Device and method for measuring Poisson's ratio of concrete

Abstract

The invention belongs to the technical field of concrete Poisson's ratio measurement, and particularly relates to a concrete Poisson's ratio measurement device and a concrete Poisson's ratio measurement method. A concrete Poisson's ratio measuring device comprises a test piece bearing platform and an optical microscopic measurement module, the test piece bearing platform comprises a lower bearing platform, a telescopic scale and an upper bearing platform, and the optical microscopic measurement module is arranged at the top of the upper bearing platform and comprises a measurement fixing support, a measurement assembly, a marker post and a fastening bolt. Fastening bolts are arranged in the middles of four frames of the measuring fixing support respectively and used for fixing a to-be-measured concrete test piece arranged on the upper bearing platform, the measuring assemblies are symmetrically arranged on the left side and the right side of the lower portion of the measuring fixing support, and the marker posts are arranged at the included angle positions of the four frames of the measuring fixing support. The position of the to-be-measured concrete test piece is rapidly positioned through the test piece bearing platform, it is guaranteed that the to-be-measured concrete test piece is located in the center of the press machine and is not biased, the actual deformation of concrete is measured through the optical microscopic measurement module, the measurement precision is high, and deviation is small.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete Poisson's ratio measurement, and in particular relates to a concrete Poisson's ratio measurement device and a measurement method. Background Art

[0002] Within the proportional limit of the material, the absolute value of the ratio of the transverse strain caused by the uniformly distributed longitudinal stress to the corresponding longitudinal strain is called Poisson's ratio, also known as the transverse variability coefficient, which is an elastic constant reflecting the transverse deformation of the material. The Poisson's ratio of concrete refers to the proportional relationship between the transverse tensile strain and the longitudinal compressive strain when the concrete is compressed. The actual value of the concrete Poisson's ratio is of great significance to the design of concrete engineering.

[0003] There are some defects in the existing concrete Poisson's ratio test detection methods: there are differences in the specimen size, test result values, and calculation formulas in the national standard and industry standard, and single-point values ​​are selected for calculation, resulting in large test errors and poor repeatability; in conventional Poisson's ratio test methods, most of them measure the lateral and vertical deformation of concrete specimens by fixing a micrometer or displacement sensor on a deformation measuring frame, and the measurement accuracy is affected by the deformation measuring frame; some use resistance strain gauges to measure the lateral and vertical deformation of the specimens. Since the resistance strain gauges used for lateral and vertical deformation have different gauge lengths and qualities, the measured data often have large deviations, poor test repeatability, and the resistance strain gauges cannot be reused, resulting in large losses. Summary of the invention

[0004] In view of the above problems, the purpose of the present invention is to provide a measuring device and method for the Poisson's ratio of concrete. The placement position of the concrete specimen to be tested is quickly located by the specimen base to ensure that the concrete specimen to be tested is located at the center of the press without bias. The actual deformation of the concrete is measured by an optical microscope measurement module, which has high measurement accuracy and small deviation compared with resistance strain gauges. The Poisson's ratio of the concrete specimen to be tested is obtained by fitting and regressing the lateral strain and vertical strain under different loads. Compared with the existing single-point calculation, the experimental error can be reduced.

[0005] The technical solution of the present invention is: a measuring device for the Poisson's ratio of concrete, comprising a specimen support and an optical microscopic measurement module, the specimen support comprising a lower support, a retractable ruler and an upper support, a concave spherical surface is provided at the center position of the upper surface of the lower support, a circular shallow groove is provided on the upper surface of the upper support, and a convex spherical surface is provided on the lower surface that matches the concave spherical surface of the lower support, the retractable ruler is located in the four diagonal directions of the lower support, the optical microscopic measurement module is arranged on the top of the upper support, and comprises a measuring fixed bracket, a measuring component, a benchmark and a fastening bolt, the measuring fixed bracket is a square frame, and fastening bolts are respectively provided at the middle positions of the four frames of the measuring fixed bracket, and the fastening bolts are used to fix the concrete specimen to be measured set on the upper support, there are two measuring components, which are symmetrically arranged on the left and right sides of the lower part of the measuring fixed bracket, and there are four benchmarks, which are respectively arranged at the angle positions of the four frames of the measuring fixed bracket.

