Steel fiber pull-out specimen casting mold, casting method and bond slip test method

Abstract

The invention discloses a steel fiber pull-out specimen casting mold, a casting method and a bonding slip test method, the mold comprising a bottom plate (1), a pair of top plates (2), a scale plate (3), bolts and nuts (4), bolt holes (5) and a slice (7); a pair of top plates and a scale plate are mounted on the bottom plate through bolts and nuts through the bolt holes, and the scale plate is located between the pair of top plates; a specimen casting hollow (21) for casting concrete is provided on the top plate, the specimen casting hollow runs through the top plate, a scale line (8) is provided on the scale plate, the slice covers the open end of the specimen casting hollow, one end of the steel fiber is inserted into the specimen casting hollow along the scale line, and the other end runs through the slice. The invention has variable specimen type, variable fiber type, angle and burial depth, improves specimen manufacturing efficiency and casting quality; can stably clamp the specimen during testing, can measure a more accurate fiber bonding slip relationship, is easy to install, disassemble and clean, and effectively reduces the test cost.

Description

Technical Field

[0001] The invention relates to a specimen mold, a specimen casting method and a performance testing method of an ultra-high performance concrete material, and in particular to a steel fiber pull-out specimen casting mold, a casting method and a bonding slip test method. Background Art

[0002] Concrete is one of the most widely used civil engineering materials. With the construction of large-scale engineering structures, ordinary concrete is increasingly unable to meet the requirements of engineering structures under complex environments and loads due to its high brittleness, easy cracking, low strength and long maintenance period. Although high-strength concrete can improve the compressive strength of concrete, it cannot improve its brittleness. Fiber concrete can improve the ductility of concrete, but the tensile stress-strain curve of fiber concrete is in the form of strain softening. In recent years, ultra-high performance concrete with a compressive strength of not less than 150MPa has been prepared by removing coarse aggregate, adding high-performance steel fibers and water reducers, and adding mineral admixtures. Multiple cracks are generated under tensile stress, and the tensile stress-strain curve realizes the form of strain hardening. It is a fiber-reinforced cement-based composite material with ultra-high strength, ultra-high ductility and ultra-high durability, and is gradually being used in the construction of complex civil engineering structures.

[0003] The key factor affecting the mechanical properties of ultra-high performance concrete is the interfacial bonding performance between high-performance steel fibers and cement matrix. In the initial stage of stress, the steel fibers and cement matrix bear the external force together; after the matrix cracks, the fibers between the cracks continue to bridge the matrix, thereby ensuring the tensile strain hardening performance and high strain capacity of ultra-high performance concrete. Therefore, it is particularly important to evaluate the interfacial bonding performance between the fiber and the cement matrix. Among the various existing evaluation methods, the single fiber pull-out test is the most commonly used test method. By changing the fiber type, fiber burial depth, fiber angle and matrix type, the entire process of a single steel fiber being pulled out of the matrix can be observed, thereby providing an experimental basis for studying the tensile strain hardening mechanism of ultra-high performance concrete. The single fiber pull-out test usually adopts two methods: single-sided pull-out and double-sided pull-out. The test results are generally pull-out force-fiber slip curves.

[0004] At present, the manufacturing method of single fiber pull-out specimens in the prior art still has the following shortcomings. First, the single fiber pull-out specimens manufactured in the prior art are mostly prismatic specimens, which are difficult to clamp with the chuck of the testing machine, and easily lead to damage to the interface between the fiber and the matrix. Secondly, the test personnel usually need to process a set of molds for the single-sided pull-out specimen and the double-sided pull-out specimen respectively, resulting in waste of consumables and working hours. Thirdly, due to the small size of the fiber, in order to determine the buried depth and angle of the fiber, especially in the double-sided pull-out, it is necessary to avoid the adhesion of the matrix on both sides of the fiber, and it takes a lot of time and energy to position the fiber and take other measures to avoid the adhesion of the matrix on both sides. Finally, due to the small pull-out load of the steel fiber and the small fiber slippage, the range of the load sensor of the testing machine is often much larger than the amount required to be observed. Many researchers use the displacement of the testing machine crossbeam as fiber slippage, and the resulting measurement error will significantly affect the accuracy of the test results. Summary of the invention

[0005] One of the purposes of the present invention is to provide a steel fiber pull-out specimen casting mold, which can flexibly adjust the steel fiber embedding depth and angle through scale lines and two scale plates, can change the type of specimen, and can simply and quickly produce specimens that meet various test requirements.

[0006] The second purpose of the present invention is to provide a method for casting a steel fiber pull-out specimen, in which a hollow space for casting the specimen is formed by a top plate, a bottom plate, a scale plate and a slice as a space for collective casting. The casting is simple and quick, and the variable cross-section structure ensures stable clamping of the specimen, which is convenient for testing operations.

