An ultra-high performance concrete resistant to high ground temperature, its preparation method and application

Abstract

The invention discloses a high ground temperature resistant ultra-high performance concrete and a preparation method and application, belonging to the technical field of building materials. The concrete comprises the following components in parts by weight: 360-520 parts of high sulfate resistant cement, 36-52 parts of silica fume, 36-52 parts of fly ash, 800-1000 parts of fine aggregate, 80-200 parts of composite phase change lightweight aggregate, 800-1000 parts of coarse aggregate, 39-78 parts of steel fiber, 1.8-10.4 parts of sodium borate, 43-125 parts of incineration garbage bottom ash, 120-130 parts of water and 5-10 parts of high-efficiency water reducing agent. The synergistic effect of high sulfate resistant cement, sodium borate, composite phase change lightweight aggregate and incineration garbage bottom ash enables the ultra-high performance concrete to not only maintain stability in a high ground temperature environment, but also improve its durability, ensuring the long-term use safety of concrete in a high ground temperature environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and particularly relates to a high geothermal resistance ultra-high performance concrete, a preparation method thereof, and an application thereof. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the understanding of the overall background of the present invention, and is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] High geothermal temperature refers to a special thermal environment where the temperature of underground rock and soil mass exceeds a certain threshold, which is an important technical challenge in engineering construction. In some areas, due to active geological structures and rich geothermal resources, the temperature of underground rock and soil mass is relatively high, bringing significant technical challenges to the construction of projects such as tunnels, mines, and underground storage facilities. In a high geothermal temperature environment, due to the high temperature, the hydration rate of concrete accelerates, which may lead to uneven distribution of hydration products. At the same time, the fluidity loss is relatively large, thus affecting the workability and the uniformity of the later strength. The performance of concrete materials will be significantly affected, especially the problem of delayed ettringite formation (DEF) is more prominent. As a chemical expansion reaction, DEF is called the "cancer of concrete", which is an expansion phenomenon caused by the reaction of calcium aluminate in the cement matrix with sulfate ions to form ettringite. In a high geothermal temperature environment, due to the enhanced activity of sulfate ions and the accelerated reaction rate, the amount of ettringite formed increases significantly, thus causing volume expansion and cracking of concrete. This not only seriously threatens the structural safety of tunnels and underground projects, but also increases the cost of later maintenance and repair. In addition, the high geothermal temperature environment will also accelerate the deterioration of the pore structure in concrete, which will also lead to uneven distribution of hydration products, further reducing the durability of the material.

[0004] Ultra-High Performance Concrete (UHPC) has become an ideal material for tunnels and underground projects due to its excellent compressive strength (>150 MPa), low porosity, and excellent durability. However, the DEF problem it faces in a high geothermal temperature environment is more severe: Although the dense microstructure of UHPC improves the erosion resistance, it also restricts the release of expansion pressure, resulting in more serious cracks caused by DEF. In addition, high geothermal temperature conditions will accelerate the chemical reaction rate and stress concentration effect in UHPC, making the crack propagation speed faster and the risk of structural damage significantly increased. This limitation hinders the wider popularization and application of UHPC in extreme environments. Summary of the Invention

[0005] To solve the deficiencies of the prior art, the object of the present invention is to provide a high geothermal resistant ultra-high performance concrete, its preparation method and application. By adding components such as composite phase change lightweight aggregate, sodium borate, and incinerated waste bottom ash, the delayed ettringite reaction (DEF) under high geothermal conditions is effectively weakened, the crack resistance and durability of the concrete are improved, and the application of ultra-high performance concrete in high geothermal environments is realized.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] In the first aspect, the present invention provides a high geothermal resistant ultra-high performance concrete, comprising the following components in parts by weight:

[0008] 360 - 520 parts of high sulfate resistant cement, 36 - 52 parts of silica fume, 36 - 52 parts of fly ash, 800 - 1000 parts of fine aggregate, 80 - 200 parts of composite phase change lightweight aggregate, 800 - 1000 parts of coarse aggregate, 39 - 78 parts of steel fiber, 1.8 - 10.4 parts of sodium borate, 43 - 125 parts of incinerated waste bottom ash, 120 - 130 parts of water, and 5 - 10 parts of high range water reducer;

[0009] The composite phase change lightweight aggregate is prepared from the following raw materials in parts by mass: 40 - 60 parts of calcium carbonate-based microporous material, 20 - 40 parts of phase change material, 15 - 25 parts of high sulfate resistant cement, and 0.5 - 2 parts of silane coupling agent; the calcium carbonate-based microporous material includes calcareous starfish skeletons.

