A fly ash geopolymer-based photovoltaic pile and a preparation method and application thereof

Abstract

The present application relates to a kind of fly ash geopolymer-based photovoltaic pile and its preparation method and application, belong to salt alkali photovoltaic pile and solid waste resource utilization technical field.The preparation method includes the following steps: S1: using coal series kaolin to prepare metakaolin;S2: after mixing with red mud and caustic soda, high-temperature calcination is carried out, then the obtained calcination product is ground and sieved, to obtain alkali fusion material;S3: the metakaolin, the alkali fusion material and fly ash are mixed, then water is injected into mould and is shaped treatment, and photovoltaic pile is obtained after demoulding and curing.The production process of photovoltaic pile in the present application is low carbon and environmentally friendly, realizes the resource utilization of red mud and fly ash;In addition, photovoltaic pile has dense three-dimensional network structure, strong alkali resistance, salt and erosion resistance, and by adjusting liquid-solid ratio and raw material ratio, the setting time can be obviously shortened, which is beneficial to the application of photovoltaic pile in offshore and saline-alkali soil photovoltaic power generation, wind power foundation structure.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization and green building materials technology, and relates to a photovoltaic pile foundation based on fly ash geopolymer and its preparation method and application, especially to a method and application of preparing geopolymer photovoltaic pile foundation by red mud and fly ash. Background Technology

[0002] Currently, the installed capacity of offshore photovoltaic (PV) and wind power, as well as inland saline-alkali land PV, in my country continues to grow. Compared to onshore PV, offshore PV has advantages such as higher power generation, less land occupation, and easier integration with other industries; compared to onshore wind power, offshore wind power has advantages such as stable and high wind speeds, large single-unit installed capacity, and no land occupation. Therefore, offshore wind and PV power generation have broad prospects. However, the marine environment is complex and the natural conditions are harsh. The foundation structures of wind and PV power generation are submerged in seawater for a long time, making them extremely susceptible to salt spray corrosion and seawater erosion, leading to structural damage. The hydration products of ordinary silicate cement, such as calcium hydroxide and aluminosilicates, readily react with Cl- in seawater. - Ions react, causing volume changes that result in a porous structure and reduced corrosion resistance, making them unsuitable for offshore construction. Meanwhile, conventional cement concrete used for photovoltaic pile foundations in inland saline-alkali lands suffers from severe corrosion and is ill-suited to resist the erosion of various chemical media.

[0003] Geopolymers are inorganic polymers with a three-dimensional network structure composed of AlO4 and SiO4 tetrahedral structural units, and have the chemical formula M. n {-(SiO2) z -AlO2}n·wH2O, where M represents K + Na + Ca 2+ The terms are isocationic, where n represents the degree of polymerization and w represents the amount of bound water. The unique three-dimensional network structure of geopolymers determines their excellent properties of high strength and resistance to acid and alkali corrosion, thus making them promising for wide application in marine construction.

[0004] Geopolymers are inorganic materials generally prepared from aluminosilicate precursors and activators. Commonly used precursors include kaolin, fly ash, and coal gangue. Among these, fly ash has a huge annual production and contains a large amount of amorphous or non-crystalline SiO2 and Al2O3, exhibiting high cementing activity, making it the highest quality aluminosilicate precursor. However, the commonly used activator for geopolymers is liquid alkali. The transportation, storage, and use of large quantities of viscous and corrosive liquid alkali are extremely inconvenient, limiting the widespread application of geopolymers.

[0005] Bayer process red mud is a waste residue generated during the Bayer process of alumina production from bauxite, and its comprehensive utilization has always been a global challenge. Bayer process red mud is characterized by high alkalinity (pH = 11.3±1) and ultrafine particle size, making it a potential geopolymer activator. However, the utilization technology of Bayer process red mud faces bottlenecks in the preparation of cementitious materials, including large fluctuations in composition and low cementitious activity. Summary of the Invention

[0006] To address the aforementioned problems in the existing technology, this invention provides a photovoltaic pile foundation based on fly ash geopolymer and its preparation method. On the one hand, it realizes the preparation and application of high-strength, corrosion-resistant fly ash geopolymer photovoltaic pile foundations; on the other hand, it realizes the synergistic resource utilization of bulk coal-based solid waste and red mud. At the same time, the use of fly ash and red mud together enhances the component stability and gelation reaction activity in the preparation of cementitious materials.

[0007] To achieve the above objectives, the present invention adopts the following technical solution.

[0008] In a first aspect, the present invention provides a method for preparing a photovoltaic pile foundation based on fly ash geopolymer, comprising the following steps:

[0009] S1: Metakaolin was prepared using coal-series kaolin;

[0010] S2: Red mud is mixed with caustic alkali and then roasted at high temperature. The roasted product is then ground and sieved to obtain alkali-fused material. The molar ratio of SiO2 / Al2O3 in the red mud is less than 2. The caustic alkali includes at least one of sodium hydroxide and potassium hydroxide. The roasting temperature is 500℃~600℃.

[0011] S3: The metakaolin prepared in step S1 and the alkali-fused material prepared in step S2 are mixed with fly ash, and then water is added to prepare a mixture slurry. The mixture slurry is poured into a mold for molding (i.e., water injection molding), and then demolded and cured to obtain a photovoltaic pile foundation based on fly ash geopolymer.

[0012] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, step S1, the method for preparing metakaolin includes the following steps:

[0013] First, the coal-based kaolin is crushed and ground, then screened. The screened coal-based kaolin is then calcined at high temperature to obtain metakaolin.

[0014] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S1, the chemical composition of the coal-series kaolin, by mass percentage, includes 42%–50% SiO2, 42%–50% Al2O3, 0.1%–0.8% alkali metal oxides, 1.5%–2.5% Fe2O3, 0.8%–1.5% TiO2, 1.8%–2.7% SO3, and other impurities.

[0015] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, the coal-series kaolin includes coal gangue.

[0016] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S1, the particle size of the crushed coal-series kaolin is less than 1 mm.

[0017] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S1, the particle size of the coal-series kaolin obtained by sieving is less than 0.125 mm.

[0018] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, the high-temperature calcination temperature in step S1 is 700℃~800℃.

[0019] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, the high-temperature calcination time in step S1 is 3-4 hours.

[0020] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S1, the heating rate of the high-temperature calcination is 5℃ / min to 10℃ / min.

[0021] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S1, the high-temperature calcination is carried out in a muffle furnace.

[0022] In this invention, metakaolin can be prepared using conventional techniques in the field.

[0023] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, the red mud in step S2 is Bayer process red mud.

[0024] In the above method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S2, the chemical composition of the red mud, by mass percentage, includes:

[0025] 22%–25% SiO2, 24%–26% Al2O3, 8%–10% alkali metal oxides, 19%–22% alkaline earth metal oxides, 15%–18% Fe2O3, 3%–5% TiO2, 2%–4% SO3, and other impurities.

[0026] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S2, the amount of caustic alkali added (or the amount added) is 10wt% to 20wt% of the total mass of red mud and caustic alkali.

[0027] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S2, red mud and caustic alkali are mixed using a dry ball mill.

[0028] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S2, when mixing red mud with caustic alkali, the rotation speed of the ball mill is set to 200-500 rpm and the grinding time is 1-5 min.

[0029] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S2, the heating rate of the calcination is 5-10℃ / min.

[0030] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, the calcination time in step S2 is 3-4 hours.

