Centrifugal forming device of oriented steel fiber concrete hollow pipe pile and using method

Abstract

The invention relates to a centrifugal forming device of a directional steel fiber concrete hollow pipe pile and a using method, the centrifugal forming device comprises a bottom plate and fixed supports, and a stainless steel threaded rod is rotatably mounted between the two fixed supports; a driven wheel is mounted at one end of the stainless steel threaded rod and connected with an output shaft of a rotary variable-speed motor through a synchronous belt and a driving wheel, and the rotary variable-speed motor is electrically connected with a frequency converter; the middle of the stainless steel threaded rod is sleeved with a PVC hollow pipe die, and the two ends of the PVC hollow pipe die are each sleeved with a ball bearing. A PVC hollow cylinder is fixedly connected between the two ball bearings; a copper coil is wound on the outer surface of the PVC hollow cylinder, and the two ends of the copper coil are electrically connected with a direct-current power supply; and fixing nuts are arranged on the stainless steel threaded rods on the outer sides of the PVC pipe caps to limit the mounting positions of the PVC hollow pipe molds on the stainless steel threaded rods. The problem that fiber orientation and distribution cannot be controlled in the centrifugal process of the steel fiber concrete pile in the prior art is solved.

Description

Technical Field

[0001] The invention relates to the technical field of steel fiber reinforced concrete manufacturing equipment, and in particular to a centrifugal forming device for directional steel fiber concrete hollow pipe piles and a use method thereof. Background Art

[0002] In the precast concrete industry, centrifugal forming is a common technology used to manufacture hollow circular reinforced concrete piles. Since concrete is characterized by high compressive strength, low tensile strength and small ultimate strain, it is a brittle material, resulting in poor toughness and easy cracking of concrete. In engineering, the concrete in the tensile stress zone of ordinary structural concrete is generally worked with cracks. The steel bars at the cracks are not effectively protected by concrete and may rust prematurely, which has a great impact on the durability of the structure. Adding steel fibers is one of the most effective ways to improve the crack resistance, toughness and tensile properties of concrete. The addition of discrete steel fibers can inhibit crack propagation through effective crack bridging, thereby significantly improving the bearing characteristics of concrete piles. At present, in the process of concrete pile manufacturing, the effectiveness of steel fibers in reinforced concrete structures depends largely on the orientation and distribution of the fibers. If the steel fibers are poorly dispersed and not arranged parallel to the tensile stress direction, the bending strength and shear strength of steel fiber components cannot be effectively improved.

[0003] In the existing centrifugal technology, the process principle is to place the pipe mold fed with steel fiber concrete mixture flat on the centrifuge. Through the rotation of the driving wheel and the driven wheel in the centrifuge, the steel fiber concrete mixture is subjected to centrifugal force and evenly distributed along the circumference of the pipe wall, gradually forming a ring-shaped hollow tubular structure. During the centrifugal forming process, the sedimentation rate of steel fibers is faster than that of coarse aggregates and sand particles with smaller particles. Steel fibers will tend to be distributed on the outer wall of the component. In concrete with different steel fiber dosages, steel fibers are most distributed on the outer wall and gradually decrease inward along the thickness direction. This causes the steel fibers to be unevenly distributed and randomly distributed in the concrete components. Doing so will significantly reduce the utilization efficiency of steel fibers in concrete, making it impossible for many steel fibers to fully play their due role, and will also greatly increase the cost of raw materials for preparing steel fiber reinforced concrete.

[0004] In view of this, the present invention provides a centrifugal forming device and a method for using a directional steel fiber concrete hollow pipe pile, which can solve the problem in the prior art that the fiber orientation and distribution of the steel fiber concrete pile cannot be controlled during the centrifugal forming process. Summary of the invention

[0005] The purpose of the present invention is to provide a centrifugal forming device for oriented steel fiber concrete and a method for using the same to solve the problems raised in the above technical background.

[0006] To achieve the above object, the technical solution adopted by the present invention is: In the first aspect, the present invention provides a centrifugal forming device for oriented steel fiber concrete hollow pipe piles, comprising a bottom plate 15 and two fixed supports symmetrically fixed on the bottom plate, a stainless steel threaded rod 5 is rotatably installed between the two fixed supports 14; the two ends of the stainless steel threaded rod extending from the two fixed supports are smooth surfaces, a driven wheel is installed at one end of the stainless steel threaded rod, and the driven wheel is driven by a driving wheel located below through a synchronous belt; the driving wheel is connected to the output shaft of a rotating variable speed motor, and the rotating variable speed motor is electrically connected to a frequency converter at the same time; A PVC hollow tube mold is mounted in the middle of the stainless steel threaded rod, and PVC tube caps 8 are installed at both ends of the PVC hollow tube mold; ball bearings are sleeved at both ends of the PVC hollow tube mold; a PVC hollow cylinder is fixedly connected between the two ball bearings; a copper coil is wound around the outer surface of the PVC hollow cylinder, and both ends of the copper coil are electrically connected to a DC power supply; A fixing nut is arranged on the stainless steel threaded rod outside the PVC pipe cap to limit the installation position of the PVC hollow pipe mold on the stainless steel threaded rod.

