a peristaltic pump at a rate of 0.67 mL / min. Magnetic stirring (1500 rpm) was maintained throughout the reaction for 20 h, followed by aging for 24 h after the reaction. Finally, impurity ions in the composite liquid early-strength agent were removed by dialysis.
[0034] Drying was performed using a spray dryer. The solid content of the dispersion was adjusted to 5.8% by low-temperature rotary evaporation. The feed rate was set to 200 mL / h, the inlet temperature to 180 ℃, and the spray pressure to 0.15 MPa. CSH@PCE composite early-strength agent dry powder was obtained in a collection bottle. The spray-dried early-strength agent product was placed in a forced-air drying oven at 50 ℃ and weighed periodically until the mass remained constant. The mass of the product before and after drying was measured, and the moisture content was calculated to be 11.27%; the spray-drying yield of the powder early-strength agent was 59.5%.
[0035] 0.1 g of dried powdered admixture was dispersed in 2 mL of water, ultrasonically dispersed for 5 min, and then diluted 20 times. The redispersible particle size distribution of the powdered admixture was tested using a dynamic light scattering instrument. The median particle size D50 was 87 nm, while the median particle size D50 of the solution before drying was 77 nm.
[0036] Example 2 Except for the spray drying conditions, all other conditions are the same as in Example 1.
[0037] The prepared CSH@PCE composite early-strength agent was dried using a spray dryer with a feed rate of 400 mL / h, an inlet temperature of 150 ℃, and a spray pressure of 0.1 MPa. The resulting CSH@PCE composite early-strength agent powder was collected in a collection bottle. The spray-dried early-strength agent product was then placed in a forced-air drying oven at 50 ℃ and weighed periodically until the mass remained constant. The mass of the product before and after drying was measured, and the moisture content was calculated to be 12.83%; the spray-drying yield of the powder early-strength agent was 45.7%. 0.1 g of the dried powder additive was dispersed in 2 mL of water, ultrasonically dispersed for 5 min, and then diluted 20 times. The redispersible particle size distribution of the powder additive was tested using a dynamic light scattering instrument, and the median particle size D50 was measured to be 82 nm.
[0038] Example 3 Except for the spray drying conditions, all other conditions were the same as in Example 1. The prepared CSH@PCE composite early-strength agent was dried using a spray dryer with a feed rate of 200 mL / h, an inlet temperature of 150 ℃, and a spray pressure of 0.1 MPa. CSH@PCE composite early-strength agent dry powder was obtained in a collection bottle. The spray-dried early-strength agent product was placed in a forced-air drying oven at 50 ℃ and weighed periodically until the mass remained constant. The mass of the product before and after drying was measured, and the moisture content was calculated to be 5.52%; the spray-drying yield of the powder early-strength agent was 42.74%. 0.1 g of the dried powder additive was dispersed in 2 mL of water, ultrasonically dispersed for 5 min, and then diluted 20 times. The redispersible particle size distribution of the powder additive was tested using a dynamic light scattering instrument, and the median particle size D50 was measured to be 66 nm.
[0039] Comparative Example 1 Except for the spray drying conditions, all other conditions were the same as in Example 2. The prepared CSH@PCE composite early-strength agent was dried using a spray dryer with a feed rate of 600 mL / h, an inlet temperature of 180 ℃, and a spray pressure of 0.1 MPa. The resulting CSH@PCE composite early-strength agent powder was collected in a collection bottle. The spray-dried early-strength agent product was placed in a forced-air drying oven at 50 ℃ and weighed periodically until the mass remained constant. The mass of the product before and after drying was measured, and the moisture content was calculated to be 12.49%; the spray-drying yield of the powder early-strength agent was 29.51%. 0.1 g of the dried powder additive was dispersed in 2 mL of water, ultrasonically dispersed for 5 min, and then diluted 20 times. The redispersible particle size distribution of the powder additive was tested using a dynamic light scattering instrument, and the median particle size D50 was measured to be 92 nm.
[0040] Comparative Example 2 Except for the spray drying conditions, all other conditions were the same as in Example 3. The prepared CSH@PCE composite early-strength agent was dried using a spray dryer with a feed rate of 400 mL / h, an inlet temperature of 180 ℃, and a spray pressure of 0.05 MPa. The resulting CSH@PCE composite early-strength agent powder was collected in a collection bottle. The spray-dried early-strength agent product was placed in a forced-air drying oven at 50 ℃ and weighed periodically until the mass remained constant. The product mass before and after drying was measured, and the moisture content was calculated to be 12.11%; the spray-drying yield of the powder early-strength agent was 23.62%. 0.1 g of the dried powder additive was dispersed in 2 mL of water, ultrasonically dispersed for 5 min, and then diluted 20 times. The redispersible particle size distribution of the powder additive was tested using a dynamic light scattering instrument, and the median particle size D50 was measured to be 47 nm.
