Method and device for accurately measuring shrinkage coefficient of concrete interface transition area

Abstract

The invention discloses a method and a device for accurately measuring the dry shrinkage coefficient of a concrete interface transition area. The method comprises the following steps: manufacturing test pieces, measuring the thickness of the interface transition area and the length of the test pieces, adjusting an experimental device to measure the deformation of each test piece, and calculating the dry shrinkage coefficient according to the measured data. The method and the device can be used for conveniently and accurately measuring the shrinkage coefficient of the interface transition area, provide important reference for the research of a concrete mesoscopic humidity cracking mechanism, and avoid repeated work at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of civil engineering materials, in particular to a method and a device for accurately measuring the shrinkage coefficient of a concrete interface transition zone. Background Art

[0002] The interfacial transition zone (ITZ) in concrete is considered to be one of the most critical interfaces in concrete. It forms an independent "third phase" between mortar and aggregate. The formation of ITZ is mainly caused by the boundary effect of coarse aggregate and the microscopic bleeding effect. ITZ has an important influence on the mechanical properties, mass transfer and heat transfer properties of concrete. It is also one of the most vulnerable areas in the concrete matrix. Studies have shown that ITZ has an important influence on the strength and failure process of concrete. Its high porosity and low strength make it a crack development area in concrete. The enriched calcium hydroxide in ITZ makes microscopic cracks more widely distributed in this area.

[0003] Due to the difference in shrinkage coefficient between ITZ and aggregate, the deformation incoordination caused by humidity gradient leads to internal constraints of concrete, which eventually leads to macroscopic cracking of concrete. Therefore, studying the shrinkage coefficient of concrete interface transition zone is of great significance to the mechanism of concrete mesoscopic moisture cracking. However, due to the special structure and tiny size of the interface transition zone, its properties cannot be directly measured.

[0004] Therefore, it is urgent to develop a method and device for accurately measuring the shrinkage coefficient of the concrete interface transition zone. Summary of the invention

[0005] The invention provides a method and a device for accurately measuring the shrinkage coefficient of a concrete interface transition zone, aiming to fill the research gap in this field and solve the problems existing in the prior art.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: A method for accurately measuring the shrinkage coefficient of a concrete interface transition zone comprises the following steps: Step 1: Make the test piece; Step 2: Test the thickness of the interface transition zone and the length of the specimen; Step 3: Adjust the test device and measure the strain of each specimen; Step 4: Calculate the shrinkage coefficient of the interface transition zone based on the recorded data.

[0007] Preferably, step one includes the following steps: using a method of pouring cement mortar on an aggregate plate of coarse aggregate to obtain a concrete specimen with uniform distribution, forming an interface transition zone between the cement mortar and the coarse aggregate to ensure the uniformity of the interface transition zone.

[0008] Preferably, the step 2 includes the following steps: using a microhardness tester to measure the change trend of the hardness at the interface between cement mortar and aggregate, and calculating the thickness of the interface transition zone based on these change trends.

[0009] Preferably, the step three includes the following steps: performing a zeroing operation on the measurement module; When the humidity adjustment module is adjusted to set the humidity, the test piece will generate strain, and the strain signal is received by the measurement module and transmitted to the calculation module.

[0010] Preferably, the step 4 includes the following steps: using the measurement module to measure the aggregate specimen, cement mortar specimen and concrete specimen to calculate their strains. For the concrete specimen, the strain calculation is as follows: ; ; Similarly, we can get: ; Therefore, the calculation formula for the shrinkage coefficient of the interface transition zone can be deduced as follows: ; Where: , , They are the shrinkage coefficients of the interface transition zone, total concrete specimen, aggregate and cement mortar respectively; , , are the shrinkage coefficients of aggregate, cement mortar, and interface transition zone, respectively; , , is the thickness of the interface transition zone, aggregate, and cement mortar; It is the difference between the final humidity and the initial humidity of the concrete specimen and is controlled by a digital humidity regulator.

[0011] As a more preferred embodiment, the step 4 includes the following steps: in the calculation formula of the shrinkage coefficient of the concrete interface transition zone, , , are all obtained from step 2, and It can be calculated by the following formula: ; Where: , , , They are the thickness of concrete specimen, interface transition zone, aggregate and cement mortar, respectively, which are measured in step 2.

[0012] A device for accurately measuring the shrinkage coefficient of a concrete interface transition zone, comprising: A fixing module, used to carry and fix the manufactured test piece; A humidity adjustment module, used to adjust the humidity in the test device; A measuring module, used for measuring the strain of each test piece after the humidity of the test device is adjusted by the humidity adjustment module; The reading module is used to display the measurement data of the measurement module.