[0031] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S2, after the high-temperature calcination is completed, the product is naturally cooled, and then the cooled calcination product is ground.

[0032] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S2, when grinding and calcining the product, the grinding speed is set to 200-500 rpm and the grinding time is 3-10 min.

[0033] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S2, sieving is performed to ensure that the particle size of the calcined product is below 0.125 mm.

[0034] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S3, the amount of alkali-fused material is 10wt% to 20wt% (e.g., 12wt%, 15wt%, or 18wt%).

[0035] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S3, the carbon content of the fly ash is less than 5% (e.g., 2%, 3%, or 4%).

[0036] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S3, the ratio of metakaolin to fly ash is controlled so that the SiO2 / Al2O3 molar ratio of the mixture is 3.5 to 4.5:1, abbreviated as 3.5 to 4.5.

[0037] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S3, the amount of water added and the liquid-solid ratio (i.e., L / S mass ratio) of the mixture are 0.3 to 0.4 (e.g., 0.32, 0.35 or 0.38).

[0038] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, step S3 includes the molding process of: pouring the mixture slurry into a mold, stirring or vibrating it, and then letting it stand to allow the mixture slurry to solidify.

[0039] In this invention, in step S3, the slurry is poured into the mold, and air bubbles in the slurry can be eliminated by stirring or vibrating.

[0040] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, step S3 includes at least one of natural curing and steam curing.

[0041] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S3, the temperature for natural curing is 18-22℃ (i.e., 20±2℃) and the humidity is 95%-98%.

[0042] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, the curing time for natural curing in step S3 is 28 days.

[0043] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S3, the temperature of steam curing is 40-80℃ and the humidity is 90%-95%.

[0044] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S3, the steam curing time is 9-15 hours.

[0045] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, in step S3, the curing is carried out using a constant temperature and humidity chamber.

[0046] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, the mold size in step S3 is 40mm*40mm*40mm.

[0047] In a second aspect, the present invention provides a photovoltaic pile foundation based on fly ash geopolymer, wherein the photovoltaic pile foundation is prepared by any of the above-described preparation methods.

[0048] A third aspect of the present invention provides an application of the above-mentioned photovoltaic pile foundation based on fly ash geopolymer, wherein the photovoltaic pile foundation based on fly ash geopolymer can be used as a special cementing material that is alkali-resistant, salt-resistant, and erosion-resistant, and can also be applied to the pile foundation structure of photovoltaic power generation and wind power in saline-alkali land, marine or tidal flats.

[0049] The above-mentioned application of photovoltaic pile foundations based on fly ash geopolymers can be used for offshore wind power and photovoltaic foundation structures, and can also be used as cement for marine construction.

[0050] The above-mentioned application of photovoltaic pile foundations based on fly ash geopolymers allows these photovoltaic pile foundations to be used as marine building cement or marine engineering cement.

[0051] In this invention, the above-mentioned technical features can be freely combined to form new technical solutions, provided they do not conflict with each other.

[0052] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0053] (1) This invention uses red mud and fly ash to prepare fly ash geopolymer photovoltaic pile foundations. It comprehensively utilizes red mud, coal-based kaolin (e.g., coal gangue), coal-based solid waste (fly ash) and other bulk solid wastes to prepare a new type of fly ash geopolymer photovoltaic pile foundation. Compared with the traditional cement production process (approximately 850 kg of carbon dioxide is emitted per ton of cement), the preparation method of the photovoltaic pile foundation based on fly ash geopolymer proposed in this invention reduces the carbon footprint, improves the utilization efficiency of bulk solid wastes, promotes the large-scale reduction and harmless disposal of bulk solid wastes from the source, and is low-carbon, green and environmentally friendly.

[0054] (2) In this invention, Bayer red mud is pretreated and then mixed with other aluminosilicate precursor materials (fly ash) to prepare geopolymers. The resulting fly ash geopolymer photovoltaic pile foundation has a dense structure. In addition, by rationally designing the dosage of alkali-fused materials, liquid-solid ratio and SiO2 / Al2O3 molar ratio, this invention enables the prepared fly ash geopolymer photovoltaic pile foundation to have high strength, fast solidification speed and excellent corrosion resistance.

[0055] (3) The fly ash geopolymer photovoltaic pile foundation prepared by the present invention can adapt to the complex natural conditions of saline-alkali land and sea, resist the scouring of seawater and salt spray corrosion, and other conditions that ordinary silicate cement cannot adapt to. Therefore, it can be used as a cement for photovoltaic / wind power pile foundation in inland saline-alkali land or marine areas. Attached Figure Description

[0056] Figure 1 This is a schematic diagram of the process for preparing photovoltaic pile foundations based on fly ash geopolymers using red mud and fly ash in accordance with the present invention. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0058] Some embodiments of the present invention provide a method for preparing a photovoltaic pile foundation based on fly ash geopolymer, comprising the following steps:

[0059] S1: Metakaolin is prepared using coal-series kaolin; specifically, the coal-series kaolin is first crushed and ground, then screened, and the screened coal-series kaolin is calcined at high temperature to obtain metakaolin.

[0060] S2: Red mud is mixed with caustic alkali and then roasted at high temperature. The roasted product is then ground and sieved to obtain alkali-fused material. The molar ratio of SiO2 / Al2O3 in the red mud is less than 2. The caustic alkali includes at least one of sodium hydroxide and potassium hydroxide. The roasting temperature is 500-600℃ (e.g., 510℃, 530℃, 550℃, 560℃ or 580℃).

[0061] S3: The metakaolin prepared in step S1 and the alkali-fused material prepared in step S2 are mixed with fly ash, and the ratio of metakaolin to fly ash is controlled so that the SiO2 / Al2O3 molar ratio of the mixture is 3.5 to 4.5:1 (e.g., 3.6:1, 3.8:1, 4:1, 4.2:1 or 4.4:1); then water is added to prepare a slurry mixture, and the slurry mixture is poured into a mold for molding (i.e., water injection molding), and then demolded and cured to obtain a photovoltaic pile foundation based on fly ash geopolymer.

[0062] In some embodiments, in step S1, the chemical composition of the coal-series kaolin includes, by mass percentage, 42%–50% SiO2, 42%–50% Al2O3, 0.1%–0.8% alkali metal oxides, 1.5%–2.5% Fe2O3, 0.8%–1.5% TiO2, 1.8%–2.7% SO3, and other impurities.

[0063] In some embodiments, the coal-bearing kaolinite includes coal gangue.

[0064] In some embodiments, in step S1, the particle size of the crushed coal-series kaolin is less than 1 mm, and the particle size of the sieved coal-series kaolin is less than 0.125 mm.

[0065] In some embodiments, in step S1, the high-temperature calcination temperature is 700℃~800℃ (e.g., 710℃, 730℃, 750℃, 760℃ or 780℃); the time is 3~4h (e.g. 3.5h); and the heating rate is 5℃ / min~10℃ / min (e.g. 6℃ / min or 8℃ / min).

[0066] In some embodiments, in step S2, the red mud is Bayer process red mud.

[0067] In some embodiments, in step S2, the chemical composition of the red mud, by mass percentage, includes: SiO2 22%–25%, Al2O3 24%–26%, alkali metal oxides 8%–10%, alkaline earth metal oxides 19%–22%, Fe2O3 15%–18%, TiO2 3%–5%, SO3 2%–4%, and other impurities.