[0007] Furthermore, a rotating bearing support 12 is installed at the top center of each fixed support, and the smooth surface portion of the stainless steel threaded rod is sleeved on the bearing of the rotating bearing support, and the stainless steel threaded rod can rotate independently relative to the rotating bearing support.

[0008] Furthermore, the ball bearing 9 is composed of an inner ring and an outer ring connected by balls 16; the PVC hollow cylinder 11 is cylindrical, and circular bosses are respectively provided on the upper and lower bottom surfaces of the PVC hollow cylinder, and screw holes 17 are provided on the bosses. The upper and lower bottom surfaces of the PVC hollow cylinder are respectively fixed together with the outer rings of the two ball bearings 9 by screws passing through corresponding screw holes, and the PVC hollow cylinder 11 can rotate relative to the PVC hollow tube mold of the inner ring of the ball bearing 9.

[0009] Furthermore, the PVC pipe cap 8 has a 24 mm opening in the center for being put on the stainless steel threaded rod 5. The PVC pipe cap 8 covers the upper and lower bottom surfaces of the PVC hollow pipe mold 18. The outer diameter of the PVC hollow pipe mold 18 is consistent with the inner diameter of the ball bearing 9, and can be inserted into the inner ring of the ball bearing and fixed together.

[0010] Furthermore, the number of turns of the copper coil 10 is 300 to 1000 turns, the length is 150 to 550 mm, and both ends of the coil are connected to the DC power supply 13 below the PVC hollow tube mold 18 .

[0011] In a second aspect, the present invention provides a method for using the centrifugal forming device for oriented steel fiber concrete hollow pipe piles, which is used to prepare oriented steel fiber concrete hollow pipe piles, comprising the steps of: Obtaining the mix ratio of the components of the steel fiber concrete, weighing the cementitious material, sand, stone, high-efficiency water reducing agent and steel fiber required for making the hollow pipe pile, and evenly mixing them to prepare a steel fiber concrete mixture; Apply lubricating oil to the inner wall of the PVC hollow pipe mold and the PVC pipe cap to facilitate subsequent demoulding; Making a steel bar frame: fix the two ends of a plurality of longitudinal steel bars on two annular connecting plates respectively, so that the longitudinal steel bars are evenly distributed along the circumference of the annular connecting plates, and the end faces of the longitudinal steel bars are flush with the end faces of the annular connecting plates, and at least one stirrup is arranged on the longitudinal steel bars between the two annular connecting plates to form a steel bar frame and place it in the PVC hollow pipe mold; Fix one end of the PVC hollow pipe mold to the stainless steel threaded rod through a PVC pipe cap and fixing bolts, and leave the other end open, and put another PVC pipe cap and fixing bolts on this side; The concrete mixture is poured into the open end of the PVC hollow pipe mold from the center hole of the annular connecting plate in 4 equal portions. After each pouring, the PVC pipe cap at the open end is fixed, and the rotating variable speed motor and the DC power supply are started. While the rotating centrifugal compaction is performed, the direction of the steel fiber in the concrete mixture is controlled by the magnetic field generated by the copper coil. After compacting one layer, the rotating variable speed motor and the DC power supply are stopped to start pouring the next layer. After all the centrifugal compaction and shaping, let it stand for a period of time for curing.

[0012] Furthermore, the annular connecting plate is a circular wooden board or a light high-strength metal plate or a polymer plate; The annular surface width of at least one of the two annular connecting plates is not greater than the thickness of the hollow pipe pile to be prepared; The process of the rotary centrifugation is: centrifugation at a rate of 60-120 r / min for 100-300 s, and then centrifugation at a rate of 300-600 r / min for 120-300 s.

[0013] Furthermore, five stirrups are arranged at the mid-span of the pipe pile, with a stirrup spacing of 95 mm, and two stirrups are respectively arranged outside the shear span of the pipe pile.

[0014] Furthermore, the inner diameter and length of the PVC hollow pipe mold are obtained, and the target wall thickness of the hollow pipe pile to be prepared is set. The steel fiber concrete mixture is divided into different materials according to the thickness required for each pouring in the PVC hollow tube mold; the thickness of all pourings is the same as the set target thickness; It is preferred that the pouring thickness is fed in a layer-by-layer increasing manner, and the direction of the magnetic field is consistent with the axial direction of the hollow pipe pile.

