Nondestructive testing method for compressive strength of lightweight aggregate concrete based on ultrasonic opposite measurement method

Abstract

The invention discloses a nondestructive testing method for the compressive strength of lightweight aggregate concrete based on an ultrasonic opposite testing method, and belongs to the field of engineering material testing, the method comprises the following steps: S1, detecting the ultrasonic transverse wave velocity and longitudinal wave velocity of each lightweight aggregate concrete reference piece; s2, calculating the equivalent bulk modulus of each lightweight aggregate concrete reference piece; s3, establishing a corrected KT model; s4, establishing a mapping relation equation set of the lightweight aggregate concrete reference piece and the corrected KT model, and optimizing and adjusting the corrected KT model; s5, the ultrasonic transverse wave velocity, the ultrasonic longitudinal wave velocity and the equivalent bulk modulus of the lightweight aggregate concrete test piece are obtained, and the volume fraction of the lightweight aggregate concrete test piece is calculated; and S6, calculating the compressive strength of the lightweight aggregate concrete test piece according to the volume fraction of the lightweight aggregate concrete test piece and the mapping relation between the mixing amount parameter and the compressive strength. The technical problem that the nondestructive testing error of the compressive strength of the lightweight aggregate concrete is relatively high is solved.

Description

Technical Field

[0001] The invention belongs to the field of engineering material testing, and in particular relates to a non-destructive testing method for the compressive strength of lightweight aggregate concrete based on an ultrasonic testing method. Background Art

[0002] Lightweight aggregate concrete has become a core material for green building systems due to its lightweight, high strength, thermal insulation and other properties. Compressive strength is a key mechanical indicator of engineering materials, and various engineering materials usually need to be tested for their compressive strength. When testing the compressive strength of engineering materials such as concrete, the traditional testing method mainly uses destructive testing of cubic material test blocks based on the relevant standards of GB / T50081. However, when testing the compressive strength of engineering materials using this method, there are usually defects such as high test block production costs, differences in curing conditions and physical structures, and the inability to achieve in-situ testing of the physical strength of the structure. Studies have shown that there is a certain correlation between ultrasonic wave velocity and concrete compressive strength. Therefore, in order to achieve accurate, efficient and low-cost testing of concrete compressive strength, a method for testing the compressive strength of concrete using ultrasound has emerged.

[0003] For example, the patent document with publication number CN115980193A discloses a method for detecting the compressive strength of plastic concrete based on ultrasound. The method establishes a compressive strength and ultrasonic wave velocity curve through test block production, test block curing, ultrasonic testing, compressive strength testing and test data collation and analysis: based on the relevant data of the measured ultrasonic wave velocity and compressive strength, the regression equation of the curve is calculated by the least squares method, and the quadratic function, exponential function and power function are selected to fit the curve of the relationship between compressive strength and ultrasonic wave velocity, and a fitting curve of the relationship between strength and wave velocity of plastic concrete within a certain range is obtained. Finally, the compressive strength of the plastic concrete is determined based on the fitting curve.

[0004] Although the above technical scheme can realize non-destructive testing of the compressive strength of concrete, when the compressive strength of concrete is tested by ultrasound, the detection model is mostly based on statistical regression methods, and lacks a mechanism analysis of the two-phase acoustic propagation characteristics of lightweight aggregate-mortar; and does not consider the coupling effect of multi-phase characteristic parameters such as the volume fraction of lightweight aggregate on ultrasonic propagation; resulting in a high prediction error in the actual test of the compressive strength of lightweight aggregate concrete, which is difficult to meet the high-precision detection requirements of the compressive strength of lightweight aggregate concrete. Summary of the Invention