[0041] Comparative Example 3 Except for the spray drying conditions, all other conditions were the same as in Example 2. The prepared CSH@PCE composite early-strength agent was dried using a spray dryer with a feed rate of 400 mL / h, an inlet temperature of 120 ℃, and a spray pressure of 0.01 MPa. CSH@PCE composite early-strength agent dry powder was obtained in a collection bottle. The spray-dried early-strength agent product was placed in a forced-air drying oven at 50 ℃ and weighed periodically until the mass remained constant. The mass of the product before and after drying was measured, and the moisture content was calculated to be 12.3%; the spray drying yield of the powder early-strength agent was 27.85%. 0.1 g of the dried powder additive was dispersed in 2 mL of water, ultrasonically dispersed for 5 min, and then diluted 20 times. The redispersible particle size distribution of the powder additive was tested using a dynamic light scattering instrument, and the measured median particle size D50 was 104 nm.
[0042] Comparative Example 4 Except for the spray drying conditions, all other conditions were the same as in Example 1. The prepared CSH@PCE composite early-strength agent was dried using a spray dryer with a feed rate of 200 mL / h, an inlet temperature of 150 ℃, and a spray pressure of 0.2 MPa. CSH@PCE composite early-strength agent dry powder was obtained in a collection bottle. The spray-dried early-strength agent product was placed in a forced-air drying oven at 50 ℃ and weighed periodically until the mass remained constant. The product mass before and after drying was measured, and the moisture content was calculated to be 4.71%; the spray drying yield of the powder early-strength agent was 58.31%. 0.1 g of the dried powder additive was dispersed in 2 mL of water, ultrasonically dispersed for 5 min, and then diluted 20 times. The redispersible particle size distribution of the powder additive was tested using a dynamic light scattering instrument, and the measured median particle size D50 was 5310 nm.
[0043] A comparison of Examples 1-3 and Comparative Examples 1-4 shows that the main factors affecting moisture content and yield are the inlet velocity, followed by spray pressure and inlet temperature. When the inlet velocity exceeds 400 mL / h, the gas-liquid ratio per unit time at the nozzle is low, the droplets are large, moisture evaporation is insufficient, and the product moisture content is high. When the inlet velocity is too high, the droplet size increases, the drying rate slows down, and some droplets easily adhere to the drying chamber wall or fail to be collected, resulting in a lower yield. To meet the requirements of commercial production and improve production efficiency while ensuring economic benefits, the preferred inlet velocity in this invention is 200 mL / h-400 mL / h. Higher spray pressure is more conducive to forming droplets with uniform particle size, thereby improving powder yield and reducing moisture content. Therefore, to increase output, the spray pressure can be appropriately increased; the preferred spray pressure in this invention is 0.1 MPa-0.15 MPa. Higher inlet temperature results in more complete moisture evaporation, lower moisture content in the obtained early-strength agent dry powder, and higher yield. The preferred inlet temperature in this invention is 150 ℃-180 ℃.
[0044] The main factors affecting the redispersible particle size are spray pressure, followed by inlet velocity, and finally inlet temperature. When the spray pressure exceeds 0.15 MPa, the excessive atomization results in extremely fine droplets and a too-fast drying rate, forming a hard shell or dense agglomerates on the particle surface, making it difficult to disperse in water. At a lower pressure of 0.05 MPa, the atomized droplets are larger, and the particles maintain a loose, redispersible structure during drying. Therefore, the spray pressure in this application should not exceed 0.15 MPa. Lower inlet velocities result in more thorough droplet drying, lower probability of wall adhesion and agglomeration, and easier dissociation of the spray-dried product in water, leading to a smaller redispersible particle size. Increasing the inlet temperature reduces wet agglomeration, resulting in a smaller redispersible particle size of the obtained dry powder. The above parameters can be adjusted to directionally control the product's moisture content, yield, and performance according to the needs of producing early-strength agent dry powder.
