Organic composite fly ash geopolymer cementing material and preparation method thereof

Abstract

The invention provides an organic composite fly ash geopolymer cementing material and a preparation method thereof, and relates to the technical field of fly ash. According to the preparation method, an organic monomer, a redox initiator, a cross-linking agent, an accelerant and the like are subjected to in-situ polymerization in alkali-activated fly ash slurry, a multi-scale synergistic modification effect is achieved, an organic-inorganic semi-interpenetrating network structure composite cementing material is formed, and through tests of compressive strength, breaking strength, bending and the like, the strength and toughness of the fly ash composite material are improved; clean production of the fly ash composite material is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of fly ash, and particularly relates to an organic composite fly ash geopolymer cementitious material and a preparation method thereof. Background Art

[0002] Fly ash is fine ash collected from flue gas during coal combustion. Its main components are silicon dioxide, aluminum oxide, and a small amount of ferric oxide, calcium oxide, magnesium oxide, sodium oxide, sulfur oxide, etc. With the rapid development of industry, the discharge of fly ash is increasing continuously. The large amount of fly ash stacked in the open not only occupies land, but also destroys the acid-base balance of the soil, pollutes water bodies and the air, causing a heavy burden on the environment and enterprises. Geopolymer materials (slurries, mortars, concretes) are inorganic silicate-aluminate compounds, and the formation of such compounds is achieved by activating industrial wastes (such as fly ash, slag) and materials containing a large amount of two elements, Si and Al, such as metakaolin. Compared with ordinary Portland cement, as a new type of non-cement-based cementitious material, geopolymers have excellent performance and are energy-saving and environmentally friendly.

[0003] Geopolymers are made by mixing alkaline solutions (such as water glass, sodium hydroxide, etc.) with industrial wastes (such as slag, fly ash, etc.). This not only reduces the cost, realizes the recycling of industrial waste materials, but also greatly reduces the discharged waste. Domestic researchers explored the changes in the compressive strength and shrinkage performance of fly ash geopolymer concrete under different curing conditions and found that the compressive strength of fly ash geopolymer concrete showed a significant increasing trend during wrapped curing, and the shrinkage rate after dry curing was greater than that of wrapped curing. By adjusting the slag ratio, water glass modulus, and water glass dosage, the influence of different mix ratios on the performance of geopolymer concrete was studied. It was found that reducing the water glass modulus and increasing the slag ratio could both promote the formation of gel, and when the water glass dosage increased, the microstructural compactness and mechanical properties of fly ash and slag-based geopolymer concrete were significantly improved. And the alkali activator, as a chemical substance used to activate the reaction of fly ash geopolymer concrete, plays an important role in promoting the reaction of reactive silicate and aluminate in fly ash with alkaline solutions (such as sodium hydroxide, water glass, potassium hydroxide, etc.) to form a hardened geopolymer cementitious material.

[0004] However, geopolymers are heterogeneous quasi-brittle materials, with disadvantages such as low tensile strength, poor toughness, and difficulty in controlling crack width after cracking. Under the action of stress, geopolymers are prone to cracking, weakening the bearing capacity and overall stability of the structure, and ultimately leading to premature deterioration or even complete loss of service function of the overall structure. By introducing new materials with different characteristics and functions into geopolymers, several of their properties can be improved and enhanced. Obtaining some special functions while maintaining the original basic mechanical properties unchanged is one of the main trends in the development of materials science, and how to effectively modify them requires continuous research. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides an organic composite fly ash geopolymer cementitious material and its preparation method. In-situ polymerization of organic monomers, redox initiators, crosslinking agents, promoters, etc. in an alkali-activated fly ash slurry achieves multi-scale synergistic modification, forming an organic-inorganic semi-interpenetrating network structure composite cementitious material, and improving the strength and toughness of fly ash composites.

[0006] The network interpenetrating organic-inorganic composite material obtained by in-situ polymerization in fly ash or concrete not only evenly disperses organic polymers in the material, improves compatibility, but also can prepare a composite material with better compactness and enhance the toughness of the material. It is an excellent new modification method with broad application prospects. It is of great significance for promoting the development of fly ash-based new materials in China, ensuring the safety and durability of infrastructure, and saving construction investment.

