Novel UHPC material for bridge expansion joints and preparation method thereof

Abstract

The invention relates to a novel UHPC material for bridge expansion joints and a preparation method thereof.The preparation method comprises the steps that S2, carbon nanofibers and residual silica fume are stirred for 2 minutes in a premixing bin at a high speed, the silica fume wraps the carbon nanofibers, electrostatic agglomeration is prevented, mixed powder is sequentially fed into a vortex chamber and an ultrasonic atomization cavity through compressed airflow after premixing, and the mixed powder is cooled to the room temperature; the fibers flow through the piezoelectric ceramic array and vibrate at high frequency, so that fiber bundles are dissociated into single fiber bundles; s3, the atomized fiber aerosol passes through a porous diffuser and is sprayed into a planetary stirrer through a second feeding port at a certain angle to participate in mixing in the step S1; and S4, the steel fibers are fed into a vibration screening box, adhered steel fiber clusters are separated through high-frequency vibration, and the separated steel fibers enter a planetary stirrer through a third feeding opening to participate in mixing in the step S1. The steel fibers and the carbon nanofibers which are uniformly distributed in the UHPC material form a dual anti-cracking mechanism, so that the impact toughness of the UHPC material is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of concrete materials, and particularly relates to a novel UHPC material for bridge expansion joints and a preparation method thereof. BACKGROUND

[0002] The bridge expansion joint is a key component in the bridge structure, and is used to adapt to the displacement caused by temperature changes, vehicle loads and concrete shrinkage and creep. The traditional expansion joint materials, such as ordinary concrete, modified asphalt or rubber, often have problems such as cracking, peeling or leakage due to insufficient strength, poor durability or poor fatigue performance, which seriously affects the service life of the bridge and driving safety. Ultra-high performance concrete (UHPC) gradually becomes an ideal choice for expansion joint materials due to its excellent mechanical properties, high durability and low permeability. However, the existing UHPC materials still have the following technical bottlenecks when applied to expansion joints.

[0003] In the new UHPC material mixed with part of nanocarbon fibers, the nanocarbon fibers have the problem of poor dispersibility. The nanocarbon fibers have high specific surface area and surface energy, and are easily agglomerated into bundles due to electrostatic action. The existing technology mostly uses mechanical stirring or surfactant dispersion, but it is difficult to achieve uniform distribution of single fibers. The agglomerated nanocarbon fibers not only reduce the reinforcing efficiency, but also form stress concentration points in the matrix, leading to the initiation of microcracks. In the traditional process, the nanocarbon fibers are directly added to the dry materials or slurry. The surface of the nanocarbon fibers has weak chemical bonding with the cement hydration products. The active components such as silica fume are easily settled by gravity and cannot effectively wrap the fibers. There are pores in the interface transition zone, which affect the load transfer efficiency.

[0004] In addition, the steel fibers are agglomerated or unevenly distributed, which will form a low bonding strength interface between the steel fibers and the matrix, reducing the compressive strength of the UHPC. The steel fibers cannot play a reinforcing role in the tensile strength and toughness after cracking. Since the steel fibers are generally packed in boxes or bags, the volume is relatively dense. Before being put into the mixer, the existing technology often uses mechanical or manual methods to disperse them, which is not only time-consuming and laborious, but also unevenly distributed. SUMMARY

[0005] In view of the above problems, the present application provides a novel UHPC material for bridge expansion joints and a preparation method thereof. The steel fibers and nanocarbon fibers uniformly distributed in the UHPC material form a double anti-cracking mechanism, and the multi-scale fibers cooperate to improve the impact toughness.

[0006] The specific technical solutions are as follows: A preparation method of a novel UHPC material for bridge expansion joints, comprising the following steps: S1, cement, nano-silica, metakaolin, quartz sand and part of silica fume are added from the first feeding port into the planetary mixer, and mixed at low speed for 5-8 minutes until uniform; S2, nano-carbon fiber and the remaining silica fume are stirred at high speed in the premixing bin for 2 minutes to wrap the nano-carbon fiber with silica fume and prevent static agglomeration, and after premixing, the mixed powder is sequentially sent into the vortex chamber and ultrasonic atomization cavity by compressed airflow, and the fiber flows through the piezoelectric ceramic array high-frequency vibration to dissociate the fiber bundle into single root state; S3, the atomized fiber aerosol passes through the multi-hole diffuser and is sprayed into the planetary mixer at a certain angle through the second feeding port to participate in the mixing of step S1; S4, the steel fiber is sent into the vibrating screening box to separate the adhered steel fiber bundle by high-frequency vibration, and the separated steel fiber enters the planetary mixer through the third feeding port to participate in the mixing of step S1; S5, the water reducing agent and the low-temperature early strength activator are dissolved in water and added into the dry material premixed in step S1 through the liquid inlet, and stirred at low speed for 5 minutes, and then the stirring speed is adjusted to medium speed for continuous stirring for 3 minutes until the slurry presents a self-leveling state.

