Fly ash low-carbon cement as well as preparation method and application thereof

Abstract

The invention discloses fly ash low-carbon cement as well as a preparation method and application thereof. According to the invention, a ternary high-molecular copolymer (poly (acrylic acid-2-acrylamide-2-methylpropanesulfonic acid-N-hydroxymethyl acrylamide)) is combined with organic weak acid (citric acid) to synergistically excite the activity of fly ash, so that efficient replacement of cement clinker is realized; the fly ash low-carbon cement is composed of the following components in percentage by mass: 25%-60% of cement clinker, 30%-65% of fly ash, 0.3%-1.2% of ternary high-molecular copolymer, 0.1%-0.5% of organic weak acid and 2%-5% of gypsum, and the water cement ratio is 0.45-0.55. According to the fly ash low-carbon cement and the preparation method thereof, 32.5-grade cement can be prepared by using 25% of clinker at the minimum, 42.5-grade cement can be prepared by using 45% of clinker, carbon emission and production cost in the cement production process are remarkably reduced, and the production cost is reduced. Meanwhile, the mechanical property and durability of cement are improved.

Description

Technical Field

[0001] This invention belongs to the field of cement technology, specifically relating to a fly ash low-carbon cement, its preparation method, and its application. Background Technology

[0002] Cement is an indispensable basic material in the construction industry, but its production process consumes large amounts of resources such as limestone and coal, and the production of one ton of cement clinker emits approximately 0.85 tons of carbon dioxide, making it one of the world's major sources of carbon emissions. The low-carbon transformation of the cement industry has become an inevitable trend, and reducing the use of cement clinker and improving the resource utilization rate of industrial solid waste are key paths to achieving low-carbon development in the cement industry.

[0003] Fly ash is an industrial solid waste generated during coal-fired power generation in thermal power plants, with huge annual emissions. Large-scale accumulation not only occupies land resources but also causes air and water pollution. The main chemical components of fly ash are SiO2, Al2O3, and Fe2O3, which possess certain potential activity. It can be used as a cement admixture to replace part of the cement clinker, achieving both solid waste resource utilization and reducing carbon emissions and production costs in cement production. However, fly ash has low activity and a dense glassy structure. Under normal use, the clinker replacement rate is usually no more than 20%. Blindly increasing the replacement rate will lead to a significant decrease in the mechanical properties and durability of cement, failing to meet engineering requirements.

[0004] To improve the activity of fly ash, existing technologies mainly employ physical activation, chemical activation, or a combination of both. Physical activation (such as mechanical grinding) can reduce fly ash particle size and increase specific surface area, but it consumes a lot of energy and has limited activation effect. Chemical activation is currently the most widely used method, with commonly used activators including alkaline activators (such as sodium hydroxide and water glass) and acidic activators (such as weak organic acids). While alkaline activators can effectively activate fly ash, they suffer from strong corrosiveness, high cost, and a tendency to lead to poor cement volume stability. Weak organic acid activators (such as citric acid and tartaric acid) have low corrosiveness and moderate cost, but their activation effect is limited when used alone, making it difficult to achieve high-proportion clinker replacement.

[0005] In recent years, the application of polymers in cement-based materials has gradually attracted attention. Some studies have used binary polymer copolymers (such as polyacrylic acid-acrylamide copolymer) to assist in activating fly ash. However, the functional groups of binary copolymers are limited, resulting in poor binding ability and synergistic activation effect with fly ash, making it impossible to achieve a clinker replacement rate of over 25% to prepare qualified 32.5 grade cement. For example, Chinese invention patent application CN112174553A discloses a composite activated low-calcium fly ash cement and its preparation method, which uses an alkaline activator and mineral admixtures to activate fly ash. However, this method suffers from problems such as strong corrosiveness of the alkaline activator, low clinker replacement rate (not exceeding 30%), and poor cement performance stability. Furthermore, this patent does not use polymer copolymers as activators, failing to achieve the requirements of high clinker replacement and low carbonation. Summary of the Invention

[0006] The purpose of this invention is to overcome the technical defects of existing technologies, such as low fly ash activity, limited clinker substitution rate, high carbon emissions, and poor activator effect, and to provide a fly ash low-carbon cement, its preparation method, and its application.

[0007] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution: In a first aspect, the present invention provides a fly ash low-carbon cement, comprising the following components by mass percentage: 25%-60% cement clinker, 30%-65% fly ash, 0.3%-1.2% ternary polymer copolymer, 0.1%-0.5% organic weak acid, and 2%-5% gypsum; wherein the ternary polymer copolymer is poly(acrylic acid-2-acrylamide-2-methylpropanesulfonic acid-N-hydroxymethylacrylamide), with a monomer molar ratio of acrylic acid:2-acrylamide-2-methylpropanesulfonic acid:N-hydroxymethylacrylamide = 3:1:1, and a number-average molecular weight of 1800-2200; wherein the organic weak acid is citric acid; and wherein the fly ash is Class F fly ash, conforming to the requirements of GB / T 1596-2017 standard, with a sieve residue of ≤30% on a 45μm square hole sieve and a loss on ignition of ≤8.0%.

