A test method for the anti-crack creep performance of lightweight foam concrete

Abstract

The present application relates to the technical field of concrete performance testing, and specifically to a method for testing the anti-crack creep performance of lightweight foam concrete, the method comprising: collecting ultrasonic signals of each period in each region of lightweight foam concrete; obtaining the acoustic wave loss coefficient of each region of lightweight foam concrete; and then obtaining the acoustic wave distortion coefficient of each period of the ultrasonic signal of each region of lightweight foam concrete; calculating the significant value of acoustic wave scattering rebound of each region of lightweight foam concrete; and then calculating the diffusion degree of each loss path of the regional window of each region of lightweight foam concrete and the diffusion non-uniformity coefficient of each region; and then obtaining the anti-crack creep factor of each region of lightweight foam concrete to test the anti-crack creep performance of lightweight foam concrete. The present application improves the accuracy of testing the anti-crack creep performance.

Description

Technical Field

[0001] The present application relates to the technical field of concrete performance testing, and in particular to a method for testing the anti-crack creep performance of lightweight foam concrete. Background Art

[0002] Lightweight foam concrete, also known as air bubble concrete, is a new type of lightweight thermal insulation material containing a large number of closed pores formed by mechanically foaming the foaming agent through the foaming system of a bubble machine, evenly mixing the foam with cement slurry, and then pouring on site or molding it through molds. It is naturally cured and has the characteristics of light weight, thermal insulation, heat insulation, fire resistance, sound insulation and frost resistance. The crack resistance and deformation performance test of lightweight foam concrete aims to improve the reliability and durability of engineering applications, which is of great significance for promoting the optimization and development of new materials and material ratios.

[0003] The crack resistance of lightweight foam concrete is tested by GB / T 50081-2002 "Standard for Test Methods of Concrete for Building Structures". Compared with the ultrasonic technology, the test of the crack resistance and creep resistance of lightweight foam concrete does not have the non-destructive and rapid detection performance; and the traditional method of using ultrasound to test the crack resistance and creep resistance of lightweight foam concrete lacks the time-frequency domain characteristic analysis of the ultrasonic signal of lightweight foam concrete, making it difficult to intuitively quantify the crack characteristics formed in lightweight foam concrete, and it is impossible to accurately detect the creep cracks inside the lightweight foam concrete, and thus it is impossible to obtain reliable and accurate test results for the crack resistance and creep resistance of lightweight foam concrete. Summary of the invention

[0004] In order to solve the above technical problems, the present application provides a method for testing the anti-crack creep performance of lightweight foam concrete to solve the existing problems.

[0005] A method for testing the anti-crack creep performance of lightweight foam concrete in this application adopts the following technical solution:

[0006] An embodiment of the present application provides a method for testing the anti-crack creep performance of lightweight foam concrete, the method comprising the following steps:

[0007] Collect ultrasonic signals of each period in each area of ​​lightweight foam concrete;

[0008] Analyze the difference between the peak values ​​of the ultrasonic signal and the slope of the peak value on the ultrasonic signal fitting curve to obtain the acoustic wave loss coefficient of each area of ​​the lightweight foam concrete;

[0009] Obtain the sound wave distortion coefficient of the ultrasonic signal in each period of each area of ​​the lightweight foam concrete through the distance between the energies of each envelope of the frequency domain signal of the ultrasonic signal, the difference between the energies of the frequency domain signal of the ultrasonic signal and the difference between the propagation time intervals of each period of the ultrasonic signal;

[0010] Based on the uncertainty of the acoustic wave loss coefficient, the acoustic wave distortion coefficient and the energy of the frequency domain signal of the ultrasonic signal, the significant value of the acoustic wave scattering rebound in each area of ​​the lightweight foam concrete is obtained;

[0011] Based on the significant value of acoustic wave scattering rebound, each loss path and the loss direction of the loss path in the regional window of each region are obtained;

[0012] Combining the difference between the significant values ​​of the acoustic wave scattering rebound and the number of regions that the loss path passes through in the regional window, the diffusion degree of each loss path in the regional window of each region of the lightweight foam concrete is obtained;

[0013] The diffusion inhomogeneity coefficient of each area of ​​lightweight foam concrete is obtained by using the differences and similarities between the significant values ​​of sound wave scattering and rebound.