[0007] Further, in step S2, the mass ratio of the nano-carbon fiber to the remaining silica fume is 1:10-12.

[0008] Further, in step S2, the diameter of the nano-carbon fiber is less than or equal to 50 nm.

[0009] Further, in step S2, the pressure of the compressed airflow is 0.4-0.6 MPa, and the compressed airflow enters tangentially to bring the mixed powder into the vortex chamber to form a cyclone separation effect.

[0010] Further, in step S2, the frequency of the piezoelectric ceramic array is 20 kHz, which can disperse the fiber bundle composed of multiple nano-carbon fibers, and through cavitation effect, the nano-carbon fiber is broken along the length direction, so that the length of the nano-carbon fiber is less than or equal to 100 nm, which is used to fill the micro-pores of UHPC.

[0011] Further, in step S3, the pore diameter of the multi-hole diffuser is 150-200 microns, and the hole axis is arranged at a cone angle of 30-45 degrees.

[0012] Further, in step S4, the steel fiber is copper-plated fine fiber, and the length of the steel fiber is less than or equal to 12 mm, and the diameter of the steel fiber is less than or equal to 0.2 mm.

[0013] Further, in step S4, the internal screen mesh of the vibrating screening box has a pore diameter of 5-12 mm.

[0014] Further, the vibrating screening box adopts an eccentric wheel motor to realize longitudinal vibration, the vibration frequency of the eccentric wheel motor is 50 Hz, and the amplitude is 0.1-1 mm.

[0015] A novel UHPC material for bridge expansion joints, wherein, in terms of mass parts, cement 100 parts; nano silicon dioxide 4-6 parts; metakaolin 7-10 parts; quartz sand 120-150 parts; silica fume 20-30 parts; nano carbon fiber 1-2 parts; steel fiber 16-25 parts; water reducing agent 1.5-2.5 parts; low-temperature early strength activator 1-1.5 parts; water-binder ratio 0.16-0.20.

[0016] Compared with the prior art, the present application has the following beneficial effects: (1) The novel UHPC material for bridge expansion joints and the preparation method thereof can uniformly wrap silica fume around nano carbon fiber through high-speed stirring of the premixing bin, inhibit electrostatic agglomeration, realize three-dimensional random distribution of the nano carbon fiber in the matrix through subsequent ultrasonic atomization and piezoelectric ceramic vibration treatment, and realize the spraying of the nano carbon fiber through the porous diffuser at a specific angle, so that the nano carbon fiber is prevented from depositing due to gravity and the dispersion uniformity is improved.

[0017] (2) The novel UHPC material for bridge expansion joints and the preparation method thereof can increase the surface roughness and active sites of the nano carbon fiber wrapped by the silica fume, promote the chemical bonding of the nano carbon fiber with the cement hydration products, and improve the interfacial bonding strength.

[0018] (3) The novel UHPC material for bridge expansion joints and the preparation method thereof can fill micropores and prevent cracking through the nano carbon fiber, can bear macroscopic load through the steel fiber, and can eliminate steel fiber lumps through the pretreatment of the vibrating screening box, so that the bending toughness of the UHPC is improved.

[0019] (4) The novel UHPC material for bridge expansion joints and the preparation method thereof can realize the improvement of the short-time compressive strength in a low-temperature environment through the compounding of the low-temperature early strength activator and the water reducing agent, and has no risk of chloride ion corrosion.

[0020] (5) The novel UHPC material for bridge expansion joints and the preparation method thereof can be compatible with existing stirring equipment through the design of the vortex chamber, the ultrasonic atomization cavity and the vibrating screening box, and the compressed air flow transportation can reduce the risk of fiber agglomeration, so that it is suitable for large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a flow chart of the method of the present application.

[0022] Figure 2 is a structural schematic diagram of the present application.