[0008] In one embodiment, the cement clinker is silicate cement clinker, and its mineral composition by mass percentage is: C3S 55%-65%, C2S 15%-25%, C3A 5%-10%, and C4AF 8%-15%.

[0009] In one embodiment, the gypsum is dihydrate gypsum with a purity ≥90% and a fineness of ≤10% residue on an 80μm square-hole sieve.

[0010] In one embodiment, when preparing 32.5 grade cement, the mass percentage of each component is as follows: cement clinker 25%-35%, fly ash 50%-65%, ternary polymer copolymer 0.5%-0.8%, organic weak acid 0.2%-0.3%, and gypsum 2%-4%; when preparing 42.5 grade cement, the mass percentage of each component is as follows: cement clinker 45%-60%, fly ash 30%-45%, ternary polymer copolymer 0.7%-1.2%, organic weak acid 0.3%-0.5%, and gypsum 3%-5%.

[0011] Secondly, this application provides a method for preparing the fly ash low-carbon cement described in the first aspect, comprising the following steps: S1. Preparation of ternary polymer copolymer: Acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and N-hydroxymethylacrylamide are added to deionized water in a molar ratio of 3:1:1, stirred and dissolved, and the pH of the system is adjusted to 6.5-7.5. 0.8%-1.2% of the total mass of monomers of ammonium persulfate initiator and 0.4%-0.6% of the chain transfer agent sodium bisulfite are added, nitrogen gas is introduced for protection, and the reaction is carried out at 70-80℃ for 3-4 hours. After cooling to room temperature, an aqueous solution of ternary polymer copolymer is obtained, which is then vacuum dried, pulverized and used for later use. S2. Raw material pretreatment: Cement clinker, fly ash and gypsum are crushed separately and passed through an 80μm square hole sieve for later use; citric acid, an organic weak acid, is crushed and passed through a 100μm square hole sieve for later use. S3. Mixed grinding: Weigh out the pretreated cement clinker, fly ash, gypsum, ternary polymer copolymer and organic weak acid according to the mass percentages of cement clinker 25%-60%, fly ash 30%-65%, ternary polymer copolymer 0.3%-1.2%, organic weak acid 0.1%-0.5% and gypsum 2%-5%, and put them into a ball mill. Control the ball milling time to 30-45 min, the ball-to-material ratio to 8:1, and the grinding temperature to ≤60℃ to obtain mixed powder; S4. Molding and curing: Mix the mixed powder obtained in step S3 with water at a water-cement ratio of 0.45-0.55, pour it into a mold, vibrate to form, and cure under standard conditions of 20±2℃ and relative humidity ≥90% for 24 hours before demolding. Continue curing until the specified age to obtain fly ash low-carbon cement products.

[0012] In one embodiment, in step S1, the amount of deionized water added is 3-5 times the total mass of the monomers; the temperature of the vacuum drying is 60-70°C, and the drying time is 12-16 hours.

[0013] In one embodiment, in step S3, the ball mill rotates at a speed of 200-250 r / min; the specific surface area of ​​the mixed powder is 350-400 m². 2 / kg.

[0014] In one embodiment, in step S4, the vibration molding frequency is 50-60Hz, the vibration time is 2-3min, and the specified age is 3d, 7d, or 28d.

[0015] Thirdly, this application provides an application of the fly ash low-carbon cement provided in the first aspect, wherein the fly ash low-carbon cement is used to prepare masonry mortar, plastering mortar, concrete components or road base materials.

[0016] In one embodiment, when used to prepare concrete components, the fly ash low-carbon cement is added at a rate of 15%-25% of the total mass of the concrete; when used to prepare road base materials, the fly ash low-carbon cement is added at a rate of 8%-12% of the total mass of the base materials.

[0017] This invention designs a ternary polymer copolymer with a specific structure and combines it with a weak organic acid to synergistically activate fly ash, achieving a high proportion of clinker substitution in cement production. It can produce 32.5 grade cement with a minimum clinker content of 25% and 42.5 grade cement with a minimum clinker content of 45%. While reducing carbon emissions and production costs in cement production, it ensures the mechanical properties and durability of cement, realizes the resource utilization of fly ash solid waste, and provides technical support for the low-carbon transformation of the cement industry. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 The infrared spectrum of the terpolymer prepared in Example 1 of this invention; Figure 2 The image shown is a scanning electron microscope image of the cement product of Example 1 of the present invention after 28 days, with a magnification of 10,000. Figure 3 The image shown is a scanning electron microscope image of the cement product of Comparative Example 1 of this invention after 28 days, with a magnification of 10,000. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] The raw materials used in this embodiment and comparative example are as follows: Cement clinker: Portland cement clinker, with a mineral composition of C3S 60%, C2S 20%, C3A 8%, and C4AF 12% by mass, which meets the requirements of GB 175-2007 "General Portland Cement" standard. Fly ash: Class F fly ash, meeting the requirements of GB / T 1596-2017 standard, with 25% residue on a 45μm square mesh sieve, 7.5% loss on ignition, 52% SiO2 content, 28% Al2O3 content, 6% Fe2O3 content, and a total mass fraction of 86% for SiO2, Al2O3, and Fe2O3. The ternary polymer copolymer monomers are acrylic acid (AA), 2-acrylamide-2-methylpropanesulfonic acid (AMPS), and N-hydroxymethylacrylamide (NMA), all of which are industrial grade with a purity of ≥98%. Organic weak acid: citric acid, industrial grade, purity ≥99%; Gypsum: Dihydrate gypsum, purity 92%, 8% residue on 80μm square mesh sieve; Initiator: Ammonium persulfate, industrial grade, purity ≥98%; Chain transfer agent: Sodium bisulfite, industrial grade, purity ≥97%; Deionized water: conductivity ≤10μS / cm.

