A method for testing the bond-slip between spontaneous combustion coal gangue aggregate concrete and steel bar

Abstract

The present application provides a kind of spontaneous combustion coal gangue aggregate concrete and the bonding slip test method of reinforcing steel, belong to building material performance test technical field, method includes: S1.existing test piece parameter and material characteristic actual measurement;S2.test equipment debugging and parameter setting;S3.loading test and original data acquisition;S4.based on the bonding slip data processing of fusion algorithm;S5.test result verification and analysis.The present application realizes the scientific quantification of spontaneous combustion coal gangue aggregate concrete and reinforcing steel bonding slip characteristics by closed-loop design and precision control, provides strong support for engineering application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building material performance testing, in particular to a bonding-slip test method for self-ignited coal gangue aggregate concrete and steel bars. BACKGROUND

[0002] As solid waste of coal mining, self-ignited coal gangue is used to make recycled aggregate concrete, which can not only reduce environmental pollution, but also reduce the cost of building materials, and is increasingly widely used in construction engineering. The bonding-slip performance of steel bars and concrete is the core to ensure the overall stress coordination of the structure, which directly affects the bearing capacity, deformation performance and durability of the structure, so accurate quantification of the bonding-slip characteristics of the two is a key prerequisite for the popularization and application of self-ignited coal gangue aggregate concrete.

[0003] The core defects of the existing test method mainly include: first, the data processing lacks systematicness. When converting the load into bonding stress, only simple fixed geometric parameters are used for calculation, without fully considering the influence of the state change of the bonding interface on the effective bonding area during the test, resulting in deviation in the calculation of bonding stress. At the same time, the slip measurement is directly measured by the apparent reading of the displacement meter, without special removal of system errors such as steel bar elastic elongation, resulting in overestimation or underestimation of the true slip. Second, the test process design is not closed-loop, and the parameter acquisition link lacks standardization and specification. The measured values of the basic parameters such as concrete strength and steel bar mechanical properties are not paid enough attention, and the design values are mostly used instead, resulting in mismatch between the loading parameter setting and the actual characteristics of the test piece. The correlation between the pre-sequence data collection and the subsequent result analysis is weak, and the data traceability is not clear, which affects the reproducibility of the test. Third, the result verification dimension is single, and only a few parallel test pieces are used for parameter comparison to judge consistency, lacking deep verification means for the accuracy of the test data, which makes it difficult to find hidden errors in the data processing process, resulting in insufficient reliability of the final output bonding-slip characteristic parameters. Fourth, the universality and pertinence of the test method are insufficient. The existing method is mostly based on ordinary natural aggregate concrete design, which does not fully adapt to the interface characteristic differences of recycled aggregate concrete, and the test parameters and process lack flexibility adjustment space, which cannot accurately capture the unique law of the bonding-slip of recycled aggregate concrete and steel bars. These deficiencies make it difficult for the existing test method to accurately quantify the true bonding-slip characteristics of concrete and steel bars, and provide insufficient support for structural design, which restricts the safe and efficient application of various concrete materials in engineering. SUMMARY

[0004] The present application provides a bonding-slip test method for self-ignited coal gangue aggregate concrete and steel bars. The whole scheme is designed through closed-loop and precise control, which realizes the scientific quantification of the bonding-slip characteristics of self-ignited coal gangue aggregate concrete and steel bars, and provides strong support for engineering application.

[0005] To achieve the above object, the present application adopts the following technical solutions:

[0006] A self-igniting coal gangue aggregate concrete and steel bar bonding and sliding test method, comprising:

[0007] S1: determining that the test object is an existing self-igniting coal gangue aggregate concrete and steel bar test piece, using a standardized test method to measure the parameters and material properties of the test piece, obtaining the geometric parameters of the test piece, the physical and mechanical properties of the self-igniting coal gangue aggregate concrete, and the material properties of the steel bar, and forming a basic parameter set;

[0008] S2: based on the basic parameter set, selecting an electronic universal testing machine, a displacement meter and a data acquisition instrument as test equipment, and completing the installation and multi-dimensional calibration of the equipment;

[0009] S3: according to the concrete axial tensile strength, the cubic compressive strength and the steel bar diameter in the basic parameter set, setting loading parameters and data acquisition parameters, the loading parameters including hierarchical loading mode, loading rate and hierarchical standard, the data acquisition parameters including acquisition frequency and data storage format; according to the set loading parameters, performing hierarchical loading test on the test piece, synchronously collecting the load data corresponding to each level of loading and the measured sliding amount of each displacement meter through the data acquisition instrument, calculating the average measured sliding amount of each level of loading, and integrating to form an original data set of loading number-load-average measured sliding amount;

[0010] S4: three progressive fusion algorithms are used to process the original data set: through the bond stress calculation algorithm, the load data in the original data set is converted into the bond stress corresponding to the loading number, combined with the steel bar diameter and the steel bar bonding length in the basic parameter set; through the sliding amount correction algorithm, based on the bond stress output by the bond stress calculation algorithm, the steel bar elastic modulus in the basic parameter set and the measured displacement meter measuring section steel bar length, the system error caused by the elastic elongation of the steel bar is removed, and the true sliding amount corresponding to the loading number is obtained; through the bond and sliding constitutive model construction algorithm, based on the bond stress output by the bond stress calculation algorithm and the true sliding amount output by the sliding amount correction algorithm, the characteristic parameters are extracted and the stiffness coefficient is fitted, the bilinear bond and sliding constitutive model is constructed, and the final data set and the constitutive model parameter set are integrated;

[0011] S5: based on the final data set and the constitutive model parameter set obtained in S4, parallel test piece consistency verification and algorithm accuracy verification are carried out, and verification results are obtained;

[0012] S6: the basic parameter set formed in S1, the original data set formed in S3, the final data set and the constitutive model parameter set formed in S4, and the verification results obtained in S5 are summarized to generate a complete test report containing the analysis conclusion of the bond and sliding properties.

[0013] In the specification, in S1, the test piece geometric parameters include concrete section size, steel bar and concrete cover thickness, steel bar bonding length, and steel bar extension length; the physical and mechanical properties of the self-ignited coal gangue aggregate concrete include cubic compressive strength, axial tensile strength, elastic modulus, and aggregate particle size range; the steel bar material properties include steel bar type, yield strength, tensile strength, elastic modulus, steel bar diameter, and steel bar surface rib height; and the standardized test method is performed according to the recommended national standard (such as GB / T 50081-2019 and GB / T 228.1-2010, or the latest standard), and all parameters are measured at least three times and averaged.

[0014] In the specification, in S2, the multi-dimensional calibration includes: calibrating the load measurement system of the electronic universal testing machine by selecting at least five calibration points in the range of 0-200 kN with a standard force sensor to ensure that the load measurement error is ≤±0.5%; calibrating the displacement meter by selecting at least six calibration points in the range of 0-10 mm with a standard gauge block to ensure that the displacement measurement error is ≤±0.01 mm; and calibrating the data acquisition instrument and the electronic universal testing machine for synchronization to ensure that the timestamps of the load data and the slip amount data are consistent.

[0015] In the specification, in S3, the loading rate is set to 0.5 mm / min; and the determination method of the grading standard is: calculating the estimated maximum bond stress based on the concrete cubic compressive strength and the steel bar diameter in the basic parameter set, loading at 10% of the estimated maximum bond stress per level in the range of 0-0.7 times the estimated maximum bond stress, loading at 5% of the estimated maximum bond stress per level in the range of 0.7-1.0 times the estimated maximum bond stress, holding the load for 30 s after each level of loading, and stopping loading when the estimated maximum bond stress decreases to 0.8 times.

[0016] In the specification, in S4, the specific process of the bond stress calculation algorithm is: first, calculating the initial bond area of the steel bar and the concrete (the initial bond area is the cylindrical side area of the steel bar and the concrete) based on the steel bar diameter and the steel bar bonding length in the basic parameter set, and then dividing the load data of each level of loading by the initial bond area to obtain the bond stress corresponding to the loading level.

[0017] In the specification, in S4, the specific process of the slip amount correction algorithm is: first, deriving the steel bar stress corresponding to the loading level based on the bond stress output by the bond stress calculation algorithm, then calculating the elastic elongation of the steel bar corresponding to the loading level by the Hook's law based on the steel bar elastic modulus in the basic parameter set and the measured displacement meter measurement segment steel bar length (the measurement segment steel bar length is the 150 mm measured when the displacement meter is installed), and finally subtracting the elastic elongation of the steel bar from the average measured slip amount corresponding to the loading level in the original data set to obtain the true slip amount.

[0018] In the specification, in S4, the specific process of the bond-slip constitutive model construction algorithm is as follows: the yield slip (the true slip when the bond stress is 0.7 times the maximum bond stress), the maximum bond stress (the maximum value of all bond stresses), the limit slip (the true slip when the bond stress drops to 0.8 times the maximum bond stress), and the residual bond stress (the bond stress corresponding to the limit slip) are extracted from the bond stress and true slip data, and then the stiffness coefficients of the rising section and the falling section of the bond-slip relationship are fitted by the least square method, and the bilinear bond-slip constitutive model covering the elastic stage, the strengthening stage and the softening stage is constructed based on the characteristic parameters and the stiffness coefficients.

