Steel fiber reinforced ultra-high performance concrete and preparation method thereof

Abstract

The invention relates to the technical field of ultra-high performance concrete, in particular to steel fiber reinforced ultra-high performance concrete and a preparation method thereof.The steel fiber reinforced ultra-high performance concrete is prepared from, by mass, 550-650 parts of Portland cement, 700-800 parts of quartz sand, 100-125 parts of composite phase change aggregate, 160-200 parts of steel fibers, 100-140 parts of silica fume, 50-70 parts of fly ash, 20-28 parts of polycarboxylate superplasticizer and 140-160 parts of deionized water. The composite phase change aggregate comprises a composite core material and an adsorption wall material, the composite core material is composed of dodecyl stearate, lauric acid and myristyl alcohol, and the adsorption wall material is modified expanded vermiculite. The ultra-high performance concrete prepared by the invention not only has mechanical properties of high strength and high toughness, but also has a good temperature regulation function, is simple in preparation process and high in stability, and can be widely applied to various complex building scenes.

Description

Technical Field

[0001] This invention relates to the field of ultra-high performance concrete technology, and in particular to a steel fiber reinforced ultra-high performance concrete and its preparation method. Background Technology

[0002] Ultra-high performance concrete (UHPC), as a new type of building material, possesses excellent properties such as high strength, high toughness, and high durability, and has been widely used in bridges, high-rise buildings, marine engineering, and other fields. With the continuous improvement of the construction industry's requirements for concrete performance, it is not only necessary to have good mechanical properties, but also to consider additional functions such as temperature regulation and crack resistance to adapt to complex service environments.

[0003] Existing ultra-high performance concrete typically improves its mechanical properties by adding steel fibers, but this single reinforcement method is insufficient to meet multifunctional requirements. Furthermore, traditional concrete is prone to cracking in environments with significant temperature variations, affecting structural stability and service life. Phase change materials (PCMs) possess the property of absorbing or releasing heat within a specific temperature range; introducing them into concrete can endow the material with temperature regulation capabilities, mitigating cracking caused by temperature stress. However, directly adding PCMs to concrete can lead to problems such as leakage and uneven dispersion, and can adversely affect the mechanical properties of the concrete.

[0004] Therefore, how to effectively combine phase change materials with steel fiber reinforcement systems to prepare ultra-high performance concrete with both excellent mechanical properties and temperature regulation function has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a steel fiber reinforced ultra-high performance concrete and its preparation method. The ultra-high performance concrete not only has high strength and high toughness mechanical properties, but also has good temperature regulation function. Moreover, the preparation process is simple and the stability is strong, which can be widely used in various complex building scenarios.

[0006] To achieve the above objectives, the present invention provides a steel fiber reinforced ultra-high performance concrete, comprising, by weight parts, 550-650 parts of silicate cement, 700-800 parts of quartz sand, 100-125 parts of composite phase change aggregate, 160-200 parts of steel fiber, 100-140 parts of silica fume, 50-70 parts of fly ash, 20-28 parts of polycarboxylate superplasticizer, and 140-160 parts of deionized water. The composite phase change aggregate comprises a composite core material and an adsorbent wall material. The composite core material is composed of dodecyl stearate, lauric acid, and myristic acid, and the adsorbent wall material is modified expanded vermiculite.

[0007] Preferably, the steel fibers have a diameter of 0.2~0.3mm and a length of 12~14mm; the quartz sand has a particle size of 0.15~0.6mm.

[0008] Preferably, the mass ratio of dodecyl stearate, lauric acid and myristol in the composite core material is 3:4:3, and the mass ratio of the composite core material to modified expanded vermiculite is 1:1.2~1.5.

[0009] Preferably, the modified expanded vermiculite is expanded vermiculite modified with silane coupling agent KH-550, the expanded vermiculite has a particle size of 1~3mm, a porosity of ≥75%, and the amount of silane coupling agent KH-550 is 1%-3% of the mass of expanded vermiculite.

