A concrete for geothermal energy piles and a method for producing the same

Abstract

This invention discloses a concrete for geothermal energy piles. The raw materials of the concrete include cementitious materials, fine aggregates, coarse aggregates, mixing water, and a water-reducing agent. Based on 100 parts by weight of the total weight of the cementitious materials, the components are: 100 parts by weight of cementitious materials, 165-185 parts by weight of fine aggregates, 210-230 parts by weight of coarse aggregates, 32-38 parts by weight of mixing water, and 1.0-1.3 parts by weight of water-reducing agent. The cementitious materials include cement, mineral powder, fly ash, activated magnesium oxide, and activated alumina micropowder. The coarse aggregates include cordierite aggregates pretreated with alkali thermal activation. This invention can reduce the coefficient of thermal expansion, meet the bearing requirements of pile foundations, and effectively resist the stress generated at the aggregate-slurry interface due to temperature cycles.

Description

Technical Field

[0001] This invention relates to the technical field of concrete manufacturing, specifically to a type of concrete for geothermal energy piles and its preparation method. Background Technology

[0002] Concrete is the most widely used building material in the world today. In traditional civil engineering, concrete structures typically operate in relatively stable temperature environments. However, with technological advancements, some new structures place extreme demands on the performance of concrete, with geothermal energy piles being one such example.

[0003] Geothermal energy piles are an innovative technology that integrates the structure of a building's pile foundation with the function of an underground heat exchanger in a ground source heat pump system. This means that the pile not only bears the load of the superstructure but also needs to act as a heat exchange medium year-round, enduring frequent and drastic temperature cycles. For example, in summer, the pile needs to release heat into the ground, and its temperature may rise to 30-40°C; while in winter, the pile needs to absorb heat from the ground, and its temperature may drop to 5-10°C or even lower. This periodic thermal expansion and contraction can generate enormous destructive stress on concrete materials, especially in the weakest link—the aggregate-slurry interface transition zone.

[0004] Due to the significant difference in the coefficients of thermal expansion between aggregates and cementitious matrix in conventional concrete, microcracks are easily generated in the interface zone under cyclic temperature loads. These microcracks not only reduce the mechanical properties and durability of the pile, but also provide channels for the intrusion of corrosive ions (such as chloride and sulfate ions) from the ground, accelerating steel corrosion and ultimately threatening the safety and service life of the entire pile foundation structure.

[0005] In existing technologies, functional materials are added to improve certain properties of concrete. For example, European patent EP3532450A1 discloses an aqueous dispersion for producing lightweight building materials, mentioning cordierite as one of the raw materials for porous ceramics. However, its core invention focuses on the lightweight properties of the material and does not address how to solve the interface problems under temperature stress. Chinese patent CN109650783B discloses the use of porous ceramics and diatomaceous earth to improve the dust absorption performance of asphalt concrete. Its technical focus is on adsorption function, similarly neglecting the volume stability and interface strengthening of concrete under temperature cycling.

[0006] Therefore, there is an urgent need in this field for a new type of concrete material that not only meets the bearing requirements of pile foundations, but more importantly, has extremely high thermal shock resistance and volume stability, and can effectively resist the stress generated at the aggregate-slurry interface due to temperature cycles, thereby ensuring the safety and durability of geothermal energy piles under long-term harsh working conditions. Summary of the Invention

[0007] This application provides a concrete for geothermal energy piles and a method for preparing the same, which can reduce the coefficient of thermal expansion, meet the bearing requirements of the pile foundation, and effectively resist the stress generated at the aggregate-slurry interface due to temperature cycles.

[0008] On one hand, this application provides a type of concrete for geothermal energy piles. The raw materials of the concrete include cementitious materials, fine aggregates, coarse aggregates, mixing water, and water-reducing agents. Based on 100 parts by weight of the total weight of the cementitious materials, the components are: 100 parts by weight of cementitious materials, 165-185 parts by weight of fine aggregates, 210-230 parts by weight of coarse aggregates, 32-38 parts by weight of mixing water, and 1.0-1.3 parts by weight of water-reducing agents. The cementitious materials include cement, mineral powder, fly ash, activated magnesium oxide, and activated alumina micro powder. The coarse aggregates include cordierite aggregates pretreated with alkali thermal activation.

[0009] By adopting the above technical solution, in the concrete hydration process, active MgO and Al2O3 react on the surface of activated cordierite aggregate to generate spinel (MgAl2O4) and MSH gel with extremely low thermal expansion coefficient in situ.