[0005] In response to the above-mentioned deficiencies in the prior art, the present invention provides a non-destructive testing method for the compressive strength of lightweight aggregate concrete based on ultrasonic testing, which solves the technical problem of high prediction error and inability to meet high-precision testing requirements.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a non-destructive testing method for the compressive strength of lightweight aggregate concrete based on ultrasonic testing method, comprising the following steps: S1. Prepare multiple groups of lightweight aggregate concrete reference pieces and measure the shear wave velocity of each lightweight aggregate concrete reference piece. and longitudinal wave velocity Conduct testing; S2, according to the shear wave velocity detected in step S1 and longitudinal wave velocity , calculate the equivalent bulk modulus of each lightweight aggregate concrete benchmark ; S3, establishing a modified KT model; S4. Based on the equivalent bulk modulus of each lightweight aggregate concrete benchmark , establish the mapping relationship equations between lightweight aggregate concrete benchmark and modified KT model, and optimize and adjust the modified KT model; S5. Obtaining ultrasonic shear wave velocity of lightweight aggregate concrete test piece and longitudinal wave velocity , and calculate the equivalent bulk modulus of lightweight aggregate concrete test pieces , calculate the volume fraction of the lightweight aggregate concrete test piece through the modified KT model optimized and adjusted in step S4 ; S6. Volume fraction of the lightweight aggregate concrete test piece calculated in step S5 The compressive strength of lightweight aggregate concrete test pieces is calculated based on the mapping relationship between dosage parameters and compressive strength.

[0007] The beneficial effects of the present invention are as follows: in this solution, a calibration system is constructed through a reference component group, and a synchronous inversion algorithm is used to realize dual parameter determination, which not only solves the measurement problem of the true bulk modulus of the lightweight aggregate phase, but also simultaneously optimizes the model calibration coefficient, so that the test results have better equivalence with engineering practice.

[0008] This proposal provides a scientific and practical solution for lightweight aggregate concrete strength assessment through innovation of theoretical models and optimization of testing methods. It achieves high reliability and high precision in non-destructive testing of lightweight aggregate concrete strength assessment, and can meet the reliability and precision requirements of test results in actual testing.

[0009] Furthermore, the step S1 is specifically as follows: S101. Select multiple test points on each lightweight aggregate concrete reference piece; S102, performing ultrasonic testing on each test point, and calculating the shear wave velocity value and the longitudinal wave velocity value of each test point; S103, screening the shear wave velocity value and the longitudinal wave velocity value of each test point to obtain the effective shear wave velocity and longitudinal wave velocity detection value of each test point; S104, take the arithmetic mean of the effective shear wave velocity value and the effective longitudinal wave velocity value respectively to obtain the shear wave velocity and longitudinal wave velocity .

[0010] The beneficial effect of the above further solution is: by testing the ultrasonic values ​​of multiple test points and screening the test results of multiple test points, the influence of extreme values ​​on the measurement results is effectively reduced, and the reliability and representativeness of the test data are improved.

[0011] Furthermore, in step S2, the equivalent bulk modulus The calculation formula is:

[0012]

[0013] Where, is the apparent density of lightweight aggregate concrete, is the volume fraction of lightweight aggregate in the lightweight aggregate concrete benchmark, is the apparent density of lightweight aggregate concrete mortar phase, is the apparent density of lightweight aggregate.

[0014] The beneficial effects of the above further scheme are: associating the shear wave velocity, longitudinal wave velocity with the volume fraction of lightweight aggregate, and quantifying the mapping relationship between the volume fraction and compressive strength through a formula, overcoming the limitation of the existing technology that only relies on a single longitudinal wave velocity indicator, greatly improving the accuracy of strength estimation, and fundamentally overcoming the strength prediction deviation problem caused by conventional regression analysis methods that do not consider changes in the volume fraction of lightweight aggregate.

[0015] Furthermore, the modified KT model is a modified KT model including a second-order scattering term:

[0016] Where, is the equivalent bulk modulus of lightweight aggregate concrete, is the volume fraction of lightweight aggregate, is the bulk modulus of the mortar matrix phase, is the shear modulus of the mortar matrix phase, is the bulk modulus of the lightweight aggregate phase, is the shape factor of the bulk modulus, is the second-order scattering coefficient.

[0017] The beneficial effects of the above further scheme are: establishing a modified Kuster-Toksöz (KT) model including a second-order scattering term, extending the effective prediction upper limit of lightweight aggregate to medium and high volume fractions, and introducing a second-order scattering term to modify the KT formula, extending the effective prediction upper limit of lightweight aggregate to medium and high volume fractions.