[0019] In the specification, in S4, the three progressive fusion algorithms realize precision optimization through parameter interaction: the bond stress output by the bond stress calculation algorithm is used as the core input parameter of the slip correction algorithm, and the true slip output by the slip correction algorithm is used to calibrate the initial bond area in the bond stress calculation algorithm; the bond stress and the true slip are used as the input of the bond-slip constitutive model construction algorithm, and the prediction result of the constitutive model construction algorithm is used to calibrate the calculation accuracy of the bond stress and the true slip in the opposite direction.

[0020] In the specification, in S5, the specific method of the parallel specimen consistency verification is as follows: the variation coefficient (variation coefficient = standard deviation / average value) of each parameter in the constitutive model parameter set of the same group of parallel specimens is calculated, and the variation coefficient of all parameters is required to be ≤5%; the specific method of the algorithm accuracy verification is as follows: the average relative error of the measured bond stress and the constitutive model predicted bond stress in the final data set is calculated, and the average relative error is required to be ≤4%.

[0021] In the specification, in S6, the complete test report contains six core parts: the specimen and material parameter part, which is traced back to the basic parameter set of S1; the test equipment and setting parameter part, which is traced back to the equipment calibration data of S2 and the loading and collection parameters of S3; the original data and test phenomenon part, which is traced back to the original data set of S3 and the specimen state record in the loading process; the algorithm processing result part, which is traced back to the final data set and the constitutive model parameter set of S4; the verification result part, which is traced back to the parallel specimen consistency verification and the algorithm accuracy verification result of S5; and the bond-slip characteristic conclusion part, which is obtained based on the analysis of all the foregoing data and results.

[0022] In summary, the present application has at least the following beneficial effects:

[0023] Test data accuracy improvement: Through standardized basic parameter measurement process and systematic data processing logic, the problems of using design value instead of measured value and system error not excluded are effectively avoided, ensuring the calculation accuracy of bond stress and true slip, and providing high-quality data support for characteristic quantification.

[0024] Process standardization and strong reproducibility: A closed-loop test process of parameter measurement → equipment debugging → loading collection → data processing → result verification → report generation is established, the operation specifications and data transmission path of each link are clearly defined, the test process can be repeated in different laboratories, and the comparability and public credibility of test results are improved.

[0025] Significant enhancement of result reliability: Through the double protection of parallel specimen consistency verification and data processing accuracy verification, all kinds of errors in the test process are fully investigated, and the output of bond slip key parameters and constitutive model is ensured to truly reflect the material interface characteristics, providing reliable basis for engineering design.

[0026] Wider material adaptability: The test process design takes into account the differences in characteristics of ordinary concrete and recycled aggregate concrete, and adapts to the performance characteristics of different materials through the basic parameter measurement link, without the need to significantly adjust the test framework to accurately quantify the bond slip characteristics of various concretes and steels.

[0027] Outstanding engineering application value: Accurately capture the stage characteristics and key influence law of bond slip, provide scientific and quantitative basis for steel selection, bond length optimization and numerical simulation analysis of concrete structure, help to improve the rationality and safety of structure design, and promote the popularization and application of green building materials such as recycled aggregate concrete. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The figure is a schematic diagram of the bond slip test method of self-igniting coal gangue aggregate concrete and steel involved in the present application.

[0029] Figure 2 The figure is a schematic diagram of the bond stress calculation algorithm process involved in the present application.

[0030] Figure 3 The figure is a schematic diagram of the slip correction algorithm process involved in the present application.

[0031] Figure 4 The figure is a schematic diagram of the bond slip constitutive model construction algorithm process involved in the present application. DETAILED DESCRIPTION

[0032] The embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0033] As Figure 1As shown, the embodiment provides a self-ignition coal gangue aggregate concrete and steel bar bonding and sliding test method, comprising:

[0034] S1. Existing test piece parameters and material characteristics are measured

[0035] 1.1 Purpose and core significance of measurement: The parameters and material characteristics of the existing test piece are the basic data source of the entire test method, and all subsequent steps (equipment selection, loading parameter setting, algorithm calculation, result verification) depend on it. Accurate measurement of these data can ensure the pertinence of the test process (adapt to the actual state of the test piece) and the reliability of the results (avoid calculation deviation caused by unknown parameters). The core goal of this step is: through standardized measurement methods, obtain three key data of test piece geometric parameters, concrete material characteristics, and steel material characteristics, provide selection basis for equipment debugging of S2, provide core input parameters for three algorithms of S4, and build a bridge between the actual state of the test piece and test analysis.

[0036] 1.2 Measurement content and detailed method

[0037] (1) Measurement of basic parameters of existing test piece

[0038] For 3 groups of existing test pieces with different steel bar diameters (3 parallel test pieces for each group), a digital caliper with an accuracy of 0.01 mm and a steel tape with an accuracy of 0.1 mm are used for measurement, and all parameters are measured 3 times to take the average value to ensure data accuracy:

[0039] Test piece type: through visual observation and drawing checking, confirm that the test piece is a center pull rod type (no other types, complete enumeration);

[0040] Concrete section size (mold inner diameter D): measure the diameter of 3 sections at both ends and in the middle of the test piece, take the average value, for example, 16mm steel bar corresponds to test piece D=80mm, 20mm corresponds to D=100mm, 25mm corresponds to D=125mm;

[0041] Steel bar and concrete cover thickness c: evenly select 4 measurement points on the side of the test piece, measure the distance from the outer edge of the steel bar to the surface of the concrete, take the average value, and the cover thicknesses corresponding to 16mm, 20mm, and 25mm steel bars are 32mm, 40mm, and 50mm, respectively;

[0042] Steel bar bonding length : Determine the effective contact length of the steel bar and the concrete by measuring the distance from the steel bar end mark to the concrete contact surface, which is 300mm, 350mm, and 400mm for the three steel bar specifications, respectively;

[0043] Steel bar extension length : Measure the length of the reinforcing steel that protrudes above the concrete surface at both ends of the test specimen. Both ends are 100 mm (uniform for all three groups of test specimens).

[0044] Initial crack inspection: Use a crack width gauge (precision 0.01 mm) to inspect the concrete surface and record the location, number, and width of initial cracks (if there are no initial cracks, record as "no visible initial cracks").

[0045] (2) Measurement of the properties of spontaneous coal gangue aggregate concrete materials

[0046] To avoid damaging the main structure of the test specimen, core samples are taken from the concrete surface of the non-bonding section of the test specimen (core diameter 50 mm, height 100 mm, 3 core samples per group of test specimens). The test is conducted in accordance with the recommended national standard, such as GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete":

[0047] Cubic compressive strength : Process the core samples into 100 mm x 100 mm x 100 mm cubic test blocks. Use a 2000 kN compression testing machine to conduct compression tests. Take the average of 3 test blocks per group, for example, the of the three groups of test specimens are 35 MPa, 36 MPa, and 37 MPa, respectively.

[0048] Axial tensile strength : Use the split tensile test method to calculate the axial tensile strength. The of the three groups of test specimens are 2.8 MPa, 2.9 MPa, and 3.0 MPa, respectively.

[0049] Elastic modulus : Through the compression elastic modulus test, measure the stress-strain relationship of concrete in the elastic stage and calculate the elastic modulus. The of the three groups of test specimens are all 3.0 x MPa.

[0050] Particle size range of spontaneous coal gangue aggregate : After breaking the core samples, conduct a sieve test using standard sieves (pore size 0.5 mm, 2.5 mm, 5 mm, 10 mm, 20 mm) to determine the aggregate particle size range as 0.5-20 mm (uniform for all three groups of test specimens).

[0051] (3) Measurement of the properties of reinforcing steel materials

[0052] Cut 200 mm long samples from the reinforcing steel that protrudes from both ends of the existing test specimen (cut 2 samples per group of test specimens to ensure that it does not affect the bonding section of the test specimen). Test in accordance with the recommended national standard, such as GB / T 228.1-2010 "Metallic Materials - Tensile Testing - Part 1: Room Temperature Test Methods":

[0053] Steel bar model: through visual observation (ribbed form) and tensile test (yield strength), the steel bars of the three groups of specimens are HRB400 grade ribbed steel bars;

[0054] Yield strength : The tensile test was carried out by using an electronic universal testing machine, and the stress value in the yield stage was recorded. The yield strength of the three groups of steel bars was 400 MPa.

[0055] Tensile strength : The maximum stress value of the tensile test was recorded. The tensile strength of the three groups of steel bars was 540 MPa.

[0056] Elastic modulus : The elastic modulus of the three groups of steel bars was calculated by the data of the elastic stage of the tensile test, which was 2.0 x MPa.

[0057] Steel bar diameter d: The diameters of three cross sections at both ends and the middle of the steel bar were measured by using a digital caliper, and the average value was taken. The d of the three groups of specimens was 16 mm, 20 mm and 25 mm respectively (corresponding to the specimen group).

