UHPC material for bridge expansion joint and preparation method thereof

Abstract

The application relates to a UHPC material for a bridge expansion joint and a preparation method thereof, and comprises the following steps: S2, nanometer carbon fibers are stirred with residual silica fume in a premixing bin at high speed for 2 minutes, so that the silica fume wraps the nanometer carbon fibers and prevents electrostatic agglomeration; after premixing, the mixed powder is sequentially sent into a vortex chamber and an ultrasonic atomization cavity through compressed airflow, and the fiber flows through a piezoelectric ceramic array high-frequency vibration to make the fiber bundle dissociate into a single state; S3, the atomized fiber aerosol passes through a porous diffuser and is sprayed into a planetary mixer through a second feeding port at a certain angle to participate in the mixing in step S1; and S4, steel fibers are sent into a vibrating screening box, and the adhered steel fiber groups are separated through high-frequency vibration, and the separated steel fibers enter the planetary mixer through a third feeding port to participate in the mixing in step S1. The steel fibers and the nanometer carbon fibers uniformly distributed in the UHPC material form a double anti-cracking mechanism, and 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 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. The 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 UHPC material partially mixed with nanocarbon fibers, the nanocarbon fibers have poor dispersibility. The nanocarbon fibers have high specific surface area and surface energy, and are extremely easy to be 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.

[0004] 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 unable to effectively wrap the fibers due to gravity settlement. There are pores in the interface transition zone, which affects the load transfer efficiency.

[0005] 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 on the tensile strength and toughness after cracking. Since the steel fibers are generally boxed or bagged, the volume is relatively dense. Before being put into the mixer, the existing technology often uses mechanical or manual methods to disperse, which is not only time-consuming and laborious, but also has uneven distribution. SUMMARY

[0006] In view of the above problems, the present application provides a 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.

[0007] The specific technical solutions are as follows:

[0008] A preparation method of a UHPC material for bridge expansion joints, comprising the following steps:

[0009] 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;

[0010] 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. After premixing, the mixed powder is sent into the vortex chamber and ultrasonic atomization cavity in sequence by compressed air flow. The fiber flows through the piezoelectric ceramic array high-frequency vibration to dissociate the fiber bundle into single state;

[0011] S3, the atomized fiber aerosol passes through the porous 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;

[0012] S4, the steel fiber is sent into the vibrating screening box to separate the adhered steel fiber bundle by high-frequency vibration. The separated steel fiber enters the planetary mixer through the third feeding port to participate in the mixing of step S1;

[0013] S5, the water reducing agent and low temperature early strength activator are dissolved in water and added into the dry material premixed in step S1 through the liquid inlet. The mixture is 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.

[0014] Further, in step S2, the mass ratio of the nano-carbon fiber to the remaining silica fume is 1:10-12.

[0015] Further, in step S2, the diameter of the nano-carbon fiber is less than or equal to 50 nm.

[0016] Further, in step S2, the pressure of the compressed air flow is 0.4-0.6 MPa, and the compressed air flow enters tangentially to bring the mixed powder into the vortex chamber to form a cyclone separation effect.

[0017] 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 the nano-carbon fiber is broken along the length direction by cavitation effect, 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.

[0018] Further, in step S3, the pore diameter of the porous diffuser is 150-200 microns, and the pore axis is arranged at a cone angle of 30-45 degrees.

[0019] Further, in step S4, the steel fiber is copper-plated fine fiber with a length less than or equal to 12 mm, and the diameter of the steel fiber is less than or equal to 0.2 mm.

[0020] Further, in step S4, the internal screen mesh of the vibrating screening box has a pore diameter of 5-12 mm.

[0021] 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.

[0022] A 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.

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] (1) The 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 being deposited due to gravity and the dispersion uniformity is improved.

[0025] (2) The 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 silica fume, promote the chemical bonding of the nano carbon fiber with cement hydration products, and improve the interfacial bonding strength.

[0026] (3) The 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.

[0027] (4) The 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.