[0018] Furthermore, in step S4, two sets of mapping relationship equations between lightweight aggregate concrete reference components and the modified KT model are established to obtain a mapping relationship equation group between lightweight aggregate concrete reference components and the modified KT model:

[0019] Where, is the equivalent bulk modulus of the first set of reference components, is the light bone volume fraction of the first group of benchmark parts, is the equivalent bulk modulus of the second set of reference components, is the light bone volume fraction of the second group of benchmarks; In step S4, the bulk modulus of the lightweight aggregate phase is calculated by the mapping relationship equation group between the lightweight aggregate concrete benchmark and the modified KT model. and the second-order scattering coefficient The calibration value of .

[0020] The beneficial effect of the above further solution is: the bulk modulus of the lightweight aggregate phase is respectively determined by the data of the two sets of reference pieces. Calculations are performed so that the two sets of equations can be mutually verified during the calculation process to ensure the accuracy of the calculation results. Furthermore, the bulk modulus of the lightweight aggregate phase The specific calculation steps are: A1, second-order scattering coefficient Optimize and adjust the coefficient value range, and adjust the second-order scattering coefficient after optimization. Substitute into the mapping relationship equation group to calculate the bulk modulus of lightweight aggregate phase in each equation ; A2. When the mapping equations of the lightweight aggregate phase bulk modulus When the error between the two solutions is less than the error threshold, the bulk modulus of the lightweight aggregate phase is The mean of the two solutions is the true bulk modulus of the lightweight aggregate phase, and the corresponding second-order scattering coefficient is It is the calibration value, otherwise, return to step A1.

[0021] The beneficial effect of the above further solution is that in the calculation process, according to the bulk modulus of the lightweight aggregate phase While verifying the value of the second-order scattering coefficient Continuously optimize and adjust to ensure the second-order scattering coefficient The value of can fit the actual situation and ensure the accuracy of subsequent calculation results.

[0022] Furthermore, the step S6 is specifically as follows: the volume fraction of lightweight aggregate of the lightweight aggregate concrete test piece is Substitute the mapping relationship between the dosage parameters and the compressive strength to calculate the compressive strength of the lightweight aggregate concrete test piece:

[0023] Where, is the compressive strength of the lightweight aggregate concrete test piece, is the compressive strength of the mortar phase, is the cylinder compressive strength of lightweight aggregate.

[0024] The beneficial effect of the above further solution is that the volume fraction of the lightweight aggregate test piece is The relationship between the parameters and the mortar phase strength and cylinder pressure strength is used to complete the estimation of the compressive strength of the lightweight aggregate test piece, while achieving the accuracy of the compressive strength estimation of the lightweight aggregate test piece and ensuring the non-destructive evaluation of the lightweight aggregate test piece. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Flow chart of a nondestructive testing method for compressive strength of lightweight aggregate concrete based on ultrasonic testing method in an embodiment of the present invention; Figure 2 This is a distribution diagram of ultrasonic testing points of the present invention. DETAILED DESCRIPTION

[0026] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concepts of the present invention are protected.

[0027] In one embodiment of the present invention, a non-destructive testing method for the compressive strength of lightweight aggregate concrete based on ultrasonic testing is provided. Figure 1 As shown, the following steps are included: S1. Prepare multiple groups of lightweight aggregate concrete test pieces and measure the ultrasonic shear wave velocity of each group of lightweight aggregate concrete reference pieces. and longitudinal wave velocity Testing was conducted. Specifically, when preparing lightweight aggregate concrete specimens, the materials were proportioned according to actual requirements. Lightweight aggregate concrete specimens were prepared. In this example, fly ash composite ceramsite with a particle size of approximately 6-8 mm was selected as the lightweight aggregate. This composite ceramsite has a cylinder compressive strength of 7 MPa, an apparent density of 1409 kg / m³, and a saturated mass water absorption of 12.8%. The concrete specimen dimensions were 150 mm × 150 mm × 150 mm. In this example, specimens from the LC1 series (corresponding to C1), LC1-A-20, LC1-A-35, and LC1-A-50 were prepared. The numbers "20," "35," and "50" represent ceramsite content of 20%, 35%, and 50%, respectively. From the multiple sets of specimens, C1, LC1-A-20, and LC1-A-50 were used as reference specimens for determining the coefficients and physical modulus of the lightweight aggregate. LC1-A-35 was used as a test specimen for verification of the results. The material proportions of each lightweight aggregate concrete specimen in this embodiment are shown in Table 1: Table 1 Test mix ratio of lightweight aggregate concrete specimens

