Photovoltaic pile foundation based on fly ash geopolymer and preparation method and application thereof

Abstract

The invention relates to a photovoltaic pile foundation based on a fly ash geopolymer and a preparation method and application of the photovoltaic pile foundation, and belongs to the technical field of saline-alkali-resistant photovoltaic pile foundations and solid waste resource utilization. The preparation method comprises the following steps: S1, preparing metakaolin from coal series kaolin; s2, red mud and caustic alkali are mixed and then subjected to high-temperature roasting, an obtained roasted product is ground and sieved, and an alkali fusion material is obtained; and S3, blending and mixing the metakaolin, the alkali fusion material and fly ash, then adding water, performing injection molding and molding treatment, and demolding and curing to obtain the photovoltaic pile foundation. The production process of the photovoltaic pile foundation is low-carbon and environment-friendly, and resource utilization of the red mud and the fly ash is achieved; besides, the photovoltaic pile foundation is of a compact three-dimensional network structure and is high in alkali, salt and erosion resistance, the solidification time can be obviously shortened by adjusting the liquid-solid ratio and the raw material ratio, and application of the photovoltaic pile foundation to photovoltaic power generation and wind power foundation structures on the sea and in saline-alkali soil is facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste resource utilization and green building materials, and relates to a photovoltaic pile foundation based on fly ash geopolymer, its preparation method and application, and particularly relates to a method for preparing a geopolymer photovoltaic pile foundation by synergistically using red mud and fly ash and its application. Background Art

[0002] At present, the installed capacity of offshore photovoltaic power generation, wind power generation and inland saline-alkali land photovoltaic power generation in China continues to grow. Compared with onshore photovoltaic power generation, offshore photovoltaic power generation has the advantages of high power generation, less land occupation and easy combination with other industries; compared with onshore wind power generation, offshore wind power generation has the advantages of stable wind speed, high wind speed, large single-unit installed capacity and no land occupation. Therefore, the prospects of offshore wind power generation and photovoltaic power generation are broad. However, the offshore environment is complex and the natural conditions are harsh. The foundation structures of wind power generation and photovoltaic power generation are immersed in seawater for a long time and are extremely vulnerable to salt spray corrosion and seawater scouring, resulting in damage to their structures. The hydration products of ordinary Portland cement, such as calcium hydroxide and aluminosilicate, are prone to react with Cl - ions in seawater, causing volume changes, resulting in loose structures and poor corrosion resistance, and it is difficult to meet the requirements of offshore buildings. At the same time, the corrosion of conventional cement concrete for photovoltaic pile foundations in inland saline-alkali land is serious, and it is difficult to resist the erosion of various chemical media.

[0003] Geopolymer is an inorganic polymer with a three-dimensional network structure composed of AlO 4 and SiO 4 tetrahedral structural units, with the chemical formula M n {-(SiO 2 ) z -AlO 2}n·wH 2 O, where M represents cations such as K + , Na + , Ca 2+ etc., n represents the degree of polymerization, and w represents the water of hydration. The unique three-dimensional network structure of geopolymer determines its excellent properties of high strength and acid-base corrosion resistance. Therefore, it has broad application prospects in the field of marine construction.

[0004] Geopolymer is generally an inorganic material prepared from aluminosilicate precursor materials and activators. Commonly used precursor materials include kaolin, fly ash, and coal gangue, etc. Among them, the annual output of fly ash is huge, and it contains a large amount of amorphous or non-crystalline SiO 2 and Al 2 O 3, with high gelling activity, is the most excellent aluminosilicate precursor material. However, the commonly used activator for geopolymers is liquid alkali. The transportation, storage, and use of a large amount of viscous and corrosive liquid alkali are extremely inconvenient, restricting the popularization and application of geopolymers.

[0005] Bayer red mud is the waste residue generated during the production of alumina by the Bayer process using bauxite. Its comprehensive utilization has always been a worldwide problem. Bayer red mud has the characteristics of high alkalinity (pH = 11.3 ± 1) and extremely fine particle size, and is a potential activator for geopolymers. However, there are technical bottlenecks such as large compositional fluctuations and low gelling activity in the process of preparing cementitious materials with Bayer red mud. Summary of the Invention

[0006] In order to solve the above problems existing in the prior art, the present 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 a high-strength and corrosion-resistant fly ash geopolymer photovoltaic pile foundation. On the other hand, it realizes the collaborative resource utilization of bulk coal-based solid waste and red mud. At the same time, fly ash is used in combination with red mud to improve the compositional stability and gelling reaction activity in the process of preparing cementitious materials.

[0007] To achieve the above object, the present invention adopts the following technical solutions.

[0008] In the first aspect of the present invention, a preparation method of a photovoltaic pile foundation based on fly ash geopolymer is provided, including the following steps:

[0009] S1: Prepare metakaolin using coal-series kaolin;

[0010] S2: Mix red mud with caustic alkali and then conduct high-temperature roasting. Then, grind and screen the obtained roasted product to obtain an alkali-fused material; wherein, the SiO 2 / Al 2 O 3 molar ratio 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°C to 600°C;

[0011] S3: Mix the metakaolin prepared in step S1 and the alkali-fused material prepared in step S2 with fly ash, then add water to prepare a mixture slurry. Pour the mixture slurry into a mold for shaping (i.e., water injection molding), and then demold and cure to obtain a photovoltaic pile foundation based on fly ash geopolymer;

[0012] In the above preparation method of the photovoltaic pile foundation based on fly ash geopolymer, in step S1, the method for preparing metakaolin includes the following steps:

[0013] First, crush and grind the coal-series kaolin, then screen it, and subject the screened coal-series kaolin to high-temperature calcination to obtain metakaolin.

[0014] In the above-mentioned preparation method of the photovoltaic pile foundation based on fly ash geopolymer, in the step S1, the chemical composition of the coal-series kaolin includes SiO 2 42% - 50%, Al 2 O 3 42% - 50%, alkali metal oxides 0.1% - 0.8%, Fe 2 O 3 1.5% - 2.5%, TiO 2 0.8% - 1.5%, SO 3 1.8% - 2.7%, and other impurities.

[0015] In the above-mentioned preparation method of the photovoltaic pile foundation based on fly ash geopolymer, the coal-series kaolin includes coal gangue.

[0016] In the above-mentioned preparation method of the photovoltaic pile foundation based on fly ash geopolymer, in the step S1, the particle size of the crushed coal-series kaolin is below 1 mm.

[0017] In the above-mentioned preparation method of the photovoltaic pile foundation based on fly ash geopolymer, in the step S1, the particle size of the screened coal-series kaolin is below 0.125 mm.

[0018] In the above-mentioned preparation method of the photovoltaic pile foundation based on fly ash geopolymer, in the step S1, the temperature of the high-temperature calcination is 700°C - 800°C.

