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

Abstract

The application discloses a kind of ultrasonic method-based light aggregate concrete compressive strength nondestructive testing methods, belong to engineering material testing field, this method includes S1, the ultrasonic transverse wave velocity and longitudinal wave velocity of each light aggregate concrete reference piece are detected;S2, the equivalent bulk modulus of each light aggregate concrete reference piece is calculated;S3, correction KT model is established;S4, the mapping relationship equation set of light aggregate concrete reference piece and correction KT model is established, and correction KT model is optimized adjustment;S5, the ultrasonic transverse wave velocity and longitudinal wave velocity of light aggregate concrete test piece, equivalent bulk modulus are obtained, and the volume fraction of light aggregate concrete test piece is calculated;S6, according to the volume fraction of light aggregate concrete test piece and the mapping relationship of compressive strength of mixing amount parameter, the compressive strength of light aggregate concrete test piece is calculated.The application solves the technical problem that the error of light aggregate concrete compressive strength nondestructive testing is higher.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of engineering material testing, and particularly relates to a non-destructive testing method for compressive strength of lightweight aggregate concrete based on ultrasonic back measurement. BACKGROUND

[0002] Lightweight aggregate concrete has become the core material of green building system due to its lightweight, high strength, heat preservation and other characteristics. As a key mechanical indicator of engineering materials, the compressive strength of various engineering materials usually needs to be detected. In the detection of the compressive strength of engineering materials such as concrete, the traditional detection method mainly destroys the cubic material test block according to the relevant standards of GB / T50081 standard, but this method has the defects of high cost of test block production, difference between curing conditions and entity structure, and inability to realize in-situ detection of structure entity strength. Research shows that there is a certain correlation between ultrasonic wave speed and concrete compressive strength. Therefore, in order to realize accurate, efficient and low-cost detection of concrete compressive strength, a method for detecting the compressive strength of concrete by ultrasonic wave has been developed.

[0003] For example, the patent document with publication number CN115980193A discloses a method for detecting the compressive strength of plastic concrete based on ultrasonic wave. The method establishes a curve of compressive strength and ultrasonic wave speed through test block production, test block curing, ultrasonic test, compressive strength test and test data arrangement and analysis. According to the determined correlation data of ultrasonic wave speed and compressive strength, the regression equation of the curve is calculated by the least square method. The quadratic function, exponential function and power function are selected for curve fitting of the relationship between compressive strength and ultrasonic wave speed. The fitting curve of the relationship between the strength and wave speed of plastic concrete in a certain range is obtained. Finally, the compressive strength of plastic concrete is determined according to the fitting curve.

[0004] The above technical solution can realize non-destructive detection of the compressive strength of concrete, but when detecting the compressive strength of concrete by ultrasonic wave, the detection model is mainly based on statistical regression method, which lacks mechanism analysis of the acoustic propagation characteristics of lightweight aggregate-mortar two-phase. And it does not consider the coupling effect of multi-phase characteristic parameters such as lightweight aggregate volume fraction on ultrasonic wave propagation. Therefore, the prediction error is high in the actual test of the compressive strength of lightweight aggregate concrete, which cannot meet the high-precision detection requirement of the compressive strength of lightweight aggregate concrete. SUMMARY

[0005] In view of the above shortcomings in the prior art, the present application provides a non-destructive testing method for compressive strength of lightweight aggregate concrete based on ultrasonic back measurement, which solves the technical problem of high prediction error and inability to meet the high-precision detection requirement.