[0010] The above-mentioned method for preparing steel fiber reinforced ultra-high performance concrete includes the following steps: S1. Preparation of composite phase change aggregate: Weigh dodecyl stearate, lauric acid and myristol, mix and melt them at 70-80℃ to form a homogeneous eutectic composite core material, add modified expanded vermiculite to the eutectic composite core material and stir at a constant temperature, then filter and dry after negative pressure adsorption to obtain composite phase change aggregate. S2. Dry mixing: Pour silicate cement, quartz sand, composite phase change aggregate, silica fume, and fly ash into a mixer and dry mix at 80-100 r / min for 2-3 minutes to obtain a dry mixture. S3. Wet material mixing: Add polycarboxylate superplasticizer and deionized water to the dry material mixture, and stir at 120-150 r / min for 3-4 min to obtain a mixed slurry; S4. Steel fiber dispersion: Add steel fibers to the mixed slurry in three batches, stirring at 60-80 r / min for 1-2 min after each addition to obtain ultra-high performance concrete.

[0011] Preferably, in S1, the mixing and melting are carried out in a constant temperature water bath, and the stirring rate during mixing and melting is 100-150 r / min.

[0012] Preferably, in S1, the modified expanded vermiculite is prepared by drying the expanded vermiculite, crushing it, and sieving it to obtain expanded vermiculite particles. The expanded vermiculite particles are then added to an ethanol solution of silane coupling agent KH-550 with a volume concentration of 10%, and stirred at a rate of 150-200 r / min for 50-60 min at a temperature of 45-55℃. Subsequently, the mixture is placed in a drying oven at 70-80℃ and dried for 10-12 h to obtain the modified expanded vermiculite.

[0013] Preferably, in S1, the temperature of the constant temperature stirring is 70-80℃, and the stirring rate is 100-150 r / min.

[0014] Preferably, in S1, the negative pressure adsorption is performed at 0.05 MPa for 30-40 min.

[0015] Preferably, in S1, filtration involves letting the material stand on a screen for 6-8 hours, and drying involves drying at 60-70°C for 12 hours.

[0016] Mechanism of the invention: Expanded vermiculite is modified with silane coupling agent KH-550 to achieve a dual load of physical adsorption and interfacial locking with the composite core material composed of dodecyl stearate, lauric acid, and myristic acid through chemical bonding and interfacial affinity. After melt infiltration and negative pressure adsorption processes, a high-adsorption-rate, leak-free composite phase change aggregate is formed. Its eutectic system can achieve heat storage in a wide temperature range of 22.5~39.8℃. The composite phase change aggregate is tightly bonded to the cement-silica fume-fly ash composite cementitious system through interfacial compatibility. With the addition of three-dimensional steel fiber mesh reinforcement, while ensuring the ultra-high performance and toughness of concrete, the temperature is passively regulated by the phase change of the core material, ultimately achieving a synergistic unity of structural load-bearing and heat storage and temperature regulation functions.

[0017] Therefore, the present invention employs the above-mentioned steel fiber reinforced ultra-high performance concrete and its preparation method, which has the following beneficial effects: (1) This invention combines steel fibers with gel materials. The steel fibers form a uniform support network inside the concrete. At the same time, they work synergistically with quartz sand and active admixtures (silica fume, fly ash) to effectively improve the compressive strength, tensile strength and toughness of ultra-high performance concrete, inhibit the generation and propagation of cracks, and meet the mechanical requirements of ultra-high performance concrete. (2) The eutectic composite core material in the composite phase change aggregate of the present invention can absorb or release heat in the temperature range of 22.5~39.8℃, realize the adaptive adjustment of the internal temperature of ultra-high performance concrete, alleviate the cracking problem caused by temperature stress, and improve the service life of ultra-high performance concrete in complex temperature environment. (3) The present invention uses expanded vermiculite modified with silane coupling agent KH-550 as an adsorption wall material, which not only improves the adsorption capacity and compatibility of organic composite core material and avoids leakage of phase change material, but also enhances the bonding strength with cement matrix, reduces interface defects, and ensures the stability and durability of the overall structure of ultra-high performance concrete. (4) The preparation method of the present invention has clear steps, easy process parameters, no need for complex equipment, facilitates large-scale industrial production, reduces production costs, and has broad application prospects.

