Test apparatus and method for concrete-rock interface bond performance under dynamic load

Abstract

This invention relates to a testing device and method for the bonding performance of concrete-rock interface under dynamic loading, belonging to the field of concrete technology. The method includes the following steps: preparing a binary concrete-rock specimen; placing the prepared binary specimen into a dynamic load-shear loading system; applying a dynamic and static load of a certain frequency and load value to the top surface of the binary specimen by changing the loading control system parameters, and recording the data obtained from a CT scanning system and a resistivity meter during the shearing process; importing the data into a data processing system for processing and analysis; determining the microscopic damage characteristics of the concrete-rock binary specimen during the shearing process; and comprehensively evaluating the bonding performance of the concrete-rock interface under dynamic loading by combining the results of shear mechanics tests. By using CT scanning and resistivity testing to comprehensively monitor microscopic damage characteristics such as cracks near the interface of the binary specimen during the shearing process, the results of the two testing methods can mutually verify and supplement each other, greatly improving the accuracy of the test.

Description

Technical Field

[0001] This invention relates to the field of concrete technology, and more particularly to a testing apparatus and method for the bonding performance of concrete-rock interface under dynamic load. Background Technology

[0002] Concrete, as a crucial component of rock mass protection, relies on excellent bonding properties between itself and the coal (rock) face for its support function to function effectively. Approximately 75% of mine roadways in my country are affected by dynamic pressure disturbance. After being subjected to mining dynamic pressure, the mechanical properties and stability of the surrounding rock significantly degrade, leading to deformation and cross-sectional shrinkage. This results in cracking and damage to the concrete lining structure, affecting the normal use and durability of the roadway and posing a serious threat to its long-term safe operation.

[0003] The concrete-rock interface, a traditionally weak surface, has always presented a technical challenge in rock mass support due to its bonding performance. Under mining-induced stress, it is prone to problems such as interface debonding and cracking, preventing the effective implementation of concrete-surrounding rock combined support. Therefore, proposing an effective experimental method to evaluate the bonding capacity between concrete and surrounding rock is of great significance for ensuring the safe mining and long-term stability of mines.

[0004] Current testing of the bonding performance of the concrete-rock binary interface mainly focuses on its peel tensile properties and shear strength. Testing methods include pull-out tests, direct shear tests, splitting tensile tests, and non-destructive testing. Among these, acoustic emission (AE) technology can characterize the location and size of cracks during the interfacial fracture process, thereby enabling quantitative analysis of interfacial microstructural damage.

[0005] In addition, some scholars have explored the impact of drill-and-blast construction on the strength of the concrete-surrounding rock interface by using a combination of a shaking table or a suspended hammer and a shearing instrument. At the same time, they have used CT scans to analyze the damage of the "concrete-rock" binary specimens after applying vibration loads.

[0006] Existing test methods for preparing "concrete-rock" binary specimens often involve casting shotcrete onto rock to create bonded specimens. However, the roughness and undulations at the interface in actual engineering are only simulated by carving grooves on one side of the rock, lacking consideration of the influence of anchor bolts and steel mesh on the "concrete-rock" binary interface during lining construction. Summary of the Invention

[0007] In order to overcome the shortcomings of the prior art, the main objective of the present invention is to provide a testing device and method for the bonding performance of concrete-rock interface under dynamic load.

[0008] To achieve the above objectives, the present invention employs the following technical solution: a testing device and method for the bonding performance of concrete-rock interface under dynamic load, comprising the following steps:

[0009] Preparation of binary concrete-rock specimens;

[0010] After applying a dynamic load of a certain frequency and load value to the prepared binary sample, the load is switched to a static load. The horizontal loader is then activated to obtain CT images of microstructural continuity failure and resistivity data of cross sections at different locations.

[0011] The acquired images and data were analyzed and processed to determine the microscopic damage characteristics of the concrete-rock binary specimen during shearing. Combined with the shear mechanics test results, the bonding performance of the concrete-rock interface under dynamic load was comprehensively evaluated.