[0028] (5) The UHPC material for bridge expansion joints and the preparation method thereof can be compatible with existing mixing 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

[0029] Figure 1 is a flow chart of the method of the present application.

[0030] Figure 2 is a structural schematic diagram of the present application.

[0031] Figure 3 is the schematic diagram of the nanometer carbon fiber atomization feeding system of the application.

[0032] Figure 4 is the schematic diagram of the steel fiber scattering feeding system structure of the application.

[0033] Figure 5 is the schematic diagram of the screening plate structure of the application.

[0034] Figure 6 is the schematic diagram of the electromagnetic dispersion box structure of the application.

[0035] Figure 7 is the schematic diagram of the middle layer electromagnet array distribution of the application.

[0036] 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

[0037] The application will be further described below in conjunction with 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.

[0038] 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 in conjunction with the embodiments.

[0039] Embodiment 1

[0040] The application provides a preparation method of UHPC material for bridge expansion joint, referring to Figure 1 , comprising the following steps:

[0041] S1, cement, nano-silica, metakaolin, quartz sand and part of silica fume are added from the first feeding port 2 into the planetary mixer, and mixed at a low speed (60 r / min) for 5-8 minutes until uniform;

[0042] S2, the nano-carbon fiber and the remaining silica fume are stirred at a high speed (200 r / min) in the premixing bin 61 for 2 minutes, so that the silica fume wraps the nano-carbon fiber, prevents static agglomeration, and after premixing, the mixed powder is sequentially sent into the vortex chamber 62 and the ultrasonic atomization cavity 63 through a compressed gas flow, and the fiber flows through the piezoelectric ceramic array 68 for high-frequency vibration to dissociate the fiber bundle into a single state;

[0043] S3, the atomized fiber aerosol passes through the porous diffuser 64, is sprayed into the planetary mixer at a certain angle through the second feeding port 3, and participates in the mixing of step S1;

[0044] S4, the steel fiber is sent into the vibrating screening box 721, and the adhered steel fiber group is separated by high-frequency vibration, and the separated steel fiber enters the planetary mixer through the third feeding port 4 and participates in the mixing of step S1;

[0045] S5, the water reducing agent and the low-temperature early strength activator are dissolved in water, and are added into the dry material premixed in step S1 through the liquid inlet 5, and are stirred at a low speed for 5 minutes, and then the stirring speed is adjusted to a medium speed (150 r / min) and continues to stir for 3 minutes, until the slurry presents a self-leveling state (the spreadability is greater than or equal to 650 mm).

[0046] The silica fume, nano-silica and metakaolin synergistically optimize the pore structure and improve the compactness and durability.

[0047] The steel fiber (macroscopic) and the nano-carbon fiber (microscopic) are combined to form a multi-level reinforced network, which significantly improves the crack resistance and toughness of the material.

[0048] Further, as a specific embodiment, in step S2, the mass ratio of the nano-carbon fiber to the remaining silica fume is 1:10-12.

[0049] Further, as a specific embodiment, in step S2, the diameter of the nano-carbon fiber is less than or equal to 50 nm.

[0050] Further, as a specific embodiment, in step S2, the pressure of the compressed gas flow is 0.4-0.6 MPa, and the compressed gas flow enters tangentially to bring the mixed powder into the vortex chamber 62 to form a cyclone separation effect.

[0051] Further, as a specific embodiment, in step S2, the frequency of the piezoelectric ceramic array 68 is 20 kHz, the fiber bundle composed of a plurality of nanocarbon fibers is disintegrated, and the nanocarbon fibers are broken in the length direction by the cavitation effect, so that the length of the nanocarbon fibers is less than or equal to 100 nm, for filling the micro-pores of the UHPC. The silica fume wrapped nanocarbon fibers can increase the surface roughness and active sites of the nanocarbon fibers, promote the chemical bonding with the cement hydration products, and improve the interfacial bonding strength.

[0052] Further, as a specific embodiment, in step S3, the pore size of the porous diffuser 64 is 150-200 microns, and the pore axis is arranged at a cone angle of 30-45 degrees.

