Device and method for testing autogenous volume deformation of concrete

Abstract

The invention relates to the technical field of detection of concrete materials, in particular to a testing device and method for autogenous volume deformation of concrete, and the testing device comprises a thermostat and a flat plate type differential capacitance sensor; the device further comprises a test piece barrel and a data acquisition instrument; the test piece barrel is a tubular body with two open ends; the flat plate type differential capacitive sensor comprises a fixed polar plate and a movable polar plate; a vibration table is arranged on the bottom wall of the inner cavity of the constant-temperature box; a plurality of accommodating holes are formed in the table surface of the vibration table, and the fixed polar plates are placed on the bottom walls of the accommodating holes; the lower end of the test piece barrel is inserted into the accommodating cavity, and the lower end of the test piece barrel is connected with the fixed polar plate; the movable polar plate is mounted in the test piece barrel, and the peripheral surface of the movable polar plate is in sliding fit with the inner wall of the test piece barrel; and the data acquisition instrument is connected with the flat plate type differential capacitance sensor.

Description

Technical Field

[0001] The present invention relates to the technical field of testing of concrete materials, and particularly to a testing device and method for autogenous volume change of concrete. Background Art

[0002] According to the relevant instruments, procedures and requirements in the "Test for Autogenous Volume Change of Concrete" in the "Test Code for Hydraulic Concrete", the autogenous volume change of concrete is measured by the method of embedding strain gauges. This method has high test accuracy, can collect data in real time, and is less affected by the outside world. However, this method has the following deficiencies: ① The deformation of early concrete is not synchronized with the deformation of the embedded strain gauges, resulting in large measurement errors; ② The embedded strain gauges are disposable consumables, and the strain gauges cannot be reused and the price of the strain gauges is relatively high.

[0003] The autogenous volume change of concrete can also be measured by a dial gauge. This method is easy to operate and has a low test cost. However, this method has the following deficiencies: ① Manual regular reading is required, which is prone to human errors; ② The degree of automation is low, and data cannot be automatically collected and analyzed; ③ It is easily affected by the environment. The dial gauge measuring device is relatively sensitive to vibration. If there is a large vibration during the test, it will affect the accuracy of the results; ④ The measurement accuracy is not high, and the measurement range is small.

[0004] In addition, the patent application with the publication number of CN108716893A discloses a non-contact testing method and device for autogenous volume change of concrete. This method uses a laser sensor to measure the autogenous volume change of concrete. Although this method improves the deficiencies of the methods of measuring with embedded strain gauges and dial gauges, this method still needs to insert the probe of the laser reflection target into the concrete. On the one hand, it destroys the integrity of the specimen, and on the other hand, it cannot obtain the overall deformation of the concrete specimen. Summary of the Invention

[0005] The main object of the present invention is to propose a testing device and method for autogenous volume change of concrete, aiming to improve the accuracy of the autogenous volume change of concrete, so as to guide technicians to better analyze the integrity and durability of concrete structures; at the same time, improve the degree of automation of the testing process, save human resources, and improve the testing efficiency.

[0006] To achieve the above object, on the one hand, the present invention provides a test device for the autogenous volume deformation of concrete, which includes a constant temperature chamber and a flat differential capacitance sensor; it also includes a specimen barrel and a data acquisition instrument; the specimen barrel is a tubular body with open ends at both ends; the flat differential capacitance sensor includes a fixed electrode plate and a movable electrode plate; a vibration table is arranged on the inner cavity bottom wall of the constant temperature chamber; a plurality of accommodation cavities are arranged on the table surface of the vibration table, and the fixed electrode plate is placed on the bottom wall of the accommodation cavity; the lower end of the specimen barrel is inserted into the accommodation cavity, and the lower end of the specimen barrel is connected to the fixed electrode plate; the movable electrode plate is installed in the specimen barrel, and the outer peripheral surface of the movable electrode plate is slidably matched with the inner wall of the specimen barrel; the data acquisition instrument is connected to the flat differential capacitance sensor.