[0068] In some embodiments, in step S2, the amount of caustic alkali added (or the amount added) is 10wt% to 20wt% of the total mass of red mud and caustic alkali (e.g., 12wt%, 15wt% or 18wt%).

[0069] In this invention, the geopolymer reaction mechanism is that the aluminosilicate precursor dissolves in a highly alkaline environment to form silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra, and undergoes a condensation reaction under the action of an activator to form a network-structured polymer, while simultaneously expelling water and hardening rapidly.

[0070] In this invention, although the red mud contains SiO2 and Al2O3, the Bayer process red mud is a waste residue generated during the Bayer process of producing alumina from bauxite. The SiO2 and Al2O3 that are soluble in an alkaline environment have already been largely dissolved during the Bayer process. Therefore, directly using Bayer process red mud to prepare geopolymers results in very little SiO2 and Al2O3 being dissolved and participating in the reaction, leading to poor activity of the Bayer process red mud. Activation is necessary to improve the leaching rate of SiO2 and Al2O3.

[0071] In some embodiments, in step S2, a dry ball mill is used to mix the red mud with the caustic alkali; when mixing the red mud with the caustic alkali, the rotation speed of the ball mill is set to 200-500 rpm (e.g., 300 rpm, 400 rpm or 450 rpm), and the grinding time is 1-5 min (e.g., 2 min, 3 min or 4 min).

[0072] In some embodiments, in step S2, the heating rate is 5-10°C / min (e.g., 6°C / min or 8°C / min); the calcination time is 3-4 h (e.g., 3.5 h).

[0073] In this invention, caustic alkali readily absorbs water in atmospheric conditions, making it difficult to preserve. The purpose of high-temperature roasting of red mud mixed with caustic alkali is to decompose the original silicate and aluminate phases in the red mud, promoting the formation of new compounds (i.e., aluminosilicate products). However, excessively high roasting temperatures can lead to sintering, causing the aluminosilicate products in the red mud to sinter and transform into more stable anorthite, resulting in a decrease in the leaching rate of SiO2 and Al2O3 in the caustic alkali. Furthermore, it also causes energy consumption and increases preparation costs. Therefore, this invention limits the high-temperature roasting temperature to 500–600°C. At this temperature, the structure of the red mud undergoes a transformation, forming an aluminosilicate product structure.

[0074] This invention involves mixing red mud with caustic alkali and then calcining it at high temperature to obtain an alkali-fused material (i.e., pre-treating the red mud); then, metakaolin, the alkali-fused material, and fly ash are mixed to prepare a geopolymer. The high-temperature calcination of the red mud with caustic alkali disrupts the structure of the silicon and aluminum minerals in the red mud, increasing their activity. The presence of caustic alkali facilitates the depolymerization of silicon and aluminum minerals in an alkaline environment, forming silicon-oxygen monomers and aluminum-oxygen monomers, which are beneficial for their participation in the geopolymer reaction process.

[0075] Generally, after high-temperature roasting, red mud requires activation with water glass or alkaline solution to obtain hydraulic properties. Using the high-temperature roasting method of red mud and caustic alkali of this invention, the presence of caustic alkali allows the roasted product to directly obtain hydraulic properties, eliminating the need for activation with water glass or alkaline solution; that is, by mixing red mud and caustic alkali and then performing high-temperature roasting, the resulting roasted product can obtain hydraulic properties without activation with water glass or alkaline solution.

[0076] In some embodiments, in step S2, after the high-temperature roasting is completed, the product is naturally cooled and then ground. When grinding the product, the grinding speed is set to 200-500 rpm and the grinding time is 3-10 min (e.g., 5 min or 8 min).

[0077] In some embodiments, in step S2, sieving is performed to reduce the particle size of the calcined product to below 0.125 mm.

[0078] In some embodiments, in step S3, the amount of alkali-fused material is 10wt% to 20wt% (e.g., 12wt%, 15wt%, or 18wt%).

[0079] In this invention, if the amount of alkali-fused material is too low, the reaction will be insufficient; if the amount is too high, the residual alkali will react with CO2 in the air to form carbonates, affecting the strength.

[0080] Fly ash is characterized by its high stability in chemical composition and high gelling reactivity. It is an ideal raw material for the preparation of geopolymers in conjunction with red mud, which is beneficial to improving the compositional stability and gelling reactivity of red mud in the process of preparing gelling materials.

[0081] In some embodiments, in step S3, the carbon content of the fly ash is less than 5% (e.g., 2%, 3%, or 4%).

[0082] In this invention, excessively high carbon content in the fly ash leads to high brittleness and poor flexural strength in the final product, the photovoltaic pile foundation based on fly ash geopolymer. Therefore, the carbon content of the fly ash is controlled to be less than 5%.

[0083] This invention introduces a large amount of aluminosilicates into the preparation of geopolymer cement by limiting the SiO2 / Al2O3 molar ratio of the mixture. The resulting geopolymer can absorb a large amount of alkali metal ions, which can greatly weaken the alkali-aggregate reaction. Therefore, compared with ordinary cement pile foundations, the photovoltaic pile foundation based on fly ash geopolymer prepared according to the method of this invention has better durability and acid and alkali corrosion resistance, that is, enhanced corrosion resistance.

[0084] In this invention, the geopolymer reaction mechanism is as follows: metakaolin and fly ash dissolve in a highly alkaline environment to form silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra, and undergo a condensation reaction under the action of an activator in the alkali-fused material to form a network-structured polymer. Simultaneously, water is discharged and the polymer hardens rapidly to prepare a photovoltaic pile foundation based on fly ash geopolymer. The highly alkaline environment is provided by the alkali-fused material obtained through high-temperature roasting of red mud and caustic alkali. This alkali-fused material contains aluminosilicate structural substances, which facilitates the condensation reaction, resulting in a more complex network-structured polymer. This improves the density of the photovoltaic pile foundation product based on fly ash geopolymer, reduces its internal porosity and average porosity, thereby reducing the permeability of the photovoltaic pile foundation product based on fly ash geopolymer and enhancing its resistance to seawater erosion.

[0085] In some embodiments, in step S3, the amount of water added is 0.3 to 0.4 (e.g., 0.32, 0.35 or 0.38) relative to the liquid-to-solid ratio (L / S mass ratio) of the mixture.

[0086] In this invention, if the amount of water added is too low, it is difficult to form a slurry; if the amount of water added is too high, it will prolong the setting time and reduce the strength of the photovoltaic pile foundation product based on fly ash geopolymer. If the liquid-to-solid ratio is higher than the above-mentioned range, on the one hand, the slurry will be difficult to solidify and harden; on the other hand, water loss during the curing process will cause a large number of pores to form in the photovoltaic pile foundation based on fly ash geopolymer, affecting the final strength. Therefore, this invention optimizes the setting time of the photovoltaic pile foundation based on fly ash geopolymer by limiting the liquid-to-solid ratio, thereby ensuring the strength of the photovoltaic pile foundation product based on fly ash geopolymer. In addition, compared with the photovoltaic pile foundation sample based on fly ash geopolymer prepared with a high liquid-to-solid ratio, the photovoltaic pile foundation sample based on fly ash geopolymer prepared with a low liquid-to-solid ratio in this invention exhibits better resistance to Cl. - Ion corrosion resistance.

[0087] In some embodiments, step S3 includes the molding process comprising: pouring the mixture slurry into a mold, stirring or vibrating it, and then allowing it to stand to form the mixture slurry.

