Method for testing shear performance of ultra-high performance concrete

Abstract

The application discloses a method for testing the shearing performance of ultra-high performance concrete, and comprises the following steps: preparing a prefabricated crack test block; two cracks are arranged on the vertical section of the prefabricated crack test block, the cracks comprise a first crack and a second crack, the first crack is connected with the second crack, an obtuse angle is formed at the connection, the two second cracks are parallel to the vertical section of the prefabricated crack test block and are located on the same horizontal line, the free ends of the two first cracks are respectively located on the surface of the prefabricated crack test block, the two first cracks are parallel, and an included angle alpha is formed between the first crack and the height direction of the prefabricated crack test block; the prefabricated crack test block is placed on a universal testing machine to perform a shearing performance test, and the maximum failure load of the prefabricated crack test block is obtained; and the shearing strength is calculated according to the maximum failure load. The preparation of the prefabricated crack test block is simple, convenient and cost-saving; the shearing test of the concrete is performed in a tensile or compressive mode, axial force is converted into shearing force, and test errors caused by insufficient double-sided shearing force are avoided.

Description

Technical Field

[0001] This invention belongs to the technical field of concrete performance testing methods, and relates to a method for testing the shear properties of ultra-high performance concrete. Background Technology

[0002] The shear strength of concrete provides an important basis for judging the integrity and stability of concrete structures. It is one of the fundamental mechanical indicators of concrete and a crucial foundation for strength theory research and finite element analysis. In recent years, ultra-high performance concrete (UHPC) has been widely used in various engineering fields such as bridges, buildings, and hydraulic structures due to its superior mechanical and durability properties. The shear strength of concrete has a certain quantitative relationship with its cubic compressive strength; therefore, the shear strength of UHPC is higher than that of ordinary concrete. However, the testing methods for concrete shear strength are not uniform both domestically and internationally, leading to significant discrepancies in research conclusions.

[0003] Currently, the shear test method that is relatively simple to operate and most easily implemented in the laboratory is the test method specified in the "Test Procedure for Hydraulic Concrete" DL / T 5150-2017. The specification stipulates that a cube with a side length of 150mm is used, and the specimen is sheared on both sides using a shear tester. The displacement in the normal and shear directions is measured using a dial indicator. However, this method has a complex test process, limited instrument functionality, and complicated calculation parameters and processes. Summary of the Invention

[0004] The purpose of this invention is to provide a method for testing the shear properties of ultra-high performance concrete, which solves the problem of complex testing procedures in the prior art.

[0005] The technical solution adopted in this invention is a method for testing the shear properties of ultra-high performance concrete, comprising the following steps:

[0006] Step 1: Prepare precast crack test blocks;

[0007] The precast crack test block is I-shaped. The vertical section of the precast crack test block has two cracks, including a first crack and a second crack. The first crack connects to the second crack, and the connection point forms an obtuse angle. The two second cracks are parallel to the vertical section of the precast crack test block and are located on the same horizontal line. The free ends of the two first cracks are located on the surface of the precast crack test block, and the two first cracks are parallel. The first cracks form an angle α with the height direction of the precast crack test block.

[0008] Step 2: Place the precast crack specimen on a universal testing machine to conduct a shear performance test and obtain the maximum failure load of the precast crack specimen.

[0009] Step 3: Calculate the shear strength based on the maximum failure load:

[0010]

[0011] In the above formula, τ represents the shear strength, with units of MPa and F. τmax The maximum destructive load is expressed in N, m is the vertical distance between the two steel plates in mm, and t is the thickness of the precast crack test block in mm.

[0012] The invention is further characterized by:

[0013] The length n of the second crack (2) is 8mm to 12mm, the thickness of the first crack (1) and the second crack (2) is 1mm to 3mm, the distance m between the two second cracks (2) is 10mm to 15mm, and α is 55° to 65°; the height of the precast crack test block is 300mm to 320mm, the width is 100mm, the thickness is 45mm to 55mm, and the height h of the vertical section is 140mm to 160mm.

[0014] In step 2, the loading rate for the shear performance test is 0.2 MPa / min to 0.4 MPa / min.