[0058] Rib height of steel bar surface : The height of the horizontal rib on the surface of the steel bar was measured, and the average value of three different ribs was taken. The rib height of the three groups of steel bars was 1.5 mm.

[0059] 1.3 Data arrangement: all the measured data were arranged into a specimen-material parameter table to clearly define the corresponding parameters of each group of specimens and ensure clear traceability of the parameters.

[0060] S2. Test equipment debugging and parameter setting

[0061] 2.1 Purpose and core significance of debugging: the performance and parameter setting of the test equipment directly determine the stability of the loading process and the accuracy of data acquisition. If the equipment selection is improper or the parameter setting is unreasonable, it may lead to abnormal failure mode of the specimen, distorted data (such as brittle failure caused by too fast loading, and slip measurement error caused by improper arrangement of displacement meter). The core goal of this step is to select appropriate test equipment based on the specimen parameters and material characteristics of S1, complete equipment installation, calibration, and set scientific loading and acquisition parameters, to provide a stable and accurate test platform for the loading test of S3, and ensure that the original data collected can truly reflect the bonding and slip behavior of the specimen.

[0062] 2.2 Equipment selection and installation debugging

[0063] (1) Core equipment selection basis and parameters

[0064] ​​​​All equipment selections are based on the specimen parameters and material properties of the S1 to ensure performance meets testing requirements.

[0065] Electronic universal testing machine: based on the concrete compressive strength of S1 , tensile strength of steel bars Calculate the maximum load requirement: The maximum bond strength of a 25mm steel bar is approximately Considering the safety factor, an electronic universal testing machine with a maximum loading force of 500kN and a loading accuracy of ±0.5% was selected to ensure a smooth loading process and accurate force measurement.

[0066] Displacement gauges: The estimated limit slip of S1 is 4.0 mm. Four resistance strain gauges with a range of 0-50 mm and a measurement accuracy of ±0.01 mm are selected to meet the requirements of slip measurement range and accuracy.

[0067] Data acquisition instrument: To ensure the synchronization of load and displacement data, a multi-channel data acquisition instrument with a sampling frequency of 10Hz and ≥8 channels is selected to support synchronous acquisition and real-time storage of load and displacement signals, avoiding errors caused by data lag.

[0068] (2) Equipment installation and precise commissioning

[0069] 1. Specimen Installation and Calibration: Slowly place the existing specimen corresponding to S1 between the upper and lower clamps of the electronic universal testing machine. The upper clamp secures the top protruding reinforcing bar (100mm extension length), and the lower clamp secures the bottom protruding reinforcing bar. Use a spirit level to calibrate the specimen's axis, ensuring it coincides with the machine's loading axis (deviation ≤ 0.5mm) to avoid uneven stress distribution caused by eccentric loading. After installation, apply a light preload (5% of the estimated maximum load) and check for looseness. Once confirmed to be normal, unload the specimen.

[0070] 2. Displacement gauge arrangement and fixing: Four displacement gauges are evenly arranged on the concrete surface of the specimen along the length of the bonded section. The specific positions are: at a distance of 1 meter from the top of the concrete surface of the specimen. place ( The bond length of S1 is used, for example, the arrangement positions of 16mm steel bar specimens are 75mm, 150mm, 225mm, and 300mm. The fixed end of the displacement gauge is bonded to the concrete surface with high-strength structural adhesive (the concrete surface is ground before bonding to remove laitance). The measuring end is fixed to the side of the protruding end of the steel bar through a magnetic base. Adjust the direction of the displacement gauge to ensure that the measuring axis is parallel to the steel bar axis (deviation ≤1°) to avoid measurement errors in slippage caused by angular deviation.

[0071] (3) Equipment calibration process

[0072] 1. Universal testing machine calibration: Use standard force sensor (accuracy ±0.1%) to calibrate the load measurement system of the testing machine, select 5 calibration points (0kN, 50kN, 100kN, 150kN, 200kN) in the range of 0-200kN, repeat measurement 3 times at each point, ensure that the load measurement error is ≤±0.5%;

[0073] 2. Displacement meter calibration: Use standard gauge block (accuracy ±0.001mm) to calibrate 4 displacement meters, select 6 calibration points in the range of 0-10mm, measure 3 times at each point, ensure that the displacement measurement error is ≤±0.01mm;

[0074] 3. Synchronization calibration: Start the data acquisition instrument and the universal testing machine, set the pre-loading rate to 0.2mm / min, unload after pre-loading to 5kN, check whether the load data recorded by the acquisition instrument and the load data displayed by the testing machine, the displacement data recorded by the displacement meter are synchronized, ensure that the time stamp is consistent, there is no delay phenomenon.

[0075] 2.3 Load and acquisition parameter setting

[0076] All parameters are calculated based on the material properties and specimen parameters of S1, to ensure scientificity and pertinence:

[0077] (1) Loading mode and rate setting

[0078] Loading mode: Use step loading mode, because there are stages of elasticity, strengthening, softening, etc. in the process of bond slip, step loading can clearly capture the stress-slip relationship of each stage, avoid key data loss caused by continuous loading;

[0079] Loading rate: based on the axial tensile strength of S1 concrete Set, about 2.8-3.0MPa, the tensile performance of concrete is weak, if the loading is too fast (>1mm / min), it will cause brittle failure of the specimen, which cannot reflect the real bond characteristics, therefore, set the loading rate v=0.5mm / min, to ensure that the loading process matches the bond failure process of the specimen.

[0080] (2) Step loading standard calculation

[0081] Estimate the maximum bond stress Based on the cube compressive strength of S1 and steel bar diameter d, the formula is:

[0082] ;

[0083] Take the 16mm steel bar specimen in S1 ( =35MPa, d=16mm) as an example, (Actual due to spontaneous combustion of coal gangue aggregate characteristics, measured about 3.2MPa, estimated for classification reference).

[0084] Classification criteria are as follows:

[0085] Elastic stage (0~0.7 ): according to each level 10% loading, for example, the estimated =8MPa, each level of loading corresponding to the load of about =0.8x15079.68≈12kN, each level of loading after holding 30s, to ensure that the stress uniformity of the specimen transmission, stable data;

[0086] Strengthening stage (0.7 ~ ): according to each level 5% loading, each level of holding 30s, this stage of bond stress growth accelerated, reduce the interval between classification can accurately capture the maximum bond stress corresponding to the slip;

[0087] Softening stage (after ): continue to load to the load drop to 0.8 , stop loading, this stage of bond interface damage, slip quickly, no need to classify, continuous loading to the target load.

[0088] (3) data acquisition parameter setting

[0089] Acquisition trigger condition: after loading, data acquisition instrument and universal testing machine synchronous trigger, real-time acquisition of each level of loading corresponding to the load data, 4 displacement meter measurement data, acquisition frequency 10Hz, to ensure that the key data of each loading stage is not lost;

[0090] Data storage format: acquisition data with time stamp-loading level-load value-displacement meter 1 data-displacement meter 2 data-displacement meter 3 data-displacement meter 4 data format stored as CSV file, convenient for subsequent S3 data arrangement and S4 algorithm call.

[0091] 2.4 Debugging result confirmation

[0092] After debugging, run the test: start the test machine, according to the set loading rate to run to 10mm displacement, check whether the equipment runs smoothly, whether the displacement meter reads normally, whether the data acquisition is synchronous. Confirm that all equipment parameters meet the requirements, record the debugging report, and make clear the equipment model, calibration data, and set parameters, to prepare for S3 loading test.

[0093] S3. Loading test and original data acquisition

[0094] 3.1 Test Objectives and Core Significance: Loading tests are the direct step in obtaining raw bond-slip data and the core of the entire testing method. Through a scientific loading process, the actual stress state of self-combusting coal gangue aggregate concrete and reinforcing steel is simulated, the relationship between load and slip is recorded, and the failure mode of the specimen is observed. This provides first-hand raw data for the S4 algorithm processing. The core objective of this step is to strictly execute the loading according to the parameters set in S2, accurately collect load and slip data, record the specimen failure process and mode, and ensure the integrity and accuracy of the raw data, laying the foundation for subsequent data processing and characteristic analysis.

[0095] 3.2 Detailed Loading Test Process

[0096] (1) Specimen installation verification and preparation

[0097] Before formal loading, a final check of the specimen installation status should be performed to avoid deviations caused by transportation and placement:

[0098] Axis verification: Use a laser rangefinder to measure the concentricity of the reinforcing bars at both ends of the specimen with the clamps of the testing machine, ensuring that the deviation is ≤0.5mm. If there is a deviation, fine-tune the position of the clamps until it meets the requirements.

[0099] Displacement gauge verification: Check the adhesion of the four displacement gauges to ensure they are not loose or detached. Use a multimeter to measure the resistance of the displacement gauges to ensure the signal is normal. Record the initial readings of the displacement gauges as the basis for calculating the slip.

[0100] Specimen condition record: The initial state of the specimen was photographed with a high-definition camera to record whether there were new cracks on the concrete surface, whether there was rust on the protruding ends of the reinforcing bars, etc., to provide a comparative basis for subsequent failure mode analysis.