[0018] The technical solution of the present invention will be further described in detail below through embodiments. Detailed Implementation

[0019] The present invention will be further described below with reference to embodiments. Unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art. The features mentioned above or in the specific examples mentioned in this invention can be combined arbitrarily, and these specific embodiments are only used to illustrate the invention and are not intended to limit the scope of the invention.

[0020] This invention provides a steel fiber reinforced ultra-high performance concrete, comprising, by weight parts: 550-650 parts silicate cement, 700-800 parts quartz sand, 100-125 parts composite phase change aggregate, 160-200 parts steel fiber, 100-140 parts silica fume, 50-70 parts fly ash, 20-28 parts polycarboxylate superplasticizer, and 140-160 parts deionized water. The composite phase change aggregate comprises a composite core material and an adsorbent wall material. The composite core material is composed of dodecyl stearate, lauric acid, and myristic acid, and the adsorbent wall material is modified expanded vermiculite.

[0021] The eutectic phase change material formed by dodecyl stearate, lauric acid and myristol in this invention has a suitable phase change temperature and high latent heat efficiency, which can effectively regulate the internal temperature of concrete. Modified expanded vermiculite, as a carrier, can not only achieve stable adsorption and encapsulation of the phase change material to avoid leakage, but also improve its compatibility with the concrete matrix and the phase change material through modification treatment, thereby enhancing the overall structural stability.

[0022] Preferably, the steel fibers have a diameter of 0.2~0.3mm and a length of 12~14mm; the quartz sand has a particle size of 0.15~0.6mm.

[0023] This invention utilizes steel fibers within the aforementioned size range to form a uniform support network within ultra-high performance concrete, significantly improving its tensile strength and toughness while inhibiting crack propagation. The use of quartz sand within the aforementioned particle size range optimizes the gradation of ultra-high performance concrete, increasing aggregate bulk density, reducing internal porosity, and enhancing matrix compactness.

[0024] Preferably, the mass ratio of dodecyl stearate, lauric acid and myristol in the composite core material is 3:4:3, and the mass ratio of the composite core material to modified expanded vermiculite is 1:1.2~1.5.

[0025] The present invention controls the mass ratio of dodecyl stearate, lauric acid and myristol to the above ratio, so that the resulting eutectic composite core material has the best phase change performance, large latent heat of phase change, stable temperature regulation effect, and good fluidity in the molten state, which is convenient for adsorption and encapsulation by modified expanded vermiculite.

[0026] This invention controls the mass ratio of composite core material to modified expanded vermiculite within the above-mentioned range, which ensures that the modified expanded vermiculite can fully adsorb and encapsulate the composite core material, avoiding leakage caused by excessive core material, while ensuring that the aggregate has sufficient temperature regulation capability and does not affect the bonding effect with the concrete matrix.

[0027] Preferably, the modified expanded vermiculite is expanded vermiculite modified with silane coupling agent KH-550, the expanded vermiculite has a particle size of 1~3mm, a porosity of ≥75%, and the amount of silane coupling agent KH-550 is 1%-3% of the mass of expanded vermiculite.

[0028] In this invention, the alkoxy group at one end of the silane coupling agent KH-550 molecule undergoes a condensation reaction with the hydroxyl group on the surface of expanded vermiculite to form a strong Si-O-Si chemical bond. The organic long-chain group at the other end is exposed on the carrier surface, causing the surface properties of expanded vermiculite to change from hydrophilic to hydrophobic, and significantly reducing the interfacial tension with the organic composite core material. On the one hand, this enhances the adsorption capacity and compatibility of expanded vermiculite with the organic composite core material, and on the other hand, it strengthens the bonding strength between expanded vermiculite and the cement matrix, avoiding interfacial defects. At the same time, the high porosity of expanded vermiculite enables efficient loading of phase change materials.