[0007] One of the purposes of the present invention is to provide a preparation method of an organic composite fly ash geopolymer cementitious material.

[0008] Another purpose of the present invention is to provide an organic composite fly ash geopolymer cementitious material prepared by this preparation method.

[0009] In order to achieve the above purposes of the present invention, the following technical solutions are specifically adopted:

[0010] In the first aspect, the present invention provides a preparation method of an organic composite fly ash geopolymer cementitious material, including the following steps:

[0011] (1) Mix and stir and age sodium silicate, alkali, and deionized water to obtain an alkali activator solution; fully stir and dissolve acrylate monomers, crosslinking agents, promoters, oxidants, and deionized water to obtain an organic in-situ polymerization solution;

[0012] (2) Pour fly ash, water, and water reducer into the neat cement mixer, add the alkali activator solution, then add the organic in-situ polymerization solution, and stir to form a flowing fly ash slurry; drop the reducing agent solution into the fly ash slurry, quickly stir to mix evenly, then quickly pour the slurry into the mold, level it, cover it with plastic wrap, let it stand and then remove the mold, and dry the specimen after curing in the standard curing room to obtain the organic composite fly ash geopolymer cementitious material.

[0013] In some embodiments, in step (1), the alkali is at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide, and its addition amount is adjusted according to the modulus and Baume degree of the alkali activator, and it is directly used in the subsequent slurry after 24-hour aging. The dosage of the alkali activator solution is 10% - 40% of the mass of fly ash, and the concentration (solid content) of the alkali activator solution is 35% - 45%.

[0014] In some embodiments, in step (1), the aging time is 24h - 48h.

[0015] In some embodiments, in step (1), the acrylate monomer is at least one of acrylamide, methacrylamide, acrylic acid, methacrylic acid, dimethylaminopropyl acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid; the dosage of the acrylate monomer is 0.5% - 10% of the mass of fly ash.

[0016] In some embodiments, in step (1), the crosslinking agent is at least one of N,N'-methylenebisacrylamide, butanediol diacrylate, 1,6-hexanediol diacrylate, and polyethylene glycol diacrylate; the dosage of the crosslinking agent is 0.2% - 5% of the mass of the acrylate monomer.

[0017] In some embodiments, in step (1), the accelerator is at least one of mercaptoacetic acid, mercaptopropionic acid, tert-dodecyl mercaptan, and tetramethylethylenediamine; the dosage of the accelerator is 0.1% - 6% of the mass of the acrylate monomer.

[0018] In some embodiments, in step (1), the oxidant is at least one of ammonium persulfate, tert-butyl hydroperoxide, potassium persulfate, hydrogen peroxide, and sodium persulfate; the dosage of the oxidant is 0.5% - 10% of the mass of the acrylate monomer.

[0019] In some embodiments, in step (1), the stirring temperature of the organic in-situ polymerization solution is 25 - 35°C.

[0020] In some embodiments, in step (2), the fly ash is secondary fly ash produced from coal combustion by Lanzhou Petrochemical Company.

[0021] In some embodiments, in step (2), the water reducing agent is a retarding polycarboxylate water reducing agent, with a water reduction rate of 30% and a solid content of 35%; the dosage of the water reducing agent is 0.5% to 5% of the mass of fly ash.

[0022] In some embodiments, in step (2), the reducing agent is at least one of sodium sulfite, ascorbic acid, ferrous sulfate, sodium bisulfate, and Rongalite; the dosage of the reducing agent is 0.3% to 5% of the mass of acrylate monomers.

[0023] In some embodiments, in step (2), the relative humidity for curing is ≥95%, and the temperature is 20 ± 2°C.

[0024] In a second aspect, the present invention provides an organic composite fly ash geopolymer cementitious material prepared by the above preparation method.

[0025] Beneficial effects:

[0026] 1. In the present invention, acrylate monomers are in-situ polymerized in the fly ash paste, and the three-dimensional organic polymer network is evenly distributed in the fly ash geopolymer. The semi-interpenetrating network structure endows the material with toughness and strength functions.