[0019] In the above-mentioned preparation method of the photovoltaic pile foundation based on fly ash geopolymer, in the step S1, the time of the high-temperature calcination is 3 - 4 h.

[0020] In the above-mentioned preparation method of the photovoltaic pile foundation based on fly ash geopolymer, in the step S1, the heating rate of the high-temperature calcination is 5°C / min - 10°C / min.

[0021] In the above-mentioned preparation method of the photovoltaic pile foundation based on fly ash geopolymer, in the step S1, the high-temperature calcination is carried out in a muffle furnace.

[0022] In the present invention, the preparation of metakaolin can adopt the conventional technical solutions in the art.

[0023] In the above-mentioned preparation method of the photovoltaic pile foundation based on fly ash geopolymer, in the step S2, the red mud is Bayer red mud.

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

[0025] SiO 2 22% - 25%, Al 2 O 3 24% - 26%, alkali metal oxides 8% - 10%, alkaline earth metal oxides 19% - 22%, Fe 2 O 3 15% - 18%, TiO 2 3% - 5%, SO 3 2% - 4%, and other impurities.

[0026] In the above method for preparing a photovoltaic pile foundation based on fly ash geopolymer, in step S2, the addition amount of caustic alkali is 10wt% - 20wt% of the total mass of the red mud and caustic alkali.

[0027] In the above method for preparing a photovoltaic pile foundation based on fly ash geopolymer, in step S2, a dry ball mill is used to mix the red mud and caustic alkali evenly.

[0028] In the above method for preparing a photovoltaic pile foundation based on fly ash geopolymer, in step S2, when mixing the red mud and 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 method for preparing a photovoltaic pile foundation based on fly ash geopolymer, in step S2, the heating rate of the roasting is 5 - 10 °C / min.

[0030] In the above method for preparing a photovoltaic pile foundation based on fly ash geopolymer, in step S2, the roasting time is 3 - 4 h.

[0031] In the above method for preparing a photovoltaic pile foundation based on fly ash geopolymer, in step S2, after the high-temperature roasting, it is naturally cooled, and then the cooled roasted product is ground.

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

[0033] In the above method for preparing a photovoltaic pile foundation based on fly ash geopolymer, in step S2, screening is performed to make the particle size of the roasted product less than 0.125 mm.

[0034] In the above preparation method of the photovoltaic pile foundation based on fly ash geopolymer, in step S3, the dosage of the alkali-fused material is 10 wt% to 20 wt% (for example, 12 wt%, 15 wt% or 18 wt%).

[0035] In the above preparation method of the photovoltaic pile foundation based on fly ash geopolymer, in step S3, the carbon content of the fly ash is less than 5% (for example, 2%, 3% or 4%).

[0036] In the above preparation method of the photovoltaic pile foundation based on fly ash geopolymer, in step S3, control the ratio of metakaolin to fly ash so that the SiO 2 / Al 2 O 3 molar ratio of the mixture is 3.5 to 4.5:1, abbreviated as 3.5 to 4.5.

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

[0038] In the above preparation method of the photovoltaic pile foundation based on fly ash geopolymer, in step S3, the shaping treatment includes: pouring the mixture slurry into a mold, and through stirring or vibration, and then standing still to make the mixture slurry take shape.

[0039] In the present invention, in step S3, when pouring the slurry into the mold, stirring or vibration can eliminate the bubbles in the slurry.

[0040] In the above preparation method of the photovoltaic pile foundation based on fly ash geopolymer, in step S3, the curing includes at least one of natural curing and steam curing.

[0041] In the above preparation method of the photovoltaic pile foundation based on fly ash geopolymer, in step S3, the temperature of the natural curing is 18 to 22 °C (i.e., 20 ± 2 °C), and the humidity is 95% to 98%.

[0042] In the above preparation method of the photovoltaic pile foundation based on fly ash geopolymer, in step S3, the curing time of the natural curing is 28 d.

[0043] In the above preparation method of the photovoltaic pile foundation based on fly ash geopolymer, in step S3, the temperature of the steam curing is 40 to 80 °C, and the humidity is 90% to 95%.

[0044] In the above preparation method of the photovoltaic pile foundation based on fly ash geopolymer, in step S3, the curing time of the steam curing is 9 to 15 h.

[0045] In the above preparation method of the photovoltaic pile foundation based on fly ash geopolymer, in step S3, the curing is carried out using a constant temperature and humidity chamber.

[0046] In the above preparation method of the photovoltaic pile foundation based on fly ash geopolymer, in step S3, the size of the mold is 40mm * 40mm * 40mm.

[0047] In the second aspect of the present invention, there is provided a photovoltaic pile foundation based on fly ash geopolymer, which is prepared by using any one of the above preparation methods.

[0048] In the third aspect of the present invention, there is provided an application of the above photovoltaic pile foundation based on fly ash geopolymer. The photovoltaic pile foundation based on fly ash geopolymer can be used as a special cementitious material resistant to alkali, salt, and erosion, and can also be applied to the pile foundation structures of photovoltaic power generation and wind power generation in saline-alkali land, the ocean, or tidal flats.

[0049] For the application of the above photovoltaic pile foundation based on fly ash geopolymer, the photovoltaic pile foundation can be used for the foundation structures of offshore wind power and photovoltaics, and can also be used as marine building cement.

[0050] For the application of the above photovoltaic pile foundation based on fly ash geopolymer, the photovoltaic pile foundation can be used as marine building cement or marine engineering cement.

[0051] In the present invention, without conflict, the above technical features can be freely combined to form new technical solutions.

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

[0053] (1) The present invention uses red mud in combination with fly ash to prepare a photovoltaic pile foundation of fly ash geopolymer, comprehensively utilizes bulk solid wastes such as red mud, coal-series kaolin (such as coal gangue), and coal-based solid waste (fly ash), and prepares a new type of photovoltaic pile foundation of fly ash geopolymer. Compared with the traditional cement production process (emitting about 850 kilograms of carbon dioxide per ton of cement), the preparation method of the photovoltaic pile foundation based on fly ash geopolymer proposed by the present invention reduces the carbon footprint, improves the utilization efficiency of bulk solid wastes, promotes the large-scale reduction and harmless treatment of bulk solid wastes from the source, and is low-carbon, green, and environmentally friendly;

[0054] (2) The present invention pretreats Bayer red mud and then mixes it with other aluminosilicate precursor materials (fly ash) to prepare geopolymers, and the obtained photovoltaic pile foundation of fly ash geopolymer has a dense structure; in addition, the present invention rationally designs the dosage of alkali-fused materials, the liquid-solid ratio, and SiO 2 / Al 2 O 3The molar ratio enables the prepared fly ash geopolymer photovoltaic pile foundation to have high strength, a fast setting 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 the sea, and resist the scouring of seawater and the conditions such as salt fog corrosion that are difficult for ordinary Portland cement to adapt to. Therefore, it can be used as the cement for photovoltaic / wind power pile foundations in inland saline-alkali land or the sea. Description of the Drawings

