DEF-inhibiting filler, crack-resistant UHPC, and preparation method and application thereof

Abstract

The present invention discloses a DEF-inhibiting filler, a crack-resistant UHPC, and a preparation method and application thereof, belonging to the technical field of building materials. The DEF-inhibiting filler comprises: calcined straw particles, phase change material, nano-alumina, silica sol, polyvinyl alcohol, a silane coupling agent, and a shrinkage-reducing agent. The crack-resistant UHPC comprises: high-sulfate-resistant cement, silica fume, calcined straw ash, nano-silica-modified plant fiber, fine aggregate, coarse aggregate, steel fiber, nano-magnesium oxide, micron-sized magnesium oxide, DEF-inhibiting filler, nano-silica aerogel, water, a shrinkage-reducing agent, and a water-reducing agent. The DEF-inhibiting filler inhibits delayed expansion reaction in high ground temperature environments. In UHPC, calcined straw ash reduces the release of hydration heat; the magnesium oxide hydration product achieves full-process expansion compensation; the aerogel reduces the overall thermal conductivity of the concrete; and the modified plant fiber reinforcement network has the ability to absorb / release water. This makes it suitable for long-term engineering applications in extreme environments.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and in particular relates to a DEF-inhibiting filler, crack-resistant UHPC, and a preparation method and application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Tunnel and underground engineering construction presents unique technical challenges depending on the geological environment. Deep tunnels, in particular, face significant safety and durability challenges in environments with high geostress and high ground temperatures. In deep underground projects, concrete structures are exposed to extreme environmental conditions such as high geostress, high ground temperature, and low humidity for extended periods, placing stringent demands on the material's crack resistance and long-term durability.

[0004] Ultra-High Performance Concrete (UHPC) is widely used in deep-buried engineering projects such as tunnels, underground spaces, and deep mines due to its excellent mechanical properties, durability, and low permeability. However, UHPC faces serious cracking issues in practical applications, which can lead to reduced structural integrity, impaired durability, and even overall safety. The cracking problem of UHPC comes from the coupling of multiple factors, especially in deep buried environments, where these cracking mechanisms are further amplified, mainly including: (1) Autogenous shrinkage cracks: UHPC uses an ultra-low water-cement ratio, which leads to a lack of internal free water in the late stage of hydration reaction. The water in the capillary pores changes from saturated to unsaturated, forming capillary negative pressure, which triggers significant autogenous shrinkage. The low humidity conditions in the deep buried environment further aggravate water loss, making autogenous shrinkage cracks more likely to occur, affecting the integrity of the structure; (2) Hydration thermal cracks: A large amount of active admixtures (such as silica fume, slag powder, etc.) are added to UHPC, which increases the hydration rate of cement. In the deep buried high ground temperature environment, the hydration heat is difficult to dissipate, and the internal temperature rises rapidly, resulting in volume expansion. Contraction occurs during the subsequent cooling process, and then temperature stress cracks are generated; (3) Delayed calcium aluminate reaction (DE F) Cracks: When concrete is exposed to high temperatures (e.g., over 70°C) for a long time in a deep-buried environment, it will induce secondary hydration reaction of the aluminate phase in cement, generating expansive calcium sulfoxide (AFt), causing volume expansion and cracking. (4) Long-term thermal stress cracks are mainly caused by long-term temperature gradients and low-frequency thermal fluctuations: During the construction phase, the heat released by cement hydration causes the UHPC temperature to be much higher than the surrounding rock. During the service phase, the heat of the surrounding rock continuously acts on the concrete surface. The temperature distribution inside the UHPC engineering structure is uneven due to thermal inertia or local thermal disturbances (e.g., groundwater flow, ventilation system start-up and shutdown). This spatial temperature gradient leads to differences in expansion in different areas, causing alternating expansion and contraction. Long-term repeated action will cause microcracks to gradually expand in stress concentration areas through low-cycle fatigue effects, eventually forming macrocracks, resulting in significant structural cracking and reducing engineering durability. Summary of the Invention

[0005] In order to address the deficiencies of the prior art, the purpose of the present invention is to provide a DEF-inhibiting filler, a crack-resistant UHPC, and a preparation method and application thereof. PCM and porous carrier encapsulation technology are used to inhibit the DEF phenomenon, combined with full-process shrinkage compensation of magnesium oxide and shrinkage reducers of different particle sizes and calcined at different temperatures, nano-SiO2-modified plant fibers are used to achieve internal curing, and nano-SiO2 aerogel is added to reduce the thermal conductivity coefficient, to construct a multi-mechanism synergistic anti-cracking system, and to achieve full-process crack control and long-term service stability improvement of ultra-high performance concrete in high ground stress and high ground temperature environments.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] In the first aspect, the present invention provides a DEF inhibition filler, comprising porous calcined straw particles, wherein a phase change material is adsorbed inside the calcined straw particles; the phase change material is dispersed with nano-alumina; the outer side of the calcined straw particles is coated with a SiO2 / PVA encapsulation layer, and a silane coupling agent modification layer and a shrinkage reducer modification layer are sequentially arranged on the surface of the SiO2 / PVA encapsulation layer.

[0008] Optionally, the raw materials for preparing the DEF suppressing filler include the following components in parts by weight:

[0009] 80-100 parts of calcined straw particles, 20-30 parts of phase change material, 2-3 parts of nano-alumina, 2-3 parts of silica sol, 0.2-0.3 parts of polyvinyl alcohol, 0.5-0.7 parts of silane coupling agent and 5-7 parts of shrinkage reducing agent.

[0010] In a second aspect, the method for preparing the above-mentioned DEF suppressing filler comprises:

[0011] S1. Adding nano-alumina to the molten phase change material, stirring evenly and then mixing with calcined straw particles, so that the phase change material is absorbed into the gaps in the calcined straw particles, and cooling to below the phase change temperature of the phase change material to obtain a filler adsorbed with the phase change material;

[0012] S2. Dissolve silica sol and polyvinyl alcohol in deionized water to obtain an encapsulation liquid, immerse the filler adsorbed with the phase change material in the encapsulation liquid, take it out, and modify it with a silane coupling agent and a shrinkage reducing agent in sequence to obtain a DEF-inhibiting filler.

