Construction application and production method of high-flowability super-early-strength concrete at-15 DEG C

Abstract

The invention discloses construction application and a production method of large-flow super-early-strength concrete at-15 DEG C. The invention relates to the technical field of building material preparation and comprises a production method of the super-early-strength concrete, and the large-flow super-early-strength concrete is prepared from a cementing material, coarse and fine aggregate and an additive, the preparation method has the advantages that the nano silicon dioxide, the deionized water and the silane coupling agent are dispersed, so that the nano silicon dioxide can be fully dispersed in the water to form uniform suspension liquid, and the silane coupling agent and hydroxyl on the surface of the nano silicon dioxide are subjected to chemical reaction; according to the present invention, the dispersion of the nano-silica in the concrete and the binding force with other materials are enhanced, the ultrasonic-assisted operation is performed on the additive mixture, and the ultrasonic cavitation effect can further promote the dispersion and the mixing of the additive molecules, such that the possible agglomeration structure can be broken, and the additives can be uniformly distributed in the system.

Description

Technical Field

[0001] This invention relates to the field of building material preparation technology, specifically to a high-flowability ultra-early strength concrete construction application at -15℃ and its production method. Background Technology

[0002] Concrete, as the most commonly used structural material in the construction industry, directly affects the quality of projects and the efficiency of construction. However, traditional concrete has shortcomings in early strength, fluidity, and frost resistance, especially when construction is required to be rapid or in low-temperature environments. For example, in winter or emergency repair projects, the strength of traditional concrete increases slowly, which cannot meet the needs of rapid construction. At the same time, it is susceptible to frost damage at low temperatures, affecting its final performance. In addition, traditional concrete requires vibration during construction, which not only increases labor intensity but also limits construction speed. Therefore, developing a new type of concrete material to solve the above problems has important practical significance and market application prospects. To this end, we propose a high-flowability ultra-early strength concrete for construction application at -15℃ and its production method. Summary of the Invention

[0003] The purpose of this invention is to provide a method for the construction application of high-flow-rate ultra-early-strength concrete at -15℃ and its production method.

[0004] To address the problems mentioned in the background art, the present invention provides the following technical solution: a method for producing high-flowability ultra-early-strength concrete, comprising a method for producing ultra-early-strength concrete, wherein the constituent materials of the high-flowability early-strength concrete include cementitious materials, coarse and fine aggregates, and additives, and the specific operation steps of the method for producing high-flowability early-strength concrete are as follows: Step 1: Select quick-setting cement as the cementing material, fly ash and stone powder as the base material, natural sand as the fine aggregate, and natural pebbles as the coarse aggregate. Mix the above materials to make a powder material for later use. Step 2: Prepare a nano-silica composite slurry by mixing nano-silica powder, silane coupling agent, dispersant and deionized water. Select polyacrylonitrile-based carbon fiber, basalt fiber, chopped glass fiber and epoxy resin emulsion to make mixed fiber, coat the surface of the fiber with binder, and remove water to obtain a high-performance fiber reinforcing agent. Step 3: Select water-reducing agent, water-retaining agent, defoamer, setting regulator, expansion agent and crack-resistant fiber as additives, mix them in sequence to form an additive mixture for later use. After mixing, add high-performance fiber reinforcing agent to form a mixed additive. Step 4: Add the processed nano-silica composite slurry to the powder material, and after stirring, add the original coarse and fine aggregates, mixed additives and antifreeze and stir again. After the process is completed, the ultra-early strength concrete product is obtained.

[0005] As a further aspect of the present invention: In step one, the components are prepared according to the following weight ratios: 275-400 parts of rapid-hardening cement, 70-90 parts of fly ash, 120-130 parts of stone powder, 350-380 parts of natural sand, and 118-128 parts of natural pebbles. These components are then added sequentially to a high-efficiency horizontal mixer and stirred at a speed of 100-150 r / min for 5-8 minutes. The stirring speed is then increased to 200-250 r / min and stirred for another 5-10 minutes. During the stirring process, samples are taken every 2-3 minutes to check the particle distribution and measure the bulk density. Once the samples pass the inspection, they are stored for later use.

[0006] As a further aspect of the present invention: In step two, nano-silica powder with a particle size of 20nm-30nm is selected and placed in a vacuum drying oven. It is dried for 4-6 hours at 60℃-80℃ and a vacuum degree of 0.05MPa-0.08MPa. The nano-silica powder, silane coupling agent, dispersant, and deionized water are added in a ratio of 1:0.02-0.03:0.01-0.02:5-8. The deionized water is then added to a reaction vessel equipped with an ultrasonic device. The ultrasonic device is turned on, and the frequency is set to 30kHz-40kHz with a power of 400W-60W. 0W, and slowly add nano-silica powder, continue ultrasonic dispersion for 30min-40min, then add silane coupling agent and continue ultrasonic reaction for 20min-30min. After ultrasonic dispersion is completed, add polycarboxylate dispersant, stir evenly and then ultrasonically disperse for 15min-20min. After dispersion is completed, raise the temperature of the reactor to 40℃-50℃, increase the stirring speed to 200r / min-300r / min, and continue stirring for 1h-2h to adsorb the polycarboxylate dispersant onto the surface of nano-silica particles, thus obtaining nano-silica composite slurry, which is then sealed and stored for later use.

[0007] As a further aspect of the present invention: In step two, polyacrylonitrile-based carbon fibers with a length of 6mm-12mm and a diameter of 7um-10um, basalt fibers with a length of 3mm-6mm and a diameter of 9um-13um, and chopped glass fibers with a length of 4mm-8mm and a diameter of 10um-15um are selected respectively. The three types of fibers are sequentially immersed in a 0.5%-1% sodium hydroxide solution for 15-20 minutes for surface activation treatment. After immersion, the fibers are rinsed with deionized water until neutral, and then dried in an oven at 60℃-80℃ for 2-3 hours. The pretreated polyacrylonitrile-based carbon fibers, basalt fibers, and chopped glass fibers are then processed according to their properties. Mix the fibers evenly in a ratio of 2:3:5, and prepare an epoxy resin emulsion as a binder. Add 10%-15% of the epoxy resin emulsion to the mixed fibers by weight. Transfer the emulsion to a high-speed mixer and set the mixing speed to 800-1000 rpm. After mixing for 15-20 minutes, spread the mixed fibers coated with the binder evenly in a mold. Cure the fibers at 50-60℃ and 40%-50% humidity for 2-3 hours. Place the pre-cured fiber material in a vacuum drying oven and dry it at 50-60℃ and 0.06-0.09MPa vacuum for 3-5 hours to remove moisture and organic solvents, thus obtaining a high-performance fiber reinforcing agent.