[0023] Figure 3 is a schematic diagram of the nanometer carbon fiber atomization feeding system of the present application.

[0024] Figure 4 is a schematic diagram of the steel fiber scattering feeding system structure of the present application.

[0025] Figure 5 is a schematic diagram of the screening plate structure of the present application.

[0026] Figure 6 is a schematic diagram of the electromagnetic dispersion box structure of the present application.

[0027] Figure 7 is a schematic diagram of the middle layer electromagnet array distribution of the present application.

[0028] In the figure: 1, mixer main body; 2, first feeding port; 3, second feeding port; 4, third feeding port; 5, liquid inlet; 6, nanometer carbon fiber atomization feeding system; 61, premixing bin; 611, discharge pipe; 62, vortex chamber; 63, ultrasonic atomization cavity; 64, porous diffuser; 65, nanometer carbon fiber bin; 66, silica ash bin; 67, compressed air pipeline; 68, piezoelectric ceramic array; 69, first corrugated sealing sleeve; 7, steel fiber scattering feeding system; 71, steel fiber bin; 721, vibrating screening box; 722, screening plate; 723, first screen mesh; 724, second screen mesh; 725, eccentric wheel motor; 73, electromagnetic dispersion module; 730, electromagnetic dispersion box; 731, first guide pipe; 732, second guide pipe; 733, second corrugated sealing sleeve; 734, top layer electromagnet array; 735, middle layer electromagnet array; 736, bottom layer electromagnet array; 74, rectangular air pipe. DETAILED DESCRIPTION

[0029] The application will be described in further detail below with reference to the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related application, and not to limit the application. In addition, it should be noted that only the parts related to the application are shown in the drawings for ease of description.

[0030] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the drawings and embodiments.

[0031] Embodiment 1 The present application provides a preparation method of a new UHPC material for bridge expansion joints, referring to Figure 1 , comprising the following steps: S1, cement, nanometer silicon dioxide, metakaolin, quartz sand and part of silica ash are added from the first feeding port 2 into the planetary mixer, and mixed at low speed (60 r / min) for 5-8 minutes until uniform; S2, the nanometer carbon fiber and the remaining silica fume are stirred at high speed (200 r / min) in the premixing bin 61 for 2 minutes, so that the silica fume wraps the nanometer carbon fiber, preventing electrostatic agglomeration, and after premixing, the mixed powder is sent into the vortex chamber 62 and the ultrasonic atomization cavity 63 in sequence through compressed airflow, and the fiber flows through the piezoelectric ceramic array 68 for high-frequency vibration to make the fiber bundle disintegrate into a single state; S3, the atomized fiber aerosol passes through the porous diffuser 64 and is sprayed into the planetary mixer through the second feeding port 3 at a certain angle to participate in the mixing of step S1; S4, the steel fiber is sent into the vibrating screening box 721 to separate the adhered steel fiber bundles through high-frequency vibration, and the separated steel fiber enters the planetary mixer through the third feeding port 4 to participate in the mixing of step S1; S5, the water reducing agent and the low-temperature early strength activator are dissolved in water and added to the dry material premixed in step S1 through the liquid inlet 5, and low-speed stirring is performed for 5 minutes, and then the stirring speed is adjusted to medium speed (150 r / min) for continuous stirring for 3 minutes, until the slurry presents a self-leveling state (the spreadability is greater than or equal to 650 mm).

[0032] The silica fume, nanometer silicon dioxide and metakaolin synergistically optimize the pore structure and improve the compactness and durability.

[0033] The steel fiber (macroscopic) and the nanometer carbon fiber (microscopic) are combined to form a multi-level reinforcing network, which significantly improves the crack resistance and toughness of the material.

[0034] Further, as a specific embodiment, in step S2, the mass ratio of the nanometer carbon fiber to the remaining silica fume is 1:10-12.

[0035] Further, as a specific embodiment, in step S2, the diameter of the nanometer carbon fiber is less than or equal to 50 nm.

[0036] Further, as a specific embodiment, in step S2, the pressure of the compressed airflow is 0.4-0.6 MPa, and the compressed airflow enters tangentially to bring the mixed powder into the vortex chamber 62 to form a cyclone separation effect.