[0022] The experimental equipment used in this embodiment and comparative example is as follows: Ball mill: Horizontal ball mill, speed 220 r / min, ball-to-material ratio 8:1; Fourier transform infrared spectrometer: Spotlight 400, test range 4000-400cm -1 ; Scanning electron microscope (SEM): SU8010, accelerating voltage 10kV; Compression testing machine: YES-2000 model, measuring range 0-2000kN; Vacuum drying oven: DZF-6050 model, temperature control accuracy ±1℃; Standard curing chamber: YH-40B type, temperature control accuracy ±2℃, humidity control accuracy ±5%.

[0023] The performance testing methods in this embodiment and the comparative example are as follows: 1. Setting time: Tested according to GB / T 1346-2011 "Standard consistency water requirement, setting time and soundness test method for cement"; 2. Soundness: Tested according to GB / T 1346-2011 "Standard Consistency Water Requirement, Setting Time and Soundness Test Methods for Cement"; 3. Mechanical properties: The compressive strength and flexural strength at 3d, 7d, and 28d were tested according to GB / T 17671-1999 "Test Method for Strength of Cement Mortar (ISO Method)"; 4. Fly ash activity index: The 28-day activity index was tested according to GB / T 1596-2017 "Fly ash for use in cement and concrete"; 5. Carbon emission calculation: Based on the amount of cement clinker used, the production of 1 ton of cement clinker emits 0.85 tons of carbon dioxide. Fly ash emits no carbon. Calculate the carbon emissions and reduction rate for each ton of cement produced. 6. Cost Calculation: Based on the market prices of various raw materials, calculate the raw material cost and cost savings for producing 1 ton of cement.

[0024] Example 1

[0025] This embodiment prepares 32.5 grade fly ash low-carbon cement, and the components are composed of the following mass percentages: cement clinker 30%, fly ash 65%, ternary polymer copolymer 0.6%, citric acid 0.4%, and gypsum 4%.

[0026] The preparation method is as follows: S1. Preparation of ternary polymer copolymer: Acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and N-hydroxymethylacrylamide were added to deionized water in a molar ratio of 3:1:1 (the amount of deionized water added was 4 times the total mass of the monomers). The mixture was stirred to dissolve, and the pH of the system was adjusted to 7.0 with NaOH solution. 1.0% of the total mass of the monomers of ammonium persulfate initiator and 0.5% of the chain transfer agent sodium bisulfite were added. Nitrogen gas was introduced for protection, and the reaction was carried out at 75°C for 3.5 h. After cooling to room temperature, an aqueous solution of ternary polymer copolymer was obtained. The copolymer was dried under vacuum at 65°C for 14 h, pulverized, and then used for later use. The number average molecular weight of the copolymer was measured to be 2000. S2. Raw material pretreatment: Cement clinker, fly ash and gypsum are crushed separately and passed through an 80μm square hole sieve for later use; citric acid is crushed and passed through a 100μm square hole sieve for later use. S3. Mixing and Grinding: Weigh the cement clinker, fly ash, gypsum, ternary polymer copolymer, and citric acid according to the above-mentioned mass percentages, and put them into a ball mill. Control the ball mill speed at 220 r / min, the ball-to-material ratio at 8:1, the grinding time at 35 min, and the grinding temperature at 55℃ to obtain a mixed powder. The specific surface area of ​​the mixed powder is measured to be 380 m². 2 / kg; S4. Molding and Curing: Mix the powder with water at a water-cement ratio of 0.50 until uniform, pour into a 40mm×40mm×160mm mold, vibrate at 55Hz for 2.5min, cure in a standard curing chamber at 20±2℃ and relative humidity ≥90% for 24h, then demold and continue curing to 3d, 7d, and 28d to obtain fly ash low-carbon cement products.

[0027] The cement products prepared in this embodiment were subjected to performance tests. The structure of the synthesized terpolymer was characterized by Fourier transform infrared spectroscopy, and the microstructure of the cement products after 28 days of hydration was observed by SEM. The results are detailed in Table 1.

[0028] Table 1: Assignment of Characteristic Absorption Peaks in Fourier Transform Infrared Spectra

[0029] Example 2 This embodiment prepares 42.5 grade fly ash low-carbon cement, and the components are composed of the following mass percentages: cement clinker 49%, fly ash 45%, ternary polymer copolymer 0.8%, citric acid 0.5%, and gypsum 4.7%.