[0014] The diffusion degree and the diffusion non-uniformity coefficient are used to obtain the anti-cracking creep factor of each area of ​​the lightweight foam concrete, and the anti-cracking creep performance of the lightweight foam concrete is tested based on the anti-cracking creep factor.

[0015] Further, the method for obtaining the acoustic wave loss coefficient is:

[0016] For the ultrasonic signals of each area of ​​the lightweight foam concrete, a peak detection algorithm is used to obtain the peak value of the ultrasonic signal, a curve fitting algorithm is used to fit all the peak values ​​of the ultrasonic signal to obtain a fitting curve, and the slope of each peak value on the fitting curve is calculated;

[0017] For each peak value of the ultrasonic signal in each area of ​​the lightweight foam concrete, the absolute value of the difference between the amplitude of the peak value and its previous adjacent peak value is calculated as the first absolute value of the difference, the product of the slope of the peak value on the fitting curve and the first absolute value of the difference is calculated as the first product, the sum of all the first products in the ultrasonic signal is calculated as the first sum, and the calculation result of the exponential function with the natural constant as the base and the first sum as the exponent is used as the sound wave loss coefficient of each area of ​​the lightweight foam concrete.

[0018] Further, the method for obtaining the acoustic wave distortion coefficient is:

[0019] Based on the energy of each envelope of the frequency domain signal of the ultrasonic signal, obtaining the sound wave frequency domain energy sequence of each frequency domain signal of the ultrasonic signal of each period in each region of the lightweight foamed concrete;

[0020] For each period of the ultrasonic signal in each area of ​​the lightweight foam concrete, the time from the emission to the reception of the ultrasonic signal is taken as the propagation time interval of the ultrasonic signal;

[0021] For the ultrasonic signal of each period in each area of ​​the lightweight foam concrete, the cumulative result of the DTW distance between the sound wave frequency domain energy sequences of all frequency domain signals except the fundamental frequency envelope of the ultrasonic signal is calculated as the first cumulative value, and the absolute value of the difference between the propagation time interval of the ultrasonic signal and the ultrasonic signal of the previous adjacent period is calculated as the second absolute value of the difference; the cumulative result of the absolute value of the difference between the energy of the fundamental frequency of the ultrasonic signal and the maximum signal energy of all other frequency domain signals is calculated as the second cumulative value;

[0022] Calculate the calculation result of an exponential function with a natural constant as the base and the absolute value of the second difference as the exponent, calculate the product of the first accumulated value and the calculation result as the second product, and use the ratio of the second product to the second accumulated value as the sound wave distortion coefficient of the ultrasonic signal of each area of ​​the lightweight foam concrete in each period.

[0023] Furthermore, the method for obtaining the sound wave frequency domain energy sequence is:

[0024] A time-frequency conversion algorithm is used to obtain the frequency domain signal of the ultrasonic signal of each period in each area of ​​the lightweight foam concrete, and the Hilbert transform is used to extract the envelopes of the frequency domain signal of the ultrasonic signal of each period in each area of ​​the lightweight foam concrete. The energy of each frequency in each envelope of the frequency domain signal of the ultrasonic signal of each period in each area of ​​the lightweight foam concrete is sequenced in the positive order of frequency as the sound wave frequency domain energy sequence of each envelope of the frequency domain signal of the ultrasonic signal of each period in each area of ​​the lightweight foam concrete.

[0025] Furthermore, the method for obtaining the significant value of the sound wave scattering rebound is:

[0026] For the ultrasonic signal of each period in each area of ​​the lightweight foam concrete, the Shannon entropy of the maximum energy of all frequency domain signals of the ultrasonic signal is calculated, the sum of the sound wave distortion coefficient of the ultrasonic signal and the Shannon entropy is calculated as the second sum, the sum of all the second sums of each area of ​​the lightweight foam concrete is calculated, and the product of the sound wave loss coefficient of each area of ​​the lightweight foam concrete and the sum is taken as the sound wave scattering rebound significance value of each area of ​​the lightweight foam concrete.