[0008] As a further aspect of the present invention: In step three, the additive components are prepared according to the following weight ratios: 0.8-1.5 parts water-reducing agent, 0.15-0.3 parts water-retaining agent, 0.4-0.7 parts defoamer, 1-2 parts setting regulator, 30-40 parts expansion agent, and 0.5-1 parts crack-resistant fiber. The additives are added sequentially to a low-speed mixer and stirred at a stirring speed of 60-80 r / min for 5-8 minutes at a temperature of 30-45℃. During the stirring process, an ultrasonic auxiliary device is turned on, and the ultrasonic frequency is set to 15kHz-20kHz with a power of 200W-300W. The ultrasonic-assisted mixing continues for 10-15 minutes. After the mixing is completed, the additive mixture is obtained and stored for later use.

[0009] As a further aspect of the present invention: In step three, before adding the high-performance fiber reinforcing agent, it is pretreated by an airflow dispersion device, and the airflow speed is controlled between 10m / s and 15m / s to disperse the fiber bundle into individual fibers. After the treatment, the pretreated high-performance fiber reinforcing agent is slowly added to the additive mixture after the initial mixing is completed, and the stirring speed of the mixer is increased to 300r / min-400r / min. The high-speed mixing continues for 15min-20min. During the high-speed mixing process, a uniform magnetic field with an intensity of 0.05T-0.1T is applied outside the mixer. The magnetic field-assisted mixing continues for 10min-15min. After the mixing is completed, a mixed additive is obtained. The mixed additive is extracted from the mixer for quality inspection, and the qualified mixed additive is transferred to a sealed storage container for later use.

[0010] As a further aspect of the present invention: In step four, the sealed nano-silica composite slurry is added to the powder material, and the nano-silica composite slurry is sprayed onto the surface of the powder material using a spraying device. The spraying pressure is controlled between 0.3MPa and 0.5MPa. After spraying, the container containing the powder material and the nano-silica composite slurry is transferred into a mixer with frequency conversion function and stirred at a stirring speed of 80r / min-100r / min for 3min-5min. After stirring, one-third of the total amount of natural sand is added sequentially, and after stirring for 1min-2min, half of the total amount of natural pebbles is added and stirred for 2min-3min. After stirring, the remaining natural sand and natural pebbles are added, and the stirring speed is increased to 150r / min-200r / min and stirred for 5min-8min to obtain uniformly mixed coarse and fine aggregates.

[0011] As a further aspect of the present invention: In step four, after the coarse and fine aggregates are mixed, a mixing additive and an antifreeze agent are added. The amount of antifreeze agent is adjusted according to the ambient temperature of the construction environment. After the addition is completed, the mixing speed is increased to 250 r / min-300 r / min, and a dynamic electric field device is set inside the mixer. The electric field strength is set between 0V / m and 50V / m and changes periodically at a frequency of 0.5Hz. The mixer is stirred for 10 min-15 min under the electric field assistance condition. During the mixing process, the slump, spread, air content and temperature of the concrete are monitored in real time using an online monitoring system. After the various performance indicators of the concrete reach the standard, the discharge port of the mixer is opened, and the prepared high-flow ultra-early strength concrete product is transported to the transportation equipment or storage container. The ambient temperature in the storage container is controlled between 15℃ and 25℃, and the humidity is maintained between 50% and 70%.

[0012] A method for constructing high-flow, ultra-early-strength concrete at -15℃ involves preheating powder materials and coarse and fine aggregates in a heated shed at -15℃ for 12-15 hours, maintaining the shed temperature between 10℃ and 15℃. The preheated powder materials are then added to a mixer and stirred for 1-2 minutes to achieve initial uniformity. Water at 40℃-50℃ is added and stirred for 2-3 minutes. Next, nano-silica composite slurry is added and stirred at 120-150 rpm for 3-5 minutes. After stirring, preheated natural sand and natural gravel are added. One-third of the natural sand is added and stirred for 1-2 minutes, followed by half of the natural gravel and stirred for 2-3 minutes. Finally, the remaining sand and gravel are added, and the stirring speed is increased to 180-220 rpm and stirred for 5 minutes. Mix for 8 minutes, then add the mixing additives and 7%-9% of the total concrete mass as antifreeze. Increase the mixing speed to 250-300 rpm and mix for 10-15 minutes. Before pouring the concrete, use a hot air gun to heat the formwork surface to above 5°C, remove ice, snow, and dirt from the formwork and reinforcing steel surfaces, and wrap the outside of the formwork with insulation cotton blankets at least 30mm thick. Use a layered pouring method, with each layer controlled at a thickness of 250mm-350mm and a time interval of 30-35 minutes between each layer. After the concrete is poured, cover the surface with a layer of plastic film, and then cover the plastic film with two layers of insulation cotton. When the concrete surface temperature is below 5°C, use an electric heater to heat the concrete surface. At a temperature of -15°C, the initial setting time is 2-3 hours and the final setting time is 4-6 hours.