[0015] In a third aspect, the present invention provides a directional steel fiber concrete hollow pipe pile obtained by the use method.

[0016] Compared with the prior art, the beneficial effects of the present invention include: 1) During the rotating centrifugal process, the concrete mixture is compacted and formed under the action of centrifugal force, and the excess slurry in the concrete is separated. The steel fibers are distributed more evenly in the concrete hollow pipe piles through the layered rotating centrifugal compaction method, which solves the problem that the steel fibers and aggregates tend to be distributed on the outer wall during the high-speed rotating centrifugal process, and gradually decrease along the thickness direction, resulting in stress concentration. At the same time, under the action of the magnetic field generated by the energized coil, the fibrous steel will be magnetized in a strong magnetic field. When the fiber direction is not perpendicular to the magnetic field direction, the magnetic S pole and magnetic N pole are formed at both ends of the fiber. The external magnetic field is applied to magnetize the steel fibers in the concrete mixture into small magnets with two poles at both ends. Then, under the action of the directional magnetic field, the two ends of the magnetized steel fibers are subjected to equal and opposite forces and rotate, and the final direction tends to be consistent with the direction of the magnetic field, achieving directional distribution.

[0017] 2) The present invention provides a concrete hollow pipe pile centrifugal forming device that can simultaneously orient the steel fiber concrete material in the magnetic field during the centrifugal compaction process, thereby solving the problem in the prior art that the fiber orientation and distribution of the steel fiber concrete pile cannot be controlled during the centrifugal process. Furthermore, since the pipe mold is mounted on a stainless steel threaded rod, the safety of the preparation process is greatly guaranteed, preventing the risk of the pipe mold detaching during high-speed rotation and centrifugation.

[0018] 3) Compared with steel fiber concrete prepared by the prior art method, the technical method provided by the present invention has an increase of 25% to 80% in flexural strength of oriented steel fiber concrete hollow pipe piles prepared by the device and method of use of the present invention if the raw material mix ratio is the same; if the product flexural strength is the same, the amount of steel fiber required for the oriented steel fiber concrete hollow pipe piles prepared by the device and method of use of the present invention is reduced by 25% to 60%. It can be seen that the present invention has made significant progress compared with the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The main structural schematic diagram of a centrifugal forming device for oriented steel fiber concrete hollow pipe piles according to an embodiment; Figure 2 It is a schematic diagram of a magnetic field orientation structure in a centrifugal forming device for oriented steel fiber concrete hollow pipe piles; Figure 3 It is a schematic diagram of a PVC hollow pipe mold in a centrifugal forming device for oriented steel fiber concrete hollow pipe piles; In the figure, frequency converter 1, rotating speed motor 2, driving wheel 3, transmission belt 4, stainless steel threaded rod 5, driven wheel 6, fixing nut 7, PVC pipe cap 8, ball bearing 9, copper coil 10, PVC hollow cylinder 11, rotating bearing support 12, DC power supply 13, fixed support 14, bottom plate 15, ball 16, screw hole 17, PVC hollow pipe mold 18. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to better understand the present application, the technical solution of the present invention is further described below in conjunction with specific embodiments and drawings.

[0021] The centrifugal forming device of the directional steel fiber concrete hollow pipe pile of the present invention (see Figure 1-3 ), including a base plate 15, two fixed supports 14, two rotating bearing supports 12, a stainless steel threaded rod 5, two fixing nuts 7, a PVC hollow pipe mold 18, two PVC pipe caps 8, two ball bearings 9, a PVC hollow cylinder 11, a copper coil 10, a driving wheel 3, a driven wheel 6, a transmission belt 4, a DC power supply 13, a rotating speed-changing motor 2, and a frequency converter 1.

[0022] Among them, a PVC hollow tube mold 18, two PVC pipe caps 8, two ball bearings 9, a PVC hollow cylinder 11, a copper coil 10, and a DC power supply 13 constitute a magnetic field orientation structure, and the remaining components constitute a rotating centrifugal structure. In the rotating centrifugal structure, two fixed supports 14 are fixed to the bottom plate 15 by screws, two rotating bearing supports 12 are respectively fixed to the two fixed supports 14 by screws, a stainless steel threaded rod 5 is sleeved on the two rotating bearing supports 12 by hexagon socket screws, two fixing nuts 7 are arranged on the stainless steel threaded rod 5 to fix the magnetic field orientation structure, one end of the stainless steel threaded rod 5 is sleeved on the driven wheel 6 by hexagon socket screws, the driven wheel and the driving wheel 3 are connected by a transmission belt 4, the rotating variable speed motor 2 is sleeved and fixed to the driving wheel by hexagon socket screws, and the frequency converter 1 is connected to the rotating variable speed motor 2 by wiring.