[0027] Further, the step of obtaining each loss path and the loss direction of each loss path in the regional window of each region includes:

[0028] Construct regional windows in each area of ​​lightweight foam concrete;

[0029] A threshold segmentation algorithm is used to obtain the segmentation threshold of the acoustic wave scattering rebound significance value of all regions in the regional window of each region, and the region where the acoustic wave scattering rebound significance value is greater than the segmentation threshold is regarded as a significant loss region;

[0030] For the regional window of each area, the center point of the area with the smallest significant value of acoustic wave scattering rebound in the regional window is connected with the center point of all other significant loss areas, and each connecting line is used as the loss path of the regional window of each area. The direction between the center point of the area with the smallest significant value of acoustic wave scattering rebound and the center point of all other significant loss areas is the loss direction of each loss path.

[0031] Furthermore, the method for obtaining the diffusion degree is:

[0032] For the regional window of each area of ​​the lightweight foam concrete, the absolute value of the difference between the significant value of the sound wave scattering rebound of each area on each loss path and the next area along the loss direction is calculated as the third absolute value of the difference, the cumulative result of all the third absolute values ​​of the difference on the loss path is calculated, and the calculation result of an exponential function with a natural constant as the base and the cumulative result as the exponent is calculated, and the product of the number of areas passed by each loss path in the regional window and the calculation result is taken as the diffusion degree of each loss path in the regional window of each area of ​​the lightweight foam concrete.

[0033] Furthermore, the method for obtaining the diffusion non-uniformity coefficient is:

[0034] The sequence of the acoustic wave scattering rebound significance values ​​of all regions on each loss path in the regional window of each region of the lightweight foam concrete is composed in the order of loss direction as the water loss sequence of each loss path in the regional window of each region of the lightweight foam concrete;

[0035] For each area of ​​lightweight foam concrete, the accumulated result of the absolute value of the difference between the significant values ​​of the acoustic scattering rebound of the calculated area and all the areas of its eight neighborhoods is taken as the third accumulated value, the accumulated result of the cosine similarity between the water loss sequences of all loss paths in the area window of the calculated area is taken as the fourth accumulated value, the sum of the fourth accumulated value and the preset parameter adjustment factor is calculated as the third sum, and the ratio of the third accumulated value to the third sum is taken as the diffusion unevenness coefficient of each area of ​​lightweight foam concrete.

[0036] Further, the method for obtaining the anti-crack creep factor is:

[0037] For each area of ​​lightweight foam concrete, the normalized result of the inverse of the product of the cumulative result of the diffusion degree of all loss paths in the regional window of the calculation area and the regional diffusion unevenness coefficient is used as the anti-cracking creep factor of each area of ​​lightweight foam concrete.

[0038] Further, the anti-crack creep property of lightweight foamed concrete is tested based on the anti-crack creep factor, including:

[0039] For each area of ​​the lightweight foam concrete, when the anti-cracking creep factor is greater than or equal to the preset anti-cracking creep threshold, the anti-cracking creep performance of the lightweight foam concrete is qualified; otherwise, the anti-cracking creep performance of the lightweight foam concrete is unqualified.

[0040] This application has at least the following beneficial effects:

[0041] The present application obtains the significant value of sound wave scattering rebound through the amplitude loss characteristics of the ultrasonic signal of lightweight foam concrete and the sound wave distortion coefficient, comprehensively considers the energy loss and signal distortion of the ultrasonic signal caused by the migration of water in the pores or cracks of the lightweight foam concrete due to internal stress relaxation, and more accurately reflects the internal water loss conditions of each region of the lightweight foam concrete; obtains the anti-cracking creep factor according to the water diffusion characteristics and uneven water loss characteristics of each region of the lightweight foam concrete, and completes the overall anti-cracking creep performance evaluation of the lightweight foam concrete on this basis, and adds the consideration of uneven water diffusion in the neighborhood range on the basis of considering the internal water loss diffusion degree of each region of the lightweight foam concrete, and more accurately intuitively quantifies the anti-cracking creep performance of the lightweight foam concrete with the time-frequency domain change characteristics of the ultrasonic signal caused by the water migration and diffusion conditions, which can further provide data-assisted support for promoting the optimization and development of new materials and material ratios, and realize a lightweight foam concrete anti-cracking creep performance testing method. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present application or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0043] Figure 1 A flow chart of a method for testing the anti-crack creep performance of lightweight foam concrete provided in one embodiment of the present application;