[0101] (2) Hierarchical loading execution and status observation

[0102] Start the electronic universal testing machine and strictly follow the loading rate (0.5 mm / min) and grading standards set in S2. During the loading process, a designated person should observe the condition of the specimen throughout.

[0103] Elastic phase (0~0.7) After each loading stage, hold the load for 30 seconds and observe whether cracks appear on the concrete surface. If cracks appear, record the loading stage number and the corresponding load value when the cracks appear. Use a crack width ruler to measure the crack width (accurate to 0.01mm) and mark the crack location;

[0104] Strengthening phase (0.7) ~ ): Hold the load for 30 s after each level, observe whether the crack expands (length, width change), whether there is evidence of slip between the reinforcement and the concrete (judged by changes in displacement meter readings), record the loading level when the maximum load occurs (corresponding );

[0105] Softening stage ( After): Continue loading, observe rapid crack propagation, concrete spalling, when the load drops to 0.8 , stop loading immediately to avoid complete specimen failure resulting in data loss; if severe concrete spalling, reinforcement pullout occurs during loading, even if the load has not dropped to 0.8 , stop loading to ensure test safety.

[0106] (3) Raw data acquisition and synchronous control

[0107] Data acquisition instrument and universal testing machine work synchronously, collect data at a frequency of 10 Hz to ensure that the timestamps of load and displacement data are consistent:

[0108] Load data acquisition: Collect the test machine output load value corresponding to each loading level (i is the loading level, starting from 1 and increasing), unit is N, accurate to 1 N;

[0109] Slip data acquisition: Collect real-time readings of 4 displacement meters (j = 1, 2, 3, 4 is the displacement meter number, i is the loading level), unit is mm, accurate to 0.001 mm;

[0110] Real-time data processing: After completing 5 levels of loading, check the integrity of the collected data. If there is data loss or abnormal fluctuations (such as sudden load drop, displacement meter reading mutation), pause loading, check equipment status, remove faults and reload to ensure continuous data without loss.

[0111] 3.3 Data processing and output

[0112] After the loading test is completed, the raw data collected is preliminarily processed:

[0113] Slip average value calculation: For each loading level i, calculate the average value of the measurements of the 4 displacement meters, the formula is:

[0114] ;

[0115] Where is the average measured slip value (mm) corresponding to the i-th loading level, eliminating the measurement error of a single displacement meter;

[0116] Raw data set construction: Construct the loading level i, load , average measured slip Integrate, form load step-load-average measured slip original dataset (n is total load step, n = 20 for 16mm specimen, n = 22 for 20mm specimen, n = 25 for 25mm specimen);

[0117] Failure mode record: Take high-definition camera to shoot the final failure mode of the specimen, record the failure type (such as concrete splitting failure, steel bar pull-out failure, bond surface shear failure), crack distribution, concrete spalling range and other information, which is saved together with the original dataset.

[0118] 3.4 Data transfer instructions

[0119] The original dataset D after sorting will be directly transferred to S4, in which the load As input parameters of algorithm 1, used for bond stress calculation; average measured slip As input parameters of algorithm 2, used for true slip correction. At the same time, the failure mode record will be used as an auxiliary basis for S5 characteristic analysis, ensuring the whole process transfer of original data from collection to processing and analysis, and providing complete data support for subsequent steps.

[0120] S4. Bond-slip data processing based on fusion algorithm

[0121] After completing the loading test in S3, the load step-load-average measured slip original dataset D has been obtained, but this dataset only contains apparent physical quantities and cannot directly reflect the true bond-slip characteristics of self-ignited coal gangue aggregate concrete and steel bars: the load needs to be converted into bond stress representing the bond capacity, the average measured slip needs to eliminate the systematic error of steel bar elastic elongation, and finally the internal relationship between bond stress and true slip needs to be quantified through mathematical model. Therefore, this step, as the core link of data processing in the whole test method, designs three algorithms that are progressive and closely connected, to realize the conversion of original load → bond stress, the correction of apparent slip → true slip, and the construction of discrete data → continuous constitutive model, all calculations taking the specimen and material parameters (such as steel bar diameter d, bond length , steel bar elastic modulus ) of S1 and the original data of S3 as input, and finally outputting the dataset and constitutive model that can be directly used for S5 verification, ensuring the logical closed loop from data collection to characteristic quantification.

[0122] 4.1 Algorithm 1: Bond stress calculation algorithm

[0123] 4.1.1 Algorithm design background and core role

[0124] Load data collected in S3 is the total tensile force that the steel bar bears, and the core index for evaluating the bond performance between concrete and steel bar is bond stress, i.e. the bond force per unit bond area, which can directly reflect the shear strength of the contact surface. If only total load is analyzed, the results cannot be compared due to different steel bar diameters and bond lengths (for example, under the same load, the stress per unit area of thin steel bars is much greater than that of thick steel bars). Therefore, the core function of this algorithm is to convert the total load of S3 into bond stress of the unified evaluation standard based on the geometric parameters (steel bar diameter d, bond length Figure 2 ) of the test specimen measured by S1, providing basic data for subsequent slip correction and constitutive model construction, and is the stress conversion hub of the entire data processing flow. The flow is shown in

[0125] 4.1.2 Model construction

[0126] This model is based on the principle of force balance, and the core is to convert the total load into bond stress per unit area through the bond area, as follows:

[0127] (1) Core parameter definition

[0128] : Total load corresponding to the i-th level of loading (N), directly taken from the S3 original data set D, for example, the 16 mm steel bar test specimen is 8000 N at the 5th level of loading, and 15000 N at the 10th level of loading; d: Steel bar diameter (mm), taken from the S1 measured results, with 3 specifications, 16 mm, 20 mm and 25 mm, corresponding to different test specimen groups; : Bond length between steel bar and concrete (mm), taken from the S1 measured results, with bond lengths of 300 mm, 350 mm and 400 mm for 16 mm, 20 mm and 25 mm steel bars, respectively; : Initial bond area between steel bar and concrete (A0), which refers to the effective contact area between steel bar and concrete, and since the contact form is a cylindrical side, it is calculated according to the cylindrical side area formula; : Bond stress corresponding to the i-th level of loading (MPa), which is the core output parameter of this algorithm; : Pi, taken as a fixed value of 3.1416 to ensure calculation accuracy. (2) Formula derivation and calculation logic

[0129] 1. First step: Calculate the initial bond area

[0130]

[0131] ​​​​The bond between steel and concrete occurs on the side of the steel, so the bond area is equal to the perimeter of the steel multiplied by the bond length, the formula is:

[0132] ;

[0133] Take a 16mm steel specimen as an example, d = 16mm, = 300mm, then = 3.1416 x 16 x 300 ≈ 15079.68 ; for a 20mm steel specimen, = 3.1416 x 20 x 350 ≈ 21991.2 ; for a 25mm steel specimen, = 3.1416 x 25 x 400 ≈ 31416 .

[0134] 2. Step 2: Calculate the bond stress

[0135] According to the balance of forces, the total load borne by the steel is equal to the total bond force provided by the bond surface, and the total bond force is equal to the bond stress multiplied by the bond area , so the formula for calculating the bond stress is:

[0136] ;

[0137] Similarly, take a 16mm steel specimen as an example, when = 8000N, = 8000 / 15079.68 ≈ 0.53MPa; when = 15000N, = 15000 / 15079.68 ≈ 0.99MPa; for a 20mm steel specimen, = 12000N, = 12000 / 21991.2 ≈ 0.54MPa.

[0138] 4.1.3 Model training

[0139] To ensure the accuracy of the bond stress calculation, the model needs to be trained and calibrated using standard specimens, the specific process is as follows:

[0140] 1. Preparation of standard specimens: In accordance with recommended national standards, such as GB / T 50204-2015 Code for Acceptance of Construction Quality of Concrete Structures, three sets of standard bond specimens with the same parameters as the test specimens were prepared (reinforcing bar diameters of 16mm, 20mm, and 25mm, bond lengths of 300mm, 350mm, and 400mm, and concrete strengths the same as those of self-igniting coal gangue aggregate concrete), with three parallel specimens in each set;

[0141] 2. Standard Test: The same loading method (staged loading, rate 0.5 mm / min) and data acquisition method as S3 were used. Simultaneously, the true bond stress of the standard specimen was obtained through direct strain gauge measurement: Five strain gauges were evenly attached along the length of the bonded section of the reinforcing steel. The stress in the reinforcing steel at each section was calculated using the strain values, and then the bond stress was inferred. ;

[0142] 3. Model calibration: The standard specimen... Substitute into the formula of this algorithm to calculate the predicted bond stress ,contrast and Relative error:

[0143] ;

[0144] The maximum relative error of each group of standard specimens is required. (For example, the maximum size of a 16mm standard specimen) =2.5%, 20mm is 2.8%, 25mm is 2.3%). If the error exceeds the range, the bond length in S1 needs to be checked. Measurement accuracy or load in S3 To improve the accuracy of data acquisition, recalibrate until the requirements are met.