[0010] Among them, highly reactive magnesium oxide (MgO) and aluminum oxide (Al2O3) micro powders are the reactants that form low-expansion products. The surface of cordierite aggregate, after alkali-thermal activation, changes from inert to active, providing an ideal chemical reaction platform. In this way, a gradient transition zone with gradient changes in chemical composition and physical properties is constructed between the cordierite aggregate and the cement stone matrix. The gradient transition zone consists of the aggregate bulk, the spinel / MSH bridging layer, and the modified cement stone matrix in sequence. This gradient transition zone can extremely effectively buffer and reduce the interfacial stress caused by thermal mismatch.

[0011] Preferably, the cementitious material comprises, by weight, 48-55 parts cement, 26-31 parts mineral powder, 14-18 parts fly ash, 2.5-4.0 parts active magnesium oxide, and 1.2-2.0 parts active alumina powder.

[0012] Preferably, in the fine aggregate, silicon carbide waste sand accounts for 20%-30% of the total weight of the fine aggregate, and the remainder is river sand.

[0013] By adopting the above technical solution, the fine aggregate in this application is composed of silicon carbide waste sand and river sand. Silicon carbide has high hardness, high thermal conductivity, and certain activity. Its waste utilization meets environmental protection requirements. Furthermore, as a geothermal exchange medium, the pile concrete requires a certain thermal conductivity, and the addition of highly thermally conductive silicon carbide helps to meet this requirement. Moreover, when compounded with river sand, the particle size distribution can be optimized, improving the density and strength of the concrete.

[0014] Preferably, in the coarse aggregate, surface-activated cordierite aggregate accounts for 25%-35% of the total weight of the coarse aggregate, and the remainder is crushed stone.

[0015] By adopting the above technical solution, the proportion of cordierite aggregate in this application is key to balancing performance and cost. If the proportion of cordierite is too low, the total amount of the transition zone formed will be insufficient, failing to significantly improve the overall thermal shock resistance of the material. If the proportion is too high, on the one hand, the cost will increase sharply, and on the other hand, the overall performance of the concrete may be affected due to the strength of the cordierite aggregate itself or its compatibility with other components of the formulation.

[0016] On the other hand, a method for preparing concrete for geothermal energy piles includes the following steps: S1, surface activation pretreatment of cordierite in the coarse aggregate; S2, adding coarse aggregate including activated cordierite aggregate, fine aggregate, and cementitious materials into a mixer and mixing evenly; S3, dissolving the water-reducing agent in the mixing water, and then adding the aqueous solution for wet mixing to obtain a concrete mixture; S4, pouring, vibrating, and curing the mixture with moisture.

[0017] Preferably, in step S1, the alkaline thermal activation pretreatment method for the cordierite aggregate is as follows: the cordierite aggregate is soaked in a sodium hydroxide solution with a mass fraction of 3%-8%, stirred at 65-75°C for 0.5-1.5 hours, and then washed and dried.

[0018] By adopting the above technical solution, this application etches the surface of cordierite to fully activate it and form sufficient active sites, while avoiding excessive corrosion that could damage the integrity of the aggregate particles, thereby ensuring that the activation reaction proceeds fully.

[0019] Preferably, in step S4, the concrete mixture obtained in step S3 is poured into the mold or pile foundation hole in a timely manner. After the pouring and vibration are completed, the specimen or component is transferred to a standard curing room or moisturized by covering with plastic film, spraying curing agent, etc. The curing environment temperature should be controlled at 20℃ ± 2℃ and the relative humidity (RH) should not be lower than 95%.

[0020] By adopting the above technical solution, standard conditions are ensured for the smooth progress and optimal effect of cement hydration and the MgO / Al2O3 interfacial reaction. Insufficient humidity will lead to water evaporation, affecting the degree of hydration and thus the strength and density of the gradient zone.

[0021] One or more technical solutions provided in this application have at least the following technical effects or advantages: 1. In the concrete hydration process, active MgO and Al2O3 react on the surface of activated cordierite aggregate to generate spinel (MgAl2O4) and MSH gel with extremely low thermal expansion coefficients in situ. This creates a gradient transition zone with varying chemical composition and physical properties between the cordierite aggregate and the cementitious matrix. This gradient transition zone can effectively buffer and reduce interfacial forces caused by thermal mismatch.