[0010] In the second aspect, the preparation method of the above high geothermal resistant ultra-high performance concrete comprises the following steps:

[0011] S1. Use the vacuum adsorption method to make the calcium carbonate-based microporous material adsorb the phase change material to obtain a composite phase change material;

[0012] S2. Mix and granulate the composite phase change material with high sulfate resistant cement, and then surface modify it with a silane coupling agent to obtain a composite phase change lightweight aggregate;

[0013] S3. Mix high sulfate resistant cement, silica fume, fly ash, fine aggregate, composite phase change lightweight aggregate, and coarse aggregate, and stir evenly;

[0014] S4. After adding a set amount of water and mixing, add a high range water reducer and mix and stir evenly, then add the remaining water and incinerated waste bottom ash, stir evenly, add sodium borate, stir evenly, and then add steel fiber to obtain a mixed slurry;

[0015] S5. Cast and mold the mixed slurry and cure it at a temperature consistent with the high geothermal environment to obtain high geothermal resistant ultra-high performance concrete.

[0016] In a third aspect, the above-mentioned application of the high geothermal-resistant ultra-high performance concrete includes applications in geothermal projects, deep-buried tunnels, nuclear power plants, or infrastructure construction in high geothermal environments.

[0017] The beneficial effects of the present invention are as follows:

[0018] 1. The present invention uses high sulfate-resistant cement, which has a low tricalcium aluminate content, reducing the risk of delayed ettringite formation (DEF) at the source; borax is incorporated to react with calcium aluminate to form stable boron-aluminum complexes, further inhibiting the formation of ettringite, reducing the expansion and cracks caused by the reaction of sulfate ions with calcium aluminate. It also acts as a reaction regulator, promoting the uniform distribution of hydration products under high-temperature conditions, slowing down the heat release during the hydration process, and improving the fluidity and workability of the concrete; composite phase change lightweight aggregates are used to regulate the temperature fluctuations in the concrete, and the processes of cement encapsulation and silane coupling agent modification enhance its bonding force with the cement matrix, enabling it to play a role stably in high-temperature environments for a long time; the incinerated bottom ash incorporated is rich in active oxides, consuming part of the calcium hydroxide through pozzolanic reactions to form denser hydration products to fill the micropores and improve the pore structure, and also reducing the sulfate ion concentration in the pore solution, reducing the formation of ettringite, and essentially reducing the risk of DEF. The synergistic effect of the four enables this ultra-high performance concrete to not only maintain stability in high geothermal environments but also improve its durability, ensuring the long-term use safety of the concrete in high geothermal environments. Description of the Drawings

[0019] The schematic diagrams in the specification forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0020] Figure 1 It is a schematic diagram of the technical route of the high geothermal-resistant ultra-high performance concrete in the embodiment. Detailed Embodiments

[0021] It should be noted that the following detailed descriptions are all exemplary and are intended to provide further explanations of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0022] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0023] A typical embodiment of the present invention provides a high-temperature-resistant ultra-high-performance concrete, comprising the following components in parts by weight:

[0024] 360 - 520 parts of high sulfate-resistant cement, 36 - 52 parts of silica fume, 36 - 52 parts of fly ash, 800 - 1000 parts of fine aggregate, 80 - 200 parts of composite phase change lightweight aggregate, 800 - 1000 parts of coarse aggregate, 39 - 78 parts of steel fiber, 1.8 - 10.4 parts of sodium borate, 43 - 125 parts of incinerated garbage bottom ash, 120 - 130 parts of water, and 5 - 10 parts of high-range water reducer;

[0025] The composite phase change lightweight aggregate is prepared from the following raw materials in parts by mass: 40 - 60 parts of calcium carbonate-based microporous material, 20 - 40 parts of phase change material, 15 - 25 parts of high sulfate-resistant cement, and 0.5 - 2 parts of silane coupling agent; the calcium carbonate-based microporous material includes calcareous starfish skeletons.

[0026] Among the above components, as Figure 1 shown, the combined use of the composite phase change lightweight aggregate, sodium borate, incinerated garbage bottom ash, and high sulfate-resistant cement enables the ultra-high-performance concrete to exhibit remarkable crack resistance and high-temperature resistance in a high-temperature environment; among them, the high sulfate-resistant cement reduces the risk of DEF by reducing the content of calcium aluminate; the composite phase change lightweight aggregate provides a temperature control effect, effectively reducing the cracks caused by temperature fluctuations, thereby reducing the internal temperature of the concrete within a certain period of time and slowing down the occurrence of DEF; sodium borate inhibits the occurrence of DEF by reacting with calcium aluminate to form a stable boron-aluminum complex; incinerated garbage bottom ash reduces the chance of sulfate reacting with calcium aluminate by filling micropores and reducing the sulfate ion concentration; thus overall improving the crack resistance and high-temperature resistance of the concrete.

