Device and method for measuring linear expansion coefficient of concrete interface transition area

Abstract

The invention relates to the field of concrete material performance test and analysis, and discloses a concrete interface transition zone linear expansion coefficient measuring device and method, the device comprises a water circulation heating mechanism and a measuring mechanism; the water circulation heating mechanism comprises a heating cylinder, a water inlet pipe, a water outlet pipe, a test baffle plate and a temperature-adjustable cold and hot integrated circulating water machine; the temperature-adjustable cold and hot integrated circulating water machine is communicated with a heating cavity on the heating cylinder through the water inlet pipe and the water outlet pipe; the testing baffle is sealed at the opening of the heating cylinder and is connected with the measuring mechanism. According to the method, the temperature of a heating cylinder is regulated and controlled through a temperature-adjustable cold and hot integrated circulating water machine, temperature circulation is performed on an in-cavity aggregate-cement mortar combined test piece for simulating temperature change in actual engineering, the overall deformation effect is amplified through multi-interface superposition, accidental errors caused by single-interface measurement are eliminated, and the measurement accuracy is improved. Accurate determination of the linear expansion coefficient of the interface transition area is achieved, and key technical reference is provided for concrete mesoscopic temperature cracking mechanism research and anti-cracking design.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of concrete material performance test analysis, in particular to a device and method for measuring the linear expansion coefficient of the interface transition zone of concrete. BACKGROUND

[0002] The interface transition zone (ITZ) is the core interface connecting the aggregate and mortar in the multiphase system of concrete, is also the "third phase" different from the aggregate and mortar, and is the key area determining the performance of concrete. At present, it is generally believed in the academic circle that it is mainly formed due to the boundary effect of coarse aggregate and the micro-zone water secretion effect. This special area not only directly affects the mechanical properties, mass and heat transfer properties of concrete, but also is the weakest link in the concrete matrix. Existing research shows that the interface transition zone plays an important role in the strength of concrete and the failure process of concrete. From the microstructure characteristics, the interface transition zone has the significant characteristics of high porosity and low strength, and the low-density calcium hydroxide (C-H) crystals are enriched in the interface transition zone. This structural characteristic directly leads to the initiation and widespread distribution of micro-cracks in the interface transition zone; at the same time, due to the large difference in the linear expansion coefficient between the interface transition zone and the aggregate, when the temperature gradient is formed in the concrete structure due to the internal and external temperature difference, the deformation of the interface transition zone and the aggregate will not be coordinated, which will lead to the constraint stress in the concrete. With the accumulation of constraint stress, the internal crack will continue to expand, and finally cause the macroscopic cracking of concrete. Therefore, the linear expansion coefficient of the interface transition zone is particularly important in the study of the micro-temperature cracking mechanism of concrete, and due to the special structure of the interface transition zone and the extremely small size, it cannot be obtained by direct measurement.

[0003] At present, there are technical bottlenecks in the direct measurement of the linear expansion coefficient of the interface transition zone (ITZ) of concrete, and the related research has long relied on empirical values, which directly restricts the research on the microstructure of concrete, the simulation accuracy of thermal stress of concrete structure, and the temperature cracking mechanism. Specifically, the ITZ is a weak area between the aggregate and the cement matrix, with a thickness of only microns, and a porous and non-uniform structure. However, the traditional thermal expansion test equipment is limited by the millimeter-level spatial resolution, and cannot realize accurate positioning and measurement of the local micro-zone, resulting in difficulty in directly obtaining the linear expansion coefficient.

[0004] Therefore, there is an urgent need for a device and method for measuring the linear expansion coefficient of the interface transition zone of concrete to overcome the limitations of the prior art. SUMMARY

[0005] In order to overcome the problems in the prior art, the present application aims to provide a device and method for measuring the linear expansion coefficient of the interface transition zone of concrete, which realizes the measurement of the linear expansion coefficient of the interface transition zone of concrete.

[0006] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions: A method for measuring linear expansion coefficient of concrete interface transition zone, comprising the following steps: S1: making test pieces, including aggregate-cement mortar combined test pieces, aggregate test pieces and cement mortar test pieces; S2: measuring the interface transition zone thickness of the aggregate-cement mortar combined test pieces and the length of each test piece; S3: placing the test pieces in a heating cylinder, and starting an adjustable temperature cold and hot integrated circulating water machine, adjusting the temperature of the heating cavity to make the test pieces deform, measuring the deformation of the test pieces by a vibrating wire strain gauge, keeping the temperature of the heating cavity unchanged, and waiting for the vibrating wire strain gauge reading to no longer change to obtain stable measurement data; S4: calculating the linear expansion coefficient of the interface transition zone according to the measured data in S2 and S3.