[0029] The above-mentioned method for preparing steel fiber reinforced ultra-high performance concrete includes the following steps: S1. Preparation of composite phase change aggregate: Weigh dodecyl stearate, lauric acid and myristol, mix and melt them at 70-80℃ to form a homogeneous eutectic composite core material, add modified expanded vermiculite to the eutectic composite core material and stir at a constant temperature, then filter and dry after negative pressure adsorption to obtain composite phase change aggregate. S2. Dry mixing: Pour silicate cement, quartz sand, composite phase change aggregate, silica fume, and fly ash into a mixer and dry mix at 80-100 r / min for 2-3 minutes to obtain a dry mixture. S3. Wet material mixing: Add polycarboxylate superplasticizer and deionized water to the dry material mixture, and stir at 120-150 r / min for 3-4 min to obtain a mixed slurry; S4. Steel fiber dispersion: Add steel fibers to the mixed slurry in three batches, stirring at 60-80 r / min for 1-2 min after each addition to obtain ultra-high performance concrete.

[0030] Preferably, in step S1, the mixing and melting are carried out in a constant-temperature water bath, and the stirring rate during mixing and melting is 100-150 r / min. The constant-temperature water bath can ensure a stable melting temperature and avoid local overheating that could lead to degradation of the phase change material's properties. The appropriate stirring rate can ensure that the three components are fully mixed to form a uniform eutectic core material.

[0031] Preferably, in S1, the modified expanded vermiculite is prepared by drying the expanded vermiculite, crushing it, and sieving it to obtain expanded vermiculite particles. The expanded vermiculite particles are then added to an ethanol solution of silane coupling agent KH-550 with a volume concentration of 10%, and stirred at a rate of 150-200 r / min for 50-60 min at a temperature of 45-55℃. Subsequently, the mixture is placed in a drying oven at 70-80℃ and dried for 10-12 h to obtain the modified expanded vermiculite.

[0032] Preferably, in step S1, the isothermal stirring temperature is 70-80℃, and the stirring rate is 100-150 r / min. The isothermal stirring temperature is consistent with the melting temperature of the eutectic core material, which can avoid the core material solidification affecting the adsorption effect. The appropriate stirring rate can ensure that the expanded vermiculite and the eutectic core material are in full contact, thereby improving the adsorption efficiency.

[0033] Preferably, in S1, the negative pressure adsorption is performed at 0.05 MPa for 30-40 minutes. The negative pressure environment can accelerate the entry of the eutectic core material into the pores of the expanded vermiculite, improve the adsorption capacity and adsorption stability, and prevent leakage of phase change material during later use.

[0034] Preferably, in step S1, filtration involves standing on a screen for 6-8 hours, and drying involves drying at 60-70°C for 12 hours. Standing filtration removes excess core material that is not adsorbed on the surface, while low-temperature drying prevents the phase change material from volatilizing or decomposing due to high temperatures, ensuring the performance stability of the composite phase change aggregate.

[0035] Example 1 A steel fiber reinforced ultra-high performance concrete comprises, by weight parts: 550 parts silicate cement, 700 parts quartz sand, 100 parts composite phase change aggregate, 160 parts steel fiber, 100 parts silica fume, 50 parts fly ash, 20 parts polycarboxylate superplasticizer, and 140 parts deionized water.

[0036] The composite core material contains dodecyl stearate, lauric acid, and myristol in a mass ratio of 3:4:3, and the composite core material to modified expanded vermiculite in a mass ratio of 1:1.2. The steel fibers have a diameter of 0.2 mm and a length of 12 mm. The quartz sand has a particle size of 0.15~0.6 mm. The modified expanded vermiculite is expanded vermiculite modified with silane coupling agent KH-550, with a particle size of 1~3 mm and a porosity of 75%. The amount of silane coupling agent KH-550 is 1% of the mass of the expanded vermiculite. According to the above proportions, 100 parts of the composite phase change aggregate contain 45.5 parts of composite core material (13.65 parts of dodecyl stearate, 18.2 parts of lauric acid, and 13.65 parts of myristol) and 54.5 parts of modified expanded vermiculite.