[0028] A vibrating table technique was used to prepare lightweight aggregate concrete specimens, and the preparation process was optimized. Based on the mix ratio of the various raw materials, a layered pouring process was employed. 60% of the mixture was first poured and pre-vibrated on a vibrating table (frequency 50±3Hz, amplitude 0.5±0.1mm) for 5 seconds. The ceramsite was then evenly spread throughout the specimens and manually leveled. The remaining 40% of the mixture was then poured and vibrated for a further 5 seconds. During the vibration process, baffles were used to limit mold movement. After vibration, the surface was immediately leveled with a trowel, covered with a damp cloth, and allowed to stand for 1 hour. After curing for 24 hours, the specimens were demolded and transferred to a standard curing room (temperature 20±2°C, relative humidity ≥95%). They were placed on a three-dimensional support to ensure contact on all six sides. Image analysis confirmed that this vibrating table technique reduced the coefficient of variation of ceramsite distribution to below 15%, significantly improving the stratification and segregation caused by aggregate floating compared to traditional methods.

[0029] When conducting ultrasonic testing, a split ultrasonic system is used to test the first wave velocity of the ultrasonic shear wave of the specimen. The first wave velocity of the shear wave , the test environment temperature must be controlled within the range of 0℃ to 40℃ to ensure data accuracy. Figure 2As shown, when selecting ultrasonic test points on lightweight aggregate concrete, the side of the lightweight aggregate concrete pouring direction is selected as the test surface, and multiple corresponding test points are marked on each of the two relative test surfaces. Subsequently, a steel tape measure or a steel ruler is used to measure the vertical distance between the two test surfaces at the height positions corresponding to the measuring points on both sides of the test surface, and the average value of the corresponding vertical distances on both sides is taken as the ultrasonic distance measurement value of each measuring point. The sound time value of the lightweight aggregate concrete specimen is then measured by ultrasonic pair measurement method, and the sound velocity value of the specimen concrete is calculated based on the sound time, and then the measured data is screened and processed: first, the 2 maximum values ​​and 2 minimum values ​​are eliminated, and then the arithmetic average of the remaining valid sound velocity values ​​is taken as the representative sound velocity value of the specimen. t Finally, this data processing method effectively reduces the influence of extreme values ​​on the measurement results and improves the reliability and representativeness of the test data. The specific data of ultrasonic wave velocity at different test points of each test piece in this embodiment are shown in Table 2: Table 2 Ultrasonic wave velocity measurement results of each specimen

[0030] S2, according to the shear wave velocity detected in step S1 and longitudinal wave velocity , calculate the equivalent bulk modulus of each lightweight aggregate concrete benchmark Specifically based on the principle of elastic dynamics, according to the ultrasonic shear wave velocity detected in step S1 and longitudinal wave velocity Calculate the equivalent bulk modulus of lightweight aggregate concrete benchmark using the elastic wave velocity-modulus formula Calculate the equivalent bulk modulus of lightweight aggregate concrete. The calculation formula is:

[0031] Where, is the apparent density of lightweight aggregate concrete, is the longitudinal wave velocity, is the shear wave velocity. The apparent density of lightweight aggregate concrete is The apparent density of lightweight aggregate concrete is related to the volume content of lightweight aggregate in concrete. The calculation formula is:

[0032] Where, is the volume fraction of lightweight aggregate in the lightweight aggregate concrete benchmark, is the apparent density of lightweight aggregate concrete mortar phase, is the apparent density of lightweight aggregate, where and All of them can be obtained through measurement. The specific measurement content is existing technology and will not be described in detail here.