[0030] The preparation method is as follows: S1. Preparation of ternary polymer copolymer: Same as in Example 1, the number-average molecular weight of the copolymer is 2000; S2. Raw material pretreatment: Same as in Example 1; S3. Mixed Grinding: Weigh the cement clinker, fly ash, gypsum, ternary polymer copolymer, and citric acid according to the above-mentioned mass percentages, and put them into a ball mill. Control the ball mill speed at 220 r / min, the ball-to-material ratio at 8:1, the grinding time at 40 min, and the grinding temperature at 58℃ to obtain a mixed powder. The specific surface area of ​​the mixed powder is measured to be 390 m². 2 / kg; S4. Molding and Curing: Mix the powder with water at a water-cement ratio of 0.48 until uniform, pour into a 40mm×40mm×160mm mold, vibrate at 55Hz for 2.5min, cure in a standard curing chamber at 20±2℃ and relative humidity ≥90% for 24h, then demold and continue curing to 3d, 7d, and 28d to obtain fly ash low-carbon cement products.

[0031] The cement products prepared in this embodiment were subjected to performance tests, and the results are detailed in the data table.

[0032] Example 3 This embodiment prepares 32.5 grade fly ash low-carbon cement, and the components are composed of the following mass percentages: cement clinker 41%, fly ash 55%, ternary polymer copolymer 0.5%, citric acid 0.2%, and gypsum 3.3%.

[0033] The preparation method is as follows: S1. Preparation of ternary polymer copolymer: Same as in Example 1, the number-average molecular weight of the copolymer is 2000; S2. Raw material pretreatment: Same as in Example 1; S3. Mixed Grinding: Weigh the cement clinker, fly ash, gypsum, ternary polymer copolymer, and citric acid according to the above-mentioned mass percentages, and put them into a ball mill. Control the ball mill speed at 220 r / min, the ball-to-material ratio at 8:1, the grinding time at 30 min, and the grinding temperature at 52℃ to obtain a mixed powder. The specific surface area of ​​the mixed powder is measured to be 360 ​​m². 2 / kg; S4. Molding and curing: Mix the powder with water at a water-cement ratio of 0.52 until uniform, pour into a 40mm×40mm×160mm mold, vibrate at 55Hz for 2.5min, and cure in a standard curing chamber at 20±2℃ and relative humidity ≥90% for 24h before demolding. Continue curing for 3d, 7d, and 28d to obtain fly ash low-carbon cement products.

[0034] The cement products prepared in this embodiment were subjected to performance tests, and the results are detailed in the data table.

[0035] Comparative Example 1 The difference between this comparative example and Example 1 is that the ternary polymer copolymer lacks the 2-acrylamide-2-methylpropanesulfonic acid (AMPS) monomer and uses a binary copolymer (poly(acrylic acid-N-hydroxymethylacrylamide)). The remaining components, amounts, and preparation methods are the same as in Example 1, which is used to verify the necessity of the AMPS monomer.

[0036] Specifically, the monomer molar ratio of the binary copolymer was acrylic acid:N-hydroxymethylacrylamide = 3:1, and the preparation method was the same as that of the terpolymer in Example 1, with a number-average molecular weight of 1900. The cement products prepared in this comparative example were subjected to performance tests, and the microstructure of the cement products after 28 days of hydration was observed using SEM. The results are detailed in the data table.

[0037] Comparative Example 2 The difference between this comparative example and Example 1 is that the ternary polymer copolymer lacks acrylic acid (AA) monomer and uses a binary copolymer (poly(2-acrylamide-2-methylpropanesulfonic acid-N-hydroxymethylacrylamide)). The remaining components, amounts and preparation methods are the same as in Example 1, which is used to verify the necessity of AA monomer.

[0038] Specifically, the monomer molar ratio of the binary copolymer was 2-acrylamide-2-methylpropanesulfonic acid:N-hydroxymethylacrylamide = 1:1, and the preparation method was the same as that of the terpolymer in Example 1. The number average molecular weight was 1850. Performance tests were performed on the cement product prepared in this comparative example, and the results are detailed in the data table.

[0039] Comparative Example 3 The difference between this comparative example and Example 1 is that the ternary polymer copolymer lacks N-hydroxymethylacrylamide (NMA) monomer and uses a binary copolymer (poly(acrylic acid-2-acrylamide-2-methylpropanesulfonic acid)). The remaining components, amounts and preparation methods are the same as in Example 1, which is used to verify the necessity of NMA monomer.

[0040] Specifically, the monomer molar ratio of the binary copolymer was acrylic acid:2-acrylamide-2-methylpropanesulfonic acid = 3:1, and the preparation method was the same as that for the terpolymer in Example 1, with a number-average molecular weight of 2050. Performance tests were conducted on the cement product prepared in this comparative example, and the results are detailed in the data table.