[0013] In a third aspect, a crack-resistant UHPC comprises the following components in parts by weight:

[0014] 360-520 parts of high sulfate-resistant cement, 36-52 parts of silica fume, 36-52 parts of calcined straw ash, 7-36 parts of nano-silica modified plant fiber, 800-1000 parts of fine aggregate, 800-1000 parts of coarse aggregate, 39-78 parts of steel fiber, 10-15 parts of low-temperature calcined nano-magnesia, 8-12 parts of high-temperature calcined micron-sized magnesium oxide, 80-200 parts of the above-mentioned DEF inhibitor filler, 5-18 parts of nano-silica aerogel, 120-130 parts of water, 2-6 parts of shrinkage reducer and 5-10 parts of water reducer.

[0015] In a fourth aspect, the method for preparing the above-mentioned crack-resistant UHPC comprises the steps of:

[0016] S3, dry-mixing high sulfate-resistant cement, silica fume, calcined straw ash, fine aggregate, coarse aggregate, nano-magnesium oxide, micron-magnesium oxide, shrinkage-reducing agent, fine aggregate, DEF-inhibiting filler and shrinkage-reducing agent to obtain a dry mix;

[0017] S4, adding 70% of the total water volume to the dry mix, adding a high-efficiency water reducer after stirring, adding the remaining 30% of the total water volume and nano-silica aerogel after stirring, and adding nano-silica modified plant fiber and steel fiber after stirring to obtain a mixed slurry;

[0018] S5. Cast the mixed slurry into a mold and cure it at a temperature consistent with the high ground temperature environment to obtain crack-resistant UHPC.

[0019] Fifthly, the application of the above-mentioned crack-resistant UHPC includes: application in geothermal projects in high geothermal environments, deep buried tunnels, nuclear power plants or infrastructure construction.

[0020] The beneficial effects of the present invention are:

[0021] 1. This invention utilizes a DEF-inhibiting filler to inhibit delayed expansion reaction (DEF) in high ground temperatures, optimizing the service stability of concrete. The DEF-inhibiting filler consists of calcined straw ash particles, a phase change material (PCM), and a SiO2 / PVA encapsulation layer. The phase change energy storage and temperature regulation mechanism, through the PCM's heat absorption during phase transition between 40°C and 60°C, effectively reduces the peak hydration heat, preventing sulfate attack and DEF expansion damage caused by the high temperatures of the internal hydration reaction. The surface is encapsulated with silica sol-polyvinyl alcohol, which enhances PCM encapsulation stability, prevents material decomposition or leakage in high-temperature environments, and strengthens the interfacial bonding between the aggregate and cement matrix. Furthermore, a shrinkage-reducing agent (SRA) is sprayed on the surface to effectively reduce moisture migration from the concrete into the DEF-inhibiting filler, reducing autogenous shrinkage stress and ensuring long-term durability. The multi-level pore structure formed after calcining straw ash at 500-600℃ has a water storage function. It can absorb excess moisture in the cement slurry in the initial stage and slowly release moisture through the humidity gradient in the later stage to compensate for the self-drying shrinkage; DEF inhibits the phase change heat absorption of the filler to reduce temperature fluctuations, while the moisture released by the porous structure reduces drying shrinkage. The two jointly inhibit the expansion of microcracks through water storage and temperature control mechanisms, achieve internal curing effect, and further reduce the occurrence of shrinkage cracks.

[0022] 2. This invention incorporates calcined straw ash and micron / nano-sized magnesium oxide into ultra-high-performance concrete (UHPC), effectively reducing hydration heat and inhibiting concrete autogenous shrinkage. Using highland barley straw ash calcined at different temperatures as a partial cement replacement reduces hydration heat release, lowers internal concrete temperature rise, and prevents cracks caused by thermal stress. Other materials, such as sulfoaluminate-based expansive agents, can exacerbate delayed ettringite reactions in high ground temperatures, while calcium oxide-based expansive agents can expand too rapidly early in high ground temperatures, failing to compensate for later contraction and increasing the risk of net shrinkage. These materials are not stable and effective in high ground temperatures. The Mg(OH)2 product of magnesium oxide hydration does not decompose at high temperatures, and the synergistic effect of micron- and nano-sized magnesium oxide, through differences in particle size and calcination temperature, enables full expansion compensation in high ground temperatures. The added plant fibers have an internal curing effect, can achieve multi-scale crack control, and improve the crack resistance of UHPC: by modifying plant fibers with nano-SiO2 of different lengths, a reinforced network that bridges cracks is constructed inside the concrete: short fibers (3~6mm) can bridge microcracks and improve early crack resistance; long fibers (6~12mm) can effectively hinder the expansion of large cracks and improve tensile toughness; nano-SiO2 modification can enhance the interfacial bonding between the fiber and the cement matrix, improve mechanical properties, and enhance the fiber's water absorption / release capacity, optimizing the internal curing effect. Nano-silica aerogel can optimize the temperature gradient of concrete and improve its long-term durability: the low thermal conductivity of nano-silica aerogel can significantly reduce the overall thermal conductivity of concrete, thereby reducing heat transfer to the surrounding rock in deep buried high-temperature environments and avoiding temperature stress concentration; its low thermal conductivity can also improve the thermal expansion characteristics of concrete, reduce cracks caused by temperature stress, and improve the long-term service performance of concrete in high-temperature environments; by optimizing the aerogel dosage, while ensuring mechanical properties, the service stability of UHPC can be further improved, making it suitable for long-term engineering applications in extreme environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0024] Figure 1 Schematic diagram of the technical route of DEF inhibition filler and crack-resistant UHPC in the examples. DETAILED DESCRIPTION

[0025] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0026] 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 form is intended to include the plural form. 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.

[0027] A typical embodiment of the present invention provides a DEF inhibition filler, comprising porous calcined straw particles, a phase change material adsorbed inside the calcined straw particles; nano-alumina is dispersed in the phase change material; the outer side of the calcined straw particles is coated with a SiO2 / PVA encapsulation layer, and a silane coupling agent modification layer and a shrinkage reducer modification layer are sequentially arranged on the surface of the SiO2 / PVA encapsulation layer.