[0022] 2. The fine aggregate in this application consists of silicon carbide waste sand and river sand. Silicon carbide has high hardness, high thermal conductivity, and certain activity. Its waste utilization complies with environmental protection requirements. Furthermore, as a geothermal exchange medium, the pile concrete requires a certain thermal conductivity, and the addition of highly thermally conductive silicon carbide helps to meet this requirement. Moreover, when compounded with river sand, it can optimize the particle size distribution and improve the density and strength of the concrete.

[0023] 3. The proportion of cordierite aggregate in this application is crucial for balancing performance and cost. If the proportion of cordierite is too low, the total amount of the transition zone formed will be insufficient, failing to significantly improve the overall thermal shock resistance of the material. If the proportion is too high, on the one hand, the cost will increase dramatically, and on the other hand, the overall performance of the concrete may be affected due to the strength of the cordierite aggregate itself or its compatibility with other components of the formulation. Detailed Implementation

[0024] This application provides a concrete for geothermal energy piles and a method for preparing the same, which can reduce the coefficient of thermal expansion, meet the bearing requirements of the pile foundation, and effectively resist the stress generated at the aggregate-slurry interface due to temperature cycles.

[0025] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0026] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or server that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or modules not explicitly listed or inherent to such processes, methods, products, or devices. Example 1

[0027] This application provides a method for preparing concrete for geothermal energy piles, the specific steps of which are as follows: S1. First, prepare a 5% sodium hydroxide (NaOH) aqueous solution and place it in a heating container resistant to alkali corrosion. Then, immerse a specified amount of cordierite coarse aggregate with a particle size of 5mm to 25mm in the above NaOH solution.

[0028] The mixture is then heated to 75°C using a device with heating and stirring functions. During the pretreatment process, gentle and continuous mechanical stirring is maintained at a speed of 50 rpm to ensure uniform heating and etching of the aggregate and to prevent local overheating or aggregate deposition.

[0029] After stirring continuously for 1 hour, the cordierite aggregate is removed and thoroughly rinsed with deionized or purified water until the rinse water is neutral. The washed aggregate is then transferred to a forced-air drying oven and dried at 90°C until the aggregate reaches a constant weight, thus obtaining surface-activated cordierite coarse aggregate.

[0030] S2. Weigh all dry raw materials strictly according to the proportions. Dry raw materials include cementitious materials, fine aggregates, and coarse aggregates. The total weight of cementitious materials is 400 kg / m³, including: 200 kg of cement (50 parts by weight, based on a total cementitious material weight of 100 parts), 112 kg of mineral powder (28 parts by weight), 64 kg of fly ash (16 parts by weight), 12 kg of activated magnesium oxide (3.0 parts by weight), and 6.4 kg of activated alumina powder (1.6 parts by weight).

[0031] The total weight of fine aggregate is 660 kg / m³ (165 parts by weight), including 165 kg of silicon carbide waste sand (accounting for 25% of the total weight of fine aggregate) and 495 kg of river sand. The total weight of coarse aggregate is 920 kg / m³ (230 parts by weight), including 276 kg of cordierite aggregate that has been thermally activated by alkali solution (accounting for 30% of the total weight of coarse aggregate) and 644 kg of crushed stone.

[0032] Add all the weighed dry materials to the mixer. Start the mixer and dry mix. The dry mixing time should be no less than 90 seconds, or until all materials are observed to be uniformly mixed.

[0033] S3. First, completely dissolve the specified amount of polycarboxylate superplasticizer in all the mixing water to prepare a superplasticizer aqueous solution. While keeping the mixer running at low speed, slowly and evenly pour the superplasticizer aqueous solution into the dry mixture. The mixing water content is 128 kg / m³. 3 (32 parts by weight), water-reducing agent is polycarboxylate water-reducing agent at 5.2 kg / m³. 3(1.3 parts by weight) After adding water, switch to high-speed wet mixing. The wet mixing time should be no less than 120 seconds, or until a concrete mixture with uniform slurry, no bleeding or segregation, and fluidity meeting design requirements is obtained.

[0034] S4. Pour the obtained concrete mixture into the mold and thoroughly vibrate it using an immersion vibrator to remove air bubbles and ensure compaction. After pouring and vibration, immediately transfer the component to a standard curing room or use methods such as covering with plastic film or spraying curing agent for moisture retention curing. The curing environment temperature should be controlled at 20℃ ± 2℃, and the relative humidity (RH) should not be lower than 95%.