[0041] Comparative Example 4 The difference between this comparative example and Example 1 is that: no ternary polymer copolymer was prepared; instead, three monomers (acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, and N-hydroxymethylacrylamide) were added individually in a molar ratio of 3:1:1 (the total mass was the same as that of the ternary copolymer in Example 1). The remaining components, dosages, and preparation methods were the same as in Example 1, and this was used to verify the necessity of monomer polymerization.

[0042] The cement products prepared in this comparative example were subjected to performance tests, and the results are detailed in the data table.

[0043] Comparative Example 5 The difference between this comparative example and Example 1 is that the organic weak acid citric acid is not added, while the remaining components, amounts, and preparation methods are the same as in Example 1, in order to verify the necessity of citric acid.

[0044] The cement products prepared in this comparative example were subjected to performance tests, and the results are detailed in the data table.

[0045] Comparative Example 6 The difference between this comparative example and Example 1 is that no ternary polymer copolymer is added, while the remaining components, amounts, and preparation methods are the same as in Example 1. This is used to verify the necessity of the ternary polymer copolymer.

[0046] The cement products prepared in this comparative example were subjected to performance tests, and the results are detailed in the data table.

[0047] Comparative Example 7 This comparative example uses conventional fly ash cement. The difference between this example and Example 1 is that no ternary polymer copolymer and citric acid are added. All other components, dosages, and preparation methods are the same as in Example 1. This example is used to compare the activation effect of the present invention.

[0048] Table 2: Setting time and soundness test data of cement in each example and comparative example

[0049] Table 3: Mechanical property test data of cement in each example and comparative example

[0050] Table 4: Fly ash activity index, carbon emissions, and cost test data for each embodiment and comparative example

[0051] Data Description This section, combining the three data tables mentioned above, provides a detailed analysis of the test data for each embodiment and comparative example, clarifying the principles behind the superior performance of the embodiments and the reasons for the poor performance of the comparative examples, highlighting the innovation of this invention and the necessity of each component. It should be noted that the fly ash activity index in this paper is tested according to the GB / T 1596-2017 standard "Fly Ash for Cement and Concrete". During the test, the same proportion of ternary polymer copolymer and citric acid as activators were added to each embodiment according to the actual mass fraction of fly ash in the cement to simulate the synergistic activation environment in the cement system. The fly ash with the added activator was mixed with standard cement in a specified proportion to prepare mortar. After curing for 28 days, the ratio of its compressive strength to the 28-day compressive strength of pure standard cement mortar was measured; this ratio is the fly ash activity index.

[0052] First, based on the setting time and soundness data in Table 2, it can be seen that the cement prepared in all examples and comparative examples has qualified soundness, indicating that the component design and preparation process of the present invention will not affect the volume stability of the cement, ensuring that the cement will not experience cracking, deformation, or other problems during use. Regarding setting time, the initial setting time of Examples 1-3 is 172-193 min, and the final setting time is 255-275 min, all meeting the setting time requirements for Grade 32.5 and Grade 42.5 cement in GB 175-2007 "General Portland Cement" (initial setting time ≥ 45 min, final setting time ≤ 600 min). Furthermore, the setting time is moderate, facilitating construction operations. Although the setting times of Comparative Examples 1-7 were within the acceptable range, there were some fluctuations: the initial setting time of Comparative Example 1 (lacking AMPS monomer) and Comparative Example 4 (monomer added alone) was shorter (155-162 min), mainly because the lack of AMPS monomer or the monomer not being polymerized resulted in insufficient dispersion of the copolymer, cement particle agglomeration, and accelerated hydration reaction rate; the initial setting time of Comparative Example 2 (lacking AA monomer) was longer (205 min) and the final setting time was longer (292 min), mainly because the lack of carboxyl groups provided by AA monomer could not effectively complex calcium ions on the surface of fly ash, resulting in poor fly ash dispersion and slowed hydration reaction rate.

[0053] Secondly, based on the mechanical property data in Table 3, it can be seen that the mechanical properties of the cement prepared in Examples 1-3 all meet the corresponding grade requirements. Specifically, the 28-day compressive strength of Example 1 (25% clinker content) is 33.2 MPa, and the 28-day compressive strength of Example 3 (35% clinker content) is 32.8 MPa, both meeting the strength requirements of grade 32.5 cement (28-day compressive strength ≥ 32.5 MPa). The 28-day compressive strength of Example 2 (45% clinker content) is 43.8 MPa, meeting the strength requirements of grade 42.5 cement (28-day compressive strength ≥ 42.5 MPa). Furthermore, the flexural strength and compressive strength at 3d, 7d, and 28d all show a steady increasing trend, indicating that the cement hydration reaction is sufficient and the structure of the hydration products is stable. The core reason for this superior performance is that the ternary polymer copolymer P(AA-AMPS-NMA) designed in this invention forms a synergistic activation system with citric acid. The carboxyl, sulfonic acid, hydroxyl, and amide groups in the ternary copolymer work synergistically, adsorbing onto the surface of fly ash and promoting the penetration of citric acid into the fly ash interior. This breaks down the dense glassy structure of the fly ash, releasing active SiO2 and Al2O3. These active components fully react with Ca(OH)2 produced during the hydration of cement clinker, generating a large amount of dense CSH gel and CAH gel, thereby significantly improving the mechanical properties of cement. Figure 2 (SEM image of Example 1 after 28 days of hydration) It can be seen that the cement hydration product is mainly dense CSH gel with uniform structure, few pores and no obvious cracks, which further proves that the synergistic activation effect is good, the fly ash activity is fully utilized and the hydration reaction is complete.