[0007] The third object of the present invention is to provide a bonding slip test method for a steel fiber pull-out specimen, which can quickly realize the fiber-matrix interface bonding performance of a single-sided or double-sided steel fiber pull-out specimen.

[0008] The present invention is achieved in that:

[0009] A steel fiber pull-out test piece casting mold comprises a bottom plate, a pair of top plates, a scale plate, bolts and nuts, bolt holes and slices; the bottom plate, the pair of top plates and the scale plate are all provided with bolt holes, the pair of top plates are respectively installed on one surface of the bottom plate through the bolts and nuts through the bolt holes, the scale plate is installed on one surface of the bottom plate through the bolts and nuts through the bolt holes, and the scale plate is located between the pair of top plates; the pair of top plates are both provided with test piece casting hollows for casting concrete, the test piece casting hollows on the pair of top plates are relatively arranged, the test piece casting hollows penetrate the top plates, so that the opening end of the test piece casting hollows is located on the contact surface between the top plate and the scale plate; scale lines are provided on the scale plate, and the scale lines are located at the opening end of the test piece casting hollows; the slices are attached to the contact surface between the scale plate and the top plate and can completely cover the opening end of the test piece casting hollows, one end of the steel fiber is inserted into the test piece casting hollow along the scale lines, and the other end of the steel fiber penetrates the slices.

[0010] The width of the closed end of the test piece during casting and hollowing is greater than the width of the open end, so that one end of the cast steel fiber extraction test piece forms an inverted cone-shaped variable cross-section end and the other end forms a fixed cross-section end.

[0011] The scale plate comprises a first scale plate and a second scale plate, both of which are provided with scale lines and bolt holes, and the first scale plate and the second scale plate are fitted together and fixed to the base plate through bolts and nuts through the bolt holes, and the steel fiber penetrates the slice and is inserted between the first scale plate and the second scale plate.

[0012] The scale lines are composed of a plurality of notches, which are distributed in a fan shape with the center of the hollowed-out opening of the test piece as the center, the angle between two adjacent notches is 15°, and the measurement range of the notches is 0°-180°.

[0013] A method for casting a steel fiber pull-out specimen comprises the following steps:

[0014] Step 11: symmetrically install a pair of top plates on one surface of the bottom plate through bolts and nuts through the bolt holes;

[0015] Step 12: placing the first scale plate of the scale plate on one surface of the bottom plate, and the two side surfaces of the first scale plate are matched and fitted with a pair of top plates respectively;

[0016] Step 13: Guide one end of the steel fiber along the scale line angle and bury it in the hollow of the test piece casting on the top plate. The buried depth of the steel fiber in the hollow of the test piece casting is determined by measuring with a ruler;

[0017] Step 14: The other end of the steel fiber passes through the steel fiber through hole reserved on the slice and fits on the surface of the first scale plate, and the second scale plate of the scale plate is covered on the first scale plate and the other end of the steel fiber;

[0018] Step 15: The scale plate is fixed to the bottom plate through bolts and nuts through the bolt holes, so that the slice covers the specimen casting hollow opening end of a top plate, and the specimen matrix is ​​cast in the specimen casting hollow;

[0019] Step 16: Curing the specimen matrix specimen cast in step 15, removing the scale plate, releasing the other end of the steel fiber, and completing the single-side steel fiber extraction specimen;

[0020] Step 17: insert the other end of the steel fiber into the specimen casting hollow of another top plate, and cast the specimen matrix in the specimen casting hollow;

[0021] Step 18: Curing the specimen matrix specimen cast in step 16, removing the scale plate and top plate, and completing the steel fiber pull-out specimen on both sides.

[0022] In the steps 15 and 17, before pouring, oil is applied to the inner wall of the pouring space formed by the hollowing out and slicing of the specimen, and the concrete is stirred and vibrated during pouring to fill the hollowing out space of the specimen.

[0023] A method for testing the bond slip of a steel fiber pull-out specimen comprises the following steps:

[0024] Step 21: Pull out the steel fiber from the specimen and fix it through the specimen fixture, and install the load sensor on the specimen fixture;

[0025] Step 22: Two sets of connectors are symmetrically installed on both sides of the fixed cross-section end of the steel fiber pull-out specimen;

[0026] Step 23: Both sets of connectors are connected to the extensometer;

[0027] Step 24: The extensometer and the load sensor are respectively connected to the acquisition system of the testing machine, the extensometer is adjusted to a suitable displacement loading speed, and the acquisition system starts loading and data acquisition;

[0028] Step 25: When the steel fiber is pulled out from the matrix of the specimen on one side, stop the test, save the data, draw the bond-slip relationship curve of the steel fiber, extract the required indicators, and complete the test.