[0028] Optionally, the DEF suppressing filler comprises the following raw materials in parts by weight:

[0029] 80-100 parts of calcined straw particles, 20-30 parts of phase change material, 2-3 parts of nano-alumina, 2-3 parts of silica sol, 0.2-0.3 parts of polyvinyl alcohol, 0.5-0.7 parts of silane coupling agent and 5-7 parts of shrinkage reducing agent.

[0030] The calcined straw particles provide the basic shape for the DEF suppressing filler.

[0031] The phase change material gives it phase change temperature control capability; a SiO2 / PVA encapsulation layer is provided on the outside to encapsulate the internal phase change material, which has a certain strength and can prevent the DEF inhibitor filler from damaging the shell structure during the mixing process with concrete.

[0032] The silane coupling agent modified layer serves as an intermediate layer between the encapsulation layer and the shrinkage reducer modified layer. Its functions include: sealing the surface micropores to prevent leakage of the phase change material and moisture intrusion; strengthening the interface bonding between the SiO2 / PVA encapsulation layer and the shrinkage reducer modified layer to ensure the integrity of the multilayer structure; and indirectly supporting the function of the shrinkage reducer by stabilizing the filler structure, so that the shrinkage reducer can effectively regulate the interface behavior of the concrete.

[0033] The functions of the shrinkage-reducing agent modified layer include: inhibiting concrete shrinkage and cracking, improving the durability of the filler-concrete interface; regulating moisture migration behavior to prevent moisture intrusion and phase change material (PCM) leakage in high ground temperature environments; and enhancing interfacial chemical bonding to ensure that DEF inhibits the synergistic force between the filler and concrete.

[0034] Optionally, 25 to 35 parts of deionized water are added during the preparation of the DEF inhibitory filler, and the deionized water is used to prepare the SiO2 / PVA encapsulation layer.

[0035] Optionally, the calcined straw particles have a particle size of 1-3 mm and a porosity of 60-70%, which is used to provide a certain strength for the DEF inhibitory filler. The surface layer of the prepared DEF inhibitory filler is relatively thin, and the particle size is also about 1-3 mm. The small-particle filler shortens the heat transfer path, which can improve the overall thermal conductivity of the concrete, accelerate the response speed of the phase change material (PCM), and is more suitable for the thermal management needs of high ground temperature environments. The micropores on the surface of the small-particle filler are more easily evenly covered by encapsulation materials such as silica sol / PVA, reducing the risk of PCM leakage. The small particle size makes the filler tend to be synergistically stressed as a whole, which can make up for the strength disadvantage of the biomass filler.

[0036] Optionally, the raw material of the calcined straw particles is highland barley straw, which comes from agricultural waste along the project.

[0037] Optionally, the phase change material includes one or more of palmitic acid, stearic acid, lauric acid and myristic acid; the phase change temperature of the phase change material is 50-60°C by controlling the ratio of different components; stearic acid (C 18 H 36 O2) melting point is about 69℃, lauric acid (C 12 H 24 O2) melting point of about 44 ° C, myristic acid (C 14 H 28 O2) has a melting point of approximately 54°C. Fatty acid materials have high thermal potential and good thermal stability. They can absorb and release heat during phase change, regulate concrete temperature, and improve the thermal management performance of DEF inhibitor fillers.

[0038] Optionally, the nano-alumina particle size is 18-32 nm, which is used to improve stability and thermal conductivity.

[0039] Optionally, the silica sol has a mass concentration of 20%, the SiO2 particle size contained in the silica sol is 10-20 nm, the pH value is about 10, and together with polyvinyl alcohol, forms a SiO2 / PVA encapsulation layer to prevent material decomposition or leakage in a high temperature environment.

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

[0041] Optionally, the shrinkage reducing agent is one or more of a polyether shrinkage reducing agent and a polyol shrinkage reducing agent.

[0042] Optionally, during the modification process of the silane coupling agent and the shrinkage reducing agent, since the modification processes of the two are carried out sequentially, the silane coupling agent is located in the bottom layer and directly bonds to the SiO2 / PVA surface to ensure interface strength; the shrinkage reducing agent is located in the outer layer and exposed to the surface to regulate moisture migration.

[0043] A typical embodiment of the present invention provides a method for preparing the above-mentioned DEF suppressing filler, comprising:

[0044] S1. Adding nano-alumina to the molten phase change material, stirring evenly and then mixing with calcined straw particles, so that the phase change material is absorbed into the gaps in the calcined straw particles, and cooling to below the phase change temperature of the phase change material to obtain a filler adsorbed with the phase change material;

[0045] S2. Dissolve silica sol and polyvinyl alcohol in deionized water to obtain an encapsulation liquid, immerse the filler adsorbed with the phase change material in the encapsulation liquid, take it out, and modify it with a silane coupling agent and a shrinkage reducing agent in sequence to obtain a DEF-inhibiting filler.

[0046] Optionally, the preparation method of calcined straw particles includes: selecting dry straw (moisture content ≤5%), crushing it to a particle size ≤5 mm, and removing impurities; calcining the crushed straw at 500±10℃ for 2~4 hours, naturally cooling it and then sieving it to obtain 1~3 mm particles, soaking it in NaOH solution, magnetically stirring (300~400rpm) for 30~40 minutes, washing it with deionized water until it is neutral, and drying it at 80~100℃ for 12~14 hours.

[0047] Optionally, in S1, the adsorption method is vacuum impregnation, and the vacuum degree is less than 10 -4 Pa, the immersion time is 3~5h to ensure that PCM completely fills the aggregate pores. After returning to normal pressure, let it stand for 3~5h to allow PCM to evenly fill the aggregate pores. Take out the filler after PCM adsorption and cool it to room temperature at a set rate.

[0048] Optionally, in S2, silica sol and polyvinyl alcohol are dissolved in deionized water and stirred until a transparent colloid is obtained to form an encapsulation liquid, wherein the mass concentration of silica sol is 5-10%, and the mass concentration of polyvinyl alcohol is 0.5-1.0%.