[0145] 4.1.4 Model Application

[0146] Load each level in the original S3 dataset D. Combined with the S1 parameters (d, ...) of the corresponding specimen By substituting each value into the algorithm formula, the bond stress at each loading level can be calculated. and with , (The average measured slip of S3) is integrated to form an intermediate dataset. (Where n is the total number of loading stages, n=20 for 16mm specimens, n=22 for 20mm specimens, and n=25 for 25mm specimens).

[0147] The core output of this dataset is It will serve as the core input parameter for Algorithm 2—Algorithm 2 needs to be based on The elastic elongation of the reinforcing bar is derived, and then the slip is corrected, realizing the transfer of stress data to slip correction, laying the foundation for subsequent elimination of systematic errors.

[0148] 4.2 Algorithm 2: Slip Correction Algorithm

[0149] 4.2.1 Algorithm Design Background and Core Function

[0150] S3 is the average measured slip measured by the displacement gauge. The actual bond slip is twofold: first, the actual bond slip between the concrete and the reinforcing steel, and second, the elastic elongation of the reinforcing steel under load. Because the reinforcing steel will undergo axial elastic deformation under tension, the slip measured by the displacement gauge is greater than the actual bond slip (for example, under a load of 10000N, the elongation of a 150mm length of 16mm reinforcing steel is about 0.04mm, accounting for more than 10% of the measured slip). If this systematic error is not eliminated, the actual slip will be seriously overestimated, leading to distortion of the subsequent constitutive model.

[0151] Therefore, the core function of this algorithm is to use the bond stress output by Algorithm 1. Based on this, combined with the mechanical parameters of the steel reinforcement in S1 (elastic modulus) ), derive the elastic elongation of the reinforcing bar, from After removing this error, the true bond slip amount is obtained. This provides reliable data on the slip dimension for building an accurate constitutive model for Algorithm 3, and is crucial for error removal in the entire data processing workflow. The workflow is as follows: Figure 3 As shown.

[0152] 4.2.2 Model Construction

[0153] This model is based on the force-stress-deformation mechanical chain derivation. It inversely calculates the reinforcing steel stress through bond stress, and then uses Hooke's law to calculate the elastic elongation, ultimately achieving slip correction, as detailed below:

[0154] (1) Definition of core parameters

[0155] The bond stress (MPa) corresponding to the i-th level of loading is taken from the output of Algorithm 1, i.e. In d: diameter of the reinforcing bar (mm), taken from the actual measurement in S1, which is completely consistent with d in Algorithm 1; : Rebar bond length (mm), taken from actual measurement in S1, and compared with Algorithm 1. completely consistent; : The steel reinforcement stress (MPa) corresponding to the i-th level of loading, which is an intermediate parameter of this algorithm; : Elastic modulus of steel reinforcement (MPa), taken from actual measurement in S1, HRB400 grade steel reinforcement. 2.0× MPa (16mm, 20mm, 25mm reinforcement are the same); : reinforcement length of displacement meter measurement section (mm), the measured value when installing displacement meter - the fixed end of displacement meter is pasted on the concrete surface, and the measurement end is pasted on the reinforcement extension end 150mm away from the concrete surface, so = 150mm (all specimens are uniform); : elastic elongation of reinforcement corresponding to the i-th level of loading (mm), intermediate parameter of the algorithm; : average measured slip corresponding to the i-th level of loading (mm), taken from the S3 original data set D; : corrected true slip corresponding to the i-th level of loading (mm), core output parameter of the algorithm.

[0156] (2) Formula derivation and calculation logic

[0157] Model derivation is divided into three steps of reinforcement stress calculation, elastic elongation calculation and true slip calculation, forming a complete mechanical chain:

[0158] 1. First step: derive reinforcement stress from bond stress

[0159] According to the balance of forces, the total tensile force borne by the reinforcement is equal to the total bond force of the bond surface - the total bond force is ( the bond area of algorithm 1), and the total tensile force is ( the cross-sectional area of reinforcement, ). Therefore:

[0160] ;

[0161] After simplification, the reinforcement stress calculation formula is obtained: ;

[0162] Taking the 16mm reinforcement specimen as an example, when = 0.53MPa, = 4x0.53x300 / 16≈39.75MPa; when = 0.99MPa, = 4x0.99x300 / 16≈74.25MPa.

[0163] 2. Second step: calculate the elastic elongation of reinforcement

[0164] According to Hooke's law, the elongation of material in the elastic stage is equal to stress x length / elastic modulus. Since the reinforcement does not reach the yield strength during the loading process (the yield strength of HRB400 reinforcement in S1 is = 400 MPa, while the maximum steel stress is about 150 MPa, it is in the elastic stage, so:

[0165] ;

[0166] Continuing to take the 16 mm steel test piece as an example, when = 39.75 MPa, ; when = 74.25 MPa, .

[0167] 3. Third step: calculate the corrected real slip amount

[0168] The real bond slip amount is equal to the average measured slip amount minus the steel elastic elongation (systematic error), so:

[0169] ;

[0170] Still taking the 16 mm steel test piece as an example, if the 5th level loading is = 0.3 mm, = 0.03 mm, then = 0.3-0.03 = 0.27 mm; the 10th level loading is = 0.8 mm, = 0.056 mm, then = 0.8-0.056 = 0.744 mm.

[0171] 4.2.3 Model training

[0172] In order to verify the accuracy of the slip correction, the strain gauge measurement comparison method is used to train and calibrate the model, and the specific process is as follows:

[0173] 1. Strain gauge installation: on the steel bars of the test piece installed in S2, symmetrically paste 2 pieces of strain gauges (model BX120-3AA, sensitivity coefficient 2.10) within the displacement meter measurement section (L = 150 mm), the paste positions are 50 mm and 100 mm away from the concrete surface respectively, covering the full length of the measurement section, and after pasting, use epoxy resin to seal to prevent moisture or falling during loading;

[0174] 2. Strain data acquisition: during the loading test in S3, the strain values of the strain gauges and (respectively, the strain of the two strain gauges) are synchronously collected, and the average strain of each level of loading is calculated ;

[0175] 3. Real elastic elongation calculation: According to the definition of strain (strain = elongation / original length), the real elastic elongation of the steel bar is calculated ;

[0176] 4. Model calibration: Substitute into the real slip formula to obtain the real measured slip ; At the same time, the model correction slip is calculated by the formula of this algorithm , and the relative error between the two is compared

[0177] ;

[0178] The maximum relative error of each group of test pieces is required (e.g. the maximum relative error of 16mm test piece is 1.8%, 20mm is 1.5%, and 25mm is 1.9%), if the error exceeds the standard, the strain gauge sticking quality or the measured value of S1 in should be checked, and recalibrated until the requirements are met. 4.2.4 Model application

[0179] Based on the intermediate data set

[0180] , the of S3, the d of S1, , , and the measured = 150mm, are calculated step by step in the order of , to obtain the of each level of loading, and integrate with to form the intermediate data set . The core output of this data set is (bond stress) and (real slip), which will be used as the core input parameters of algorithm 3, and algorithm 3 needs to build a bond stress-real slip constitutive model based on these two parameters, realize the transmission of corrected data to model construction, and provide a basis for subsequent quantitative bond characteristics.

[0181] 4.3 Algorithm 3: Bond slip constitutive model construction algorithm

[0182] 4.3.1 Algorithm design background and core role

[0183] Through algorithm 1 and algorithm 2, we have obtained discrete data points of real slip-bond stress (i.e. in and However, discrete data cannot be directly used for engineering design or numerical simulation. For example, when calculating the deformation of a self-igniting coal gangue aggregate concrete structure, it is necessary to know the bond stress corresponding to any slip amount, which requires a continuous mathematical model (constitutive model) to describe the relationship between the two.

[0184] Therefore, the core function of this algorithm is: based on Using discrete data, a bilinear bond-slip constitutive model (covering both the rising and falling stages of bond stress) is constructed. This model quantifies the variation of bond stress with actual slip and outputs key model parameters (such as maximum bond stress, yield slip, and stiffness coefficient). It provides a mathematical description of bond characteristics for S5 result verification and subsequent engineering applications, and is the core of the relational quantification in the entire data processing workflow. The workflow is as follows: Figure 4 As shown.

[0185] 4.3.2 Model Construction

[0186] This model adopts a bilinear form, dividing the bond-slip relationship into an ascending segment (elastic-strengthening segment) and a descending segment (softening segment). First, the model characteristic parameters are defined, then the piecewise formula is derived, and finally the stiffness coefficient is fitted by the least squares method.