[0007] Preferably, a control cabinet is arranged on one side of the constant temperature chamber; a display screen is arranged on the control cabinet; a data processor is arranged inside the control cabinet, the data acquisition instrument is connected to the data processor, and the data processor is connected to the display screen; a temperature sensor is arranged on the inner wall of the constant temperature chamber for detecting the temperature of the inner cavity of the constant temperature chamber; a temperature controller is arranged inside the control cabinet; the temperature sensor is connected to the temperature controller; the temperature controller is connected to the constant temperature chamber for control.

[0008] Preferably, a data memory is arranged inside the control cabinet; the data memory is respectively connected to the data processor and the data acquisition instrument; the data memory is used for storing the data collected by the data acquisition instrument and the data processed by the data processor; a USB interface is arranged on the panel of the control cabinet; the USB interface is connected to the data memory.

[0009] Preferably, the flat differential capacitance sensor and the data acquisition instrument are connected through a signal conditioning circuit, and the signal conditioning circuit includes a capacitor voltage converter, an amplifier circuit and a filter connected in series in sequence.

[0010] Preferably, an annular groove is arranged on the top surface of the fixed electrode plate, and the depth of the annular groove is not less than 10 mm; the lower end of the specimen barrel is inserted into the annular groove.

[0011] Preferably, the movable electrode plate is in the shape of a circular plate, and the thickness of the movable electrode plate is not less than 20 mm; the sensitivity of the flat differential capacitance sensor is 2 pF / μm and the resolution is 0.1 μm.

[0012] On the other hand, the present invention also provides a test method for the autogenous volume deformation of concrete. Using the above test device, it includes the following steps:

[0013] S1. Device debugging: Set the sampling frequency, sampling time interval and acquisition channel parameters of the data acquisition instrument, move the active plate of the flat differential capacitance sensor up and down in the test piece barrel to conduct trial data acquisition, and determine the reliability of the installation of the flat differential capacitance sensor and the reliability of the signal conditioning circuit connection;

[0014] S2. Forming the test piece and installing the sensor: placing the fixed electrode plate with butter on the upper surface into the receiving hole of the vibration table, inserting the test piece barrel with butter on the inner wall into the receiving hole, and connecting the lower end of the test piece barrel to the fixed electrode plate; loading the concrete mixture into the test piece barrel, and starting the vibration table to vibrate and compact the concrete mixture; placing the movable electrode plate with butter on the lower surface into the test piece barrel, and pressing the movable electrode plate on the concrete mixture;

[0015] S3. Provide a constant temperature environment: start the thermostat and maintain the internal temperature of the thermostat at 20℃±2℃;

[0016] S4. Concrete autogenous volume deformation measurement and data recording: measure and record the measurement time and capacitance value output by the flat differential capacitance sensor according to the measurement cycle, and store the recorded data in a data storage device;

[0017] S5, calculation of concrete autogenous volume deformation: calculating the concrete autogenous volume deformation according to the data recorded in step S4, and storing the calculation result in a data storage device;

[0018] S6. Data analysis: based on the concrete autogenous volume deformation calculated in step S5, a curve of the concrete autogenous volume deformation changing with time and a curve of the concrete autogenous volume deformation rate changing with time are plotted.

[0019] Preferably, in step S4, the measurement cycle is as follows: measure once each at 2h, 6h, 12h and 24h after molding, then measure twice a day for two weeks, then measure twice a week for half a year, then measure twice a month for one year.

[0020] Preferably, in the step S2, if there is floating slurry on the surface of the compacted concrete mixture, the floating slurry is removed and then the movable electrode plate with butter coated on the lower surface is placed; if there is no floating slurry on the surface of the compacted concrete mixture, the movable electrode plate with butter coated on the lower surface is directly placed; in the step S2, the thickness of the butter coated on the fixed electrode plate, the specimen barrel and the movable electrode plate is not less than 0.5 mm.

[0021] Preferably, in step S6, before performing data analysis, the calculation results of step S5 need to be screened to eliminate abnormal data. The method for judging abnormal data is: if the capacitance value collected at a certain moment is too different from the data at adjacent moments and the calculated deformation does not conform to the trend of the autogenous volume deformation of concrete, it can be judged as abnormal data.