[0027] 2. The present invention can achieve "zero emission" of waste during preparation. The in-situ polymerization directly in the fly ash paste enables the full utilization of organic and inorganic components, and each participates in the reaction. The process is simple, and the problem of fly ash treatment is creatively solved by chemical methods, achieving "zero emission" of waste.

[0028] 3. In the present invention, the water reducing agent has good dispersibility and dispersibility retention ability for the fly ash paste at a low dosage, and at the same time improves the strength of the composite cementitious material.

[0029] The present invention has been described in detail above, but the above embodiments are essentially illustrative and are not intended to limit the present invention. In addition, the present invention is not limited by any theory described in the foregoing prior art or the invention content or the following examples. Specific embodiments

[0030] The following examples are used to further illustrate the present invention. It should be noted that the following examples are provided for illustrative purposes only and do not constitute a limitation on the scope of protection required by the present invention.

[0031] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are all conventional raw materials, reagents, methods in the art.

[0032] The fly ash is secondary fly ash generated from coal combustion by Lanzhou Petrochemical Company.

[0033] Performance testing:

[0034] The test methods for the flexural and compressive strengths of concrete refer to the specifications GB / T 17671-2021 and GB / T 50081-2019. The size of the test specimens is 40mm×40mm×160mm. The paste is filled into the test mold in two times, and vibrated 15 times each time to remove air bubbles. After molding, the specimens are covered with a film and cured with the mold at a temperature of (20±2)°C and a humidity of >95% for 1 day, then demolded and continuously cured under standard conditions until 3 days, 7 days, and 28 days for compressive strength and flexural strength tests. The toughness test measures the flexural deflection through a three-point bending test, with a loading speed of 2mm / min.

[0035] Comparative Example 1

[0036] (1) Take 245 g of water glass with a modulus of 3.28, 3.0 g of sodium hydroxide, and add 15 mL of deionized water to a beaker with a magnetic stirrer. Stir and age for 24 hours on a magnetic stirrer.

[0037] (2) Pour 1000 g of fly ash, 250 mL of tap water, and 13.5 g of polycarboxylate water reducer (water reduction rate of 30%, solid content of 35%) into a neat paste mixer, add the alkali activator solution prepared in (1), stir slowly for 2 minutes and then stir quickly for 2 minutes to stir into a flowing fly ash paste.

[0038] (3) Quickly pour the paste into a triple steel mold of 40mm×40mm×160mm, level it with a spatula, cover it with plastic wrap, and demold after standing for 24 hours. Cure the test specimens in a standard curing room with a relative humidity of ≥95% and a temperature of 20±2°C.

[0039] It was measured that the 3-day, 7-day, and 28-day compressive strengths of the obtained fly ash geopolymer cementitious materials were 8.5 MPa, 11.6 MPa, and 13.0 MPa respectively; the 3-day, 7-day, and 28-day flexural strengths were 2.4 MPa, 3.2 MPa, and 3.4 MPa respectively, and the strength was good. The flexural deflection was 0.1 mm, and the toughness was poor.

[0040] Comparative Example 2

[0041] (1) Take 245 g of water glass with a modulus of 3.28, 3.0 g of sodium hydroxide, and add 15 mL of deionized water to a beaker with a magnetic stirrer. Stir and age for 24 hours on a magnetic stirrer.

[0042] (2) Add 15 g of acrylamide, 0.4 g of potassium persulfate, 0.3 g of N,N'-methylenebisacrylamide, 0.1 g of mercaptoacetic acid, and 50 mL of deionized water to a beaker, control the solution temperature at 35°C, and stir for 30 min until completely dissolved to obtain an organic in-situ polymerization solution.

[0043] (3) Pour 1000 g of fly ash, 250 mL of tap water, and 13.5 g of polycarboxylate water reducer (water reduction rate is 30%, solid content is 35%) into a neat cement mortar mixer, add the alkali activator solution prepared in (1), stir slowly for 2 minutes and then stir quickly for 2 minutes to stir into a flowing fly ash slurry.

[0044] (4) Quickly pour the slurry into a triple steel mold of 40 mm × 40 mm × 160 mm, level it with a spatula, cover it with plastic wrap, and demold after standing for 24 h. Cure the test blocks in a standard curing room with a relative humidity ≥ 95% and a temperature of 20 ± 2°C.