[0006] The measuring fixed bracket includes a main frame, which is provided with a plurality of frame positioning holes, frame fixing holes and measuring component fixing holes. A horizontal observation bubble is provided on the upper part of the main frame. There are four frame positioning holes, which are located at the four corners of the square measuring fixed bracket. There are four frame fixing holes, which are located in the middle of the four frames of the square measuring fixed bracket. There are four measuring component fixing holes, which are symmetrically arranged on both sides of the fixed bracket where the measuring component is located. The horizontal observation bubbles are arranged on both sides of the fixed bracket where the measuring component is located.

[0007] The concave spherical surface connecting the upper support platform and the lower support platform is provided with lubricating grease, and the lubricating grease is graphite calcium-based lubricating grease.

[0008] The measuring component comprises an optical microscope measuring lens, the optical microscope measuring lens is fixedly connected to a measuring component fixing rod, a fastening sleeve is provided on the top of the measuring component fixing rod, and the measuring component fixing rod is fixedly connected to a measuring fixing bracket through the fastening sleeve.

[0009] The optical microscope measuring lens is a high-precision optical microscope measuring lens, the magnification is continuously adjustable between 1 and 100,000 times, the characteristic image pixels are not less than 3 million, and the upper end of the measuring component fixing rod is a double mountain-shaped threaded screw.

[0010] The pole is a foldable pole.

[0011] A method for measuring the Poisson's ratio of concrete, using the above-mentioned device for measuring the Poisson's ratio of concrete, comprises the following steps: S1: Place the specimen support platform on the pressure testing machine, extend the four retractable rulers on the lower support platform, and make the extension amounts of the four retractable rulers to the four corners of the lower pressure plate of the testing machine consistent, ensuring that the specimen support platform is located at the center of the lower pressure plate of the testing machine; S2: Take out the concrete specimen to be tested and place it on the specimen support. When a 150mm×150mm×300mm prism specimen is used, the size of the bottom surface of the specimen is the same as that of the specimen support, so that the bottom surface of the concrete specimen to be tested is completely in contact with the lower support; when a ∅150mm×300mm cylindrical specimen is used, the bottom surface of the concrete specimen to be tested is completely located in the circular shallow groove of the upper support to ensure the uniformity of the force on the specimen; S3: Start the pressure testing machine and crush the concrete specimen to be tested at a speed of 0.5MPa / s~0.8MPa / s. Crush three pieces in succession to obtain the axial compressive strength load values ​​of the three concrete specimens respectively. Then calculate the load values ​​of the three concrete specimens by the arithmetic mean method and record them as F, which is the failure load of the concrete specimen; S4: Take out the concrete specimen to be tested, adjust the measurement fixing bracket to be in a horizontal state, and fix the measurement fixing bracket to be in a stable state; install the optical microscopic measurement module on the fixed measurement fixing bracket, repeat steps S1 and S2 to put the concrete specimen to be tested with the measurement fixing bracket and the optical microscopic measurement module installed into the pressure testing machine; S5: Start the pressure tester to preload, load to the initial load value F0 with a reference stress of 0.5MPa, maintain constant load for 60s, then immediately and continuously and evenly load to a stress of 0.4F, repeat the preloading three times. During the preloading process, observe whether the transverse strain and vertical strain values ​​in the tester measurement data analysis and calculation components are normal, and make adjustments if necessary; S6: After the preloading is completed, a formal test is carried out. The press is started to load the concrete specimen to be tested. The loading speed is the same as that in the preloading stage. The image data collected by the optical microscopy measurement module is analyzed, and the lateral strain and vertical strain of the concrete specimen to be tested under different loads are calculated. The same data collected by the optical microscopy measurement modules on both sides are arithmetic averaged. S7: With the vertical strain value from F0 to 0.5F as the X-axis and the corresponding lateral strain value from F0 to 0.5F as the Y-axis, draw a scatter plot of lateral strain / vertical strain, draw the corresponding trend line in the scatter plot, and calculate the binary linear relationship between lateral strain and vertical strain, as shown in Formula 1. The coefficient a in the relationship is the Poisson's ratio of concrete. (1) Where: Y f is the lateral strain value corresponding to the specimen when the load is f; X f is the vertical strain value corresponding to the specimen when the load is f; a is the Poisson's ratio of concrete; b is the coefficient to be determined.