[0006] In order to achieve the above-mentioned purposes, the technical scheme adopted by the present application is as follows: a non-destructive testing method for the compressive strength of lightweight aggregate concrete based on the ultrasonic method, comprising the following steps:

[0007] S1, preparing a plurality of lightweight aggregate concrete reference pieces, detecting the transverse wave velocity and the longitudinal wave velocity of each lightweight aggregate concrete reference piece;

[0008] S2, calculating the equivalent bulk modulus of each lightweight aggregate concrete reference piece according to the transverse wave velocity and the longitudinal wave velocity detected in step S1;

[0009] S3, establishing a modified KT model;

[0010] S4, establishing a mapping relationship equation group of the lightweight aggregate concrete reference piece and the modified KT model according to the equivalent bulk modulus of each lightweight aggregate concrete reference piece, and optimizing and adjusting the modified KT model;

[0011] S5, obtaining the ultrasonic transverse wave velocity and the longitudinal wave velocity of the lightweight aggregate concrete test piece, and calculating the equivalent bulk modulus of the lightweight aggregate concrete test piece, and calculating the volume fraction of the lightweight aggregate concrete test piece through the modified KT model optimized in step S4;

[0012] S6, calculating the compressive strength of the lightweight aggregate concrete test piece according to the volume fraction of the lightweight aggregate concrete test piece calculated in step S5, and the mapping relationship between the dosage parameter and the compressive strength.

[0013] The beneficial effects of the present application are as follows: in the present scheme, the calibration system is constructed by the reference piece group, and the double parameter determination is realized by using the synchronous inversion algorithm, which not only solves the measurement problem of the real volume modulus of lightweight aggregate, but also optimizes the model calibration coefficient, so that the test result has better equivalence with the engineering practice.

[0014] In the present scheme, the theoretical model is innovated and the detection method is optimized, which provides a scientific and practical solution for the strength evaluation of lightweight aggregate concrete, realizes the high reliability and high precision of the non-destructive testing of the strength evaluation of lightweight aggregate concrete, and can meet the reliability and precision requirements of the test results in actual detection.

[0015] Further, the step S1 is specifically as follows:

[0016] ​S101, selecting multiple test points on each lightweight aggregate concrete reference element;

[0017] S102, ultrasonic testing is performed on each test point, and the shear wave velocity value and the longitudinal wave velocity value of each test point are calculated;

[0018] 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 the longitudinal wave velocity detection value of each test point;

[0019] S104, respectively taking the arithmetic mean of the effective shear wave velocity value and the effective longitudinal wave velocity value to obtain the shear wave velocity and the longitudinal wave velocity .

[0020] The beneficial effects of the above further scheme are: by testing the ultrasonic wave 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 detection data are improved.

[0021] Further, in step S2, the calculation formula of the equivalent bulk modulus is:

[0022]

[0023]

[0024] In the formula, is the apparent density of the lightweight aggregate concrete, is the volume fraction of the lightweight aggregate in the lightweight aggregate concrete reference element, is the apparent density of the lightweight aggregate concrete mortar phase, is the apparent density of the lightweight aggregate.

[0025] The beneficial effects of the above further scheme are: the shear wave velocity, the longitudinal wave velocity and the volume fraction of the lightweight aggregate are associated, and the mapping relationship between the volume fraction and the compressive strength is quantified by the formula, overcoming the limitation of the prior art which only relies on a single longitudinal wave velocity index, greatly improving the strength estimation accuracy, and fundamentally overcoming the strength prediction deviation problem caused by not considering the change of the volume fraction of the lightweight aggregate in the conventional regression analysis method.

[0026] Further, the modified KT model is a modified KT model containing a second-order scattering term:

[0027]

[0028] In the formula, is the equivalent bulk modulus of the lightweight aggregate concrete, is the volume fraction of the lightweight aggregate, a bulk modulus of the mortar matrix phase, a shear modulus of the mortar matrix phase, a bulk modulus of the lightweight aggregate phase, a shape factor of the bulk modulus, a coefficient of the second-order scattering term.

[0029] The beneficial effect of the further scheme is that a modified Kuster-Toksöz (KT) model containing a second-order scattering term is established, and the effective upper limit of the prediction of the lightweight aggregate is extended to a medium-high volume fraction. The KT formula is modified by introducing the second-order scattering term, and the effective upper limit of the prediction of the lightweight aggregate is extended to a medium-high volume fraction.