[0013] Preferably, the fixing module includes an iron shell, which is a box with an opening on the top. The bottom of the iron shell is provided with bases that are symmetrical in pairs about the middle position of the bottom of the iron shell. The iron shell forms a supporting fit with the test platform through the bases. A rotatable cover is hinged on one side of the top of the iron shell, and the rotatable cover forms a releasable sealing fit with the opening of the iron shell.

[0014] As a more preferred embodiment, the humidity adjustment module includes a humidity regulator arranged on one side of the iron shell, the output end of the humidity regulator forms a humidity control cooperation with the iron shell, a humidity adjustment port is provided on the side opposite to the iron shell and the humidity regulator, and the iron shell is connected to the humidity adjustment port through a plurality of built-in pipes.

[0015] Further, the measurement module includes a high-precision strain gauge disposed in an iron housing; The reading module includes an electronic reader arranged on one side of the iron shell, the high-precision strain gauge forms an inductive match with each test piece, and the electronic reader is electrically connected with the high-precision strain gauge to form a reading match.

[0016] Beneficial effects of the present invention: A method and device for accurately measuring the shrinkage coefficient of the transition zone of the concrete interface is proposed. The device controls the humidity in the device through a humidity regulator, and adds or subtracts the humidity of the environment where the concrete specimen is located to simulate the humidity changes in actual engineering. The device can connect multiple measuring devices in series to test concrete specimens, cement mortar specimens, and aggregate specimens at the same time, which is easy to operate and saves time. Through this determination method, the shrinkage coefficient of the transition zone of the interface can be accurately determined, which provides a reference for the study of the concrete mesoscopic humidity cracking mechanism in actual engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the overall structure of the present invention; Figure 2 The schematic diagram of the structure of the poured concrete specimen; Figure 3The strain cloud diagram of the three-phase model specimen when the humidity changes from 80% to 100%; Figure 4 The strain cloud diagram of the concrete specimen when the humidity changes from 80% to 100%; In the figure: 1. Electronic readout; 2. Humidity adjustment port; 3. High-precision strain gauge; 4. Base; 5. Humidity regulator; 6. Iron casing; 7. Rotatable cover; 8. Cement mortar; 9. Interface transition zone; 10. Coarse aggregate. DETAILED DESCRIPTION

[0018] As follows, embodiments are further described with reference to the accompanying drawings.

[0019] As a preferred embodiment 1, a method for accurately measuring the shrinkage coefficient of a concrete interface transition zone comprises the following steps: Step 1: Make the test piece; Step 2: Test the thickness of the interface transition zone and the length of the specimen; Step 3: Adjust the test device and measure the strain of each specimen; Step 4: Calculate the shrinkage coefficient of the interface transition zone based on the recorded data.

[0020] like Figure 2 As shown, preferably, the step one includes the following steps: using a method of pouring cement mortar 8 on an aggregate plate of coarse aggregate 10 to obtain a concrete specimen with uniform distribution, forming an interface transition zone 9 between the cement mortar 8 and the coarse aggregate 10 to ensure the uniformity of the interface transition zone 9.

[0021] Preferably, the step 2 includes the following steps: using a microhardness tester to measure the change trend of the hardness at the interface between cement mortar and aggregate, and calculating the thickness of the interface transition zone based on these change trends.

[0022] Preferably, the step three includes the following steps: performing a zeroing operation on the measurement module; When the humidity adjustment module is adjusted to set the humidity, the test piece will generate strain, and the strain signal is received by the measurement module and transmitted to the calculation module.

[0023] Preferably, the step 4 includes the following steps: using the measurement module to measure the aggregate specimen, cement mortar specimen and concrete specimen to calculate their strains. For the concrete specimen, the strain calculation is as follows: ; ; Similarly, we can get: ; Therefore, the calculation formula for the shrinkage coefficient of the interface transition zone can be deduced as follows: ; Where: , , They are the shrinkage coefficients of the interface transition zone, total concrete specimen, aggregate and cement mortar respectively; , , are the shrinkage coefficients of aggregate, cement mortar, and interface transition zone, respectively; , , is the thickness of the interface transition zone, aggregate, and cement mortar; It is the difference between the final humidity and the initial humidity of the concrete specimen and is controlled by a digital humidity regulator.