[0012] The technical effects of the present invention are: 1. The present invention quickly locates the placement position of the concrete specimen to be tested through the specimen support platform, ensuring that the concrete specimen to be tested is located at the center of the press without bias; 2. The present invention uses an optical microscopy measurement module to measure the actual deformation of the concrete, which has high measurement accuracy and small deviation compared to the resistance strain gauge; 3. The present invention obtains the Poisson's ratio of the concrete specimen to be tested through the fitting regression of the lateral strain and the vertical strain under different loads, which can reduce the test error compared to the existing single-point calculation.

[0013] The following is a further description with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The present invention is a structural front view of a device for measuring the Poisson's ratio of concrete according to an embodiment of the present invention.

[0015] Figure 2 The present invention is a top view of the structure of a device for measuring the Poisson's ratio of concrete according to an embodiment of the present invention.

[0016] Figure 3 The present invention is a structural side view of a device for measuring the Poisson's ratio of concrete according to an embodiment of the present invention.

[0017] Figure 4 It is a schematic diagram of the structure of the measuring component according to an embodiment of the present invention.

[0018] Figure 5 Schematic diagram of the structure of the benchmark of the embodiment of the present invention.

[0019] Figure numerals: 1-specimen support platform; 2-optical microscope measurement module; 101-lower support platform; 102-retractable ruler; 103-upper support platform; 201-measuring fixed bracket; 2011-main frame; 2012-frame positioning hole; 2013-frame fixing hole; 2014-measuring component fixing hole; 2015-horizontal observation bubble; 202-measuring component; 2021-optical microscope measuring lens; 2023-measuring component fixing rod; 2024-fastening sleeve; 203-benchmark rod; 204-fastening bolt. DETAILED DESCRIPTION Example 1

[0020] like Figure 1~Figure 5As shown, a measuring device for the Poisson's ratio of concrete comprises a specimen support 1 and an optical microscopic measurement module 2, wherein the specimen support 1 comprises a lower support 101, a retractable scale 102 and an upper support 103, wherein a concave spherical surface is provided at the center of the upper surface of the lower support 101, a circular shallow groove is provided on the upper surface of the upper support 103, and a convex spherical surface is provided on the lower surface to match the concave spherical surface of the lower support 101, the retractable scale 102 is located in the four diagonal directions of the lower support 101, and the optical microscopic measurement module 2 is arranged on the top of the upper support 103, and comprises a measuring The measuring fixed bracket 201, the measuring component 202, the benchmark 203 and the fastening bolts 204, the measuring fixed bracket 201 is a square frame, the middle positions of the four frames of the measuring fixed bracket 201 are respectively provided with fastening bolts 204, the fastening bolts 204 are used to fix the concrete specimen to be measured set on the upper platform 103, the measuring components 202 have two, symmetrically arranged on the left and right sides of the lower part of the measuring fixed bracket 201, the benchmarks 203 have four, respectively arranged at the angle positions of the four frames of the measuring fixed bracket 201.

[0021] During actual use, the present invention quickly locates the placement position of the concrete specimen to be tested through the specimen base 1, ensuring that the concrete specimen to be tested is located at the center of the press without bias; the optical microscopy measurement module 2 is used to measure the actual deformation of the concrete, which has high measurement accuracy and small deviation compared to the resistance strain gauge. Example 2

[0022] Preferably, on the basis of Example 1, in this embodiment, preferably, the measuring fixed bracket 201 includes a main frame 2011, and the main frame 2011 is provided with a plurality of frame positioning holes 2012, frame fixing holes 2013 and measuring component fixing holes 2014, and a horizontal observation bubble 2015 is provided on the upper part of the main frame 2011, and four frame positioning holes 2012 are provided, which are located at the four corners of the square measuring fixed bracket 201, and four frame fixing holes 2013 are provided, which are located in the middle of the four frames of the square measuring fixed bracket 201, and four measuring component fixing holes 2014 are provided, which are symmetrically arranged in pairs on both sides of the fixed bracket 201 where the measuring component 202 is located, and the horizontal observation bubble 2015 is arranged on both sides of the fixed bracket 201 where the measuring component 202 is located.

