Sensor-based non-destructive testing method and system for early hydration strength of cement

Abstract

The application belongs to the technical field of nondestructive testing, and particularly relates to a sensor-based nondestructive testing method and system for early hydration strength of cement, which comprises the following steps: S1, emitting a predetermined waveform of a creeping wave excitation signal to a cement test piece to be measured at a plurality of preset hydration time points, and receiving a response signal after the cement test piece is propagated; S2, performing continuous wavelet transform on the response signal, identifying a connected region with maximum energy and a duration meeting a preset condition in a wavelet coefficient time-frequency matrix as a creeping wave signal wave packet; S3, calculating a creeping wave propagation speed according to an energy gravity time of the creeping wave signal wave packet; performing Fourier transform on the creeping wave signal wave packet, extracting a center frequency, and calculating a difference between the center frequency of the creeping wave signal wave packet and that of the creeping wave excitation signal to obtain a frequency offset. The application fully utilizes the advantage information of two parameters of the creeping wave propagation speed and the creeping wave attenuation index at different stages, and realizes accurate and reliable prediction of the early hydration strength of the cement.

Description

Technical Field

[0001] This invention belongs to the field of non-destructive testing technology, specifically relating to a sensor-based non-destructive testing method and system for the early hydration strength of cement. Background Technology

[0002] The early hydration strength of cement is a crucial basis for evaluating the quality of concrete projects and determining key construction milestones such as formwork removal and prestressing. Traditional cement strength testing primarily relies on destructive testing of mechanical specimens. Non-destructive testing can assess cement hydration strength without damaging the cement product. Traditional ultrasonic testing methods typically evaluate cement strength development by measuring the propagation velocity of ultrasonic longitudinal waves in cement specimens. Existing methods often rely on sound velocity while neglecting energy attenuation during propagation, yet attenuation characteristics precisely reflect the material's internal viscosity and microstructural changes. Furthermore, current technologies often use the energy ratio or amplitude ratio of the received to transmitted signals as attenuation indicators.

[0003] However, cement exhibits viscoelastic characteristics in the early hydration stage, resulting in a strong filtering effect on ultrasonic waves. This alters the spectrum of the received signal, causing a shift in the center frequency compared to the excitation signal. This frequency shift significantly impacts energy calculations, rendering the resulting attenuation indices inaccurate in reflecting the material's intrinsic dissipation characteristics and consequently affecting the reliability of strength predictions. Furthermore, the cement hydration process can be divided into several distinct stages, including induction, acceleration, and deceleration phases. The microstructure formation mechanisms and strength growth patterns differ across these stages, all of which influence the accuracy of early hydration strength testing. Summary of the Invention

[0004] This invention provides a sensor-based non-destructive testing method and system for early hydration strength of cement, which solves the technical problems in the prior art of early hydration strength testing of cement, which affect the accuracy and reliability of prediction due to neglecting energy attenuation, frequency offset interference and failure to consider the differences in hydration stages.

[0005] In a first aspect, the present invention provides a sensor-based non-destructive testing method for the early hydration strength of cement, comprising the following steps:

[0006] S1, at multiple preset hydration time points, transmit a creeping excitation signal of a predetermined waveform to the cement specimen to be tested, and receive the response signal after propagation through the cement specimen.

[0007] S2, perform continuous wavelet transform on the response signal, identify the connected region with the maximum energy and the duration meeting the preset conditions in the wavelet coefficient time-frequency matrix, and use it as the creeping wave signal packet;

[0008] S3. Calculate the creeping wave propagation speed based on the energy centroid time of the creeping wave signal packet; perform a Fourier transform on the creeping wave signal packet to extract the center frequency, and calculate the difference between the center frequency of the creeping wave signal packet and the center frequency of the creeping wave excitation signal to obtain the frequency offset; based on the frequency offset, perform a nonlinear correction on the energy ratio of the creeping wave signal packet and the creeping wave excitation signal to obtain the corrected creeping wave attenuation index.