[0022] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows:

[0023] (1) By adopting the test device and method for autogenous volume deformation of concrete provided by the present invention, test result data with higher precision and the actual deformation condition of autogenous volume deformation specimens of concrete can be obtained; meanwhile, the degree of automation of the test process is improved, human resources are reduced, and the test efficiency is increased.

[0024] (2) The test device provided by the present invention has a built-in vibration function and provides a test temperature environment, which is convenient for specimen molding. After the specimen is molded, there is no need to transport the specimen to the test environment for curing. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the structures shown in these drawings.

[0026] Figure 1 is a schematic structural diagram of the test device provided by the present invention;

[0027] Figure 2 is a schematic connection diagram of the data acquisition instrument and the flat differential capacitance sensor in the present invention;

[0028] Figure 3 is a top view of the fixed electrode plate in the present invention;

[0029] Figure 4 is a schematic diagram when the fixed electrode plate cooperates with the specimen barrel in the present invention;

[0030] Figure 5 is a schematic diagram of the main interface of the operation interface;

[0031] Figure 6 is a schematic diagram of the input interface of the operation interface;

[0032] Figure 7 is a schematic diagram of the display interface of the operation interface;

[0033] Figure 8 is a schematic diagram of the data display of the operation interface;

[0034] Figure 9 is a schematic diagram of the graphic display of the operation interface.

[0035] Description of the attached reference numerals: 1. Thermostatic chamber; 2. Flat differential capacitance sensor; 2a. Fixed electrode plate; 2b. Movable electrode plate; 2c. Annular groove; 3. Vibration table; 3a. Accommodating cavity; 4. Specimen barrel; 5. Data acquisition instrument; 5a. Capacitance-voltage converter; 5b. Amplification circuit; 5c. Filter; 6. Control cabinet; 7. Display screen; 8. Temperature sensor; 9. USB interface; 10. Sealing cover. Specific implementation mode

[0036] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0037] Combined with Figures 1 to 4 As shown in the figure, on the one hand, this embodiment provides a test device for the autogenous volume deformation of concrete, including a thermostatic chamber 1 and a flat differential capacitance sensor 2; it also includes a specimen barrel 4 and a data acquisition instrument 5; the specimen barrel 4 is a tubular body with both ends open; the flat differential capacitance sensor 2 includes a fixed electrode plate 2a and a movable electrode plate 2b; a vibration table 3 is arranged on the inner cavity bottom wall of the thermostatic chamber 1; a plurality of accommodating cavities 3a are arranged on the tabletop of the vibration table 3, and the fixed electrode plate 2a is placed on the bottom wall of the accommodating cavity 3a; the lower end of the specimen barrel 4 is inserted into the accommodating cavity 3a, and the lower end of the specimen barrel 4 is connected to the fixed electrode plate 2a; the movable electrode plate 2b is installed in the specimen barrel 4, and the outer peripheral surface of the movable electrode plate 2b is slidably matched with the inner wall of the specimen barrel 4; the data acquisition instrument 5 is connected to the flat differential capacitance sensor 2.

[0038] Furthermore, a control cabinet 6 is arranged on one side of the thermostatic chamber 1; a display screen 7 is arranged on the control cabinet 6; a data processor is arranged inside the control cabinet 6, and the data processor is used to process and analyze the data collected by the data acquisition instrument 5. The data acquisition instrument 5 is connected to the data processor, and the data processor and the data acquisition instrument 5 are respectively connected to the display screen 7. The display screen 7 is used to display the data collected by the data acquisition instrument 5 and the processing results of the data processor.

[0039] In this embodiment, a temperature sensor 8 is provided on the inner wall of the thermostatic chamber 1 for detecting the temperature inside the thermostatic chamber 1; a temperature controller is provided inside the control cabinet 6; the temperature sensor 8 is connected to the temperature controller; the temperature controller is connected to the thermostatic chamber 1 for control. When the temperature sensor 8 detects that the temperature inside the thermostatic chamber 1 is too low, the temperature controller can start the heater in the thermostatic chamber 1 for heating; when the temperature sensor 8 detects that the temperature inside the thermostatic chamber 1 is too high, the temperature controller can start the cooler in the thermostatic chamber 1 for cooling to ensure that the temperature inside the thermostatic chamber 1 is within the set temperature range.