[0024] As a more preferred embodiment, the step 4 includes the following steps: in the calculation formula of the shrinkage coefficient of the concrete interface transition zone, , , are all obtained from step 2, and It can be calculated by the following formula: ; Where: , , , They are the thickness of concrete specimen, interface transition zone, aggregate and cement mortar, respectively, which are measured in step 2.

[0025] like Figure 1 As shown in the figure, as a preferred embodiment 2, a device for accurately measuring the shrinkage coefficient of the transition zone of the concrete interface comprises: A fixing module, used to carry and fix the manufactured test piece; A humidity adjustment module, used to adjust the humidity in the test device; A measuring module, used for measuring the strain of each test piece after the humidity of the test device is adjusted by the humidity adjustment module; The reading module is used to display the measurement data of the measurement module.

[0026] Preferably, the fixing module comprises an iron shell 6, which is a box with an opening at the top, and the bottom of the iron shell 6 is provided with bases 4 symmetrical in pairs about the middle position of the bottom of the iron shell 6, and the iron shell 6 forms a support fit with the test platform through the base 4, and a rotatable cover plate 7 is hinged on one side of the top of the iron shell 6, and the rotatable cover plate 7 forms a releasable blocking fit with the opening of the iron shell 6. A limiter is provided at the bottom of the inner part of the iron shell 6 to perform a detachable limit fit on the test piece.

[0027] Preferably, the humidity regulating module includes a humidity regulator 5 arranged on one side of the iron shell 6, the output end of the humidity regulator 5 forms a humidity control cooperation with the iron shell 6, and a humidity regulating port 2 is provided on the side opposite to the iron shell 6 and the humidity regulator 5, and the iron shell 6 is connected to the humidity regulating port 2 through a plurality of built-in pipes.

[0028] Preferably, the humidity regulator 5 adopts the XH-W3005 digital humidity controller, including a display screen, a controller, a humidifier and a humidity sensor. The sensing end of the humidity sensor forms a sensing cooperation with the humidity in the iron shell 6. When it exceeds the range, the humidifier is controlled to dehumidify, and when it is below the range, the humidifier is controlled to humidify.

[0029] Preferably, the measuring module comprises a high-precision strain gauge 3 disposed in an iron housing 6, the high-precision strain gauge 3 being disposed at an opening of the iron housing 6 and forming an elastic clamping fit with the iron housing 6 for the test piece; The reading module includes an electronic reader 1 disposed on one side of the iron housing 6 , and the high-precision strain gauge 3 forms an inductive match with each test piece, and the electronic reader 1 and the high-precision strain gauge 3 are electrically connected to form a reading match.

[0030] Preferably, the high-precision strain gauge 3 used is model BX120-80AA, which has a high-precision digital display function and an accuracy of up to 0.1με.

[0031] During use, the test piece is limitedly installed in the iron shell 6, and the test piece is elastically clamped by the high-precision strain gauge 3 and the iron shell 6, the rotatable cover 7 is closed, and the humidity in the box is controlled by the humidity regulator 5. The internal moisture is allowed to flow slowly through the humidity adjustment port 2 to form a stable and uniform humidity atmosphere as much as possible, and the length change of the test piece under different humidity conditions is sensed and reset to zero initially. The changing sensing data is displayed by the electronic reader 1.

[0032] Preferably, the electronic reader 1 can be an electronic reader with a calculation function, which can automatically calculate the required data after the calculation formula is input.

[0033] As a preferred embodiment 3, the size of the aggregate plate of the coarse aggregate 10 in the concrete specimen is 25 mm in radius and 20 mm in height, and the size of the concrete specimen is 25 mm in radius and 40 mm in height; The initial humidity was set at 80% RH.

[0034] As a preferred embodiment 4, sample preparation: In order to accurately determine the shrinkage coefficient of the concrete interface transition zone, it is recommended to use a sample with a diameter of 50 mm and a height of 40 mm for measurement. At the same time, cement mortar samples and aggregate samples of the same size need to be prepared.

[0035] Step 1: To meet the measurement requirements of the device, a concrete sample with a diameter of 50 mm and a height of 40 mm needs to be prepared. The cement mortar is poured on the aggregate plate to ensure the uniform distribution of the concrete sample in the interface transition zone. First, place the aggregate plate at the bottom of the mold, and then pour the cement mortar. At the same time, cement mortar and aggregate samples of the same specifications need to be prepared. Before testing, the surface of all samples needs to be polished smooth.

[0036] The specifications of the aggregate plate are 50mm in diameter and 20mm in height. When pouring, try to make the thickness of the cement mortar layer equal to that of the aggregate layer to reduce possible errors.