[0044] Figure 2 A schematic diagram of ultrasonic signal collection for lightweight foam concrete provided in one embodiment of the present application;

[0045] Figure 3 A schematic diagram of a partial time domain waveform of an ultrasonic signal of a lightweight foam concrete having good anti-crack creep performance provided by an embodiment of the present application;

[0046] Figure 4A schematic diagram of a partial time domain waveform of an ultrasonic signal of a lightweight foam concrete with poor anti-crack creep performance provided by an embodiment of the present application;

[0047] Figure 5 A schematic diagram of the ultrasonic signal propagation time interval in each cycle in a lightweight foam concrete area provided by an embodiment of the present application;

[0048] Figure 6 A frequency domain schematic diagram of an ultrasonic signal of each cycle in a lightweight foam concrete area provided by an embodiment of the present application. DETAILED DESCRIPTION

[0049] In order to further explain the technical means and effects adopted by the present application to achieve the predetermined invention purpose, the following is a detailed description of a method for testing the anti-crack creep performance of lightweight foam concrete proposed in the present application, its specific implementation method, structure, features and effects, in combination with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "another embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.

[0050] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0051] The specific scheme of the method for testing the anti-crack creep performance of lightweight foam concrete provided in the present application is described in detail below with reference to the accompanying drawings.

[0052] An embodiment of the present application provides a method for testing the anti-crack creep performance of lightweight foam concrete. Specifically, the following method for testing the anti-crack creep performance of lightweight foam concrete is provided. Figure 1 , the method comprises the following steps:

[0053] Step S1, collecting ultrasonic signals of each period in each area of ​​lightweight foam concrete.

[0054] In the process of testing the anti-crack creep performance of lightweight foam concrete in this application, the lightweight foam concrete is treated in a constant load manner, specifically: the constant load is uniformly applied to the concrete specimen, and the side of the lightweight foam concrete to be tested is uniformly divided into N 10 10 Area, an ultrasonic signal meter is used to obtain ultrasonic signals in each area, the ultrasonic signal acquisition time interval is 1min, and the total acquisition time is 12h; in order to prevent the ultrasonic signal from being seriously disturbed by the external environmental noise and seriously affecting the subsequent analysis, this application uses wavelet transform to denoise the ultrasonic signals in each area. Since ultrasonic signal acquisition and wavelet transform are both well-known technologies, the specific acquisition process will not be described in detail. The implementer can set the total number of ultrasonic signal areas and the ultrasonic signal denoising algorithm according to the actual situation, and determine the period of the ultrasonic signal according to the ultrasonic signal emission frequency of the lightweight foam concrete. The process of obtaining the signal period according to the signal frequency is a well-known technology and will not be described in detail in this embodiment.

[0055] The schematic diagram of ultrasonic signal collection of lightweight foam concrete is shown in the figure. Figure 2 As shown, in Figure 2 1 is the constant load force at each position of the lightweight foam concrete specimen, wherein the arrow directions are perpendicular to the surface of the lightweight foam concrete; 2 is the lightweight foam concrete specimen to be tested; 3 is a partial area of ​​the lightweight foam concrete specimen to be tested; 4, 5, and 6 are all center points of the surface area of ​​the lightweight foam concrete; 7 is the distance interval between the center points of the surface area of ​​the lightweight foam concrete, and the value of the distance interval in this embodiment is 20 cm, and the implementer can select other values ​​according to actual conditions; 8 is an ultrasonic signal meter; 9 represents the ultrasonic signal of each area of ​​the lightweight foam concrete after computer preprocessing.

[0056] So far, the ultrasonic signals of various areas of the lightweight foam concrete to be detected can be obtained by the above method.