[0054] In contrast, the mechanical properties of all the proportions failed to meet the corresponding grade requirements, with 28-day compressive strengths all below 32.5 MPa. The main reasons are as follows: Comparative Examples 1-3 (lacking any monomer in the terpolymer): Comparative Example 1 lacks AMPS monomer, and the binary copolymer (poly(acrylic acid-N-hydroxymethylacrylamide)) lacks sulfonic acid groups, failing to effectively improve the dispersibility of fly ash and enhance the copolymer's binding capacity with water, leading to fly ash agglomeration and incomplete hydration reaction; Comparative Example 2 lacks AA monomer, and the binary copolymer (poly(2-acrylamide-2-methylpropanesulfonic acid-N-hydroxymethylacrylamide)) lacks carboxyl groups, failing to undergo complexation reaction with calcium ions on the fly ash surface, resulting in decreased adsorption capacity of the copolymer for fly ash and significantly weakened activation effect; Comparative Example 3 lacks NMA monomer, and the binary copolymer (poly(acrylic acid-2-acrylamide-2-methylpropanesulfonic acid)) lacks hydroxyl and amide groups, failing to form hydrogen bonds with hydroxyl groups on the fly ash surface, resulting in insufficient bonding strength between the copolymer and fly ash, and failing to promote cross-linking between copolymer molecules, thus failing to form a stable adsorption layer, leading to easy agglomeration of the active component and insufficient participation in the hydration reaction. Figure 3(SEM image of Comparative Example 1 after 28 days of hydration) It can be seen that the cement hydration products have a loose structure, low CSH gel content, and a large number of pores and cracks. The surface of fly ash particles is not fully activated, which is in stark contrast to Example 1. This proves that the absence of any monomon in the terpolymer will prevent the achievement of the expected activation effect, and the cement strength will decrease significantly.

[0055] Comparative Example 4 (monomers added individually, without polymerization): The three monomers did not undergo polymerization. When added individually, the functional groups of each monomer could not work synergistically, and the monomer molecules were too small to form a stable adsorption layer on the fly ash surface. This prevented the citric acid from penetrating into the fly ash and also prevented the adsorption of the active components generated by dissolution. Consequently, the activity of the fly ash could not be effectively activated, and the mechanical properties of the cement decreased significantly. The 28-day compressive strength was only 21.5 MPa, far lower than the 33.2 MPa of Example 1. This proves that the three monomers must undergo polymerization to form a terpolymer, and adding them individually has no activating effect.

[0056] Comparative Example 5 (without citric acid): Lacking the synergistic effect of the organic weak acid, the terpolymer alone cannot effectively dissolve the glassy structure of fly ash, and cannot release the internal active SiO2 and Al2O3. The fly ash activity is not fully activated, the content of CSH gel and CAH gel in the hydration products is low, the mechanical properties of cement are poor, and the 28-day compressive strength is 24.3 MPa, which does not meet the requirements of grade 32.5 cement. This proves that citric acid is an indispensable component in the synergistic activation system, and the lack of citric acid will lead to a significant decrease in the activation effect.

[0057] Comparative Example 6 (without terpolymer): Without the adsorption and dispersion effects of terpolymer, citric acid cannot effectively penetrate into the fly ash, and the active components produced by dissolution are prone to agglomeration and cannot fully participate in the hydration reaction. The activation effect of fly ash is poor, the mechanical properties of cement are poor, and the 28-day compressive strength is 23.9 MPa, which does not meet the requirements of grade 32.5 cement. This proves that terpolymer is an indispensable component in the synergistic activation system, and the lack of terpolymer will lead to a significant decrease in activation effect.

[0058] Comparative Example 7 (without terpolymer and citric acid): Without any activator, the glassy structure of fly ash could not be destroyed, and its activity could not be activated. It could only participate in the hydration reaction by relying on its own potential activity. The hydration reaction was extremely incomplete, and the cement mechanical properties were the worst. The 28-day compressive strength was only 21.2 MPa, which did not meet the requirements of grade 32.5 cement. This further proved the necessity and superiority of the synergistic activation system (terpolymer + citric acid) of the present invention.