[0030] Further, in step S4, a mapping relationship equation of the two groups of lightweight aggregate concrete reference pieces and the modified KT model is established, and a mapping relationship equation group of the lightweight aggregate concrete reference pieces and the modified KT model is obtained:

[0031]

[0032] In the formula, an equivalent bulk modulus of the first group of reference pieces, a lightweight aggregate volume fraction of the first group of reference pieces, an equivalent bulk modulus of the second group of reference pieces, a lightweight aggregate volume fraction of the second group of reference pieces;

[0033] In step S4, the bulk modulus of the lightweight aggregate phase and the calibration value of the coefficient of the second-order scattering term are calculated by the mapping relationship equation group of the lightweight aggregate concrete reference pieces and the modified KT model.

[0034] The beneficial effect of the further scheme is that the bulk modulus of the lightweight aggregate phase is calculated by the data of the two groups of reference pieces respectively, so that the calculation process can be verified according to the two groups of equations, and the accuracy of the calculation result is ensured.

[0035] Further, the bulk modulus of the lightweight aggregate phase is calculated by the following steps:

[0036] A1, the coefficient of the second-order scattering term is optimized and adjusted in the coefficient value interval, and the second-order scattering term coefficient after the optimization and adjustment is substituted into the mapping relationship equation group to calculate the bulk modulus of the lightweight aggregate phase of each equation.

[0037] A2, when the bulk modulus of the lightweight aggregate phase When the error between the two solutions is less than the error threshold, the bulk modulus of the lightweight aggregate phase... The mean of the two solutions is the true bulk modulus of the lightweight aggregate phase, and the corresponding second-order scattering term coefficients are... If it is the calibration value, then return to step A1.

[0038] The beneficial effect of the above further scheme is that, during the calculation process, the bulk modulus of lightweight aggregate is used as a reference. While verifying the numerical values, the coefficients of the second-order scattering term were also examined. Continuous optimization and adjustments are made to ensure the coefficients of the second-order scattering term. The value of can fit the actual situation, ensuring the accuracy of subsequent calculation results.

[0039] Further, step S6 specifically involves: determining the volume fraction of lightweight aggregate in the lightweight aggregate concrete test specimen. Substituting the admixture parameters into the mapping relationship between admixture dosage and compressive strength, calculate the compressive strength of the lightweight aggregate concrete test specimen:

[0040]

[0041] In the formula, The compressive strength of the lightweight aggregate concrete test specimen. The compressive strength of the mortar phase. The compressive strength of lightweight aggregate.

[0042] The beneficial effect of the above further scheme is: through the volume fraction of lightweight aggregate test specimens The relationship between parameters and mortar phase strength and cylinder compressive strength enables the estimation of compressive strength of lightweight aggregate test specimens, ensuring the accuracy of compressive strength estimation while guaranteeing non-destructive evaluation of lightweight aggregate test specimens. Attached Figure Description

[0043] Figure 1 This is a flowchart of the non-destructive testing method for the compressive strength of lightweight aggregate concrete based on ultrasonic testing in an embodiment of the present invention;

[0044] Figure 2 This is a distribution diagram of the ultrasonic testing points for this invention. Detailed Implementation

[0045] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0046] In an embodiment of the present application, a non-destructive testing method for the compressive strength of lightweight aggregate concrete based on ultrasonic wave detection method, as shown in the following steps: Figure 1

[0047] S1, preparing lightweight aggregate concrete test pieces, a plurality of groups of lightweight aggregate concrete reference pieces are prepared, and the ultrasonic wave transverse wave velocity and the longitudinal wave velocity of each group of lightweight aggregate concrete reference pieces are detected; specifically, when the lightweight aggregate concrete test pieces are prepared, the materials are matched according to actual needs, and the lightweight aggregate concrete test pieces are prepared; in this embodiment, the particle size of the fly ash composite ceramsite is about 6-8 mm, the compressive strength of the composite ceramsite is 7 MPa, the apparent density is 1409 kg / m³, and the saturated water absorption is 12.8%. The size of the concrete test piece is 150 mm x 150 mm x 150 mm. In this embodiment, LC1 series (corresponding to C1), LC1-A-20, LC1-A-35, and LC1-A-50 test pieces are prepared, wherein the numbers "20", "35", and "50" represent the ceramsite content of 20%, 35%, and 50%, respectively. C1, LC1-A-20, and LC1-A-50 in the plurality of test pieces are used as reference pieces to solve the coefficient and the physical modulus of the lightweight aggregate, and LC1-A-35 is used as a test piece to verify the results. The material matching of each lightweight aggregate concrete test piece in this embodiment is shown in Table 1:

