Formula design method of metakaolin-based geopolymer composite cementing material

Abstract

The invention relates to a scheme design method of a metakaolin-based geopolymer composite cementing material, and belongs to the field of waste resource utilization. The problems that the geopolymer coagulation time is too short, the obdurability is low, the alkalinity is high, the cost is high, the engineering application is limited, the geopolymer is difficult to replace cement by a single precursor raw material, industrial waste is accumulated and the like due to a common alkali activator at present are solved. The preparation method comprises the following steps: firstly, preparing a geopolymer, mixing metakaolin, slag powder and silica fume to obtain precursor powder, selecting a sodium hydroxide solution to adjust the modulus of water glass, and sufficiently and uniformly mixing the materials to obtain a geopolymer cementing material; and determining the optimal formula of the geopolymer material through coagulation time determination, fluidity determination and compression and fracture resistance tests. The formula of the metakaolin-based geopolymer composite cementing material is optimized, and the obdurability of the material is improved, so that a green material capable of replacing cement is provided, the utilization problem of industrial waste is improved, and the geopolymer performance is effectively improved.

Description

Technical Field

[0001] This application is a method for formulating a metakaolin-based geopolymer composite cementitious material, belonging to the field of utilization of waste resources. Background Art

[0002] Transporting waste to landfills is one of the means of disposal. However, the waste transported to landfills is usually incinerated, but incineration also produces a large amount of carbon dioxide, which has an adverse impact on the environment.

[0003] Metakaolin is a highly reactive artificial pozzolanic material that can undergo a pozzolanic reaction to produce hydration products similar to cement. Metakaolin is formed by calcining kaolin at 500 - 800 °C to remove most of the chemically bound water by dehydroxylation, resulting in the formation of mullite minerals. By rapidly calcining metakaolin or using mechanical compaction methods, better particle morphology can be obtained, thereby reducing the water demand. Metakaolin can be used alone as a raw material for preparing geopolymers or can be mixed with materials such as fly ash, slag, and red mud. Geopolymers prepared using metakaolin have high strength, fast curing, and good workability.

[0004] Slag powder, also known as granulated blast furnace slag powder, is a solid waste obtained from the mining and smelting processes of metal minerals. The stacking of slag powder occupies a large amount of land and at the same time brings pollution risks to air, soil, and water resources, causing a heavy environmental burden. During the research process, it was found that slag, by being processed into slag powder or slag aggregates, can be used as a concrete admixture to improve the workability of concrete, enhance its durability, reduce the consumption of raw materials, lower energy consumption, and greenhouse gas emissions; using slag powder to replace part of the cement can reduce the burden on landfills and reduce waste emissions; compared with Portland cement, the energy required to produce an equal amount of slag powder is nearly 90% lower, which significantly reduces the total energy consumption of producing concrete, reduces the dependence on Portland cement, and thus reduces the extraction and consumption of raw materials.

[0005] Silica fume, also known as silicon powder or microsilica, is a by-product of industrial production processes. It has been found that silica fume has pozzolanic activity and can be used as a cement filler to improve low-temperature strength; silica fume can be used to prepare mesoporous adsorbents due to its small particle size, high activity, and high silica content; silica fume can be used as a concrete admixture to improve the compressive, flexural, and tensile strengths of concrete, reduce porosity and water absorption to enhance durability.

[0006] Geopolymer is a new type of cementitious material mainly composed of inorganic silicon-oxygen tetrahedra and aluminum-oxygen octahedra. It is polymerized from natural minerals (such as metakaolin, zeolite) and solid wastes (such as silica fume, fly ash, slag), and has a three-dimensional network structure in space. Due to its excellent physical and chemical properties, such as high strength, durability, high temperature resistance, etc., it has been widely applied and studied in many fields. Geopolymer can be used as a cementitious material to replace traditional cement for the preparation of high-performance building materials. Since Si-O and Al-O in the geopolymer network structure are difficult to react with acids (except HF acid) at room temperature, acid-resistant materials can be prepared with it. Experimental comparison shows that the acid-resistant performance of geopolymer in sulfuric acid is better than that of Portland cement. Therefore, as a green building material, geopolymer has great potential to replace traditional cementitious materials, and has received extensive attention due to its low cost, wide source and special structure.

[0007] However, although geopolymer, as a new type of inorganic cementitious material, has good environmental friendliness and excellent performance, there are still some problems and challenges in practical applications. A large amount of alkali activator needs to be added during the preparation of geopolymer to promote the hydration reaction. Currently, the commonly used alkali activator is a mixed solution of sodium silicate and sodium hydroxide. However, there are also problems such as too fast setting time, high alkalinity and high cost, which limit its application in practical engineering; during the reaction process of geopolymer, the precursor needs to have rich silicon and aluminum substances, such as fly ash, metakaolin, silica fume and slag. The content of silicon and aluminum substances often affects the synthesis of geopolymer. Similarly, the calcium source also affects the synthesis process of geopolymer. From the current research situation, a single precursor raw material is not enough to make geopolymer replace the potential of cement. Therefore, it is necessary to further study the influence of composite precursors on the geopolymer reaction process.