[0056] Figure 1 is a schematic flow chart of the preparation of a photovoltaic pile foundation based on fly ash geopolymer by using red mud in cooperation with fly ash according to the present invention. Specific Embodiments

[0057] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

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

[0059] S1: Prepare metakaolin by using coal-series kaolin; specifically including: first crush and grind the coal-series kaolin, then screen it, and subject the screened coal-series kaolin to high-temperature calcination to obtain metakaolin;

[0060] S2: Mix red mud with caustic alkali and then perform high-temperature roasting, and then grind and screen the obtained roasted product to obtain an alkali-fused material; wherein, the SiO 2 / Al 2 O 3 molar ratio 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 °C (for example, 510 °C, 530 °C, 550 °C, 560 °C or 580 °C);

[0061] S3: Mix and proportion the metakaolin prepared in step S1 and the alkali-fused material prepared in step S2 with fly ash, and control the ratio of the metakaolin to the fly ash so that the SiO 2 / Al 2 O 3The molar ratio is 3.5 to 4.5:1 (for example, 3.6:1, 3.8:1, 4:1, 4.2:1, or 4.4:1); then water is added to prepare a mixture slurry, and the mixture slurry is poured into a mold for molding treatment (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 the step S1, the chemical composition of the coal-series kaolin includes SiO 2 42% to 50%, Al 2 O 3 42% to 50%, alkali metal oxides 0.1% to 0.8%, Fe 2 O 3 1.5% to 2.5%, TiO 2 0.8% to 1.5%, SO 3 1.8% to 2.7%, and other impurities.

[0063] In some embodiments, the coal-series kaolin includes coal gangue.

[0064] In some embodiments, in the 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 the step S1, the temperature of the high-temperature calcination is 700°C to 800°C (for example, 710°C, 730°C, 750°C, 760°C, or 780°C); the time is 3 to 4 h (for example, 3.5 h), and the heating rate is 5°C / min to 10°C / min (for example, 6°C / min or 8°C / min).

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

[0067] In some embodiments, in the step S2, the chemical composition of the red mud includes, by mass percentage: SiO 2 22% to 25%, Al 2 O 3 24% to 26%, alkali metal oxides 8% to 10%, alkaline earth metal oxides 19% to 22%, Fe 2 O 3 15% to 18%, TiO 2 3% to 5%, SO 3 2% to 4%, and other impurities.

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

[0069] In the present 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 polycondensation reaction under the action of an activator to form a high polymer with a network structure, while discharging water and rapidly hardening.

[0070] In the present invention, although red mud contains SiO 2 and Al 2 O 3 , but Bayer red mud is the waste residue generated during the production of alumina by the Bayer process of bauxite. The SiO 2 and Al 2 O 3 that can be dissolved in an alkaline environment have basically been leached out in the Bayer process. Therefore, when directly using Bayer red mud to prepare geopolymers, the SiO 2 and Al 2 O 3 that can be leached out and participate in the reaction are very few, resulting in poor activity of Bayer red mud, and it is necessary to activate it to improve the leaching rate of SiO 2 and Al 2 O 3 .

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

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

[0073] In the present invention, caustic alkali is extremely easy to absorb water in the atmospheric environment and is not easy to store. Mixing red mud and caustic alkali and then roasting at high temperature aims to decompose the original silicate and aluminate phases in red mud and promote the formation of new compounds (i.e., aluminosilicate products). However, if the roasting temperature is too high, on the one hand, sintering will occur, causing the aluminosilicate products in red mud to sinter and transform into more stable calcium feldspar, resulting in SiO 2 and Al 2 O 3The leaching rate in caustic alkali decreases; on the other hand, it will also cause energy loss and increase the preparation cost. Therefore, the present invention defines the temperature of high-temperature roasting as 500-600 °C. When roasting at this temperature, the structure of the red mud changes to form an aluminosilicate product structure.

[0074] The present invention adopts a method of mixing red mud with caustic alkali and then performing high-temperature roasting to obtain an alkali-fused material (i.e., pretreating the red mud); then mixing metakaolin, the alkali-fused material and fly ash to prepare a geopolymer. Among them, after mixing red mud with caustic alkali and performing high-temperature roasting, the roasting can disorder the structures of silicon and aluminum minerals in the red mud and improve their activity. The presence of caustic alkali is conducive to the depolymerization of silicon and aluminum minerals in an alkaline environment to form silicon oxygen monomers and aluminum oxygen monomers, which is conducive to participating in the geopolymer reaction process.

[0075] Generally, after the red mud is treated by high-temperature roasting, it still needs to go through an activation process with water glass or an alkali solution to obtain hydraulic properties. By using the high-temperature roasting method of red mud and caustic alkali of the present invention, the presence of caustic alkali can directly endow the roasted product with hydraulic properties, eliminating the activation process with water glass or an alkali solution; that is, after mixing red mud with caustic alkali and performing high-temperature roasting treatment, the obtained roasted product can obtain hydraulic properties without being activated by water glass or an alkali solution.

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

[0077] In some embodiments, in step S2, screening is performed to make the particle size of the roasted product less than 0.125 mm.

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

[0079] In the present invention, if the dosage of the alkali-fused material is too low, the reaction is insufficient; if the dosage is too high, the residual alkali will react with CO 2 in the air to form carbonate, affecting the strength.

[0080] Fly ash has the characteristics of high chemical composition stability and high gelling reaction activity. It is an ideal raw material for synergistically preparing geopolymers with red mud, which is conducive to improving the composition stability and gelling reaction activity of red mud in the process of preparing cementitious materials.

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

[0082] In the present invention, if the carbon content of the fly ash is too high, it will lead to high brittleness and poor flexural performance of the final product, i.e., the photovoltaic pile foundation product based on fly ash geopolymer. Therefore, the carbon content of the fly ash is controlled to be less than 5%.

[0083] In the present invention, by limiting the SiO 2 / Al 2 O 3 molar ratio, a large amount of aluminosilicate is introduced during the preparation of geopolymer cement. The formed 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 by the method of the present invention has better durability and acid and alkali corrosion resistance, that is, the corrosion resistance is enhanced.

