Solid waste-based geopolymer and preparation method thereof

Abstract

The invention relates to the technical field of solid waste material recycling, in particular to a solid waste-based geopolymer and a preparation method thereof. The solid waste-based geopolymer comprises the following components in parts by mass: 400-500 parts of fly ash; 400 to 500 parts of mineral powder; 40-60 parts of a sodium hydroxide aqueous solution; 200 to 400 parts of water; the solid content of the nano waterborne epoxy emulsion is 30-62%, the particle size of the nano waterborne epoxy emulsion is 100-900 nm, and the nano waterborne epoxy emulsion accounts for 3-9% of the total mass. According to the invention, the compactness of a matrix is enhanced, shrinkage cracking caused by water evaporation is reduced, the toughness and anti-permeability of the material are improved, the compactness of an interface is enhanced, the saltpetering condition of the matrix is inhibited, and wide application in the field of building materials is facilitated.

Description

Technical Field

[0001] This invention relates to the field of solid waste material recycling technology, and in particular to a solid waste-based geopolymer and its preparation method. Background Technology

[0002] Geopolymers are produced by chemically reacting silica-alumina raw materials with alkali to generate an amorphous gel that acts as a binder. After dehydration and hardening, the gel forms a geopolymer with a network structure. The large volume of industrial solid waste provides ample raw materials for geopolymer production. Alkali-activated geopolymers offer advantages such as low energy consumption, low carbon dioxide emissions, high temperature resistance, corrosion resistance, and high mechanical strength, making them one of the most promising new materials to replace cement-based building materials. However, commonly used alkali activators for geopolymers are mostly sodium-potassium alkaline solutions, whose high alkalinity can lead to efflorescence, affecting the material's aesthetics and durability.

[0003] Combining organic nanomaterials with solid waste-based cementitious materials can improve the density of the materials and reduce efflorescence, but it can also lead to problems affecting strength. How to effectively combine nano-organic polymer materials with solid waste-based cementitious materials and give full play to the advantages of both has become the key to solving the efflorescence problem of solid waste-based cementitious materials. Summary of the Invention

[0004] The purpose of this invention is to provide a solid waste-based geopolymer and its preparation method to solve the above-mentioned technical problems.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a solid waste-based geopolymer, comprising the following components in parts by weight: 400-500 parts of fly ash; 400-500 parts of mineral powder; 40-60 parts of sodium hydroxide aqueous solution; 200-400 parts water; Nano-aqueous epoxy emulsion with a solid content of 30-62% and a particle size of 800-900 nm; Among them, nano-aqueous epoxy emulsion accounts for 3%-9% of the total mass.

[0006] Nano-aqueous epoxy emulsions are incorporated into the pores of solid waste-based cementitious materials (solid waste-based geopolymers). This structure bonds tightly with the cementitious material matrix, forming a dense organic-inorganic composite layer that effectively blocks the migration pathways of moisture and soluble alkali ions, significantly reducing the risk of efflorescence. When the solid waste-based geopolymer is used as a coating, the flexible film generated during the coagulation process further enhances interfacial adhesion and improves crack resistance.

[0007] The emulsion has good permeability and dispersion stability. It can exist stably in alkaline environment and gradually crosslink and solidify, effectively playing a filling and reinforcing role, and improving the durability and impermeability of the material.

[0008] Nano-aqueous epoxy emulsions contain a large number of hydroxyl groups. Nanoparticles can quickly penetrate into the micropores and capillaries of the solid waste-based polymer matrix through capillary action. During the hydration process of the spherical nanoemulsion, the nano-spherical structure acts as a filler material to fill the pores of the cementitious material. It can also undergo ring-opening addition reactions during the hydration process to generate a membrane structure. The molecular cross-linking process works synergistically with the hydration reaction of the solid waste-based cementitious material. After the reaction, an organic-inorganic interpenetrating network is formed, forming hydrogen bonds and chemical bonds on the substrate surface, and forming spherical particles and flexible membranes in the matrix to seal the pores and improve the microstructure of the material.