[0049] Optionally, in S2, the filler adsorbed with phase change material is immersed in the encapsulation liquid for 60 to 90 seconds, taken out and drained, dried below the phase change temperature for 2 to 4 hours, sprayed with silane coupling agent to seal the surface micropores, and dried at 60 to 80°C for 2 to 4 hours. Then, the shrinkage reducing agent SRA is sprayed to evenly cover the surface of the aggregate, and naturally dried for 12 to 14 hours; ensure the stable adsorption of SRA and improve the crack resistance of the aggregate.

[0050] A typical embodiment of the present invention provides a crack-resistant UHPC, comprising the following components in parts by weight:

[0051] 360-520 parts of high sulfate-resistant cement, 36-52 parts of silica fume, 36-52 parts of calcined straw ash, 7-36 parts of nano-silica modified plant fiber, 800-1000 parts of fine aggregate, 800-1000 parts of coarse aggregate, 39-78 parts of steel fiber, 10-15 parts of low-temperature calcined nano-magnesia, 8-12 parts of high-temperature calcined micron-sized magnesium oxide, 80-200 parts of the above-mentioned DEF inhibitor filler, 5-18 parts of nano-silica aerogel, 120-130 parts of water, 2-6 parts of shrinkage reducer and 5-10 parts of water reducer.

[0052] Among the above components, calcined straw ash, as a partial substitute for cement, can reduce the release of hydration heat, lower the temperature rise inside concrete, and prevent cracks caused by thermal stress; the hydration product of magnesium oxide, Mg(OH)2, does not decompose at high temperatures, and the synergistic effect of micron- and nano-magnesium oxide can achieve full-process expansion compensation through differences in particle size and calcination temperature; the low thermal conductivity of nano-silica aerogel can significantly reduce the overall thermal conductivity of concrete, thereby reducing heat transfer to the surrounding rock in a deep buried high-temperature environment and avoiding temperature stress concentration; nano-SiO2 modified plant fibers of different lengths construct a reinforced network that bridges cracks inside the concrete, and have the ability to absorb / release water, optimizing the internal curing effect, thereby improving the service stability of UHPC and enabling it to adapt to long-term engineering applications in extreme environments.

[0053] Optionally, the high-sulfate-resistant cement is selected from 52.5 grade or 52.5R grade high-sulfate-resistant cement; the content of tricalcium aluminate is low (C3A≤5%), which means that the content of calcium aluminate in the cement that can react with sulfate ions to form ettringite (AFt) is low; therefore, the use of high-sulfate-resistant cement significantly reduces the probability of DEF occurrence, thereby effectively avoiding the crack problem caused by the expansion of ettringite; it can reduce the potential negative impact of sulfate on concrete, enhance the crack resistance and high temperature resistance of concrete; and has good compatibility with polycarboxylic acid-based high-efficiency water reducers.

[0054] Optionally, the calcined straw ash includes low-temperature calcined straw ash and medium-temperature calcined straw ash in a mass ratio of 1:(0.8~1.2); the low-temperature calcined straw ash is calcined at a low temperature below 500°C, is mainly composed of amorphous SiO2, and has a porous structure that can adsorb ions in the early stage of hydration; the medium-temperature calcined straw ash is calcined at 500~600°C, contains highly active SiO2 / Al2O3, and continuously generates CSH gel in the middle and late stages of the hydration reaction. The two types of calcined straw ashes are compounded to synergistically achieve low heat + high strength characteristics, which are suitable for temperature control projects in high ground temperature and high ground stress environments.

[0055] Optionally, the plant fibers modified with nano-silica are selected from one or more of barley straw fibers, wheat straw fibers, flax fibers and bamboo fibers, and include short fibers of 3 to 6 mm and long fibers of 6 to 12 mm, wherein the volume ratio of the short fibers to the long fibers is 1 to 1.5, and the short fibers are used to fill micropores in the concrete to inhibit early plastic shrinkage; the long fibers are used to span microcracks and improve crack resistance by dissipating energy through fiber pull-out.

[0056] 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.

[0057] Optionally, the coarse aggregate has a Mohs hardness of not less than 8, an elastic modulus of 400-450 GPa, and a density of 3300 kg / m 3 .

[0058] Optionally, the particle size of the high-temperature calcined micron-sized magnesium oxide is 5-10 μm, the calcination temperature is 800-1000°C, and the specific surface area is 0.16-0.34 m 2 / g; the particle size of the low-temperature calcined nano-magnesium oxide is 100~500nm, the calcination temperature is 500~600℃, and the specific surface area is 3.36~16.8m 2 / kg.

[0059] The high-temperature calcined micron-sized magnesium oxide undergoes grinding and calcination processes in sequence. The high-temperature calcination can promote the growth of magnesium oxide grains, reconstruct the lattice, reduce lattice defects, form a dense crystal structure, thereby reducing surface energy and improving thermodynamic stability. The high temperature causes the desorption of surface hydroxyl groups (-OH); delays its dissolution rate in an alkaline environment; and forms a slow-release MgO component.

[0060] The low-temperature calcined nano-scale magnesium oxide is subjected to a grinding and calcining process in sequence. Compared with the high-temperature calcination process, the low-temperature calcination has limited crystal growth, small particle size and high defect retention; low-temperature dehydration can also retain a large number of surface hydroxyl groups and lattice distortion, and the high specific surface area provides rich reaction sites to accelerate the early Mg 2+ Release; can quickly react with cement hydration products (such as Ca(OH)2) to generate expansive Mg(OH)2, offsetting plastic shrinkage stress in time.

[0061] The hydration reaction of nano-scale magnesium oxide occurs in the early stage of concrete curing, and the hydration reaction of micron-scale magnesium oxide occurs in the middle and late stages of concrete curing; by further increasing the hydration rate of nano-scale magnesium oxide and further slowing down the hydration rate of micron-scale magnesium oxide by controlling the calcination temperature, the time period in which the magnesium oxide expansion agent produces a shrinkage compensation effect can be further expanded, thereby realizing full-process shrinkage compensation in a high ground temperature environment.

[0062] Optionally, the nano-silica aerogel has an average particle size of 20-40 nm, a porosity of ≥94%, and a thermal conductivity of 0.016-0.018 W / (m•K).