[0023] The ball bearing 9 is composed of an inner ring and an outer ring connected by balls 16. In the magnetic field orientation structure, the PVC hollow cylinder 11 is cylindrical, and circular bosses are respectively arranged on the upper and lower bottom surfaces of the PVC hollow cylinder, and screw holes 17 are arranged on the bosses. The upper and lower bottom surfaces of the PVC hollow cylinder are respectively fixed together with the outer rings of the two ball bearings 9 by screws passing through the corresponding screw holes. The PVC pipe cap 8 is covered on the PVC hollow pipe mold 18 to form an integral body, the two ends of which are respectively embedded in the inner rings of the two ball bearings and fixed by hexagon socket screws, which pass through the through holes of the corresponding inner rings and press against the side wall of the PVC hollow pipe mold to connect the two into a relatively fixed integral body, so that the PVC hollow cylinder 11 can rotate relative to the PVC hollow pipe mold of the inner ring of the ball bearing 9 without interference.

[0024] The copper coil 10 is wound around the outer wall of the PVC hollow cylinder 11 , and both ends of the coil are connected to a DC power source 13 .

[0025] The bottom plate 15 is a rectangular iron plate with a certain thickness, and the iron plate is 1600mm long, 300mm wide and 10mm thick. There are 4 screw holes on both sides of the bottom plate, and the screw holes on both sides are 90mm apart, which are used to be connected and fixed with the fixed support 14.

[0026] The fixed support 14 is a T-shaped structure, including a wing plate and a web perpendicular to the wing plate, the wing plate is 200 mm long, 120 mm wide and 10 mm thick. The web is 400 mm long, 200 mm wide and 20 mm thick. The left and right sides of the wing plate are respectively provided with two screw holes to connect and fix with the bottom plate, and the top center of the web is provided with two screw holes to connect and fix with the rotating bearing support 12.

[0027] The inner diameter of the rotating bearing support 12 is 24 mm. The two ends of the stainless steel threaded rod 5 are sleeved on the two rotating bearing supports 12. The rotating bearing supports are fixed together with the web of the fixed support by hexagon socket screws.

[0028] The stainless steel threaded rod 5 is 1250 mm long and 24 mm in diameter. The middle section has a 900 mm thread for fixing the nut 7. The left and right sides of the stainless steel threaded rod are smooth surfaces, that is, the stainless steel threaded rod between the two rotating bearing supports is provided with threads.

[0029] The inner diameters of the driving wheel 3 and the driven wheel 6 are both 24 mm, and the two are connected by a transmission belt 4. The driven wheel 6 is sleeved with the stainless steel threaded rod 5, and the driving wheel 3 is sleeved with the rotating speed motor 2, and the speed of the rotating speed motor 2 is controlled by the inverter 1.

[0030] The PVC pipe cap 8 has a 24mm opening in the center for being put on the stainless steel threaded rod 5. The PVC pipe cap 8 covers the upper and lower bottom surfaces of the PVC hollow pipe mold 18. The diameter of the PVC hollow pipe mold 18 is consistent with the inner diameter of the ball bearing 9, and can be inserted into the inner ring of the ball bearing and fixed together.

[0031] The number of turns of the copper coil 10 is 300 to 1000 turns, and the length is 150 to 550 mm. Both ends of the coil are connected to the DC power supply 13 below the PVC hollow tube mold 18.

[0032] The method for using the centrifugal forming device of the oriented steel fiber concrete hollow pipe pile of the present invention is to prepare the oriented steel fiber concrete hollow pipe pile, and the specific steps are as follows: According to the mix ratio of the steel fiber concrete components determined by the known design method, the cementitious material, sand, stone, high-efficiency water reducing agent and steel fiber required for making the hollow pipe pile are weighed, and the weighed cementitious material, sand, stone, high-efficiency water reducing agent and steel fiber are put into a mixer and mixed evenly to prepare a steel fiber concrete mixture; Apply lubricating oil to the inner wall of the PVC hollow pipe mold and the PVC pipe cap to facilitate subsequent demoulding; Making a steel bar frame: fix the two ends of a plurality of longitudinal steel bars on two annular connecting plates respectively, so that the longitudinal steel bars are evenly distributed along the circumference of the annular connecting plates, and the end faces of the longitudinal steel bars are flush with the end faces of the annular connecting plates, and at least one stirrup is arranged on the longitudinal steel bars between the two annular connecting plates to form a steel bar frame and place it in the PVC hollow pipe mold; Fix one end of the PVC hollow pipe mold to the stainless steel threaded rod through a PVC pipe cap and fixing bolts, and leave the other end open, and put another PVC pipe cap and fixing bolts on this side; The concrete mixture is poured into the open end of the PVC hollow pipe mold from the center hole of the annular connecting plate in 4 equal portions. After each pouring, the PVC pipe cap at the open end is fixed, and the rotating variable speed motor and the DC power supply are started. While the rotating centrifugal compaction is performed, the direction of the steel fiber in the concrete mixture is controlled by the magnetic field generated by the copper coil. After compacting one layer, the rotating variable speed motor and the DC power supply are stopped to start pouring the next layer. After all the centrifugal compaction and forming, the PVC hollow pipe mold is removed from the stainless steel threaded rod and placed upright on the indoor floor for 24 hours before being removed from the mold and moved into the curing room for curing, maintaining the temperature at 20±2℃ and the relative humidity ≥90%. When the specimen is cured to the specified age of 28 days, the specimen is taken out of the curing room to obtain a directional steel fiber concrete hollow pipe pile.