[0084] In the present invention, the geopolymer reaction mechanism is as follows: metakaolin and fly ash dissolve in a highly alkaline environment to form silicon-oxygen tetrahedrons and aluminum-oxygen tetrahedrons, and under the action of an alkali-fused material activator, a polycondensation reaction occurs to form a high polymer with a network structure, while discharging water and rapidly hardening to prepare a photovoltaic pile foundation based on fly ash geopolymer; among them, since the highly alkaline environment is provided by the alkali-fused material obtained by high-temperature roasting of red mud and caustic alkali, and the alkali-fused material contains aluminosilicate structural substances, it is beneficial to the progress of the polycondensation reaction, thereby forming a more complex network-structured high polymer, which is beneficial to improving the compactness of the structure of the photovoltaic pile foundation product based on fly ash geopolymer, reducing the porosity and average pore size of its internal structure, and further reducing the permeability of the photovoltaic pile foundation product based on fly ash geopolymer, and enhancing its seawater erosion resistance.

[0085] In some embodiments, in the step S3, the addition amount of water and the liquid-solid ratio (L / S mass ratio) of the mixture are 0.3 - 0.4 (for example, 0.32, 0.35 or 0.38).

[0086] In the present invention, if the addition amount of water is too low, it is difficult to form a slurry; if the addition amount of water 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-solid ratio is higher than the above range value, on the one hand, it will make it difficult for the slurry to solidify and harden, and on the other hand, water loss during the curing process will cause a large number of holes to form in the photovoltaic pile foundation based on fly ash geopolymer, affecting the final strength. Therefore, the present invention optimizes the setting time of the photovoltaic pile foundation based on fly ash geopolymer by limiting the liquid-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 specimens based on fly ash geopolymer prepared with a high liquid-solid ratio, the photovoltaic pile foundation specimens based on fly ash geopolymer prepared by the present invention with a low liquid-solid ratio show better anti-Cl - ion corrosion ability.

[0087] In some embodiments, in step S3, the forming process includes: pouring the mixture slurry into a mold, eliminating air bubbles in the slurry by stirring or vibrating, and then standing still to form the mixture slurry.

[0088] In the present invention, in step S3, when pouring the slurry into the mold, air bubbles in the slurry can be eliminated by stirring or vibrating.

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

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

[0091] In the present invention, 28 d is the international standard curing time in this field. Those skilled in the art can also choose other curing times, and the present invention does not specifically limit the time of natural curing.

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

[0093] In the above - mentioned preparation method of the photovoltaic pile foundation based on fly - ash geopolymer, in step S3, the size of the mold is 40mm * 40mm * 40mm.

[0094] In the present invention, the size of the mold is determined to be 40mm * 40mm * 40mm according to the size of the specimen used for testing the compressive strength in the cement mortar strength test method (ISO method) of GB / T 17671 - 2021; those skilled in the art can also select molds of other sizes according to actual needs, and the present invention does not specifically limit the size of the mold.

[0095] Some embodiments of the present invention also provide a photovoltaic pile foundation based on fly - ash geopolymer, which is prepared by using any of the above - mentioned 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 cementitious material resistant to alkali, salt, and erosion, and can also be applied to the pile foundation structures of photovoltaic power generation and wind power generation in saline - alkali land, the ocean, or tidal flats.

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

[0098] The photovoltaic pile foundation based on fly ash geopolymer prepared by the preparation method according to the present invention, compared with the ordinary Portland cement pile foundation, on the one hand, reduces carbon emissions during the production process of the fly ash geopolymer photovoltaic pile foundation, realizes the resource utilization of solid waste, and is green and environmentally friendly; on the other hand, the geopolymer has a dense three-dimensional network structure, has stronger seawater erosion resistance, and can significantly shorten the setting time by appropriately adjusting the liquid-solid ratio and raw material ratio, which is beneficial to the application of the photovoltaic pile foundation in the foundation structures of offshore photovoltaic power generation and wind power.

[0099] According to the provisions of GB / T31289-2014 "Marine Portland Cement", the setting time of the photovoltaic pile foundation specimen based on fly ash geopolymer is tested according to GB / T1346-2011 "Test Methods for Water Requirement of Normal Consistency, Setting Time and Soundness of Cement"; the strength is tested according to GB / T17671-2021 "Test Method for Cement Mortar Strength (ISO Method)"; 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 Portland cement, the initial setting time is required to be not earlier than 45 min and the final setting time is not later than 600 min; the 28-day chloride ion diffusion coefficient of marine Portland cement is not greater than 1.5×10 -12 m 2 / s.

[0100] Example 1

[0101] A preparation method of a photovoltaic pile foundation based on fly ash geopolymer, comprising the following steps.

[0102] S1. Prepare metakaolin from coal-series kaolin: First, crush the coal-series kaolin with the chemical composition shown in Table 1 to a particle size of less than 1 mm, screen the particle size to less than 0.125 mm after grinding, put it into a muffle furnace for high-temperature calcination, the heating rate is 10 °C / min, the calcination temperature is 700 °C, the calcination time is 3 h, and take it out after natural cooling to obtain metakaolin.

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

[0104]

[0105] S2. Preparation of alkali-fused materials using red mud: Mix red mud with the chemical composition shown in Table 2 and NaOH in a mass ratio of 85 wt%:15 wt%. Set the rotation speed of the dry ball mill to 300 rpm and grind for 3 min to mix the red mud and NaOH evenly. Then put the mixture into a muffle furnace for high-temperature roasting. The heating rate is 10 °C / min, the roasting temperature is 550 °C, and the roasting time is 3 h. After roasting, cool it naturally, take out the roasted product, and grind it using a ball mill. Set the ball milling speed to 300 rpm and the grinding time to 5 min. Then screen the ground material and take the screened material with a particle size of less than 0.125 mm 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 foundations based on fly ash geopolymers using fly ash: Add 10 wt% of the alkali-fused material, adjust the ratio of metakaolin to fly ash to control the SiO 2 / Al 2 O 3 molar ratio to 3.5:1, abbreviated as 3.5, add water to make the liquid-solid ratio (i.e., the mass ratio of the total water to the mixture) 0.3, stir for 5 min to obtain a mixed slurry, pour the mixed slurry into a mold with a size of 40 mm * 40 mm * 40 mm, vibrate and defoam for 5 min, and demold after one day for natural curing. The temperature of natural curing is 18 - 22 °C, the humidity is 95% - 98%, and the curing time is 28 d to obtain a test sample of the photovoltaic pile foundation based on fly ash geopolymer.

[0110] Table 3 shows the formula design and performance test results of the photovoltaic pile foundations based on fly ash geopolymers prepared in each example and comparative example of the present invention. Table 4 shows the strength grade standards of "Marine Portland Cement" in GB / T 31289-2014.

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

[0112]

[0113]

[0114] Table 4 Strength values of marine portland cement

[0115]

[0116] As shown in Table 3, after testing, the initial setting time of the photovoltaic pile foundation specimen based on fly ash geopolymer prepared in this example is 62 min, and the final setting time is 312 min; the compressive strength at 3 days is 17.79 MPa; the compressive strength at 28 days is 35.96 MPa; the chloride ion diffusion coefficient is 0.9*10 -12 . It meets the requirements of the setting time, strength and chloride ion diffusion coefficient of the 32.5-grade marine portland cement specified in GB / T 31289-2014 "Marine Portland Cement".