[0088] In this invention, in step S3, the slurry is poured into the mold, and air bubbles in the slurry can be eliminated by stirring or vibrating.

[0089] In some embodiments, step S3 includes at least one of natural curing and steam curing.

[0090] In some embodiments, in step S3, the temperature for natural curing is 18-22℃ (i.e., 20±2℃), the humidity is 95%-98%, and the curing time is 28 days.

[0091] In this invention, 28 days is the international standard maintenance time in the field. Those skilled in the art can also choose other maintenance times. This invention does not specifically limit the time for natural maintenance.

[0092] In some embodiments, in step S3, the steam curing temperature is 40–80°C, the humidity is 90%–95%, and the curing time is 9–15 hours.

[0093] In the above-mentioned method for preparing photovoltaic pile foundations based on fly ash geopolymers, the mold size in step S3 is 40mm*40mm*40mm.

[0094] In this invention, the mold size is determined to be 40mm*40mm*40mm according to the size of the specimen used for testing compressive strength in GB / T 17671-2021 Cement Mortar Strength Test Method (ISO Method); those skilled in the art may also choose other sizes of molds according to actual needs, and this invention does not specifically limit the mold size.

[0095] Some embodiments of the present invention also provide a photovoltaic pile foundation based on fly ash geopolymer, wherein the photovoltaic pile foundation is prepared by any of the above-described preparation methods.

[0096] Some embodiments of the present invention also provide an application of the above-mentioned photovoltaic pile foundation based on fly ash geopolymer. The photovoltaic pile foundation based on fly ash geopolymer can be used as a special cementing material that is alkali-resistant, salt-resistant, and erosion-resistant, and can also be applied to the pile foundation structure of photovoltaic power generation and wind power in saline-alkali land, marine or tidal flats.

[0097] In some embodiments, the fly ash-based photovoltaic pile foundation can be used for offshore wind power and photovoltaic foundation structures, and can also be used as marine building cement.

[0098] The photovoltaic pile foundation based on fly ash geopolymer prepared according to the method of the present invention has the following advantages compared with ordinary silicate cement pile foundation: First, the production process of fly ash geopolymer photovoltaic pile foundation reduces carbon emissions and realizes the resource utilization of solid waste, making it green and environmentally friendly. Second, the geopolymer has a dense three-dimensional network structure, which has stronger resistance to seawater erosion. Furthermore, by appropriately adjusting the liquid-solid ratio and raw material ratio, the solidification time can be significantly shortened, which is beneficial for the application of photovoltaic pile foundation in the foundation structure of offshore photovoltaic power generation and wind power.

[0099] According to GB / T31289-2014 "Marine Silicate Cement", the setting time of photovoltaic pile foundation samples based on fly ash aggregates is tested according to GB / T1346-2011 "Standard Consistency Water Requirement, Setting Time and Soundness Test Analysis of Cement"; the strength is tested according to GB / T17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)"; and the chloride ion diffusion coefficient is tested according to JC / T1086 "Test Method for Chloride Ion Diffusion Coefficient of Cement". According to GB / T31289-2014, for marine silicate cement, the initial setting time should not be earlier than 45 minutes and the final setting time should not be later than 600 minutes; the chloride ion diffusion coefficient of marine silicate cement at 28 days should not exceed 1.5*10. -12 m 2 / s.

[0100] Example 1

[0101] A method for preparing a photovoltaic pile foundation based on fly ash geopolymer includes the following steps.

[0102] S1. Preparation of metakaolin from coal-based kaolin: First, crush the coal-based kaolin with the chemical composition shown in Table 1 to a particle size of less than 1 mm, grind it, and then sieve it to a particle size of less than 0.125 mm. Then, put it into a muffle furnace for high-temperature calcination at a heating rate of 10℃ / min, a calcination temperature of 700℃, and a calcination time of 3 h. After natural cooling, take it out to obtain metakaolin.

[0103] Table 1 Chemical composition of coal-series kaolin

[0104]

[0105] S2. Preparation of alkali-fused material using red mud: Red mud with the chemical composition shown in Table 2 was mixed with NaOH at a mass ratio of 85wt%:15wt%. A dry ball mill was set at 300 rpm for 3 minutes to ensure uniform mixing of the red mud and NaOH. The mixture was then placed in a muffle furnace for high-temperature calcination at a heating rate of 10℃ / min, a calcination temperature of 550℃, and a calcination time of 3 hours. After calcination, the mixture was allowed to cool naturally, and the calcined product was removed and ground using a ball mill at 300 rpm for 5 minutes. The ground material was then sieved, and the sieve material with a particle size below 0.125 mm was collected to obtain the alkali-fused material. Table 2 shows the chemical composition of the red mud.

[0106] Table 2 Chemical composition of red mud

[0107]

[0108]

[0109] S3. Preparation of photovoltaic pile foundation based on fly ash geopolymer using fly ash: Add 10wt% alkali-fused material, adjust the ratio of metakaolin to fly ash to control the SiO2 / Al2O3 molar ratio in the mixture to be 3.5:1 (abbreviated as 3.5), add water to make the liquid-solid ratio (i.e., the mass ratio of total water to mixture) 0.3, stir for 5 min to obtain a mixed slurry, pour the mixed slurry into a mold with a size of 40mm*40mm*40mm, vibrate to defoam for 5 min, demold after one day and allow for natural curing; the natural curing temperature is 18-22℃, the humidity is 95%-98%, and the curing time is 28 days to obtain a photovoltaic pile foundation test sample based on fly ash geopolymer.

[0110] Table 3 shows the formulation design and performance test results of the photovoltaic pile foundations based on fly ash geopolymers prepared in various embodiments and comparative examples of the present invention. Table 4 shows the strength grade standard of GB / T 31289-2014 "Marine Silicate Cement".

[0111] Table 3. Formulation design and performance test results of photovoltaic pile foundations based on fly ash geopolymers

[0112]

[0113]

[0114] Table 4 Strength values ​​of marine silicate cement

[0115]

[0116] As shown in Table 3, the photovoltaic pile foundation samples based on fly ash geopolymer prepared in this embodiment had an initial setting time of 62 min and a final setting time of 312 min; a 3-day compressive strength of 17.79 MPa; a 28-day compressive strength of 35.96 MPa; and a chloride ion diffusion coefficient of 0.9 × 10⁻⁶. -12 It meets the requirements for setting time, strength, and chloride ion diffusion coefficient of grade 32.5 marine silicate cement as specified in GB / T 31289-2014 "Marine Silicate Cement".

[0117] Example 2

[0118] A method for preparing a photovoltaic pile foundation based on fly ash geopolymer includes the following steps.

[0119] S1. Preparation of metakaolin from coal-based kaolin: First, the coal-based kaolin is crushed to a particle size of less than 1 mm, ground, and then sieved to a particle size of less than 0.125 mm. It is then placed in a muffle furnace for high-temperature calcination at a heating rate of 10℃ / min, a calcination temperature of 700℃, and a calcination time of 3 h. After natural cooling, it is taken out to obtain metakaolin. The chemical composition of the coal-based kaolin is shown in Table 1.