[0035] In this application, a gradient transition zone with varying chemical composition and physical properties is constructed. This gradient transition zone consists sequentially of the aggregate bulk, the spinel / MSH bridging layer, and the modified cementitious matrix. This gradient transition zone effectively buffers and reduces interfacial stress caused by thermal mismatch. Furthermore, this gradient transition zone is not formed in a single step; its formation is a dynamic process that continues throughout the key steps. It begins with water addition and mixing in step S3, and gradually develops, strengthens, and ultimately forms during curing in step S4.

[0036] Firstly, in S1, the alkaline thermal activation treatment transforms the surface of the cordierite aggregate from inert to an active surface with high surface energy, rich in reactive ≡Si-O. - and ≡Al-O - Site. This step itself does not form a transition zone, but rather lays the foundation for subsequent in-situ reactions. Then, the dry mixing in S2 ensures that the activated magnesium oxide (MgO) and activated alumina (Al2O3) micro powders can be uniformly and tightly adhered to the surface of the activated cordierite aggregate.

[0037] Then, through the addition of water and stirring in step S3, the synergistic hydration reaction is triggered upon the addition of water, causing the cement to hydrate rapidly and creating a highly alkaline environment throughout the system. On the surface of the activated cordierite aggregate, the reaction begins, and the highly alkaline environment prompts the activation layer to release Si. 4+ Al 3+ Ions. Simultaneously, the active Al₂O₃ and MgO micropowder adhering to the surface begin to dissolve, providing Al... 3+ and Mg 2+ These ions begin to react on the activated surface and in its adjacent region, generating spinel (MgAl2O4) nuclei and MSH gel.

[0038] The curing process in step S4 is crucial for the strengthening and formation of the gradient transition zone. During the curing period, the dissolution of active MgO and Al2O3 and their reaction with the silicon components at the interface continue, causing the spinel and MSH gel bridging layer to thicken and strengthen continuously. The newly formed crystalline and gel phases form strong chemical bonds with the cordierite aggregate and cement stone matrix, truly integrating the aggregate, bridging layer, and matrix into a unified whole. As the reactant concentration decreases from the interface to the matrix interior, the density and properties of the final product also exhibit a gradient change, thus forming an ideal gradient transition zone for the coefficient of thermal expansion. Example 2

[0039] The difference between Example 2 and Example 1 is that the ratio of silicon carbide waste to cordierite aggregate is different in Example 2. Specifically, the silicon carbide waste in the fine aggregate is 198 kg / m³. 3 It accounts for 30% of the fine aggregate content, and river sand is 462 kg / m³. 3 It accounts for 70% of the fine aggregate. Cordierite aggregate in the coarse aggregate is 322 kg / m³. 3 It accounts for 35% of the coarse aggregate content, with crushed stone at 598 kg / m³. 3 It accounts for 65% of the coarse aggregate content. Example 3

[0040] The difference between Example 3 and Example 1 is that the ratio of silicon carbide waste to cordierite aggregate is different in Example 3. Specifically, the silicon carbide waste in the fine aggregate is 132 kg / m³. 3 River sand accounts for 20% of the fine aggregate content, while river sand accounts for 80% of the fine aggregate at 528 kg / m³. Cordierite accounts for 230 kg / m³ of the coarse aggregate. 3 It accounts for 25% of the coarse aggregate content, with crushed stone at 690 kg / m³. 3 It accounts for 75% of the coarse aggregate content.

[0041] Comparative Example Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses conventional C40 concrete. Specifically, the cementitious material content is only 400 kg / m³. 3 P·O42.5 cement; fine aggregate is 660 kg / m³ 3 Natural river sand; coarse aggregate is 920 kg / m³ 3 Ordinary crushed stone; mixing water is 160 kg / m³ 3 The water-reducing agent is a 4 kg / m³ polycarboxylate superplasticizer. The preparation method involves conventional mixing, pouring, and curing.

[0042] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the cementitious material in Comparative Example 2 does not contain active magnesium oxide and alumina micropowder. Specifically, the cementitious material has a density of 400 kg / m³. 3 The composition includes 50 parts cement, 28 parts mineral powder, and 22 parts fly ash to make up the difference. The coarse aggregate contains 30% activated cordierite aggregate, the same as in Example 1.

[0043] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that ordinary cordierite aggregate was used in the coarse aggregate of Comparative Example 3, and the cordierite aggregate was not subjected to alkaline thermal activation treatment. Other components and preparation methods are the same as in Example 1.