[0029] The specimen fixture includes a variable-section fixture and a fixed-section fixture; the variable-section end of the single-sided steel fiber pullout specimen is fixedly clamped by the variable-section fixture, and the fixed-section end of the single-sided steel fiber pullout specimen is fixedly connected to the fixed-section fixture; the two variable-section ends of the double-sided steel fiber pullout specimen are both fixedly clamped by the variable-section fixture.

[0030] The variable-section fixture is in a U-shaped structure, and the opening width of the U-shaped structure is smaller than the inner width, so that the U-shaped structure can match and clamp the variable-section end of the steel fiber pull-out specimen, and a load sensor is installed on the variable-section fixture through a fixing plate; the fixed-section fixture is provided with a U-shaped groove, and a pair of clamps are provided in the U-shaped groove, and a pair of locking bolts are threaded into the fixed-section fixture and respectively tightened on the pair of clamps, so that the pair of clamps are clamped on both sides of the steel fiber.

[0031] Each group of connecting parts includes two symmetrically arranged L-shaped connecting pieces, one end of the L-shaped connecting piece is installed on the fixed cross-section end of the steel fiber pull-out specimen, and the other end of the L-shaped connecting piece is perpendicular to the side wall of the steel fiber pull-out specimen. The other ends of the two L-shaped connecting pieces of each group of connecting parts are parallel to each other, and the distance between the other ends of the two L-shaped connecting pieces is greater than the minimum clamping range of the extensometer.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The present invention can quickly cast single-sided and double-sided steel fiber pull-out specimens using only one set of molds. The mold has a simple structure and is easy to assemble, disassemble, clean, and demould.

[0034] 2. The mold of the present invention can accurately locate the embedding angle and embedding depth of the steel fiber through the scale lines, which greatly reduces the preparation work for specimen production and effectively reduces the test cost. The embedding angle can be adjusted through the scale lines according to actual needs, and the type and embedding depth of the specimen can also be changed. It has high operational flexibility and a wide range of applications.

[0035] 3. The mold of the present invention can be used to cast a large number of steel fiber pull-out specimens at one time, saving specimen production time, with accurate size, which can speed up the test progress and reduce the test cost.

[0036] 4. The steel fiber pull-out specimen cast by the mold of the present invention can be stably clamped by the fixture through the variable-section end and the fixed-section end of precise size, which is beneficial to maintaining the stability of the specimen during testing, thereby effectively reducing the test error and the probability of fiber and matrix interface damage caused by improper operation.

[0037] 5. The testing method of the present invention uses simple equipment, is easy to install, and has simple testing operations, which is conducive to completing the fiber-matrix interface bonding slip test efficiently and accurately, and significantly reduces the error of the test. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a top view of a casting mold for a steel fiber pull-out specimen of the present invention;

[0039] Figure 2 It is a side sectional view of a casting mold for a steel fiber pull-out specimen of the present invention;

[0040] Figure 3 It is a cross-sectional view of a single-sided steel fiber pull-out specimen cast by using the steel fiber pull-out specimen casting method of the present invention;

[0041] Figure 4 It is a cross-sectional view of a double-sided steel fiber pull-out specimen cast by using the steel fiber pull-out specimen casting method of the present invention;

[0042] Figure 5 It is a test state diagram of the bonding slip test method of the steel fiber pull-out specimen on one side of the present invention;

[0043] Figure 6 It is a side sectional view of the installation of a fixed-section fixture in the bonding and slip test method of a single-sided steel fiber pull-out specimen of the present invention;

[0044] Figure 7 It is a test state diagram of the bonding slip test method of the double-sided steel fiber pull-out specimen of the present invention;

[0045] Figure 8 It is a bond-slip relationship curve of steel fiber tested by the bond-slip test method of the double-sided steel fiber pull-out specimen of the present invention.

[0046] In the figure, 1 bottom plate, 2 top plate, 21 specimen casting hollow, 3 scale plate, 31 first scale plate, 32 second scale plate, 4 bolts and nuts, 5 bolt holes, 6 steel fiber, 7 slices, 8 scale lines, 100 steel fiber pull-out specimen, 201 variable section fixture, 202 fixed section fixture, 2021 U-shaped groove, 2022 clip, 2023 locking bolt, 300 connecting piece, 400 extensometer, 500 fixing plate, 600 load sensor. DETAILED DESCRIPTION