[0040] A data memory is provided inside the control cabinet 6; the data memory is respectively connected to the data processor and the data acquisition instrument 5; the data memory is used to store the data collected by the data acquisition instrument 5 and the data processed by the data processor; a USB interface 9 is provided on the panel of the control cabinet 6; the USB interface 9 is connected to the data memory. By using the USB interface 9, the data stored in the data memory can be copied.

[0041] Combined with Figure 2 As shown, the flat differential capacitance sensor 2 is connected to the data acquisition instrument 5 through a signal conditioning circuit, and the signal conditioning circuit includes a capacitance voltage converter 5a, an amplifier circuit 5b, and a filter 5c connected in series in sequence. In this embodiment, the filter 5c uses a MAX292 filter produced by Maxim Integrated Products; the amplifier circuit 5b uses an AD620 amplifier circuit module produced by Analog Devices, which has a variable gain setting function. The capacitance voltage converter 5a is used to realize the conversion between capacitance and voltage. The output end of the capacitance voltage converter 5a is connected to the input end of the amplifier circuit 5b. The amplification factor of the amplifier circuit 5b can be set according to the amplitude of the output signal of the flat differential capacitance sensor 2 and the input requirements of the data acquisition instrument 5 to ensure that the output signal is within the effective measurement range of the data acquisition instrument 5. The output end of the amplifier circuit 5b is connected to the input end of the filter 5c to filter out high-frequency noise interference and make the output signal more stable. The cut-off frequency of the low-pass filter is set to 1 - 10 Hz; the output end of the filter 5c is connected to the analog signal input channel of the data acquisition instrument 5. When connecting the capacitance voltage converter 5a, the amplifier circuit 5b, and the filter 5c, ensure that the connection is firm to avoid loose connection.

[0042] Combined with Figure 3 and Figure 4 As shown, an annular groove 2c is provided on the top surface of the fixed electrode plate 2a, and the depth of the annular groove 2c is not less than 10 mm; the lower end of the specimen barrel 4 is inserted into the annular groove 2c. By providing the annular groove 2c, it is convenient for the specimen barrel 4 to be connected to the fixed electrode plate 2a.

[0043] In this embodiment, the movable electrode plate 2b is in the shape of a circular plate, the diameter of the movable electrode plate 2b is φ200mm, and the thickness of the movable electrode plate 2b is not less than 20mm. The thickness of the movable electrode plate 2b should not be too small to ensure the contact area between the outer periphery of the movable electrode plate 2b and the inner wall surface of the specimen barrel 4, and to prevent the movable electrode plate 2b from being prone to flipping due to too small contact area. The sensitivity of the flat-plate differential capacitance sensor 2 is 2pF / μm, and the resolution is 0.1μm. The material of the specimen barrel 4 is galvanized sheet iron, the inner diameter of the specimen barrel 4 is φ200mm, and the height of the specimen barrel 4 is 560mm. A sealing cover 10 is provided at the top of the specimen barrel 4. A through hole for the cable of the movable electrode plate 2b is provided at the center of the sealing cover 10. The fixed electrode plate 2a is a circular plate body with a specification of φ210mm×20mm.

[0044] On the other hand, this embodiment also provides a test method for the autogenous volume deformation of concrete. Using the above test device, it includes the following steps:

[0045] S1. Device debugging: Set the sampling frequency, sampling time interval and acquisition channel parameters of the data acquisition instrument 5. Move the movable electrode plate 2b of the flat-plate differential capacitance sensor 2 up and down in the specimen barrel 4 to perform trial data acquisition, and determine the reliability of the installation of the flat-plate differential capacitance sensor 2 and the reliability of the connection of the signal conditioning circuit.