[0013] Compared with the prior art, the beneficial effects of the present invention by adopting the above technical solution are as follows: This invention disperses nano-silica, deionized water, and a silane coupling agent, enabling the nano-silica to be fully dispersed in water to form a uniform suspension. The silane coupling agent then reacts chemically with the hydroxyl groups on the surface of the nano-silica, enhancing its dispersibility in concrete and its bonding strength with other materials. Ultrasonic-assisted mixing of the additive mixture further promotes the dispersion and mixing of additive molecules, breaking down any potential agglomerates and ensuring uniform distribution of the additives within the system. High-speed mixing of the high-performance fiber reinforcing agent utilizes the strong shear force generated by the high-speed stirring to fully integrate the high-performance fiber reinforcing agent with the additive mixture, ensuring uniform dispersion of the fibers within the additive system. Furthermore, the use of a magnetic field during high-speed mixing of the high-performance fiber reinforcing agent and the additive mixture influences the direction and state of movement of the additive molecules and fibers, promoting their interaction and bonding, further improving the uniformity and stability of the mixture. This invention, through layered addition and gradually accelerated mixing, enables coarse and fine aggregates to be fully dispersed in the system of powder materials and nano-silica composite slurry, optimizing the particle size distribution of concrete and improving its density and stability. By adding a dynamic electric field device during the addition of mixed additives and antifreeze, the dynamic electric field can promote the migration and diffusion of additive molecules and ions in the concrete system, enhance their interaction with other materials, and make the mixed additives and antifreeze more uniformly dispersed in the concrete, further improving the overall performance of the concrete. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the concrete preparation process in an embodiment of the present invention; Figure 2 This is a comparison chart of concrete fluidity test data in an embodiment of the present invention; Figure 3 This is a comparison chart of concrete compressive strength test data in an embodiment of the present invention; Figure 4 This is a comparison chart of concrete freeze-thaw resistance test data in embodiments of the present invention; Figure 5 This is a comparison chart of the changes in concrete properties during the solidification process in an embodiment of the present invention. Detailed Implementation

[0015] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0016] As attached Figure 1 - Appendix Figure 5 As shown, this invention discloses a method for producing high-flowability, ultra-early-strength concrete, comprising a method for producing ultra-early-strength concrete. The components of the high-flowability, early-strength concrete include cementitious materials, coarse and fine aggregates, and additives. The specific operating steps of the high-flowability, early-strength concrete production method are as follows: Step 1: Select quick-setting cement as the cementing material, fly ash and stone powder as the base material, natural sand as the fine aggregate, and natural pebbles as the coarse aggregate. Mix the above materials to make a powder material for later use. Step 2: Prepare a nano-silica composite slurry by mixing nano-silica powder, silane coupling agent, dispersant and deionized water. Select polyacrylonitrile-based carbon fiber, basalt fiber, chopped glass fiber and epoxy resin emulsion to make mixed fiber, coat the surface of the fiber with binder, and remove water to obtain a high-performance fiber reinforcing agent. Step 3: Select water-reducing agent, water-retaining agent, defoamer, setting regulator, expansion agent and crack-resistant fiber as additives, mix them in sequence to form an additive mixture for later use. After mixing, add high-performance fiber reinforcing agent to form a mixed additive. Step 4: Add the processed nano-silica composite slurry to the powder material, and after stirring, add the original coarse and fine aggregates, mixed additives and antifreeze and stir again. After the process is completed, the ultra-early strength concrete product is obtained.

[0017] In one embodiment of the present invention: In step one, the components are prepared according to the following weight ratios: 275-400 parts of rapid-hardening cement, 70-90 parts of fly ash, 120-130 parts of stone powder, 350-380 parts of natural sand, and 118-128 parts of natural pebbles (natural pebbles are natural gravel with a particle size of 5mm-10mm, conforming to GB / T 14685-2011 "Construction Gravel and Crushed Stone" standard). These components are added sequentially to a high-efficiency horizontal mixer and stirred at a stirring speed of 100r / min-150r / min for 5min-8min. Then, the stirring speed is increased to 200r / min-250r / min and stirred for 5min-10min. During the stirring process, samples are taken every 2min-3min to check the particle distribution and measure the bulk density. After passing the inspection, the samples are stored for later use.

[0018] In one embodiment of the present invention: In step two, nano-silica powder with a particle size of 20nm-30nm is selected and placed in a vacuum drying oven. It is dried for 4-6 hours at 60℃-80℃ and a vacuum degree of 0.05MPa-0.08MPa. The nano-silica powder, silane coupling agent, dispersant, and deionized water are added to a reaction vessel equipped with an ultrasonic device at a ratio of 1:0.02-0.03:0.01-0.02:5-8. The ultrasonic device is then turned on, and the frequency is set to 30kHz-40kHz, and the power to 400W-60W. 0W, and slowly add nano-silica powder, continue ultrasonic dispersion for 30min-40min, then add silane coupling agent and continue ultrasonic reaction for 20min-30min. After ultrasonic dispersion is completed, add polycarboxylate dispersant, stir evenly and then ultrasonically disperse for 15min-20min. After dispersion is completed, raise the temperature of the reactor to 40℃-50℃, increase the stirring speed to 200r / min-300r / min, and continue stirring for 1h-2h to adsorb the polycarboxylate dispersant onto the surface of nano-silica particles, thus obtaining nano-silica composite slurry, which is then sealed and stored for later use.

[0019] In one embodiment of the present invention: In step two, polyacrylonitrile-based carbon fibers with a length of 6mm-12mm and a diameter of 7um-10um, basalt fibers with a length of 3mm-6mm and a diameter of 9um-13um, and chopped glass fibers with a length of 4mm-8mm and a diameter of 10um-15um are selected respectively. The three types of fibers are sequentially immersed in a 0.5%-1% sodium hydroxide solution for 15min-20min for surface activation treatment. After immersion, the fibers are rinsed with deionized water until neutral, and then dried in an oven at 60℃-80℃ for 2h-3h. The pretreated polyacrylonitrile-based carbon fibers, basalt fibers, and chopped glass fibers are then sorted according to their properties. Mix the fibers evenly in a ratio of 2:3:5, and prepare an epoxy resin emulsion as a binder. Add 10%-15% of the epoxy resin emulsion to the mixed fibers by weight. Transfer the emulsion to a high-speed mixer and set the mixing speed to 800-1000 rpm. After mixing for 15-20 minutes, spread the mixed fibers coated with the binder evenly in a mold. Cure the fibers at 50-60℃ and 40%-50% humidity for 2-3 hours. Place the pre-cured fiber material in a vacuum drying oven and dry it at 50-60℃ and 0.06-0.09MPa vacuum for 3-5 hours to remove moisture and organic solvents, thus obtaining a high-performance fiber reinforcing agent.