[0009] A further improvement to this scheme, the preparation method of the nano-aqueous epoxy emulsion is as follows: S1. Add bisphenol A epoxy resin and polyethylene glycol monomethyl ether to the reaction flask, heat to 60±5°C, and stir until completely dissolved. S2. The dibutyltin dilaurate catalyst is dissolved in isophorone diisocyanate and slowly added dropwise to the S1 solution at 60±5°C. After the addition is complete, the temperature is raised to 80±5°C and the reaction is maintained at this temperature for 3±0.5 hours. Isophorone diisocyanate, as a coupling agent, has low reactivity and is easier to control. The aliphatic chain structure gives it better flexibility and chemical resistance.

[0010] S3. Slowly add silane coupling agent to the S2 system and continue the reaction for 2 ± 0.5 hours; S4. Cool the system to below 50°C, adjust the pH of the system to 6.0-6.5 with glacial acetic acid; preheat deionized water to 60°±5°C, and slowly add hot water dropwise to the S3 solution; S5. Maintain the stirring speed at 400-500 rpm. As hot water is added to the S4 solution, the appearance of the solution changes instantly from a transparent paste to a milky white opaque liquid. At this point, quickly pour in the remaining hot water and immediately increase the stirring speed to 1200-1500 rpm. Continue stirring at this high speed for 30±10 minutes to form a nanoemulsion with uniform particle size.

[0011] A further improvement to this solution is that the raw material ratio of the nano-aqueous epoxy emulsion is: 100 parts of bisphenol A type epoxy resin 20-30 parts of polyethylene glycol monomethyl ether 5-10 parts of isophorone diisocyanate Silane coupling 3-6 parts 0.1-2 parts of dibutyltin dilaurate 100-200 parts of deionized water.

[0012] Further improvements to this solution include: the bisphenol A type epoxy resin is E-51 with an epoxy value of 0.51, forming the main film and providing key properties; the polyethylene glycol monomethyl ether is MPEG-2000, where longer-chain (molecular weight 2000) PEG forms a thicker and more stable hydration layer with excellent alkali resistance; and the silane coupling agent is KH-560, whose epoxy groups can react with the resin, and the methoxy groups hydrolyze into silanol groups in the alkaline environment of the geopolymer, combining with the inorganic network to achieve "molecular bridging".

[0013] Mechanism for preventing efflorescence: The essence of alkali bloom is that unreacted alkali metal ions (Na⁺, K⁺) migrate to the surface with water molecules through interconnected capillaries, and react with CO2 in the air to form white carbonates.

[0014] 1. The improved emulsion of this invention has a particle size in the nanometer range. These tiny particles can effectively penetrate and fill the nanoscale capillary pores in the geopolymer slurry. This greatly increases the tortuosity of the migration paths of water and ions, effectively blocking their movement. Furthermore, unlike traditional inert fillers (such as silica fume), these nanoparticles are flexible organic polymers that can form tough plugs that are not easily damaged by matrix shrinkage or microcracks.

[0015] 2. When the nano-epoxy emulsion is added to the solid waste substrate polymer, it forms a dense hydrophobic polymer film on the inner wall of the pores and the surface of the particles. This film greatly reduces the wettability of the substrate to water, fundamentally cutting off the "carrier" required for ion migration—water. Furthermore, its alkali resistance ensures that the emulsion will not break down or fail in a strongly alkaline environment, thus allowing this protective film to form completely.

[0016] 3. The KH-560 silane coupling agent introduced in the improvement is key. Its methoxy group (-OCH3) hydrolyzes to silanol groups (-Si-OH) under alkaline conditions. These silanol groups can undergo condensation reactions with aluminosilicate species in the geopolymer network to form strong -Si-O-Si- or -Si-O-Al- chemical bonds. This chemical bonding, on the one hand, firmly anchors the organic phase to the inorganic network; on the other hand, the coupling agent itself and its reaction sites can adsorb or fix some free alkali metal ions, reducing the number of migratable free ions.

[0017] In summary, the anti-efflorescence effect is achieved through a synergistic effect of "physical filling, hydrophobic film formation, and chemical fixation".

[0018] Mechanisms for enhancing strength and toughness Geopolymers are inherently brittle and contain microcracks.

[0019] 1. When epoxy emulsion is added to the geopolymer matrix of solid waste, it forms a cross-linked organic polymer network that interpenetrates with the inorganic network of the geopolymer. When the material is subjected to stress, the rigid inorganic network provides strength and modulus, while the flexible organic network absorbs and disperses energy, preventing the propagation of microcracks. This significantly improves the flexural strength (toughness) and fracture energy of the material.