[0007] The application is further provided that: in step S2, the hardness change trend of the cement mortar and the aggregate at the interface of the aggregate-cement mortar combined test pieces is measured by a microhardness tester, and the interface transition zone thickness is obtained by taking the hardness change of 20% as a threshold to judge the interface transition zone boundary.

[0008] Based on the microhardness gradient method, the ITZ boundary is accurately defined through the hardness mutation point at the mortar-aggregate interface, and the boundary blur problem caused by interference in all directions in the traditional image method is solved.

[0009] The application is further provided that: in step S3, when the test pieces are placed in the heating cylinder, one end of the test pieces slightly exceeds the heating cylinder to ensure that the test baffle is in full contact with the surface of the test pieces, and the test baffle is prevented from contacting the shell and the heating cylinder. The part of the test pieces exceeding the heating cylinder is wrapped with heat preservation asbestos to keep the temperature of the test pieces consistent.

[0010] The application is further provided that: in step S4, the linear expansion coefficient is calculated by the following formula: The linear expansion coefficient calculation formula of the test pieces is:

[0011] In the formula: is the linear expansion coefficient of the test pieces, ; is the strain of the test pieces generated by heating, ; is the difference between the final temperature and the initial temperature of the test pieces, ; based on the formula, the linear expansion coefficient of the aggregate test pieces , the linear expansion coefficient of the cement mortar test pieces are calculated respectively. For the aggregate-cement mortar combined test pieces, the deformation is:

[0012] Also have:

[0013] Accordingly, the interface transition zone of the aggregate-cement mortar combination specimen is derived as follows:

[0014] In the formula, The deformation of the aggregate-cement mortar combination specimen, The deformation of the aggregate-cement mortar combination specimen, The linear expansion coefficient of the aggregate-cement mortar combination specimen, The thickness of the interface transition zone, the aggregate plate and the cement mortar in the aggregate-cement mortar combination specimen, The difference between the final temperature and the initial temperature of the aggregate-cement mortar combination specimen, The total deformation of the aggregate-cement mortar combination specimen.

[0015] The present application further provides that the thickness of the cement mortar is Calculated by the following formula:

[0016] In the formula, The length of the aggregate-cement mortar combination specimen.

[0017] The present application also relates to a concrete interface transition zone linear expansion coefficient measuring device, which is suitable for the above-mentioned concrete interface transition zone linear expansion coefficient measuring method, and comprises a water circulation heating mechanism and a measuring mechanism. The water circulation heating mechanism comprises a heating cylinder, a water inlet pipe, a water outlet pipe and an adjustable temperature cold and hot integrated circulating water machine, the heating cylinder is provided with a heating cavity, and the adjustable temperature cold and hot integrated circulating water machine is connected with the heating cavity through the water inlet pipe and the water outlet pipe respectively. The water circulation heating mechanism further comprises a test baffle, which is arranged at the opening of the heating cylinder and connected with the measuring mechanism.

[0018] In actual use, the specimen is placed in the heating cylinder and in contact with the test baffle, the set temperature of the adjustable temperature cold and hot integrated circulating water machine is adjusted, the temperature of the water in the heating cavity is changed by the adjustable temperature cold and hot integrated circulating water machine to adjust the temperature of the specimen, and the aggregate-cement mortar combination specimen is heated to simulate the temperature change in actual engineering.

[0019] The water circulation heating mechanism further comprises a shell and a bearing platform, the shell is arranged on the bearing platform, and the heating cylinder is arranged in the shell.

[0020] The shell and the heating cylinder are provided with heat insulation cotton.

[0021] The heat insulation cotton plays a heat preservation role and prevents the temperature of the heating cylinder from fluctuating.

[0022] The measuring mechanism comprises a test special cable, a frequency reading instrument and a vibrating wire strain gauge, the vibrating wire strain gauge is connected with the frequency reading instrument through the test special cable, one end of the vibrating wire strain gauge is fixed on the shell through a bolt, and the other end is connected with the test baffle.