[0009] S4. Determine the hydration stage of cement based on the weighted combination of the creeping wave propagation velocity and the corrected creeping wave attenuation index; and based on the hydration stage, select one from the power function model with creeping wave propagation velocity as the main prediction parameter and the exponential function model with the corrected creeping wave attenuation index as the main prediction parameter to calculate the early hydration strength of cement.

[0010] Furthermore, the creeping excitation signal of the predetermined waveform emitted to the cement specimen under test includes:

[0011] A sinusoidal pulse signal with a center frequency of 50kHz and containing 5 cycles is used as the creeping excitation signal, and is generated and output by an arbitrary waveform generator at a sampling frequency of 10MHz.

[0012] Furthermore, connected regions with maximum energy and durations satisfying preset conditions are identified in the wavelet coefficient time-frequency matrix, including:

[0013] Morlet complex wavelet is used as the wavelet mother function;

[0014] Set the energy threshold to 30% of the maximum value in the wavelet coefficient time-frequency matrix, and identify all connected regions with energy greater than the energy threshold;

[0015] Among all identified connected regions whose duration meets the preset conditions, the connected region with the largest energy integral value is selected as the creeping wave signal packet.

[0016] Furthermore, the creeping wave propagation speed is calculated based on the energy centroid time of the creeping wave signal packet, including:

[0017] Through formula Calculate the creeping wave propagation velocity V, where L is a fixed distance between the transmitting and receiving transducers. The energy centroid time of the creeping wave signal packet. This is the transmission time of the creeping wave excitation signal.

[0018] Furthermore, based on the frequency offset, a nonlinear correction is performed on the energy ratio of the creeping wave signal packet to the creeping wave excitation signal, including:

[0019] Calculate the energy of the climbing wave excitation signal With creeping wave signal wave packet energy Energy ratio ;

[0020] By correcting the formula The corrected creepage attenuation index was calculated. ,in This is the frequency offset. and These are pre-calibrated correction factors.

[0021] Furthermore, based on a weighted combination of the creeping wave propagation velocity and the corrected creeping wave attenuation index, the cement hydration stages are determined, including:

[0022] Establish a hydration stage discriminant ,in and These represent the creep propagation velocity normalized to the [0, 1] interval and the corrected creep attenuation index, respectively. and The weighting coefficients and Z is the weighted combination discriminant value;

[0023] When Z is less than the first threshold, it is determined to be the induction period; when Z is between the first and second thresholds, it is determined to be the acceleration period; when Z is greater than the second threshold, it is determined to be the deceleration period.

[0024] Furthermore, based on the hydration stage, a power function model with creeping wave propagation velocity as the main prediction parameter and an exponential function model with the modified creeping wave attenuation index as the main prediction parameter are selected to calculate the early hydration strength of cement, including:

[0025] When determining whether the hydration stage is the induction phase or the acceleration phase, a power function model is used. Calculate the early hydration intensity S, where V is the creeping wave propagation velocity, and a and b are model fitting parameters;

[0026] When the hydration stage is determined to be a deceleration period, an exponential function model is used. Calculate the early hydration intensity S, where is the corrected creep attenuation index, and c, d, and e are the model fitting parameters.

[0027] Secondly, the present invention provides a sensor-based non-destructive testing system for the early hydration strength of cement, comprising the following modules:

[0028] The receiving module is used to transmit a creeping excitation signal of a predetermined waveform to the cement specimen under test at multiple preset hydration time points, and to receive the response signal after it has propagated through the cement specimen.

[0029] The identification module is used to perform continuous wavelet transform on the response signal and identify the connected regions with the maximum energy and a duration that meet the preset conditions in the wavelet coefficient time-frequency matrix as the climbing wave signal packet.

[0030] The correction module is used to calculate the creeping wave propagation speed based on the energy centroid time of the creeping wave signal packet; perform Fourier transform on the creeping wave signal packet to extract the center frequency, and calculate the difference between the center frequency of the creeping wave signal packet and the center frequency of the creeping wave excitation signal to obtain the frequency offset; based on the frequency offset, perform nonlinear correction on the energy ratio of the creeping wave signal packet and the creeping wave excitation signal to obtain the corrected creeping wave attenuation index.