[0048] Table 1 Test mixing ratio of lightweight aggregate concrete test piece

[0049]

[0050] In the preparation of lightweight aggregate concrete test pieces, a vibration table vibration process is adopted and the preparation process is optimized: according to the mixing ratio of each raw material, a layered pouring process is adopted, 60% of the mixture is poured first, and pre-vibration is performed on the vibration table (frequency 50±3 Hz, amplitude 0.5±0.1 mm) for 5 seconds; then evenly spread all the ceramsite, manually assist to flatten, then pour the remaining 40% of the mixture and continue to vibrate for 5 seconds, and a baffle is used to limit the displacement of the test mold during vibration. Immediately after vibration, a trowel is used to flatten the surface, and a wet cloth is covered for 1 hour. The test piece is demolded after 24 hours of mold curing, and is placed in a standard curing room (temperature 20±2℃, relative humidity ≥95%) to ensure a six-sided contact curing environment. Image analysis verification shows that the vibration table process reduces the coefficient of variation of ceramsite distribution to less than 15%, significantly improving the stratification problem caused by the floating of aggregate compared with the traditional method.

[0051] When ultrasonic detection is performed, a split-type ultrasonic system is used to test the first wave velocity of the ultrasonic transverse wave and the first wave velocity of the transverse wave ​The ambient temperature for testing must be controlled within the range of 0℃ to 40℃ to ensure data accuracy. (See attached image) Figure 2 As shown, when selecting ultrasonic test points on lightweight aggregate concrete, the side of the lightweight aggregate concrete in the pouring direction is selected as the test surface, and multiple corresponding test points are marked on each of the two opposite test surfaces. Then, using a steel tape measure or steel ruler, the vertical distance between the two test surfaces is measured at the height of the corresponding test points on both sides of the test surface. The average value of the corresponding vertical distances on both sides is taken as the ultrasonic distance value for each test point. Next, the acoustic time value of the lightweight aggregate concrete specimen is measured using the ultrasonic pairing method, and the sound velocity value of the concrete specimen is calculated based on this acoustic time. The measured data is then filtered: first, the two maximum values ​​and two minimum values ​​are removed; then, the arithmetic mean of the remaining effective sound velocity values ​​is taken as the representative sound velocity value of the specimen. t Ultimately, this data processing method effectively reduced the impact of extreme values ​​on the measurement results, improving the reliability and representativeness of the test data. The specific data of ultrasonic wave velocities at different test points of each specimen in this embodiment are shown in Table 2:

[0052] Table 2. Measurement results of ultrasonic wave velocity for each specimen

[0053]

[0054] S2. Based on the transverse wave velocity detected in step S1 With longitudinal wave velocity Calculate the equivalent bulk modulus of each lightweight aggregate concrete reference component. Specifically, based on the principles of elastic dynamics, and according to the ultrasonic transverse wave velocity detected in step S1... With longitudinal wave velocity The equivalent bulk modulus of the lightweight aggregate concrete reference component was calculated using the elastic wave velocity-modulus formula. Calculations are performed. The equivalent bulk modulus of lightweight aggregate concrete is included. The calculation formula is:

[0055]

[0056] In the formula, The apparent density of lightweight aggregate concrete. For longitudinal wave velocity, The transverse wave velocity. The apparent density of lightweight aggregate concrete. The apparent density of lightweight aggregate concrete is related to the volumetric content of lightweight aggregate in the concrete. The calculation formula is:

[0057]

[0058] In the formula, a volume fraction of the lightweight aggregate in the lightweight aggregate concrete reference piece, an apparent density of the lightweight aggregate concrete mortar phase, an apparent density of the lightweight aggregate, wherein and can be measured, and the specific measurement content is the prior art, which is not described here.