[0037] Further, as a specific embodiment, in step S2, the frequency of the piezoelectric ceramic array 68 is 20 kHz, which can disperse the fiber bundle composed of multiple nanometer carbon fibers, and through cavitation effect, the nanometer carbon fiber is broken along the length direction, so that the length of the nanometer carbon fiber is less than or equal to 100 nm, which is used to fill the micro-pores of the UHPC. The silica fume wrapping the nanometer carbon fiber can increase the surface roughness and active sites of the nanometer carbon fiber, promote the chemical bonding with the cement hydration product, and improve the interfacial bonding strength.

[0038] Further, as a specific embodiment, in step S3, the pore diameter of the porous diffuser 64 is 150-200 microns, and the pore axis is arranged at a 30-45 degree cone angle.

[0039] Further, as a specific embodiment, in step S4, the steel fiber is a copper-plated fine fiber, with a length of less than or equal to 12 mm, and a diameter of less than or equal to 0.2 mm.

[0040] Further, as a specific embodiment, in step S4, the internal screen of the vibrating screening bin 721 has a screen diameter of 5-12 mm.

[0041] Further, as a specific embodiment, the vibrating screening bin 721 is implemented to vibrate longitudinally using an eccentric motor 725, with a vibration frequency of 50 Hz and an amplitude of 0.1-1 mm.

[0042] Further, as a specific embodiment, in step S5, a special activator is introduced, such as a sulphoaluminate cement and lithium salt composite, to achieve a 1d strength of ≥25 MPa in a low temperature environment (5-10℃) and shorten the curing period.

[0043] A new UHPC material for bridge expansion joints, wherein, in terms of mass parts, cement 100 parts; nano-silicon dioxide 4-6 parts; metakaolin 7-10 parts; quartz sand 120-150 parts; silica fume 20-30 parts; nano-carbon fiber 1-2 parts; steel fiber 16-25 parts; water reducing agent 1.5-2.5 parts; low-temperature early strength activator 1-1.5 parts; water-binder ratio 0.16-0.20. The cement used is 52.5 cement, which provides the main hydration products and ensures early strength. The diameter of nano-silicon dioxide is 20 nm, which has a nano-level filling effect and significantly improves the strength of the interface transition zone. The metakaolin is high-activity metakaolin, which can provide an aluminum phase and optimize the C-S-H gel structure. The particle size of the quartz sand is 0.1-0.3 mm, which has a fine gradation and reduces defects. The silica fume can fill pores, promote secondary hydration, and improve density. The nano-carbon fiber can be microscopically dispersed and inhibit the propagation of micro-cracks. The steel fiber can be macroscopically enhanced, improving tensile and flexural strength. The water reducing agent is a polycarboxylic acid water reducing agent, which reduces the water-binder ratio to 0.16 and ensures fluidity. The low-temperature early strength activator is sulphoaluminate + lithium salt, which accelerates hydration in a low-temperature environment. Water is used to control the water-binder ratio and ensure workability.

[0044] Example 2 Based on Example 1, step 4 further includes the following steps: S41, the vibrated and screened steel fiber falls into the electromagnetic dispersion bin 730, which utilizes the magnetic permeability of the steel fiber to uniformly disperse it in a changing magnetic field; S42, the steel fiber first falls into the top electromagnetic array 734 which generates magnetic field switching along the left-right direction, when energized, the steel fiber is affected by the horizontal magnetic field and its length direction tends to arrange along the left-right horizontal direction, when de-energized, the steel fiber falls down to the middle electromagnetic array 735 under the action of its own gravity; S43, the middle electromagnetic array 735 generates magnetic field switching along the front-back direction, when energized, the steel fiber is affected by the horizontal magnetic field and its length direction tends to arrange along the front-back horizontal direction, when de-energized, the steel fiber falls down to the bottom electromagnetic array 736 under the action of its own gravity; S43, the bottom electromagnetic array 736 generates magnetic field switching along the left-right direction, when energized, the steel fiber is affected by the horizontal magnetic field and its length direction tends to arrange along the left-right horizontal direction, when de-energized, the steel fiber falls down to the third feeding port 4 under the action of its own gravity.

[0045] The steel fiber passes through the vibrating screen and the electromagnetic dispersion module 73 to ensure uniform distribution of the single steel fiber.

[0046] Example 3 On the basis of example 2, with reference to Figure 2 , the planetary mixer comprises a mixer body 1, the mixer body 1 is provided with a first feeding port 2, a second feeding port 3 and a third feeding port 4 and a liquid inlet 5, the second feeding port 3 is provided with a nano carbon fiber atomization feeding system 6, and the third feeding port 4 is provided with a steel fiber dispersion feeding system 7.