[0023] In summary, the beneficial effects of the above technical solutions of the present application are as follows: 1. The temperature of the heating cylinder is controlled by the temperature-adjustable cold and hot integrated water circulation machine, the aggregate-cement mortar combined test piece is heated to simulate the temperature change in the actual engineering. The device can be connected with multiple measuring devices, and the aggregate-cement mortar combined test piece, the cement mortar test piece and the aggregate test piece can be tested at the same time, which simplifies the operation process and greatly shortens the test time. Through the determination method, the interface transition zone linear expansion coefficient can be accurately determined, which provides a reference for the research of concrete mesoscopic temperature cracking mechanism and anti-cracking design in actual engineering.

[0024] 2. The overall deformation effect of the multi-interface superposition amplification ITZ is effectively eliminated, the error problem caused by accidental factors in single interface measurement is effectively eliminated, and the accuracy and objectivity of data and conclusions are ensured; based on the microhardness gradient method, the ITZ boundary is accurately defined through the hardness sudden change point at the mortar-aggregate interface, the boundary blur problem caused by interference in the traditional image method is solved, and the foundation for accurate calculation of the linear expansion coefficient is laid. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed for the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0026] Figure 1 The concrete interface transition zone linear expansion coefficient determination device; Figure 2 The aggregate-cement mortar combined test piece schematic diagram; Figure 3 The analysis model displacement nephogram when the temperature changes from 20 DEG C to 30 DEG C in embodiment 1; Figure 4 Figure 1 shows the displacement cloud map of the analysis model in Example 1 when the temperature is changed from 20℃ to 40℃.

[0027] In the figures, the meanings of the reference numerals are as follows: 1, test cable, 2, frequency reading instrument, 3, vibrating wire strain gauge, 4, fixing bolt, 5, thermal insulation cotton, 6, test baffle, 7, test piece, 8, water outlet pipe, 9, water inlet pipe, 10, adjustable temperature cold and hot integrated circulating water machine, 11, shell, 12, bearing platform, 13, heating cavity, 101, heating cylinder; 100, aggregate plate, 200, cement mortar. DETAILED DESCRIPTION

[0028] In order for those skilled in the art to better understand the technical solutions of the present application, the technical solutions of the present application will be described clearly and completely below in combination with the drawings of the present application. Other similar embodiments obtained by those skilled in the art without creative labor on the basis of the embodiments in the present application shall all belong to the scope of protection of the present application.

[0029] The present application will be further described below in combination with the drawings and preferred embodiments.

[0030] Example 1 As shown in Figures 1-4 , a method for measuring the linear expansion coefficient of the concrete interface transition zone, which is a preferred embodiment of the present application, uses a device for measuring the linear expansion coefficient of the concrete interface transition zone and comprises the following steps: S1: making a test piece 7, which includes an aggregate-cement mortar combined test piece, an aggregate test piece and a cement mortar test piece; The method for making the aggregate-cement mortar combined test piece is to polish the four sides of the aggregate plate 100 to be flat with 800-mesh fine sandpaper, then place it vertically on the bottom surface in a mold, and then pour the cement mortar 200 in the mold to obtain the aggregate-cement mortar combined test piece. The structure of the aggregate-cement mortar combined test piece is shown in Figure 2 .

[0031] The size of the aggregate plate 100 in the aggregate-cement mortar combined test piece is 20mm in length and width, 5mm in thickness, and the number is 10, and the placement interval must be greater than 2mm. The size of the aggregate-cement mortar combined test piece is 20mm in length and width, and 100mm in height.

[0032] Prepare a cement mortar test piece and an aggregate test piece of the same size as the aggregate-cement mortar combined test piece. The cement mortar of the cement mortar test piece is consistent in composition with the cement mortar of the aggregate-cement mortar combined test piece, and the aggregate plate 100 of the aggregate test piece is consistent in composition with the aggregate plate 100 of the aggregate-cement mortar combined test piece. Before testing, polish each surface of the test piece to be flat.

[0033] S2: Measure the interface transition zone thickness of the aggregate-cement mortar combination specimen and the length of each specimen 7; The hardness change trend of the cement mortar 200 and the aggregate plate 100 at the junction of the aggregate-cement mortar combination specimen is measured by using a microhardness tester, and the hardness change of 20% is taken as the threshold to determine the interface transition zone boundary to obtain the interface transition zone thickness. The instrument used for interface transition zone thickness test is HV-1000 microhardness tester.