[0023] During actual use, the measuring and fixing bracket 201 of the present invention includes a main frame 2011, and the main frame 2011 is provided with a plurality of frame positioning holes 2012, frame fixing holes 2013 and measuring component fixing holes 2014, which are respectively used for frame positioning, frame fixing and measuring component fixing, and the horizontal observation bubble 2015 is used to judge the horizontal state of the main frame 2011. Example 3

[0024] Preferably, on the basis of Example 1 or Example 2, in this embodiment, preferably, grease is provided in the concave spherical surface where the upper support 103 and the lower support 101 are connected, and the grease is graphite calcium-based grease.

[0025] During actual use, grease is provided in the concave spherical surface connecting the upper support 103 and the lower support 101 of the present invention to improve the stability and overall stability of the specimen support 1. Example 4

[0026] Preferably, on the basis of Example 1 or Example 3, in this embodiment, preferably, the measuring component 202 includes an optical microscope measuring lens 2021, the optical microscope measuring lens 2021 is fixedly connected to a measuring component fixing rod 2023, a fastening sleeve 2024 is provided on the top of the measuring component fixing rod 2023, and the measuring component fixing rod 2023 is fixedly connected to the measuring fixed bracket 201 through the fastening sleeve 2024.

[0027] During actual use, the present invention installs the optical microscope measuring lens 2021 on the measuring component fixing rod 2023, passes the measuring component fixing rod 2023 through the measuring system fixing hole to connect with the measuring fixing bracket, and adjusts the fastening depth of the fastening sleeve 2024 to make the optical microscope measuring lens 2021 located at the middle height position of the concrete specimen to be measured. Example 5

[0028] Preferably, on the basis of Example 1 or Example 4, in this embodiment, preferably, the optical microscope measuring lens 2021 is a high-precision optical microscope measuring lens, the magnification is continuously adjustable between 1 times and 100,000 times, the characteristic image pixels are not less than 3 million, and the upper end of the measuring component fixing rod 2023 is a double mountain type threaded screw.

[0029] During actual use, the optical microscope measuring lens 2021 described in the present invention is a high-precision optical microscope measuring lens with a magnification continuously adjustable between 1 and 100,000 times and a characteristic image pixel of not less than 3 million, ensuring that the optical microscope measuring lens 2021 can accurately measure the actual deformation of concrete, with higher measurement accuracy and smaller deviation than resistance strain gauges. Example 6

[0030] Preferably, on the basis of Example 1 or Example 5, in this embodiment, preferably, the marker 203 is a foldable marker.

[0031] During actual use, the benchmark 203 described in the present invention is a foldable benchmark. Take out the Poisson's ratio specimen to be measured, place the benchmark 203 around the specimen, pass through the frame positioning holes 2012 at the four corners of the measuring fixed bracket to connect with the measuring fixed bracket, make the measuring fixed bracket in a horizontal state by fine-tuning and observing the horizontal observation bubble, fix the measuring fixed bracket to be in a stable state, fold the benchmark and remove it, and complete the horizontal adjustment of the measuring fixed bracket. Example 7