[0187] (1) Definition of model feature parameters

[0188] Maximum bond stress (MPa) All in the dataset The maximum value represents the limit of the bond strength between concrete and steel reinforcement, for example, in a 16mm specimen. =3.2MPa, 20mm is 3.5MPa, 25mm is 3.8MPa; Yield slip (mm), bond stress reaches 0.7 The corresponding actual slip amount at this time indicates that microcracks begin to appear at the bond interface, entering the strengthening stage. Extraction method: In Found Closest to 0.7 Data points, corresponding That is For example, a 16mm specimen with a diameter of 0.7 mm. =2.24MPa, corresponding to =0.8mm, therefore =0.8mm; Limit slip (mm), load decreases to 0.8 The corresponding actual slip amount at this time indicates that the bond interface is severely damaged, the slip amount increases significantly, and the bond stress enters a stable residual stage. Extraction method: during the later stage of loading... from Decreased to 0.8 The corresponding , for example, 0.8 =2.56 MPa, corresponding =3.5 mm, so =3.5 mm; : residual bond stress (MPa), ultimate slip corresponding bond stress, equal to 0.8 , representing the residual carrying capacity after the failure of the bonding interface, for example, 16 mm specimen =2.56 MPa; : stiffness coefficient of the ascending segment (MPa / mm), reflecting the stiffness of the bonding interface in the elastic stage, which needs to be obtained by least squares fitting; : stiffness coefficient of the descending segment (MPa / mm), reflecting the stress decay rate of the bonding interface in the softening stage, which needs to be obtained by least squares fitting; : predicted bond stress corresponding to the i-th level of loading (MPa), the calculation result of the constitutive model, used to verify the accuracy of the model.

[0189] (2) Piecewise formula of the bilinear constitutive model

[0190] 1. Ascending segment ( ): In this stage, the bonding interface has no obvious cracks, and the bond stress is linearly related to the true slip, and the formula is:

[0191] ;

[0192] Taking the 16 mm specimen as an example, if =2.49 MPa / mm, when =0.5 mm, =2.49 x 0.5 ≈ 1.245 MPa; when =0.8 mm ( ), =2.49 x 0.8 ≈ 1.99 MPa (close to 0.7 =2.24 MPa, the error is due to the fitting accuracy, within the allowable range).

[0193] 2. Descending segment ( ) : In this stage, cracks appear and expand in the bonding interface, and the bond stress decreases linearly with the increase of the true slip, and the formula is:

[0194] ;

[0195] Still taking the 16 mm specimen as an example, if =0.70 MPa / mm, when = 1.5mm, = 3.2-0.70x(1.5-0.8) = 3.2-0.49 = 2.71MPa; when = 3.5mm ( ), = 3.2-0.70x(3.5-0.8) = 3.2-1.89 = 1.31MPa (here because the actual data fluctuation, need to be optimized by fitting , the results closer to the measured value).

[0196] (3) stiffness coefficient fitting logic (least squares)

[0197] The core objective of the fitting is to make the model prediction of the bonding stress and the measured bonding stress The mean square error is minimum, the specific derivation is as follows:

[0198] 1. The fitting of the rising stiffness :

[0199] For all data points that meet (Recorded as m, 16mm test piece m=8), the mean square error objective function :

[0200] ;

[0201] In order to make minimum, the partial derivative of and let the derivative be 0:

[0202] ;

[0203] After simplification, the fitting formula of is obtained:

[0204] ;

[0205] Taking the 16mm test piece as an example, the of the m=8 rising segment data points is 10.2MPa·mm, , then =10.2 / 4.1≈2.49MPa / mm.

[0206] 2. The fitting of the descending stiffness :

[0207] For all data points that meet (Recorded as p, 16mm test piece p=12), the mean square error objective function :

[0208] ;

[0209] For the partial derivative and let the derivative be 0, after simplification, the fitting formula is obtained:

[0210] ;

[0211] Take 16mm specimen as an example, p = 12 descending segment data points = 8.6MPa·mm, then = 8.6 / 12.3≈0.70MPa / mm.

[0212] 4.3.3 Model training

[0213] To ensure the generalization ability of the constitutive model (applicable to the bond-slip characteristics of the same type of spontaneous combustion coal gangue aggregate concrete and steel bars), cross-validation method is used for training, and the specific process is as follows:

[0214] 1. Data division: the middle data set is randomly divided into training set (70% data points, used for fitting stiffness coefficient) and validation set (30% data points, used for verifying model accuracy) according to the ratio of 7:3, for example, 16mm specimen has 20 data points, 14 in the training set and 6 in the validation set; 20mm specimen has 22 data points, 15 in the training set and 7 in the validation set; 25mm specimen has 25 data points, 18 in the training set and 7 in the validation set;

[0215] 2. Training set fitting: use the training set and , calculate and through the above fitting formula, and build the preliminary constitutive model;

[0216] 3. Validation set evaluation: substitute the validation set into the preliminary constitutive model to calculate the predicted bond stress , and compare it with the measured of the validation set to calculate the determination coefficient (reflecting the goodness of fit of the model, the closer to 1, the higher the model accuracy):

[0217] ;

[0218] In the formula, q is the number of data points in the validation set, is the average value of the validation set . The requirement is (for example, 16mm specimen ​= 0.96, 0.95 for 20 mm, 0.97 for 25 mm), if not satisfied, re-divide the training set and validation set (a total of 3 times, take the optimal result), or remove abnormal data points (such as abnormal generated by device fluctuations during loading), and re-fit until the requirements are met.

[0219] 4.3.4 Model Application

[0220] Substitute the of all data points in into the constitutive model (select the rising or falling segment formula according to the size of and ), calculate the of each loading stage, and integrate with to form the final data set ; at the same time, sort out the model characteristic parameters and stiffness coefficients to form the constitutive model parameter set , for example, the of the 16 mm specimen is {2.49 MPa / mm, 0.70 MPa / mm, 0.8 mm, 3.2 MPa, 3.5 mm, 2.56 MPa}, the of the 20 mm specimen is {2.65 MPa / mm, 0.68 MPa / mm, 0.9 mm, 3.5 MPa, 3.8 mm, 2.8 MPa}, and the of the 25 mm specimen is {2.72 MPa / mm, 0.65 MPa / mm, 1.0 mm, 3.8 MPa, 4.0 mm, 3.04 MPa}.

[0221] The three progressive fusion algorithms of S4 form a complete closed loop through forward data transmission + backward feedback calibration, and the specific closed loop is as follows:

[0222] 1. Forward data transmission chain: original data set (S3 output) → bond stress calculation algorithm (output bond stress) → slip correction algorithm (output true slip) → bond slip constitutive model construction algorithm (output predicted bond stress, predicted slip), realizing the forward transformation from original data to quantitative model;

[0223] 2. Reverse feedback calibration chain:

[0224] The true slip output by the slip correction algorithm is used in reverse to calibrate the initial bond area in the bond stress calculation algorithm (according to the true slip to judge the bond stage, adjust the effective bond area, and optimize the bond stress calculation accuracy);

[0225] The predicted bond stress and the predicted slip amount output by the bond-slip constitutive model construction algorithm are respectively used to calibrate the measured bond stress of the bond stress calculation algorithm and the true slip amount of the slip correction algorithm (if the deviation between the predicted value and the measured value exceeds the threshold, the calculation parameters of the previous algorithm are adjusted).

[0226] The end of S4 takes the satisfaction of the preset threshold for the processing accuracy of all algorithms as the core condition, and specifically needs to meet the following three requirements at the same time before the algorithm processing can be terminated and the final data set and the constitutive model parameter set are output:

[0227] 1. The bond stress calculation algorithm accuracy meets the standard: after feedback calibration by the slip correction algorithm, the relative error between the calculated value of the bond stress and the measured bond stress of the standard specimen is ≤2% (model training accuracy requirement of algorithm 1);

[0228] 2. The slip correction algorithm accuracy meets the standard: after feedback calibration by the bond-slip constitutive model construction algorithm, the relative error between the calculated value of the true slip amount and the measured true slip amount of the strain gauge is ≤1.5% (model training accuracy requirement of algorithm 2);

[0229] 3. The bond-slip constitutive model fitting goodness meets the standard: the determination coefficient of the predicted bond stress of the constitutive model and the measured bond stress is ≥0.95 (model training accuracy requirement of algorithm 3), and the model characteristic parameters (yield slip amount, maximum bond stress, etc.) have no abnormal fluctuations.

[0230] When the above three accuracy indicators all meet the preset threshold, and the parameters after feedback calibration between algorithms tend to be stable (the deviation after two consecutive calibrations is ≤0.5%), the S4 closed-loop processing is terminated, and the final data set (true slip amount-measured bond stress-predicted bond stress) and the constitutive model parameter set (stiffness coefficient, characteristic parameter) are formally output.

[0231] The final data set and the parameter set P will be directly used as the core input of S5 - S5 needs to verify the algorithm accuracy, analyze the bond-slip characteristics based on P, realize the transfer of data processing to result verification and analysis, and lay the foundation for the conclusion output of the entire test method.

[0232] This step completes the core conversion from S3 original data to quantified bond characteristics through the layer-by-layer progression and close connection of the three algorithms: algorithm 1 converts the load into bond stress, solving the problem of missing stress dimension data; algorithm 2 removes the slip amount systematic error based on the bond stress, solving the problem of distorted slip dimension data; algorithm 3 constructs the constitutive model based on the corrected stress-slip data, solving the problem of discrete data that cannot be used in engineering.

[0233] S5. Test result verification and analysis ​​

[0234] 5.1 Verification and analysis purpose and core significance

[0235] S4 completes the transformation from raw data to constitutive model through three algorithms, but the accuracy of the algorithm processing results and the consistency of the parallel specimens need to be confirmed through scientific verification, otherwise the model parameters cannot be used for engineering application. The core goal of this step is to ensure the reliability of data processing through multidimensional verification based on the final data set ( ) and the constitutive model parameter set P( ) output by S4, and to deeply analyze the bond-slip characteristics of spontaneous combustion coal gangue aggregate concrete and steel bars, refine key rules, and provide scientific basis for engineering design and material optimization.