[0034] According to the current related research, the interface transition zone thickness and strength are mainly related to the type of aggregate and the water-cement ratio of the cement mortar 200, and the interface thickness is usually 40-100 At the same time, the strength of the interface is significantly lower than that of the aggregate and mortar part, so the microhardness of the cement mortar 200 and the aggregate plate 100 at the junction of the aggregate-cement mortar combination specimen is measured by using a microhardness tester. The diamond indenter used in the microhardness test is a inverted pyramid four-sided pyramid with a face angle of 136°, and the test load is 0.098N. The length of the diagonal line of the test indentation is usually 10-20 During the test, the first point is punched at the joint, and then every 5 points are punched along the vertical aggregate direction, and the cement mortar 200 and the aggregate plate 100 are tested at the junction of the mortar side 100 The range within which the hardness changes rapidly is recorded as the boundary of the interface transition zone, and the length of this interval is the thickness of the interface transition zone.

[0035] In order to accurately obtain the interface transition zone thickness of the aggregate-cement mortar combination specimen, three places where the mortar and the aggregate meet in the specimen are selected, and the microhardness tester is used to test the interface transition zone thickness of the four sides of the specimen. Each side is selected five places with the same interval for measurement, and finally the measurement results are averaged to obtain the interface transition zone thickness.

[0036] At the same time, high-precision vernier calipers are also used to accurately measure the length of the aggregate specimen, the cement mortar specimen, and the aggregate-cement mortar combination specimen and record them.

[0037] The test principle of the Vickers microhardness tester is as follows: the Vickers hardness test is to use a 136° right rhombus diamond indenter to press into the surface of the tested object with a specified test force. After a specified holding test force time, the test force is removed, and the indentation diagonal line on the surface of the specimen is measured by using a micrometer eyepiece. The average pressure of the conical surface area of the indentation is calculated, which is the Vickers hardness value. The calculation formula is:

[0038] In the formula, is the Vickers hardness, is the experimental force, The average value of the lengths of the two diagonal lines of the indentation is taken as the indentation length.

[0039] In the formula, The indentation depth is taken as the indentation length, The average value of the lengths of the two diagonal lines of the indentation is taken as the indentation length.

[0040] S3: The test piece 7 is placed in the heating cylinder 101, and the temperature-adjustable cold and hot integrated circulating water machine 10 is turned on. The temperature of the heating cavity 13 is adjusted to deform the test piece 7. The deformation of the test piece 7 is measured by the vibrating wire strain gauge 3. The temperature of the heating cavity is kept unchanged. When the reading of the vibrating wire strain gauge no longer changes, stable measurement data is obtained. Specifically, the test piece 7 is placed in the heating cylinder 101 after the surface of the test piece 7 is smeared with a heat-conducting grease. The temperature-adjustable cold and hot integrated circulating water machine 10 is turned on. The initial temperature of the test piece is 20℃. Hot water flows in the heating cavity 13. After the temperature stabilizes, the deformation of the test piece 7 is measured by the vibrating wire strain gauge 3. When the test piece 7 is placed in the heating cylinder 101, one end of the test piece 7 slightly exceeds the heating cylinder 101 to ensure that the test baffle 6 is in full contact with the surface of the test piece 7 and to avoid the test baffle 6 from contacting the shell 11 and the heating cylinder 101, which would affect the results. The part of the test piece that exceeds the heating cylinder is wrapped with heat-insulating asbestos to keep the temperature of the test piece consistent.

[0041] After the reading of the frequency reading instrument 2 stabilizes, it is set to zero. The set temperature of the temperature-adjustable cold and hot integrated circulating water machine 10 is adjusted to 30℃, and the set temperature of 30℃ is kept unchanged. The change in the reading of the frequency reading instrument 2 is continuously observed. After the reading of the frequency reading instrument 2 stabilizes, the reading is recorded.

[0042] S4: According to the data measured in S2 and S3, the linear expansion coefficient of the interface transition zone is calculated.

[0043] The formula for calculating the linear expansion coefficient of the test piece is:

[0044] In the formula, The linear expansion coefficient of the test piece is taken as the linear expansion coefficient of the test piece, ;The strain of the test piece generated by heating is taken as the linear expansion coefficient of the test piece, ; The difference between the final temperature and the initial temperature of the test piece is taken as the linear expansion coefficient of the test piece, ; Based on the formula, the linear expansion coefficient of the aggregate test piece , and the linear expansion coefficient of the cement mortar test piece are calculated. ; For the aggregate-cement mortar combined test piece, the deformation is:

[0045] Also have:

[0046] Accordingly, the interface transition zone of the aggregate-cement mortar combination specimen is derived as follows:

[0047] In the formula, The deformation of the aggregate-cement mortar combination specimen, The deformation of the aggregate-cement mortar combination specimen, The linear expansion coefficient of the aggregate-cement mortar combination specimen, The thickness of the interface transition zone, the aggregate plate 100, and the cement mortar 200 in the aggregate-cement mortar combination specimen, The difference between the final temperature and the initial temperature of the aggregate-cement mortar combination specimen, The total deformation of the aggregate-cement mortar combination specimen.