[0020] 2. Well-dispersed nano-epoxy particles act as nucleation sites before solidification and become second-phase particles after solidification. When microcracks encounter these flexible particles, the crack tips are blunted or need to bypass the particles, consuming more energy. More importantly, the epoxy polymer chains can span across the crack, generating bridging stress and preventing further crack propagation. The strong interfacial bonding provided by KH-560 ensures that stress can be effectively transferred from the inorganic phase to the organic phase, avoiding interfacial debonding as a new defect.

[0021] 3. The nano-filling effect makes the matrix more compact, which macroscopically translates to a further increase in compressive strength.

[0022] In summary, the strength improvement is achieved through "constructing interpenetrating networks for toughening, nanoparticle pinning and bridging, and reducing porosity".

[0023] Mechanism for reducing water absorption The high water absorption rate stems from the abundant hydrophilic channels and hydroxyl groups within the geopolymer.

[0024] 1. Epoxy resin itself is a highly hydrophobic polymer material. Its nano-distribution significantly alters the chemical properties of the pore surface, changing it from hydrophilic to hydrophobic. This increases the contact angle of water on the material surface and within the internal pores, creating a "lotus leaf effect" that makes it difficult for water to penetrate.

[0025] 2. As described in the anti-efflorescence mechanism, the filling effect of nanoparticles not only blocks the pores but also refines the macropores into smaller, less interconnected pores. The driving force for water absorption through capillary action is significantly weakened.

[0026] The water absorption rate can be greatly reduced, which will directly lead to a leap in resistance to freeze-thaw cycles and resistance to harmful ion corrosion.

[0027] In summary, the reduction in water absorption rate is achieved through "the intrinsic hydrophobicity of epoxy resin and the more tortuous pores created by nanofilling".

[0028] On the other hand, the present invention provides a method for preparing a solid waste-based geopolymer, comprising the following steps: (1) First, ball mill and sieve the fly ash and mineral powder, and then mix them thoroughly to obtain a mixed powder. (2) Dissolve sodium hydroxide in water, pour the solution into the mixed powder and stir evenly; (3) Stir the nano-aqueous epoxy emulsion evenly, then pour it into the mixed powder and continue stirring; In a further improvement to this scheme, in step (1), the mixing speed is 500-2000 r / min and the mixing time is 5-15 min; In step (2), the mixing speed is 2000-3000 r / min, and the mixing time is 15-30 min; In step (3), the mixing speed is 1000-2000 r / min and the mixing time is 2-3 min.

[0029] The beneficial effects of this invention are: This invention prepares a high-strength cementitious material based on solid waste materials, such as fly ash and mineral powder, by activating their activity with alkaline sodium hydroxide. Modification of the aqueous nanoemulsion increases the adhesion between organic and inorganic materials, filling pores and improving the density of the solid waste-based cementitious material. This effectively blocks the penetration of external moisture and corrosive media, thereby enhancing the corrosion resistance and durability of the solid waste-based cementitious material. Simultaneously, the nanospherical structure improves the mechanical properties of the coating, enhances its crack resistance, and further extends the material's service life. Adding nano-polymer emulsions to solid waste materials not only improves the mechanical properties of the solid waste-based cementitious material matrix and enhances its anti-efflorescence properties, but also reduces the environmental pollution impact of large quantities of waste, thus protecting the environment. Attached Figure Description

[0030] Figure 1 This invention relates to the variation of flexural strength of solid waste-based geopolymers with different modified aqueous nanoemulsions; Figure 2 This invention relates to the water absorption rate of solid waste-based geopolymers by adding different modified water-based nanoemulsions.

[0031] Figure 3 This invention relates to the quality of alkali-pan-oxidizing products obtained by adding different modified aqueous nanoemulsions to solid waste base geopolymers. Detailed Implementation

[0032] This invention provides a solid waste-based geopolymer, composed of components comprising the following parts by mass: 400-500 parts of fly ash; 400-500 parts of mineral powder; 40-60 parts of sodium hydroxide aqueous solution; 200-400 parts water; Nano-aqueous epoxy emulsion with a solid content of 30-62% and a particle size of 800-900 nm; Among them, nano-aqueous epoxy emulsion accounts for 3%-9% of the total mass.