[0046] S2. Molding the specimen and installing the sensor: Place the fixed electrode plate 2a with butter smeared on its upper surface in the accommodation cavity 3a of the vibrating table 3, insert the specimen barrel 4 with butter smeared on its inner wall into the accommodation cavity 3a, and connect the lower end of the specimen barrel 4 to the fixed electrode plate 2a; Pour the concrete mixture into the specimen barrel 4, start the vibrating table 3 to vibrate the concrete mixture until it is dense; Place the movable electrode plate 2b with butter smeared on its lower surface in the specimen barrel 4, and press the movable electrode plate 2b on the concrete mixture. At the same time, cover the sealing cover 10 on the top of the specimen barrel 4, seal between the sealing cover 10 and the specimen barrel 4, and also seal the cable through hole at the center of the sealing cover 10 and the cable of the movable electrode plate 2b. The purpose of smearing butter is to prevent the molded specimen from adhering to the fixed electrode plate 2a, the specimen barrel 4 and the movable electrode plate 2b. In addition, the aggregate with a particle size exceeding 40mm needs to be removed from the concrete mixture.

[0047] S3. Providing a constant temperature environment: Start the constant temperature box 1 and keep the internal temperature of the constant temperature box 1 at 20°C±2°C.

[0048] S4. Measurement and data recording of the autogenous volume deformation of concrete: Measure according to the measurement cycle, record the measurement time and the capacitance value output by the flat differential capacitance sensor 2, and store the recorded data in the data memory. Specifically, the measurement cycle is as follows: Measure once at 2h, 6h, 12h, and 24h after molding, then measure twice a day until two weeks, then measure twice a week until half a year, and then measure twice a month until one year.

[0049] S5. Calculation of the autogenous volume deformation of concrete: Calculate the autogenous volume deformation of concrete according to the data recorded in step S4, and store the calculation result in the data memory.

[0050] S6. Data analysis: According to the autogenous volume deformation of concrete calculated in step S5, plot the curve of the autogenous volume deformation of concrete changing with time and the curve of the autogenous volume deformation rate of concrete changing with time. The development trend of the autogenous volume deformation of concrete can be understood through the curves.

[0051] In step S1, when performing trial acquisition, observe whether the acquired data is stable and reasonable. If the data fluctuates greatly or abnormal values appear, check whether the installation of the flat differential capacitance sensor 2 is loose and whether the connection circuit is correct, and make corresponding adjustments. At the same time, observe whether the acquisition data and the analysis curve graph displayed in real time on the display screen 7 are normal to ensure the correct recording and analysis of relevant data during the test process.

[0052] In step S2, if there is floating slurry on the surface of the compacted concrete mixture, remove the floating slurry and then place the movable electrode plate 2b with butter smeared on its lower surface; if there is no floating slurry on the surface of the compacted concrete mixture, directly place the movable electrode plate 2b with butter smeared on its lower surface; in step S2, the thickness of the butter smeared on the fixed electrode plate 2a, the specimen barrel 4, and the movable electrode plate 2b is not less than 0.5 mm.

[0053] In step S6, before performing data analysis, it is necessary to screen the calculation results of step S5 to eliminate abnormal data. The judgment method of abnormal data is as follows: If the capacitance value acquired at a certain moment differs greatly from the data at the adjacent moment and the calculated deformation amount does not conform to the autogenous volume deformation trend of concrete, it can be judged as abnormal data. When performing data screening, it is necessary to select a reference value, and take the value measured for the first time, that is, 2 hours after molding, as the reference value.

[0054] In step S5, the calculation method for calculating the autogenous volume deformation of concrete is as follows:

[0055] When the concrete specimen inside the specimen barrel 4 expands or contracts, the distance between the fixed electrode plate 2a and the movable electrode plate 2b changes, resulting in a change in capacitance. According to the capacitance calculation formula The capacitance change amount can be calculated, that is:

[0056]

[0057] Where: ε -- dielectric constant of the medium between the plates; A -- effective area of the plates; d 1 -- distance between the plates after deformation; d 0 -- distance between the plates before deformation.