[0047] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0048] Please see attached Figure 1 and attached Figure 2 A steel fiber pull-out specimen casting mold comprises a bottom plate 1, a pair of top plates 2, a scale plate 3, bolts and nuts 4, bolt holes 5 and a slice 7; the bottom plate 1, the pair of top plates 2 and the scale plate 3 are all provided with bolt holes 5, the pair of top plates 2 are respectively installed on one surface of the bottom plate 1 through the bolts and nuts 4 through the bolt holes 5, the scale plate 3 is installed on one surface of the bottom plate 1 through the bolts and nuts 4 through the bolt holes 5, and the scale plate 3 is located between the pair of top plates 2; the pair of top plates 2 are each provided with a specimen casting hollow 21 for pouring concrete, a The specimen casting hollow 21 on the top plate 2 is arranged relatively, and the specimen casting hollow 21 passes through the top plate 2, so that the open end of the specimen casting hollow 21 is located on the contact surface between the top plate 2 and the scale plate 3; the scale plate 3 is provided with scale lines 8, and the scale lines 8 are located at the open end of the specimen casting hollow 21; the slice 7 is attached to the contact surface between the scale plate 3 and the top plate 2 and can completely cover the open end of the specimen casting hollow 21, one end of the steel fiber 6 is inserted into the specimen casting hollow 21 along the scale line 8, and the other end of the steel fiber 6 passes through the slice 7.

[0049] The width of the closed end of the specimen casting hollow 21 is greater than the width of the open end, so that one end of the cast steel fiber pullout specimen forms an inverted cone-shaped variable cross-section end and the other end forms a fixed cross-section end. The variable cross-section end and fixed cross-section end structure of the steel fiber pullout specimen can make it easier for the specimen fixture to stably clamp the steel fiber pullout specimen and is not easy to damage the steel fiber pullout specimen.

[0050] The scale plate 3 includes a first scale plate 31 and a second scale plate 32, both of which are provided with scale lines 8 and bolt holes 5, and the first scale plate 31 and the second scale plate 32 are fitted together and fixed to the base plate 1 through bolts and nuts 4 through the bolt holes 5, and the steel fiber 6 passes through the slice 7 and is inserted between the first scale plate 31 and the second scale plate 32, so as to facilitate the positioning and fixing of the steel fiber 6.

[0051] The scale line 8 is composed of a plurality of notches, which are distributed in a fan shape with the opening center of the test piece casting hollow 21 as the center. Preferably, the notches can be processed on the scale plate 3 by an engraving machine, the length of the notches is 15 mm, the depth and width are both 0.3 mm, the angle between two adjacent notches is 15°, and the measurement range of the plurality of notches is 0°-180°, so as to meet the angle adjustment of the steel fiber 6.

[0052] The opening size of the casting hollow 21 is 30*14 mm, which is convenient for the arrangement of the steel fiber 6.

[0053] The total thickness of the first scale plate 31 and the second scale plate 32 is equivalent to the thickness of the top plate 2. Preferably, the thickness of the first scale plate 31 and the second scale plate 32 is 7 mm, and the thickness of the top plate 2 is 14 mm.

[0054] Preferably, the slice 7 can be made of a polytetrafluoroethylene film slice with a smooth surface and reserved steel fiber through holes. The length of the slice 7 is 30 mm, the width is 14 mm, and the thickness is 0.1-0.2 mm. The smooth surface of the polytetrafluoroethylene film slice can effectively prevent the cement-based material used for casting from adhering to the scale plate 3.

[0055] Preferably, the thickness of the bottom plate 1 is 6-10 mm, the diameter of the bolt hole 5 is 6 mm, the bottom plate 1, a pair of top plates 2 and the scale plate 3 can be made of acrylic plates by laser cutting, and the bolt holes 5 on the bottom plate 1, a pair of top plates 2 and the scale plate 3 correspond to each other, ensuring that a pair of top plates 2 and the scale plate 3 can be installed on one surface of the bottom plate 1, and the pair of top plates 2 are symmetrically fitted on both sides of the scale plate 3.

[0056] Preferably, a plurality of specimen casting hollows 21 can be provided on a top plate 2, so that a plurality of steel fiber extraction specimens can be cast at one time through the casting mold of the present invention, which is suitable for batch production and can speed up the test progress.

[0057] Please see attached Figure 3 and attached Figure 4 , a casting method for a steel fiber pull-out specimen comprises the following steps:

[0058] Step 11: A pair of top plates 2 are symmetrically mounted on one surface of the bottom plate 1 through bolts and nuts 4 and bolt holes 5 .

[0059] Step 12: Place the first scale plate 31 of the scale plate 3 on one surface of the bottom plate 1 , and the two side surfaces of the first scale plate 31 are matched and fitted with a pair of top plates 2 respectively.

[0060] Step 13: Guide one end of the steel fiber 6 along the angle of the scale line 8 and bury it in the specimen casting hollow 21 of the top plate 2. According to the test design requirements, the angle of the steel fiber 6 can be adjusted and positioned by the scale line 8, and the buried depth of the steel fiber 6 in the specimen casting hollow 21 can be determined and adjusted by measuring with a ruler, thereby ensuring the accuracy of the buried angle and buried depth of the steel fiber 6, thereby improving the accuracy of the bond slip test.