[0020] In one embodiment of the present invention: In step three, the additive components are prepared according to the following weight ratios: 0.8-1.5 parts water-reducing agent, 0.15-0.3 parts water-retaining agent, 0.4-0.7 parts defoamer, 1-2 parts setting regulator, 30-40 parts expansion agent, and 0.5-1 parts crack-resistant fiber. The additives are added to a low-speed mixer in sequence and stirred at a stirring speed of 60-80 r / min for 5-8 minutes at a temperature of 30-45℃. During the stirring process, the ultrasonic auxiliary device is turned on, and the ultrasonic frequency is set to 15kHz-20kHz and the power is 200W-300W. The ultrasonic-assisted mixing continues for 10-15 minutes. After the mixing is completed, the additive mixture is obtained and stored for later use.

[0021] The ultrasonic frequency was selected in the range of 30kHz-40kHz to match the resonant frequency of the nanoparticles and promote dispersion.

[0022] A magnetic field strength of 0.05T-0.1T can effectively regulate the molecular orientation of additives and prevent fiber aggregation.

[0023] In one embodiment of the present invention: In step three, before adding the high-performance fiber reinforcing agent for mixing, it is pretreated by an airflow dispersion device, and the airflow speed is controlled between 10m / s and 15m / s to disperse the fiber bundle into individual fibers. After the treatment is completed, the pretreated high-performance fiber reinforcing agent is slowly added to the additive mixture after the initial mixing is completed, and the stirring speed of the mixer is increased to 300r / min-400r / min. The high-speed mixing continues for 15min-20min. During the high-speed mixing process, a uniform magnetic field with an intensity of 0.05T-0.1T is applied outside the mixer. The magnetic field-assisted mixing continues for 10min-15min. After the mixing is completed, a mixed additive is obtained. The mixed additive is extracted from the mixer for quality inspection, and the qualified mixed additive is transferred to a sealed storage container for later use.

[0024] In one embodiment of the present invention: In step four, the sealed nano-silica composite slurry is added to the powder material, and the nano-silica composite slurry is sprayed onto the surface of the powder material using a spraying device. The spraying pressure is controlled between 0.3MPa and 0.5MPa. After spraying, the container containing the powder material and the nano-silica composite slurry is transferred into a mixer with frequency conversion function and stirred at a stirring speed of 80r / min-100r / min for 3min-5min. After stirring, one-third of the total amount of natural sand is added and stirred for 1min-2min. Then, half of the total amount of natural pebbles is added and stirred for 2min-3min. After stirring, the remaining natural sand and natural pebbles are added, and the stirring speed is increased to 150r / min-200r / min and stirred for 5min-8min to obtain uniformly mixed coarse and fine aggregates.

[0025] In one embodiment of the present invention: In step four, after the coarse and fine aggregates are mixed, a mixing additive and an antifreeze are added. The amount of antifreeze is adjusted according to the ambient temperature of the construction environment. After the addition is completed, the mixing speed is increased to 250 r / min-300 r / min, and a dynamic electric field device is set inside the mixer. The dynamic electric field device consists of an alternating power supply and electrode plates with an electrode spacing of 10 cm. Ion migration is driven by periodic voltage changes. The electric field strength is set between 0 V / m and 50 V / m and changes periodically at a frequency of 0.5 Hz. The mixer is stirred for 10 min-15 min under electric field assistance. During the mixing process, the slump, spread, air content, and temperature of the concrete are monitored in real time using an online monitoring system. After the various performance indicators of the concrete reach the standard, the discharge port of the mixer is opened, and the prepared high-flow ultra-early strength concrete product is transported to the transportation equipment or storage container. The ambient temperature in the storage container is controlled between 15℃ and 25℃, and the humidity is maintained between 50% and 70%.

[0026] A method for constructing high-flow, ultra-early-strength concrete at -15℃ involves preheating powder materials and coarse and fine aggregates in a heated shed at -15℃ for 12-15 hours, maintaining the shed temperature between 10℃ and 15℃. The preheated powder materials are then added to a mixer and mixed for 1-2 minutes to achieve initial homogeneity. Water at 40℃-50℃ is added and mixing continues for 2-3 minutes. Next, nano-silica composite slurry is added and mixed at 120-150 rpm for 3-5 minutes. After mixing, preheated natural sand and natural gravel are added. One-third of the natural sand is added and mixed for 1-2 minutes, followed by half of the natural gravel and mixed for 2-3 minutes. Finally, the remaining sand and gravel are added, and the mixing speed is increased to 180-220 rpm for 5-8 minutes. Finally, a mixing additive and other additives are added to the total concrete volume. Add 7%-9% antifreeze agent, adjusting the dosage according to the recommended dosage in the "Code for Construction Engineering in Winter" for -15℃ environment, and verify its antifreeze performance through freeze-thaw cycle test. Increase the stirring speed to 250r / min-300r / min and stir for 10min-15min. Before pouring concrete, use a hot air gun to heat the surface of the formwork to above 5℃, remove ice, snow and dirt from the surface of the formwork and reinforcing bars, and wrap the outside of the formwork with insulation cotton blankets with a thickness of not less than 30mm. Use a layered pouring method, with the thickness of each layer controlled at 250mm-350mm, and the time interval between each layer is 30min-35min. After the concrete is poured, cover the surface with a layer of plastic film, and then cover the plastic film with two layers of insulation cotton. When the concrete surface temperature is below 5℃, use an electric heater to heat the concrete surface. In a temperature environment of -15℃, the initial setting time is 2h-3h, and the final setting time is 4h-6h.