[0117] Example 2

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

[0119] S1. Preparation of metakaolin from coal-series kaolin: First, crush the coal-series kaolin to a particle size of less than 1 mm, screen the particle size of less than 0.125 mm after grinding, put it into a muffle furnace for high-temperature calcination, with a heating rate of 10 °C / min, a calcination temperature of 700 °C, and a calcination time of 3 h. Take it out after natural cooling to obtain metakaolin; among them, the chemical composition of the coal-series kaolin is shown in Table 1.

[0120] S2. Preparation of alkali-fused material using red mud: Mix the red mud with the chemical composition shown in Table 2 and NaOH according to a mass ratio of 85 wt%:15 wt%. Among them, set the rotation speed of the dry ball mill to 300 rpm and the grinding time to 3 min to make the red mud and NaOH evenly mixed; then, put the mixture into a muffle furnace for high-temperature roasting, where the heating rate is controlled at 10 °C / min, the roasting temperature is 550 °C, and the roasting time is 3 h; after roasting, cool naturally, take out the roasted product, and grind it with a ball mill. Set the ball mill rotation speed to 300 rpm and the grinding time to 5 min; then screen the ground material and take the screened material with a particle size of less than 0.125 mm to obtain the alkali-fused material. Table 2 shows the chemical composition of the red mud.

[0121] S3. Preparation of a photovoltaic pile foundation based on fly ash geopolymer using fly ash: Add 10 wt% of the alkali-fused material, adjust the ratio of metakaolin to fly ash to control the SiO 2 / Al 2 O 3 molar ratio to 4, add water to make the liquid-solid ratio 0.4, stir for 5 min to obtain a mixed slurry, pour the mixed slurry into a mold of 40 mm * 40 mm * 40 mm, vibrate and defoam for 5 min, and demold after one day for natural curing; among them, the temperature of natural curing is 20±2 °C, the humidity is 95-98%, and the curing time is 28 d to obtain a photovoltaic pile foundation specimen based on fly ash geopolymer.

[0122] After testing, the initial setting time of the photovoltaic pile foundation specimen based on fly ash geopolymer is 94 min, and the final setting time is 475 min; the 3-day compressive strength is 14.84 MPa; the 28-day compressive strength is 33.21 MPa; the chloride ion diffusion coefficient is 1.4*10 -12 . It meets the requirements of the setting time, strength and chloride ion diffusion coefficient of the 32.5-grade marine portland cement specified in GB / T31289-2014 "Marine Portland Cement".

[0123] Example 3

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

[0125] S1. Prepare metakaolin from coal-series kaolin: First, crush the coal-series kaolin to a particle size of less than 1 mm, screen the particle size of less than 0.125 mm after grinding, put it into a muffle furnace for high-temperature calcination, with a heating rate of 10 °C / min, a calcination temperature of 700 °C, and a calcination time of 3 h. Take it out after natural cooling to obtain metakaolin; among them, the chemical composition of the coal-series kaolin is shown in Table 1.

[0126] S2. Prepare alkali-fused material from red mud: Mix the red mud with the chemical composition shown in Table 2 and NaOH according to a mass ratio of 85 wt%:15 wt%. Among them, set the rotation speed of the dry ball mill to 300 rpm and the grinding time to 3 min to make the red mud and NaOH evenly mixed; then, put the mixture into a muffle furnace for high-temperature roasting, where the heating rate is 10 °C / min, the roasting temperature is 550 °C, and the roasting time is 3 h; after roasting, cool it naturally, take out the roasted product, and grind it with a ball mill. Set the ball mill rotation speed to 300 rpm and the grinding time to 5 min; then screen the ground material and take the screened material with a particle size of less than 0.125 mm to obtain the alkali-fused material.

[0127] S3. Prepare a photovoltaic pile foundation based on fly ash geopolymer using fly ash: Add 10 wt% of the alkali-fused material, adjust the ratio of metakaolin to fly ash to control the SiO 2 / Al 2 O 3 molar ratio to be 4.5:1, abbreviated as 4.5, add water to make the liquid-solid ratio 0.35, stir for 5 min to obtain a mixed slurry, pour the mixed slurry into a mold with a size of 40 mm * 40 mm * 40 mm, vibrate and defoam for 5 min, and demold after one day for natural curing; among them, the temperature of natural curing is 20 ± 2 °C, the humidity is 95% - 98%, and the curing time is 28 d to obtain a photovoltaic pile foundation specimen based on fly ash geopolymer.

[0128] After testing, the initial setting time of the photovoltaic pile foundation specimen based on fly ash geopolymer is 75 min, and the final setting time is 374 min; the compressive strength at 3 days is 16.38 MPa; the compressive strength at 28 days is 34.84 MPa; the chloride ion diffusion coefficient is 1.1*10 -12 , meeting the requirements of the setting time, strength and chloride ion diffusion coefficient of the 32.5-grade marine portland cement specified in GB / T31289-2014 "Marine Portland Cement".

[0129] Example 4

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

[0131] S1. Prepare metakaolin from coal-series kaolin: First, crush the coal-series kaolin to a particle size of less than 1 mm, grind it and screen the particle size to less than 0.125 mm, put it into a muffle furnace for high-temperature calcination, with a heating rate of 10 °C / min, a calcination temperature of 700 °C, and a calcination time of 3 h. Take it out after natural cooling to obtain metakaolin; among them, the chemical composition of the coal-series kaolin is shown in Table 1.

[0132] S2. Prepare an alkali-fused material from red mud: Mix the red mud with the chemical composition shown in Table 2 and NaOH in a mass ratio of 85 wt%:15 wt%. Among them, set the rotation speed of the dry ball mill to 300 rpm and grind for 3 min to make the red mud and NaOH evenly mixed; then, put the mixture into a muffle furnace for high-temperature roasting, where the heating rate is 10 °C / min, the roasting temperature is 550 °C, and the roasting time is 3 h; after roasting, cool it naturally, take out the roasted product, and grind it with a ball mill. Set the ball mill rotation speed to 300 rpm and the grinding time to 5 min; then screen the ground material and take the screened material with a particle size of less than 0.125 mm to obtain the alkali-fused material.

[0133] S3. Prepare a photovoltaic pile foundation based on fly ash geopolymer using fly ash: Add 15 wt% of the alkali-fused material, adjust the ratio of metakaolin to fly ash to control the SiO 2 / Al 2 O 3 molar ratio to be 3.5, add water to make the liquid-solid ratio 0.4, stir for 5 min to obtain a mixed slurry, pour the mixed slurry into a mold with a size of 40 mm * 40 mm * 40 mm, vibrate and defoam for 5 min, and demold after one day for natural curing; among them, the temperature of natural curing is 20±2 °C, the humidity is 95% - 98%, and the curing time is 28 d to obtain a photovoltaic pile foundation specimen based on fly ash geopolymer.