[0061] Step 14: The other end of the steel fiber 6 passes through the steel fiber through hole reserved on the slice 7 and adheres to the surface of the first scale plate 31. Tweezers can be used to temporarily fix the steel fiber 6 to prevent it from shifting, and the second scale plate 32 of the scale plate 3 covers the first scale plate 31 and the other end of the steel fiber 6.

[0062] Step 15: The scale plate 3 is fixed to the base plate 1 by means of bolts and nuts 4 through bolt holes 5, thereby fixing the steel fiber 6 between the first scale plate 31 and the second scale plate 32, so that the slice 7 covers the open end of the specimen casting hollow 21 of a top plate 2, and the specimen matrix is ​​cast in the specimen casting hollow 21.

[0063] Preferably, before pouring, oil can be applied on the inner wall of the pouring space formed by the hollowing out 21 and the slice 7 of the specimen to facilitate demoulding at a later stage.

[0064] Preferably, ultra-high performance concrete may be used for casting the base material, and appropriate stirring and vibration may be performed during casting to allow the ultra-high performance concrete to fill the space of the test piece casting hollow 21 .

[0065] Step 16: Curing the specimen matrix cast in step 15 for 1 day, removing the scale plate 3, releasing the other end of the steel fiber 6, and completing the single-sided steel fiber extraction specimen 100.

[0066] Step 17: insert the other end of the steel fiber 6 into the specimen casting hollow 21 of another top plate 2, and cast the specimen matrix in the specimen casting hollow 21.

[0067] Preferably, before pouring, oil can be applied on the inner wall of the pouring space formed by the hollowing out 21 and the slice 7 of the specimen to facilitate demoulding at a later stage.

[0068] Preferably, ultra-high performance concrete may be used for casting the base material, and appropriate stirring and vibration may be performed during casting to allow the ultra-high performance concrete to fill the space of the test piece casting hollow 21 .

[0069] Step 18: Curing the specimen matrix cast in step 16 for 2 days, removing the scale plate 3 and the top plate 2, and completing the double-sided steel fiber pull-out specimen 100.

[0070] Please see attached Figure 5 and attached Figure 7 , a bond slip test method for a steel fiber pull-out specimen, comprising the following steps:

[0071] Step 21: Fix the steel fiber pull-out specimen 100 by a specimen fixture, and install a load sensor 600 on the specimen fixture. The range of the load sensor 600 used should be slightly larger than the maximum load of the steel fiber pull-out specimen, and the error should not be higher than 0.5% of the range. The specimen fixture can be made of steel material by laser or wire cutting technology, with high strength and not easy to deform, so that it can reliably and matchingly clamp the fixed cross-section end and the variable cross-section end of the steel fiber pull-out specimen 100.

[0072] The specimen fixture includes a variable-section fixture 201 and a fixed-section fixture 202; the variable-section end of the single-sided steel fiber pullout specimen is fixedly clamped by the variable-section fixture 201, and the fixed-section end of the single-sided steel fiber pullout specimen is fixedly connected to the fixed-section fixture 202; both variable-section ends of the double-sided steel fiber pullout specimen are fixedly clamped by the variable-section fixture 201; the single-sided or double-sided steel fiber pullout specimen 100 can be effectively fixed, which is convenient for maintaining the stability of the steel fiber pullout specimen 100 during the test, and does not damage the steel fiber pullout specimen 100.

[0073] The variable cross-section fixture 201 is in a U-shaped structure, and the opening width of the U-shaped structure is smaller than the inner width, so that the U-shaped structure can match and clamp the variable cross-section end of the steel fiber pullout specimen 100, and is not easy to fall off, thereby improving the fixing reliability of the steel fiber pullout specimen 100. The load sensor 600 is installed on the variable cross-section fixture 201 through the fixing plate 500.

[0074] Please see attached Figure 6 The fixed-section clamp 202 is provided with a U-shaped groove 2021, and a pair of clamps 2022 are provided in the U-shaped groove 2021. A pair of locking bolts 2023 are screwed into the fixed-section clamp 202 and respectively tightened on the pair of clamps 2022, so that the pair of clamps 2022 are clamped on both sides of the steel fiber 6, ensuring stable clamping of the fixed-section end of the single-sided steel fiber pull-out specimen.

[0075] Step 22: Two groups of connecting pieces 300 are symmetrically installed on both sides of the fixed cross-sectional end of the steel fiber pull-out specimen 100. The specific installation method is: each group of connecting two pieces 300 includes two symmetrically arranged L-shaped connecting pieces, one end of the L-shaped connecting piece is bonded and installed on the fixed cross-sectional end of the steel fiber pull-out specimen 100 by 502 glue, and the other end of the L-shaped connecting piece is perpendicular to the side wall of the steel fiber pull-out specimen 100, and the other ends of the two L-shaped connecting pieces of each group of connecting pieces 300 are parallel to each other.