[0059] Furthermore, combining the fly ash activity index, carbon emission, and cost data in Table 4, it can be seen that the 28-day fly ash activity index of Examples 1-3 all reached over 86%, with Example 1 having the highest activity index at 88.6%. This indicates that the synergistic activation system of the present invention can effectively improve fly ash activity, far exceeding the activity indices of the comparative examples (55.3%-65.2%), further verifying the excellent synergistic activation effect. In terms of carbon emissions, the carbon emissions per ton of cement in Examples 1-3 ranged from 212.5 to 382.5 kg, with a carbon emission reduction rate of 55.0%-75.0%. Example 1 (25% clinker content) had the lowest carbon emissions, at only 212.5 kg, with a carbon emission reduction rate of 75.0%, significantly lower than conventional cement (approximately 850 kg of carbon emissions per ton), fully demonstrating the low-carbon advantages of the present invention. In terms of cost, the cost of cement raw materials in Examples 1-3 is 280-320 yuan per ton. Compared with conventional cement (the cost of raw materials per ton is about 355 yuan), the cost can be saved by 35-75 yuan per ton. Among them, Example 1 saves the most cost, up to 75 yuan, which has significant economic benefits.

[0060] Although the carbon emissions and costs of each comparative example are basically the same as those of Example 1 (all with 25% clinker content), their mechanical properties are substandard, making them unsuitable for practical application. Therefore, even with lower costs and carbon emissions, they lack practical application value. This further illustrates that the synergistic activation system (terpolymer + citric acid) of this invention can not only achieve high-proportion clinker substitution, reduce carbon emissions and costs, but also ensure the mechanical properties of cement, achieving a balance of all three and possessing significant technical advantages and application value.

[0061] Finally, combining Figure 1 (Infrared spectrum of the terpolymer) and Table 1 show that the 3200-3600 cm⁻¹ range in the spectrum... -1 The characteristic absorption peak of the hydroxyl group (-OH) appears at 1710 cm⁻¹. -1 The characteristic absorption peaks of the carboxyl group (-COOH) appear on both sides, at 1030-1040 cm⁻¹. -1 The characteristic absorption peak of the sulfonic acid group (-SO3H) appears at 1650 cm⁻¹. -1 The presence of characteristic absorption peaks of amide groups (-CONH-) on both sides, which correspond to the characteristic functional groups of the three monomers (AA, AMPS, NMA) in the ternary copolymer, proves that the three monomers have been successfully polymerized to form the target ternary polymer copolymer, providing a structural basis for the excellent effect of the synergistic excitation system.

[0062] The ternary polymer copolymer (P(AA-AMPS-NMA)) designed in this invention, in combination with citric acid, synergistically activates the activity of fly ash. The carboxyl, sulfonic acid, hydroxyl, and amide groups in the ternary copolymer work synergistically with citric acid to effectively break the glassy dense structure of fly ash, releasing active SiO2 and Al2O3, thereby increasing the activity index of fly ash to over 85%. It can achieve the preparation of 32.5 grade cement with a minimum clinker content of 25% and 42.5 grade cement with a clinker content of 45%, which is far higher than the clinker substitution rate of existing technologies (usually not exceeding 20%).

[0063] This invention replaces cement clinker with a high proportion of fly ash, which can reduce carbon dioxide emissions by 250-450 kg per ton of fly ash low-carbon cement produced, with a carbon emission reduction rate of 25%-45%. At the same time, it realizes the resource utilization of fly ash solid waste and reduces the environmental pollution caused by fly ash accumulation, which has significant environmental benefits.

[0064] As an industrial solid waste, fly ash is much cheaper than cement clinker. A high proportion of fly ash substitution can significantly reduce the raw material cost of cement production, saving 50-80 yuan per ton of cement. At the same time, the preparation process of ternary polymer copolymers is simple and the raw materials are readily available. The organic weak acid citric acid is inexpensive, which further reduces the production cost of cement and has good economic benefits.

[0065] The synergistic effect of ternary polymer copolymers and citric acid can promote the full hydration reaction of cement, generating more CSH gel and CAH gel, making the structure of cement hydration products more compact. At the same time, ternary copolymers can be adsorbed on the surface of cement particles, reducing cement particle agglomeration, improving the fluidity and uniformity of cement paste, thereby enhancing the mechanical properties and durability of cement. The 28-day compressive strength of 32.5 grade cement is ≥32.5MPa, and the 28-day compressive strength of 42.5 grade cement is ≥42.5MPa. Its impermeability and frost resistance are superior to those of conventional fly ash cement.

[0066] Through comparative verification, it was found that the absence of any monomonet in the ternary polymer copolymer prevented the achievement of the expected activation effect, resulting in a significant decrease in cement strength. When the three monomers were not polymerized and were added individually, they had no activation effect. The absence of any one of the organic weak acid, ternary copolymer, or fly ash led to a significant decrease in cement performance, proving that all materials used in this invention are necessary and indispensable, and that the technical solution has clear innovation and feasibility.

[0067] The preparation method of the present invention does not require complex equipment and processes. It can achieve large-scale production using conventional ball milling, mixing and curing equipment. It is simple to operate, has low energy consumption, and is suitable for industrial promotion and application.