[0033] The preparation method of the nano-aqueous epoxy emulsion is as follows: Step 1: Synthesizing alkali-resistant nonionic waterborne epoxy resin Equip a stirrer, thermometer, condenser, constant pressure dropping funnel, and nitrogen inlet tube to a four-necked flask. The entire process is carried out under nitrogen protection.

[0034] Add 100g of E-51 epoxy resin and 25g of MPEG-2000 to the reaction flask. Heat to 60±2°C and stir until MPEG-2000 is completely dissolved and the mixture is homogeneous.

[0035] Dissolve 0.15 g of dibutyltin dilaurate catalyst in 8 g of isophorone diisocyanate and place the solution in a dropping funnel. Slowly add the solution dropwise to the mixture at 60 ± 2°C, controlling the addition time to approximately 1 hour. After the addition is complete, raise the temperature to 80 ± 2°C and maintain the reaction temperature for 3 hours.

[0036] Maintain the temperature at 80±2°C and slowly add 5g of KH-560 silane coupling agent to the system. Continue the reaction for 2 hours. At this time, the epoxy groups of KH-560 react with the remaining small amount of -NCO or hydroxyl groups on the resin chain, introducing silane groups into the polymer chain ends.

[0037] Step 2: Conversely, emulsify. After the reaction is complete, cool the system to below 50°C. Adjust the pH of the system to 6.0 with a small amount of glacial acetic acid.

[0038] Maintain the stirring speed at 400 rpm. Preheat 160g of deionized water to 60°C.

[0039] Add hot water dropwise to the first step product at a constant and slow rate using a dropping funnel.

[0040] Initial stage (W / O type): Water is added as the dispersed phase, and the viscosity of the system gradually increases, becoming very viscous and transparent or semi-transparent.

[0041] Conversely, the inflection point occurs when the added water reaches approximately 40% of the total water volume (approximately 64g). The system viscosity suddenly and drastically decreases, and the appearance instantly changes from a transparent / paste-like consistency to a milky white, opaque liquid. This indicates that the continuous phase has transitioned from an oil phase to an aqueous phase (O / W type).

[0042] Once the reverse inflection point is reached, quickly pour in the remaining water. Immediately increase the stirring speed to 1200 rpm and continue stirring at this high speed for 30 minutes to allow the resin to be fully sheared and dispersed, forming a nanoemulsion with uniform particle size.

[0043] Stop heating and stirring, and filter the emulsion through a 200-mesh sieve to remove any trace amounts of gel particles that may be present. Cool at room temperature to obtain the final product, an alkali-resistant nano-aqueous epoxy emulsion with a particle size of 100-900 nm.

[0044] Example 1 Preparation of a solid waste-based geopolymer: The fly ash and mineral powder were thoroughly mixed at a ratio of 1:1 to obtain a uniformly mixed powder. The mixing speed was 500 r / min and the mixing time was 5 min. Sodium hydroxide was dissolved in water to prepare a 5 mol / L alkaline solution; Take 1300g (i.e., 650g each of fly ash and mineral powder) of the above uniformly mixed powder and place it in a stirring container. Add 650g of 5mol / L alkaline solution and stir at 2000r / min for 15min to allow the fly ash and mineral powder to fully react and activate. Then add 3% nano-aqueous epoxy emulsion by mass of total mass, and continue stirring at 2000 r / min for 2 min until a uniform viscous slurry is formed.

[0045] Example 2 The difference from Example 1 is the addition of 5% nano-aqueous epoxy emulsion.

[0046] Example 3 The difference from Example 1 is the addition of 7% nano-aqueous epoxy emulsion.

[0047] Example 4 The difference from Example 1 is the addition of 9% nano-aqueous epoxy emulsion.

[0048] Example 5 The difference from Example 1 is the addition of 11% nano-aqueous epoxy emulsion.

[0049] Comparative Example 1: No nano-aqueous epoxy emulsion added (0%).

[0050] Example 6: Performance Testing Flexural strength was tested according to the standard GB / T 17671-2021, "Test Method for Strength of Cement Mortar (ISO Method)". Water absorption was tested according to the standard ASTM C1585. The solid waste-based composite coating materials obtained in Examples 1-4 and the comparative example were poured into a triple mold (40 mm * 40 mm * 160 mm) to prepare 5 sets of samples. After curing in a curing room (temperature 20 ± 2℃, relative humidity ≥ 95%) for one day, the samples were demolded and cured at room temperature for 28 days. Then, flexural strength tests were performed (test results are shown in the figure). Figure 1 As shown), 5 groups (20 mm * 20 mm * 20 mm) of samples were prepared to test the water absorption rate (test results are shown in the figure). Figure 2 (As shown).