[0076] In the test of the double-sided steel fiber pullout specimen 100, the two L-shaped connecting pieces are symmetrically arranged on the double-sided specimen base of the steel fiber pullout specimen 100. In the test of the single-sided steel fiber pullout specimen 100, the two L-shaped connecting pieces are symmetrically arranged on the specimen base of the steel fiber pullout specimen 100 and the fixed section fixture 202, and the width of the fixed section fixture 202 should be equivalent to the width of the fixed section end of the single-sided steel fiber pullout specimen 100 to ensure symmetrical installation and uniform force of the two L-shaped connecting pieces.

[0077] Step 23: Both sets of connectors 300 are connected to the extensometer 400, and the minimum clamping range of the extensometer 400 is slightly smaller than the spacing between the other ends of the two L-shaped connectors, ensuring that the extensometer 400 is reliably connected to the steel fiber pull-out specimen 100 through the connector 300.

[0078] Step 24: The extensometer 400 and the load sensor 600 are respectively connected to the acquisition system of the testing machine, the extensometer 400 is adjusted to a suitable displacement loading speed, and the acquisition system starts loading and data acquisition. Preferably, the minimum displacement loading speed of the testing machine is not higher than 0.5 mm / min, and the acquisition system of the testing machine can collect the load sensor data of the load sensor 600 and the deformation data of the extensometer 400. The range of the extensometer 400 should be slightly larger than the slip value that may be generated by the steel fiber pull-out specimen 100, and its accuracy should not be less than 0.001 mm.

[0079] Step 25: When the steel fiber 6 is pulled out from the matrix of the specimen on one side, the test is stopped, the data is saved, the bond-slip relationship curve of the steel fiber is drawn, the required indicators are extracted, and the test is completed.

[0080] In the tests of the single-sided steel fiber pull-out specimen 100 and the double-sided steel fiber pull-out specimen 100, the specimen fixture, connector 300, extensometer 400, testing machine and other equipment and accessories used are all kept consistent to ensure the accuracy of the test.

[0081] Embodiment 1:

[0082] The casting material is ultra-high performance concrete.

[0083] Steel fiber type: diameter 0.3mm, length 25mm, hook-shaped end.

[0084] Steel fiber angle: 0 degrees.

[0085] Steel fiber burial depth: 5mm and 10mm.

[0086] PTFE slice size: thickness 0.2mm, length 30mm, width 14mm.

[0087] The size of the bottom plate 1 is: length 230mm, width 200mm, thickness 6mm. There are 4 rows of bolt holes 5 on the bottom plate 1. The center of the first row of bolt holes 5 is 20mm away from the end of the bottom plate 1. The distance between the second row of bolt holes 5 and the first row of bolt holes 5 is 40mm. The third and fourth rows of bolt holes 5 are symmetrically arranged with the first and second rows of bolt holes 5 about the central axis of the length direction of the bottom plate 1. The diameter of the bolt holes 5 is 3mm, and the distance between adjacent bolt holes 5 is 70mm.

[0088] The dimensions of the top plate 2 are as follows: length 230 mm, width 80 mm, thickness 14 mm, two rows of bolt holes 5 are opened on the top plate 2, the center of the bolt hole 5 is 20 mm away from the end of the top plate 2, the spacing between the bolt holes 5 is 70 mm, and the spacing between the two rows of bolt holes 5 is 40 mm. Three test specimen casting hollows 21 are set on the top plate 2.

[0089] The dimensions of the specimen casting hollow 21 are: height 60mm, opening end width 30mm, top width 55mm, and rounded corners on both sides of the top. The variable section end length of the specimen casting hollow 21 is 40mm, and the fixed section end length is 20mm.

[0090] The dimensions of the first scale plate 31 and the second scale plate 32 are: length 230mm, width 40mm, thickness 7mm. Three scale lines 8 are set at intervals at both ends of the scale plate 3, and the distance between adjacent scale lines 8 is 70mm. A row of bolt holes 5 is opened along the center line of the length direction of the plate. The bolt holes 5 have a diameter of 3mm and a distance of 70mm.

[0091] Step 11: A pair of top plates 2 are symmetrically mounted on one surface of the bottom plate 1 through bolts and nuts 4 and bolt holes 5 .

[0092] Step 12: Place the first scale plate 31 of the scale plate 3 on one surface of the bottom plate 1 , and the two side surfaces of the first scale plate 31 are matched and fitted with a pair of top plates 2 respectively.

[0093] Step 13: One ends of two steel fibers 6 are respectively embedded in the two test piece casting hollows 21 along the 0 degree of the scale line 8, and the embedding depths of the two steel fibers 6 are 5 mm and 10 mm.