[0031] The calculation module is used to determine the hydration stage of cement based on a weighted combination of the creeping wave propagation velocity and the corrected creeping wave attenuation index; and based on the hydration stage, it selects one of the following models to calculate the early hydration strength of cement: a power function model with creeping wave propagation velocity as the main prediction parameter and an exponential function model with the corrected creeping wave attenuation index as the main prediction parameter.

[0032] Furthermore, the creeping excitation signal of the predetermined waveform emitted to the cement specimen under test includes:

[0033] A sinusoidal pulse signal with a center frequency of 50kHz and containing 5 cycles is used as the creeping excitation signal, and is generated and output by an arbitrary waveform generator at a sampling frequency of 10MHz.

[0034] Furthermore, connected regions with maximum energy and durations satisfying preset conditions are identified in the wavelet coefficient time-frequency matrix, including:

[0035] Morlet complex wavelet is used as the wavelet mother function; the energy threshold is set to 30% of the maximum value in the wavelet coefficient time-frequency matrix, and all connected regions with energy greater than the energy threshold are identified; among all identified connected regions whose duration meets the preset conditions, the connected region with the largest energy integral value is selected as the creeping wave signal packet.

[0036] The beneficial effects are as follows: By calculating the frequency offset of the creeping wave signal relative to the creeping wave excitation signal, and using this as a basis for nonlinear correction of the creeping wave attenuation index, a creeping wave attenuation index parameter that can truly reflect the internal microstructure and energy dissipation characteristics of the material is obtained. This invention weights and combines the creeping wave propagation velocity with the corrected creeping wave attenuation index, making the prediction model highly compatible with the physical and mechanical properties of the material at a specific stage. It fully utilizes the advantageous information of both the creeping wave propagation velocity and the creeping wave attenuation index at different stages, achieving accurate and reliable prediction of the early hydration strength of cement. Attached Figure Description

[0037] Figure 1This is a flowchart of a sensor-based non-destructive testing method for the early hydration strength of cement. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] An embodiment of the sensor-based non-destructive testing method for early hydration strength of cement provided by this invention:

[0040] like Figure 1 As shown, the sensor-based non-destructive testing method for early hydration strength of cement includes the following steps:

[0041] S1, at multiple preset hydration time points, transmits a creeping excitation signal of a predetermined waveform to the cement specimen under test, and receives the response signal after propagation through the cement specimen.

[0042] Specifically, cement specimens prepared according to standard proportions were placed in a constant temperature and humidity curing environment. Measurements were taken every hour, starting 3 hours after casting, and continued for 72 hours. A signal generator produced a five-cycle sinusoidal pulse modulated with a Hanning window at a center frequency of 500 kHz as the excitation signal. After amplification by a power amplifier, the pulse drove an ultrasonic transducer with a wedge at a specific angle as the transmitting sensor. The ultrasonic transducer was placed on the specimen surface at the first critical angle to excite creeping waves (also known as subsurface longitudinal waves), which are non-uniform waves generated in the second medium when a longitudinal wave enters the second medium at an angle near the first critical angle from the first medium. A second identical transducer was placed 100 mm away from the transmitting transducer as the receiving sensor to receive the response signal. The received signal was amplified by a preamplifier and then acquired and stored by a data acquisition card at a sampling rate of 20 MHz. Simultaneously, to monitor the curing environment and perform temperature compensation on the measurement results, a temperature sensor was also placed near the specimen surface to synchronously record the surface temperature of the cement specimen and the ambient temperature and humidity.

[0043] In an optional embodiment, transmitting a creeping excitation signal of a predetermined waveform to the cement specimen under test includes:

[0044] A sinusoidal pulse signal with a center frequency of 50kHz and containing 5 cycles is used as the creeping excitation signal, and is generated and output by an arbitrary waveform generator at a sampling frequency of 10MHz.

[0045] Specifically, a sine wave with a center frequency of 50kHz is selected as the fundamental signal, and a signal segment containing five complete cycles is extracted. To reduce spectral leakage, a Hanning window function is used to window the five-cycle sine pulse signal, ensuring a smooth transition to zero at the beginning and end of the signal, thus forming a concentrated energy wave packet. The signal is generated using hardware. The digital waveform data defined above is loaded into an arbitrary waveform generator. Preferably, the sampling frequency of the arbitrary waveform generator is 10MHz to ensure high signal fidelity. The arbitrary waveform generator is started, and it converts the digital waveform into an analog voltage signal according to the set sampling frequency, continuously outputting a creeping excitation signal of a predetermined waveform to excite the cement specimen under test.