[0032] A method for measuring the Poisson's ratio of concrete, using the above-mentioned device for measuring the Poisson's ratio of concrete, comprises the following steps: S1: Place the specimen support 1 on the pressure testing machine, extend the four retractable rulers 102 on the lower support 101, and make the extension amounts of the four retractable rulers 102 to the four corners of the lower pressure plate of the testing machine consistent, to ensure that the specimen support 1 is located at the center of the lower pressure plate of the testing machine; S2: Take out the concrete specimen to be tested and place it on the specimen support 1. When a 150mm×150mm×300mm prism specimen is used, the size of the bottom surface of the specimen is the same as that of the specimen support 1, so that the bottom surface of the concrete specimen to be tested is completely in contact with the lower support 101; when a ∅150mm×300mm cylindrical specimen is used, the bottom surface of the concrete specimen to be tested is completely located in the circular shallow groove of the upper support 103 to ensure the uniformity of the force on the specimen; S3: Start the pressure testing machine and crush the concrete specimen to be tested at a speed of 0.5MPa / s~0.8MPa / s. Crush three pieces in succession to obtain the axial compressive strength load values ​​of the three concrete specimens respectively. Then calculate the load values ​​of the three concrete specimens by the arithmetic mean method and record them as F, which is the failure load of the concrete specimen; S4: Take out the concrete specimen to be tested, adjust the measurement fixing bracket 201 to be in a horizontal state, and fix the measurement fixing bracket 201 to be in a stable state; install the optical microscopic measurement module 2 on the fixed measurement fixing bracket 201, repeat steps S1 and S2 to put the concrete specimen to be tested with the measurement fixing bracket 201 and the optical microscopic measurement module 2 installed into the pressure testing machine; S5: Start the pressure tester to preload, load to the initial load value F0 with a reference stress of 0.5MPa, maintain constant load for 60s, then immediately and continuously and evenly load to a stress of 0.4F, repeat the preloading three times. During the preloading process, observe whether the transverse strain and vertical strain values ​​in the tester measurement data analysis and calculation components are normal, and make adjustments if necessary; S6: After the preloading is completed, a formal test is carried out, and the press is started to load the concrete specimen to be tested. The loading speed is the same as that in the preloading stage. The image data collected by the optical microscopy measurement module 2 is analyzed, and the lateral strain and vertical strain of the concrete specimen to be tested under different loads are calculated. The same data collected by the optical microscopy measurement modules 2 on both sides are arithmetic averaged; S7: With the vertical strain value from F0 to 0.5F as the X-axis and the corresponding lateral strain value from F0 to 0.5F as the Y-axis, draw a scatter plot of lateral strain / vertical strain, draw the corresponding trend line in the scatter plot, and calculate the binary linear relationship between lateral strain and vertical strain, as shown in Formula 1. The coefficient a in the relationship is the Poisson's ratio of concrete. (1) Where: Y f is the lateral strain value corresponding to the specimen when the load is f; X f is the vertical strain value corresponding to the specimen when the load is f; a is the Poisson's ratio of concrete; b is the coefficient to be determined.

[0033] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A device for measuring the Poisson's ratio of concrete, characterized in that: The invention comprises a specimen support platform (1) and an optical microscopic measurement module (2), wherein the specimen support platform (1) comprises a lower support platform (101), a retractable scale (102) and an upper support platform (103), wherein a concave spherical surface is provided at the center of the upper surface of the lower support platform (101), a circular shallow groove is provided on the upper surface of the upper support platform (103), and a convex spherical surface is provided on the lower surface that matches the concave spherical surface of the lower support platform (101), wherein the retractable scale (102) is located in four diagonal directions of the lower support platform (101), and the optical microscopic measurement module (2) is arranged on the top of the upper support platform (103), and comprises a measurement fixing bracket (201 ), a measuring assembly (202), a benchmark (203) and a fastening bolt (204), the measuring fixed bracket (201) being a square frame, fastening bolts (204) are respectively arranged at the middle positions of the four frames of the measuring fixed bracket (201), the fastening bolts (204) are used to fix the concrete specimen to be measured arranged on the upper support platform (103), there are two measuring assemblies (202), which are symmetrically arranged on the left and right sides of the lower part of the measuring fixed bracket (201), and there are four benchmarks (203), which are respectively arranged at the angle positions of the four frames of the measuring fixed bracket (201).

2. A measuring device for the Poisson's ratio of concrete according to claim 1, characterized in that: The measurement fixing bracket (201) comprises a main frame (2011), the main frame (2011) being provided with a plurality of frame positioning holes (2012), frame fixing holes (2013) and measurement component fixing holes (2014); a horizontal observation bubble (2015) is provided on the upper part of the main frame (2011); four frame positioning holes (2012) are provided and are located at the four corners of the square measurement fixing bracket (201); four frame fixing holes (2013) are provided and are located at the middle positions of the four frames of the square measurement fixing bracket (201); four measurement component fixing holes (214) are provided and are symmetrically arranged in pairs on both sides of the fixing bracket (201) where the measurement component (202) is located; and the horizontal observation bubble (2015) is provided on both sides of the fixing bracket (201) where the measurement component (202) is located.