[0027] In one embodiment of the present invention: in step one, the rapid-hardening cement is selected with a specific surface area of ​​400 m². 2 / kg-450m 2The rapid-hardening cement ( / kg) is finely processed using an air classifier. The airflow velocity is set at 15m / s-20m / s, causing the cement particles to be classified according to size under the influence of the airflow. Oversized or undersized particles are removed, retaining cement particles with a diameter concentrated between 3µm and 30µm, accounting for no less than 80%. After processing, a second screening is performed using a vibrating screen at a vibration frequency of 50Hz-60Hz, an amplitude of 3mm-5mm, and a screen mesh size of 0.9mm to further remove any remaining lumps or impurities. Grade I fly ash is selected, with a water requirement not exceeding 95% and a fineness not exceeding 12%. Before drying, the fly ash is cleaned using an ultrasonic cleaning device. Add an appropriate amount of deionized water to the tank, turn on the ultrasonic generator, set the frequency to 20kHz-30kHz, the power to 200W-300W, and the cleaning time to 15-20 minutes. Utilize the cavitation effect of ultrasound to remove minute impurities and adsorbed gases from the surface of the fly ash particles. After cleaning, place the particles in a drying device at a temperature of 80℃-100℃ for 2-3 hours to remove excess moisture. Use stone powder with a calcium carbonate content of not less than 92% and a particle size between 0.15mm and 0.75mm. In addition to magnetic separation to remove iron, further purification is achieved using electrostatic separation technology. The stone powder is fed into an electrostatic separation device with a voltage of 30kV-40kV and an electrode spacing of 5cm-8cm. This process separates impurities with different charges from the stone powder. Afterward, the stone powder undergoes surface modification treatment. The stone powder and silane coupling agent are mixed at a mass ratio of 100:1-3 and stirred in a high-speed mixer at a speed of 800-1000 rpm for 20-30 minutes. This allows the silane coupling agent to coat the surface of the stone powder particles, enhancing the bonding performance between the stone powder and cement paste, and improving the density and early strength of the concrete. The natural sand selected is medium sand with a fineness modulus between 2.5 and 2.8 and a mud content of less than 2%. After washing and drying, the natural sand is ball-milled. The sand is placed in a ball mill, and the mill speed is controlled at 150-200 rpm. The grinding time is 30-60 minutes. Through ball milling, the surface of natural sand particles becomes rougher and the edges become more distinct, increasing their mechanical interlocking force with cement paste. At the same time, some sand particles are ground finer, optimizing the sand gradation and improving the filling performance and fluidity of concrete. High-quality natural pebbles with a particle size of 5mm-10mm and a crushing index of no more than 8% are selected. After being washed with a high-pressure water gun, the natural pebbles are soaked in an acrylic emulsion with a concentration of 0.5%-1% for 30-60 minutes. After being taken out, they are dried in an environment of 50℃-60℃ for 2-3 hours. The polymer forms a protective film on the surface of the pebbles, enhancing the bonding strength between the pebbles and cement paste and improving the overall mechanical properties of concrete.

[0028] In one embodiment of the present invention: In step two, nano-silica has extremely high specific surface area and activity, which can fill the tiny pores inside the concrete, improve the microstructure, and enhance the density. It can also undergo a secondary reaction with cement hydration products to generate more hydrated calcium silicate gel, thereby improving the early and later strength of the concrete. Studies have shown that adding an appropriate amount of nano-silica composite slurry can increase the 3-day strength of concrete by 20%-30% and the 28-day strength by 15%-20%. At the same time, it can also enhance the impermeability and durability of concrete, reduce the chloride ion permeability coefficient, and improve the service life of concrete in harsh environments.

[0029] In one embodiment of the present invention: In step two, the synergistic effect of multiple fibers can effectively improve the toughness and crack resistance of concrete. Carbon fiber has high strength and high modulus, which can significantly enhance the tensile strength of concrete. Basalt fiber is resistant to high temperature and has good chemical stability, which can improve the durability of concrete. Short-cut glass fiber is inexpensive and has good dispersibility, which can increase the toughness of concrete. When concrete is subjected to tension or impact, the fibers can prevent the generation and propagation of cracks, thereby improving the crack resistance of concrete by 30%-50%. In addition, it can also improve the impact resistance and fatigue performance of concrete, making it suitable for projects with high material performance requirements such as bridges and hydraulic structures. Example

[0030] Weigh out 320 parts by weight of rapid-hardening cement, 80 parts by weight of fly ash, 125 parts by weight of stone powder, 360 parts by weight of natural sand, and 123 parts by weight of natural pebbles. Add them to a high-efficiency horizontal mixer in sequence. First, mix at 120 r / min for 6 minutes, then increase the speed to 220 r / min and mix for 7 minutes. Take samples every 2.5 minutes during the process to check. The particle distribution is uniform and the bulk density meets the requirements. Keep the samples for later use.

[0031] Nano-silica powder with a particle size of 25 mm was selected and dried in a vacuum drying oven at 65℃ and a vacuum degree of 0.06 MPa for 5 h. Nano-silica powder, silane coupling agent, dispersant and deionized water were prepared in a ratio of 1:0.025:0.015:6. Deionized water was added to a reaction vessel equipped with an ultrasonic device, and the ultrasonic device was turned on at a frequency of 35 kHz and a power of 500 W. Nano-silica powder was slowly added and ultrasonically dispersed for 35 min. Silane coupling agent was added and ultrasonic reaction was continued for 25 min. Polycarboxylate dispersant was added and ultrasonically dispersed for 18 min. Finally, the temperature of the reaction vessel was raised to 45℃, the stirring speed was increased to 250 r / min, and stirring was carried out for 1.5 h. The mixture was then sealed and stored.

[0032] Polyacrylonitrile-based carbon fibers with a length of 8 mm and a diameter of 8 μm, basalt fibers with a length of 4 mm and a diameter of 11 μm, and chopped glass fibers with a length of 6 mm and a diameter of 12 μm were selected. The three types of fibers were soaked in a 0.8% sodium hydroxide solution for 18 min, rinsed with deionized water until neutral, and dried in an oven at 70℃ for 2.5 h. They were then mixed at a mass ratio of 2:3:5, and 12% of the total fiber mass of epoxy resin emulsion was added. The mixture was stirred at 900 r / min for 18 min in a high-speed mixer. The mixed fibers with the binder were evenly spread in a mold and cured at 55℃ and 45% humidity for 2.5 h. Finally, they were dried in a vacuum drying oven at 55℃ and 0.07 MPa for 4 h to obtain a high-performance fiber reinforcing agent.