[0015] In step 2, if the shear performance test is a compressive shear performance test, adjust the ball joint of the universal testing machine to make the precast crack specimen contact the loading plane evenly and uniformly.

[0016] In step 2, if the shear performance test is a tensile shear performance test, the fixture is installed on the universal testing machine, the precast crack specimen is put into the fixture and the center line of the precast crack specimen is aligned with the axis of the fixture, and pre-tensioning is performed before the test.

[0017] The preload during the pre-tensioning process is 15% to 20% of the failure load.

[0018] The beneficial effects of this invention are as follows: The method for testing the shear strength of ultra-high performance concrete is simple to prepare using precast cracked test blocks, can be performed using conventional equipment and instruments, is convenient to operate, and saves costs; the concrete shear test is conducted by both tension and compression methods, and by converting axial force into shear force, the test error caused by insufficient shear force on both sides is avoided; the simple mechanical processing formula can accurately calculate the shear strength, optimizing the complicated calculation process in the test specifications. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the precast crack test block in the shear performance testing method for ultra-high performance concrete of the present invention;

[0020] Figure 2 This is a schematic diagram of the compressive shear stress of a precast crack specimen in the shear performance testing method for ultra-high performance concrete of the present invention.

[0021] Figure 3 This is a schematic diagram of the tensile shear stress of a precast cracked specimen in the shear performance testing method for ultra-high performance concrete of this invention.

[0022] In the diagram, 1 is the first crack, and 2 is the second crack. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0024] The method for testing the shear properties of ultra-high performance concrete includes the following steps:

[0025] Step 1: Prepare precast crack test blocks, such as Figure 1 As shown, the precast crack test block is I-shaped. The vertical section of the precast crack test block has two cracks, including a first crack 1 and a second crack 2. The first crack 1 connects to the second crack 2, and the connection point forms an obtuse angle. The two second cracks 2 are parallel to the vertical section of the precast crack test block and are located on the same horizontal line. The free ends of the two first cracks 1 are located on the surface of the precast crack test block, and the two first cracks 1 are parallel. The first crack 1 forms an angle α with the height direction of the precast crack test block.

[0026] The length n of the second crack 2 is 8mm to 12mm, the thickness of the first crack 1 and the second crack 2 is 1mm to 3mm, the distance m between the two second cracks 2 is 10mm to 15mm, and α is 55° to 65°; the height of the precast crack test block is 300mm to 320mm, the width is 100mm, the thickness is 45mm to 55mm, and the height h of the vertical section is 140mm to 160mm.

[0027] The specific preparation method for precast crack test blocks is as follows: First, two precast crack steel plates are arranged as follows... Figure 1 The arrangement of cracks is fixed to prevent them from loosening, falling off, or deflecting. Concrete is then poured onto the precast cracked steel plate. When the concrete has initially set, the precast cracked steel plate is gently loosened and pulled out. When pulling out the steel plate, the tip of the crack in the specimen must not be damaged. Cracks are formed at the location of the precast cracked steel plate to obtain a precast cracked specimen. After standard curing for 24 to 48 hours, the specimen is demolded and placed in a standard curing room for curing until the specified age before being taken out for testing.

[0028] Step 2: Place the precast crack specimen on a WDW-100 microcomputer-controlled electronic universal testing machine to conduct tensile or compressive shear performance tests to obtain the maximum failure load of the precast crack specimen; the loading rate for the shear performance test is 0.2MPa / min to 0.4MPa / min.

[0029] If the shear performance test is a compressive shear performance test, adjust the ball joint of the universal testing machine to make the precast crack specimen contact the lower pressure plate plane evenly and smoothly, and apply continuous and uniform loading to the precast crack specimen to obtain the maximum destructive load of the precast crack specimen.

[0030] If the shear performance test is a tensile shear performance test, a fixture of the same size as the precast crack specimen is installed on the universal testing machine. The precast crack specimen is placed into the fixture, and the centerline of the precast crack specimen is aligned with the axis of the fixture. Two pre-tensioning tests are performed before the test, with the pre-tension load being 15% to 20% of the failure load. The purpose of the pre-tensioning is to adjust the axis of the specimen to coincide with the loading axis of the testing machine, so as to avoid inaccurate test results due to eccentric loading. After that, the formal test is carried out to obtain the maximum failure load of the precast crack specimen.