[0027] Optionally, the high sulfate-resistant cement is selected from 52.5-grade or 52.5R-grade high sulfate-resistant cement; the lower content of tricalcium aluminate means that the content of calcium aluminate in the cement that can react with sulfate ions to form ettringite (AFt) is less; therefore, using high sulfate-resistant cement significantly reduces the occurrence probability of DEF, thus effectively avoiding the crack problem caused by ettringite expansion; it can reduce the potential negative impact of sulfate on the concrete, enhance the crack resistance and high-temperature resistance of the concrete; and has good compatibility with polycarboxylate-based high-range water reducer.

[0028] Optionally, the amorphous silica content in the silica fume is greater than 95 wt%, the specific surface area is greater than 21.0 m 2 / g, the specific gravity (compared with the density of water) is greater than 2.2, and it is an ultra-fine dry powder that has not been fully densified.

[0029] Optionally, the fly ash is Class I or Class II fly ash, with a specific surface area greater than 400 m 2 / kg, a strength activity index greater than 70%, and a density of 2470 kg / m 3 .

[0030] Optionally, the fine aggregate is river sand or quartz sand, with a fineness modulus of 2.3 - 3.0, a particle size of 0.075 - 0.35 mm, and an average particle size of 0.2 mm.

[0031] Optionally, the Mohs hardness value of the coarse aggregate is above 8, the elastic modulus is 400 - 450 GPa, and the density is 3300 kg / m 3 .

[0032] Optionally, the steel fiber is a copper - plated straight steel fiber with an average length of 13 mm and an average diameter of 0.16 mm.

[0033] Optionally, the sodium borate is a powder with a particle size of 0.1 - 0.5 mm to ensure uniform distribution and reaction efficiency in the concrete matrix.

[0034] Optionally, the incinerated waste bottom ash is the bottom ash obtained after the municipal solid waste is incinerated at a high temperature of 900 - 1200 °C; its particle size distribution is: the part with a particle size of 0.075 - 1 mm accounts for 60% - 70% of the mass ratio, and the part with a particle size of 1 - 4.75 mm accounts for 30% - 40% of the mass ratio; the finally obtained incinerated waste bottom ash particles need to meet the concrete design requirements and have good pozzolanic activity; it consumes calcium hydroxide through the pozzolanic effect to generate dense secondary cementitious products to fill the pores, reduce the risk of crack generation, and at the same time reduce the concentration of sulfate ions to alleviate the deterioration effect of DEF.

[0035] Optionally, the high - range water - reducing agent is a polycarboxylate - based water - reducing agent, with a solid content greater than 35% and a density of 1100 kg / m 3 .

[0036] Optionally, the structure of the composite phase - change lightweight aggregate is: the phase - change material is adsorbed in the calcium carbonate - based microporous material, the outside of the calcium carbonate - based microporous material is coated with a high - sulfate - resistant cement shell, and the surface of the high - sulfate - resistant cement shell is modified by a silane coupling agent.

[0037] Optionally, in the composite phase - change lightweight aggregate, the phase - change material includes one or more of stearic acid, lauric acid, and myristic acid, and the phase - change temperature is 50 - 70 °C; the melting point of stearic acid (C 18 H 36 O2) is about 69 °C, the melting point of lauric acid (C 12 H 24 O2) is about 44 °C, and the melting point of myristic acid (C 14 H 28O2) The melting point is about 54°C. Fatty acid materials have high thermal potential and good thermal stability, can absorb and release heat in the composite phase change lightweight aggregate, regulate the temperature of the concrete, and improve the thermal management performance of the composite phase change lightweight aggregate.

[0038] Optionally, the particle size of the composite phase change lightweight aggregate is 6 - 10 mm, which is equivalent to the particle size of the coarse aggregate. The selection of this particle size range takes into account the matching with the size of the coarse aggregate, ensuring good workability of the concrete. It ensures that during the processes of concrete mixing, pouring, and forming, the aggregates can be evenly distributed and effectively embedded in the cement matrix, thereby improving the strength and stability of the concrete. Selecting a particle size range equivalent to that of the coarse aggregate can improve the heat insulation performance without affecting the mechanical properties and workability of the concrete. Too small a particle size will increase the surface area of the material, resulting in poor fluidity of the concrete and possibly too high a viscosity, making it difficult to distribute evenly and increasing the difficulty of mixing and pouring. Too large a particle size will lead to poor fluidity of the concrete and affect the construction performance.

[0039] The calcium carbonate-rich starfish skeleton (starfish shell) in the composite phase change lightweight aggregate is rich in calcium carbonate (CaCO3), has a high hardness, naturally has a pore structure, has a high specific surface area and pore volume, and can be used as an adsorption substrate for the composite phase change material. The starfish skeleton (such as the cushion star) is a biomineralized porous ceramic material composed of double-scale single-crystal calcium carbonate. The micron-scale structure is a regular diamond-type triple-period minimal surface (TPMS), and the atomic-scale structure is single-crystal calcite. Among them, the double-scale single-crystal structure combining the high-strength TPMS framework at the micron scale and single-crystal calcite at the atomic scale has the characteristics of both light weight (low density) and high strength (compressive strength > 12 MPa). Its pores have the characteristics of regular arrangement, and the ordered pore structure (porosity > 70%) is more conducive to the uniform adsorption of the phase change material and reduces local stress concentration.