[0051] The quality test of the efflorescence product is as follows: Before the efflorescence experiment, the sample was cured under standard curing conditions for 7 days, sealed with epoxy resin on all sides, and supported by a bracket at the bottom so that the water level was about 3 mm above the bracket. After placing the sample on the bracket for 3 days, an image of the efflorescence on the sample surface was taken. The white product on the sample surface was scraped off, weighed, and characterized by XRD. The test results are as follows. Figure 3 As shown.

[0052] The test data shows that with the increase of the nano-aqueous epoxy emulsion content, the flexural strength of the material increases, while the water absorption and efflorescence continuously decrease, indicating that the nano-emulsion effectively improves the material's density and interfacial bonding ability. Simultaneously, the epoxy resin undergoes a synergistic reaction with fly ash and mineral powder hydration products under alkaline conditions, forming a denser gel structure that further fills capillary pores and enhances the matrix's impermeability and mechanical stability.

[0053] As the emulsion content in Example 5 increased, the efflorescence, flexural strength, and water absorption rate changed very little compared to Example 4, indicating that its content can play a greater role within a suitable range.

[0054] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle 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 solid waste-based geopolymer, characterized in that, The components comprise the following parts by mass: 400-500 parts of fly ash; 400-500 parts of mineral powder; 40-60 parts of sodium hydroxide aqueous solution; 200-400 parts water; Nano-aqueous epoxy emulsion with a solid content of 30-62% and a particle size of 100-900 nm; Among them, nano-aqueous epoxy emulsion accounts for 3%-9% of the total mass.

2. The solid waste-based geopolymer according to claim 1, characterized in that, The preparation method of nano-aqueous epoxy emulsion is as follows: S1. Add bisphenol A epoxy resin and polyethylene glycol monomethyl ether to the reaction flask, heat to 60±5°C, and stir until completely dissolved. S2. Dissolve the dibutyltin dilaurate catalyst in isophorone diisocyanate and slowly add it dropwise to the S1 solution at 60±5°C. After the addition is complete, raise the temperature to 80±5°C and keep the reaction at this temperature for 3±0.5 hours. S3. Slowly add silane coupling agent to the S2 system and continue the reaction for 2 ± 0.5 hours; S4. Cool the system to below 50°C and adjust the pH of the system to 6.0-6.5; preheat the deionized water to 60°±5°C and slowly add hot water dropwise to the S3 solution; S5. Maintain the stirring speed at 400-500 rpm. As hot water is added to the S4 solution, the appearance of the solution changes instantly from a transparent paste to a milky white opaque liquid. At this point, quickly pour in the remaining hot water and immediately increase the stirring speed to 1200-1500 rpm. Continue stirring at this high speed for 30±10 minutes to form a nanoemulsion with uniform particle size.

3. The solid waste-based geopolymer according to claim 2, characterized in that, The raw material ratio of the nano-aqueous epoxy emulsion is: 100 parts of bisphenol A type epoxy resin; 20-30 parts of polyethylene glycol monomethyl ether; 5-10 parts of isophorone diisocyanate; Silane coupling 3-6 parts; 0.1-2 parts of dibutyltin dilaurate; 100-200 parts of deionized water.

4. A solid waste-based geopolymer according to claim 2, characterized in that, The bisphenol A type epoxy resin is E-51 with an epoxy value of 0.51; the polyethylene glycol monomethyl ether is MPEG-2000; and the silane coupling agent is KH-560.

5. The method for preparing solid waste-based geopolymers according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Thoroughly mix fly ash and mineral powder to obtain a mixed powder; (2) Dissolve sodium hydroxide in water, pour the solution into the mixed powder and stir evenly; (3) Stir the nano-aqueous epoxy emulsion evenly, then pour it into the mixed powder and continue stirring.

6. The preparation method according to claim 5, characterized in that, In step (1), the mixing speed is 500-2000 r / min, and the mixing time is 5-15 min; In step (2), the mixing speed is 2000-3000 r / min, and the mixing time is 15-30 min; In step (3), the mixing speed is 1000-2000 r / min and the mixing time is 2-3 min.

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