[0058] According to the measured capacitance change ΔC, from the sensitivity calculation formula of the differential capacitance sensor the autogenous volume deformation of concrete can be calculated, that is:

[0059]

[0060] Where: Δd -- autogenous volume deformation of concrete; ΔC -- capacitance change caused by the deformation of concrete before and after measurement according to the measurement period; S -- sensitivity of the sensor.

[0061] The above process is automatically calculated by the data processor, and the calculation result is saved to the data memory.

[0062] In this embodiment, two specimen barrels 4 are arranged in the thermostat of the test device. During the test, the measurements of two groups of specimens are carried out simultaneously, and the average value of the measured values of the two groups of specimens is used as the result.

[0063] Combined with Figures 5 to 9 As shown, the operation interface of the test device provided in this embodiment consists of a main interface, an input interface and a display interface. The main interface includes "information entry", "start test", "result display" and "data copy"; the input interface is "information entry", including sample number, tester information, circuit amplification factor, filter cut-off frequency, data acquisition parameters, sensor sensitivity, etc.; the display interface is divided into data display and graphic display. The data display includes measurement time, capacitance value, autogenous volume deformation of concrete, and the graphic display can select to view the curve of autogenous volume deformation of concrete changing with time or the curve of autogenous volume deformation rate of concrete changing with time.

[0064] To ensure the test environment of the specimen, during the whole test process, do not open the door of the thermostat 1; if the data is abnormal, close the door immediately after opening the door for processing; during the test process, you can click the "result display" button to enter the display interface to view the test data or existing graphics at any time to predict whether the autogenous volume deformation of concrete is abnormal; insert a USB flash drive into the USB interface and click the "data copy" button to copy the saved data for further analysis.

[0065] The above are only the preferred embodiments of the present invention, and do not thereby limit the patent scope of the present invention. Any equivalent structural transformation made under the inventive concept of the present invention by using the content of the specification and drawings of the present invention, or any direct / indirect application in other related technical fields is included within the patent protection scope of the present invention.

Claims

1. A testing device for the spontaneous volume deformation of concrete, comprising a constant temperature box (1) and a flat plate differential capacitance sensor (2); characterized in that: It also includes a test piece barrel (4) and a data acquisition instrument (5); the test piece barrel (4) is a tubular body with open ends; the flat plate differential capacitance sensor (2) includes a fixed electrode plate (2a) and a movable electrode plate (2b); a vibration table (3) is arranged on the bottom wall of the inner cavity of the constant temperature box (1); a plurality of accommodating holes (3a) are arranged on the table surface of the vibration table (3), and the fixed electrode plate (2a) is placed on the bottom wall of the accommodating hole (3a); The lower end of the test piece barrel (4) is inserted into the accommodating hole (3a), and the lower end of the test piece barrel (4) is connected to the fixed electrode plate (2a); the movable electrode plate (2b) is installed in the test piece barrel (4), and the outer peripheral surface of the movable electrode plate (2b) is slidably matched with the inner wall of the test piece barrel (4); The data acquisition instrument (5) is connected to the flat-plate differential capacitance sensor (2).

2. A testing device for the autogenous volume deformation of concrete as claimed in claim 1, characterized in that: A control cabinet (6) is arranged on one side of the thermostatic box (1); a display screen (7) is arranged on the control cabinet (6); A data processor is arranged inside the control cabinet (6), the data acquisition device (5) is connected to the data processor, and the data processor is connected to the display screen (7); A temperature sensor (8) is arranged on the inner wall of the thermostatic box (1) for detecting the temperature of the inner cavity of the thermostatic box (1); a temperature controller is arranged inside the control cabinet (6); the temperature sensor (8) is connected to the temperature controller; and the temperature controller is control-connected to the thermostatic box (1).

3. A testing device for the autogenous volume deformation of concrete as claimed in claim 2, characterized in that: A data storage device is provided inside the control cabinet (6); the data storage device is connected to the data processor and the data acquisition device (5) respectively; the data storage device is used to store data collected by the data acquisition device (5) and store data processed by the data processor; a USB interface (9) is provided on the panel of the control cabinet (6); the USB interface (9) is connected to the data storage device.