[0048] The thickness of the cement mortar 200 The formula is as follows:

[0049] In the formula, The length of the aggregate-cement mortar combination specimen.

[0050] The linear expansion coefficient of the interface transition zone of the concrete is accurately measured by the method and device provided by the application. The aggregate-cement mortar combination specimen with a water-cement ratio of 0.5 is tested together with the cement mortar specimen and the aggregate specimen, wherein the aggregate material is limestone, and the aggregate-cement mortar combination specimen is poured according to the pouring method described in the application. The interface thickness is measured according to the method for measuring the interface thickness described in the application, and the average value of multiple measurements is 84.37 μm. The measurement data is shown in Table 1. The linear expansion coefficient of the interface transition zone is determined by the method without calculating the linear expansion coefficient of the aggregate-cement mortar combination specimen, so it is not calculated.

[0051]

[0052] The data in the above table is substituted into the linear expansion coefficient calculation formula of the interface transition zone to calculate that the linear expansion coefficient of the interface transition zone is at 20-30℃, and To verify the accuracy of the determination results, a large finite element analysis software Abaqus is used to establish a three-phase linear expansion model considering cement mortar, interface transition zone and concrete. Since only the deformation of the specimen in one direction needs to be considered, and all interface properties are the same in the finite element analysis, a specimen with the same height as the specimen described in the patent is established, which is a aggregate-cement mortar composite specimen from top to bottom, and the measured parameters are imported into the software to verify the accuracy of the method proposed in the patent.

[0053] The model adopts 4-node quadrilateral elements, with a total of 45225 nodes and 44800 elements, and the minimum element size is half of the interface thickness. The boundary conditions of the model are the same as the measuring device, and the constraints along the z-axis and x-axis are applied to the bottom and side surfaces of the model respectively. Finally, the displacement cloud of the model is analyzed, as shown in Figure 3 、 Figure 4 .

[0054] The results show that the maximum displacement of the model appears on the upper surface, and the strain can be calculated by , which is 94.93 and 189.1 , respectively. The error with the strain measured by the vibrating wire strain gauge is not more than 10%, which shows that the determination results by the method described in the invention are accurate, and the method and device for accurately measuring the linear expansion coefficient of the interface transition zone of concrete provided by the invention can accurately measure the linear expansion coefficient of the interface transition zone.

[0055] Example 2 As shown in Figure 1 , a device for measuring the linear expansion coefficient of the interface transition zone of concrete is suitable for the method for measuring the linear expansion coefficient of the interface transition zone of concrete described in Example 1, which comprises a water circulation heating mechanism and a measuring mechanism. The water circulation heating mechanism comprises a heating cylinder 101, a water inlet pipe 9, a water outlet pipe 8 and a temperature-adjustable cold and hot integrated circulating water machine 10, the heating cylinder 101 is provided with a heating cavity 13, and the temperature-adjustable cold and hot integrated circulating water machine 10 is connected with the heating cavity 13 through the water inlet pipe 9 and the water outlet pipe 8 respectively. The water circulation heating mechanism further comprises a test baffle 6, which is arranged at the opening of the heating cylinder 101, and the test baffle 6 is connected with the measuring mechanism.

[0056] In actual use, the specimen 7 is placed in the heating cylinder 101 and contacts with the test baffle 6, the set temperature of the temperature-adjustable cold and hot integrated circulating water machine 10 is adjusted, the temperature-adjustable cold and hot integrated circulating water machine 10 changes the temperature of the water in the heating cavity 13 to adjust the temperature of the specimen 7, and the heating of the aggregate-cement mortar composite specimen is used to simulate the temperature change in the actual engineering.

[0057] In the embodiment, the temperature-adjustable cold and hot integrated circulating water machine 10 is a QX-6A-HC cold and hot integrated circulating water machine.

[0058] The water circulating heating mechanism further comprises a shell 11 and a bearing platform 12, the shell 11 is arranged on the bearing platform 12, and the heating cylinder 101 is arranged in the shell 11. The shell 11 is made of metal, and the shell 11 supports the heating cylinder 101.

[0059] Heat insulation cotton 5 is arranged between the shell 11 and the heating cylinder 101. The heat insulation cotton 5 plays a heat preservation role and prevents the temperature of the heating cylinder 101 from fluctuating.