[0047] Further, as a specific embodiment, with reference to Figure 1 , Figure 2 and Figure 3 , the nano carbon fiber atomization feeding system 6 comprises a premixing bin 61, a vortex chamber 62, an ultrasonic atomization cavity 63 and a porous diffuser 64; the upper end of the premixing bin 61 is provided with a nano carbon fiber bin 65 and a silica ash bin 66 capable of quantitative feeding, a discharge pipe 611 of the premixing bin 61 is in communication with a feeding port of the vortex chamber 62, and the discharge pipe 611 is provided with a discharge valve and a compressed air pipeline 67 for introducing airflow. Inert gas, preferably nitrogen, is introduced into the premixing bin 61 during work, and when stirring, the silica ash with a particle size of 0.1 μm is adsorbed on the surface of the nano carbon fiber by Van der Waals force to form an electrostatic shielding layer. The vortex chamber 62 is located below the premixing bin 61, the compressed air pipeline 67 is tangentially connected at 45 degrees, 0.5 MPa compressed air carrying mixed powder enters the vortex chamber 62 at a speed of 15 m / s, and the nano carbon fiber group collides with the wall to be dissociated by using the cyclone separation principle.

[0048] The upper end of the second feeding port 3 is sleeved with a first corrugated sealing sleeve 69, the upper end of the first corrugated sealing sleeve 69 is connected with the lower end surface of the vortex chamber 62, and the ultrasonic atomization cavity 63 is located inside the first corrugated sealing sleeve 69.

[0049] The ultrasonic atomization cavity 63 is located below the vortex chamber 62, the piezoelectric ceramic array 68 is arranged in a ring shape on the ultrasonic atomization cavity 63, the multi-hole diffuser 64 is arranged at an outlet position of the ultrasonic atomization cavity 63 and is located at the position of the second feeding port 3, and the atomized flow is expanded into a 30° conical spray. The piezoelectric ceramic array 68 selects 6 groups of PZT-8 piezoelectric ceramics, and the phase difference is 120° and the vibration is alternated.

[0050] Further, as a specific embodiment, referring to Figure 1 、 Figure 2 and Figure 4 , the steel fiber scattering and feeding system 7 comprises a steel fiber bin 71, a vibrating screening module, an electromagnetic dispersion module 73 and a rectangular air pipe 74; the vibrating screening module comprises a vibrating screening box 721, the steel fiber bin 71 is arranged above the vibrating screening box 721, a screening plate 722 is horizontally arranged inside the vibrating screening box 721, and an eccentric wheel motor 725 is arranged on the vibrating screening box 721. The frequency of the eccentric wheel motor 725 is 50 Hz, the amplitude is adjustable by 0.1-1 mm, the larger steel fiber groups adhered are separated through high-frequency vibration of the eccentric wheel motor 725, and the up-and-down vibration of the eccentric wheel motor 725 prevents the steel fiber from blocking the screening plate 722.

[0051] Further, referring to Figure 4 and Figure 5 , the screening plate 722 is symmetrically provided with a first screen 723 and a second screen 724.

[0052] Further, referring to Figure 4 、 Figure 6 and Figure 7 , the electromagnetic dispersion module 73 comprises an electromagnetic dispersion box 730 arranged below the vibrating screening box 721, the electromagnetic dispersion box 730 is symmetrically provided with a first guide pipe 731 and a second guide pipe 732 for the steel fibers falling from the first screen 723 and the second screen 724 to pass through respectively, a top electromagnetic iron array 734, a middle electromagnetic iron array 735 and a bottom electromagnetic iron array 736 are sequentially arranged on the first guide pipe 731 and the second guide pipe 732 from top to bottom.

[0053] The upper end of the first guide pipe 731 and the second guide pipe 732 is respectively sleeved with a second corrugated sealing sleeve 733, the upper end of the second corrugated sealing sleeve 733 is connected with the lower end surface of the screening plate 722, and the first screen 723 and the second screen 724 are respectively located at the upper end of the two second corrugated sealing sleeves 733. The steel fibers falling from the first screen 723 and the second screen 724 can fall into the first guide pipe 731 and the second guide pipe 732 through the second corrugated sealing sleeve 733. The arrangement of the second corrugated sealing sleeve 733 can reduce the vibration of the vibrating screening box 721 and conduct it to the first guide pipe 731 and the second guide pipe 732.