[0046] S2 performs continuous wavelet transform on the response signal and identifies the connected region with the maximum energy and a duration that meets the preset conditions in the wavelet coefficient time-frequency matrix, which is then used as the creeping wave signal packet.

[0047] Specifically, for each acquired response signal, a complex Morlet wavelet is used as the mother wavelet for continuous wavelet transform to generate a two-dimensional wavelet coefficient time-frequency matrix. In one embodiment, the energy threshold is 20% of the maximum coefficient amplitude in the wavelet coefficient time-frequency matrix, and all points with amplitudes greater than the energy threshold are marked as high-energy points. A connected component labeling algorithm from image processing is used to divide spatially adjacent high-energy points into several independent connected regions. The total energy of each connected region is calculated, i.e., the sum of squares of all wavelet coefficients within the connected region, and the span of the connected region on the time axis is calculated as the duration. The connected region with the maximum total energy and a duration between 5 μs and 25 μs is selected; the time-domain signal segment corresponding to the connected region is the wave packet of the creeping wave signal to be identified.

[0048] In an optional embodiment, identifying connected regions with maximum energy and durations satisfying preset conditions in the wavelet coefficient time-frequency matrix includes:

[0049] Morlet complex wavelet is used as the wavelet mother function; the energy threshold is set to 30% of the maximum value in the wavelet coefficient time-frequency matrix, and all connected regions with energy greater than the energy threshold are identified; among all identified connected regions whose duration meets the preset conditions, the connected region with the largest energy integral value is selected as the creeping wave signal packet.

[0050] Specifically, the received time-domain signal undergoes continuous wavelet transform processing. The Morlet complex wavelet is chosen as the fundamental function for analysis, generating a two-dimensional wavelet coefficient time-frequency matrix. The matrix values ​​represent the energy distribution of the signal at different times and frequencies. For example, a 1024×512 matrix is ​​obtained, where each element represents the energy at a time-frequency point. Energy filtering and region identification are then performed. In the generated time-frequency matrix, the maximum energy value of all coefficients is found, assumed to be 1.5. An energy threshold of 0.45 is set based on this maximum value. The entire matrix is ​​traversed, and coefficients with energy values ​​greater than 0.45 are marked. Connected regions formed by these marked points are then identified.

[0051] Select from the filtered connected regions. Examine the span (duration) of each connected region on the time axis, and eliminate connected regions that do not meet the preset time range, such as those less than 50 μs or greater than 200 μs. For connected regions that meet the duration condition, calculate the sum of the energy values ​​of all coefficients within the connected region, i.e., the energy integral. Compare the energy integral values, and select the connected region with the largest energy integral value as the creeping wave signal packet.

[0052] S3. Calculate the creeping wave propagation speed based on the energy centroid time of the creeping wave signal packet; perform a Fourier transform on the creeping wave signal packet to extract the center frequency, and calculate the difference between the center frequency of the creeping wave signal packet and the center frequency of the creeping wave excitation signal to obtain the frequency offset; based on the frequency offset, perform a nonlinear correction on the energy ratio of the creeping wave signal packet and the creeping wave excitation signal to obtain the corrected creeping wave attenuation index.

[0053] Specifically, for the identified creeping wave signal packet, the time point representing the centroid is calculated by performing a time-weighted average of the squares of the time-domain waveform amplitude, which serves as the precise arrival time of the creeping wave. Subtracting the energy centroid time of the creeping wave excitation signal from the arrival time yields the pure propagation time of the creeping wave. Dividing the distance between the transmitting and receiving transducers (100mm) by the pure propagation time gives the creeping wave propagation speed. Applying a Fast Fourier Transform to the time-domain data of the creeping wave signal packet yields the spectrum. The frequency point with the largest amplitude is found in the spectrum; this frequency is the center frequency of the response signal corresponding to the creeping wave signal packet. Subtracting the center frequency of the creeping wave signal packet from the center frequency of the creeping wave excitation signal (500kHz) yields the frequency offset.