[0033] Weigh out 1.2 parts by weight of water-reducing agent, 0.2 parts by weight of water-retaining agent, 0.5 parts by weight of defoamer, 1.5 parts by weight of setting regulator, 35 parts by weight of expansion agent, and 0.8 parts by weight of crack-resistant fiber. Add them to a low-speed mixer and stir for 6 minutes at 38℃ and 70 r / min. At the same time, turn on the ultrasonic auxiliary device and set the ultrasonic frequency to 18 kHz and the power to 250 W. After ultrasonic-assisted mixing for 12 minutes, add the high-performance fiber reinforcing agent, which has been pretreated by an airflow dispersion device, slowly into the additive mixture. Increase the stirring speed to 350 r / min and apply a uniform magnetic field with an intensity of 0.07 T to the outside of the mixer. Continue stirring for 12 minutes. After passing the test, seal and store.

[0034] The sealed nano-silica composite slurry was sprayed onto the surface of the powder material using a spraying device with a spray pressure of 0.4 MPa. It was then transferred to a variable frequency mixer and stirred at a speed of 90 r / min for 4 minutes. Then, one-third of the natural sand was added and stirred for 1.5 minutes, followed by half of the natural pebbles and stirred for 2.5 minutes. The remaining sand and pebbles were then added, and the stirring speed was increased to 180 r / min and stirred for 6 minutes. Mixed additives and antifreeze (8% of the total concrete mass) were added, and the stirring speed was increased to 280 r / min. A dynamic electric field device was installed inside the mixer, with the electric field strength set between 0 V / m and 50 V / m and periodically varied at a frequency of 0.5 Hz. The mixture was stirred for 12 minutes, and various performance indicators were monitored in real time. The material was discharged after passing the test.

[0035] In an environment of -15℃, the powder materials and coarse and fine aggregates are preheated in a heated shed 13 hours in advance, with the shed temperature controlled at 12℃. Before construction, the surface of the formwork is heated to 8℃ with a hot air gun. Ice, snow, and dirt are removed from the formwork and reinforcing steel surfaces. A 40mm thick insulation blanket is wrapped around the outside of the formwork. Concrete is delivered to the pouring location using a pumping device, with pumping pressure and flow rate controlled to maintain a free-fall height of approximately 1.5m. The concrete slowly and evenly fills the formwork space, achieving self-leveling without vibration. During the pouring process, a designated person observes the concrete flow to ensure it fills all corners of the formwork. Any localized flow is reported immediately. If the flow is obstructed, gently guide it with a wooden pole to avoid external interference that could damage the concrete structure. After the concrete is poured, immediately cover the surface with a layer of plastic film, sealing it tightly to prevent moisture evaporation. Then cover the plastic film with two layers of insulation cotton, ensuring they overlap tightly. Install temperature sensors inside and on the surface of the concrete, measuring the temperature every 0.5 hours. When the concrete surface temperature drops below 5°C, use an electric heater to heat the surface, maintaining it between 5°C and 8°C. In this way, at a temperature of -15°C, the initial setting time of the concrete is controlled within 2.5 hours, and the final setting time within 5 hours.

[0036] Performance testing experiments on high-flow-rate, ultra-early-strength concrete: The properties and characteristics of high-flowability ultra-early strength concrete prepared at -15℃ were tested, including flowability, compressive strength, freeze-thaw resistance, and changes in properties from laying to solidification.

[0037] The following equipment was prepared according to the given formula: high-flowability ultra-early strength concrete, 150mm×150mm×150mm cube mold, 100mm×100mm×400mm prism mold for frost resistance testing, curing chamber (capable of simulating -15℃ environment), curing room (standard temperature 20±2℃, relative humidity above 95%), pressure testing machine, frost resistance testing machine, slump cylinder, spread tester, electronic scale, thermometer, hygrometer, stopwatch, etc.

[0038] Equipment: preheating shed, hot air gun, thermal insulation quilt, pumping equipment, spraying device, mixer, ultrasonic device, vacuum drying oven, drying oven, high-speed mixing equipment, airflow dispersion equipment, dynamic electric field device, temperature sensor, electric heater, and plastic film.

[0039] Liquidity test: At -15℃, take an appropriate amount of freshly prepared concrete and fill it into a slump cone in three layers. Use a tamping rod to tamp each layer 25 times evenly. After tamping the top layer, scrape off the excess concrete and smooth it.

[0040] Lift the slump cone vertically and measure the slump of the concrete mixture. At the same time, use a steel ruler to measure the maximum and minimum diameters of the expanded concrete. Take the average value as the spread and record the data.

[0041] Repeat the above steps 3 times and take the average value as the slump and spread data of the concrete.

[0042] Specific data is attached. Figure 2 As shown.

[0043] Compressive strength test: Following standard methods, 150mm×150mm×150mm cubic specimens were prepared using concrete mixture at -15℃, with 3 specimens per group, for a total of 5 groups.

[0044] After the specimens were prepared, they were immediately covered with a plastic film and then placed in a curing chamber at -15℃. The specimens were removed after 1 hour, 2 hours, 2.5 hours (initial setting time), 5 hours (final setting time), and 28 days. After being placed in a standard curing room (temperature 20±2℃, relative humidity above 95%) until room temperature, the compressive strength was tested using a pressure testing machine. The failure load was recorded, and the compressive strength was calculated. Specific data are attached. Figure 3 As shown.

[0045] Antifreeze performance test: Three prism specimens of 100mm×100mm×400mm were made in an environment of -15℃. Three specimens were made in each group.

[0046] After curing the specimens in a -15℃ curing chamber for 24 hours, they were placed in an antifreeze testing machine for freeze-thaw cycle testing. The freeze-thaw cycle conditions were set as follows: freezing temperature -15℃, freezing time 4 hours, thawing temperature 20℃, thawing time 4 hours. After 0, 25, and 50 freeze-thaw cycles, the specimens were removed, the surface moisture was wiped dry, and the compressive strength was tested using a compression testing machine. The data were recorded, and the compressive strength loss rate was calculated. Specific data are attached. Figure 4 As shown.

[0047] Test on changes in properties during solidification: In an environment of -15℃, a flat test area was selected, and concrete was transported to the area using pumping equipment for paving to simulate actual construction conditions.