[0033] The steel fiber is a low-carbon steel material. The operation process of preparing the steel fiber concrete mixture is to put the weighed cementitious material, sand and stone into the mixer in turn, dry mix until uniform, gradually add all the weighed steel fibers during the mixing process, continue to stir until the mixture is uniform, add the weighed mixing water and high-efficiency water reducer, and continue to stir for 120 to 300 seconds. By adjusting the amount of water reducer or the amount of mixing water, the slump of the concrete mixture is controlled between 40 mm and 160 mm.

[0034] In a further technical solution, the number of turns of the copper coil is 300 to 1000 and the length is 150 to 550 mm. When a direct current of 1 to 30 volts and 0.1 to 20 amperes is connected, a magnetic induction intensity of 1.0×10 -3T~20.0×10 -3 T's magnetic field.

[0035] In a further technical solution, the above-mentioned rotary centrifugation process is: centrifugation at a rate of 60-120 r / min for 100-300 s, and then centrifugation at a rate of 300-600 r / min for 120-300 s.

[0036] Example 1 The first step is to prepare the steel fiber concrete mixture The mass proportion of the concrete components with strength grade C30 determined by the known design method is water: cement: sand: stone: high-efficiency water reducer: steel fiber = 185: 440: 532: 1244: 4.4: 47. The required amount of water, cement, sand, stone, high-efficiency water reducer and steel fiber are weighed. The steel fiber used is end hook steel fiber, made of low carbon steel, with a diameter of 0.5 mm and an aspect ratio of 40. The weighed cement, sand and stone are put into the mixer and mixed evenly, and then all the weighed steel fibers are added while mixing until they are evenly mixed, and then the weighed mixing water and high-efficiency water reducer are added, and the mixing is continued for 90 seconds. The slump of the concrete mixture is 100 mm.

[0037] Step 2: Make the steel frame Fix 8 longitudinal bars with a diameter of 12.3mm on two hollow round wooden boards, and fix the two ends of the longitudinal bars on the openings of the hollow round wooden boards along the circumference. Set 5 stirrups with a diameter of 4.23mm in the middle of the pipe pile span with a spacing of 95mm. Add two stirrups outside the shear span of the pipe pile to form a steel frame, and put the steel frame into the PVC hollow pipe mold.

[0038] The setting of the hollow round wood board can make it impossible to see the steel bars outside the finished hollow pipe pile, that is, the steel bars will not be exposed. The hollow part of the hollow round wood board can be convenient for pouring and can fix and support the longitudinal bars. The overall weight of the steel frame will not be too large.

[0039] The third step is layered centrifugal orientation. The steel fiber concrete mixture prepared in the first step was poured into a PVC hollow pipe mold with a length of 800 mm and a diameter of 200 mm from one end of the PVC hollow pipe mold in layers with a thickness of 1 cm, 1.5 cm, and 2.5 cm to form a steel fiber concrete hollow pipe pile with a wall thickness of 50 mm. After each layer was poured, the PVC pipe cap was covered, and the rotating variable speed motor and the DC power supply were started for centrifugal orientation. The centrifugal speed and centrifugal time were controlled by the frequency converter. The centrifugal time lasted for 30 minutes. The DC power supply was turned on to energize the coil to form a magnetic field to apply a magnetic field to the steel fiber concrete mixture prepared in the first step. The direction of the magnetic field was consistent with the axis direction of the hollow pipe pile. The magnetic induction intensity in the above coil was 10.0×10 -3T. Then turn off the above-mentioned rotating variable speed motor, repeat the above-mentioned steps to pour three layers of steel fiber concrete, cut off the DC power supply of the above-mentioned coil, remove the PVC hollow pipe mold containing the centrifugally formed steel fiber concrete from the centrifugal forming device and stand it upright on the indoor floor.