[0040] Optionally, the silane coupling agent is one or more of KH550, KH560, KH570, or KH792.

[0041] A typical implementation manner of the present invention provides the preparation method of the above-mentioned high geothermal resistance ultra-high performance concrete, including the following steps:

[0042] S1. Use the method of vacuum adsorption to make the calcium carbonate-based microporous material adsorb the phase change material to obtain the composite phase change material;

[0043] S2. Mix and granulate the composite phase change material with high sulfate-resistant cement, and then surface-modify it with a silane coupling agent to obtain the composite phase change lightweight aggregate;

[0044] S3. Mix high sulfate-resistant cement, silica fume, fly ash, fine aggregate, composite phase change lightweight aggregate, and coarse aggregate, and stir evenly;

[0045] S4. After adding a set amount of water and mixing, add a high-range water reducer and mix evenly. Then add the remaining water and incinerated waste bottom ash. After mixing evenly, add sodium borate, and after mixing evenly, add steel fibers to obtain a mixed slurry.

[0046] S5. Cast the mixed slurry and cure it at a temperature consistent with the high geothermal environment to obtain high geothermal resistant ultra-high performance concrete.

[0047] In the above process, through vacuum impregnation, the phase change material is adsorbed into the pores of the calcium carbonate-based microporous material, thereby improving the phase change energy storage function of the composite material; the composite phase change material is granulated and cured by mixing with high sulfate-resistant cement, and surface modification is carried out using a silane coupling agent to enhance its bonding force with the cement matrix; in the subsequent process, sodium borate and incinerated waste bottom ash are added to further consume calcium aluminate and sulfate ions, reducing the possibility of ettringite formation from the source; this material system not only weakens the temperature gradient during the hydration heat release process, reduces the shrinkage rate, but also significantly improves the crack resistance and durability of UHPC in high geothermal environments.

[0048] Optionally, in S1, the calcium carbonate-based microporous material is cleaned and dried to remove surface impurities and organic substances; it is rinsed repeatedly with deionized water to ensure no residues; then the starfish shell is dried, and the drying temperature is controlled at 50°C to 70°C for a duration of not less than 24 hours to remove moisture and maintain its structural integrity; deionized water is water obtained by removing dissolved ions (such as sodium, calcium, magnesium, etc.) in water; it has a low conductivity and is suitable for applications requiring high-purity water sources, and is usually used in cleaning and dissolution processes to avoid interference of minerals in water with samples or processes.

[0049] Optionally, in S1, after mixing the calcium carbonate-based microporous material and the phase change material, place them in a vacuum environment and heat to a temperature above the phase change temperature of the phase change material for vacuum impregnation treatment; the vacuum degree of the vacuum environment is less than 10 -4 Pa, and vacuum impregnation is carried out for 3 - 5 h; ensure that the calcium carbonate-based microporous material is completely immersed in the liquid phase change material, and the internal gas escapes under the action of vacuum, so that the phase change material is gradually adsorbed into the calcium carbonate-based microporous material to form a composite phase change material.

[0050] Optionally, in S2, mix and stir the composite phase change material with a high sulfate-resistant cement slurry for granulation to achieve cement encapsulation. The purpose of cement encapsulation is to wrap the composite phase change material in the cement slurry to form a strong outer shell to prevent the phase change material from leaking; the viscosity of the cement slurry should be moderate, which can completely wrap the composite phase change lightweight aggregate without causing incomplete encapsulation, and the thickness of the encapsulated cement shell is 1 - 3 mm.

[0051] Optionally, in S2, the stirring speed is 300 - 500 rpm. Stirring is carried out to ensure the uniformity of the cement slurry and avoid the generation of bubbles, so that the encapsulated composite phase change lightweight aggregate presents solid granular calcium, and the phase change material is firmly encapsulated in the cement shell, ensuring its long-term stability and thermal management effect in the final concrete product.

[0052] Optionally, in S2, the obtained composite phase change lightweight aggregate is cured for more than 28 days in a standard curing environment (20 ± 1°C, 95 ± 2% relative humidity) to ensure its structural stability and strength.

[0053] Optionally, in S3, stir at a low speed for 2 - 3 minutes; in S4, after adding the remaining water and incinerated waste bottom ash, stir at a low speed for 3 - 5 minutes, and after adding sodium borate, stir at a medium speed for 3 - 5 minutes; in S5, stir at a high speed for 1 - 2 minutes before pouring.