[0033] The equivalent bulk modulus of each lightweight aggregate concrete benchmark is and equivalent shear modulus The calculation results are shown in Table 3: Table 3 Modulus parameters of benchmark lightweight aggregate concrete

[0034] S3. Establish a modified KT model. The specific modified KT model is a modified Kuster-Toksöz (KT) model including a second-order scattering term. According to the modified KT model and the bulk modulus The established equation is:

[0035] Where, is the equivalent bulk modulus of lightweight aggregate concrete, is the volume fraction of lightweight aggregate, is the bulk modulus of the mortar matrix phase, is the shear modulus of the mortar matrix phase, and The volume fraction of lightweight aggregate can be tested The reference part is 0, is the bulk modulus of the lightweight aggregate phase, is the shape factor of the bulk modulus. In this embodiment, the lightweight aggregate is preferably spherical. , is the second-order scattering coefficient.

[0036] S4. Based on the equivalent bulk modulus of each lightweight aggregate concrete benchmark , establish a mapping relationship equation group between the lightweight aggregate concrete benchmark and the modified KT model, and optimize and adjust the modified KT model; specifically, in this embodiment, the LC1-A-20 and LC1-A-50 parameters in the benchmark group are used as test data to establish a mapping relationship equation between the two groups of specimen test data and the modified model, where the equivalent bulk modulus of the lightweight aggregate concrete specimen is Bulk modulus of lightweight aggregate The system of equations is:

[0037] Where, is the equivalent bulk modulus of the LC1-A-20 specimen, is the light bone volume fraction of the LC1-A-20 specimen, is the equivalent bulk modulus of the LC1-A-50 specimen, is the light bone volume fraction of the LC1-A-50 specimen. Substituting the reference piece data measured in step S2 into the above equations yields the following equations:

[0038] Adjust the second-order scattering coefficient by optimization The numerical value of the lightweight aggregate phase is solved simultaneously to obtain the bulk modulus of each equation , when the bulk modulus of lightweight aggregate phase When the error between the two solutions is less than the error threshold, the bulk modulus of the lightweight aggregate phase is The mean of the two solutions is the true bulk modulus of the lightweight aggregate phase , the corresponding second-order scattering coefficient This is the calibration value of the formula, otherwise the second-order scattering coefficient Continue to optimize and adjust within the coefficient value range.

[0039] Specifically, the second-order scattering coefficient The second-order scattering coefficient is optimized and adjusted between 0.1 and 0.5. Substitute into the two equations respectively, when The range is The error between the two solutions is ≤0.001 and is a positive number. The mean of the two solutions is the true bulk modulus of the lightweight aggregate phase. , the corresponding second-order scattering coefficient The specific results of iterative calculation of the above equations in this embodiment are shown in Table 4: Table 4 Calculation results of mapping relationship equations

[0040] S5. Obtain the equivalent bulk modulus of the lightweight aggregate concrete test piece using the calculation formula in step S2. The calculation formula of the lightweight aggregate concrete test piece is Substitute the calculation formula into the modified KT model and calculate the volume fraction of the lightweight aggregate concrete test piece ; Specifically, the equivalent bulk modulus of lightweight aggregate concrete test pieces is Substituting the calculation formula into the modified KT model in step S3 yields:

[0041] The apparent density of lightweight aggregate concrete Substitute the calculation formula into the bulk modulus established by the modified KT model above The equation is:

[0042] The second-order scattering coefficient calculated according to the previous steps True bulk modulus of lightweight aggregate , and the actual measured shear wave velocity of the lightweight aggregate concrete test piece and longitudinal wave velocity Data, solve the above equation to obtain the volume fraction of lightweight aggregate in the concrete test piece The preferred lightweight aggregate volume fraction of the lightweight aggregate concrete specimen in this embodiment is The calculation results are shown in Table 5: Table 5 Calculation results of lightweight aggregate volume fraction of test pieces

[0043] The volume fraction of the lightweight aggregate test piece of the LC1-A-35 specimen is calculated by the calculation formula in step S5. Compared with the designed mix ratio, the relative error of the calculated result is 2.17%, indicating that this calculation method has high calculation accuracy.