[0236] 5.2 Consistency verification of parallel specimens

[0237] The consistency of parallel specimens is the basis for the reliability of test results. If the parameters of parallel specimens in the same group differ too much, it indicates that there are systematic errors in the test process (such as specimen installation deviation, uneven loading). The verification process is as follows:

[0238] Parameter statistics: For the constitutive model parameter set P of each group of 3 parallel specimens, calculate the average value and standard deviation S of each parameter, for example, the 3 specimens of the 16mm steel specimen group are 3.1MPa, 3.2MPa, and 3.3MPa, the average value =3.2MPa, and the standard deviation S=0.1MPa;

[0239] Coefficient of variation calculation: The coefficient of variation CV is used to measure the relative dispersion degree of the parameter, and the calculation formula is:

[0240] ;

[0241] Calculate CV for each parameter of each group of specimens;

[0242] Consistency judgment standard: Set the coefficient of variation as qualified, if the CV of all parameters meets the requirements, it means that the test results of parallel specimens are consistent, take the average value of the parameters of the 3 specimens as the final constitutive parameters of the group of specimens; if the CV of a parameter is >5%, check back the loading process of S3 (whether there is eccentric loading), and the algorithm calculation of S4 (whether there are data abnormalities), and recalculate after eliminating errors.

[0243] Take the 16mm steel specimen group as an example, the coefficients of variation of each parameter are: the CV of =1.2%, the CV of =1.5%, The CV of is 3.1%, the CV of is 2.8%, and the CV of is 3.1%. All of them meet

[0244] 5.3 Algorithm Accuracy Verification

[0245] The algorithm accuracy directly determines the reliability of the constitutive model, and it needs to be verified by comparing the measured values with the model prediction values:

[0246] Calculation of the average relative error: Based on the final dataset of S4 , calculate the measured bond stress of each group of specimens and the predicted bond stress The average relative error of is calculated by the formula:

[0247] ;

[0248] In the formula, n is the total number of loading levels, and this index reflects the overall accuracy of the algorithm processing;

[0249] Accuracy judgment criterion: Set as qualified. If the requirements are met, it means that the bond stress calculation of Algorithm 1, the slip correction of Algorithm 2, and the model fitting of Algorithm 3 are all accurate and reliable; if > 4%, trace back and check the bond area calculation of Algorithm 1 (such as measurement value), the elastic modulus value of Algorithm 2, and the characteristic parameter extraction of Algorithm 3, and recalculate after optimization.

[0250] Taking the 20mm steel bar specimen group as an example, n = 22, = 0.78, then = 0.78 / 22 × 100% ≈ 3.5%, meeting the accuracy requirements.

[0251] 5.4 Analysis of Bond-Slip Characteristics

[0252] Based on the finally verified constitutive parameters and combined with the failure mode of the specimens, deeply analyze the bond-slip characteristics:

[0253] Drawing of the bond stress-slip curve: Taking the true slip amount as the abscissa and the bond stress as the ordinate, draw the curve of each group of specimens, clearly showing the characteristics of the three stages of the elastic stage (linear growth of stress and slip), the strengthening stage (slower stress growth and accelerated slip), and the softening stage (stress decline and rapid growth of slip);

[0254] Analysis of the Influence of Key Parameters: By comparing the parameters of three groups of specimens with different rebar diameters, the influence of rebar diameter on bond-slip characteristics was analyzed: as the rebar diameter increases from 16mm to 25mm, the maximum bond stress... The yield slip increased from 3.2 MPa to 3.8 MPa (due to the increased bonding area and thus the increased total bond strength). Increasing the diameter from 0.8mm to 1.0mm (the contact area between the thicker steel bar and the concrete is larger, and the stress required for initial slippage is higher), the ultimate slippage amount The thickness was increased from 3.5mm to 4.0mm (the ribs of the thicker steel bars have a stronger mechanical interlocking effect with the concrete, requiring greater slippage upon failure).

[0255] Analysis of the destruction mechanism: combined with The curves and failure modes of the specimens show that the bond failure between the self-igniting coal gangue aggregate concrete and the reinforcing steel is mainly shear failure of the bond surface, accompanied by concrete splitting. There are no cracks in the elastic stage, longitudinal cracks appear along the bond length in the strengthening stage, cracks expand and local spalling of concrete occurs in the softening stage, and finally the relative slippage between the reinforcing steel and the concrete occurs due to the exhaustion of the bond surface shear strength.

[0256] 5.5 Verification and Analysis Results Output

[0257] The consistency verification data, algorithm accuracy verification data, and characteristic analysis conclusions were compiled into a booklet, clearly defining the final constitutive parameters for each group of specimens. Curves and key influencing factors. These results will be directly incorporated into the S6 test report, providing quantitative basis for engineering applications (such as in the design of self-igniting coal gangue aggregate concrete structures, where the corresponding maximum bond stress and slip parameters can be selected based on the steel bar diameter), and also providing a reference for subsequent related research.

[0258] S6. Test Report Generation

[0259] 6.1 Purpose and Core Significance of the Report

[0260] The test report is the final outcome of the entire testing process. It requires not only a systematic review of test data and results, but also a clear understanding of data sources, testing methods, and characteristic patterns. This provides engineers and researchers with a complete, reproducible, and applicable technical document. The core objective of this step is to summarize all information from S1 to S5, forming a clearly structured, data-rich, and definitive test report. This ensures the traceability and repeatability of the test results, providing authoritative evidence for the application of bond-slip characteristics between self-igniting coal gangue aggregate concrete and reinforcing steel.

[0261] 6.2 Core Content and Arrangement Logic of the Report

[0262] The report is logically structured as parameter-equipment-data-processing-verification-conclusion, with each section clearly stating the data source to ensure traceability.

[0263] (1) Report Summary and Test Overview

[0264] Abstract: This paper briefly describes the test objective (quantifying the bond-slip characteristics of self-igniting coal gangue aggregate concrete and reinforcing steel), test objects (three groups of existing center-tied rod specimens with different reinforcing steel diameters), core test method (graded loading + fusion algorithm data processing), and key results (maximum bond stress, yield slip, etc.). The curve characteristics and core conclusions (the influence of rebar diameter on bond slip properties) facilitate a quick understanding of the overall test results.

[0265] Test Overview: Specify the standards on which the test was conducted (GB / T 50081-2019, GB / T 228.1-2010, etc.), the test time, the test location, and the personnel involved, to ensure that the test process is traceable.

[0266] (2) Existing specimens and material parameters

[0267] Detailed measured data for S1 are listed, including:

[0268] Basic parameters of the specimens: type and quantity of each group of specimens, concrete cross-sectional dimensions D, protective layer thickness c, and bond length. Length of rebar extension Specify the parameter measurement tools, number of measurements, and average value;

[0269] Concrete material properties: cubic compressive strength of each group of specimens Axial tensile strength Elastic modulus Aggregate particle size range Attach photos of the testing process and original test data (such as the load-displacement curve of the compressive strength test).

[0270] Reinforcing steel material properties: steel type and yield strength for each group of specimens. ,tensile strength Elastic modulus Diameter d, Rib height Attached are the tensile test report and measured data records.

[0271] (3) Test equipment and parameter settings

[0272] This section explains the equipment selection and parameter settings for S2, including:

[0273] Equipment list: Model, specifications, and accuracy of electronic universal testing machine, displacement gauge, and data acquisition instrument, with equipment calibration certificates attached;

[0274] Equipment installation and commissioning: specimen installation method, displacement gauge placement, calibration process and results (such as load calibration curve, displacement calibration data);

[0275] Loading and Acquisition Parameters: Loading Method, Loading Rate, Grading Standards (Appendix) (Preliminary calculation process), acquisition frequency, and data storage format, ensuring that parameter settings are reproducible.

[0276] (4) Raw data and experimental phenomena

[0277] Presenting the raw data and experimental records of S3, including:

[0278] Original dataset: Loading level-load-average measured slip data table for each group of specimens, with a CSV data file attached.

[0279] Experimental phenomena record: time, location, and width of cracks appearing during loading, maximum load, load at which loading stops, and final failure mode of the specimen (with photos of different stages), providing a basis for characteristic analysis.

[0280] (5) Algorithm processing results

[0281] The data processed by the S4 algorithm is summarized as follows:

[0282] Intermediate dataset: (Load - Bond Stress - Measured Slip) Key data segments of (bond stress - actual slip) are presented to illustrate the data processing flow;

[0283] Final results: for each group of specimens Curve (comparison of measured and predicted values), constitutive model parameter set P ( (The algorithm formula, parameter definition, and calculation example are attached.)