[0094] Step 14: The other end of the steel fiber 6 passes through the steel fiber through hole reserved on the slice 7 and adheres to the surface of the first scale plate 31. The steel fiber 6 is temporarily fixed with tweezers, and the second scale plate 32 of the scale plate 3 covers the first scale plate 31 and the other end of the steel fiber 6.

[0095] Step 15: The scale plate 3 is fixed to the base plate 1 by means of bolts and nuts 4 through bolt holes 5, thereby fixing the steel fiber 6 between the first scale plate 31 and the second scale plate 32, so that the slice 7 covers the open end of the specimen casting hollow 21 of a top plate 2, the inner wall of the casting space is oiled, and two specimen bases are cast in the specimen casting hollow 21 with ultra-high performance concrete.

[0096] Step 16: The two specimen substrates cast in step 15 are cured for 1 day, the scale plate 3 is removed, the other end of the steel fiber 6 is released, and the single-sided steel fiber extraction specimen 100 is completed.

[0097] Step 21: The steel fiber is pulled out of the specimen 100 and fixed by a specimen fixture, and a load sensor 600 is installed on the specimen fixture;

[0098] Step 22: symmetrically install two sets of connecting pieces 300 on both sides of the fixed cross-section end of the steel fiber pull-out specimen 100;

[0099] Step 23: Both sets of connecting pieces 300 are connected to the extensometer 400;

[0100] Step 24: The extensometer 400 and the load sensor 600 are respectively connected to the acquisition system of the testing machine, the extensometer 400 is adjusted to a suitable displacement loading speed, and loading and data acquisition are started;

[0101] Step 25: When the steel fiber 6 is pulled out from the matrix of one side of the specimen, stop the test, save the data, and draw the bond-slip relationship curve of the steel fiber. Figure 8 In the figure, the bond-slip relationship curve of the steel fiber drawn with a straight line represents the steel fiber pull-out specimen 100 with a buried depth of 5 mm, and the bond-slip relationship curve of the steel fiber drawn with a dotted line represents the steel fiber pull-out specimen 100 with a buried depth of 10 mm. The required performance indicators can be extracted from the bond-slip relationship curve of the steel fiber to complete the test.

[0102] The above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A steel fiber pull-out specimen casting mold, characterized by: The invention comprises a bottom plate (1), a pair of top plates (2), a scale plate (3), bolts and nuts (4), bolt holes (5) and a slice (7); the bottom plate (1), the pair of top plates (2) and the scale plate (3) are all provided with bolt holes (5); the pair of top plates (2) are respectively installed on one surface of the bottom plate (1) through bolts and nuts (4) through the bolt holes (5); the scale plate (3) is installed on one surface of the bottom plate (1) through bolts and nuts (4) through the bolt holes (5); the scale plate (3) is located between the pair of top plates (2); the pair of top plates (2) are all provided with a test piece casting hollow (21) for casting concrete; the pair of top plates (2) are The specimen casting hollows (21) on the top plate (2) are arranged opposite to each other, and the specimen casting hollows (21) penetrate the top plate (2), so that the opening end of the specimen casting hollows (21) is located on the contact surface between the top plate (2) and the scale plate (3); the scale plate (3) is provided with scale lines (8), and the scale lines (8) are located at the opening end of the specimen casting hollows (21); the slice (7) is attached to the contact surface between the scale plate (3) and the top plate (2) and can completely cover the opening end of the specimen casting hollows (21), one end of the steel fiber (6) is inserted into the specimen casting hollows (21) along the scale lines (8), and the other end of the steel fiber (6) penetrates the slice (7); The width of the closed end of the test piece casting hollow (21) is greater than the width of the open end, so that after the casting, the steel fiber is pulled out of the test piece, one end forms an inverted cone-shaped variable cross-section end, and the other end forms a fixed cross-section end; The scale plate (3) comprises a first scale plate (31) and a second scale plate (32), and scale lines (8) and bolt holes (5) are provided on the first scale plate (31) and the second scale plate (32). The first scale plate (31) and the second scale plate (32) are arranged in close contact with each other and are fixed on the bottom plate (1) through bolts and nuts (4) through the bolt holes (5). The steel fiber (6) penetrates the slice (7) and is inserted between the first scale plate (31) and the second scale plate (32).

2. The steel fiber pull-out specimen casting mold according to claim 1 is characterized in that: The scale line (8) is composed of a plurality of notches, which are distributed in a fan shape with the opening center of the test piece casting hollow (21) as the center, the angle between two adjacent notches is 15°, and the measurement range of the plurality of notches is 0°-180°.