4. A testing device for the autogenous volume deformation of concrete as claimed in claim 3, characterized in that: The flat plate differential capacitance sensor (2) is connected to the data acquisition instrument (5) via a signal conditioning circuit, and the signal conditioning circuit comprises a capacitance voltage converter (5a), an amplifier circuit (5b) and a filter (5c) which are sequentially connected in series.

5. A testing device for the autogenous volume deformation of concrete as claimed in claim 1, characterized in that: An annular groove (2c) is provided on the top surface of the fixed electrode plate (2a), and the depth of the annular groove (2c) is not less than 10 mm; the lower end of the test piece barrel (4) is inserted into the annular groove (2c).

6. A testing device for the autogenous volume deformation of concrete as claimed in claim 1, characterized in that: The active electrode plate (2b) is in the shape of a circular plate, and the thickness of the active electrode plate (2b) is not less than 20 mm; the sensitivity of the flat differential capacitance sensor (2) is 2 pF / μm, and the resolution is 0.1 μm.

7. A method for testing the autogenous volume deformation of concrete, characterized in that: The test device according to claim 4 comprises the following steps: S1. Device debugging: setting the sampling frequency, sampling time interval and acquisition channel parameters of the data acquisition instrument (5), moving the active plate (2b) of the flat plate differential capacitance sensor (2) up and down in the test piece barrel (4) to conduct trial data acquisition, and determining the reliability of the installation of the flat plate differential capacitance sensor (2) and the reliability of the signal conditioning circuit connection; S2. Forming a test piece and installing a sensor: placing a fixed electrode (2a) with butter on its upper surface in a receiving hole (3a) of a vibration table (3), inserting a test piece barrel (4) with butter on its inner wall in the receiving hole (3a), and connecting the lower end of the test piece barrel (4) to the fixed electrode (2a); placing a concrete mixture in the test piece barrel (4), and starting the vibration table (3) to vibrate and compact the concrete mixture; placing a movable electrode (2b) with butter on its lower surface in the test piece barrel (4), and pressing the movable electrode (2b) on the concrete mixture; S3, providing a constant temperature environment: starting the thermostat (1) to maintain the internal temperature of the thermostat (1) at 20°C ± 2°C; S4, concrete autogenous volume deformation measurement and data recording: measuring and recording the measurement time and the capacitance value output by the flat differential capacitance sensor (2) according to the measurement cycle, and storing the recorded data in a data storage device; S5, calculation of concrete autogenous volume deformation: calculating the concrete autogenous volume deformation according to the data recorded in step S4, and storing the calculation result in a data storage device; S6. Data analysis: based on the concrete autogenous volume deformation calculated in step S5, a curve of the concrete autogenous volume deformation changing with time and a curve of the concrete autogenous volume deformation rate changing with time are plotted.

8. A method for testing the autogenous volume deformation of concrete as claimed in claim 7, characterized in that: In step S4, the measurement cycle is as follows: measure once each at 2h, 6h, 12h, and 24h after molding, then measure twice a day for two weeks, then measure twice a week for half a year, then measure twice a month for one year.

9. A method for testing the autogenous volume deformation of concrete as claimed in claim 7, characterized in that: In the step S2, if there is floating slurry on the surface of the compacted concrete mixture, the floating slurry is removed and then the movable electrode plate (2b) with butter applied to the lower surface is placed; if there is no floating slurry on the surface of the compacted concrete mixture, the movable electrode plate (2b) with butter applied to the lower surface is directly placed; in the step S2, the thickness of the butter applied to the fixed electrode plate (2a), the test piece barrel (4) and the movable electrode plate (2b) is not less than 0.5 mm.

10. A method for testing the autogenous volume deformation of concrete as claimed in claim 7, characterized in that: In step S6, before performing data analysis, the calculation results of step S5 need to be screened to eliminate abnormal data. The method for judging abnormal data is: if the capacitance value collected at a certain moment is too different from the data at adjacent moments and the calculated deformation does not conform to the trend of the self-generated volume deformation of concrete, it can be judged as abnormal data.

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