[0134] After testing, the initial setting time of the photovoltaic pile foundation specimen based on fly ash geopolymer is 86 min, and the final setting time is 446 min; the compressive strength at 3 days is 18.30 MPa; the compressive strength at 28 days is 36.73 MPa; the chloride ion diffusion coefficient is 1.3*10 -12 , meeting the requirements of the setting time, strength and chloride ion diffusion coefficient of the 32.5-grade marine portland cement specified in GB / T 31289-2014 "Marine Portland Cement".

[0135] Example 5

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

[0137] S1. Prepare metakaolin from coal-series kaolin: First, crush the coal-series kaolin to a particle size of less than 1 mm, grind and screen the particle size to less than 0.125 mm, put it into a muffle furnace for high-temperature calcination, with a heating rate of 10 °C / min, a calcination temperature of 700 °C, and a calcination time of 3 h. Take it out after natural cooling to obtain metakaolin; among them, the chemical composition of the coal-series kaolin is shown in Table 1.

[0138] S2. Prepare an alkali-fused material from red mud: Mix the red mud with the chemical composition shown in Table 2 and NaOH according to a mass ratio of 85 wt%:15 wt%. Among them, set the rotation speed of the dry ball mill to 300 rpm and grind for 3 min to make the red mud and caustic alkali evenly mixed; then, put the mixture into a muffle furnace for high-temperature roasting, where the heating rate is 10 °C / min, the roasting temperature is 550 °C, and the roasting time is 3 h; after roasting, cool naturally, take out the roasted product, and grind it with a ball mill. Set the ball mill rotation speed to 300 rpm and the grinding time to 5 min; then screen the ground material and take the screened material with a particle size of less than 0.125 mm to obtain the alkali-fused material.

[0139] S3. Prepare a photovoltaic pile foundation based on fly ash geopolymer using fly ash: Add 15 wt% of the alkali-fused material, adjust the ratio of metakaolin to fly ash to control the SiO 2 / Al 2 O 3 molar ratio to 4, add water to make the liquid-solid ratio 0.35, stir for 5 min to obtain a mixed slurry, pour the mixed slurry into a mold of 40 mm * 40 mm * 40 mm, vibrate and defoam for 5 min, and demold after one day for natural curing; among them, the temperature of natural curing is 20±2 °C, the humidity is 95% - 98%, and the curing time is 28 d to obtain a photovoltaic pile foundation specimen based on fly ash geopolymer.

[0140] After testing, the initial setting time of the photovoltaic pile foundation specimen based on fly ash geopolymer is 69 min, and the final setting time is 356 min; the 3-day compressive strength is 22.82 MPa; the 28-day compressive strength is 39.68 MPa; the chloride ion diffusion coefficient is 9.1*10 -13 , meeting the requirements of the setting time, strength and chloride ion diffusion coefficient of the 32.5-grade marine portland cement specified in GB / T31289-2014 "Marine Portland Cement".

[0141] Example 6

[0142] A preparation method of a photovoltaic pile foundation based on fly ash geopolymer, comprising the following steps.

[0143] S1. Prepare metakaolin from coal-series kaolin: First, crush the coal-series kaolin to a particle size of less than 1 mm, screen the particle size of less than 0.125 mm after grinding, put it into a muffle furnace for high-temperature calcination, with a heating rate of 10 °C / min, a calcination temperature of 700 °C, and a calcination time of 3 h. Take it out after natural cooling to obtain metakaolin; among them, the chemical composition of the coal-series kaolin is shown in Table 1.

[0144] S2. Prepare an alkali-fused material from red mud: Mix the red mud with the chemical composition shown in Table 2 and NaOH according to a mass ratio of 85 wt%:15 wt%. Among them, set the rotation speed of the dry ball mill to 300 rpm and grind for 3 min to make the red mud and NaOH evenly mixed; then, put the mixture into a muffle furnace for high-temperature roasting, where the heating rate is 10 °C / min, the roasting temperature is 550 °C, and the roasting time is 3 h; after roasting, cool naturally, take out the roasted product, and grind it with a ball mill. Among them, set the ball mill rotation speed to 300 rpm and the grinding time to 5 min; then screen the ground material and take the screened material with a particle size of less than 0.125 mm to obtain the alkali-fused material.

[0145] S3. Prepare a photovoltaic pile foundation based on fly ash geopolymer using fly ash: Add 15 wt% of the alkali-fused material, adjust the ratio of metakaolin to fly ash to control the SiO 2 / Al 2 O 3 molar ratio to be 4.5, 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 of 40 mm * 40 mm * 40 mm, vibrate and defoam for 5 min, and demold after one day for natural curing; among them, the temperature of natural curing is 20±2 °C, the humidity is 95-98%, and the curing time is 28 d to obtain a photovoltaic pile foundation specimen based on fly ash geopolymer.

[0146] After testing, the initial setting time of the photovoltaic pile foundation specimen based on fly ash geopolymer is 57 min, and the final setting time is 281 min; the 3-day compressive strength is 26.35 MPa; the 28-day compressive strength is 45.36 MPa; the chloride ion diffusion coefficient is 5.8*10 -13 , meeting the requirements of the setting time, strength and chloride ion diffusion coefficient of the 42.5-grade marine portland cement specified in GB / T31289-2014 "Marine Portland Cement".

[0147] Example 7

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

[0149] S1. Prepare metakaolin from coal-series kaolin: First, crush the coal-series kaolin to a particle size of less than 1 mm, screen the particle size of less than 0.125 mm after grinding, put it into a muffle furnace for high-temperature calcination, with a heating rate of 10 °C / min, a calcination temperature of 700 °C, and a calcination time of 3 h. Take it out after natural cooling to obtain metakaolin; among them, the chemical composition of the coal-series kaolin is shown in Table 1.

[0150] S2. Prepare an alkali-fused material from red mud: Mix the red mud with the chemical composition shown in Table 2 and NaOH according to a mass ratio of 85 wt%:15 wt%. Among them, set the rotation speed of the dry ball mill to 300 rpm and grind for 3 min to make the red mud and NaOH evenly mixed; then, put the mixture into a muffle furnace for high-temperature roasting, where the heating rate is 10 °C / min, the roasting temperature is 550 °C, and the roasting time is 3 h; after roasting, cool naturally, take out the roasted product, and grind it with a ball mill, where the ball milling speed is set to 300 rpm and the grinding time is 5 min; then screen the ground material and take the screened material with a particle size of less than 0.125 mm to obtain the alkali-fused material.