[0054] Optionally, in S5, use a vibrating table to vibrate slightly for 1 - 2 minutes during the pouring process, which helps to discharge bubbles and improve its compactness.

[0055] Optionally, in S5, cover with a plastic film after pouring to prevent surface water loss.

[0056] A typical embodiment of the present invention provides the application of the above-mentioned high geothermal ultra-high performance concrete, including: applications in geothermal projects, deep-buried tunnels, nuclear power plants or infrastructure construction in high geothermal environments; this material system provides a safer and more reliable material solution for underground engineering and tunnel construction in high geothermal environments.

[0057] Example 1

[0058] A high geothermal ultra-high performance concrete includes the following components in parts by weight:

[0059] 480 parts of 52.5R grade high sulfate-resistant cement, 48 parts of incompletely densified silica fume, 48 parts of Class I fly ash, 900 parts of fine aggregate, 135 parts of composite phase change lightweight aggregate, 1000 parts of coarse aggregate, 3.6 parts of sodium borate, 39 parts of steel fiber, 43 parts of incinerated waste bottom ash, 130 parts of tap water, and 8 parts of polycarboxylate-based high-range water reducer;

[0060] Among them, the composite phase change lightweight aggregate is prepared from the following raw materials in parts by mass: 40 parts of calcium carbonate-based microporous material, 20 parts of phase change material, 15 parts of high sulfate-resistant cement, and 0.5 parts of silane coupling agent (the parts by mass of the raw materials for preparing the composite phase change lightweight aggregate are not the same as those of the high geothermal ultra-high performance concrete, only indicating different preparation steps).

[0061] The amorphous silica content in the incompletely encrypted silica fume is greater than 95 wt%, the specific surface area is greater than 21.0 m 2 / g, and the specific density (compared with the density of water) is greater than 2.2.

[0062] The specific surface area of Class I fly ash is greater than 400 m 2 / kg, the strength activity index is greater than 70%, and the density is 2470 kg / m 3 .

[0063] The fine aggregate is river sand, the fineness modulus is 2.5, and the average particle size is 0.2 mm.

[0064] The coarse aggregate is basalt, the Mohs hardness value is above 8, the elastic modulus is greater than 400 GPa, and the density is 3300 kg / m 3 .

[0065] The steel fiber is a copper-plated straight steel fiber with an average length of 13 mm and an average diameter of 0.16 mm. Its tensile strength is greater than 2500 MPa, the elastic modulus is 200 GPa, and the density is 7800 kg / m 3 .

[0066] Sodium borate is a powder with a particle size of 0.1 - 0.5 mm and is a commercially available high-purity product.

[0067] The incinerated waste bottom ash is the bottom ash obtained after the domestic waste is incinerated at a high temperature of 900 - 1200 °C; the bottom ash is mechanically crushed and screened, and its particle size distribution is: the part with a particle size of 0.075 - 1 mm accounts for 60% - 70% of the mass ratio, and the part with a particle size of 1 - 4.75 mm accounts for 30% - 40% of the mass ratio.

[0068] The high-range water reducer is a polycarboxylate-based water reducer, its solid content is greater than 35%, and the density is 1100 kg / m 3 .

[0069] In the composite phase change lightweight aggregate, the calcium carbonate-based microporous material is a calcareous starfish skeleton; the silane coupling agent is selected as KH550, the high sulfate-resistant cement is 52.5R grade high sulfate-resistant cement; the phase change material is selected as stearic acid (C 18 H 36 O2) and myristic acid (C 14 H 28 O2) with a mass ratio of 1:1, so that the phase change temperature of the phase change material is 50 °C.

[0070] The preparation method includes the following steps:

[0071] S1. Wash the selected calcium carbonate-based starfish bones with deionized water to remove surface impurities and ensure no residues. Then dry them at 50 °C for 24 h, dry and filter, grind and sieve to obtain starfish microporous materials with a set particle size. Mix it with the uniformly mixed phase change materials and place them in a vacuum drying oven. Control the vacuum degree to 10 -4 Pa, the temperature is 50 °C, and vacuum impregnation is carried out for 4 hours to make the calcium carbonate-based microporous materials adsorb the phase change materials, obtaining composite phase change materials.

[0072] S2. Mix the composite phase change materials with 52.5R grade high sulfate-resistant cement slurry and stir at a speed of 500 rpm for 3 - 5 min to ensure that the slurry uniformly wraps the composite phase change materials. Make the mixture into particles with a particle size of 8 ± 2 mm through a granulator. Place the granulated materials in a standard curing environment (20 ± 1 °C, 95 ± 2% relative humidity) for 28 days to fully hydrate the cement and form a stable structure. After curing, use a mechanical crusher to crush the particles at a speed of 1500 rpm, control the crushing strength to avoid damaging the microporous structure, and screen out qualified particles of 8 ± 2 mm through the standard screening method. Immerse the screened particles in a silane coupling agent KH550 solution (concentration 1 - 2 wt%), stir and process at 50 - 60 °C for 30 - 60 min, and then dry in an 80 °C oven for 2 hours to obtain composite phase change lightweight aggregates with hydrophobic surfaces and enhanced interfacial bonding strength.