[0040] Step 4: Prepare directional steel fiber concrete hollow pipe piles The PVC hollow pipe mold filled with the centrifugally formed steel fiber concrete in the third step was placed indoors for 24 hours and then demolded. The mold was moved into a curing room for curing, with the temperature maintained at 20±2°C and the relative humidity ≥90%. When the specimens were cured to the prescribed age of 28 days, they were taken out of the curing room to obtain directional steel fiber concrete hollow pipe piles. The three-point loading test was performed on the pipe piles, and the peak shear load was measured to be 105kN.

[0041] Comparative Example 1 Except for the lack of the magnetic field orientation process in the third step, the other steps are the same as those in Example 1.

[0042] Similarly, when the specimens were cured to the prescribed age of 28 days, they were taken out from the curing room to obtain hollow pipe piles. A three-point loading test was carried out on the pipe piles, and the peak shear load was measured to be 89 kN.

[0043] The raw material ratio, steel fiber dosage and steel bar quantity of Example 1 are the same as those of Comparative Example 1, but the 28d shear peak load of the oriented steel fiber concrete hollow pipe pile obtained in Example 1 is 15% higher than that of the hollow pipe pile obtained in Comparative Example 1.

[0044] Comparative Example 2 The layered pouring in the third step is changed to full pouring, and the other steps are the same as in Example 1.

[0045] Similarly, when the specimens were cured to the prescribed age of 28 days, they were taken out from the curing room to obtain hollow pipe piles. A three-point loading test was performed on the pipe piles, and the peak shear load was measured to be 86 kN.

[0046] The raw material ratio, steel fiber dosage and steel bar quantity of Example 1 and Comparative Example 2 are the same, but the 28d shear peak load of the oriented steel fiber concrete hollow pipe pile obtained in Example 1 is 18% higher than that of the hollow pipe pile obtained in Comparative Example 2.

[0047] Comparative Example 3 The layered pouring in the third step is changed to full pouring, and the magnetic field orientation process is removed. The other steps are the same as in Example 1.

[0048] Similarly, when the specimens were cured to the prescribed age of 28 days, they were taken out from the curing room to obtain hollow pipe piles. The pipe piles were subjected to a three-point loading test, and the peak shear load was measured to be 80 kN.

[0049] The raw material ratio, steel fiber dosage and steel bar quantity of Example 1 and Comparative Example 3 are the same, but the 28d shear peak load of the oriented steel fiber concrete hollow pipe pile obtained in Example 1 is 24% higher than that of the hollow pipe pile obtained in Comparative Example 3.

[0050] Example 2 The first step is to prepare the steel fiber concrete mixture The mass proportion of the concrete components with strength grade C30 determined by the known design method is water: cement: sand: stone: high-efficiency water reducer: steel fiber = 185: 440: 532: 1244: 4.4: 47. The required amount of water, cement, sand, stone, high-efficiency water reducer and steel fiber are weighed. The steel fiber used is end hook steel fiber, made of low carbon steel, with a diameter of 0.5 mm and an aspect ratio of 40. The weighed cement, sand and stone are put into the mixer and mixed evenly, and then all the weighed steel fibers are added while mixing until they are evenly mixed, and then the weighed mixing water and high-efficiency water reducer are added, and the mixing is continued for 90 seconds. The slump of the concrete mixture is 100 mm.

[0051] Step 2: Make the steel frame Fix 8 longitudinal bars with a diameter of 12.3mm on two hollow round wood boards, fix the two ends of the longitudinal bars on the openings of the hollow round wood boards along the circumference, set 5 stirrups with a diameter of 4.23mm in the middle of the pipe pile span, with a spacing of 95mm, and add two stirrups outside the shear span of the pipe pile to form a steel frame, and put the steel frame into the PVC hollow pipe mold. The outer diameter of the hollow round wood board is equivalent to the inner diameter of the PVC hollow pipe mold, and can be put into the PVC hollow pipe mold without too much gap between the two.