[0044] S6. Volume fraction of the lightweight aggregate concrete test piece calculated in step S5 Calculate the compressive strength of lightweight aggregate concrete test pieces. Specific lightweight aggregate volume fraction of lightweight aggregate passing through the lightweight aggregate test piece The mapping relationship between parameters and compressive strength completes the strength estimation and evaluation of lightweight aggregate concrete. The calculation formula of the compressive strength of lightweight aggregate concrete is:

[0045] Where, Indicates the compressive strength of lightweight aggregate concrete test piece, Indicates the compressive strength of the mortar phase, Indicates the cylinder compressive strength of lightweight aggregate, including the compressive strength of mortar Compressive strength of lightweight aggregate It can be obtained by actual testing according to the national standard "Test Method for Light Aggregate", among which the compressive strength of the mortar phase is Compressive strength of lightweight aggregate The actual detection method is a prior art and will not be described in detail here.

[0046] In this embodiment, the lightweight aggregate volume fraction of the lightweight aggregate test piece calculated in step S5 is Substituting this into the compressive strength calculation formula, the predicted compressive strength value of the LC1-A-35 test piece is calculated to be 41.8 MPa. Compared with the measured compressive strength of 43.7 MPa, the relative error is only -4.3%, indicating that this calculation method has high prediction accuracy.

[0047] Compared with the existing technology, this scheme introduces a second-order scattering correction term into the Kuster-Toksöz (KT) model, extending the effective prediction range of lightweight aggregate volume fraction from ϕ≤0.1 of the traditional method to ϕ≤0.5, breaking through the detection limitations of existing technology for high-content lightweight aggregate concrete. The method can be extended to the performance evaluation of other multiphase composite materials.

[0048] A calibration system was constructed through a standard specimen group, and a synchronous inversion algorithm was used to achieve dual parameter determination. This not only solved the measurement problem of the true bulk modulus of the lightweight aggregate phase, but also simultaneously optimized the model calibration coefficient, making the test results more equivalent to engineering practice.

[0049] By correlating transverse and longitudinal wave velocities with the volume fraction of lightweight aggregate and quantifying the relationship between volume fraction and compressive strength through formulas, this approach overcomes the limitations of existing technologies that rely solely on a single metric, namely longitudinal wave velocity, significantly improving the accuracy of strength estimation. This approach fundamentally overcomes the strength prediction bias caused by conventional regression analysis methods that fail to account for variations in lightweight aggregate volume fraction.

[0050] Ultrasonic testing enables full-thickness penetration testing of components, reducing material loss compared to traditional destructive testing and providing full-range nondestructive testing capabilities. By overcoming the limitations of surface nondestructive testing techniques like the rebound method, this method establishes a mapping model between ultrasonic parameters and internal strength, enabling in-situ, true assessment of the overall internal strength of components.

[0051] Therefore, this solution provides a scientific and practical solution for lightweight aggregate concrete strength assessment through innovation of theoretical models and optimization of detection methods, achieving high reliability and high precision in non-destructive testing of lightweight aggregate concrete strength assessment, and meeting the reliability and precision requirements of test results in actual testing.

Claims

1. A nondestructive testing method for the compressive strength of lightweight aggregate concrete based on ultrasonic testing, characterized in that: The following steps are involved: S1. Prepare multiple groups of lightweight aggregate concrete reference pieces and measure the shear wave velocity of each lightweight aggregate concrete reference piece. and longitudinal wave velocity Conduct testing; S2, according to the shear wave velocity detected in step S1 and longitudinal wave velocity , calculate the equivalent bulk modulus of each lightweight aggregate concrete benchmark ; S3, establishing a modified KT model; S4. Based on the equivalent bulk modulus of each lightweight aggregate concrete benchmark , establish the mapping relationship equations between lightweight aggregate concrete benchmark and modified KT model, and optimize and adjust the modified KT model; S5. Obtaining ultrasonic shear wave velocity of lightweight aggregate concrete test piece and longitudinal wave velocity , and calculate the equivalent bulk modulus of lightweight aggregate concrete test pieces , calculate the volume fraction of the lightweight aggregate concrete test piece through the modified KT model optimized and adjusted in step S4 ; S6. Volume fraction of the lightweight aggregate concrete test piece calculated in step S5 The compressive strength of lightweight aggregate concrete test pieces is calculated based on the mapping relationship between dosage parameters and compressive strength.