3. The device for measuring the Poisson's ratio of concrete according to claim 1, characterized in that: Lubricating grease is provided in the concave spherical surface where the upper support platform (103) and the lower support platform (101) are connected, and the lubricating grease is graphite calcium-based lubricating grease.

4. The device for measuring the Poisson's ratio of concrete according to claim 1, characterized in that: The measuring component (202) comprises an optical microscope measuring lens (2021), the optical microscope measuring lens (2021) is fixedly connected to a measuring component fixing rod (2023), a fastening sleeve (2024) is provided on the top of the measuring component fixing rod (2023), and the measuring component fixing rod (2023) is fixedly connected to a measuring fixing bracket (201) via the fastening sleeve (2024).

5. A device for measuring the Poisson's ratio of concrete according to claim 4, characterized in that: The optical microscope measuring lens (2021) is a high-precision optical microscope measuring lens, the magnification of which is continuously adjustable between 1 and 100,000 times, the characteristic image pixels are not less than 3 million, and the upper end of the measuring component fixing rod (2023) is a double-mountain-shaped threaded screw.

6. The device for measuring the Poisson's ratio of concrete according to claim 1, characterized in that: The pole (203) is a foldable pole.

7. A method for measuring the Poisson's ratio of concrete, using the device for measuring the Poisson's ratio of concrete as claimed in claim 1, characterized in that: The following steps are involved: S1: placing the specimen support platform (1) on the pressure testing machine, extending the four retractable rulers (102) on the lower support platform (101) so that the extension amounts of the four retractable rulers (102) to the four corners of the lower pressure plate of the testing machine are consistent, and ensuring that the specimen support platform (1) is located at the center of the lower pressure plate of the testing machine; S2: Take out the concrete specimen to be tested and place it on the specimen support (1). When a 150mm×150mm×300mm prism specimen is used, the size of the bottom surface of the specimen is the same as that of the specimen support (1), so that the bottom surface of the concrete specimen to be tested is completely in contact with the lower support (101); when a ∅150mm×300mm cylindrical specimen is used, the bottom surface of the concrete specimen to be tested is completely located in the circular shallow groove of the upper support (103) to ensure uniform force on the specimen; S3: Start the pressure testing machine and crush the concrete specimen to be tested at a speed of 0.5MPa / s~0.8MPa / s. Crush three pieces in succession to obtain the axial compressive strength load values ​​of the three concrete specimens respectively. Then calculate the load values ​​of the three concrete specimens by the arithmetic mean method and record them as F, which is the failure load of the concrete specimen; S4: taking out the concrete specimen to be tested, adjusting the measurement fixing bracket (201) to be in a horizontal state, and fixing the measurement fixing bracket (201) to be in a stable state; installing the optical microscopic measurement module (2) on the fixed measurement fixing bracket (201), and repeating steps S1 and S2 to place the concrete specimen to be tested with the measurement fixing bracket (201) and the optical microscopic measurement module (2) installed in the pressure testing machine; S5: Start the pressure tester to preload, load to the initial load value F0 with a reference stress of 0.5MPa, maintain constant load for 60s, then immediately and continuously and evenly load to a stress of 0.4F, repeat the preloading three times. During the preloading process, observe whether the transverse strain and vertical strain values ​​in the tester measurement data analysis and calculation components are normal, and make adjustments if necessary; S6: After the preloading is completed, a formal test is carried out, the press is started to load the concrete specimen to be tested, the loading speed is the same as that in the preloading stage, the image data collected by the optical microscopic measurement module (2) is analyzed, the lateral strain and vertical strain of the concrete specimen to be tested under different loads are calculated, and the arithmetic average of the same type of data collected by the optical microscopic measurement modules (2) on both sides is taken; S7: With the vertical strain value from F0 to 0.5F as the X-axis and the corresponding lateral strain value from F0 to 0.5F as the Y-axis, draw a scatter plot of lateral strain / vertical strain, draw the corresponding trend line in the scatter plot, and calculate the binary linear relationship between lateral strain and vertical strain, as shown in formula (1). The coefficient a in the relationship is the Poisson's ratio of concrete. （1） Where: Y f is the lateral strain value corresponding to the specimen when the load is f; X f is the vertical strain value corresponding to the specimen when the load is f; a is the Poisson's ratio of concrete; b is the coefficient to be determined.

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