[0054] The top layer electromagnet array 734 includes a first U-shaped electromagnet, a second U-shaped electromagnet and a third U-shaped electromagnet, the first U-shaped electromagnet is arranged on the left side of the first guide pipe 731 with the opening downward, the second U-shaped electromagnet is arranged between the first guide pipe 731 and the second guide pipe 732 with the opening downward, and the third U-shaped electromagnet is arranged on the right side of the second guide pipe 732 with the opening downward. The first U-shaped electromagnet and the second U-shaped electromagnet are opposite poles, and the third U-shaped electromagnet and the second U-shaped electromagnet are opposite poles. The magnetic field intensity of the first U-shaped electromagnet, the second U-shaped electromagnet and the third U-shaped electromagnet is 0.1-0.3T, the steel fiber is magnetically conductive, the energized first U-shaped electromagnet, the second U-shaped electromagnet and the third U-shaped electromagnet can generate a magnetic field, which can attract the falling steel fiber, and the magnetic field direction is along the left-right horizontal direction, the steel fiber will be straightened (like using a magnet to straighten a curved needle), the sticky group will be forcibly separated, and the straightness and dispersion of the interlaced steel fiber are realized. Continuously turning on and off the magnetic field can make the steel fiber be attracted and then released, continue to be attracted and then released, so as to realize the first electromagnetic dispersion work of the continuous steel fiber.

[0055] The middle layer electromagnet array 735 includes a fourth U-shaped electromagnet, a fifth U-shaped electromagnet, a sixth U-shaped electromagnet and a seventh U-shaped electromagnet, the fourth U-shaped electromagnet and the fifth U-shaped electromagnet are arranged on the front and back sides of the first guide pipe 731 respectively with the opening downward, the sixth U-shaped electromagnet and the seventh U-shaped electromagnet are arranged on the front and back sides of the second guide pipe 732 respectively with the opening downward, the fourth U-shaped electromagnet and the fifth U-shaped electromagnet are opposite poles, and the sixth U-shaped electromagnet and the seventh U-shaped electromagnet are opposite poles. The working principle of the middle layer electromagnet array 735 is similar to that of the top layer electromagnet array 734, and the steel fibers have been partially separated under the action of the top layer electromagnet array 734. The fourth U-shaped electromagnet, the fifth U-shaped electromagnet, the sixth U-shaped electromagnet and the seventh U-shaped electromagnet are energized to generate a magnetic field that can attract the falling steel fibers, and the direction of the magnetic field lines is along the front and back horizontal direction, so that the steel fibers are redirected and straightened, further forcibly separate the small fiber groups, and realize further dispersion of the steel fibers. Continuously switching the magnetic field can attract the steel fibers, then release them, continue to attract them and then release them, so as to realize the second electromagnetic dispersion of the continuous steel fibers.

[0056] The bottom layer electromagnet array 736 includes an eighth U-shaped electromagnet, a ninth U-shaped electromagnet and a tenth U-shaped electromagnet, the eighth U-shaped electromagnet is arranged on the left side of the first guide pipe 731 with the opening downward, the ninth U-shaped electromagnet is arranged between the first guide pipe 731 and the second guide pipe 732 with the opening downward, and the tenth U-shaped electromagnet is arranged on the right side of the second guide pipe 732 with the opening downward. The eighth U-shaped electromagnet and the ninth U-shaped electromagnet are opposite poles, and the tenth U-shaped electromagnet and the ninth U-shaped electromagnet are opposite poles. The working principle of the bottom layer electromagnet array 736 is similar to that of the top layer electromagnet array 734, and the remaining small fiber groups are continuously dispersed by electromagnetic force, and finally the steel fibers are dispersed into single fibers and fall into the third feeding port 4.

[0057] The rectangular air pipes 74 are provided in two, and the two rectangular air pipes 74 are arranged at the outer lower ends of the first guide pipe 731 and the second guide pipe 732 respectively, four high-pressure gas flow nozzles are arranged around the four edges of each rectangular air pipe 74, and the dispersed steel fibers are uniformly blown into the third feeding port 4 through the high-pressure gas flow nozzles. The gas pressure of the high-pressure gas flow nozzle is 0.2-0.5MPa, the gas flow direction forms an angle of 30° with the falling direction of the steel fibers, and a vortex is formed to assist the dispersion.