[0073] S3. Add high sulfate-resistant cement, silica fume, fly ash, fine aggregate, composite phase change lightweight aggregate and coarse aggregate into a mixer at one time and mix at low speed for 3 min until uniform.

[0074] S4. Add 91 parts (70% of the total water volume) of water to the mixture, stir evenly, add a high-performance water reducer, mix and stir evenly, then add 39 parts of water and incinerated garbage bottom ash, stir at low speed for 5 min until uniform, slowly add sodium borate through a square-hole sieve and stir at medium speed for 3 min. After having good fluidity (manifested as the cementitious material can completely wrap the aggregate and the cross-section of the aggregate cannot be seen), slowly add steel fibers to prevent the steel fibers from agglomerating, and continue to stir at medium speed for 5 min until uniform.

[0075] S5. After high-speed stirring for 2 min, pour and mold. During the pouring process, use a vibrating table to vibrate slightly for 2 min to discharge air bubbles and improve its density; after pouring, cover with a plastic film to prevent surface water loss, and demold after 24 h; place the demolded specimens in a 90 °C environment for 24 h to simulate a high geothermal environment, then remove the heating device to make the specimens gradually cool down, and test the linear expansion rate of the specimens on the 28th day, 60th day and 90th day respectively; test its compressive strength on the 28th day.

[0076] Example 2

[0077] An ultra-high performance concrete resistant to high geothermal temperature, comprising the following components in parts by weight:

[0078] 360 parts of 52.5R grade high sulfate-resistant cement, 36 parts of incompletely encrypted silica fume, 36 parts of class I fly ash, 800 parts of fine aggregate, 80 parts of composite phase change lightweight aggregate, 800 parts of coarse aggregate, 1.8 parts of sodium borate, 39 parts of steel fiber, 43 parts of incinerated garbage bottom ash, 120 parts of tap water and 5 parts of polycarboxylate-based high-range water reducer;

[0079] Among them, the composite phase change lightweight aggregate is prepared from the following raw materials in parts by mass: 48 parts of calcium carbonate-based microporous material, 24 parts of phase change material, 16 parts of high sulfate-resistant cement and 0.8 part of silane coupling agent.

[0080] The specifications and preparation methods of each raw material are the same as those in Example 1.

[0081] Example 3

[0082] An ultra-high performance concrete resistant to high geothermal temperature, comprising the following components in parts by weight:

[0083] 520 parts of 52.5R grade high sulfate-resistant cement, 52 parts of incompletely encrypted silica fume, 52 parts of class I fly ash, 1000 parts of fine aggregate, 200 parts of composite phase change lightweight aggregate, 1000 parts of coarse aggregate, 10.4 parts of sodium borate, 78 parts of steel fiber, 125 parts of incinerated garbage bottom ash, 130 parts of tap water and 10 parts of polycarboxylate-based high-range water reducer;

[0084] Among them, the composite phase change lightweight aggregate is prepared from the following raw materials in parts by mass: 60 parts of calcium carbonate-based microporous material, 40 parts of phase change material, 25 parts of high sulfate-resistant cement and 1.5 parts of silane coupling agent.

[0085] The specifications and preparation methods of each raw material are the same as those in Example 1.

[0086] Comparative Example 1

[0087] An ultra-high performance concrete resistant to high geothermal temperature, which is different from Example 1 in that: ordinary portland cement is used to replace the 52.5R grade high sulfate-resistant cement in Example 1. The specifications and preparation methods of other raw materials are the same as those in Example 1.

[0088] Comparative Example 2

[0089] An ultra-high performance concrete resistant to high geothermal temperature, which is different from Example 1 in that: sodium borate is not added. The specifications and preparation methods of other raw materials are the same as those in Example 1.

[0090] Comparative Example 3

[0091] A high geothermal-resistant ultra-high performance concrete, which is different from Example 1 in that: incinerated waste bottom ash is not added. The specifications of other raw materials and the preparation method are the same as those in Example 1.

[0092] Comparative Example 4

[0093] A high geothermal-resistant ultra-high performance concrete, which is different from Example 1 in that: composite phase change lightweight aggregate, sodium borate and incinerated waste bottom ash are not added. The specifications of other raw materials and the preparation method are the same as those in Example 1.