[0045] Test case The CSH@PCE composite early-strength agent dry powder prepared in Examples 1-3 or Comparative Examples 1-4 above was used. A baseline cementitious system with 60% fly ash and 40% clinker, and a water-cement ratio of 0.6 was selected. The early-strength agent was added at a solid content of 0.2% of the total mass of the cementitious components (fly ash and clinker). A control group was also included, using only a baseline cementitious system with 60% fly ash and 40% clinker, and a water-cement ratio of 0.6, without the addition of the early-strength agent dry powder. The early-strength agent was first added to water and stirred evenly, followed by the addition of fly ash and clinker. The mixture was stirred using a paste mixer according to the standard procedure in national standard GB / T 1346-2011, and then tested or poured into molds. The rheological properties, setting time, and mechanical strength properties of the cementitious material after adding the CSH@PCE composite early-strength agent dry powder were tested.
[0046] The flow characteristics of the slurry were studied using a rheometer, and rheological curves were obtained under a controlled shear rate mode. The shear rate setting mode was initially 100 s. -1 Pre-shear at a rate of 30 s, remain still for 30 s, and then at a rate of 20 s. -1 50 s -1 100 s -1 150s -1 200 s -1 250 s -1 300 s -1 350 s -1 400 s -1 450 s -1 500 s -1 550 s -1 600 s -1 The shear rate was measured at the beginning, and each shear rate was held for 30 s.
[0047] The setting time was tested according to the method in the national standard GB / T 1346-2011.
[0048] After demolding, the stone specimens were cured in a standard curing chamber until the designed age, and their compressive strength was tested using a direct shear tester in accordance with the national standard GB / T 17671.
[0049]
[0050] The comparison between Examples 1-3, Comparative Examples 1-4, and the control group shows that at 20 s - ¹At low shear rates, the apparent viscosity of all slurries ranged from 0.44 to 0.61 Pa·s, with the blank control group exhibiting the highest viscosity at 0.605 Pa·s. The viscosity of all groups with added powdered admixtures was lower than that of the control group. With increasing shear rate, the viscosity decreased significantly, with the viscosity of all slurries decreasing at a shear rate of 500 s⁻¹. - The apparent viscosity decreased to the range of 0.055–0.095 Pa·s at ¹, while the control group still had the highest viscosity. Examples 1-3 still exhibited low viscosity across the entire shear rate range, demonstrating good flowability; Comparative Example 1 showed higher viscosity at low shear rates and lower viscosity at high shear rates; Comparative Example 2 had the lowest spray pressure and the smallest redispersible particle size, resulting in significantly lower viscosity than other groups across the entire shear rate range; Comparative Examples 3-4 showed higher viscosity across the entire shear rate range than the examples. The above comparisons show that the slurry viscosity significantly decreased after adding CSH@PCE composite early-strength agent dry powder compared to the slurry without the agent, thus improving flowability. This is because, on the one hand, the spherical early-strength agent particles formed by spray drying have a "ball effect" in the system, reducing inter-particle friction; on the other hand, the adsorption and hydrophilicity of PCE, as well as electrostatic repulsion and steric hindrance, reduce inter-particle friction, enhance water film thickness, and improve slurry flowability.
[0051] After incorporating spray-dried CSH@PCE early-strength agent powder, both the initial and final setting times of the slurry were shortened. The initial and final setting times of the blank control group slurry were 656 min and 735 min, respectively; the initial setting times of Examples 1-3 ranged from 566 to 599 min, and the final setting times ranged from 627 to 692 min, showing significant setting-promoting effects; the initial setting times of Comparative Examples 1, 3, and 4 ranged from 631 to 648 min, and the final setting times ranged from 715 to 731 min, exhibiting some setting-promoting effects; the initial setting time of Comparative Example 2 was 562 min, and the final setting time was 610 min, showing significant setting-promoting effects, but the yield under these conditions was low, which is not conducive to commercial application. The principle behind shortening the setting time is that the CSH@PCE early-strength agent powder can be uniformly distributed and rapidly dispersed in the slurry, providing a large number of effective nucleation sites, thereby promoting the early formation of hydration products and significantly shortening the setting time. The differences in performance between different groups of samples indicate that spray drying process parameters have a significant impact on the performance of powder admixtures. Samples with better redispersibility and smaller particle size tend to have a stronger coagulation-promoting effect.