[0037] Step preparation two: Determine the hardness and length of the interface transition zone. A Vickers hardness test is performed using a microhardness tester to determine the thickness of the concrete interface transition zone. Measurements are made within 100 microns on the mortar side of the interface between the cement mortar and the aggregate, and the points where the hardness changes significantly are marked to determine the boundary of the transition zone. At the same time, a precision vernier caliper is used to measure and record the length of each specimen. The Vickers hardness measurement is performed by pressing a 136-degree diamond indenter into the material, maintaining a certain force, and measuring the diagonal length of the indentation to calculate the Vickers hardness value. This process ensures accuracy and provides key data to understand the performance of the material. The calculation formula for the Vickers hardness value is: ; In the formula, For experimental force, is the average length of the two diagonal lines of the indentation, is the Vickers hardness. The relationship between the indentation depth and the diagonal is: ; In the formula, is the diagonal length, is the indentation depth.

[0038] Step 3: Humidity adjustment and specimen preparation. First, evenly cover the surface of the concrete specimen with silica gel to maintain a moist state. Place the specimen in a constant humidity control box, set up a humidifier and a dehumidifier at the same time, and set the initial humidity ratio to 80%RH. After the humidity is balanced, install the high-precision strain gauge. When the high-precision strain gauge reading is stable, return it to zero, then adjust the humidifier humidity to 100%RH, and observe the changes in the high-precision strain gauge until the reading is stable. In addition, ensure that the silica gel around the constant humidity control box is well insulated and connected to the humidity regulator through a pipe. Through the above steps, the humidity linear expansion of concrete specimens under different humidity conditions can be accurately measured.

[0039] Step 4: Calculation of shrinkage coefficient of interface transition zone. The calculation formula of shrinkage coefficient of concrete specimen is: ; Where: is the difference between the final humidity and the initial humidity of the concrete specimen. . is the strain of concrete caused by humidity, ; is the shrinkage coefficient of concrete, ; In the present invention, when the humidity regulator is adjusted to set the humidity, the specimen will be deformed. The strain of the aggregate specimen, cement mortar specimen and concrete specimen can be measured by a high-precision strain gauge.

[0040] in is known, It can be measured, It can be calculated by the following formula.

[0041] ; In the formula, is the length of the concrete specimen, measured in step 2.

[0042] Experimental data: The method and device for accurately determining the wet expansion coefficient of the concrete interface transition zone provided by the present invention are used to test concrete specimens, cement mortar specimens and aggregate specimens with a water-cement ratio of 0.5. The concrete specimens are prepared by the casting method described in the present invention. The interface thickness is measured by the method for measuring the thickness of the interface transition zone described in the present invention. The average value of the thickness of the interface transition zone obtained by multiple measurements is 30 The measurement data are shown in Table 1:

[0043] Table 1 Substitute the data in the above table into the formula It can be calculated that the shrinkage coefficient of the interface transition zone at 80-90%RH is , 90-100%RH . In order to verify the accuracy of the measurement results, a three-phase wet expansion model considering cement mortar, interface transition zone and concrete was established using the large-scale commercial finite element analysis software Abaqus. Since only the deformation of the specimen in one direction needs to be considered, a two-dimensional three-phase concrete model with a height consistent with the specimen described in the patent and a width equal to the diameter of the specimen described in the patent was established, and the measured parameters were imported into the software to verify the accuracy of the method proposed in the patent. The model uses a 4-node quadrilateral unit, with a total of 2055 nodes and 6333 units, and the minimum unit size is half the thickness of the interface. The boundary conditions of the model are the same as those of the measuring device, and constraints along the y-axis and x-axis are applied to the bottom and side surfaces of the model respectively.

[0044] like Figure 3~Figure 4 As shown in the figure, the displacement cloud diagram of the final analysis model is shown in the figure. Figure 3 The humidity is from 80 Change to 100 The displacement cloud diagram of the three-phase model specimen, Figure 4 The humidity is from 80 Change to 100 The displacement cloud diagram of the concrete specimen shows that the maximum displacement of the model appears on the upper surface, and the error with the data measured by the strain gauge is no more than 6.5%. This shows that the measurement result obtained by the method described in the present invention is accurate. Therefore, the precise measurement method and device for the shrinkage coefficient of the concrete interface transition zone provided by the present invention can accurately measure the shrinkage coefficient of the interface transition zone.