[0045] It is measured that the 3-day, 7-day, and 28-day compressive strengths of the obtained organic composite fly ash geopolymer cementitious material are 7.4 MPa, 9.8 MPa, and 10.4 MPa respectively; the 3-day, 7-day, and 28-day flexural strengths are 1.9 MPa, 2.4 MPa, and 3.0 MPa respectively, and the strength is good. The bending deflection is 0.2 mm and the toughness is poor.

[0046] Example 3

[0047] (1) Take 245 g of water glass with a modulus of 3.28, 3.0 g of potassium hydroxide, and add 15 mL of deionized water to a beaker with a magnetic stirrer, and stir and age on a magnetic stirrer for 24 hours.

[0048] (2) Add 15 g of acrylamide, 0.4 g of potassium persulfate, 0.3 g of N,N'-methylenebisacrylamide, 0.1 g of mercaptoacetic acid, and 50 mL of deionized water to a beaker, control the solution temperature at 35°C, and stir for 30 min to completely dissolve it to obtain an organic in-situ polymerization solution.

[0049] (3) Dissolve 0.5 g of ferrous sulfate in 5 mL of deionized water to form a solution.

[0050] (4) Pour 1000 g of fly ash, 250 mL of tap water, and 13.5 g of polycarboxylate water reducer into a neat cement mortar mixer, add the alkali activator solution prepared in (1), add the organic in-situ polymerization solution prepared in (2), stir slowly for 2 minutes and then stir quickly for 2 minutes to stir into a flowing fly ash slurry.

[0051] (5) Add the solution prepared in (3) to the fly ash slurry in (4), quickly stir for 0.5 minutes, then quickly pour the slurry into a triple steel mold of 40 mm × 40 mm × 160 mm, level it with a spatula, cover it with plastic wrap, and demold after standing for 24 h. Cure the test blocks in a standard curing room with a relative humidity ≥ 95% and a temperature of 20 ± 2°C.

[0052] The measured 3-day, 7-day, and 28-day compressive strengths of the obtained organic composite fly ash geopolymer cementitious material were 8.8 MPa, 11.4 MPa, and 12.9 MPa respectively; the 3-day, 7-day, and 28-day flexural strengths were 2.5 MPa, 3.3 MPa, and 3.7 MPa respectively, with good strength. The bending deflection was 1.7 mm and the toughness was good.

[0053] Example 4

[0054] (1) Take 274 g of water glass with a modulus of 3.28, 4.1 g of sodium hydroxide, add 20 mL of deionized water to a beaker with a magnetic stirrer, and stir and age for 24 hours on a magnetic stirrer;

[0055] (2) Add 10 g of acrylamide, 2 g of acrylic acid, 0.35 g of ammonium persulfate, 0.3 g of 1,6-hexanediol diacrylate, 0.2 g of mercaptopropionic acid, and 50 mL of deionized water to a beaker, control the solution temperature at 35 °C, and stir for 30 min to completely dissolve it to obtain an organic in-situ polymerization solution;

[0056] (3) Dissolve 0.3 g of ferrous sulfate in 5 mL of deionized water to form a solution;

[0057] (4) Pour 1000 g of fly ash, 250 mL of tap water, and 16 g of polycarboxylate water reducer into a mortar mixer, add the alkali activator solution prepared in (1), add the organic in-situ polymerization solution prepared in (2), stir slowly for 2 minutes and then stir quickly for 2 minutes to stir into a flowing fly ash slurry;

[0058] (5) Add the solution prepared in (3) to the fly ash slurry in (4), stir quickly for 0.5 minutes, then quickly pour the slurry into a triple steel mold of 40 mm × 40 mm × 160 mm, level it with a spatula, cover it with plastic wrap, and let it stand for 24 h before demolding. Cure the test blocks in a standard curing room with a relative humidity ≥ 95% and a temperature of 20 ± 2 °C.

[0059] The measured 3-day, 7-day, and 28-day compressive strengths of the obtained organic composite fly ash geopolymer cementitious material were 8.9 MPa, 12.0 MPa, and 13.0 MPa respectively; the 3-day, 7-day, and 28-day flexural strengths were 2.7 MPa, 3.5 MPa, and 3.8 MPa respectively, with good strength. The bending deflection was 1.4 mm and the toughness was good.