[0054] The total energy is calculated by summing the squares of the time-domain amplitudes of the creeping wave signal packets. The total energy of the creeping excitation signal is then calculated. The original energy ratio is obtained by dividing the total energy of the creeping wave signal packets by the total energy of the creeping excitation signal. Based on a correction model established through extensive calibration experiments, such as a quadratic polynomial correction function for frequency offset, the correction coefficient is equal to 1 + a × frequency offset + b × the square of the frequency offset. The frequency offset calculated in the previous step is substituted into the function to calculate the correction coefficient. The original energy ratio is multiplied by the correction coefficient to obtain the corrected creeping attenuation index.

[0055] In an optional embodiment, calculating the creeping wave propagation speed based on the energy centroid time of the creeping wave signal packet includes:

[0056] Through formula Calculate the creeping wave propagation velocity V, where L is a fixed distance between the transmitting and receiving transducers. The energy centroid time of the creeping wave signal packet. This is the transmission time of the creeping wave excitation signal.

[0057] Specifically, obtain the initial parameters required for the calculation. Pre-measure a fixed distance L between the center points of the transmitting and receiving transducers, for example, a fixed distance of 150 mm. Simultaneously, record the transmission time of the creeping excitation signal emitted from the arbitrary waveform generator. It can usually be set as the origin of the time coordinate system, that is... =0μs, calculate the energy centroid time of the creeping wave signal packet. Using the region of the creeping wave signal packet in the wavelet coefficient time-frequency matrix determined in the previous step, the energy values ​​of all points within the region are weighted and averaged over time to obtain a unique time point, which is the energy centroid time. For example, the calculated energy centroid time... =62.5μs.

[0058] The obtained fixed distance L=150mm, energy center of gravity time =62.5μs, and the emission time =0μs, substituting into the creeping wave propagation velocity calculation formula V=L÷( - The final calculation result is 2.4 mm / μs, or 2400 m / s.

[0059] In an optional embodiment, a nonlinear correction is performed on the energy ratio of the creeping wave signal packet to the creeping wave excitation signal based on the frequency offset, including:

[0060] Calculate the energy of the climbing wave excitation signal With creeping wave signal wave packet energy Energy ratio By correcting the formula The corrected creepage attenuation index was calculated. ,in This is the frequency offset. and These are pre-calibrated correction factors.

[0061] Specifically, the uncorrected energy ratio is calculated. The energy of the climbing excitation signal is obtained by integrating the square of the time-domain waveform amplitude of the original transmitted climbing excitation signal. For example, the calculated value is 10.0 units of energy. The energy values ​​of the corresponding regions in the time-frequency matrix of the wavelet coefficients of the identified creeping wave signal packet are summed to obtain the creeping wave signal packet energy. For example, the calculated value is 1.2 units of energy. Calculate the ratio R between the two, i.e., R = 0.12.

[0062] To obtain the necessary parameters for correction, calculate the energy centroid frequency of the creeping wave signal packet and compare it with the center frequency of the creeping excitation signal (50kHz) to obtain the frequency offset Δf, for example, -3.5kHz. Use correction coefficients obtained through prior calibration experiments, such as α=0.05 and β=0.002. Apply a nonlinear correction formula to calculate the attenuation index. Substitute the energy ratio R=0.12, the frequency offset Δf=-3.5, and the correction coefficients α and β into the correction formula. The denominator is 0.8495. The corrected creeping wave attenuation index is then calculated. It is approximately equal to 0.141.

[0063] S4. Determine the hydration stage of cement based on the weighted combination of the creeping wave propagation velocity and the corrected creeping wave attenuation index; and based on the hydration stage, select one from the power function model with creeping wave propagation velocity as the main prediction parameter and the exponential function model with the corrected creeping wave attenuation index as the main prediction parameter to calculate the early hydration strength of cement.