[0031] Step 3: Calculate the shear strength based on the maximum failure load:

[0032]

[0033] In the above formula, τ is the shear strength (MPa), and F τmax The maximum destructive load (N) is given, m is the vertical distance between the two steel plates (mm), and t is the thickness of the precast crack test block (mm).

[0034] Through the above methods, the present invention provides a simple method for testing the shear strength of ultra-high performance concrete. The preparation of precast cracked test blocks is straightforward, and the test can be conducted using conventional equipment and instruments, making it convenient and cost-effective. By performing shear tests on concrete through both tension and compression, the axial force is converted into shear force, avoiding test errors caused by insufficient shear force on both sides. The use of simple mechanical formulas allows for more accurate calculation of shear strength, optimizing the complex calculation process in test specifications.

[0035] Example 1

[0036] Step 1: First, embed two precast cracked steel plates, then pour concrete. When the concrete has initially set, gently loosen and pull out the precast cracked steel plates to obtain an I-shaped precast cracked test block. The vertical section of the precast cracked test block has two cracks, including a first crack 1 and a second crack 2. The first crack 1 connects to the second crack 2, forming an obtuse angle at the connection point. The two second cracks 2 are parallel to the vertical section of the precast cracked test block and located on the same horizontal line. The free ends of the two first cracks 1 are located on the surface of the precast cracked test block and are parallel. The first crack 1 forms a 65° angle with the height direction of the precast cracked test block. The length n of the second crack 2 is 10mm, the thickness of the first crack 1 and the second crack 2 is 2mm, and the distance m between the two second cracks 2 is 15mm. The precast cracked test block has a height of 300mm, a width of 100mm, a thickness of 55mm, and a vertical section height h of 140mm.

[0037] Step 2: Place the precast crack specimen on a universal testing machine to conduct a compressive shear performance test, see... Figure 2 The ball joint of the universal testing machine was adjusted to make the precast crack specimen contact the lower pressure plate plane evenly and smoothly. The precast crack specimen was continuously and uniformly loaded at a loading speed of 0.2 MPa / min, and the maximum destructive load of the precast crack specimen was obtained as 4125 N.

[0038] Step 3: Calculate the shear strength, as shown in Table 1.

[0039] Example 2

[0040] Step 1: First, embed two precast cracked steel plates, then pour concrete. When the concrete has initially set, gently loosen and pull out the precast cracked steel plates to obtain an I-shaped precast cracked test block. The vertical section of the precast cracked test block has two cracks, including a first crack 1 and a second crack 2. The first crack 1 connects to the second crack 2, forming an obtuse angle at the connection point. The two second cracks 2 are parallel to the vertical section of the precast cracked test block and located on the same horizontal line. The free ends of the two first cracks 1 are located on the surface of the precast cracked test block and are parallel to each other. The first crack 1 forms a 55° angle with the height direction of the precast cracked test block. The length n of the second crack 2 is 10mm, the thickness of the first crack 1 and the second crack 2 is 2mm, and the distance m between the two second cracks 2 is 10mm. The precast cracked test block has a height of 300mm, a width of 100mm, a thickness of 45mm, and a vertical section height h of 140mm.

[0041] Step 2: Place the precast crack specimen on a universal testing machine to conduct a compressive shear performance test. Adjust the ball joint of the universal testing machine to make the precast crack specimen and the lower pressure plate plane make flat and uniform contact. Apply continuous and uniform loading to the precast crack specimen at a loading speed of 0.3 MPa / min to obtain the maximum failure load of the precast crack specimen of 2340 N.

[0042] Step 3: Calculate the shear strength, as shown in Table 1.

[0043] Example 3

[0044] Step 1: First, embed two precast cracked steel plates, then pour concrete. When the concrete has initially set, gently loosen and pull out the precast cracked steel plates to obtain an I-shaped precast cracked test block. The vertical section of the precast cracked test block has two cracks, including a first crack 1 and a second crack 2. The first crack 1 connects to the second crack 2, forming an obtuse angle at the connection point. The two second cracks 2 are parallel to the vertical section of the precast cracked test block and located on the same horizontal line. The free ends of the two first cracks 1 are located on the surface of the precast cracked test block and are parallel to each other. The first crack 1 forms a 60° angle with the height direction of the precast cracked test block. The length n of the second crack 2 is 10mm, the thickness of the first crack 1 and the second crack 2 is 2mm, and the distance m between the two second cracks 2 is 10mm. The precast cracked test block has a height of 300mm, a width of 100mm, a thickness of 55mm, and a vertical section height h of 140mm.