[0052] Comparisons of Examples 1-3, Comparative Examples 1-4, and the control group show that the early strength of all cementitious materials after adding CSH@PCE composite early-strength agent dry powder was improved to varying degrees. Examples 1-3 showed a significant effect: compared to the cementitious materials without the early-strength agent, the 12-hour compressive strength increased by 60%-80%, and the 1-day compressive strength increased by 6.2%-10.3%. Comparative Example 1 showed a 26.7% increase in 12-hour compressive strength and a 3.4% increase in 1-day compressive strength, indicating a certain effect on improving early strength. Comparative Example 2 showed a 66.7% increase in 12-hour compressive strength and an 8.3% increase in 1-day compressive strength, significantly improving early strength. Comparative Examples 3 and 4 showed only minor effects: 6.7% and 13.3% increase in 12-hour compressive strength, and 4.1% and 2.8% increase in 1-day compressive strength, respectively, compared to the cementitious materials without the early-strength agent. The above analysis shows that the CSH@PCE early-strength agent dry powder provided by this invention has a good effect on improving the fluidity of fly ash cementitious slurry, reducing setting time, and improving the early strength of cementitious materials. Powder admixture samples with significant early-strength effects usually have smaller redispersible particle size and higher nucleation activity, which can rapidly induce the formation of hydration products.
[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for preparing a dry powder of a composite early-strength agent for a fly ash cementitious system, characterized in that, Includes the following steps: Polycarboxylate superplasticizer PCE was dissolved in water and the pH was adjusted to 11-13 to prepare the reaction base solution; Ca- and Si-source precursor solutions were added to the reaction substrate, stirred and reacted, and purified by dialysis to obtain a composite early strength agent for fly ash cementitious system. The prepared fly ash cementitious system composite early strength agent was spray-dried to obtain fly ash cementitious system composite early strength agent dry powder. The operating parameters for spray drying are: liquid inlet rate of 200 mL / h-400 mL / h, inlet temperature of 150 ℃-180 ℃, and spray pressure of 0.1 MPa-0.15 MPa.
2. The preparation method according to claim 1, characterized in that, The method further includes: placing the spray-dried early strength agent product in a forced-air drying oven at 50-60 ℃ and weighing it periodically until the mass remains unchanged.
3. The preparation method according to claim 1, characterized in that, The stirring reaction time is 20-24 h; the stirring is magnetic stirring at a speed of 1000-2000 rpm; and / or, the pH adjuster is NaOH or HNO3; and / or, the mass fraction of the NaOH solution is 30-50%, and the molar concentration of the HNO3 solution is 1-3 mol / L.
4. The preparation method according to claim 1, characterized in that, The Ca source is a calcium nitrate solution; the Si source is a sodium metasilicate solution; and / or, the concentrations of the calcium nitrate solution and the sodium metasilicate solution are 1-2 M; and / or, the volume ratio of the Ca and Si source precursor solutions to the reaction substrate is 0.1-0.
15.
5. The preparation method according to claim 1, characterized in that, The preparation method of PCE is as follows: add acrylic acid, methyl allyl polyoxyethylene ether-2400 (HPEG 2400), initiator and chain transfer agent into a container according to a preset ratio, then add water and stir until completely dissolved to obtain a mixed solution; The mixed solution was subjected to a polymerization reaction, and solid PCE was obtained by dialysis to remove impurities and freeze-drying.
6. The preparation method according to claim 5, characterized in that, The initiator is I2959; and / or, the chain transfer agent is mercaptoacetic acid; and / or, the ratio of acrylic acid, HPEG 2400, initiator and chain transfer agent is (100-110):(14-16):(1-1.2):1; and / or, the polymerization reaction temperature is 20-25 ℃ and the time is 4-6 h; and / or, the polymerization reaction is irradiated with ultraviolet lamps with a power of 15-20 W and a wavelength of 360-370 nm.
7. The preparation method according to claim 1, characterized in that, The concentration of the PCE solution is 3%-6%.
8. The dry powder of composite early strength agent for fly ash cementitious system prepared by the preparation method according to any one of claims 1 to 7.
9. The application of the composite early-strength agent dry powder of the fly ash cementitious system as described in claim 8 in fly ash-based cementitious materials.
10. A fly ash-based cementitious material, characterized in that, The product is composed of the following components by mass fraction: 50-70% fly ash, 30-50% cement clinker, and the dry powder of the composite early strength agent of the fly ash cementitious system described in claim 8 accounts for 0.1-0.3% of the total mass of fly ash and cement clinker, with a water-cement ratio of 0.5-0.7.