[0044] Performance testing experiment This application tests the mechanical properties, thermal properties, durability properties, and thermal shock resistance properties of Examples 1-3 and Comparative Examples 1-3.

[0045] 1. Mechanical properties: The 28-day compressive strength and 28-day flexural strength were tested according to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete".

[0046] 2. Thermal properties: The coefficient of thermal expansion was tested according to ASTM E228-17, "Standard Test Method for Linear Coefficient of Thermal Expansion," with a temperature range of 20-80℃. The thermal conductivity was tested according to ASTM C1113, "Measuring Thermal Conductivity by Heat Flow Meter Method."

[0047] 3. Durability: The impermeability grade is tested according to GB / T 50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete".

[0048] 4. Thermal Shock Resistance: The thermal shock resistance test, also known as the thermal cycling test, simulates the temperature cycle of a geothermal energy pile. The specimen (100mm×100mm×400mm) is placed in an environmental chamber and subjected to 100 temperature cycles (each cycle: 5℃ for 2 hours → temperature rise to 40℃ for 2 hours → temperature drop to 5℃). After cycling, the compressive strength loss rate is tested and compared with the initial 28-day strength. The mass loss rate after cycling is calculated by weighing.

[0049] The data from Examples 1-3 and Comparative Examples 1-3 are summarized in Table 1 below. Table 1

[0050] Firstly, the mechanical properties were analyzed. Tests on compressive and flexural strength showed that the 28-day compressive strength of all examples exceeded 50 MPa, and the flexural strength exceeded 6.0 MPa, meeting the standard requirements and surpassing the strength level of ordinary C40 concrete in Comparative Example 1. Furthermore, Comparative Example 2 exhibited the lowest strength.

[0051] The high strength of the example is due to the formation of a chemically bonded gradient transition zone between the activated cordierite aggregate and the cement matrix, which greatly strengthens the weakest interface and thus improves the overall mechanical properties. The spinel and MSH gel generated by the reactive oxides also contribute to the strength.

[0052] Comparative Example 2 showed the lowest strength, indicating that simply adding activated cordierite without providing sufficient reactive materials (MgO, Al2O3) cannot generate high-strength products at the interface. Its interface strengthening effect is limited, and it may even become a weakness due to insufficient bonding with ordinary slurry after aggregate surface etching. Comparative Example 3 contained active oxides but no activated cordierite, so its strength was comparable to ordinary concrete. This indicates that the active oxides reacted dispersedly in the matrix, lacking the guidance of an activated interface. Its strengthening effect could not be concentrated in the interface area most in need of strengthening, thus its overall strength improvement was not significant.

[0053] Secondly, thermal performance analysis was conducted. This application tested the thermal conductivity and coefficient of thermal expansion. It was found that Example 2 had the highest thermal conductivity. Furthermore, the coefficient of thermal expansion in the examples was significantly lower than that in all comparative examples. The coefficient of thermal expansion in the examples was between 7.2 and 7.8, while the coefficients in the comparative examples were all above 9.8, with the coefficient of thermal expansion of ordinary concrete in Comparative Example 1 reaching as high as 11.5.

[0054] Because the embodiments contain highly thermally conductive silicon carbide fine aggregate and cordierite coarse aggregate, the thermal conductivity is better. Embodiment 2 has the highest thermal conductivity due to the highest content of these two materials. This demonstrates that the present invention, while pursuing thermal shock resistance, also considers the functional requirements of geothermal piles as heat exchangers. Furthermore, the low coefficient of thermal expansion is attributed to the in-situ formation of spinel and MSH gel with extremely low coefficients of thermal expansion in the interface region. These low-expansion phases form a gradient transition zone at the interface, microscopically altering the overall thermal deformation behavior of the concrete.

[0055] The coefficient of thermal expansion in Comparative Example 3 was improved compared to Comparative Examples 1 and 2, demonstrating that the reaction of the active oxide in the matrix can indeed reduce the coefficient of thermal expansion to some extent, but the effect is far less than that in the examples because it lacks interface guidance, and the effect is macroscopic and dispersed. The improvement in Comparative Example 2 was very limited, demonstrating that without active oxides, a significant reduction in the coefficient of thermal expansion cannot be achieved by activating cordierite itself.