[0053] Further, as a specific embodiment, in step S4, the steel fiber is a copper-plated micro-fiber, the length of which is less than or equal to 12 mm, and the diameter of the steel fiber is less than or equal to 0.2 mm.

[0054] Further, as a specific embodiment, in step S4, the internal screen mesh size of the vibrating screening bin 721 is 5-12 mm.

[0055] Further, as a specific embodiment, the vibrating screening bin 721 is longitudinally vibrated by using an eccentric wheel motor 725, the vibration frequency of the eccentric wheel motor 725 is 50 Hz, and the amplitude is 0.1-1 mm.

[0056] Further, as a specific embodiment, in step S5, a special activator is introduced, such as a composite of sulphoaluminate cement and lithium salt, to achieve 1d strength ≥25 MPa in a low temperature environment (5-10℃), and shorten the curing period.

[0057] A kind of UHPC material for bridge expansion joint, wherein, by 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;Nanometer 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.Cement selects 52.5 cement, provides main hydration product, guarantees early strength.Nano silicon dioxide is 20nm in diameter, nanoscale filling effect, significantly improves interface transition zone strength.Metakaolin is high-activity metakaolin, can provide aluminum phase, optimize C-S-H gel structure.The particle size of quartz sand is 0.1-0.3mm, fine gradation, reduces defects.Silica fume can fill pores, promote secondary hydration, improve density.Nanometer carbon fiber can be micro-dispersed, inhibit microcrack propagation.Steel fiber can be macroscopically enhanced, tensile and bending strength is improved.Water reducing agent is polycarboxylic acid water reducing agent, reduces water-binder ratio to 0.16, guarantees fluidity.Low temperature early strength activator is sulphoaluminate + lithium salt, accelerates hydration under low temperature environment.Water is used to control water-binder ratio, ensure workability.

[0058] Example 2

[0059] On the basis of example 1, the following steps are further included in step 4:

[0060] S41, the steel fiber after screening falls into the electromagnetic dispersion box 730, and the steel fiber is uniformly dispersed in the changing magnetic field by using the magnetic conductivity of the steel fiber;

[0061] S42, the steel fiber first falls into the top electromagnet array 734 which turns on and off the magnetic field in the left-right direction, when energized, the length direction of the steel fiber tends to be arranged in the left-right horizontal direction under the influence of the horizontal magnetic field, when de-energized, the steel fiber falls downward to the middle electromagnet array 735 under the influence of its own gravity;

[0062] S43, the middle electromagnet array 735 generates a magnetic field which turns on and off in the front-back direction, when energized, the length direction of the steel fiber tends to be arranged in the front-back horizontal direction under the influence of the horizontal magnetic field, when de-energized, the steel fiber falls downward to the bottom electromagnet array 736 under the influence of its own gravity;

[0063] S43, the bottom electromagnet array 736 generates a magnetic field which turns on and off in the left-right direction, when energized, the length direction of the steel fiber tends to be arranged in the left-right horizontal direction under the influence of the horizontal magnetic field, when de-energized, the steel fiber falls downward to the third feeding port 4.

[0064] The steel fiber passes through the vibration screening and electromagnetic dispersion module 73, to ensure that the single steel fiber is uniformly distributed.

[0065] Example 3

[0066] On the basis of Embodiment 2, with reference to Figure 2 , the planetary mixer comprises a mixer body 1, a first feeding port 2, a second feeding port 3 and a third feeding port 4 are arranged on the mixer body 1, and a liquid inlet 5 is arranged on the mixer body 1, 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 scattering feeding system 7.

[0067] 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 a discharge valve and a compressed air pipeline 67 for introducing airflow are arranged on the discharge pipe 611. Inert gas, preferably nitrogen, is introduced into the premixing bin 61 during work. When stirring, silica ash with a particle size of 0.1 μm is adsorbed on the surface of 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 an angle of 45 degrees, 0.5 MPa compressed air carries the mixed powder into 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.

[0068] 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.