[0151] S3. Prepare a photovoltaic pile foundation based on fly ash geopolymer using fly ash: Add 20 wt% of the alkali-fused material, adjust the ratio of metakaolin to fly ash to control the SiO 2 / Al 2 O 3 molar ratio to be 3.5, add water to make the liquid-solid ratio 0.35, stir for 5 min to obtain a mixed slurry, pour the mixed slurry into a mold of 40 mm * 40 mm * 40 mm, vibrate and defoam for 5 min, and demold after one day for natural curing; among them, the temperature of natural curing is 20 ± 2 °C, the humidity is 95% - 98%, and the curing time is 28 d to obtain a photovoltaic pile foundation specimen based on fly ash geopolymer.

[0152] After testing, the initial setting time of the photovoltaic pile foundation specimen based on fly ash geopolymer is 61 min, and the final setting time is 308 min; the compressive strength at 3 days is 24.45 MPa; the compressive strength at 28 days is 42.89 MPa; the chloride ion diffusion coefficient is 6.9*10 -13 , meeting the requirements of the setting time, strength and chloride ion diffusion coefficient of the 42.5 grade marine portland cement specified in GB / T31289-2014 "Marine Portland Cement".

[0153] Example 8

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

[0155] S1. Prepare metakaolin from coal-series kaolin: First, crush the coal-series kaolin to a particle size of less than 1 mm, grind it and sieve the particle size to less than 0.125 mm, put it into a muffle furnace for high-temperature calcination, with a heating rate of 10 °C / min, a calcination temperature of 700 °C, and a calcination time of 3 h. Take it out after natural cooling to obtain metakaolin; among them, the chemical composition of the coal-series kaolin is shown in Table 1.

[0156] S2. Prepare an alkali-fused material from red mud: Mix the red mud with the chemical composition shown in Table 2 and NaOH in a mass ratio of 85 wt%:15 wt%. Among them, set the rotation speed of the dry ball mill to 300 rpm and grind for 3 min to make the red mud and NaOH evenly mixed; then, put the mixture into a muffle furnace for high-temperature roasting, where the heating rate is 10 °C / min, the roasting temperature is 550 °C, and the roasting time is 3 h; after roasting, cool it naturally, take out the roasted product, and grind it with a ball mill, where the ball mill rotation speed is set to 300 rpm and the grinding time is 5 min; then screen the ground material and take the screened material with a particle size of less than 0.125 mm to obtain the alkali-fused material.

[0157] S3. Prepare a photovoltaic pile foundation based on fly ash geopolymer using fly ash: Add 20 wt% of the alkali-fused material, adjust the ratio of metakaolin to fly ash to control the SiO 2 / Al 2 O 3 molar ratio to be 4, 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 of 40 mm * 40 mm * 40 mm, vibrate and defoam for 5 min, and demold after one day for natural curing; among them, the temperature of natural curing is 20±2 °C, the humidity is 95% - 98%, and the curing time is 28 d to obtain a photovoltaic pile foundation specimen based on fly ash geopolymer.

[0158] After testing, the initial setting time of the photovoltaic pile foundation specimen based on fly ash geopolymer is 49 min, and the final setting time is 254 min; the 3-day compressive strength is 32.43 MPa; the 28-day compressive strength is 54.95 MPa; the chloride ion diffusion coefficient is 2.5*10 -13 , meeting the requirements of the setting time, strength and chloride ion diffusion coefficient of the 42.5-grade marine portland cement specified in GB / T31289-2014 "Marine Portland Cement".

[0159] Example 9

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

[0161] S1. Prepare metakaolin from coal-series kaolin: First, crush the coal-series kaolin to a particle size of less than 1 mm, screen the particle size of less than 0.125 mm after grinding, put it into a muffle furnace for high-temperature calcination, with a heating rate of 10 °C / min, a calcination temperature of 700 °C, and a calcination time of 3 h. Take it out after natural cooling to obtain metakaolin; among them, the chemical composition of the coal-series kaolin is shown in Table 1.

[0162] S2. Prepare an alkali-fused material from red mud: Mix the red mud with the chemical composition shown in Table 2 and NaOH in a mass ratio of 85 wt%:15 wt%. Among them, set the rotation speed of the dry ball mill to 300 rpm and grind for 3 min to make the red mud and NaOH evenly mixed; then, put the mixture into a muffle furnace for high-temperature roasting, where the heating rate is 10 °C / min, the roasting temperature is 550 °C, and the roasting time is 3 h; after roasting, cool it naturally, take out the roasted product, and grind it with a ball mill. Set the ball mill rotation speed to 300 rpm and the grinding time to 5 min; then screen the ground material and take the screened material with a particle size of less than 0.125 mm to obtain the alkali-fused material.

[0163] S3. Prepare a photovoltaic pile foundation based on fly ash geopolymer using fly ash: Add 20 wt% of the alkali-fused material, adjust the ratio of metakaolin to fly ash to control the SiO 2 / Al 2 O 3 molar ratio to be 4.5, add water to make the liquid-solid ratio 0.4, stir for 5 min to obtain a mixed slurry, pour the mixed slurry into a mold of 40 mm*40 mm*40 mm, vibrate and defoam for 5 min, and demold after one day for natural curing; among them, the temperature of natural curing is 20±2 °C, the humidity is 95-98%, and the curing time is 28 d to obtain a photovoltaic pile foundation specimen based on fly ash geopolymer.

[0164] After testing, the initial setting time of the photovoltaic pile foundation specimen based on fly ash geopolymer is 77 min, and the final setting time is 387 min; the 3-day compressive strength is 23.06 MPa; the 28-day compressive strength is 39.76 MPa; the chloride ion diffusion coefficient is 8.5*10 -13 , meeting the requirements of the setting time, strength and chloride ion diffusion coefficient of the 32.5-grade marine portland cement specified in GB / T 31289-2014 "Marine Portland Cement".

[0165] Comparative Example 1

[0166] A preparation method of a photovoltaic pile foundation based on fly ash geopolymer, which is different from Example 1 in that in step S2, the roasting temperature is 400 °C and the roasting time is 3 h. The remaining steps and process parameters are the same as those in Example 1.

[0167] After testing, the initial setting time of the photovoltaic pile foundation specimen based on fly ash geopolymer prepared in this comparative example is 104 min, and the final setting time is 486 min; the 3-day compressive strength is 10.36 MPa; the 28-day compressive strength is 18.69 MPa; the chloride ion diffusion coefficient is 7.9*10 -12 , not meeting the requirements of the setting time, strength and chloride ion diffusion coefficient specified in GB / T31289-2014 "Marine Portland Cement".