[0012] More specifically, the analysis and processing includes the following steps:

[0013] Three-dimensional reconstruction was performed on CT images showing disruption of microstructural continuity to obtain the porosity W of the microstructural parameter pore model. ρ The equivalent maximum radius of pores, D ρp Number of pores N p Examine the structural parameters in detail;

[0014] The microstructure parameters are compared with the initial microstructure parameters of the binary sample. The greater the change between the two, the weaker the interfacial adhesion performance.

[0015] The resistivity of each measuring point during the shear failure process is averaged and compared with the initial average resistivity of the binary sample at that point. The larger the increment, the weaker the interfacial bonding performance.

[0016] More specifically, the formula for comprehensively evaluating the bond performance of the concrete-rock interface under dynamic load is as follows:

[0017] σ=σ max +α(aΔW ρ +bΔD ρp +cΔN p )+βΔR

[0018] Where σ is the comprehensive evaluation index of the bonding performance of the binary system, σ max ΔW represents the peak stress obtained from the shear mechanics test. ρ ΔD represents the porosity increment before and after shear failure. ρp ΔN represents the equivalent maximum radius increment of the pores before and after shear failure. p ΔR represents the increase in the number of pores before and after shear failure, α and β represent the increase in the average resistivity at each point before and after shear failure, a, b, and c represent the influence coefficients of pore and cross-sectional resistivity, respectively, and a, b, and c represent the influence weight ratios of each pore parameter.

[0019] More specifically, the preparation of the binary sample includes the following steps:

[0020] Obtain a cuboid rock sample with dimensions of 100mm×100mm×50mm after grinding, and place the rock sample into a mold.

[0021] Several threaded steel wires are evenly spread on the top of the rock sample, and the length of the threaded steel wires is 10-20mm.

[0022] Obtain concrete with the appropriate mix proportions for the working conditions, pour the concrete into a mold, and vibrate it. After curing for 28 days, obtain a cubic sample with dimensions of 100mm×100mm×100mm, with the concrete layer and the rock layer both having a height of 50mm.

[0023] More specifically, the loading control system is used to apply a dynamic load of a certain frequency and load value or a static load of a certain load value to the binary specimen.

[0024] A shear failure process monitoring system is used to acquire CT images of microstructural continuity failure and resistivity data of cross-sections at different locations;

[0025] The data processing system analyzes and processes the acquired CT images, resistivity, and shear stress values ​​to determine the microscopic damage characteristics and shear mechanical properties of the concrete-rock binary specimen during the shearing process.

[0026] More specifically, the loading control system includes:

[0027] Support frame;

[0028] The shear box for the binary sample is located on one side of the top of the support frame;

[0029] A hydraulic horizontal loader is located on the other side of the top of the support frame;

[0030] A pad is placed on the side of the shear box of the binary specimen away from the hydraulic horizontal loader;

[0031] A horizontal reaction baffle is provided on the support frame and located on the side away from the pad block, and is connected to the side wall of the pad block;

[0032] The reaction plate is fixed to the support frame at the bottom by multiple columns and is located above the top of the shear box;

[0033] A normal static-dynamic load loader is installed on the reaction plate, with its telescopic end facing downward and penetrating the reaction plate. By changing the loading control system parameters, a dynamic load and static load of a certain frequency and load value are applied to the top surface of the binary sample, and the shear rate of the hydraulic horizontal loader is adjusted.

[0034] The hydraulic horizontal loader contacts the side wall of the shear box, and the contact end of the hydraulic horizontal loader is equipped with a horizontal stress sensor for collecting the shear stress of the sample. The stress value obtained by the horizontal stress sensor is transmitted to the data processing system.

[0035] More specifically, the shear box of the binary sample is provided with a transparent window on the front side, and the transparent window is made of acrylic sheet.

[0036] More specifically, the shear failure process monitoring system includes a CT scanning system for acquiring images, a resistivity tester for acquiring resistivity data, and several sensor connectors respectively connected to the CT scanning system and the resistivity tester.

[0037] More specifically, the CT scanning system includes an X-ray source and a detector.