[0063] A typical embodiment of the present invention provides a method for preparing the above-mentioned crack-resistant UHPC, comprising the steps of:

[0064] S3, dry-mixing high sulfate-resistant cement, silica fume, fine aggregate, coarse aggregate, low-temperature calcined nano-sized magnesia, high-temperature calcined micron-sized magnesia, shrinkage-reducing agent, fine aggregate, DEF-inhibiting filler and shrinkage-reducing agent to obtain a dry mix;

[0065] S4, adding 60-70% of the total water volume to the dry mix, adding a high-efficiency water reducer after stirring, adding the remaining water and calcined straw ash after stirring, then adding nano-silica aerogel, and adding nano-silica modified plant fiber and steel fiber after stirring to obtain a mixed slurry;

[0066] S5. Cast the mixed slurry into a mold and cure it at a temperature consistent with the high ground temperature environment to obtain crack-resistant UHPC.

[0067] Optionally, the preparation method of the nano-silica modified plant fiber includes: cutting the naturally dried plant fiber into a set length, immersing the fiber in an ethanol-ammonia water-tetraethoxysilane (TEOS) mixed sol, ultrasonically dispersing for 20 to 30 minutes, standing to react for 24 to 36 hours, so that the tetraethoxysilane (TEOS) is hydrolyzed and condensed to generate amorphous nano-SiO2, which is evenly deposited on the fiber surface, and then drying to obtain the nano-silica modified plant fiber.

[0068] Optionally, in S3, stir at low speed for 2-3 minutes.

[0069] Optionally, in S4, stirring is continued for 3 to 5 minutes after all the water and nano-silica aerogel are added.

[0070] Optionally, in S4, after adding the steel fiber, stir at medium speed for 3-5 minutes;

[0071] Optionally, in S5, high-speed stirring is performed for 1-2 minutes before pouring.

[0072] Optionally, in S5, a vibrating table can be used to lightly vibrate for 1-2 minutes during pouring to help expel bubbles and improve its density.

[0073] Optionally, in S5, after pouring is completed, it is covered with plastic film to prevent surface moisture loss, and demoulding is carried out after 24 hours.

[0074] Optionally, in S5, a self-adhesive curing film is covered on the concrete surface after demolding to avoid bubbles and wrinkles during the laying process; and the concrete covered with the self-adhesive curing film is continued to be cured under set temperature conditions for a set time.

[0075] A typical embodiment of the present invention provides applications of the above-mentioned crack-resistant UHPC, including applications in geothermal projects, deep tunnels, nuclear power plants, or infrastructure construction in high-temperature environments.

[0076] Example 1

[0077] A DEF inhibition filler is prepared by preparing raw materials including the following components in parts by weight: 80 parts of calcined straw particles, 20 parts of phase change material, 2 parts of nano-alumina, 2 parts of silica sol (SiO2), 0.2 parts of polyvinyl alcohol (PVA), 25 parts of deionized water, 5 parts of shrinkage reducing agent (SRA) and 0.5 parts of silane coupling agent.

[0078] Calcined straw pellets are derived from agricultural waste of highland barley.

[0079] The phase change material is a mixture of palmitic acid and stearic acid in a mass ratio of 6:4.

[0080] The nano-alumina has a particle size of 18 to 32 nm.

[0081] The silica sol has a mass concentration of 20%, a silica particle size of 10-20 nm, and a pH value of 10.

[0082] Polyvinyl alcohol was added in the form of a 10% by mass concentration polyvinyl alcohol solution.

[0083] The preparation method comprises:

[0084] S1. Select palmitic acid and stearic acid in a set amount and mix them. Heat them to 70°C to melt, then add nano-alumina and continue stirring for 30 minutes to improve stability and thermal conductivity, and obtain composite PCM at room temperature. Select dry highland barley straw (moisture content ≤ 5%), grind it to a particle size ≤ 5 mm, and remove impurities. Put the ground straw into a muffle furnace, calcine it at 500±10°C for 2 hours, cool it naturally, sieve it to obtain 1~3 mm particles, soak it in NaOH solution, stir it magnetically (300 rpm) for 30 minutes, wash it with deionized water until it is neutral, and then dry it at 80°C for 12 hours to obtain calcined straw particles. Put the calcined straw particles (1~3 mm) into a vacuum tank, and evacuate it to 10⁻ 4 Pa; inject molten composite PCM at 60°C, maintain vacuum impregnation for 3 hours, then gradually restore normal pressure and continue to stand for 3 hours to ensure that the PCM is completely filled in the pores of the aggregate, take out the aggregate after adsorbing PCM, cool it from 70°C at a rate of 2°C / min to obtain filler with adsorbed phase change material.

[0085] S2. Dissolve silica sol and polyvinyl alcohol in deionized water and stir until a transparent colloidal encapsulation liquid is obtained. Immerse the filler adsorbed with phase change material in the encapsulation liquid for 60 seconds, remove it, drain the excess liquid, and spread it flat on a tray (weighing the remaining encapsulation liquid, it can be seen that this embodiment consumes 2 parts of silica sol (SiO2), 0.2 parts of polyvinyl alcohol (PVA), and 25 parts of deionized water). Dry it at 60°C for 2 hours, and then spray the hydrolyzed solution of silane coupling agent KH-550 (silane coupling agent KH-550, deionized water, and anhydrous ethanol are mixed in a volume ratio of 1:5:20). The mixture was mixed and magnetically stirred for 10 minutes to form a hydrolyzed liquid, which was then evenly sprayed onto the surface of the encapsulated aggregate in the form of a spray. The sprayed aggregate was spread flat on a tray and placed in a 60°C oven for 30 minutes. It was then naturally cooled to room temperature to seal the surface micropores. A polyol shrinkage reducing agent (SRA) was then sprayed on the surface to evenly cover the aggregate surface. The mixture was naturally dried at 20±5°C for 12 hours to ensure stable adsorption of SRA, improve the crack resistance of the aggregate, and obtain a DEF-inhibiting filler.

[0086] The tested properties include compressive strength of 9.6 MPa, phase change temperature of 55°C, thermal conductivity of 0.41 W / (m·K), and PCM leakage rate of 2%.