[0060] Note:

[0061] Comparative Example 1 was without the organic in-situ polymerization system, and it was only the performance of the geopolymer cementitious material formed by fly ash under the action of an alkali activator.

[0062] Comparative Example 2 is based on Comparative Example 1 and includes adding an organic in-situ polymerization solution in step (2), but not adding the reducing agent solution in step (3). After curing, a fly ash geopolymer binder material is obtained.

[0063] It was found that the toughness was poor, indicating that the lack of the reducing agent solution could not perform in-situ polymerization well.

[0064] Example 3 includes adding an organic in-situ polymerization solution in step (2) and simultaneously adding the reducing agent solution in step (3). After curing, an organic composite fly ash geopolymer binder material is obtained. Both the strength and toughness are good.

[0065] The above examples are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that: within the scope of the spirit and essence defined by the claims of the present invention, the technical solutions described in the foregoing examples can be modified, or some or all of the technical features can be equivalently replaced; and these modifications or replacements are still within the scope defined by the claims of the present invention.

Claims

1. A preparation method of an organic composite fly ash geopolymer cementitious material, characterized in that It includes the following steps: (1) Mix and stir and age sodium silicate, alkali, and deionized water to obtain an alkali activator solution; fully stir and dissolve acrylate monomers, crosslinking agents, accelerators, oxidants, and deionized water to obtain an organic in-situ polymerization solution; (2) Pour fly ash, water, and water reducer into a neat mortar mixing pan, add the alkali activator solution, and then add the organic in-situ polymerization solution, and stir to form a flowing fly ash slurry; drip a reducing agent solution into the fly ash slurry, quickly stir to mix evenly, then quickly pour the slurry into a mold, level it, cover it with plastic wrap, let it stand and then remove the mold, cure the specimen in a standard curing room and then dry it to obtain an organic composite fly ash geopolymer cementitious material.

2. The preparation method according to claim 1, wherein In step (1), the alkali is at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

3. The preparation method according to claim 1, characterized in that, In step (1), the dosage of the alkali activator solution is 10% - 40% of the mass of fly ash.

4. The preparation method according to claim 1, characterized in that, In step (1), the aging time is 24h - 48h.

5. The preparation method according to claim 1, wherein In step (1), the acrylate monomer is at least one of acrylamide, methylacrylamide, acrylic acid, methacrylic acid, dimethylaminopropyl acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid; the dosage of the acrylate monomer is 0.5% - 10% of the mass of fly ash; The crosslinking agent is at least one of N,N'-methylenebisacrylamide, butanediol diacrylate, 1,6-hexanediol diacrylate, and polyethylene glycol diacrylate; the dosage of the crosslinking agent is 0.2% - 5% of the mass of the acrylate monomer; The accelerator is at least one of mercaptoacetic acid, mercaptopropionic acid, tert-dodecyl mercaptan, and tetramethylethylenediamine; the dosage of the accelerator is 0.1% - 6% of the mass of the acrylate monomer; The oxidant is at least one of ammonium persulfate, tert-butyl hydroperoxide, potassium persulfate, hydrogen peroxide, and sodium persulfate; the dosage of the oxidant is 0.5% - 10% of the mass of the acrylate monomer.

6. The preparation method according to claim 1, characterized in that, In step (1), the stirring temperature of the organic in-situ polymerization solution is 25 - 35°C.

7. The preparation method according to claim 1, wherein, In step (2), the water reducer is a retarder polycarboxylate water reducer; the dosage of the water reducer is 0.5% - 5% of the mass of fly ash.

8. The preparation method according to claim 1, characterized in that, In step (2), the reducing agent is at least one of sodium sulfite, ascorbic acid, ferrous sulfate, sodium bisulfate, and Rongalite; the dosage of the reducing agent is 0.3% - 5% of the mass of the acrylate monomer.

9. The preparation method according to claim 1, characterized in that, In step (2), the relative humidity of curing is ≥95%, and the temperature is 20±2°C.

10. An organic composite fly ash geopolymer cementitious material, characterized in that, Prepared by the preparation method according to any one of claims 1 - 9.