[0056] Furthermore, this application tested durability, and data observation showed that the impermeability grade of the embodiments was significantly higher than that of the comparative examples. Impermeability is directly related to the density of concrete, especially the density of the interface zone. The dense gradient transition zone in the embodiments effectively blocked the seepage channels, thereby significantly improving impermeability.

[0057] Finally, this application analyzes thermal shock resistance based on strength loss rate and mass loss rate. Simulating actual working conditions, this application found that the compressive strength loss rate in the embodiments was ≤4.0%, while the comparative examples were all above 8.0%. Furthermore, the mass loss rate mainly reflects the spalling or deterioration of the material surface. During thermal cycling, the surface and interior temperature difference is greatest, resulting in the most concentrated interfacial stress, which easily leads to the detachment of the surface material. The lower mass loss rate in the embodiments compared to ordinary concrete indicates that the concrete surface integrity in this application is excellent. This is due to the formation of a chemically bonded gradient transition zone, where aggregates and paste deform synergistically during thermal expansion and contraction, avoiding the generation of huge shear stresses at the interface that could lead to spalling.

[0058] It should be noted that the order of the embodiments described above is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. Furthermore, specific embodiments have been described above. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps described in the claims can be performed in a different order than that shown in the embodiments and still achieve the desired result. Additionally, the processes depicted do not necessarily require a specific or sequential order to achieve the desired result. In some implementations, multitasking and parallel processing are also possible or may be advantageous.

[0059] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

[0060] This specification and accompanying drawings are merely illustrative examples of this application and are intended to cover any and all modifications, variations, combinations, or equivalents within the scope of this application. Clearly, those skilled in the art can make various alterations and modifications to this application without departing from its scope. Therefore, if such modifications and modifications fall within the scope of this application and its equivalents, this application intends to include such modifications and modifications.

Claims

1. A concrete for geothermal energy piles, characterized in that, The raw materials for the concrete include cementitious materials, fine aggregates, coarse aggregates, mixing water, and water-reducing agents. Based on a total weight of 100 parts by weight of the cementitious material, the components are: 100 parts by weight of cementitious material, 165-185 parts by weight of fine aggregate, 210-230 parts by weight of coarse aggregate, 32-38 parts by weight of mixing water, and 1.0-1.3 parts by weight of water-reducing agent. The cementitious material includes cement, mineral powder, fly ash, activated magnesium oxide, and activated alumina micro powder; The coarse aggregate includes cordierite aggregate that has undergone alkali thermal activation pretreatment.

2. Concrete for geothermal energy piles according to claim 1, characterized in that, The cementitious material comprises, by weight, 48-55 parts cement, 26-31 parts mineral powder, 14-18 parts fly ash, 2.5-4.0 parts active magnesium oxide, and 1.2-2.0 parts active alumina powder.

3. Concrete for geothermal energy piles according to claim 2, characterized in that, In the fine aggregate, silicon carbide waste sand accounts for 20%-30% of the total weight of the fine aggregate, and the remainder is river sand.

4. The concrete for geothermal energy piles according to claim 2, wherein In the coarse aggregate, surface-activated cordierite aggregate accounts for 25%-35% of the total weight of the coarse aggregate, and the remainder is crushed stone.

5. A method of producing concrete for geothermal energy piles according to any one of claims 1 to 4, characterized in that, The following steps are included: S1. Surface activation pretreatment is performed on the cordierite in the coarse aggregate; S2. Add coarse aggregates, fine aggregates, and cementing materials, including activated cordierite aggregates, into a mixer and dry mix them evenly. S3. Dissolve the water-reducing agent in the mixing water, then add the aqueous solution to wet mix to obtain the concrete mixture; S4. Pour the mixture, vibrate it, and keep it moist for curing.

6. The method for preparing concrete for geothermal energy piles as described in claim 5, characterized in that, In step S1, the alkaline thermal activation pretreatment method for the cordierite aggregate is as follows: The cordierite aggregate is soaked in a sodium hydroxide solution with a mass fraction of 3%-8% and stirred at 65-75℃ for 0.5-1.5 hours, then washed and dried.

7. The method for preparing concrete for geothermal energy piles as described in claim 5, characterized in that, In step S4, the concrete mixture obtained in step S3 is poured into the mold or pile foundation hole in a timely manner. After the pouring and vibration are completed, the specimen or component is transferred to the standard curing room or moisturized by covering with plastic film, spraying curing agent, etc. The curing environment temperature should be controlled at 20℃ ± 2℃ and the relative humidity (RH) should not be lower than 95%.

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