Claims

1. A method for accurately determining the shrinkage coefficient of the concrete interface transition zone, It is characterized in that The following steps are involved: Step 1: Make the test piece; Step 2: Test the thickness of the interface transition zone and the length of the specimen; Step 3: Adjust the test device and measure the strain of each specimen; Step 4: Calculate the shrinkage coefficient of the interface transition zone based on the recorded data.

2. A method for accurately determining the shrinkage coefficient of the concrete interface transition zone according to claim 1, It is characterized in that The step one comprises the following steps: using a method of pouring cement mortar (8) on an aggregate plate of coarse aggregate (10) to obtain a concrete specimen with uniform distribution, wherein an interface transition zone (9) is formed between the cement mortar (8) and the coarse aggregate (10) to ensure the uniformity of the interface transition zone (9).

3. A method for accurately determining the shrinkage coefficient of the concrete interface transition zone according to claim 1, It is characterized in that The second step includes the following steps: using a microhardness tester to measure the change trend of the hardness at the interface between cement mortar and aggregate, and calculating the thickness of the interface transition zone based on these change trends.

4. A method for accurately determining the shrinkage coefficient of the concrete interface transition zone according to claim 1, It is characterized in that The step three includes the following steps: performing a zeroing operation on the measurement module; When the humidity adjustment module is adjusted to set the humidity, the test piece will generate strain, and the strain signal is received by the measurement module and transmitted to the calculation module.

5. A method for accurately determining the shrinkage coefficient of the concrete interface transition zone according to claim 1, It is characterized in that The step 4 includes the following steps: using the measurement module to measure the aggregate specimen, cement mortar specimen and concrete specimen to calculate their strains. For the concrete specimen, its strain calculation is as follows: ； ； Similarly, we can get: ； Therefore, the calculation formula for the shrinkage coefficient of the interface transition zone can be deduced as follows: ； Where: , , They are the shrinkage coefficients of the interface transition zone, total concrete specimen, aggregate and cement mortar respectively; , , are the shrinkage coefficients of aggregate, cement mortar, and interface transition zone, respectively; , , is the thickness of the interface transition zone, aggregate, and cement mortar; It is the difference between the final humidity and the initial humidity of the concrete specimen and is controlled by a digital humidity regulator.

6. A method for accurately determining the shrinkage coefficient of the concrete interface transition zone according to claim 5, It is characterized in that The step 4 includes the following steps: In the calculation formula of the shrinkage coefficient of the transition zone of the concrete interface, , , are all obtained from step 2, and It can be calculated by the following formula: ； Where: , , , They are the thickness of concrete specimen, interface transition zone, aggregate and cement mortar, respectively, which are measured in step 2.

7. A device for accurately measuring the shrinkage coefficient of the transition zone of the concrete interface, It is characterized in that include: A fixing module, used to carry and fix the manufactured test piece; A humidity adjustment module, used to adjust the humidity in the test device; A measuring module, used for measuring the strain of each test piece after the humidity of the test device is adjusted by the humidity adjustment module; The reading module is used to display the measurement data of the measurement module.

8. A device for accurately measuring the shrinkage coefficient of the concrete interface transition zone according to claim 7, It is characterized in that The fixing module comprises an iron shell (6), the iron shell (6) being a box body with an opening at the top, the bottom of the iron shell (6) being provided with bases (4) symmetrical in pairs about the middle position of the bottom of the iron shell (6), the iron shell (6) being supported and matched with the test platform through the bases (4), and a rotatable cover plate (7) being hingedly connected to one side of the top of the iron shell (6), the rotatable cover plate (7) being in releasable sealing cooperation with the opening of the iron shell (6).

9. A device for accurately measuring the shrinkage coefficient of the concrete interface transition zone according to claim 8, It is characterized in that The humidity regulating module comprises a humidity regulator (5) arranged on one side of an iron casing (6); an output end of the humidity regulator (5) cooperates with the inside of the iron casing (6) to form a humidity control; a humidity regulating port (2) is arranged on a side of the iron casing (6) opposite to the humidity regulator (5); the inside of the iron casing (6) is connected to the humidity regulating port (2) via a plurality of built-in pipes.

10. A device for accurately measuring the shrinkage coefficient of the concrete interface transition zone according to claim 9, It is characterized in that The measuring module comprises a high-precision strain gauge (3) arranged in an iron housing (6); The reading module comprises an electronic reader (1) arranged on one side of the iron housing (6); the high-precision strain gauge (3) forms an inductive match with each test piece; the electronic reader (1) and the high-precision strain gauge (3) are electrically connected to form a reading match.

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