[0038] More specifically, the shear box of the binary sample is provided with two rows of resistivity test holes at the top and bottom, respectively. The two rows of resistivity test holes located on the same plane are symmetrically arranged, and each row of resistivity test holes includes a number of resistivity test holes.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] 1. This invention proposes a method for comprehensively monitoring microscopic damage characteristics such as cracks near the interface of concrete-rock composite samples during shearing by using CT scanning and resistivity testing. The results of the two testing methods can verify and supplement each other, greatly improving the accuracy of the test.

[0041] 2. The designed experimental setup can perform shear tests on binary specimens after applying dynamic loads, avoiding the impact of changing different specimens on the accuracy of experimental results. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the structure of the present invention;

[0043] Figure 2 These are the stress-strain curves from the direct shear test of the concrete-rock binary system in this embodiment of the invention.

[0044] Figure 3 This is a flowchart of the steps of the present invention.

[0045] Explanation of reference numerals in the attached drawings: 1. Support frame, 2. Detector, 3. Column, 4. Resistivity meter, 5. Data processing system, 6. X-ray source, 7. Loading control system, 8. Horizontal reaction baffle, 9. Pad, 10. Reaction plate, 11. Normal static-dynamic load loader, 12. Transparent window, 13. Horizontal stress sensor, 14. Hydraulic horizontal load loader, 15. Shear box. Detailed Implementation

[0046] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0047] Example:

[0048] See Figure 1 The testing device includes a dynamic load-shear loading system and a shear failure process monitoring system. The dynamic load-shear loading system consists of, from top to bottom, a normal static-dynamic load loader 11, a reaction plate 10, a column 3, a loading control system 7, a horizontal reaction baffle 8, a pad 9, a binary specimen shear box 15, a hydraulic horizontal loader 14, and a bottom support frame 1. One end of the normal static-dynamic load loader 11 passes through the top of the shear box 15 and contacts the top of the binary specimen. By changing the parameters of the loading control system 7, a dynamic load and a static load of a certain frequency and load value can be applied to the top surface of the binary specimen. The reaction plate 10 is connected to the column 3 by four bolts and fixed to the support frame 1 at the bottom to ensure the stability of the normal static-dynamic load loader 11. The horizontal reaction baffle 8 is connected to the pad block 9 to fix the position of the upper shear box 15 during the shearing process. The binary shear box 15 is used to place the concrete-rock binary specimen. It has a transparent window 12 made of acrylic plate on its front side, which can be used to take pictures to record the failure process of the shear band. The hydraulic horizontal loader 14 contacts the side wall of the lower shear box 15. The shearing rate of the hydraulic horizontal loader 14 in the loading control system 7 is set to apply the horizontal shear load. The contact end is equipped with a horizontal stress sensor 13 to collect the shear stress of the specimen. The obtained stress value is transmitted to the data processing system. The shear mechanics test results are used to evaluate the bonding performance of the concrete-rock interface under different working conditions from a macroscopic scale.

[0049] The shear failure monitoring system comprises an X-ray source 6, a detector 2, a resistivity meter 4, and connected sensor connectors and a data processing system. The CT scanning system, composed of the X-ray source 6 and detector 2, records the shear failure process of the binary sample in real time, acquiring microstructural continuity failure characteristics such as shear band cracks and pores. Two rows of copper nails are inserted at equal intervals at 1 / 4 and 3 / 4 distances from the front boundary on the upper and lower surfaces of the shear box 15. The resistivity meter 4 determines the size of pores and cracks at corresponding locations by measuring the resistivity of the binary sample between the two symmetrical copper nails at different positions on the upper and lower surfaces. The results measured by the CT scanning system and the resistivity meter 4 are transmitted to the data processing system for processing and analysis, comprehensively judging the microstructural damage characteristics of the concrete-rock binary sample during the shear process, providing a microscale basis for evaluating its macroscopic bonding performance and mechanism analysis.

[0050] The specific experimental steps are as follows:

[0051] Step 1: Prepare a cubic rock mass. Place a 100mm×100mm×50mm rectangular rock, after cutting and grinding, into a mold with an opening on the top and bottom surfaces and a closed side, measuring 100mm×100mm×100mm.