[0037] The aforementioned steel fiber reinforced ultra-high performance concrete is prepared through the following steps: S1. Preparation of modified expanded vermiculite: After drying, the expanded vermiculite is crushed and sieved to obtain expanded vermiculite particles of 1~3 mm. These particles are then added to a 10% (v / v) ethanol solution of silane coupling agent KH-550 and stirred at 150 r / min for 50 min at 45 °C. Subsequently, the particles are dried in a 70 °C drying oven for 10 h to obtain modified expanded vermiculite.

[0038] Preparation of composite phase change aggregate: Dodecyl stearate, lauric acid and myristol were weighed in a mass ratio of 3:4:3 and stirred and melted in a constant temperature water bath at 70℃ at 100 r / min to form a homogeneous eutectic composite core material. Modified expanded vermiculite was added to the eutectic composite core material and stirred at a constant temperature of 70℃ at 100 r / min. Then, it was adsorbed under negative pressure at 0.05 MPa for 30 min, filtered by standing on a sieve for 6 h, and dried at 60℃ for 12 h to obtain composite phase change aggregate.

[0039] S2. Dry mixing: Pour silicate cement, quartz sand, composite phase change aggregate, silica fume, and fly ash into a mixer and dry mix at 80 r / min for 2 minutes to obtain a dry mixture.

[0040] S3. Wet material mixing: Add polycarboxylate superplasticizer and deionized water to the dry material mixture and stir at 120 r / min for 3 min to obtain a mixed slurry.

[0041] S4. Steel fiber dispersion: Steel fibers are added to the mixed slurry in three parts, and stirred at 60 r / min for 1 min after each addition to obtain ultra-high performance concrete.

[0042] Example 2 A steel fiber reinforced ultra-high performance concrete comprises, by weight parts: 600 parts silicate cement, 750 parts quartz sand, 110 parts composite phase change aggregate, 180 parts steel fiber, 120 parts silica fume, 60 parts fly ash, 24 parts polycarboxylate superplasticizer, and 150 parts deionized water.

[0043] The composite core material contains dodecyl stearate, lauric acid, and myristol in a mass ratio of 3:4:3, and the composite core material to modified expanded vermiculite in a mass ratio of 1:1.35. The steel fibers have a diameter of 0.25 mm and a length of 13 mm. The quartz sand has a particle size of 0.15~0.6 mm. The modified expanded vermiculite is expanded vermiculite modified with silane coupling agent KH-550, with a particle size of 1~3 mm, a porosity of 78%, and the amount of silane coupling agent KH-550 is 2% of the mass of the expanded vermiculite. According to the above proportions, 110 parts of the composite phase change aggregate contain 46.8 parts of composite core material (14.04 parts of dodecyl stearate, 18.72 parts of lauric acid, and 14.04 parts of myristol) and 63.2 parts of modified expanded vermiculite.

[0044] The aforementioned steel fiber reinforced ultra-high performance concrete is prepared through the following steps: S1. Preparation of modified expanded vermiculite: After drying, the expanded vermiculite is crushed and sieved to obtain expanded vermiculite particles of 1~3 mm. These particles are then added to a 10% (v / v) ethanol solution of silane coupling agent KH-550 and stirred at 180 r / min for 55 min at 50 °C. Subsequently, the particles are dried in a drying oven at 75 °C for 11 h to obtain modified expanded vermiculite.

[0045] Preparation of composite phase change aggregate: Dodecyl stearate, lauric acid and myristol were weighed in a mass ratio of 3:4:3 and stirred and melted in a constant temperature water bath at 75℃ at 120 r / min to form a homogeneous eutectic composite core material. Modified expanded vermiculite was added to the eutectic composite core material and stirred at a constant temperature of 75℃ at 120 r / min. Then, it was adsorbed under negative pressure at 0.05 MPa for 35 min, filtered by standing on a sieve for 7 h, and dried at 65℃ for 12 h to obtain composite phase change aggregate.

[0046] S2. Dry mixing: Pour silicate cement, quartz sand, composite phase change aggregate, silica fume, and fly ash into a mixer and dry mix at 90 r / min for 2.5 min to obtain a dry mixture.