[0120] S2. Preparation of alkali-fused material using red mud: Red mud with the chemical composition shown in Table 2 was mixed with NaOH at a mass ratio of 85wt%:15wt%. The dry ball mill was set at a speed of 300 rpm for 3 minutes to ensure uniform mixing of the red mud and NaOH. The mixture was then placed in a muffle furnace for high-temperature calcination, with a heating rate of 10℃ / min, a calcination temperature of 550℃, and a calcination time of 3 hours. After calcination, the mixture was allowed to cool naturally, and the calcined product was removed and ground using a ball mill at a speed of 300 rpm for 5 minutes. The ground material was then sieved, and the sieve material with a particle size of less than 0.125 mm was collected to obtain the alkali-fused material. Table 2 shows the chemical composition of the red mud.

[0121] S3. Preparation of photovoltaic pile foundation based on fly ash geopolymer using fly ash: 10wt% alkali-fused material was added, and the ratio of metakaolin to fly ash was adjusted to control the SiO2 / Al2O3 molar ratio of the mixture to be 4. Water was added to make the liquid-solid ratio 0.4. The mixture was stirred for 5 minutes to obtain a mixed slurry. The mixed slurry was poured into a mold with a size of 40mm*40mm*40mm, and the mold was vibrated to defoam for 5 minutes. After one day, the mold was removed and allowed to cure naturally. The natural curing temperature was 20±2℃, the humidity was 95-98%, and the curing time was 28 days to obtain a photovoltaic pile foundation sample based on fly ash geopolymer.

[0122] The test results showed that the initial setting time of the photovoltaic pile foundation sample based on fly ash geopolymer was 94 min, and the final setting time was 475 min; the 3-day compressive strength was 14.84 MPa; the 28-day compressive strength was 33.21 MPa; and the chloride ion diffusion coefficient was 1.4 × 10⁻⁶. -12 It meets the requirements for setting time, strength, and chloride ion diffusion coefficient of grade 32.5 marine silicate cement as specified in GB / T31289-2014 "Marine Silicate Cement".

[0123] Example 3

[0124] A method for preparing a photovoltaic pile foundation based on fly ash geopolymer includes the following steps.

[0125] S1. Preparation of metakaolin from coal-based kaolin: First, the coal-based kaolin is crushed to a particle size of less than 1 mm, ground, and then sieved to a particle size of less than 0.125 mm. It is then placed in a muffle furnace for high-temperature calcination at a heating rate of 10℃ / min, a calcination temperature of 700℃, and a calcination time of 3 h. After natural cooling, it is taken out to obtain metakaolin. The chemical composition of the coal-based kaolin is shown in Table 1.

[0126] S2. Preparation of Alkali-Fused Material from Red Mud: Red mud with the chemical composition shown in Table 2 was mixed with NaOH at a mass ratio of 85wt%:15wt%. The dry ball mill was set at a speed of 300 rpm for 3 min to ensure uniform mixing of the red mud and NaOH. Then, the mixture was placed in a muffle furnace for high-temperature calcination at a heating rate of 10℃ / min, a calcination temperature of 550℃, and a calcination time of 3 h. After calcination, the mixture was allowed to cool naturally, and the calcined product was removed and ground using a ball mill at a speed of 300 rpm for 5 min. The ground material was then sieved, and the sieved material with a particle size of less than 0.125 mm was collected to obtain the alkali-fused material.

[0127] S3. Preparation of photovoltaic pile foundation based on fly ash geopolymer using fly ash: 10wt% of alkali-fused material was added, and the ratio of metakaolin to fly ash was adjusted to control the SiO2 / Al2O3 molar ratio in the mixture to be 4.5:1 (abbreviated as 4.5). Water was added to make the liquid-solid ratio 0.35, and the mixture was stirred for 5 minutes to obtain a mixed slurry. The mixed slurry was poured into a mold with a size of 40mm*40mm*40mm, and the mold was vibrated to defoam for 5 minutes. After one day, the mold was removed and allowed to cure naturally. The natural curing temperature was 20±2℃, the humidity was 95%~98%, and the curing time was 28 days to obtain a photovoltaic pile foundation sample based on fly ash geopolymer.

[0128] Tests showed that the initial setting time of the photovoltaic pile foundation sample based on fly ash geopolymer was 75 min, and the final setting time was 374 min; the 3-day compressive strength was 16.38 MPa; the 28-day compressive strength was 34.84 MPa; and the chloride ion diffusion coefficient was 1.1*10⁻⁶. -12 It meets the requirements of GB / T31289-2014 "Marine Silicate Cement" for the setting time, strength and chloride ion diffusion coefficient of grade 32.5 marine silicate cement.

[0129] Example 4

[0130] A method for preparing a photovoltaic pile foundation based on fly ash geopolymer includes the following steps.

[0131] S1. Preparation of metakaolin from coal-based kaolin: First, the coal-based kaolin is crushed to a particle size of less than 1 mm, ground, and then sieved to a particle size of less than 0.125 mm. It is then placed in a muffle furnace for high-temperature calcination at a heating rate of 10℃ / min, a calcination temperature of 700℃, and a calcination time of 3 h. After natural cooling, it is taken out to obtain metakaolin. The chemical composition of the coal-based kaolin is shown in Table 1.

[0132] S2. Preparation of alkali-fused material using red mud: Red mud with the chemical composition shown in Table 2 is mixed with NaOH at a mass ratio of 85wt%:15wt%. The dry ball mill is set to a speed of 300 rpm and the mixture is ground for 3 minutes to ensure uniform mixing of the red mud and NaOH. Then, the mixture is placed in a muffle furnace for high-temperature calcination. The heating rate is 10℃ / min, the calcination temperature is 550℃, and the calcination time is 3 hours. After calcination, the mixture is allowed to cool naturally, and the calcined product is removed and ground using a ball mill. The ball mill speed is set to 300 rpm and the grinding time is 5 minutes. The ground material is then sieved, and the sieved material with a particle size of less than 0.125 mm is obtained.

[0133] S3. Preparation of photovoltaic pile foundation based on fly ash geopolymer using fly ash: 15wt% alkali-fused material was added, and the ratio of metakaolin to fly ash was adjusted to control the SiO2 / Al2O3 molar ratio of the mixture to be 3.5. Water was added to make the liquid-solid ratio 0.4. The mixture was stirred for 5 minutes to obtain a mixed slurry. The mixed slurry was poured into a mold with a size of 40mm*40mm*40mm, and the mold was vibrated to defoam for 5 minutes. After one day, the mold was removed and natural curing was carried out. The natural curing temperature was 20±2℃, the humidity was 95%~98%, and the curing time was 28 days to obtain a photovoltaic pile foundation sample based on fly ash geopolymer.

[0134] The test results showed that the initial setting time of the photovoltaic pile foundation sample based on fly ash geopolymer was 86 min, and the final setting time was 446 min; the 3-day compressive strength was 18.30 MPa; the 28-day compressive strength was 36.73 MPa; and the chloride ion diffusion coefficient was 1.3*10⁻⁶. -12 It meets the requirements of GB / T 31289-2014 "Marine Silicate Cement" for setting time, strength and chloride ion diffusion coefficient of grade 32.5 marine silicate cement.

[0135] Example 5

[0136] A method for preparing a photovoltaic pile foundation based on fly ash geopolymer includes the following steps.

[0137] S1. Preparation of metakaolin from coal-based kaolin: First, the coal-based kaolin is crushed to a particle size of less than 1 mm, ground, and then sieved to a particle size of less than 0.125 mm. It is then placed in a muffle furnace for high-temperature calcination at a heating rate of 10℃ / min, a calcination temperature of 700℃, and a calcination time of 3 h. After natural cooling, it is taken out to obtain metakaolin. The chemical composition of the coal-based kaolin is shown in Table 1.