[0052] Step 2: Prepare concrete. Weigh out water, cement, gravel, and sand according to the concrete mix proportions for the corresponding working conditions. Mix the above ingredients and put them into a mixer to stir evenly.

[0053] Step 3: Prepare binary specimens of concrete-rock composite. Before pouring concrete onto the rock surface, evenly spread 10-20 mm long and 2 mm diameter threaded steel wires on the rock surface to simulate the influence of anchor rods and steel mesh on the interface in actual lining projects. Pour the mixed concrete into the mold and vibrate it thoroughly on the vibrating table to ensure full contact between the cast-in-place concrete and the rock interface and that the concrete is free of air bubbles. After curing for 28 days, obtain cubic specimens with a concrete layer and a rock layer height of 50 mm each and a size of 100 mm × 100 mm × 100 mm.

[0054] Step 4: Apply a load to the prepared binary specimen to simulate the disturbance to the mine roadway lining structure. Place the prepared specimen into a shear box 15 with internal dimensions of 100mm×100mm×100mm. Start the loading control system 7 to bring the normal static-dynamic load loader 11 and the hydraulic horizontal load loader 14 into contact with the specimen and the shear box 15, and then stop the movement of the loaders. Set a certain loading frequency and load value to apply a dynamic load to the top of the binary specimen through the normal loader to simulate the disturbance of mining stress to the mine roadway lining structure. After applying the dynamic load, stop applying the normal dynamic load, and apply a static load to the top of the specimen.

[0055] Step 5: Collect relevant data during the shearing process. Initiate a CT scan, using X-ray source 6 and detector 2 to capture the shearing failure characteristics of the binary sample, obtaining continuous cross-sectional images of the shearing process. Transmit these images to the data processing system for three-dimensional reconstruction to obtain the microstructural changes such as cracks and pores near the shear band. Turn on the resistivity meter 4 and use two clamps at the test end to attach to two symmetrical copper nails at different positions to test the resistivity of the cross-section of the binary sample at different locations during the shearing process, thereby indirectly analyzing the generation and development characteristics of pores and cracks at the corresponding locations. Simultaneously, start the horizontal loader to move the lower shear box 15 horizontally at a constant rate, and use the horizontal stress sensor 13 to collect stress values ​​in real time. Stop shearing when the shear stress decreases significantly or the horizontal shear displacement reaches 12 mm.

[0056] The bond properties of concrete and rock under different dynamic loads were evaluated by combining the results of shear mechanics tests, CT scans, and resistivity tests. Details are as follows:

[0057] Regarding the results of the shear mechanics test:

[0058] After dynamic loading is applied to a concrete-rock interface, the interfacial bond performance is typically evaluated based on the location of the failure point on the stress-strain curve of the direct shear test at the binary interface. That is, the peak shear stress is used as the evaluation index for bond performance; a higher peak shear stress value is considered to indicate better interfacial bond performance. For example... Figure 2 As shown, when the shear strain (i.e., shear displacement / length of the specimen in the shear direction) of conditions 1 and 2 reaches 3.04 and 6.04 respectively, the two curves show peak values. The magnitude of the stress peak point reflects the strength of the interfacial bonding ability. Therefore, the interfacial bonding performance of the specimen in condition 1 is stronger than that of the specimen in condition 2.

[0059] CT scan results:

[0060] The shearing process of a concrete-rock binary specimen under dynamic loading was captured in real time using CT scans to identify microstructural features such as cracks and pores near the interface. The CT scan results were imported into AVIZO software for 3D reconstruction. Then, a software segmentation algorithm was used to optimize the segmentation of the sandstone images, thereby obtaining the 3D structure of pores and cracks near the binary interface at different times during the shearing process. Finally, the porosity W of the pore model was extracted using software commands. ρ The equivalent maximum radius of pores, D ρp Number of pores N p The interfacial bonding performance is evaluated by the changes in the aforementioned micro-parameters after shear failure compared to the start of shear.

[0061] Table 1 shows the porosity W of two binary specimens under working conditions 1 and 2 after dynamic loading and shear testing, obtained by CT scanning at the point of failure. ρ The equivalent maximum radius of pores, D ρp Number of pores N p The values ​​are shown in Table 2, which represents the increase of the three parameters at the initial shear time for the two types of samples.