[0058] The technical features of the above-mentioned embodiments can be combined arbitrarily, and in order to make the description simple, all possible combinations of the technical features in the above-mentioned embodiments are not described, however, as long as the combination of the technical features does not exist contradictory, it should be considered as the scope of the present application.

[0059] The above described embodiments only express the implementation of the present application, the description is more specific and detailed, but it cannot be understood as the limitation of the patent scope of the present application. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A method for preparing a novel UHPC material for bridge expansion joints, characterized in that, Includes the following steps: S1. Add cement, nano-silica, metakaolin, quartz sand and some silica fume into the planetary mixer through the first feed inlet and mix at low speed for 5-8 minutes until uniform. S2, the nanofibers and the remaining silica fume are stirred at high speed in the premix chamber for 2 minutes, so that the silica fume encapsulates the nanofibers and prevents static agglomeration. After premixing, the mixed powder is sent into the vortex chamber and the ultrasonic atomization chamber in sequence by compressed air. The fibers flow through the piezoelectric ceramic array and the high-frequency vibration causes the fiber bundle to dissociate into a single state. S3, the atomized fiber aerosol is sprayed into the planetary mixer at a certain angle through the second feed port via a porous diffuser to participate in the mixing in step S1; S4, the steel fibers are fed into the vibrating screen box, and the sticky steel fiber clumps are separated by high frequency vibration. The separated steel fibers enter the planetary mixer through the third feed port and participate in the mixing in step S1. S5. Dissolve the water-reducing agent and the low-temperature early strength activator in water and add them to the premixed dry material in step S1 through the liquid inlet. Stir at low speed for 5 minutes, then adjust the stirring speed to medium speed and continue stirring for 3 minutes until the slurry reaches a self-leveling state.

2. The preparation method of a novel UHPC material for bridge expansion joints according to claim 1, characterized in that, In step S2, the mass ratio of the carbon nanofibers to the remaining silica fume is 1:10-12.

3. The method for preparing a novel UHPC material for bridge expansion joints according to claim 1, characterized in that, In step S2, the diameter of the carbon nanofiber is less than or equal to 50 nm.

4. The preparation method of a novel UHPC material for bridge expansion joints according to claim 1, characterized in that, In step S2, the pressure of the compressed airflow is 0.4-0.6 MPa. The compressed airflow enters tangentially, carrying the mixed powder into the vortex chamber to form a cyclone separation effect.

5. The method for preparing a novel UHPC material for bridge expansion joints according to claim 1, characterized in that, In step S2, the frequency of the piezoelectric ceramic array is 20kHz, which can break apart the fiber bundle composed of multiple carbon nanofibers and cause the carbon nanofibers to break along the length direction through cavitation effect, so that the length of the carbon nanofibers is less than or equal to 100nm, which is used to fill the micropores of UHPC.

6. The method for preparing a novel UHPC material for bridge expansion joints according to claim 1, characterized in that, In step S3, the pore diameter of the porous diffuser is 150-200 micrometers, and the pore axis is set with a cone angle of 30-45 degrees.

7. The method for preparing a novel UHPC material for bridge expansion joints according to claim 1, characterized in that, In step S4, the steel fiber is a copper-plated microfiber with a length of less than or equal to 12 mm and a diameter of less than or equal to 0.2 mm.

8. The method for preparing a novel UHPC material for bridge expansion joints according to claim 1, characterized in that, In step S4, the mesh size of the screen inside the vibrating screening box is 5-12mm.

9. The method for preparing a novel UHPC material for bridge expansion joints according to claim 8, characterized in that, The vibrating screen box uses an eccentric wheel motor to achieve longitudinal vibration. The vibration frequency of the eccentric wheel motor is 50Hz and the amplitude is 0.1-1mm.

10. A novel UHPC material for bridge expansion joints, characterized in that, Made by the preparation method according to any one of claims 1 to 9; wherein, by mass parts, there are 100 parts of cement; 4-6 parts of nano-silica; 7-10 parts of metakaolin; 120-150 parts of quartz sand; and 20-30 parts of silica fume; 1-2 parts of carbon nanofiber; 16-25 parts steel fiber; 1.5-2.5 parts water-reducing agent; 1-1.5 parts of low-temperature early strength activator; Water-to-binder ratio: 0.16-0.20.

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