[0138] S2. Preparation of alkali-fused material using red mud: Red mud with the chemical composition shown in Table 2 is mixed with NaOH at a mass ratio of 85wt%:15wt%. The dry ball mill is set to a speed of 300 rpm and the mixture is ground for 3 minutes to ensure uniform mixing of the red mud and caustic alkali. Then, the mixture is placed in a muffle furnace for high-temperature calcination at a heating rate of 10℃ / min, a calcination temperature of 550℃, and a calcination time of 3 hours. After calcination, the mixture is allowed to cool naturally, and the calcined product is then removed and ground using a ball mill at a speed of 300 rpm for 5 minutes. The ground material is then sieved, and the sieved material with a particle size of less than 0.125 mm is obtained.

[0139] S3. Preparation of photovoltaic pile foundation based on fly ash geopolymer using fly ash: 15wt% alkali-fused material was added, and the ratio of metakaolin to fly ash was adjusted to control the SiO2 / Al2O3 molar ratio in the mixture to be 4. Water was added to make the liquid-solid ratio 0.35. The mixture was stirred for 5 minutes to obtain a mixed slurry. The mixed slurry was poured into a mold with a size of 40mm*40mm*40mm, and the mold was vibrated to defoam for 5 minutes. After one day, the mold was removed and allowed to cure naturally. The natural curing temperature was 20±2℃, the humidity was 95%~98%, and the curing time was 28 days to obtain a photovoltaic pile foundation sample based on fly ash geopolymer.

[0140] The photovoltaic pile foundation sample based on fly ash geopolymer showed an initial setting time of 69 min and a final setting time of 356 min; a 3-day compressive strength of 22.82 MPa; a 28-day compressive strength of 39.68 MPa; and a chloride ion diffusion coefficient of 9.1 × 10⁻⁶. -13 It meets the requirements of GB / T31289-2014 "Marine Silicate Cement" for the setting time, strength and chloride ion diffusion coefficient of grade 32.5 marine silicate cement.

[0141] Example 6

[0142] A method for preparing a photovoltaic pile foundation based on fly ash geopolymer includes the following steps.

[0143] S1. Preparation of metakaolin from coal-based kaolin: First, the coal-based kaolin is crushed to a particle size of less than 1 mm, ground, and then sieved to a particle size of less than 0.125 mm. It is then placed in a muffle furnace for high-temperature calcination at a heating rate of 10℃ / min, a calcination temperature of 700℃, and a calcination time of 3 h. After natural cooling, it is taken out to obtain metakaolin. The chemical composition of the coal-based kaolin is shown in Table 1.

[0144] S2. Preparation of alkali-fused material using red mud: Red mud with the chemical composition shown in Table 2 is mixed with NaOH at a mass ratio of 85wt%:15wt%. The dry ball mill is set to a speed of 300 rpm and the mixture is ground for 3 minutes to ensure uniform mixing of the red mud and NaOH. Then, the mixture is placed in a muffle furnace for high-temperature calcination. The heating rate is 10℃ / min, the calcination temperature is 550℃, and the calcination time is 3 hours. After calcination, the mixture is allowed to cool naturally, and the calcined product is removed and ground using a ball mill. The ball mill speed is set to 300 rpm and the grinding time is 5 minutes. The ground material is then sieved, and the sieved material with a particle size of less than 0.125 mm is obtained.

[0145] S3. Preparation of photovoltaic pile foundation based on fly ash geopolymer using fly ash: 15wt% alkali-fused material was added, and the ratio of metakaolin to fly ash was adjusted to control the SiO2 / Al2O3 molar ratio of the mixture to be 4.5. Water was added to make the liquid-solid ratio 0.3. The mixture was stirred for 5 minutes to obtain a mixed slurry. The mixed slurry was poured into a mold with a size of 40mm*40mm*40mm, and the mold was vibrated to defoam for 5 minutes. After one day, the mold was removed and allowed to cure naturally. The natural curing temperature was 20±2℃, the humidity was 95-98%, and the curing time was 28 days to obtain a photovoltaic pile foundation sample based on fly ash geopolymer.

[0146] The test results showed that the initial setting time of the photovoltaic pile foundation sample based on fly ash geopolymer was 57 min, and the final setting time was 281 min; the 3-day compressive strength was 26.35 MPa; the 28-day compressive strength was 45.36 MPa; and the chloride ion diffusion coefficient was 5.8 × 10⁻⁶. -13 It meets the requirements of GB / T31289-2014 "Marine Silicate Cement" for setting time, strength and chloride ion diffusion coefficient of grade 42.5 marine silicate cement.

[0147] Example 7

[0148] A method for preparing a photovoltaic pile foundation based on fly ash geopolymer includes the following steps.

[0149] S1. Preparation of metakaolin from coal-based kaolin: First, the coal-based kaolin is crushed to a particle size of less than 1 mm, ground, and then sieved to a particle size of less than 0.125 mm. It is then placed in a muffle furnace for high-temperature calcination at a heating rate of 10℃ / min, a calcination temperature of 700℃, and a calcination time of 3 h. After natural cooling, it is taken out to obtain metakaolin. The chemical composition of the coal-based kaolin is shown in Table 1.

[0150] S2. Preparation of alkali-fused material using red mud: Red mud with the chemical composition shown in Table 2 is mixed with NaOH at a mass ratio of 85wt%:15wt%. The dry ball mill is set to a speed of 300 rpm and the mixture is ground for 3 minutes to ensure uniform mixing of the red mud and NaOH. Then, the mixture is placed in a muffle furnace for high-temperature calcination. The heating rate is 10℃ / min, the calcination temperature is 550℃, and the calcination time is 3 hours. After calcination, the mixture is allowed to cool naturally, and the calcined product is removed and ground using a ball mill. The ball mill speed is set to 300 rpm and the grinding time is 5 minutes. The ground material is then sieved, and the sieved material with a particle size of less than 0.125 mm is obtained.

[0151] S3. Preparation of photovoltaic pile foundation based on fly ash geopolymer using fly ash: 20wt% alkali-fused material was added, and the ratio of metakaolin to fly ash was adjusted to control the SiO2 / Al2O3 molar ratio of the mixture to be 3.5. Water was added to make the liquid-solid ratio 0.35. The mixture was stirred for 5 minutes to obtain a mixed slurry. The mixed slurry was poured into a mold with a size of 40mm*40mm*40mm, and the mold was vibrated to defoam for 5 minutes. After one day, the mold was removed and natural curing was carried out. The natural curing temperature was 20±2℃, the humidity was 95%~98%, and the curing time was 28 days to obtain a photovoltaic pile foundation sample based on fly ash geopolymer.

[0152] The initial setting time of the photovoltaic pile foundation sample based on fly ash geopolymer was tested to be 61 min, and the final setting time was 308 min; the 3-day compressive strength was 24.45 MPa; the 28-day compressive strength was 42.89 MPa; and the chloride ion diffusion coefficient was 6.9 × 10⁻⁶. -13 It meets the requirements of GB / T31289-2014 "Marine Silicate Cement" for setting time, strength and chloride ion diffusion coefficient of grade 42.5 marine silicate cement.

[0153] Example 8

[0154] A method for preparing a photovoltaic pile foundation based on fly ash geopolymer includes the following steps.