[0008] In view of this, this application provides a method for designing the formula of metakaolin-based geopolymer composite gel material, using metakaolin, slag powder and silica fume as precursor raw materials, and adjusting the modulus of sodium silicate with sodium hydroxide for mix ratio design. During the geopolymer reaction process, metakaolin mainly plays the role of active silicon-aluminum source and participates in the formation of the three-dimensional network structure of geopolymer. Slag powder contains active silicate and aluminate, and these components can dissolve under alkaline conditions to form active monomers of silicon and aluminum, participate in the gelation process of geopolymer, and promote the formation of the three-dimensional network structure. The addition of silica fume may affect the setting time of geopolymer. By adjusting the dosage of silica fume, the construction performance of geopolymer can be optimized, the setting time and strength of geopolymer can be improved, and the toughness of metakaolin-based geopolymer composite gel material can be enhanced. Summary of the Invention

[0009] (1) Technical Problem

[0010] The purpose of this application is to provide a method for formulating a metakaolin-based geopolymer composite cementitious material. This design method uses metakaolin, slag powder, and silica fume as composite precursor powders, and selects sodium hydroxide to adjust the modulus of sodium silicate. The two act together to improve the strength of the cementitious material and improve the setting time of the cementitious material, solving the problems that currently commonly used alkali activators cause the geopolymer to have too fast setting time, low strength and toughness, high alkalinity, high cost, limiting its engineering applications, it is difficult for a single precursor raw material to make the geopolymer replace cement, and industrial waste accumulation. Thus, the formulation of the metakaolin-based geopolymer composite cementitious material is optimized, its strength and toughness are improved, and a green material that can replace cement is provided.

[0011] (2) Technical solution

[0012] As a green material, geopolymers have great potential to replace cement in the road field. To solve the problems that currently commonly used alkali activators cause the geopolymer to have too fast setting time, low strength and toughness, high alkalinity, high cost, limiting its engineering applications, it is difficult for a single precursor raw material to make the geopolymer replace cement, and industrial waste accumulation, the technical solution adopted in this application is as follows: First, the precursor powders are selected as metakaolin, slag powder, and silica fume, and a suitable orthogonal test is designed. Four-level design orthogonal tests are carried out separately by four factors: the modulus of sodium silicate, the content of silica fume (metakaolin:slag powder = 2:1), the content of alkali activator, and the water-binder ratio (the ratio of water content to cementitious material). Among them, the modulus of sodium silicate is 1.0, 1.2, 1.4, and 1.6, the content of silica fume is 0%, 15%, 30%, and 45%, the content of alkali activator is 30%, 35%, 40%, and 45%, and the water-binder ratio is 0.3, 0.32, 0.34, and 0.36; Finally, the setting time and fluidity are measured, standard cement mortar compressive and flexural specimens are made for testing, and the best formula of the geopolymer is finally determined.

[0013] (3) Beneficial effects

[0014] This application designs the mix ratio of the metakaolin-based geopolymer, uses sodium hydroxide to adjust the modulus of sodium silicate, and explores the influence of different sodium silicate moduli on the properties of geopolymer hydration products; adopts the content of alkali activator to explore the influence of the alkali solution content on the reaction process and products of the geopolymer; adopts the factor of silica fume content to explore the influence of the addition of silica fume on the setting time, mechanical properties and other properties of the geopolymer; adopts the factor of water-binder ratio to explore the influence of water content on the geopolymer. Through multi-faceted comparative exploration, the mechanical mechanism of the geopolymer is studied, and a mix ratio design with the best performance is proposed.