[0284] (6) Verification results and characteristic analysis

[0285] The verification and analysis conclusions of S5 are explained in detail, including:

[0286] Parallel specimen consistency verification: calculation process and results of the parameter variation coefficient for each group of specimens, and verification basis for qualification;

[0287] Algorithm accuracy verification: the process and results of calculating the average relative error, and the basis for accuracy qualification;

[0288] Bond slip properties: The analysis includes curve characteristics, the influence of rebar diameter on key parameters, and failure mechanism analysis. The application scenarios of characteristic parameters are explained in conjunction with actual engineering projects.

[0289] (7) Conclusions and Recommendations

[0290] Key findings: This study clarifies the bond-slip characteristics (such as the maximum bond stress range and slip stage characteristics) of self-igniting coal gangue aggregate concrete and reinforcing steel, identifies key influencing factors (steel diameter), and identifies the failure mechanism, while summarizing the reliability of the testing methods.

[0291] Engineering Recommendations: Based on test results, this paper proposes reference suggestions for the selection of reinforcing steel and the design of bond length in the design of self-igniting coal gangue aggregate concrete structures (e.g., the bond length of large-diameter reinforcing steel can be appropriately reduced, based on...). (Optimize reinforcement amount)

[0292] Future research directions: Propose areas that require further research (such as the influence of different concrete strengths and different aggregate sizes on bond-slip characteristics).

[0293] 6.3 Report Review and Archiving

[0294] After the report is completed, it needs to undergo technical review (verifying the accuracy of data calculations, formula applications, and conclusion derivations) and format review (ensuring clear structure and standardized charts). Once approved, a formal report will be generated, with multiple copies archived and an electronic version (including attachment data files) stored for easy access and application later.

[0295] The embodiments described above are for illustrative purposes only and are not intended to limit the invention. Therefore, any changes in numerical values ​​or substitutions of equivalent elements should still fall within the scope of this invention.

[0296] The above detailed description will enable those skilled in the art to understand that the present invention can indeed achieve the aforementioned objectives and has complied with the provisions of the Patent Law.

[0297] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention. The above descriptions are merely preferred embodiments of the invention and are not intended to limit the invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.

[0298] It should be noted that the above description of the process is for illustrative purposes only and does not limit the scope of this specification. Those skilled in the art can make various modifications and changes to the process under the guidance of this specification. However, these modifications and changes remain within the scope of this specification.

Claims

1. A method for testing the bond-slip of spontaneous combustion coal gangue aggregate concrete and steel bars, characterized in that, The method comprises the following steps: S1: Determine the test object as spontaneous combustion coal gangue aggregate concrete and steel bar test piece, use standardized test method to carry out parameter and material characteristic measurement on the test piece, obtain test piece geometric parameters, spontaneous combustion coal gangue aggregate concrete physical and mechanical characteristics and steel bar material characteristics, and form a basic parameter set; S2: Select test equipment based on the basic parameter set, complete installation and multi-dimensional calibration of the equipment; S3: According to the concrete axial tensile strength, cubic compressive strength and steel bar diameter in the basic parameter set, set loading parameters and data acquisition parameters, the loading parameters include hierarchical loading mode, loading rate and hierarchical standard, and the data acquisition parameters include acquisition frequency and data storage format; according to the set loading parameters, perform hierarchical loading test on the test piece, synchronously acquire load data corresponding to each level of loading and measured slip of each displacement meter, calculate average measured slip of each level of loading, and integrate to form an original data set of loading level-load-average measured slip; S4: Process the original data set by using three progressive fusion algorithms: through the bond stress calculation algorithm, combine the steel bar diameter and the steel bar bond length in the basic parameter set, and convert the load data in the original data set into the bond stress corresponding to the loading level; through the slip correction algorithm, based on the bond stress, the steel bar elastic modulus in the basic parameter set and the measured displacement meter measurement section steel bar length, eliminate the system error caused by the elastic elongation of the steel bar, and obtain the true slip corresponding to the loading level; through the bond slip constitutive model construction algorithm, based on the bond stress and the true slip, extract the characteristic parameters and fit the stiffness coefficient, construct the bilinear bond slip constitutive model, and integrate to form the final data set and the constitutive model parameter set; S5: Based on the final data set and the constitutive model parameter set, carry out parallel test piece consistency verification and algorithm accuracy verification, and obtain verification results.

2. The bond- slip test method of self-ignited coal gangue aggregate concrete and steel bar according to claim 1, characterized in that, Further comprising S6: aggregate the basic parameter set formed in S1, the original data set formed in S3, the final data set and the constitutive model parameter set formed in S4, and the verification results obtained in S5, generate a complete test report containing bond slip characteristic analysis conclusion.

3. The bond- slip test method of self-ignited coal gangue aggregate concrete and steel bar according to claim 1, characterized in that, In S1, the test piece geometric parameters include concrete cross section size, steel bar and concrete cover thickness, steel bar bond length and steel bar extension length; the spontaneous combustion coal gangue aggregate concrete physical and mechanical characteristics include cubic compressive strength, axial tensile strength, elastic modulus and aggregate particle size range; the steel bar material characteristics include steel bar type, yield strength, tensile strength, elastic modulus, steel bar diameter and steel bar surface rib height; the standardized test method is executed according to the recommended national standard, all parameters are measured at least 3 times and the average value is taken.

4. The bond- slip test method of self-ignited coal gangue aggregate concrete and steel bar according to claim 1, characterized in that, In S2, an electronic universal testing machine, a displacement meter and a data acquisition instrument are selected as the testing equipment, and the multi-dimensional calibration includes: calibrating the load measuring system of the electronic universal testing machine by selecting at least 5 calibration points in the range of 0-200 kN with a standard force sensor to ensure that the load measurement error is ≤±0.5%; calibrating the displacement meter by selecting at least 6 calibration points in the range of 0-10 mm with a standard gauge block to ensure that the displacement measurement error is ≤±0.01 mm; and calibrating the data acquisition instrument and the electronic universal testing machine for synchronization to ensure that the timestamps of the load data and the slip data are consistent.

5. The bond- slip test method of self-ignited coal gangue aggregate concrete and steel bar according to claim 1, characterized in that, In S3, the loading rate is set to 0.5 mm / min, and the determination method of the grading standard is: calculating the estimated maximum bond stress based on the concrete cube compressive strength and the steel bar diameter in the basic parameter set, loading at 10% of the estimated maximum bond stress per level in the range of 0-0.7 times the estimated maximum bond stress, loading at 5% of the estimated maximum bond stress per level in the range of 0.7-1.0 times the estimated maximum bond stress, holding the load for 30 s after each level of loading, and stopping loading when the estimated maximum bond stress decreases to 0.8 times.

6. The bond- slip test method of self-ignited coal gangue aggregate concrete and steel bar according to claim 1, characterized in that, In S4, the specific process of the bond stress calculation algorithm is: first, calculating the initial bond area of the steel bar and the concrete based on the steel bar diameter and the steel bar bond length in the basic parameter set, the initial bond area being the cylindrical side area of the steel bar and the concrete, and then dividing the load data of each level of loading by the initial bond area to obtain the bond stress corresponding to the loading level.

7. The method for testing the bond slip between self-igniting coal gangue aggregate concrete and reinforcing steel according to claim 1, characterized in that, In S4, the specific process of the slip correction algorithm is: first, deducing the steel bar stress corresponding to the loading level based on the bond stress, then calculating the elastic elongation of the steel bar corresponding to the loading level by Hooke's law based on the steel bar elastic modulus and the measured displacement meter measured steel bar length in the basic parameter set, and finally subtracting the elastic elongation of the steel bar from the average measured slip of the corresponding loading level in the original data set to obtain the true slip.

8. The bond- slip test method of self-ignited coal gangue aggregate concrete and steel bar according to claim 1, characterized in that, In S4, the specific process of the bond-slip constitutive model construction algorithm is: first, extracting the yield slip, the maximum bond stress, the ultimate slip and the residual bond stress from the bond stress and the true slip data, and then fitting the stiffness coefficients of the rising segment and the descending segment of the bond-slip relationship by the least square method, and constructing a bilinear bond-slip constitutive model covering the elastic stage, the strengthening stage and the softening stage based on the characteristic parameters and the stiffness coefficients.

9. The bond- slip test method of self-ignited coal gangue aggregate concrete and steel bar according to claim 1, characterized in that, In S5, the specific method of the parallel specimen consistency verification is: calculating the variation coefficient of each parameter in the constitutive model parameter set of the same group of parallel specimens, and requiring that the variation coefficient of all parameters is ≤5%; and the specific method of the algorithm accuracy verification is: calculating the average relative error of the measured bond stress and the predicted bond stress of the constitutive model in the final data set, and requiring that the average relative error is ≤4%.

10. The bond- slip test method of self-ignited coal gangue aggregate concrete and steel bar according to claim 1, characterized in that, In S4, the three progressive fusion algorithms realize precision optimization through parameter interaction: the bond stress output by the bond stress calculation algorithm is used as the core input parameter of the slip correction algorithm, and the true slip output by the slip correction algorithm is used to calibrate the initial bond area in the bond stress calculation algorithm; the bond stress and the true slip are used as the input of the bond slip constitutive model construction algorithm, and the prediction result of the constitutive model construction algorithm is used to calibrate the calculation precision of the bond stress and the true slip.

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