[0168] Comparative Example 2

[0169] A preparation method of a photovoltaic pile foundation based on fly ash geopolymer, which is different from Example 1 in that step S2 is different, and the remaining steps and process parameters are the same as those in Example 1. Specifically, step S2 is as follows:

[0170] S2. Using red mud to prepare an alkali-fused material: Mix the red mud with the chemical composition shown in Table 2 and NaOH in a mass ratio of 85 wt%:15 wt%. Among them, set the rotation speed of the dry ball mill to 300 rpm and grind for 3 min to make the red mud and NaOH evenly mixed; then screen the ground material, and take the screened material with a particle size of less than 0.125 mm. This screened material is not roasted and directly serves as the alkali-fused material.

[0171] After testing, the initial setting time of the photovoltaic pile foundation specimen based on fly ash geopolymer prepared in this comparative example is 136 min, and the final setting time is 584 min; the 3-day compressive strength is 6.28 MPa; the 28-day compressive strength is 10.35 MPa; the chloride ion diffusion coefficient is 1.3*10 -13 , not meeting the requirements of the setting time, strength and chloride ion diffusion coefficient specified in GB / T31289-2014 "Marine Portland Cement".

[0172] Comparative Example 3

[0173] A preparation method of a photovoltaic pile foundation based on fly ash geopolymer, which is different from Example 1 in that in step S2, the calcination temperature is 800 °C and the calcination time is 3 h. The remaining steps and process parameters are the same as those in Example 1.

[0174] After testing, the initial setting time of the photovoltaic pile foundation specimen based on fly ash geopolymer prepared in this comparative example is 78 min, and the final setting time is 403 min; the 3-day compressive strength is 13.42 MPa; the 28-day compressive strength is 21.08 MPa; the chloride ion diffusion coefficient is 5.6*10 -12 , which does not meet the requirements of the setting time, strength and chloride ion diffusion coefficient specified in GB / T 31289-2014 "Marine Portland Cement".

[0175] Comparative Example 4

[0176] A preparation method of a photovoltaic pile foundation based on fly ash geopolymer, which is different from Example 1 in that the dosage of the alkali-fused material in step S3 is different, and the remaining steps and process parameters are the same as those in Example 1. Specifically, step S3 is as follows:

[0177] S3. Use fly ash to prepare a photovoltaic pile foundation based on fly ash geopolymer: Add 5 wt% of the alkali-fused material, adjust the ratio of metakaolin to fly ash to control the SiO 2 / Al 2 O 3 molar ratio 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 of 40 mm * 40 mm * 40 mm, vibrate and defoam for 5 min, and demold after one day for natural curing; among them, the temperature of natural curing is 20±2 °C, the humidity is 95% - 98%, and the curing time is 28 d to obtain a photovoltaic pile foundation specimen based on fly ash geopolymer.

[0178] After testing, the initial setting time of the photovoltaic pile foundation specimen based on fly ash geopolymer prepared in this comparative example is 112 min, and the final setting time is 453 min; the 3-day compressive strength is 6.81 MPa; the 28-day compressive strength is 11.08 MPa; the chloride ion diffusion coefficient is 1.1*10 -12 , which does not meet the requirements of the setting time, strength and chloride ion diffusion coefficient specified in GB / T 31289-2014 "Marine Portland Cement".

[0179] In summary, the present invention involves mixing red mud with caustic soda and then subjecting the mixture to high-temperature roasting to obtain an alkali-fused material; then mixing metakaolin, the alkali-fused material, and fly ash to prepare a geopolymer. Among them, when red mud is mixed with caustic soda and subjected to high-temperature roasting, the roasting can disorder the structures of silicon and aluminum minerals in the red mud, improving their activity. The presence of caustic soda is conducive to the depolymerization of silicon and aluminum minerals in an alkaline environment to form silicon-oxygen monomers and aluminum-oxygen monomers, which is beneficial to participating in the geopolymer reaction process. By using the high-temperature roasting method of red mud and caustic soda of the present invention, the presence of caustic soda can endow the roasted product with hydraulic properties directly, eliminating the need for the activation process with water glass or an alkali solution.

[0180] In addition, the present invention optimizes the setting time of the photovoltaic pile foundation based on fly ash geopolymer by limiting the liquid-solid ratio, thereby ensuring the strength of the photovoltaic pile foundation product based on fly ash geopolymer. Compared with the photovoltaic pile foundation specimen based on fly ash geopolymer prepared with a high liquid-solid ratio, the photovoltaic pile foundation specimen based on fly ash geopolymer prepared with a low liquid-solid ratio in the present invention exhibits better resistance to - Cl-ion corrosion.

Claims

1. A method for preparing a photovoltaic pile foundation based on fly ash geopolymer, characterized in that: The preparation method comprises the following steps: S1: Metakaolin is prepared using coal-bearing kaolin; S2: Mixing red mud and caustic soda and then calcining them at high temperature, then grinding and sieving the calcined product to obtain an alkali-melted material; wherein the SiO2 / Al2O3 molar ratio in the red mud is less than 2; the caustic soda comprises at least one of sodium hydroxide and potassium hydroxide; and the calcination temperature is 500°C to 600°C; S3: blending the metakaolin, the alkali-fused material and fly ash, controlling the ratio of the metakaolin to the fly ash, and making the SiO2 / Al2O3 molar ratio of the mixture be 3.5-4.5:1; then adding water to prepare a mixture slurry, pouring the mixture slurry into a mold for molding, and then demolding and curing to obtain a photovoltaic pile foundation based on fly ash geopolymer.

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

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

4. The method for preparing a photovoltaic pile foundation based on fly ash geopolymer according to claim 3, characterized in that: In step S2, the amount of caustic soda added is 10wt% to 20wt% of the total mass of red mud and caustic soda; or In the step S2, the heating rate of the calcination is 5°C / min to 10°C / min, and the calcination time is 3 to 4 hours.

5. The method for preparing a photovoltaic pile foundation based on fly ash geopolymer according to any one of claims 1 to 4, characterized in that: In step S2, when mixing the red mud and the caustic soda, the rotation speed is set to 200-500 rpm and the grinding time is set to 1-5 min; or In the step S2, when grinding the calcined product, the grinding speed is set to 200-500 rpm and the grinding time is set to 3-10 min; or In the step S2, the calcined product is screened to have a particle size of less than 0.125 mm.

6. The method for preparing a photovoltaic pile foundation based on fly ash geopolymer according to any one of claims 1 to 4, characterized in that: In the step S3, the amount of the alkali-melting material is 10wt% to 20wt%; or In the step S3, the liquid-to-solid ratio of the added water to the mixed material is 0.3 to 0.

4.

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

8. A photovoltaic pile foundation based on fly ash geopolymer, characterized in that: The fly ash geopolymer-based photovoltaic pile foundation is prepared by the method for preparing a fly ash geopolymer-based photovoltaic pile foundation 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 cementitious material that is resistant to alkali, salt and corrosion, and can also be applied to pile foundation structures for photovoltaic power generation and wind power in saline-alkali land, ocean or tidal flats.

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