[0015] This application combines waste materials with an alkali activator to convert them into a new cementitious material, which not only has good mechanical properties, impermeability and freeze-thaw resistance, but also has a simple preparation process. Metakaolin-based geopolymers prepared with metakaolin, slag powder, silica fume, water glass and sodium hydroxide as raw materials have good environmental and economic benefits. By recycling waste materials, not only the negative impact caused by the accumulation of waste materials is reduced, but also better economy is achieved, with good economic and environmental benefits. Specific implementation mode

[0016] This application provides a method for designing the formula of a metakaolin-based geopolymer composite cementitious material, and its specific implementation steps are as follows:

[0017] (1) Conduct raw material test and detection on metakaolin, slag powder, silica fume, water glass, sodium hydroxide powder and water to make the technical indicators of the raw materials meet the relevant specification technical requirements;

[0018] (2) Use the orthogonal test method to determine the optimal mix ratio of the geopolymer. An orthogonal test with four levels is designed by four factors: water glass modulus, silica fume content, alkali activator content and water-binder ratio. Among them, the water glass modulus is 1.0, 1.2, 1.4 and 1.6, the silica fume content is 0%, 15%, 30% and 45%, the alkali activator content is 30%, 35%, 40% and 45%, and the water-binder ratio is 0.3, 0.32, 0.34 and 0.36;

[0019] (3) Weigh a certain mass of sodium hydroxide and dissolve it in water to prepare a sodium hydroxide solution. Add the sodium hydroxide solution to the corresponding mass of water glass to adjust the water glass modulus to 1.0, 1.2, 1.4 and 1.6 respectively to prepare an alkali activator;

[0020] (4) Prepare a precursor powder with metakaolin, slag and silica fume according to a certain ratio. Add the alkali activator prepared in step (3) to the precursor powder, mix evenly with a mortar mixer, and use the cement paste fluidity test in the "Test Method for Homogeneity of Concrete Admixtures" (GB / T 8077-2023) to measure the fluidity of the cement paste of this metakaolin-based geopolymer, and use the setting time test in the "Test Method for Properties of Fresh Concrete" (GB / T 50080-2016) to measure the setting time of this metakaolin-based geopolymer;

[0021] (5) Repeat steps (3) and (4) to prepare metakaolin-based geopolymer, pour it into a mold of 40mm×40mm×160mm, vibrate and level it to obtain metakaolin-based geopolymer specimens, cure them in an incubator at 20°C for 1 day and then demold, and then place them in a constant temperature curing box for curing for 3 days, 7 days and 28 days respectively, and then conduct compressive and flexural tests in accordance with the "Testing Method for the Strength of Cement Mortar (ISO Method)" (GB / T 17671-2021);

[0022] (6) Based on the test results of fluidity, setting time, compressive strength and flexural strength, determine the optimal formulations of metakaolin, slag powder, silica fume and alkali activator in the metakaolin-based geopolymer composite binder, and prepare the metakaolin-based geopolymer composite binder.

Claims

1. A method for designing a formula of a metakaolin-based polymer composite cementitious material, characterized in that The specific steps of this method are as follows: (1) Conduct raw material tests on kaolin, slag powder, silica fume, water glass, sodium hydroxide powder and water to ensure that the technical indicators of the raw materials meet the relevant technical requirements; (2) The orthogonal test method was used to determine the optimal mix ratio of geopolymer. A four-level orthogonal test was conducted based on the water glass modulus, silica fume content, alkali activator content, and water-binder ratio. The water glass modulus was 1.0, 1.2, 1.4, and 1.6; the silica fume content was 0%, 15%, 30%, and 45%; the alkali activator content was 30%, 35%, 40%, and 45%; and the water-binder ratio was 0.3, 0.32, 0.34, and 0.

36. (3) weighing a certain mass of sodium hydroxide and dissolving it in water to obtain a sodium hydroxide solution, adding the sodium hydroxide solution to a corresponding mass of water glass to adjust the modulus of the water glass so that the modulus of the water glass is 1.0, 1.2, 1.4 and 1.6 respectively, to obtain an alkali activator; (4) using metakaolin, slag and silica fume in a certain ratio to prepare a precursor powder, adding the alkali activator prepared in step (3) to the precursor powder, mixing them evenly in a slurry stirring pot, using the cement slurry fluidity test in the "Concrete Admixture Homogeneity Test Method" (GB / T 8077-2023) to determine the slurry fluidity of the metakaolin-based polymer, and using the "Ordinary Concrete Mixture Performance Test Method" (GB / T 50080-2016) The setting time test is used to determine the setting time of the metakaolin-based polymer; (5) Repeat steps (3) and (4) to prepare a metakaolin-based polymer, pour it into a 40 mm × 40 mm × 160 mm mold, vibrate and smooth it to obtain a metakaolin-based polymer specimen, place it in a constant temperature box at 20° C. for curing for 1 day, then demold it, and then place it in a constant temperature curing box for curing for 3 days, 7 days and 28 days respectively, and then perform compression and flexural tests according to the "Test Method for Strength of Cement Mortar (ISO) Method" (GB / T17671-2021); (6) Based on the test results of fluidity, setting time, compression resistance and flexural strength, the optimal formula of metakaolin, slag powder, silica fume and alkali activator in the metakaolin-based polymer composite cementitious material is determined to prepare the metakaolin-based polymer composite cementitious material.