3. A method for casting a specimen using the steel fiber extraction specimen casting mold according to claim 1, characterized in that: The following steps are involved: Step 11: symmetrically install a pair of top plates (2) on one surface of the bottom plate (1) through bolts and nuts (4) and bolt holes (5); Step 12: placing the first scale plate (31) of the scale plate (3) on one surface of the bottom plate (1), and the two side surfaces of the first scale plate (31) are matched and fitted with a pair of top plates (2) respectively; Step 13: Guide one end of the steel fiber (6) along the angle of the scale line (8) and bury it in the test piece casting hollow (21) of the top plate (2). The buried depth of the steel fiber (6) in the test piece casting hollow (21) is determined by measuring with a ruler; Step 14: The other end of the steel fiber (6) passes through the steel fiber through hole reserved on the slice (7) and is attached to the surface of the first scale plate (31), and the second scale plate (32) of the scale plate (3) is covered on the first scale plate (31) and the other end of the steel fiber (6); Step 15: The scale plate (3) is fixed to the bottom plate (1) through bolts and nuts (4) via bolt holes (5), so that the slice (7) covers the open end of the specimen casting hollow (21) of a top plate (2), and the specimen matrix is ​​cast in the specimen casting hollow (21); Step 16: curing the specimen matrix specimen cast in step 15, removing the scale plate (3), releasing the other end of the steel fiber (6), and completing the single-sided steel fiber extraction specimen (100); Step 17: inserting the other end of the steel fiber (6) into the specimen casting hollow (21) of another top plate (2), and casting the specimen matrix in the specimen casting hollow (21); Step 18: Curing the specimen base specimen cast in step 16, removing the scale plate (3) and the top plate (2), and completing the double-sided steel fiber pull-out specimen (100).

4. The method for casting a steel fiber pull-out specimen according to claim 3 is characterized in that: In the above-mentioned steps 15 and 17, before pouring, oil is applied to the inner wall of the pouring space formed by the hollowing out (21) and the slice (7) of the specimen, and the concrete is stirred and vibrated during pouring to fill the space of the hollowing out (21) of the specimen.

5. A bonding slip test method for a specimen cast by the steel fiber pull-out specimen casting method according to claim 3, characterized in that: The following steps are involved: Step 21: The steel fiber is pulled out of the test piece (100) and fixed by a test piece fixture, and a load sensor (600) is installed on the test piece fixture; Step 22: symmetrically installing two sets of connecting pieces (300) on both sides of the fixed cross-section end of the steel fiber pull-out specimen (100); Step 23: Both sets of connecting parts (300) are connected to the extensometer (400); Step 24: The extensometer (400) and the load sensor (600) are respectively connected to the acquisition system of the testing machine, the extensometer (400) is adjusted to a suitable displacement loading speed, and the acquisition system starts loading and data acquisition; Step 25: When the steel fiber (6) is pulled out from the matrix of the specimen on one side, the test is stopped, the data is saved, the bond-slip relationship curve of the steel fiber is drawn, the required index is extracted, and the test is completed.

6. The bonding slip test method of a steel fiber pull-out specimen according to claim 5, characterized in that: The specimen fixture comprises a variable-section fixture (201) and a fixed-section fixture (202); the variable-section end of the single-sided steel fiber pullout specimen is fixedly clamped by the variable-section fixture (201), and the fixed-section end of the single-sided steel fiber pullout specimen is fixedly connected to the fixed-section fixture (202); and both variable-section ends of the double-sided steel fiber pullout specimen are fixedly clamped by the variable-section fixture (201).

7. The bonding slip test method of a steel fiber pull-out specimen according to claim 6, characterized in that: The variable-section clamp (201) is in a U-shaped structure, and the opening width of the U-shaped structure is smaller than the inner width, so that the U-shaped structure can match and clamp the variable-section end of the steel fiber pull-out specimen (100), and a load sensor (600) is installed on the variable-section clamp (201) through a fixing plate (500); the fixed-section clamp (202) is provided with a U-shaped groove (2021), and a pair of clamping plates (2022) are provided in the U-shaped groove (2021), and a pair of locking bolts (2023) are screwed into the fixed-section clamp (202) and respectively pressed against the pair of clamping plates (2022), so that the pair of clamping plates (2022) are clamped on both sides of the steel fiber (6).

8. The bonding slip test method of a steel fiber pull-out specimen according to claim 5, characterized in that: Each group of connecting parts (300) comprises two symmetrically arranged L-shaped connecting pieces, one end of the L-shaped connecting piece is installed at the fixed cross-section end of the steel fiber pull-out specimen (100) through (502), the other end of the L-shaped connecting piece is perpendicular to the side wall of the steel fiber pull-out specimen (100), and the other ends of the two L-shaped connecting pieces of each group of connecting parts (300) are parallel to each other, and the distance between the other ends of the two L-shaped connecting pieces is greater than the minimum clamping range of the extensometer (400).

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