[0155] S1. Preparation of metakaolin from coal-based kaolin: First, the coal-based kaolin is crushed to a particle size of less than 1 mm, ground, and then sieved to a particle size of less than 0.125 mm. It is then placed in a muffle furnace for high-temperature calcination at a heating rate of 10℃ / min, a calcination temperature of 700℃, and a calcination time of 3 h. After natural cooling, it is taken out to obtain metakaolin. The chemical composition of the coal-based kaolin is shown in Table 1.

[0156] S2. Preparation of alkali-fused material using red mud: Red mud with the chemical composition shown in Table 2 is mixed with NaOH at a mass ratio of 85wt%:15wt%. The dry ball mill is set to a speed of 300 rpm and the mixture is ground for 3 minutes to ensure uniform mixing of the red mud and NaOH. Then, the mixture is placed in a muffle furnace for high-temperature calcination. The heating rate is 10℃ / min, the calcination temperature is 550℃, and the calcination time is 3 hours. After calcination, the mixture is allowed to cool naturally, and the calcined product is removed and ground using a ball mill. The ball mill speed is set to 300 rpm and the grinding time is 5 minutes. The ground material is then sieved, and the sieved material with a particle size of less than 0.125 mm is obtained.

[0157] S3. Preparation of photovoltaic pile foundation based on fly ash geopolymer using fly ash: 20wt% alkali-fused material was added, and the ratio of metakaolin to fly ash was adjusted to control the SiO2 / Al2O3 molar ratio in the mixture to be 4. Water was added to make the liquid-solid ratio 0.3. The mixture was stirred for 5 minutes to obtain a mixed slurry. The mixed slurry was poured into a mold with a size of 40mm*40mm*40mm, and the mold was vibrated to defoam for 5 minutes. After one day, the mold was removed and natural curing was carried out. The natural curing temperature was 20±2℃, the humidity was 95%~98%, and the curing time was 28 days to obtain a photovoltaic pile foundation sample based on fly ash geopolymer.

[0158] The test results showed that the initial setting time of the photovoltaic pile foundation sample based on fly ash geopolymer was 49 min, and the final setting time was 254 min; the 3-day compressive strength was 32.43 MPa; the 28-day compressive strength was 54.95 MPa; and the chloride ion diffusion coefficient was 2.5 × 10⁻⁶. -13 It meets the requirements of GB / T31289-2014 "Marine Silicate Cement" for setting time, strength and chloride ion diffusion coefficient of grade 42.5 marine silicate cement.

[0159] Example 9

[0160] A method for preparing a photovoltaic pile foundation based on fly ash geopolymer includes the following steps.

[0161] S1. Preparation of metakaolin from coal-based kaolin: First, the coal-based kaolin is crushed to a particle size of less than 1 mm, ground, and then sieved to a particle size of less than 0.125 mm. It is then placed in a muffle furnace for high-temperature calcination at a heating rate of 10℃ / min, a calcination temperature of 700℃, and a calcination time of 3 h. After natural cooling, it is taken out to obtain metakaolin. The chemical composition of the coal-based kaolin is shown in Table 1.

[0162] S2. Preparation of alkali-fused material using red mud: Red mud with the chemical composition shown in Table 2 is mixed with NaOH at a mass ratio of 85wt%:15wt%. The dry ball mill is set to a speed of 300 rpm and the mixture is ground for 3 minutes to ensure uniform mixing of the red mud and NaOH. Then, the mixture is placed in a muffle furnace for high-temperature calcination. The heating rate is 10℃ / min, the calcination temperature is 550℃, and the calcination time is 3 hours. After calcination, the mixture is allowed to cool naturally, and the calcined product is removed and ground using a ball mill. The ball mill speed is set to 300 rpm and the grinding time is 5 minutes. The ground material is then sieved, and the sieved material with a particle size of less than 0.125 mm is obtained.

[0163] S3. Preparation of photovoltaic pile foundation based on fly ash geopolymer using fly ash: 20wt% alkali-fused material was added, and the ratio of metakaolin to fly ash was adjusted to control the SiO2 / Al2O3 molar ratio in the mixture to be 4.5. Water was added to make the liquid-solid ratio 0.4. The mixture was stirred for 5 minutes to obtain a mixed slurry. The mixed slurry was poured into a mold with a size of 40mm*40mm*40mm, and the mold was vibrated to defoam for 5 minutes. After one day, the mold was removed and allowed to cure naturally. The natural curing temperature was 20±2℃, the humidity was 95-98%, and the curing time was 28 days to obtain a photovoltaic pile foundation sample based on fly ash geopolymer.

[0164] The test results showed that the initial setting time of the photovoltaic pile foundation sample based on fly ash geopolymer was 77 min, and the final setting time was 387 min; the 3-day compressive strength was 23.06 MPa; the 28-day compressive strength was 39.76 MPa; and the chloride ion diffusion coefficient was 8.5 × 10⁻⁶. -13 It meets the requirements of GB / T 31289-2014 "Marine Silicate Cement" for setting time, strength and chloride ion diffusion coefficient of grade 32.5 marine silicate cement.

[0165] Comparative Example 1

[0166] A method for preparing photovoltaic pile foundations based on fly ash geopolymers differs from Example 1 in that, in step S2, the calcination temperature is 400℃ and the calcination time is 3 hours. The remaining steps and process parameters are the same as in Example 1.

[0167] The photovoltaic pile foundation samples based on fly ash geopolymer prepared in this comparative example showed an initial setting time of 104 min and a final setting time of 486 min; a 3-day compressive strength of 10.36 MPa; a 28-day compressive strength of 18.69 MPa; and a chloride ion diffusion coefficient of 7.9 × 10⁻⁶. -12 It does not meet the requirements for setting time, strength and chloride ion diffusion coefficient specified in GB / T31289-2014 "Marine Silicate Cement".

[0168] Comparative Example 2

[0169] A method for preparing photovoltaic pile foundations based on fly ash geopolymers differs from Example 1 in that step S2 is different, while the remaining steps and process parameters are the same as in Example 1. Specifically, step S2 is as follows:

[0170] S2. Preparation of alkali-fused material using red mud: Red mud with the chemical composition shown in Table 2 is mixed with NaOH at a mass ratio of 85wt%:15wt%. The dry ball mill is set to a speed of 300rpm and the mixture is ground for 3min to ensure uniform mixing of the red mud and NaOH. The ground material is then sieved, and the sieved material with a particle size of less than 0.125mm is taken. This sieved material is not roasted and is used directly as the alkali-fused material.

[0171] The photovoltaic pile foundation samples based on fly ash geopolymer prepared in this comparative example showed an initial setting time of 136 min and a final setting time of 584 min; a 3-day compressive strength of 6.28 MPa; a 28-day compressive strength of 10.35 MPa; and a chloride ion diffusion coefficient of 1.3 × 10⁻⁶. -13 It does not meet the requirements for setting time, strength and chloride ion diffusion coefficient specified in GB / T31289-2014 "Marine Silicate Cement".

[0172] Comparative Example 3

[0173] A method for preparing photovoltaic pile foundations based on fly ash geopolymers differs from Example 1 in that, in step S2, the calcination temperature is 800℃ and the calcination time is 3 hours. The remaining steps and process parameters are the same as in Example 1.

[0174] The photovoltaic pile foundation samples based on fly ash geopolymer prepared in this comparative example showed an initial setting time of 78 min and a final setting time of 403 min; a 3-day compressive strength of 13.42 MPa; a 28-day compressive strength of 21.08 MPa; and a chloride ion diffusion coefficient of 5.6 × 10⁻⁶. -12 It does not meet the requirements for setting time, strength and chloride ion diffusion coefficient specified in GB / T31289-2014 "Marine Silicate Cement".