[0052] The third step is layered centrifugal orientation. The steel fiber concrete mixture prepared in the first step was poured into a PVC hollow pipe mold with a length of 800 mm and a diameter of 200 mm from one end of the PVC hollow pipe mold in layers with a thickness of 1 cm, 2 cm, and 2 cm to form a steel fiber concrete hollow pipe pile with a wall thickness of 50 mm. After each layer was poured, the PVC pipe cap was covered, and the rotating variable speed motor and the DC power supply were started for centrifugal orientation. The centrifugal speed and centrifugal time were controlled by the frequency converter. The centrifugal time lasted for 30 minutes. The DC power supply was turned on to energize the coil to form a magnetic field to apply a magnetic field to the steel fiber concrete mixture prepared in the first step. The direction of the magnetic field was consistent with the axial direction of the hollow pipe pile. The magnetic induction intensity in the above coil was 8.0×10 -3 T. Then turn off the above-mentioned rotating variable speed motor, repeat the above-mentioned steps to pour three layers of steel fiber concrete, cut off the DC power supply of the above-mentioned coil, remove the PVC hollow pipe mold containing the centrifugally formed steel fiber concrete from the centrifugal forming device and stand it upright on the indoor floor.

[0053] Step 4: Prepare directional steel fiber concrete hollow pipe piles The PVC hollow pipe mold filled with the centrifugally formed steel fiber concrete in the third step was left to stand indoors for 24 hours, then demolded and moved into a curing room for curing, with the temperature maintained at 20±2°C and the relative humidity ≥90%. When the specimens were cured to the prescribed age of 28 days, they were taken out of the curing room to obtain directional steel fiber concrete hollow pipe piles. A three-point loading test was performed on the pipe piles, and the peak shear load was measured to be 99kN.

[0054] Comparative Example 4 Except for the lack of the magnetic field orientation process in the third step, the other steps are the same as those in Example 2.

[0055] Similarly, when the specimens were cured to the prescribed age of 28 days, they were taken out from the curing room to obtain hollow pipe piles. A three-point loading test was carried out on the pipe piles, and the peak shear load was measured to be 87 kN.

[0056] The raw material ratio, steel fiber dosage and steel bar quantity of Example 1 are the same as those of Comparative Example 1, but the 28d shear peak load of the oriented steel fiber concrete hollow pipe pile obtained in Example 1 is 12% higher than that of the hollow pipe pile obtained in Comparative Example 1.

[0057] Comparative Example 5 The layered pouring in the third step is changed to full pouring, and the other steps are the same as in Example 1.

[0058] Similarly, when the specimens were cured to the prescribed age of 28 days, they were taken out from the curing room to obtain hollow pipe piles. The three-point loading test was carried out on the pipe piles, and the peak shear load was measured to be 83 kN.

[0059] The raw material ratio, steel fiber dosage and steel bar quantity of Example 1 and Comparative Example 2 are the same, but the 28d shear peak load of the oriented steel fiber concrete hollow pipe pile obtained in Example 1 is 16% higher than that of the hollow pipe pile obtained in Comparative Example 2.

[0060] Comparative Example 6 The layered pouring in the third step is changed to full pouring, and the magnetic field orientation process is removed. The other steps are the same as in Example 1.

[0061] Similarly, when the specimens were cured to the prescribed age of 28 days, they were taken out from the curing room to obtain hollow pipe piles. A three-point loading test was carried out on the pipe piles, and the peak shear load was measured to be 75 kN.

[0062] The raw material ratio, steel fiber dosage and steel bar quantity of Example 1 and Comparative Example 3 are the same, but the 28d shear peak load of the oriented steel fiber concrete hollow pipe pile obtained in Example 1 is 24% higher than that of the hollow pipe pile obtained in Comparative Example 3.

[0063] In the above embodiment: the number of turns of the copper coil used is selected within the range of 300 to 1000 turns, and the coil length is related to the length of the tube mold to ensure that it is longer than the length of the PVC hollow tube mold placed in the cavity of the coil skeleton, and the shape and size of the cavity are determined according to the shape and size of the PVC hollow tube mold poured with the steel fiber concrete mixture placed therein; the selected range of the ball bearing diameter used is related to the outer diameter of the tube mold to ensure that the tube mold can be sleeved on the ball bearing.

[0064] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A centrifugal forming device for oriented steel fiber concrete hollow pipe piles, comprising a bottom plate and two fixed supports symmetrically fixed on the bottom plate, characterized in that: A stainless steel threaded rod is rotatably installed between two fixed supports; both ends of the stainless steel threaded rod extending from the two fixed supports are smooth surfaces, a driven wheel is installed at one end of the stainless steel threaded rod, and the driven wheel is driven by a driving wheel located below through a synchronous belt; the driving wheel is connected to the output shaft of the rotating speed-changing motor, and the rotating speed-changing motor is electrically connected to the frequency converter at the same time; Install a PVC hollow pipe mold in the middle of the stainless steel threaded rod, and install PVC pipe caps at both ends of the PVC hollow pipe mold; Ball bearings are sleeved at both ends of the PVC hollow tube mold; a PVC hollow cylinder is fixedly connected between the two ball bearings; a copper coil is wound around the outer surface of the PVC hollow cylinder, and both ends of the copper coil are electrically connected to a DC power supply; A fixing nut is arranged on the stainless steel threaded rod outside the PVC pipe cap to limit the installation position of the PVC hollow pipe mold on the stainless steel threaded rod.