[0087] Example 2

[0088] A crack-resistant UHPC comprises the following components in parts by weight: 480 parts of 52.5R grade high-sulfate-resistant cement, 48 parts of undensified silica fume, 48 parts of calcined straw ash, 28 parts of nano-silica-modified plant fiber, 900 parts of fine aggregate, 135 parts of the DEF inhibitor of Example 1, 1000 parts of coarse aggregate, 12 parts of low-temperature calcined nano-sized magnesium oxide, 10 parts of high-temperature calcined micron-sized magnesium oxide, 39 parts of steel fiber, 12 parts of nano-silica aerogel, 4 parts of a shrinkage-reducing agent, 130 parts of tap water, and 8 parts of a polycarboxylic acid-based high-efficiency water reducer.

[0089] The calcined straw ash is made of calcined highland barley straw ash, which is agricultural waste along the line. After natural drying, it is ground into a particle size less than 100 μm by a ball mill; it is then divided into two equal volumes, calcined at a low temperature of 500°C and a medium temperature of 600°C, and then mixed.

[0090] The amorphous silicon dioxide content in the undensified silica fume is greater than 95wt% and the specific surface area is greater than 21.0m 2 / g, and its specific density (ratio to the density of water) is greater than 2.2.

[0091] The fine aggregate is river sand with a fineness modulus of 2.5 and an average particle size of 0.2 mm.

[0092] The coarse aggregate is basalt, with a Mohs hardness of not less than 8, an elastic modulus greater than 400GPa, and a density of 3300kg / m 3 .

[0093] The average particle size of nano-sized magnesium oxide calcined at low temperature is 400nm, and the average particle size of micron-sized magnesium oxide calcined at high temperature is 6µm.

[0094] 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, elastic modulus is 200 GPa, and density is 7800 kg / m 3 .

[0095] The average particle size of nano-silica aerogel is 25nm, the porosity is ≥94%, the thermal conductivity is 0.018 W / (m•K), and the density is 150 kg / m 3 .

[0096] The high-efficiency water reducer is a polycarboxylic acid water reducer with a solid content greater than 35% and a density of 1100 kg / m 3 .

[0097] The shrinkage reducing agent is a polyether shrinkage reducing agent.

[0098] The raw materials of nano-silica modified plant fibers include barley straw and wheat straw, including equal volume ratios of 3-6 mm short fibers and 6-12 mm long fibers, with a fiber diameter of 10-300 μm; the fibers are immersed in an ethanol-ammonia-TEOS mixed sol, ultrasonically dispersed for 20 minutes, and allowed to react for 24 hours, so that tetraethoxysilane (TEOS) is hydrolyzed and condensed to generate amorphous nano-SiO2, which is evenly deposited on the fiber surface.

[0099] The preparation method comprises:

[0100] S3. High sulfate-resistant cement, silica fume, fine aggregate, coarse aggregate, nano-magnesium oxide, micron-magnesium oxide, shrinkage-reducing agent, fine aggregate, DEF-inhibiting filler and shrinkage-reducing agent are mixed and dry-mixed at a low speed for 3 minutes to obtain a dry mix.

[0101] S4. Add 70% of the total water volume to the dry mix and stir. Add high-efficiency water reducer. After stirring, add the remaining water and calcined straw ash and stir for 5 minutes. When the fresh concrete has good fluidity, slowly add nano-silica aerogel through a square hole sieve and continue stirring at medium speed for 5 minutes until uniform. Then slowly add steel fiber and nano-silica modified plant fiber and stir to obtain a mixed slurry.

[0102] S5. Stir the mixed slurry at high speed for 2 minutes and then cast it into shape. During casting, use a vibrating table to lightly vibrate for 2 minutes to expel bubbles. Cover it with plastic film after casting to prevent surface moisture loss and demould it after 24 hours. Cover the demoulding concrete surface with a self-adhesive curing film to avoid bubbles and wrinkles during the laying process. Continue to cure the concrete covered with the self-adhesive curing film at a temperature of 60±2℃ and a humidity of 55±2% until the set time.

[0103] Example 3

[0104] A crack-resistant UHPC comprises the following components in parts by weight: 360 parts of high-sulfate-resistant cement, 36 parts of silica fume, 36 parts of calcined straw ash, 7 parts of nano-silica-modified plant fiber, 800 parts of fine aggregate, 800 parts of coarse aggregate, 39 parts of steel fiber, 10 parts of low-temperature calcined nano-magnesium oxide, 8 parts of high-temperature calcined micron-sized magnesium oxide, 80 parts of the DEF-inhibiting filler in Example 1, 5 parts of nano-silica aerogel, 120 parts of water, 2 parts of a shrinkage-reducing agent, and 5 parts of a water-reducing agent.

[0105] The specifications of the raw materials and the preparation method are the same as those in Example 2.

[0106] Example 4

[0107] A crack-resistant UHPC comprises the following components in parts by weight: 520 parts of high-sulfate-resistant cement, 52 parts of silica fume, 52 parts of calcined straw ash, 36 parts of nano-silica-modified plant fiber, 1000 parts of fine aggregate, 1000 parts of coarse aggregate, 78 parts of steel fiber, 15 parts of low-temperature calcined nano-magnesium oxide, 12 parts of high-temperature calcined micron-sized magnesium oxide, 200 parts of the DEF-inhibiting filler of Example 1, 18 parts of nano-silica aerogel, 130 parts of water, 6 parts of a shrinkage-reducing agent, and 10 parts of a water-reducing agent.

[0108] The specifications of the raw materials and the preparation method are the same as those in Example 2.

[0109] Comparative Example 1

[0110] A crack-resistant ultra-high performance concrete is different from Example 2 in that calcined straw ash is not added. Other raw material specifications and preparation methods are the same as those of Example 2.

[0111] Comparative Example 2

[0112] A crack-resistant ultra-high performance concrete differs from Example 2 in that nano-SiO2-modified plant fibers are not added. Other raw material specifications and preparation methods are the same as those of Example 2.

[0113] Comparative Example 3

[0114] A crack-resistant ultra-high performance concrete is different from Example 2 in that low-temperature calcined nano-magnesium oxide and high-temperature calcined micron-magnesium oxide are not added. Other raw material specifications and preparation methods are the same as those of Example 2.