[0048] From the start of concrete laying, the internal temperature of the concrete is measured with a thermometer every 30 minutes, and the surface humidity of the concrete is measured with a hygrometer. The data are recorded.

[0049] Before the concrete initially sets, the change in the concrete's fluidity is measured every 30 minutes using a slump cone and a spread meter, and the slump and spread data are recorded.

[0050] Observe the state of the concrete at initial and final setting, record the initial and final setting times, and compare them with the expected initial setting time of 2.5 hours and final setting time of 5 hours. Specific data is attached. Figure 5 As shown.

[0051] Analysis of experimental results: According to the fluidity test data, the average slump of the concrete is 230mm and the average spread is 600mm, which shows good fluidity and meets the requirements of high-flow concrete. It can be self-leveled and constructed in an environment of -15℃.

[0052] Compressive strength test data show that the concrete exhibits significant strength increases during the initial and final setting stages. The compressive strength is 5.0 MPa at 1 hour, 32.0 MPa at 2.5 hours of initial setting, 41.0 MPa at 5 hours of final setting, and 55.0 MPa at 28 days. This indicates that the concrete has excellent ultra-early strength performance, can quickly reach high strength, and meets the requirements of rapid construction.

[0053] In the freeze-thaw resistance test, after 50 freeze-thaw cycles, the compressive strength loss rate was 20%, indicating that the concrete has good freeze-thaw resistance at -15℃ and can meet the engineering requirements in low-temperature environments.

[0054] Data on the changes in properties during solidification show that, over time, the internal temperature of the concrete gradually increases, the surface humidity gradually decreases, and the fluidity gradually decreases until initial and final setting. The initial and final setting times are basically consistent with expectations, at 2.5 hours and 5 hours respectively, proving that the curing measures at -15℃ are effective and the concrete can solidify in the expected time, meeting the construction schedule requirements.

[0055] Based on the above examples and test results, it can be concluded that this high-flowability ultra-early strength concrete exhibits excellent performance at -15℃, and all performance indicators meet the design requirements. It has significant advantages and broad application prospects in rapid construction, emergency repair projects, and construction in low-temperature environments.

[0056] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

[0057] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0058] The above description is merely an example and illustration of the present invention. Any modifications, additions, or substitutions made by those skilled in the art to the specific embodiments described, as long as they do not deviate from the invention or exceed the scope defined in the claims, shall fall within the protection scope of the present invention.

[0059] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for producing high-flow-rate ultra-early-strength concrete, comprising a method for producing ultra-early-strength concrete, characterized in that: The components of high-flowability early-strength concrete include cementitious materials, coarse and fine aggregates, and additives. The specific operating steps of the high-flowability early-strength concrete production method are as follows: Step 1: Select quick-setting cement as the cementing material, fly ash and stone powder as the base material, natural sand as the fine aggregate, and natural pebbles as the coarse aggregate. Mix the above materials to make a powder material for later use. Step 2: Prepare a nano-silica composite slurry by mixing nano-silica powder, silane coupling agent, dispersant and deionized water. Select polyacrylonitrile-based carbon fiber, basalt fiber, chopped glass fiber and epoxy resin emulsion to make mixed fiber, coat the surface of the fiber with binder, and remove water to obtain a high-performance fiber reinforcing agent. Step 3: Select water-reducing agent, water-retaining agent, defoamer, setting regulator, expansion agent and crack-resistant fiber as additives, mix them in sequence to form an additive mixture for later use. After mixing, add high-performance fiber reinforcing agent to form a mixed additive. Step 4: Add the processed nano-silica composite slurry to the powder material, and after stirring, add the original coarse and fine aggregates, mixed additives and antifreeze and stir again. After the process is completed, the ultra-early strength concrete product is obtained.

2. The method for producing high-flow, ultra-early-strength concrete according to claim 1, characterized in that: In step one, the components are prepared according to the following weight ratios: 275-400 parts of rapid-hardening cement, 70-90 parts of fly ash, 120-130 parts of stone powder, 350-380 parts of natural sand, and 118-128 parts of natural pebbles. These components are added sequentially to a high-efficiency horizontal mixer and stirred at a speed of 100-150 r / min for 5-8 minutes. The stirring speed is then increased to 200-250 r / min and stirred for another 5-10 minutes. During the stirring process, samples are taken every 2-3 minutes to check the particle distribution and measure the bulk density. Once the samples pass the inspection, they are stored for later use.

3. The method for producing high-flow, ultra-early-strength concrete according to claim 2, characterized in that: In step two, nano-silica powder with a particle size of 20nm-30nm is selected and placed in a vacuum drying oven. It is dried for 4-6 hours at 60℃-80℃ and a vacuum of 0.05MPa-0.08MPa. The nano-silica powder, silane coupling agent, dispersant, and deionized water are added in a ratio of 1:0.02-0.03:0.01-0.02:5-8. The deionized water is then added to a reaction vessel equipped with an ultrasonic device. The ultrasonic device is turned on, set to a frequency of 30kHz-40kHz and a power of 400W-600W, and the mixture is slowly... After adding nano-silica powder and continuously ultrasonically dispersing for 30-40 minutes, add silane coupling agent and continue ultrasonic reaction for 20-30 minutes. After ultrasonic dispersion is completed, add polycarboxylate dispersant, stir evenly, and then ultrasonically disperse for 15-20 minutes. After dispersion is completed, raise the temperature of the reactor to 40℃-50℃ and increase the stirring speed to 200r / min-300r / min, and continue stirring for 1-2 hours to adsorb the polycarboxylate dispersant onto the surface of the nano-silica particles, thus obtaining nano-silica composite slurry, which is then sealed and stored for later use.