[0059] wherein the equivalent volume modulus and the equivalent shear modulus of each lightweight aggregate concrete reference piece are calculated.

[0060] Table 3: Modulus parameters of the reference group lightweight aggregate concrete

[0061]

[0062] S3, a modified KT model is established; specifically, the modified Kuster-Toksöz (KT) model containing a second-order scattering term is used, wherein the equation is established according to the modified KT model and the volume modulus The equation is:

[0063]

[0064] In the formula, is the equivalent volume modulus of the lightweight aggregate concrete, is the volume fraction of the lightweight aggregate, is the volume modulus of the mortar matrix phase, is the shear modulus of the mortar matrix phase, and can be obtained by testing the lightweight aggregate volume fraction of the reference piece, is the volume modulus of the lightweight aggregate phase, is the shape factor of the volume modulus, and preferably in this embodiment the lightweight aggregate is spherical, , is the coefficient of the second-order scattering term.

[0065] S4, according to the equivalent volume modulus of each lightweight aggregate concrete reference piece, a mapping relationship equation group of the lightweight aggregate concrete reference piece and the modified KT model is established, and the modified KT model is optimized and adjusted; specifically, in this embodiment, the parameters of LC1-A-20 and LC1-A-50 in the reference group are used as test data to establish a mapping relationship equation of two groups of test data and the modified model, wherein the equivalent volume modulus of the lightweight aggregate concrete test piece and the volume modulus of the lightweight aggregate phase form the equation group:

[0066]

[0067] wherein, is the equivalent volume modulus of the LC1-A-20 test piece, is the light aggregate volume fraction of the LC1-A-20 test piece, is the equivalent volume modulus of the LC1-A-50 test piece, is the light aggregate volume fraction of the LC1-A-50 test piece. Substituting the reference piece data measured in step S2 into the above equation set, the following equation set is obtained:

[0068]

[0069] by optimizing the value of the coefficient of the second-order scattering term and simultaneously solving the light aggregate phase volume modulus of each equation, when the error of the two solutions of the light aggregate phase volume modulus is less than the error threshold, the average of the two solutions of the light aggregate phase volume modulus is the real volume modulus of the light aggregate phase , and the corresponding coefficient of the second-order scattering term is the calibration value of the formula, otherwise the coefficient of the second-order scattering term is continuously optimized and adjusted in the coefficient value range.

[0070] Specifically, the coefficient of the second-order scattering term is optimized and adjusted between 0.1 and 0.5, and by substituting the adjusted coefficient of the second-order scattering term into the equation set, two equation sets are respectively solved, when the range of is , the error of the two equation solutions is ≤0.001, and is a positive number, and the average of the two solutions is obtained. The real volume modulus of the light aggregate phase , and the corresponding coefficient of the second-order scattering term is the calibration value of the formula. The iterative calculation results of the above equation set in the embodiment are shown in Table 4:

[0071] Table 4 Calculation results of the mapping relationship equation set

[0072]

[0073] S5, by the calculation formula of step S2, the calculation formula of the equivalent volume modulus of the light aggregate concrete test piece is obtained, and the calculation formula of the equivalent volume modulus of the light aggregate concrete test piece is substituted into the modified KT model, and the volume fraction of the light aggregate concrete test piece is calculated;

[0074] Specifically, the equivalent bulk modulus of the lightweight aggregate concrete test piece is calculated according to the following formula: The correction KT model in step S3 is substituted into the calculation formula of the apparent density of the lightweight aggregate concrete to obtain:

[0075]

[0076] The apparent density of the lightweight aggregate concrete is calculated according to the following formula: The bulk modulus of the lightweight aggregate concrete test piece is calculated according to the following formula:

[0077]