2. The centrifugal forming device according to claim 1, characterized in that: A rotating bearing support is installed at the top center of each fixed support. The smooth surface portion of the stainless steel threaded rod is sleeved on the bearing of the rotating bearing support. The stainless steel threaded rod can rotate independently relative to the rotating bearing support.

3. The centrifugal forming device according to claim 1, characterized in that: The ball bearing is composed of an inner ring and an outer ring connected by balls; the PVC hollow cylinder is cylindrical, and circular bosses are respectively arranged on the upper and lower bottom surfaces of the PVC hollow cylinder, and screw holes are arranged on the bosses. The upper and lower bottom surfaces of the PVC hollow cylinder are respectively fixed together with the outer rings of the two ball bearings by screws passing through corresponding screw holes, and the PVC hollow cylinder can rotate relative to the PVC hollow tube mold of the inner ring of the ball bearing.

4. The centrifugal forming device according to claim 1, characterized in that: There is a 24mm opening in the center of the PVC pipe cap for sleeve onto the stainless steel threaded rod. The PVC pipe cap covers the upper and lower bottom surfaces of the PVC hollow pipe mold. The outer diameter of the PVC hollow pipe mold is consistent with the inner diameter of the ball bearing, and can be inserted into the inner ring of the ball bearing and fixed together.

5. The centrifugal forming device according to claim 1, characterized in that: The number of turns of the copper coil is 300 to 1000 turns, the length is 150 to 550 mm, and both ends of the coil are connected to a DC power supply below the PVC hollow tube mold.

6. A method for using the centrifugal forming device for oriented steel fiber concrete hollow pipe piles according to any one of claims 1 to 5, characterized in that: For preparing directional steel fiber concrete hollow pipe piles, the steps are: Obtaining the mix ratio of the components of the steel fiber concrete, weighing the cementitious material, sand, stone, high-efficiency water reducing agent and steel fiber required for making the hollow pipe pile, and evenly mixing them to prepare a steel fiber concrete mixture; Apply lubricating oil to the inner wall of the PVC hollow pipe mold and the PVC pipe cap to facilitate subsequent demoulding; Making a steel bar frame: fix the two ends of a plurality of longitudinal steel bars on two annular connecting plates respectively, so that the longitudinal steel bars are evenly distributed along the circumference of the annular connecting plates, and the end faces of the longitudinal steel bars are flush with the end faces of the annular connecting plates, and at least one stirrup is arranged on the longitudinal steel bars between the two annular connecting plates to form a steel bar frame and place it in the PVC hollow pipe mold; Fix one end of the PVC hollow pipe mold to the stainless steel threaded rod through a PVC pipe cap and fixing bolts, and leave the other end open, and put another PVC pipe cap and fixing bolts on this side; The concrete mixture is poured into the open end of the PVC hollow pipe mold from the center hole of the annular connecting plate in 4 equal portions. After each pouring, the PVC pipe cap at the open end is fixed, and the rotating variable speed motor and the DC power supply are started. While the rotating centrifugal compaction is performed, the direction of the steel fiber in the concrete mixture is controlled by the magnetic field generated by the copper coil. After compacting one layer, the rotating variable speed motor and the DC power supply are stopped to start pouring the next layer. After all the centrifugal compaction and shaping, let it stand for a period of time for curing.

7. The method of use according to claim 6, characterized in that: The annular connecting plate is a circular wooden board or a light high-strength metal plate or a polymer plate; The annular surface width of at least one of the two annular connecting plates is not greater than the thickness of the hollow pipe pile to be prepared; The process of the rotary centrifugation is: centrifugation at a rate of 60-120 r / min for 100-300 s, and then centrifugation at a rate of 300-600 r / min for 120-300 s.

8. The method of use according to claim 6, characterized in that: Five stirrups are set at the mid-span of the pipe pile with a stirrup spacing of 95mm, and two stirrups are added outside the shear span of the pipe pile.

9. The method of use according to claim 6, characterized in that: Get the inner diameter and length of the PVC hollow pipe mold, and set the target wall thickness of the hollow pipe pile to be prepared. The steel fiber concrete mixture is divided into different materials according to the thickness required for each pouring in the PVC hollow tube mold; the thickness of all pourings is the same as the set target thickness; It is preferred that the pouring thickness is fed in a layer-by-layer increasing manner, and the direction of the magnetic field is consistent with the axial direction of the hollow pipe pile.

10. An oriented steel fiber concrete hollow pipe pile obtained by the method according to any one of claims 6 to 9.

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