[0064] Specifically, the creeping wave propagation velocity and the corrected creeping wave attenuation index measured at different time points are normalized to ensure their values ​​are between 0 and 1. A weighted combination index is set, which equals the normalized creeping wave propagation velocity multiplied by a weighting coefficient of 0.7, plus the normalized creeping wave attenuation index multiplied by a weighting coefficient of 0.3. A stage division threshold, such as 0.5, is set. When the weighted combination index is less than 0.5, the cement is determined to be in the early stage of hydration, and an exponential function model is used, where D is the product of the corrected creeping wave attenuation index and another constant. When the weighted combination index is greater than or equal to 0.5, the cement is determined to be in the middle to late stage of hydration, and a power function model is used. All constants A, B, C, and D in the model are predetermined by fitting destructive test data of synchronously produced mechanical specimens at different ages with corresponding non-destructive testing parameters.

[0065] In an optional embodiment, the cement hydration stage is determined based on a weighted combination of the creeping wave propagation velocity and a modified creeping wave attenuation index, including:

[0066] Establish a hydration stage discriminant ,in and These represent the creep propagation velocity normalized to the [0, 1] interval and the corrected creep attenuation index, respectively. and The weighting coefficients and Z is the weighted combination discriminant value; when Z is less than the first threshold, it is determined to be the induction period; when Z is between the first threshold and the second threshold, it is determined to be the acceleration period; when Z is greater than the second threshold, it is determined to be the deceleration period.

[0067] Specifically, the two key measured indicators are normalized. Assuming that the creeping wave propagation speed V varies from 1500 m / s to 3000 m / s based on historical experimental data, the corrected creeping wave attenuation index... The variation range is from 0.1 to 0.9. For a certain measurement, V = 1800 m / s was obtained. =0.2. Normalized creeping wave propagation speed. =0.2. Normalized creepage attenuation index =0.125.

[0068] Calculate the weighted combination discriminant value Z and set the weighting coefficients. It is 0.7. The two coefficients, 0.3 and 0.8, reflect the empirical judgment of the importance of creeping wave propagation velocity and creeping wave attenuation index at different hydration stages. Substituting the normalized values ​​and weights into the discriminant formula, Z is calculated to be approximately 0.1775. The hydration stage is determined by comparing the weighted combined discriminant value with the threshold. The calculated weighted combined discriminant value Z 0.1775 is compared with two preset thresholds, 0.3 and 0.8. Because 0.1775 is less than the first threshold 0.3, the current cement specimen is determined to be in the induction period. If the weighted combined discriminant value Z in a subsequent measurement is 0.65, it will be determined to be in the acceleration period because it falls between 0.3 and 0.8.

[0069] In an optional embodiment, based on the hydration stage, a power function model with creeping wave propagation velocity as the primary prediction parameter and an exponential function model with a modified creeping wave attenuation index as the primary prediction parameter are selected to calculate the early hydration strength of cement, including:

[0070] When determining whether the hydration stage is the induction phase or the acceleration phase, a power function model is used. The early hydration intensity S is calculated, where V is the creeping wave propagation velocity, and a and b are model fitting parameters; when the hydration stage is determined to be a deceleration period, an exponential function model is used. Calculate the early hydration intensity S, where is the corrected creep attenuation index, and c, d, and e are the model fitting parameters.

[0071] Specifically, the appropriate strength prediction model is selected based on the cement hydration stage determined in the previous step. For example, in a single measurement, the current hydration stage is determined to be the acceleration phase through discriminant calculation. A power function model, i.e., S=a×Vᵇ‎, with the creeping wave propagation velocity as the main prediction parameter, is selected to calculate the early hydration strength of the cement.

[0072] Calculations are performed using the selected model and real-time measurement data. It is assumed that the fitting parameters for the power function model, a = 1.5 × 10⁻⁶, have been determined through calibration experiments. -8 b=2.8. The creeping wave propagation velocity obtained in this measurement is V=2100m / s. Substituting the values ​​into the model formula, the calculated result is that the early hydration strength of the cement is approximately 15.3MPa. If in another measurement it is determined that the hydration stage has entered the deceleration period, then switch to the exponential function model. If the model parameters c, d, and e are 45, 55, and 10 respectively, and the measured corrected attenuation index... =0.7, then the early hydration strength S is approximately 44.9 MPa.