2. The nondestructive testing method for compressive strength of lightweight aggregate concrete based on ultrasonic testing method according to claim 1, characterized in that: The step S1 is specifically as follows: S101. Select multiple test points on each lightweight aggregate concrete reference piece; S102, performing ultrasonic testing on each test point, and calculating the shear wave velocity value and the longitudinal wave velocity value of each test point; S103, screening the shear wave velocity value and the longitudinal wave velocity value of each test point to obtain the effective shear wave velocity and longitudinal wave velocity detection value of each test point; S104, take the arithmetic mean of the effective shear wave velocity value and the effective longitudinal wave velocity value respectively to obtain the shear wave velocity and longitudinal wave velocity .

3. The nondestructive testing method for compressive strength of lightweight aggregate concrete based on ultrasonic testing method according to claim 1, characterized in that: In step S2, the equivalent bulk modulus The calculation formula is: Where, is the apparent density of lightweight aggregate concrete, is the volume fraction of lightweight aggregate in the lightweight aggregate concrete benchmark, is the apparent density of lightweight aggregate concrete mortar phase, is the apparent density of lightweight aggregate.

4. The nondestructive testing method for compressive strength of lightweight aggregate concrete based on ultrasonic testing method according to claim 1, characterized in that: In step S3, the modified KT model is a modified KT model including a second-order scattering term: Where, is the equivalent bulk modulus of lightweight aggregate concrete, is the volume fraction of lightweight aggregate, is the bulk modulus of the mortar matrix phase, is the shear modulus of the mortar matrix phase, is the bulk modulus of the lightweight aggregate phase, is the shape factor of the bulk modulus, is the second-order scattering coefficient.

5. The nondestructive testing method for compressive strength of lightweight aggregate concrete based on ultrasonic testing method according to claim 4, characterized in that: In step S4, two sets of mapping relationship equations between lightweight aggregate concrete reference components and the modified KT model are established to obtain a mapping relationship equation group between lightweight aggregate concrete reference components and the modified KT model: Where, is the equivalent bulk modulus of the first set of reference components, is the volume fraction of lightweight aggregate of the first group of benchmark pieces, is the equivalent bulk modulus of the second set of reference components, is the volume fraction of lightweight aggregate of the second group of benchmark pieces; In step S4, the bulk modulus of the lightweight aggregate phase is calculated by the mapping relationship equation group between the lightweight aggregate concrete benchmark and the modified KT model. and the second-order scattering coefficient The calibration value of .

6. The nondestructive testing method for compressive strength of lightweight aggregate concrete based on ultrasonic testing according to claim 5, characterized in that: The bulk modulus of the lightweight aggregate phase The specific calculation steps are: A1, second-order scattering coefficient Optimize and adjust the coefficient value range, and adjust the second-order scattering coefficient after optimization. Substitute into the mapping relationship equation group to calculate the bulk modulus of lightweight aggregate phase in each equation ; A2. When the mapping equations of the lightweight aggregate phase bulk modulus When the error between the two solutions is less than the error threshold, the bulk modulus of the lightweight aggregate phase is The mean of the two solutions is the true bulk modulus of the lightweight aggregate phase, and the corresponding second-order scattering coefficient is It is the calibration value, otherwise, return to step A1.

7. The nondestructive testing method for compressive strength of lightweight aggregate concrete based on ultrasonic testing method according to claim 1, characterized in that: The step S6 is specifically as follows: the volume fraction of lightweight aggregate of the lightweight aggregate concrete test piece is Substitute the mapping relationship between the dosage parameters and the compressive strength to calculate the compressive strength of the lightweight aggregate concrete test piece: Where, is the compressive strength of the lightweight aggregate concrete test piece, is the compressive strength of the mortar phase, is the cylinder compressive strength of lightweight aggregate.

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