[0175] Comparative Example 4

[0176] A method for preparing photovoltaic pile foundations based on fly ash geopolymers differs from Example 1 in that the dosage of the alkali-fused material in step S3 is different, while the remaining steps and process parameters are the same as in Example 1. Specifically, step S3 is as follows:

[0177] S3. Preparation of photovoltaic pile foundation based on fly ash geopolymer using fly ash: Add 5wt% alkali-fused material, adjust the ratio of metakaolin to fly ash to control the SiO2 / Al2O3 molar ratio in the mixture to be 3.5, add water to make the liquid-solid ratio 0.3, stir for 5 min to obtain a mixed slurry, pour the mixed slurry into a mold with a size of 40mm*40mm*40mm, vibrate to defoam for 5 min, demold after one day and allow for natural curing; the natural curing temperature is 20±2℃, the humidity is 95%~98%, and the curing time is 28d to obtain a photovoltaic pile foundation sample based on fly ash geopolymer.

[0178] The photovoltaic pile foundation samples based on fly ash geopolymer prepared in this comparative example showed an initial setting time of 112 min and a final setting time of 453 min; a 3-day compressive strength of 6.81 MPa; a 28-day compressive strength of 11.08 MPa; and a chloride ion diffusion coefficient of 1.1 × 10⁻⁶. -12 It does not meet the requirements for setting time, strength and chloride ion diffusion coefficient specified in GB / T31289-2014 "Marine Silicate Cement".

[0179] In summary, this invention involves mixing red mud with caustic alkali and then calcining it at high temperature to obtain an alkali-fused material; subsequently, metakaolin, the alkali-fused material, and fly ash are mixed to prepare a geopolymer. The high-temperature calcination of the red mud with caustic alkali disrupts the structure of the silicon and aluminum minerals in the red mud, increasing their activity. The presence of caustic alkali facilitates the depolymerization of silicon and aluminum minerals in an alkaline environment, forming silicon-oxygen and aluminum-oxygen monomers, which are beneficial for their participation in the geopolymer reaction process. Using the high-temperature calcination method of red mud with caustic alkali of this invention, the presence of caustic alkali allows the calcined product to directly acquire hydraulic properties, eliminating the need for water glass or alkaline solution activation processes.

[0180] Furthermore, this invention optimizes the setting time of fly ash-based photovoltaic pile foundations by limiting the liquid-to-solid ratio, thereby ensuring the strength of the fly ash-based photovoltaic pile foundation products. Compared to fly ash-based photovoltaic pile foundation samples prepared with a high liquid-to-solid ratio, the fly ash-based photovoltaic pile foundation samples prepared with a low liquid-to-solid ratio in this invention exhibit better resistance to Cl. - Ion corrosion resistance.

Claims

1. A method for preparing photovoltaic pile foundations based on fly ash geopolymers, characterized in that, The preparation method includes the following steps: S1: Metakaolin was prepared using coal-series kaolin; S2: Red mud is mixed with caustic alkali and then roasted at high temperature. The roasted product is then ground and sieved to obtain alkali-fused material. The red mud contains a SiO2 / Al2O3 molar ratio of less than 2. The caustic alkali includes at least one of sodium hydroxide and potassium hydroxide. The roasting temperature is 500℃~600℃. The amount of caustic alkali added is 10 wt%~20 wt% of the total mass of the red mud and the caustic alkali. S3: The metakaolin, the alkali-fused material, and fly ash are mixed and blended, and the ratio of metakaolin to fly ash is controlled so that the SiO2 / Al2O3 molar ratio of the mixture is 3.5~4.5:1; then water is added to prepare a slurry mixture, the slurry mixture is poured into a mold for molding, and then demolded and cured to obtain a photovoltaic pile foundation based on fly ash geopolymer. In step S3, the amount of water added is 0.3 to 0.4 of the liquid-solid ratio of the mixture.

2. The method for preparing photovoltaic pile foundations based on fly ash geopolymers according to claim 1, characterized in that, In step S1, the method for preparing metakaolin includes the following steps: First, the coal-series kaolin is crushed and ground, then sieved. The sieved coal-series kaolin is then calcined at high temperature to obtain metakaolin. In step S1, the temperature of the high-temperature calcination is 700℃~800℃; the heating rate of the high-temperature calcination is 5℃ / min~10℃ / min; or, In step S1, the particle size of the crushed coal-series kaolin is less than 1 mm; or, The particle size of the coal-series kaolin obtained by screening is less than 0.125 mm.

3. The method for preparing photovoltaic pile foundations based on fly ash geopolymers according to claim 1, characterized in that... In step S1, the chemical composition of the coal-series kaolin, by mass percentage, includes 42%~50% SiO2, 42%~50% Al2O3, 0.1%~0.8% alkali metal oxides, 1.5%~2.5% Fe2O3, 0.8%~1.5% TiO2, 1.8%~2.7% SO3, and other impurities; or In step S2, the red mud is Bayer process red mud; or In step S2, the chemical composition of the red mud, in terms of mass percentage, includes: SiO2 22%~25%, Al2O3 24%~26%, alkali metal oxides 8%~10%, alkaline earth metal oxides 19%~22%, Fe2O3 15%~18%, TiO2 3%~5%, SO3 2%~4%, and other impurities; or In step S3, the carbon content of the fly ash is less than 5%.

4. The method for preparing photovoltaic pile foundations based on fly ash geopolymers according to claim 3, characterized in that, In step S2, the heating rate of the calcination is 5℃ / min to 10℃ / min, and the calcination time is 3 to 4 h.

5. The method for preparing photovoltaic pile foundations based on fly ash geopolymers according to any one of claims 1-4, characterized in that, In step S2, when mixing the red mud with the caustic alkali, the rotation speed is set to 200-500 rpm and the grinding time is 1-5 min; or In step S2, when grinding the calcined product, the grinding speed is set to 200~500 rpm and the grinding time is 3~10 min; or In step S2, sieving is performed to reduce the particle size of the calcined product to below 0.125 mm.

6. The method for preparing photovoltaic pile foundations based on fly ash geopolymers according to any one of claims 1-4, characterized in that, In step S3, the amount of alkali-fused material is 10 wt% to 20 wt%.

7. The method for preparing photovoltaic pile foundations based on fly ash geopolymers according to claim 6, characterized in that, In step S3, the molding process includes: pouring the mixture slurry into a mold, stirring or vibrating it, and then allowing it to stand to form the mixture slurry; or In step S3, the maintenance includes at least one of natural maintenance and steam maintenance; The natural curing temperature is 20±2℃ and the humidity is 95%~98%; the steam curing temperature is 40℃~80℃ and the humidity is 90~95%.

8. A photovoltaic pile foundation based on fly ash geopolymer, characterized in that, The photovoltaic pile foundation based on fly ash geopolymer is prepared using the method for preparing a photovoltaic pile foundation based on fly ash geopolymer according to any one of claims 1-7.

9. An application of a photovoltaic pile foundation based on fly ash geopolymer according to claim 8, characterized in that the photovoltaic pile foundation can be used as a special cementing material that is alkali-resistant, salt-resistant, and erosion-resistant, and can also be applied to the pile foundation structure of photovoltaic power generation and wind power in saline-alkali land, marine or tidal flats.

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