[0115] Comparative Example 4

[0116] A crack-resistant ultra-high performance concrete differs from Example 2 in that no DEF inhibitor filler is added. Other raw material specifications and preparation methods are the same as those of Example 2.

[0117] Comparative Example 5

[0118] A crack-resistant ultra-high performance concrete differs from Example 2 in that no nano-silica aerogel is added. Other raw material specifications and preparation methods are the same as those of Example 2.

[0119] Comparative Example 6

[0120] A crack-resistant ultra-high performance concrete was prepared. This concrete differed from Example 2 in that ordinary Portland cement was used instead of the 52.5R grade high-sulfate-resistant cement in Example 2. Furthermore, no DEF inhibitor, nano-silica aerogel, low-temperature calcined nano-magnesium oxide, high-temperature calcined micro-magnesium oxide, or calcined straw ash were added. Other raw material specifications and preparation methods were the same as in Example 2, serving as a blank control.

[0121] Comparative Example 7

[0122] A DEF suppression filler is different from Example 1 in that no shrinkage reducing agent (SRA) is added, and other raw material specifications and preparation methods are the same as those of Example 1.

[0123] Comparative Example 8

[0124] A crack-resistant ultra-high performance concrete is different from Example 2 in that the DEF-inhibiting filler prepared in Comparative Example 7 is used instead of the DEF-inhibiting filler prepared in Example 1. Other raw material specifications and preparation methods are the same as those in Example 2.

[0125] Comparative Example 9

[0126] A crack-resistant ultra-high performance concrete is provided, which differs from Example 2 in that all calcined straw ash is obtained by low-temperature calcination at 500° C., excluding calcined straw ash obtained by calcination at 600° C. Other raw material specifications and preparation methods are the same as those of Example 2.

[0127] Comparative Example 10

[0128] A crack-resistant ultra-high performance concrete, which differs from Example 2 in that the added plant fiber is not modified. Other raw material specifications and preparation methods are the same as those of Example 2.

[0129] Performance testing includes:

[0130] Each embodiment and comparative example was prepared into a test piece with a size of 40*40*40mm;

[0131] The expansion degree of each embodiment and comparative example was tested during the preparation process;

[0132] After covering with self-adhesive curing film and curing for a set time, test the compressive strength of the specimen;

[0133] Using the flat plate method, after 24 hours of high ground temperature curing, the number of cracks on the entire surface of the sample was detected, the crack area was calculated based on the length and width of the crack, and the ratio of the crack area to the surface area of the sample was calculated;

[0134] According to GB∕T 50082-2009 Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete, the water penetration resistance test is used to assess the anti-permeability grade;

[0135] The performance test results are shown in Table 1.

[0136] Table 1 Experimental data results statistics

[0137]

[0138] Compared with the comparative examples, Example 2 exhibits excellent comprehensive performance, especially in terms of compressive strength, crack resistance and impermeability.

[0139] Experimental data show that the compressive strength of Example 2 reaches 150.2 MPa, which is much higher than that of Comparative Example 6 (128.6 MPa), and is also improved to varying degrees compared with other comparative examples.

[0140] The number of cracks per unit area in Example 2 is 10.8 / m 2 , much lower than the comparative example 6 (21.6 / m 2 ), cracks are reduced by 50%. The total cracking area per unit area is reduced from 2213.5mm in comparative example 6 to 2 / m 2 Down to 454mm 2 / m 2, a 79.5% reduction. Key factors contributing to the crack reduction: Calcined highland barley straw ash, as a pozzolanic active material, partially replaces cement, reducing hydration heat. DEF inhibitors, through phase change energy storage materials (PCMs), reduce hydration heat accumulation and temperature rise, inhibiting DEF expansion and improving the long-term volume stability of concrete. Nano-SiO2 modification enhances the interfacial bonding between the fiber and the cement matrix, providing crack bridging capabilities at varying scales, and improving the fiber's water absorption and release capacity, optimizing internal curing. The dual-scale magnesium oxide early and long-term shrinkage compensation mechanism effectively reduces autogenous shrinkage and drying shrinkage cracking. Nano-SiO2 aerogel reduces the thermal conductivity of concrete, reduces heat transfer to the surrounding rock, optimizes temperature gradients, reduces temperature stress cracking, and improves long-term service performance in high-temperature environments. SRA spraying reduces the surface tension of water in the concrete capillaries, reducing autogenous shrinkage stress. It also reduces the incidence of plastic shrinkage cracking through surface moisturizing.

[0141] The reduction in cracks not only improves the overall strength of the concrete but also significantly enhances its high-temperature resistance and impermeability. The impermeability rating of Example 2 is higher than that of the comparative example, indicating that the example exhibits superior long-term service performance in deep, high-temperature environments. The optimized temperature gradient control and crack suppression mechanisms enable the concrete to maintain structural stability in high-temperature, low-humidity environments, reducing damage caused by temperature stress and humidity gradients, thereby improving its durability in extreme underground engineering environments.

[0142] Combining these innovations, the present invention provides a crack-resistant ultra-high performance concrete suitable for deep buried high ground temperature environments. It is not only superior to existing UHPC in terms of crack resistance, strength and durability, but also improves service stability and reduces environmental burden by optimizing temperature gradients and resource utilization of calcined barley straw ash. The present invention can effectively reduce the hydration heat peak, inhibit DEF, reduce temperature stress cracks, and ensure the long-term service performance of concrete in high ground temperature and low humidity environments. By comparing the examples with the comparative examples, the present invention significantly optimizes the structural stability of UHPC, reduces cracks, and improves impermeability, fully demonstrating the effectiveness and innovation of the proposed method in deep ground engineering.

[0143] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A DEF suppressing filler, characterized in that: The invention comprises porous calcined straw particles, wherein a phase change material is adsorbed inside the calcined straw particles; the phase change material is dispersed with nano-alumina; the outer surface of the calcined straw particles is coated with a SiO2 / PVA encapsulation layer, and a silane coupling agent modification layer and a shrinkage reducing agent modification layer are sequentially provided on the surface of the SiO2 / PVA encapsulation layer; The calcined straw particles are calcined at 500±10° C. for 2-4 hours, have a particle size of 1-3 mm, and a porosity of 60-70%. The phase change material includes one or more of palmitic acid, stearic acid, lauric acid, and myristic acid.