[0045] Step 2: Place the precast crack specimen on a universal testing machine to conduct a compressive shear performance test. Adjust the ball joint of the universal testing machine to make the precast crack specimen and the lower pressure plate plane make flat and uniform contact. Apply continuous and uniform loading to the precast crack specimen at a loading speed of 0.4 MPa / min to obtain the maximum failure load of the precast crack specimen of 2972 ​​N.

[0046] Step 3: Calculate the shear strength, as shown in Table 1.

[0047] Example 4

[0048] Step 1: First, embed two precast cracked steel plates, then pour concrete. When the concrete has initially set, gently loosen and pull out the precast cracked steel plates to obtain an I-shaped precast cracked test block. The vertical section of the precast cracked test block has two cracks, including a first crack 1 and a second crack 2. The first crack 1 connects to the second crack 2, forming an obtuse angle at the connection point. The two second cracks 2 are parallel to the vertical section of the precast cracked test block and located on the same horizontal line. The free ends of the two first cracks 1 are located on the surface of the precast cracked test block and are parallel to each other. The first crack 1 forms a 65° angle with the height direction of the precast cracked test block. The length n of the second crack 2 is 10mm, the thickness of the first crack 1 and the second crack 2 is 2mm, and the distance m between the two second cracks 2 is 15mm. The precast cracked test block has a height of 300mm, a width of 100mm, a thickness of 55mm, and a vertical section height h of 140mm.

[0049] Step 2: Install a fixture of the same size as the precast crack specimen on the universal testing machine. Fit the precast crack specimen into the fixture, aligning the centerline of the specimen with the fixture axis. Perform two pre-tensioning operations before the test, with the tensioning direction shown in the diagram. Figure 3The preload was 15% of the failure load; then a formal test was conducted with a loading rate of 0.2 MPa / min, and the maximum failure load of the precast cracked specimen was 4042 N.

[0050] Step 3: Calculate the shear strength, as shown in Table 1.

[0051] Example 5

[0052] Step 1: First, embed two precast cracked steel plates, then pour concrete. When the concrete has initially set, gently loosen and pull out the precast cracked steel plates to obtain an I-shaped precast cracked test block. The vertical section of the precast cracked test block has two cracks, including a first crack 1 and a second crack 2. The first crack 1 connects to the second crack 2, forming an obtuse angle at the connection point. The two second cracks 2 are parallel to the vertical section of the precast cracked test block and located on the same horizontal line. The free ends of the two first cracks 1 are located on the surface of the precast cracked test block and are parallel to each other. The first crack 1 forms a 60° angle with the height direction of the precast cracked test block. The length n of the second crack 2 is 10mm, the thickness of the first crack 1 and the second crack 2 is 2mm, and the distance m between the two second cracks 2 is 15mm. The precast cracked test block has a height of 300mm, a width of 100mm, a thickness of 45mm, and a vertical section height h of 140mm.

[0053] Step 2: Install a fixture of the same size as the precast crack specimen on the universal testing machine. Fit the precast crack specimen into the fixture and align the centerline of the precast crack specimen with the axis of the fixture. Perform two pre-tensioning tests before the test, with the pre-tensioning load being 15% of the failure load. Then, conduct the formal test with a loading speed of 0.3 MPa / min. The maximum failure load of the precast crack specimen is 3443 N.

[0054] Step 3: Calculate the shear strength, as shown in Table 1.