[0062] Table 2 shows that the porosity W in condition 2 after shear failure is... ρ The equivalent maximum radius of pores, D ρp Number of pores N p The increase values ​​are all significantly greater than the corresponding values ​​of condition 1. This indicates that the condition 2 sample has more pores and cracks during the shearing process, and the damage is more significant. It can be considered that its interfacial bonding performance is weaker than that of the condition 1 sample.

[0063] Table 1. Microscopic parameters of CT scans during binary shear failure under two working conditions.

[0064]

[0065] Table 2. Increase in microscopic parameters of CT scans after binary shearing under two working conditions.

[0066]

[0067] Resistivity test results:

[0068] The resistivity of cross-sections at different locations of a concrete-rock binary specimen was measured during the shear process after dynamic loading, thereby indirectly analyzing the generation and development characteristics of pores and cracks at the corresponding locations. The principle is that after cracks are generated, air replaces the original rock or concrete. Since the conductivity of air is much lower than that of solids, the conductivity of the corresponding cross-section decreases, i.e., the resistivity value increases.

[0069] The specific method is as follows: the resistivity value measured at each measuring point at each moment is averaged, and the interfacial bonding performance is evaluated by the change in the average resistivity of each point after shear failure compared with that at the beginning of shear.

[0070] According to Table 3, the resistivity increase of condition 2 after shear failure is significantly greater than the corresponding value of condition 1. Therefore, it can be concluded that the shear failure of condition 2 is more significant, and its interfacial bonding performance is weaker than that of condition 1.

[0071] Table 3. Increase in resistivity of binary material after shearing under two operating conditions.

[0072] Operating conditions Resistivity (kΩ) Operating Condition 1 312 Operating Condition 2 422

[0073] Based on the above tests, a comprehensive evaluation formula for the bond performance of concrete-rock interface under dynamic load is proposed:

[0074] σ=σ max +α(aΔW ρ +bΔD ρp +cΔN p )+βΔR

[0075] Where σ is the comprehensive evaluation index of the bonding performance of the binary system, σ max ΔW represents the peak stress obtained from the shear mechanics test. ρ ΔD represents the porosity increment before and after shear failure. ρp ΔN represents the equivalent maximum radius increment of the pores before and after shear failure. p ΔR represents the increase in the number of pores before and after shear failure, α and β represent the increase in the average resistivity at each point before and after shear failure, a, b, and c represent the influence coefficients of pore and cross-sectional resistivity, respectively, and a, b, and c represent the influence weight ratios of each pore parameter.

[0076] It should be noted that, in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0077] The above embodiments are merely illustrative examples of the present invention and do not constitute a limitation on the scope of protection of the present invention. Any designs that are the same as or similar to the present invention are within the scope of protection of the present invention.

Claims

1. A method for testing the bond performance of a concrete-rock interface under dynamic loading, characterized in that, It comprises the following steps: Preparation of concrete-rock binary sample body, including: uniformly spreading several threaded steel wires on the top of the rock sample, the length of the threaded steel wire is 10-20 mm; After applying dynamic load of a certain frequency and load value to the prepared binary sample body, switching to static load, starting the horizontal loader and obtaining CT images of microstructure continuity damage and resistivity data of different position sections; Analyzing and processing the obtained images and data, determining the mesoscopic damage characteristics of the concrete-rock binary sample body in the shearing process, and comprehensively evaluating the interfacial bonding performance of concrete-rock under dynamic load combined with the shearing mechanical test results; The formula for comprehensively evaluating the interfacial bonding performance of concrete-rock under dynamic load is: wherein, is a binary bonding performance comprehensive evaluation index, is the stress peak value obtained by the shear mechanical test, is the porosity increment before and after shear failure, is the porosity equivalent maximum radius increment before and after shear failure, is the number of pores increment before and after shear failure, is the increment of the average value of the resistivity of each point before and after shear failure, and α and β are the influence coefficients of the porosity and the cross-sectional resistivity, respectively, a, b, c are the influence weight ratios of each pore parameter, respectively; The analysis and processing comprises the following steps: The CT image of the microstructure continuity damage is reconstructed in three dimensions to obtain the porosity of the microstructure parameter pore model W ρ , pore equivalent maximum radius D ρp , pore number N p microstructure parameters Comparing the microstructure parameters with the initial microstructure parameters of the binary sample body, the greater the change between the two, the weaker the interfacial bonding performance; Obtaining the average value of the resistivity of each measuring point in the shearing damage process, and comparing the increment with the average value of the initial resistivity of the binary sample body at that point, the greater the increment, the weaker the interfacial bonding performance.