[0069] The ultrasonic atomization cavity 63 is located below the vortex chamber 62, and the piezoelectric ceramic array 68 is arranged in a ring shape on the ultrasonic atomization cavity 63. The porous diffuser 64 is arranged at the outlet position of the ultrasonic atomization cavity 63 and is located at the position of the second feeding port 3, which expands the atomized flow into a 30° conical spray. The piezoelectric ceramic array 68 selects 6 groups of PZT-8 piezoelectric ceramics with a phase difference of 120° and alternating vibration.

[0070] Further, as a specific embodiment, with reference to Figure 1 、 Figure 2 and Figure 4The steel fiber dispersing feeding system 7 comprises a steel fiber bin 71, a vibrating screening module, an electromagnetic dispersing 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 at 0.1-1 mm, the larger steel fiber groups adhered to each other 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 being clamped on the screening plate 722.

[0071] Further, referring to Figure 4 and Figure 5 , the first screen 723 and the second screen 724 are symmetrically arranged on the screening plate 722.

[0072] Further, referring to Figure 4 , Figure 6 and Figure 7 , the electromagnetic dispersing module 73 comprises an electromagnetic dispersing box 730 arranged below the vibrating screening box 721, the inside of the electromagnetic dispersing box 730 is symmetrically vertically provided with a first guide pipe 731 for the steel fiber falling from the first screen 723 to pass through and a second guide pipe 732 for the steel fiber falling from the second screen 724 to pass through, 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.

[0073] The upper end of the first guide pipe 731 and the upper end of the second guide pipe 732 are 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 position of the two second corrugated sealing sleeves 733. The steel fiber falling from the first screen 723 and the second screen 724 can fall into the inside of 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 generated by the vibrating screening box 721 from being transmitted to the first guide pipe 731 and the second guide pipe 732.

[0074] The top 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 to attract the falling steel fiber, and the direction of the magnetic force line is along the left-right horizontal direction, so that the steel fiber is straightened (like using a magnet to straighten a curved paper clip), the sticky group is forcibly separated, and the straightness and dispersion of the steel fiber are realized. The continuous steel fiber is first electromagnetically dispersed.

[0075] The middle 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 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 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 electromagnet array 735 is similar to that of the top electromagnet array 734, and the steel fiber has been partially separated under the action of the top electromagnet array 734, the energized fourth U-shaped electromagnet, the fifth U-shaped electromagnet, the sixth U-shaped electromagnet and the seventh U-shaped electromagnet generate a magnetic field to attract the falling steel fiber, and the direction of the magnetic force line is along the front-back horizontal direction, so that the steel fiber is straightened, and the small fiber group is forcibly separated, thereby realizing further dispersion of the steel fiber. The continuous steel fiber is secondarily electromagnetically dispersed by continuously switching the magnetic field to attract the steel fiber and then releasing it.

[0076] The bottom 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 provided on the left side of the first guide pipe 731 with an opening facing downward, the ninth U-shaped electromagnet is provided between the first guide pipe 731 and the second guide pipe 732 with an opening facing downward, and the tenth U-shaped electromagnet is provided on the right side of the second guide pipe 732 with an opening facing 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 electromagnet array 736 is similar to that of the top electromagnet array 734, which continues to electromagnetically disperse the remaining small fiber groups and finally disperses the steel fibers into single state and falls into the third feeding port 4.

[0077] The rectangular air pipes 74 are provided at the outer lower ends of the first guide pipe 731 and the second guide pipe 732, and four high-pressure gas flow nozzles are arranged around each rectangular air pipe 74. 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 nozzles is 0.2-0.5MPa, the gas flow direction is 30° to the falling direction of the steel fibers, and vortex auxiliary dispersion is formed.

[0078] The technical features of the above-mentioned embodiments can be combined in any way. In order to make the description simple, all possible combinations of the technical features in the above-mentioned embodiments are not described, but as long as the combination of the technical features does not exist contradictory, it should be considered as the scope of the present application.

[0079] The above-mentioned embodiments only express the implementation of the present application, and the description is more specific and detailed, but it cannot be understood as a limitation of the 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, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A method for preparing 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 method for preparing 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 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 method for preparing 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 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 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 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 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 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.

Images