[0047] S3. Wet material mixing: Add polycarboxylate superplasticizer and deionized water to the dry material mixture and stir at 130 r / min for 3.5 min to obtain a mixed slurry.

[0048] S4. Steel fiber dispersion: Steel fibers are added to the mixed slurry in three parts, and stirred at 70 r / min for 1.5 min after each addition to obtain ultra-high performance concrete.

[0049] Example 3 A steel fiber reinforced ultra-high performance concrete comprises, by weight parts: 650 parts silicate cement, 800 parts quartz sand, 125 parts composite phase change aggregate, 200 parts steel fiber, 140 parts silica fume, 70 parts fly ash, 28 parts polycarboxylate superplasticizer, and 160 parts deionized water.

[0050] The composite core material contains dodecyl stearate, lauric acid, and myristol in a mass ratio of 3:4:3, and the composite core material to modified expanded vermiculite in a mass ratio of 1:1.5. The steel fibers have a diameter of 0.3 mm and a length of 14 mm. The quartz sand has a particle size of 0.15~0.6 mm. The modified expanded vermiculite is expanded vermiculite modified with silane coupling agent KH-550, with a particle size of 1~3 mm and a porosity of 80%. The amount of silane coupling agent KH-550 is 3% of the mass of the expanded vermiculite. According to the above proportions, 125 parts of the composite phase change aggregate contain 50 parts of the composite core material (15 parts dodecyl stearate, 20 parts lauric acid, and 15 parts myristol) and 75 parts of modified expanded vermiculite.

[0051] The preparation method is as follows: S1. Preparation of modified expanded vermiculite: After drying, the expanded vermiculite is crushed and sieved to obtain expanded vermiculite particles of 1~3mm. These particles are then added to a 10% (v / v) ethanol solution of silane coupling agent KH-550 and stirred at 200r / min for 60min at 55℃. Subsequently, the particles are dried in an 80℃ drying oven for 12h to obtain modified expanded vermiculite.

[0052] Preparation of composite phase change aggregate: Dodecyl stearate, lauric acid and myristol were weighed in a mass ratio of 3:4:3 and stirred and melted in an 80℃ constant temperature water bath at 150 r / min to form a homogeneous eutectic composite core material. Modified expanded vermiculite was added to the eutectic composite core material and stirred at 80℃ at 150 r / min. Then, it was adsorbed under negative pressure at 0.05 MPa for 40 min, filtered by standing on a sieve for 8 h, and dried at 70℃ for 12 h to obtain composite phase change aggregate.

[0053] S2. Dry mixing: Pour silicate cement, quartz sand, composite phase change aggregate, silica fume, and fly ash into a mixer and dry mix at 100 r / min for 3 minutes to obtain a dry mixture.

[0054] S3. Wet material mixing: Add polycarboxylate superplasticizer and deionized water to the dry material mixture and stir at 150 r / min for 4 min to obtain a mixed slurry.

[0055] S4. Steel fiber dispersion: Steel fibers are added to the mixed slurry in three parts, and stirred at 80 r / min for 2 min after each addition to obtain ultra-high performance concrete.

[0056] Comparative Example An ultra-high performance concrete comprises, by weight parts: 550 parts silicate cement, 800 parts quartz sand, 160 parts steel fiber, 100 parts silica fume, 50 parts fly ash, 20 parts polycarboxylate superplasticizer, and 140 parts deionized water. The steel fiber has a diameter of 0.2 mm and a length of 12 mm; the quartz sand has a particle size of 0.15-0.6 mm; there is no composite phase change aggregate; and the remaining components and parameters are consistent with those of Example 1.

[0057] The above-mentioned method for preparing ultra-high performance concrete is as follows: S1. Dry mixing: Pour silicate cement, quartz sand, silica fume, and fly ash into a mixer and dry mix at 80 r / min for 2 minutes to obtain a dry mixture.