[0068] In summary, this invention, by designing a ternary polymer copolymer P (AA-AMPS-NMA) with a specific structure and combining it with citric acid to form a synergistic activation system, effectively solves the technical problems of low fly ash activity, limited clinker substitution rate, and high carbon emissions in existing technologies. It achieves the technical goal of preparing 32.5 grade cement with a minimum clinker content of 25% and 42.5 grade cement with a 45% clinker content. Comparative verification shows that the absence of any single monomer in the ternary copolymer will fail to meet the technical requirements; the three monomers have no effect if added individually without polymerization; and the absence of any one of the organic weak acid, the ternary copolymer, or fly ash will lead to a significant decrease in cement performance, proving that all materials used in this invention are necessary and indispensable. Furthermore, the preparation process of this invention is simple, easy to industrialize, and has significant environmental, economic, and social benefits.

[0069] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A fly ash low-carbon cement, characterized in that, It is composed of the following components by mass percentage: cement clinker 25%-60%, fly ash 30%-65%, ternary polymer copolymer 0.3%-1.2%, organic weak acid 0.1%-0.5%, and gypsum 2%-5%; the ternary polymer copolymer is poly(acrylic acid-2-acrylamide-2-methylpropanesulfonic acid-N-hydroxymethylacrylamide), with a monomer molar ratio of acrylic acid:2-acrylamide-2-methylpropanesulfonic acid:N-hydroxymethylacrylamide = 3:1:1, and a number average molecular weight of 1800-2200; the organic weak acid is citric acid; the fly ash has a 45μm square hole sieve residue ≤30% and a loss on ignition ≤8.0%.

2. The fly ash low-carbon cement according to claim 1, characterized in that, The cement clinker is silicate cement clinker, and its mineral composition by mass percentage is: C3S 55%-65%, C2S 15%-25%, C3A 5%-10%, and C4AF 8%-15%.

3. The fly ash low-carbon cement according to claim 1, characterized in that, The gypsum is dihydrate gypsum with a purity of ≥90% and a fineness of ≤10% residue on an 80μm square-hole sieve.

4. The fly ash low-carbon cement according to claim 1, characterized in that, When preparing grade 32.5 cement, the mass percentage of each component is as follows: cement clinker 25%-35%, fly ash 50%-65%, ternary polymer copolymer 0.5%-0.8%, organic weak acid 0.2%-0.3%, and gypsum 2%-4%. When preparing grade 42.5 cement, the mass percentage of each component is as follows: cement clinker 45%-60%, fly ash 30%-45%, ternary polymer copolymer 0.7%-1.2%, organic weak acid 0.3%-0.5%, and gypsum 3%-5%.

5. A method for preparing fly ash low-carbon cement as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Preparation of ternary polymer copolymer: Acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and N-hydroxymethylacrylamide are added to deionized water in a molar ratio of 3:1:1, stirred and dissolved, and the pH of the system is adjusted to 6.5-7.

5. 0.8%-1.2% of the total mass of monomers of ammonium persulfate initiator and 0.4%-0.6% of the chain transfer agent sodium bisulfite are added, nitrogen gas is introduced for protection, and the reaction is carried out at 70-80℃ for 3-4 hours. After cooling to room temperature, an aqueous solution of ternary polymer copolymer is obtained, which is then vacuum dried, pulverized and used for later use. S2. Raw material pretreatment: Cement clinker, fly ash and gypsum are crushed separately and passed through an 80μm square hole sieve for later use; citric acid, an organic weak acid, is crushed and passed through a 100μm square hole sieve for later use. S3. Mixed grinding: Weigh out the pretreated cement clinker, fly ash, gypsum, ternary polymer copolymer and organic weak acid according to the mass percentages of cement clinker 25%-60%, fly ash 30%-65%, ternary polymer copolymer 0.3%-1.2%, organic weak acid 0.1%-0.5% and gypsum 2%-5%, and put them into a ball mill. Control the ball milling time to 30-45 min, the ball-to-material ratio to 8:1, and the grinding temperature to ≤60℃ to obtain mixed powder; S4. Molding and curing: Mix the mixed powder obtained in step S3 with water at a water-cement ratio of 0.45-0.55, pour it into a mold, vibrate to form, and cure under standard conditions of 20±2℃ and relative humidity ≥90% for 24 hours before demolding. Continue curing until the specified age to obtain fly ash low-carbon cement products.

6. The preparation method according to claim 5, characterized in that, In step S1, the amount of deionized water added is 3-5 times the total mass of the monomer; the temperature of vacuum drying is 60-70℃, and the drying time is 12-16h.

7. The preparation method according to claim 5, characterized in that, In step S3, the rotational speed of the ball mill is 200-250 r / min; the specific surface area of ​​the mixed powder is 350-400 m². 2 / kg.

8. The preparation method according to claim 5, characterized in that, In step S4, the vibration molding frequency is 50-60Hz, the vibration time is 2-3min, and the specified age is 3 days, 7 days, or 28 days.

9. An application of fly ash low-carbon cement as described in any one of claims 1-4, characterized in that, The fly ash low-carbon cement is used to prepare masonry mortar, plastering mortar, concrete components, or road base materials.

10. The application according to claim 9, characterized in that, When used to prepare concrete components, the fly ash low-carbon cement content is 15%-25% of the total mass of the concrete; when used to prepare road base materials, the fly ash low-carbon cement content is 8%-12% of the total mass of the base materials.

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