[0078] The second-order scattering term coefficient calculated according to the previous steps is substituted into the following formula: The real bulk modulus of the lightweight aggregate phase is substituted into the above formula, and the actual measured shear wave velocity of the lightweight aggregate concrete test piece is substituted into the following formula: The actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the above formula, and the actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the following formula: The actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the above formula, and the actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the following formula: The actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the above formula, and the actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the following formula: The actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the above formula, and the actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the following formula: The actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the above formula, and the actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the following formula:

[0079] The actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the above formula, and the actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the following formula:

[0080]

[0081] The actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the above formula, and the actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the following formula: The actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the above formula, and the actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the following formula:

[0082] The actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the above formula, and the actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the following formula: The actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the above formula, and the actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the following formula: The actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the above formula, and the actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the following formula:

[0083]

[0084] In the formula, the actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the above formula, and the actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the following formula: The actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the above formula, and the actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the following formula: The actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the above formula, and the actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the following formula: The actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the above formula, and the actual measured longitudinal wave velocity of the lightweight aggregate concrete test piece is substituted into the following formula:​ Compressive strength of lightweight aggregate The compressive strength of the mortar phase can be obtained through actual testing according to the national standard "Test Methods for Lightweight Aggregates". Compressive strength of lightweight aggregate The actual detection method is based on existing technology, and will not be elaborated here.

[0085] In this embodiment, the volume fraction of lightweight aggregate in the lightweight aggregate test specimen calculated in step S5 is used. Substituting the values ​​into the compressive strength calculation formula, the predicted compressive strength of the LC1-A-35 test specimen is 41.8 MPa. Compared with the measured compressive strength of 43.7 MPa, the relative error is only -4.3%, indicating that the calculation method has high prediction accuracy.

[0086] Compared to existing technologies, this approach introduces a second-order scattering term correction term into the Kuster-Toksöz (KT) model, extending the effective prediction range of lightweight aggregate volume fraction from ϕ≤0.1 in traditional methods to ϕ≤0.5. This breaks through the limitations of existing technologies in detecting high-content lightweight aggregate concrete, and the method can be extended to the performance evaluation of other multiphase composite materials.

[0087] By constructing a calibration system using standard specimen sets and employing a synchronous inversion algorithm to determine dual parameters, the problem of measuring the true bulk modulus of lightweight aggregate phase was solved, and the model calibration coefficients were simultaneously optimized, resulting in better equivalence between the test results and engineering practice.

[0088] By correlating transverse and longitudinal wave velocities with the volume fraction of lightweight aggregate and quantifying the mapping relationship between volume fraction and compressive strength using a formula, this method overcomes the limitations of existing technologies that rely solely on a single longitudinal wave velocity index, significantly improving the accuracy of strength estimation. This approach fundamentally overcomes the strength prediction bias caused by conventional regression analysis methods that do not consider variations in the volume fraction of lightweight aggregate.

[0089] Ultrasonic testing is employed to achieve full-thickness penetration testing of components, reducing material loss compared to traditional destructive testing and providing comprehensive non-destructive testing capabilities. Overcoming the limitations of surface non-destructive testing techniques such as springback testing, an in-situ accurate assessment of the overall internal strength of components is achieved by constructing a mapping model between ultrasonic parameters and internal strength.

[0090] Therefore, this solution provides a scientific and practical solution for the strength assessment of lightweight aggregate concrete by innovating the theoretical model and optimizing the testing method. It achieves high reliability and high accuracy of non-destructive testing for the strength assessment of lightweight aggregate concrete, and can meet the reliability and accuracy requirements of test results in actual testing.