[0058] S2. Wet material mixing: Add polycarboxylate superplasticizer and deionized water to the dry material mixture and stir at 120 r / min for 3 min to obtain a mixed slurry.

[0059] S3. Steel fiber dispersion: Steel fibers are added to the mixed slurry in three parts, and stirred at 60 r / min for 1 min after each addition to obtain ultra-high performance concrete.

[0060] Performance testing The performance of the ultra-high performance concrete prepared in Examples 1-3 and the comparative example was tested according to the following standard method. The test environment was room temperature of 25℃ and relative humidity of 60%. Three test blocks were prepared for each group of samples. The test results were averaged. The specific test method is as follows, and the test results are shown in Table 1.

[0061] Compressive strength test: According to the "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" (GB / T 50081-2019), 100mm×100mm×100mm test blocks were used to determine the compressive strength at 7d and 28d, respectively, with a loading rate of 0.5MPa / s.

[0062] Tensile strength test: According to the Technical Specification for Application of Ultra-High Performance Concrete (T / CECS 1009-2020), 40mm×40mm×160mm test blocks were used to determine the 28-day tensile strength through splitting tensile test, with a loading rate of 0.05MPa / s.

[0063] Phase change latent heat test: According to the differential scanning calorimeter (DSC) method for determining the phase change temperature and latent heat of phase change of phase change materials (GB / T 29513-2013), the test temperature range is 0~80℃, the heating rate is 10℃ / min, and the latent heat of phase change value is recorded. Permeability resistance test: According to the "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete" (GB / T50082-2009), the stepwise pressure method is adopted. Φ175mm×Φ185mm×150mm test blocks are used, and the pressure rate is 0.1MPa / 8h until water seepage occurs at the end face of the test block. The permeability resistance grade corresponding to the pressure at this time is recorded.

[0064] Temperature regulation performance test: Prepare a 100mm×100mm×100mm test block, place it in a temperature cycling chamber, set the temperature between 20~50℃ and cycle (heating rate 5℃ / h, cooling rate 5℃ / h), record the temperature change at the center of the test block through the built-in temperature sensor, and calculate the temperature fluctuation range (take the average value after 3 cycles).

[0065] Table 1 Test data of different ultra-high performance concretes

[0066] As shown in Table 1, the 7-day and 28-day compressive strengths and 28-day tensile strengths of Examples 1-3 are slightly higher than those of the comparative example, and all far exceed the standard requirements for ultra-high performance concrete. This indicates that the addition of composite phase change aggregate not only did not weaken the mechanical properties of concrete, but also further optimized the overall mechanical properties due to the good interfacial bonding between the porous structure of modified expanded vermiculite and the cement matrix, combined with the reinforcing effect of steel fibers.

[0067] The comparative example without composite phase change aggregate showed zero latent heat of phase change and a temperature fluctuation range of 8.6℃, indicating a lack of temperature regulation capability. In contrast, Examples 1-3 all exhibited good latent heat of phase change and temperature stability. Furthermore, with increasing composite phase change aggregate content, the latent heat of phase change increased while the temperature fluctuation range decreased. This is because the composite core material (dodecyl stearate-lauric acid-myristol eutectic system) can efficiently absorb and release heat in the 20~50℃ range. The encapsulation effect of modified expanded vermiculite ensures the stable performance of the composite core material, effectively mitigating the impact of ambient temperature changes on the interior of the concrete and meeting the application requirements in scenarios with large temperature differences.

[0068] The impermeability grades of Examples 1-3 are all P12, which is higher than the P10 of the comparative example, indicating that the addition of composite phase change aggregate improves the density of concrete. Modified expanded vermiculite fills the internal pores of concrete, while the silane coupling agent KH-550 enhances the interfacial bond between aggregate and cement matrix, reducing seepage channels, thereby improving impermeability and helping to extend the service life of concrete in humid environments.