[0060] The measuring mechanism comprises a test special cable 1, a frequency reading instrument 2 and a vibrating wire strain gauge 3, the vibrating wire strain gauge 3 is connected with the frequency reading instrument 2 through the test special cable 1; one end of the vibrating wire strain gauge 3 is fixed on the shell 11 through a fixing bolt 4, and the other end is connected with the test baffle 6.

[0061] In the embodiment, the vibrating wire strain gauge 3 is a YD-YBJ vibrating wire concrete surface strain gauge, and the measurement accuracy is 0.1 .

[0062] Finally, it should be noted that the above content is only used to illustrate the technical solutions of the present application, and is not a limitation on the protection scope of the present application. Simple modifications or equivalent replacements of the technical solutions of the present application made by those skilled in the art do not deviate from the essence and scope of the technical solutions of the present application.

Claims

1. A method of determining the linear expansion coefficient of the interface transition zone of concrete, characterized in that, The method comprises the following steps: S1: making test pieces, which include aggregate-cement mortar combination test pieces, aggregate test pieces and cement mortar test pieces; S2: measuring the interface transition zone thickness of the aggregate-cement mortar combination test pieces and the lengths of the test pieces; S3: heating the test pieces until the test pieces no longer deform, and recording the deformation of the test pieces; S4: calculating the linear expansion coefficient of the interface transition zone according to the data measured in S2 and S3.

2. The method of claim 1, wherein In step S2, the hardness change trend of the cement mortar and aggregate interface of the aggregate-cement mortar combination test piece is measured by using a microhardness tester to determine the interface transition zone boundary to obtain the interface transition zone thickness.

3. The method of claim 1, wherein the method further comprises: In step S4, the linear expansion coefficient is calculated by the following formula: The linear expansion coefficient calculation formula of the test piece is: In the formula: is the linear expansion coefficient of the test piece, ; is the strain generated by heating of the test piece, ; is the difference between the final temperature and the initial temperature of the test piece, ; Based on the formula, the linear expansion coefficient of the aggregate sample is calculated , the linear expansion coefficient of the cement mortar sample ; For the aggregate-cement mortar composite specimen, the deformation thereof is: : Meanwhile, there are: Accordingly, the linear expansion coefficient calculation formula of the interface transition zone of the aggregate-cement mortar combination test piece is: In the formula, is the deformation of the aggregate-cement mortar composite specimen, is the deformation of the aggregate-cement mortar composite specimen, is the linear expansion coefficient of the aggregate-cement mortar composite specimen, is the thickness of the aggregate-cement mortar composite specimen, is the difference between the final temperature and the initial temperature of the aggregate-cement mortar composite specimen, is the total deformation of the aggregate-cement mortar composite specimen.

4. The method of claim 3, wherein the method further comprises: The thickness of the cement mortar is calculated by the following formula: In the formula, L is the length of the aggregate-cement mortar composite test piece.

5. A concrete interface transition zone linear expansion coefficient measuring device suitable for use in the concrete interface transition zone linear expansion coefficient measuring method according to any one of claims 1 to 4, characterized by, The water circulation heating mechanism comprises a heating cylinder, a water inlet pipe, a water outlet pipe and an adjustable temperature cold and hot integrated circulating water machine, the heating cylinder is provided with a heating cavity, and the adjustable temperature cold and hot integrated circulating water machine is connected with the heating cavity through the water inlet pipe and the water outlet pipe respectively. The water circulation heating mechanism further comprises a test baffle, which is arranged at the opening of the heating cylinder, and the test baffle is connected with the measuring mechanism. The water circulation heating mechanism further comprises a shell and a bearing platform, the shell is arranged on the bearing platform, and the heating cylinder is arranged in the shell.

6. The apparatus for measuring the linear expansion coefficient of a concrete interface transition zone according to claim 5, wherein Heat insulation cotton is arranged between the shell and the heating cylinder.

7. The apparatus for measuring the linear expansion coefficient of a concrete interface transition zone according to claim 6, wherein The measuring mechanism comprises a test special cable, a frequency reading instrument and a vibrating wire strain gauge, the vibrating wire strain gauge is connected with the frequency reading instrument through the test special cable, one end of the vibrating wire strain gauge is fixed on the shell through a bolt, and the other end is connected with the test baffle.

8. The apparatus for measuring the linear expansion coefficient of a concrete interface transition zone according to claim 7, wherein ​

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