[0055] Example 6

[0056] Step 1: First, embed two precast cracked steel plates, then pour concrete. When the concrete has initially set, gently loosen and pull out the precast cracked steel plates to obtain an I-shaped precast cracked test block. The vertical section of the precast cracked test block has two cracks, including a first crack 1 and a second crack 2. The first crack 1 connects to the second crack 2, forming an obtuse angle at the connection point. The two second cracks 2 are parallel to the vertical section of the precast cracked test block and located on the same horizontal line. The free ends of the two first cracks 1 are located on the surface of the precast cracked test block and are parallel to each other. The first crack 1 forms a 55° angle with the height direction of the precast cracked test block. The length n of the second crack 2 is 10mm, the thickness of the first crack 1 and the second crack 2 is 2mm, and the distance m between the two second cracks 2 is 10mm. The precast cracked test block has a height of 300mm, a width of 100mm, a thickness of 45mm, and a vertical section height h of 140mm.

[0057] Step 2: Install a fixture of the same size as the precast crack specimen on the universal testing machine. Fit the precast crack specimen into the fixture and align the centerline of the precast crack specimen with the axis of the fixture. Perform two pre-tensioning tests before the test, with the pre-tensioning load being 15% of the failure load. Then, conduct the formal test with a loading speed of 0.4 MPa / min. The maximum failure load of the precast crack specimen is 2160 N.

[0058] Step 3: Calculate the shear strength, as shown in Table 1.

[0059] The test results of the above embodiments are shown in Table 1.

[0060] Table 1

[0061]

[0062] The following results can be obtained by combining the experimental results of Examples 1 to 4:

[0063] When the loading rate is between 0.2 MPa / min and 0.4 MPa / min, the impact on the shear strength of ultra-high performance concrete is minimal. Loading rates within this range can ensure that ultra-high performance concrete obtains relatively accurate tensile strength within a certain time. When the distance between the two second cracks is between 10 mm and 15 mm, and the angle between the first crack 1 and the second crack is between 55° and 65°, the impact on the shear strength of ultra-high performance concrete is small. Within this range, the accuracy of the concrete shear performance test can be guaranteed. As shown in Table 1, within the range of various factors, the shear strength of ultra-high performance concrete is approximately 5 MPa.

Claims

1. A method for testing the shear performance of ultra-high performance concrete, characterized in that, The method comprises the following steps: Step 1, preparing a pre-crack test block; The prefabricated crack test block is an I-shaped type, two cracks are arranged on the vertical section of the prefabricated crack test block, the cracks include a first crack (1) and a second crack (2), the first crack (1) is connected with the second crack (2), and an obtuse angle is formed at the connection, the two second cracks (2) are parallel to the vertical section of the prefabricated crack test block and located on the same horizontal line, the free ends of the two first cracks (1) are respectively located on the surface of the prefabricated crack test block, and the two first cracks (1) are parallel, and the first crack (1) forms an included angle with the height direction of the prefabricated crack test block α ​ The length of the second crack (2) n The thickness of the first crack (1) and the second crack (2) is 8mm to 12mm, the thickness of the second crack (2) is 1mm to 3mm, and the distance m between the two second cracks (2) is 10mm to 15mm. α The angle is 55°~65°; the precast crack test block has a height of 300mm~320mm, a width of 100mm, a thickness of 45mm~55mm, and a vertical section height of 55°~65°. h The diameter is 140mm~160mm; Step 2, placing the pre-crack test block on a universal testing machine to perform a shear performance test, and obtaining a maximum failure load of the pre-crack test block; The loading speed of the shear performance test is 0.2-0.4 MPa / min; Step 3, calculating the shear strength according to the maximum failure load: In the above formula, τ is the shear strength, in MPa, F τmax is the maximum breaking load, in N, m is the vertical distance between the two steel plates, in mm, t is the thickness of the pre-cracked test block, in mm.

2. The method of testing the shear performance of ultra-high performance concrete according to claim 1, wherein, In step 2, if the shear performance test is a compression shear performance test, the ball hinge of the universal testing machine is adjusted to make the pre-crack test block in contact with the loading plane flatly and uniformly.

3. The method of testing the shear performance of ultra-high performance concrete according to claim 1, wherein, In step 2, if the shear performance test is a tensile shear performance test, the clamp is installed on the universal testing machine, the pre-crack test block is sleeved in the clamp, the center line of the pre-crack test block is aligned with the axis of the clamp, and pre-tension is performed before the test.

4. The method of testing the shear performance of ultra-high performance concrete according to claim 3, wherein, The pre-tension load in the pre-tension process is 15-20% of the failure load.

Images