[0094] Comparative Example 5

[0095] A high geothermal-resistant ultra-high performance concrete, which is different from Example 1 in that: ordinary Portland cement is used to replace the 52.5R grade high sulfate-resistant cement in Example 1; and composite phase change lightweight aggregate, sodium borate and incinerated waste bottom ash are not added. The specifications of other raw materials and the preparation method are the same as those in Example 1, serving as a blank control.

[0096] Comparative Example 6

[0097] A high geothermal-resistant ultra-high performance concrete, which is different from Example 1 in that: the calcium carbonate-based microporous material uses coral skeleton fragments instead of calcareous starfish skeletons, and the composite phase change lightweight aggregate prepared has the same specifications as those in Example 1. The specifications of other raw materials and the preparation method are the same as those in Example 1. The experimental data of each example and comparative example were statistically analyzed, and the results are shown in Table 1.

[0098] Table 1 Statistical table of experimental data results

[0099]

[0100] It can be seen that: the 28-day expansion rate of Comparative Example 5 as a blank control is as high as 0.086%, and the 91-day expansion rate further increases to 0.092%, indicating that a serious delayed ettringite reaction has occurred inside the specimens in the high geothermal environment, resulting in a significant expansion of the concrete volume. After adding different effective components and applying high sulfate-resistant cement in Comparative Examples 1 to 4 respectively, the expansion rates measured at 28 days, 60 days and 91 days all decreased to varying degrees. In the ultra-high performance concrete (UHPC) with the mix ratio of Example 1, the 28-day expansion rate is only 0.014%, and the 91-day expansion rate always remains below 0.020%. This result shows that the high geothermal-resistant ultra-high performance concrete and its preparation method in Example 1 can significantly inhibit the generation of delayed ettringite in the concrete, thereby effectively reducing the expansion rate of UHPC.

[0101] The compressive strength of Example 1 is the highest, and its excellent performance benefits from the synergistic effect of each component. The relatively high cement content (480 parts) provides strong gelling ability, enhancing the overall strength and stability of the concrete. The addition of steel fibers (39 parts) effectively improves the crack resistance and toughness of the concrete, preventing the crack propagation caused by temperature difference stress and further enhancing the compressive strength. The composite phase change lightweight aggregate (135 parts) effectively reduces the crack generation under high-temperature environments by regulating temperature fluctuations and reducing thermal expansion stress, enhancing the high-temperature resistance of the concrete. The incinerated garbage bottom ash (43 parts) improves the pore structure of the concrete, increases its compactness, and enhances its impermeability and long-term durability. Sodium borate (3.6 parts) inhibits the delayed ettringite formation (DEF), reduces the cracks caused by expansion, and further improves the stability and crack resistance of the concrete. The strength of Comparative Example 4 (138 MPa) is the lowest. Removing the composite phase change lightweight aggregate, sodium borate, and incinerated garbage bottom ash reduces the heat insulation and crack resistance of the concrete, thus affecting the compressive strength.

[0102] In common ultra-high performance concrete (UHPC), due to the high content of binders (such as cement, silica fume, fly ash, etc.) reaching 800 - 1000 kg / m³, the heat released during the hydration reaction will form a significant temperature gradient inside the concrete, thereby generating a large temperature stress field. This temperature stress is prone to causing material cracking, and the generation of cracks not only weakens the integrity of UHPC but also significantly reduces its mechanical properties and durability. In high geothermal environments, the delayed ettringite formation (DEF) further exacerbates this deterioration phenomenon. The ettringite generated by the reaction of calcium aluminate and sulfate ions produces expansion stress inside the material, resulting in the deepening and expansion of cracks.

[0103] In the present invention, by incorporating composite phase change lightweight aggregate, sodium borate, and incinerated garbage bottom ash, and selecting high sulfate-resistant cement, the content of the binder is overall reduced (the content of the binder in Example 1 is actually reduced to 624) kg / m 3 , reducing the heat of hydration reaction. Also, by adding specific components, the performance of UHPC is optimized from multiple aspects: The composite phase change lightweight aggregate provides a temperature control effect, effectively reducing the cracks caused by temperature fluctuations, and reducing the internal temperature of the concrete, slowing down the occurrence of DEF, thereby improving the crack resistance and high-temperature resistance of the concrete; Sodium borate effectively inhibits the occurrence of DEF by regulating the hydration rate and forming stable boron-aluminum complexes; The incinerated garbage bottom ash simultaneously has the effect of generating dense secondary gelling products with calcium hydroxide in the cement matrix to optimize the pore structure and reducing the concentration of sulfate ions to relieve DEF; The high sulfate-resistant cement reduces the possibility of ettringite formation at the source due to its low tricalcium aluminate (C3A) content; Comprehensively improving the durability and stability of the concrete in high geothermal environments.