2. The method for testing the bonding performance of concrete-rock interface under dynamic load according to claim 1, characterized in that, The preparation of the binary sample body comprises the following steps: Obtaining a cuboid rock sample with a size of 100mm×100mm×50mm after grinding, and placing the rock sample into a shaped mold; Obtaining concrete with a corresponding working condition ratio, pouring the concrete into the shaped mold, and vibrating and processing, demolding and curing for 28 days to obtain a cubic sample with a size of 100mm×100mm×100mm, and the height of the concrete layer and the rock layer is 50mm.

3. A testing device for implementing the testing method of the concrete-rock interface bonding performance under the dynamic load according to claim 1, characterized in that, It comprises: A loading control system for applying dynamic load of a certain frequency and load value or static load of a certain load value to the binary sample body; A shearing damage process monitoring system for obtaining CT images of microstructure continuity damage and resistivity data of different position sections; A data processing system for analyzing and processing the obtained CT images, resistivity and shearing stress values, and determining the mesoscopic damage characteristics and shearing mechanical properties of the concrete-rock binary sample body in the shearing process.

4. The apparatus for testing the bond performance of concrete-rock interface under dynamic load according to claim 3, characterized in that, The loading control system comprises: A support frame (1); A binary sample shearing box (15) arranged on one side of the top of the support frame (1); An oil pressure horizontal loader (14) arranged on the other side of the top of the support frame (1); A cushion block (9) arranged on the side of the binary sample shearing box (15) away from the oil pressure horizontal loader (14); A horizontal reaction force baffle (8) arranged on the support frame (1) and located on the side away from the cushion block (9) and connected with the side wall of the cushion block (9); A reaction force plate (10) fixed to the bottom support frame (1) by a plurality of vertical columns (3) and located above the top of the shearing box (15); A normal static-dynamic load loader (11) is arranged on the counterforce plate (10), with its telescopic end downward and penetrating the counterforce plate (10), and by changing the parameters of the loading control system (7), dynamic load and static load of a certain frequency and load value are applied on the top surface of the binary sample, and the shear rate of the oil pressure horizontal loader (14) is regulated; The oil pressure horizontal loader (14) is in contact with the side wall of the shear box (15), and the contact end of the oil pressure horizontal loader (14) is provided with a horizontal stress sensor (13) for collecting the shear stress of the sample, and the stress value obtained by the horizontal stress sensor (13) is transmitted to the data processing system.

5. The device for testing the bonding performance of concrete-rock interface under dynamic load according to claim 4, characterized in that, The front side of the shear box (15) of the binary sample is provided with a transparent window (12) made of acrylic plate.

6. The device for testing the bonding performance of concrete-rock interface under dynamic load according to claim 3, characterized in that, The shear failure process monitoring system comprises a CT scanning system for acquiring images, a resistivity tester (4) for acquiring resistivity data, and a plurality of sensor connectors connected to the CT scanning system and the resistivity tester (4) respectively.

7. The device for testing the bonding performance of concrete-rock interface under dynamic load according to claim 6, characterized in that, The CT scanning system comprises an X-ray source (6) and a detector (2).

8. The device for testing the bonding performance of concrete-rock interface under dynamic load according to claim 3, characterized in that, The shear box (15) of the binary sample is provided with two rows of resistivity test holes at the top and the bottom respectively, and the two rows of resistivity test holes are symmetrically arranged on the same plane, and each row of resistivity test holes comprises a plurality of resistivity test holes.

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