2. The DEF suppressing filler according to claim 1, wherein The preparation comprises the following raw materials in parts by weight: 80-100 parts of calcined straw particles, 20-30 parts of phase change material, 2-3 parts of nano-alumina, 2-3 parts of silica sol, 0.2-0.3 parts of polyvinyl alcohol, 0.5-0.7 parts of silane coupling agent and 5-7 parts of shrinkage reducing agent.

3. The DEF suppressing filler according to claim 1, wherein: The silane coupling agent includes one or more of KH550, KH560, KH570 and KH792.

4. The DEF suppressing filler according to claim 1, wherein The shrinkage reducing agent is one or more of a polyether shrinkage reducing agent and a polyol shrinkage reducing agent.

5. A method for preparing a DEF suppressing filler according to any one of claims 1 to 4, characterized in that: include: S1. Adding nano-alumina to the molten phase change material, stirring evenly and then mixing with calcined straw particles, so that the phase change material is absorbed into the gaps in the calcined straw particles, and cooling to below the phase change temperature of the phase change material to obtain a filler adsorbed with the phase change material; S2. Dissolve silica sol and polyvinyl alcohol in deionized water to obtain an encapsulation liquid, immerse the filler adsorbed with the phase change material in the encapsulation liquid, take it out, and modify it with a silane coupling agent and a shrinkage reducing agent in sequence to obtain a DEF-inhibiting filler.

6. The method for preparing a DEF suppressing filler according to claim 5, wherein: The adsorption method is vacuum impregnation, and the vacuum degree is less than 10 -4 Pa, the immersion time is 3~5h to ensure that PCM completely fills the aggregate pores. After returning to normal pressure, let it stand for 3~5h to allow PCM to evenly fill the aggregate pores. Take out the filler after PCM adsorption and cool it to room temperature at a set rate.

7. The method for preparing a DEF suppressing filler according to claim 5, wherein: In S2, the filler adsorbed with the phase change material is immersed in the encapsulation liquid for 60 to 90 seconds, taken out and drained, dried below the phase change temperature for 2 to 4 hours, sprayed with a silane coupling agent and dried, then sprayed with a shrinkage reducing agent and dried for 12 to 14 hours.

8. A crack-resistant UHPC, characterized in that: The invention 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 calcined straw ash, 7-36 parts of nano-silica modified plant fiber, 800-1000 parts of fine aggregate, 800-1000 parts of coarse aggregate, 39-78 parts of steel fiber, 10-15 parts of low-temperature calcined nano-sized magnesium oxide, 8-12 parts of high-temperature calcined micron-sized magnesium oxide, 80-200 parts of the DEF inhibitor filler according to any one of claims 1 to 4, 5-18 parts of nano-silica aerogel, 120-130 parts of water, 2-6 parts of shrinkage reducer and 5-10 parts of water reducer.

9. The crack-resistant UHPC according to claim 8, characterized in that: The high sulfate-resistant cement is selected from 52.5 grade or 52.5R grade high sulfate-resistant cement.

10. The crack-resistant UHPC according to claim 8, characterized in that: The calcined straw ash includes low-temperature calcined straw ash and medium-temperature calcined straw ash in a mass ratio of 1:(0.8-1.2).

11. The crack-resistant UHPC according to claim 8, characterized in that: The nano-silica modified plant fibers are selected from one or more of barley straw fibers, wheat straw fibers, flax fibers and bamboo fibers; the plant fibers include short fibers of 3 to 6 mm and long fibers of 6 to 12 mm, and the volume ratio of the short fibers to the long fibers is 1 to 1.

5.

12. The crack-resistant UHPC according to claim 8, characterized in that: 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.

13. The crack-resistant UHPC according to claim 8, characterized in that: The coarse aggregate has a Mohs hardness of not less than 8, an elastic modulus of 400-450 GPa, and a density of 3300 kg / m 3 .

14. The crack-resistant UHPC according to claim 8, characterized in that: The nano-silica aerogel has an average particle size of 20-40 nm, a porosity of ≥94%, and a thermal conductivity of 0.016-0.018 W / (m•K).

15. The crack-resistant UHPC according to claim 8, characterized in that: The particle size of the high-temperature calcined micron-sized magnesium oxide is 5-10µm, and the calcination temperature is 800-1000°C. The particle size of the low-temperature calcined nano-sized magnesium oxide is 100-500nm, and the calcination temperature is 500-600°C.

16. A method for preparing crack-resistant UHPC according to any one of claims 8 to 15, characterized in that: Including steps: S3, dry-mixing high sulfate-resistant cement, silica fume, fine aggregate, coarse aggregate, low-temperature calcined nano-sized magnesia, high-temperature calcined micron-sized magnesia, DEF-inhibiting filler, and shrinkage-reducing agent to obtain a dry mix; S4, adding 60-70% of the total water volume to the dry mix, adding a high-efficiency water reducer after stirring, adding the remaining water and calcined straw ash after stirring, then adding nano-silica aerogel, and adding nano-silica modified plant fiber and steel fiber after stirring to obtain a mixed slurry; S5. Cast the mixed slurry into a mold and cure it at a temperature consistent with the high ground temperature environment to obtain crack-resistant UHPC.

17. The method for preparing crack-resistant UHPC according to claim 16, wherein: The preparation method of nano-silica modified plant fiber includes: cutting the naturally dried plant fiber to a set length, immersing the fiber in an ethanol-ammonia water-tetraethoxysilane mixed sol, ultrasonically dispersing for 20 to 30 minutes, and allowing the reaction to proceed for 24 to 36 hours to allow the tetraethoxysilane to hydrolyze and condense to generate amorphous nano-SiO2, which is uniformly deposited on the fiber surface, and then drying to obtain the nano-silica modified plant fiber.

18. A use of the crack-resistant UHPC according to any one of claims 8 to 15, characterized in that: include: Applications in geothermal projects, deep tunnels, nuclear power plants or infrastructure construction in high ground temperature environments.

Images