4. The method for producing high-flow, ultra-early-strength concrete according to claim 3, characterized in that: In step two, polyacrylonitrile-based carbon fibers with a length of 6mm-12mm and a diameter of 7um-10um, basalt fibers with a length of 3mm-6mm and a diameter of 9um-13um, and chopped glass fibers with a length of 4mm-8mm and a diameter of 10um-15um are selected respectively. The three types of fibers are sequentially immersed in a 0.5%-1% sodium hydroxide solution for 15-20 minutes for surface activation treatment. After immersion, the fibers are rinsed with deionized water until neutral and then dried in an oven at 60℃-80℃ for 2-3 hours. The pretreated polyacrylonitrile-based carbon fibers, basalt fibers, and chopped glass fibers are then dried in a mass ratio of 2:

3. Mix the fibers evenly in a 5:1 ratio, and prepare an epoxy resin emulsion as a binder. Add 10%-15% of the epoxy resin emulsion to the mixed fibers by weight of the total fibers. Transfer the emulsion to a high-speed mixer and set the mixing speed to 800-1000 rpm. After mixing for 15-20 minutes, spread the mixed fibers coated with the binder evenly in a mold. Cure the fibers at 50-60℃ and 40%-50% humidity for 2-3 hours. Place the pre-cured fiber material in a vacuum drying oven and dry it at 50-60℃ and 0.06-0.09 MPa for 3-5 hours. After removing moisture and organic solvents, a high-performance fiber reinforcing agent is obtained.

5. The method for producing high-flow, ultra-early-strength concrete according to claim 4, characterized in that: In step three, the additive components are prepared according to the following weight ratios: 0.8-1.5 parts water-reducing agent, 0.15-0.3 parts water-retaining agent, 0.4-0.7 parts defoamer, 1-2 parts setting regulator, 30-40 parts expansion agent, and 0.5-1 parts crack-resistant fiber. The additives are added sequentially to a low-speed mixer and stirred at a stirring speed of 60-80 r / min for 5-8 minutes at a temperature of 30-45℃. During the stirring process, the ultrasonic auxiliary device is turned on, and the ultrasonic frequency is set to 15kHz-20kHz and the power to 200W-300W. The ultrasonic-assisted mixing continues for 10-15 minutes. After the mixing is completed, the additive mixture is obtained and stored for later use.

6. The method for producing high-flow, ultra-early-strength concrete according to claim 5, characterized in that: In step three, before adding the high-performance fiber reinforcing agent, it is pretreated by an airflow dispersion device, with the airflow speed controlled between 10m / s and 15m / s to disperse the fiber bundle into individual fibers. After treatment, the pretreated high-performance fiber reinforcing agent is slowly added to the additive mixture after preliminary mixing, and the stirring speed of the mixer is increased to 300r / min-400r / min. High-speed mixing continues for 15min-20min. During high-speed mixing, a uniform magnetic field with an intensity of 0.05T-0.1T is applied outside the mixer, and magnetic field-assisted mixing continues for 10min-15min. After mixing, a mixed additive is obtained. The mixed additive is extracted from the mixer for quality testing, and the qualified mixed additive is transferred to a sealed storage container for later use.

7. The method for producing high-flow, ultra-early-strength concrete according to claim 6, characterized in that: In step four, the sealed nano-silica composite slurry is added to the powder material. The nano-silica composite slurry is sprayed onto the surface of the powder material using a spraying device. The spraying pressure is controlled between 0.3MPa and 0.5MPa. After spraying, the container containing the powder material and the nano-silica composite slurry is transferred to a mixer with variable frequency function and stirred at a stirring speed of 80r / min-100r / min for 3min-5min. After stirring, one-third of the total amount of natural sand is added and stirred for 1min-2min. Then, half of the total amount of natural pebbles is added and stirred for 2min-3min. After stirring, the remaining natural sand and natural pebbles are added, and the stirring speed is increased to 150r / min-200r / min and stirred for 5min-8min to obtain uniformly mixed coarse and fine aggregates.

8. The method for producing high-flow, ultra-early-strength concrete according to claim 7, characterized in that: In step four, after the coarse and fine aggregates are mixed, a mixing additive and antifreeze are added. The amount of antifreeze is adjusted according to the ambient temperature. After the addition is complete, the mixing speed is increased to 250-300 r / min. A dynamic electric field device is set inside the mixer, with the electric field strength set between 0V / m and 50V / m and periodically varying at a frequency of 0.5Hz. The mixer is stirred for 10-15 minutes under electric field assistance. During the mixing process, the slump, spread, air content, and temperature of the concrete are monitored in real time using an online monitoring system. After all the performance indicators of the concrete meet the standards, the mixer outlet is opened, and the prepared high-flow, ultra-early-strength concrete is transported to the transport equipment or storage container. The ambient temperature in the storage container is controlled between 15℃ and 25℃, and the humidity is maintained between 50% and 70%.

9. A method for producing high-flowability, high-early-strength concrete according to any one of claims 1-8, characterized in that: Under an environment of -15℃, preheat the powder materials and coarse and fine aggregates in a heated greenhouse, maintaining the greenhouse temperature between 10℃ and 15℃ for 12-15 hours. Add the preheated powder materials to a mixer and mix for 1-2 minutes until initially homogeneous. Add water at 40℃-50℃ and continue mixing for 2-3 minutes. Then add the nano-silica composite slurry and mix at 120-150 rpm for 3-5 minutes. After mixing, add the preheated natural sand and natural pebbles. First, add one-third of the natural sand and mix for 1-2 minutes, then add half of the natural pebbles and mix for 2-3 minutes. Finally, add the remaining sand and pebbles and increase the mixing speed to 180-220 rpm for 5-8 minutes. Then add the mixed additives and antifreeze (7%-9% of the total concrete mass), increase the mixing speed to 250r / min-300r / min, and mix for 10-15 minutes. Before pouring the concrete, use a hot air gun to heat the surface of the formwork to above 5°C, remove ice, snow, and dirt from the formwork and reinforcing steel surfaces, and wrap the outside of the formwork with insulation cotton blankets with a thickness of not less than 30mm. Use a layered pouring method, with each layer controlled at a thickness of 250mm-350mm and a time interval of 30-35 minutes between each layer. After the concrete is poured, cover the surface with a layer of plastic film, and then cover the plastic film with two layers of insulation cotton. When the concrete surface temperature is below 5°C, use an electric heater to heat the concrete surface. At a temperature of -15°C, the initial setting time is 2-3 hours and the final setting time is 4-6 hours.

Images