[0069] Therefore, the present invention adopts the above-mentioned steel fiber reinforced ultra-high performance concrete and its preparation method. Through the synergistic effect of composite phase change aggregate and steel fiber reinforcement system, the concrete has excellent mechanical properties, temperature regulation function and durability. Compared with traditional steel fiber ultra-high performance concrete, it has a wider range of application scenarios and higher practical value.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A type of steel fiber reinforced ultra-high performance concrete, characterized in that: The composition by weight includes 550-650 parts silicate cement, 700-800 parts quartz sand, 100-125 parts composite phase change aggregate, 160-200 parts steel fiber, 100-140 parts silica fume, 50-70 parts fly ash, 20-28 parts polycarboxylate superplasticizer, and 140-160 parts deionized water. The composite phase change aggregate includes a composite core material and an adsorbent wall material. The composite core material is composed of dodecyl stearate, lauric acid, and myristic acid, and the adsorbent wall material is modified expanded vermiculite.

2. The steel fiber reinforced ultra-high performance concrete according to claim 1, characterized in that: The steel fibers have a diameter of 0.2~0.3mm and a length of 12~14mm; the quartz sand has a particle size of 0.15~0.6mm.

3. The steel fiber reinforced ultra-high performance concrete according to claim 1, characterized in that: The mass ratio of dodecyl stearate, lauric acid and myristol in the composite core material is 3:4:3, and the mass ratio of the composite core material to modified expanded vermiculite is 1:1.2~1.

5.

4. The steel fiber reinforced ultra-high performance concrete according to claim 1, characterized in that: The modified expanded vermiculite is expanded vermiculite modified with silane coupling agent KH-550. The particle size of the expanded vermiculite is 1~3mm, the porosity is ≥75%, and the amount of silane coupling agent KH-550 is 1%-3% of the mass of the expanded vermiculite.

5. A method for preparing steel fiber reinforced ultra-high performance concrete as described in any one of claims 1-4, characterized in that: Includes the following steps: S1. Preparation of composite phase change aggregate: Weigh dodecyl stearate, lauric acid and myristol, mix and melt them at 70-80℃ to form a homogeneous eutectic composite core material, add modified expanded vermiculite to the eutectic composite core material and stir at a constant temperature, then filter and dry after negative pressure adsorption to obtain composite phase change aggregate. S2. Dry mixing: Pour silicate cement, quartz sand, composite phase change aggregate, silica fume, and fly ash into a mixer and dry mix at 80-100 r / min for 2-3 minutes to obtain a dry mixture. S3. Wet material mixing: Add polycarboxylate superplasticizer and deionized water to the dry material mixture, and stir at 120-150 r / min for 3-4 min to obtain a mixed slurry; S4. Steel fiber dispersion: Add steel fibers to the mixed slurry in three batches, stirring at 60-80 r / min for 1-2 min after each addition to obtain ultra-high performance concrete.

6. The method for preparing steel fiber reinforced ultra-high performance concrete according to claim 5, characterized in that: In S1, the mixing and melting are carried out in a constant temperature water bath, and the stirring rate during mixing and melting is 100-150 r / min.

7. The method for preparing steel fiber reinforced ultra-high performance concrete according to claim 5, characterized in that: In S1, the modified expanded vermiculite is prepared by drying the expanded vermiculite, crushing it, and sieving it to obtain expanded vermiculite particles. The expanded vermiculite particles are added to an ethanol solution of silane coupling agent KH-550 with a volume concentration of 10%, and stirred at a rate of 150-200 r / min for 50-60 min at a temperature of 45-55℃. Then, it is placed in a drying oven at 70-80℃ and dried for 10-12 h to obtain modified expanded vermiculite.

8. The method for preparing steel fiber reinforced ultra-high performance concrete according to claim 5, characterized in that: In S1, the temperature for constant temperature stirring is 70-80℃, and the stirring rate is 100-150 r / min.

9. The method for preparing steel fiber reinforced ultra-high performance concrete according to claim 5, characterized in that: In S1, negative pressure adsorption is performed at 0.05 MPa for 30-40 min.

10. The method for preparing steel fiber reinforced ultra-high performance concrete according to claim 5, characterized in that: In S1, filtration involves letting the sample stand on a screen for 6-8 hours, and drying involves drying at 60-70℃ for 12 hours.

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