[0073] An embodiment of the sensor-based non-destructive testing system for early hydration strength of cement provided by this invention includes the following modules:

[0074] The receiving module is used to transmit a creeping excitation signal of a predetermined waveform to the cement specimen under test at multiple preset hydration time points, and to receive the response signal after it has propagated through the cement specimen.

[0075] The identification module is used to perform continuous wavelet transform on the response signal and identify the connected regions with the maximum energy and a duration that meet the preset conditions in the wavelet coefficient time-frequency matrix as the climbing wave signal packet.

[0076] The correction module is used to calculate the creeping wave propagation speed based on the energy centroid time of the creeping wave signal packet; perform Fourier transform on the creeping wave signal packet to extract the center frequency, and calculate the difference between the center frequency of the creeping wave signal packet and the center frequency of the creeping wave excitation signal to obtain the frequency offset; based on the frequency offset, perform nonlinear correction on the energy ratio of the creeping wave signal packet and the creeping wave excitation signal to obtain the corrected creeping wave attenuation index.

[0077] The calculation module is used to determine the hydration stage of cement based on a weighted combination of the creeping wave propagation velocity and the corrected creeping wave attenuation index; and based on the hydration stage, it selects one of the following models to calculate the early hydration strength of cement: a power function model with creeping wave propagation velocity as the main prediction parameter and an exponential function model with the corrected creeping wave attenuation index as the main prediction parameter.

[0078] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A sensor-based non-destructive testing method for early-stage cement hydration strength, characterized in that, Includes the following steps: S1, at multiple preset hydration time points, transmit a creeping excitation signal of a predetermined waveform to the cement specimen to be tested, and receive the response signal after propagation through the cement specimen. S2, perform continuous wavelet transform on the response signal, identify the connected region with the maximum energy and the duration meeting the preset conditions in the wavelet coefficient time-frequency matrix, and use it as the creeping wave signal packet; S3. Calculate the creeping wave propagation speed based on the energy centroid time of the creeping wave signal packet; perform a Fourier transform on the creeping wave signal packet to extract the center frequency, and calculate the difference between the center frequency of the creeping wave signal packet and the center frequency of the creeping wave excitation signal to obtain the frequency offset; based on the frequency offset, perform a nonlinear correction on the energy ratio of the creeping wave signal packet and the creeping wave excitation signal to obtain the corrected creeping wave attenuation index. S4. Determine the hydration stage of cement based on the weighted combination of the creeping wave propagation velocity and the corrected creeping wave attenuation index; and based on the hydration stage, select one from the power function model with creeping wave propagation velocity as the main prediction parameter and the exponential function model with the corrected creeping wave attenuation index as the main prediction parameter to calculate the early hydration strength of cement.

2. The sensor-based non-destructive testing method for early-stage cement hydration strength according to claim 1, characterized in that, The cement specimen to be tested is emitted with a creeping excitation signal of a predetermined waveform, including: A sinusoidal pulse signal with a center frequency of 50kHz and containing 5 cycles is used as the creeping excitation signal, and is generated and output by an arbitrary waveform generator at a sampling frequency of 10MHz.

3. The sensor-based non-destructive testing method for early-stage cement hydration strength according to claim 1, characterized in that, Identify connected regions with maximum energy and durations satisfying preset conditions in the wavelet coefficient time-frequency matrix, including: Morlet complex wavelet is used as the wavelet mother function; Set the energy threshold to 30% of the maximum value in the wavelet coefficient time-frequency matrix, and identify all connected regions with energy greater than the energy threshold; Among all identified connected regions whose duration meets the preset conditions, the connected region with the largest energy integral value is selected as the creeping wave signal packet.

4. The sensor-based non-destructive testing method for early hydration strength of cement according to claim 1, characterized in that, The creeping wave propagation speed is calculated based on the energy centroid time of the creeping wave signal packet, including: Through formula Calculate the creeping wave propagation velocity V, where L is a fixed distance between the transmitting and receiving transducers. The energy centroid time of the creeping wave signal packet. This is the transmission time of the creeping wave excitation signal.