Claims

1. A method for non-destructive testing of the compressive strength of lightweight aggregate concrete based on the ultrasonic method, characterized in that, Comprising the following steps: S1, preparing multiple groups of lightweight aggregate concrete reference pieces, detecting the transverse wave velocity of each lightweight aggregate concrete reference piece and the longitudinal wave velocity ; S2, calculating the shear wave velocity of each lightweight aggregate concrete reference member based on the longitudinal wave velocity of each lightweight aggregate concrete reference member with the longitudinal wave velocity , calculating the equivalent bulk modulus of each lightweight aggregate concrete reference member ; S3, establishing a modified KT model; S4. Equivalent bulk modulus of each lightweight aggregate concrete reference element A mapping relationship equation set between the lightweight aggregate concrete reference elements and the modified KT model is established to optimize and adjust the modified KT model. S5, acquiring the ultrasonic transverse wave velocity of the lightweight aggregate concrete test piece with the longitudinal wave velocity , and calculating the equivalent bulk modulus of the lightweight aggregate concrete test piece ; adjusting the modified KT model through step S4 to calculate the volume fraction of the lightweight aggregate concrete test piece ; S6、According to the volume fraction of the lightweight aggregate concrete test piece calculated in step S5 and the mapping relationship between the content parameter and the compressive strength to calculate the compressive strength of the lightweight aggregate concrete test piece. In step S3, the modified KT model is a modified KT model containing a second-order scattering term: wherein Eeff is the equivalent bulk modulus of the lightweight concrete, Vf is the volume fraction of the lightweight aggregate, Ems is the bulk modulus of the mortar matrix phase, Gms is the shear modulus of the mortar matrix phase, Ea is the bulk modulus of the lightweight aggregate phase, Sh is the shape factor of the bulk modulus, is the coefficient of the second order scattering term; In step S4, the mapping relationship equation of the two groups of lightweight aggregate concrete reference pieces and the modified KT model is established, and the mapping relationship equation group of the lightweight aggregate concrete reference pieces and the modified KT model is obtained: wherein K1 is the equivalent bulk modulus of the first set of reference pieces, K1 is the equivalent bulk modulus of the first set of reference pieces, K2 is the equivalent bulk modulus of the second set of reference pieces, K2 is the equivalent bulk modulus of the second set of reference pieces, In step S4, the volume modulus of the lightweight aggregate phase is calculated by the mapping relationship equation set of the lightweight aggregate concrete reference member and the correction KT model and the calibration value of the second-order scattering term coefficient ​ The step S6 specifically includes: determining the volume fraction of lightweight aggregate of the lightweight aggregate concrete test piece The compressive strength of the lightweight aggregate concrete test piece is calculated by substituting the mapping relationship between the content parameter and the compressive strength. In the formula, The compressive strength of the light-weight aggregate concrete test piece, The compressive strength of the mortar phase, The cylinder compressive strength of the light-weight aggregate.

2. The method according to claim 1, wherein, The step S1 is specifically: S101, selecting a plurality of test points on each lightweight aggregate concrete reference piece; S102, ultrasonic testing is performed on each test point, and the shear wave velocity value and the longitudinal wave velocity value of each test point are calculated; S103, the shear wave velocity value and the longitudinal wave velocity value of each test point are screened 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 and the effective longitudinal wave velocity, respectively, to obtain the shear wave velocity. With longitudinal wave velocity .

3. The method according to claim 1, wherein, In step S2, the equivalent bulk modulus The formula for calculating the equivalent bulk modulus is: wherein is the apparent density of the lightweight aggregate concrete, is the volume fraction of the lightweight aggregate in the lightweight aggregate concrete reference element, is the apparent density of the lightweight aggregate concrete mortar phase, is the apparent density of the lightweight aggregate.

4. The method according to claim 1, wherein, The volume modulus of the lightweight aggregate phase The calculating step is specifically: A1, coefficient of the second order scattering term Optimizing and adjusting the coefficient of the second order scattering term in the coefficient value interval Substitute into the mapping relationship equation set to calculate the lightweight aggregate phase volume modulus of each equation ; A2、When the error of the two solutions of the lightweight aggregate phase bulk modulus is less than the error threshold, the average of the two solutions of the lightweight aggregate phase bulk modulus is the real bulk modulus of the lightweight aggregate phase, and the corresponding second-order scattering term coefficient is the calibration value, otherwise, return to step A1.

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