[0104] The coral sand in Comparative Example 6 is a natural inorganic porous material formed by coral skeletal fragments, with calcium carbonate as the main component and a randomly distributed pore structure. It can also be used for encapsulation after adsorbing solid-liquid phase change materials to form phase change energy storage materials, but its structural uniformity is poor, which may lead to uneven thickness of the encapsulation layer or a high risk of leakage. This is because: 1. The porous structure and relatively large pores of starfish skeletons enable them to more evenly load phase change materials and provide stable heat storage capacity; while the pores of coral skeletons are smaller, and the ability to load phase change materials is poor. 2. Starfish skeletons are composed of single-crystal calcium carbonate (calcite) and have a highly ordered crystal structure. The dual-scale structure can avoid stress concentration and has a higher cylinder compressive strength, making it difficult for cracks to expand when subjected to external forces, thus reducing the risk of phase change material leakage and improving the aggregate strength; the structure of the randomly distributed pores in coral sand is prone to stress concentration and difficult to prevent crack expansion, resulting in lower strength of the prepared aggregate and a risk of phase change material leakage.

[0105] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An ultra-high performance concrete resistant to high ground temperatures, characterized in that: The composition comprises the following components in parts by weight: 360-520 parts of high sulfate-resistant cement, 36-52 parts of silica fume, 36-52 parts of fly ash, 800-1000 parts of fine aggregate, 80-200 parts of composite phase-change lightweight aggregate, 800-1000 parts of coarse aggregate, 39-78 parts of steel fiber, 1.8-10.4 parts of sodium borate, 43-125 parts of bottom ash from incinerated garbage, 120-130 parts of water and 5-10 parts of high-efficiency water reducing agent; The composite phase-change lightweight aggregate is prepared from the following raw materials in parts by mass: 40-60 parts of calcium carbonate-based microporous material, 20-40 parts of phase-change material, 15-25 parts of high sulfate-resistant cement and 0.5-2 parts of silane coupling agent; the calcium carbonate-based microporous material includes calcareous starfish skeleton.

2. The high ground temperature resistant ultra-high performance concrete according to claim 1, characterized in that: The particle gradation of the incinerated garbage bottom ash is as follows: the particle size of 0.075-1 mm accounts for 60%-70% of the mass ratio; the particle size of 1-4.75 mm accounts for 30%-40% of the mass ratio.

3. The high ground temperature resistant ultra-high performance concrete according to claim 1, characterized in that: The structure of the composite phase-change lightweight aggregate is as follows: the phase-change material is adsorbed in the calcium carbonate-based microporous material, the calcium carbonate-based microporous material is coated with a high-sulfate-resistant cement shell, and the surface of the high-sulfate-resistant cement shell is modified by a silane coupling agent.

4. The high ground temperature resistant ultra-high performance concrete according to claim 1, characterized in that: The phase change material includes one or more of stearic acid, lauric acid and myristic acid, and the phase change temperature is 50-70°C.

5. The high ground temperature resistant ultra-high performance concrete according to claim 1, characterized in that: The particle size of the composite phase-change lightweight aggregate is 6-10 mm.

6. A method for preparing high ground temperature resistant ultra-high performance concrete according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Using a vacuum adsorption method to make the calcium carbonate-based microporous material adsorb the phase change material to obtain a composite phase change material; S2, mixing the composite phase change material with high sulfate resistance cement to form granules, and then surface modifying the granules with a silane coupling agent to obtain a composite phase change lightweight aggregate; S3, mixing high sulfate-resistant cement, silica fume, fly ash, fine aggregate, composite phase-change lightweight aggregate and coarse aggregate, and stirring evenly; S4, add a set amount of water and mix, add a high-efficiency water reducer and mix well, then add the remaining water and the bottom ash of the incinerated garbage, stir well, add sodium borate, stir well, add steel fiber, and obtain a mixed slurry; S5. Casting the mixed slurry into a mold and curing it under high ground temperature conditions to obtain high ground temperature resistant ultra-high performance concrete.

7. The method for preparing high ground temperature resistant ultra-high performance concrete according to claim 6, characterized in that: In S1, the calcium carbonate-based microporous material and the phase change material are mixed, placed in a vacuum environment, and heated to a temperature above the phase change temperature of the phase change material for vacuum impregnation treatment.

8. The method for preparing high ground temperature resistant ultra-high performance concrete according to claim 6, characterized in that: In S2, the obtained composite phase change lightweight aggregate is cured for more than 28 days under a standard curing environment.

9. The method for preparing high ground temperature resistant ultra-high performance concrete according to claim 6, characterized in that: In S5, a vibrating table was used to vibrate lightly for 1-2 minutes during the pouring process.

10. An application of high ground temperature resistant ultra-high performance concrete according to any one of claims 1 to 5, characterized in that: This includes applications in geothermal projects, deep tunnels, nuclear power plants or infrastructure construction in high geothermal environments.

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