5. The sensor-based non-destructive testing method for early-stage cement hydration strength according to claim 1, characterized in that, Based on the frequency offset, a nonlinear correction is performed on the energy ratio of the creeping wave signal packet to the creeping wave excitation signal, including: Calculate the energy of the climbing wave excitation signal With creeping wave signal wave packet energy Energy ratio ; By correcting the formula The corrected creepage attenuation index was calculated. ,in This is the frequency offset. and These are pre-calibrated correction factors.

6. The sensor-based non-destructive testing method for early hydration strength of cement according to claim 1, characterized in that, The hydration stages of cement are determined based on a weighted combination of the creeping wave propagation velocity and the corrected creeping wave attenuation index, including: Establish a hydration stage discriminant ,in and These represent the creep propagation velocity normalized to the [0, 1] interval and the corrected creep attenuation index, respectively. and The weighting coefficients and Z is the weighted combination discriminant value; When Z is less than the first threshold, it is determined to be the induction period; when Z is between the first and second thresholds, it is determined to be the acceleration period; when Z is greater than the second threshold, it is determined to be the deceleration period.

7. The sensor-based non-destructive testing method for early hydration strength of cement according to claim 6, characterized in that, Based on the hydration stage, a power function model with creeping wave propagation velocity as the main prediction parameter and an exponential function model with the modified creeping wave attenuation index as the main prediction parameter are selected to calculate the early hydration strength of cement, including: When determining whether the hydration stage is the induction phase or the acceleration phase, a power function model is used. Calculate the early hydration intensity S, where V is the creeping wave propagation velocity, and a and b are model fitting parameters; When the hydration stage is determined to be a deceleration period, an exponential function model is used. Calculate the early hydration intensity S, where is the corrected creep attenuation index, and c, d, and e are the model fitting parameters.

8. A sensor-based non-destructive testing system for early hydration strength of cement, characterized in that, Includes the following modules: The receiving module is used to transmit a creeping excitation signal of a predetermined waveform to the cement specimen under test at multiple preset hydration time points, and to receive the response signal after it has propagated through the cement specimen. The identification module is used to perform continuous wavelet transform on the response signal and identify the connected regions with the maximum energy and a duration that meet the preset conditions in the wavelet coefficient time-frequency matrix as the climbing wave signal packet. The correction module is used to calculate the creeping wave propagation speed based on the energy centroid time of the creeping wave signal packet; perform Fourier transform on the creeping wave signal packet to extract the center frequency, and calculate the difference between the center frequency of the creeping wave signal packet and the center frequency of the creeping wave excitation signal to obtain the frequency offset; based on the frequency offset, perform nonlinear correction on the energy ratio of the creeping wave signal packet and the creeping wave excitation signal to obtain the corrected creeping wave attenuation index. The calculation module is used to determine the hydration stage of cement based on a weighted combination of the creeping wave propagation velocity and the corrected creeping wave attenuation index; and based on the hydration stage, it selects one of the following models to calculate the early hydration strength of cement: a power function model with creeping wave propagation velocity as the main prediction parameter and an exponential function model with the corrected creeping wave attenuation index as the main prediction parameter.

9. The sensor-based non-destructive testing system for early hydration strength of cement according to claim 8, characterized in that, The cement specimen to be tested is emitted with a creeping excitation signal of a predetermined waveform, including: A sinusoidal pulse signal with a center frequency of 50kHz and containing 5 cycles is used as the creeping excitation signal, and is generated and output by an arbitrary waveform generator at a sampling frequency of 10MHz.

10. The sensor-based non-destructive testing system for early hydration strength of cement according to claim 8, characterized in that, Identify connected regions with maximum energy and durations satisfying preset conditions in the wavelet coefficient time-frequency matrix, including: Morlet complex wavelet is used as the wavelet mother function; the energy threshold is set to 30% of the maximum value in the wavelet coefficient time-frequency matrix, and all connected regions with energy greater than the energy threshold are identified; among all identified connected regions whose duration meets the preset conditions, the connected region with the largest energy integral value is selected as the creeping wave signal packet.

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