[0057] Step S2, based on the difference between the peak values ​​of the ultrasonic signal and the slope of the peak value on the ultrasonic signal fitting curve, obtain the acoustic wave loss coefficient of each area of ​​the lightweight foam concrete; based on the distance between the energies of each envelope of the frequency domain signal of the ultrasonic signal, the difference between the energies of the frequency domain signal of the ultrasonic signal and the difference between the propagation time intervals of each cycle of the ultrasonic signal, obtain the acoustic wave distortion coefficient of the ultrasonic signal in each period of the lightweight foam concrete in each area; based on the uncertainty of the acoustic wave loss coefficient, the acoustic wave distortion coefficient and the energy of the frequency domain signal of the ultrasonic signal, obtain the acoustic wave scattering rebound significance value of each area of ​​the lightweight foam concrete.

[0058] In the process of testing the anti-cracking creep performance of lightweight foam concrete using the constant load method, if the anti-cracking creep performance of lightweight foam concrete is poor, as the lightweight foam concrete naturally hardens, the stress relaxation inside the lightweight foam concrete is small due to insufficient creep capacity, which increases the risk of drying shrinkage and cracking, and the moisture loss is serious, resulting in larger shrinkage and holes and cracks inside the lightweight foam concrete, affecting the performance of the lightweight foam concrete.

[0059] In the ultrasonic signals of various areas of lightweight foam concrete, although lightweight foam concrete itself will produce a large number of holes in the molding process, resulting in energy and amplitude loss of ultrasonic signals, the shrinkage and hole cracks caused by severe water loss inside the lightweight foam concrete will enhance the scattering and absorption of ultrasonic signals. The ultrasonic signal changes with time during the propagation process, causing more significant energy loss. The more significant the shrinkage and hole cracks inside the lightweight foam concrete, the greater the degree of the acoustic wave loss coefficient of the ultrasonic signal, and the more significant the change in the acoustic wave loss coefficient.

[0060] Furthermore, the schematic diagram of the partial time domain waveform of the ultrasonic signal of lightweight foam concrete with good anti-crack creep performance is shown in Figure 3 As shown in the figure, the schematic diagram of the partial time domain waveform of the ultrasonic signal of lightweight foam concrete with poor anti-crack creep performance is as follows Figure 4 shown in Figure 3 and Figure 4 Compared with the lightweight foam concrete with better anti-cracking creep performance, the lightweight foam concrete with poor anti-cracking creep performance has more obvious shrinkage and void cracks inside, resulting in more obvious time domain amplitude loss of ultrasonic signals.

[0061] Based on the above analysis, the ultrasonic signal of any area of ​​lightweight foam concrete is taken as an example for subsequent analysis. The ultrasonic signal is converted into the time domain, and the AMPD (Automatic multiscale-based peak detection) peak detection algorithm is used to obtain all peak amplitudes of the ultrasonic signal. All the peak peaks in the ultrasonic signal are used as input to obtain the fitting curve of the peak peaks of the ultrasonic signal using the least squares method. The slope of the fitting curve at each peak signal in the ultrasonic signal is obtained through the above fitting curve. Among them, the AMPD peak detection algorithm and the least squares method are both well-known technologies, and the specific acquisition process will not be described in detail.

[0062] Further, according to the above analysis, in order to reflect the obvious degree of shrinkage and hole and crack phenomena in lightweight foam concrete, the acoustic wave loss coefficient of each area in the lightweight foam concrete is obtained based on the difference between the peak values ​​of the ultrasonic signal and the slope of the peak value on the fitting curve of the ultrasonic signal. The acquisition method is: for each peak value of the ultrasonic signal in each area of ​​the lightweight foam concrete, the absolute value of the difference between the peak value and the amplitude of the previous adjacent peak value is calculated as the first absolute value of the difference, the product of the slope of the peak value on the fitting curve and the first absolute value of the difference is calculated as the first product, the sum of all the first products in the ultrasonic signal is calculated as the first sum, and the calculation result of the exponential function with the natural constant as the base and the first sum as the exponent is used as the acoustic wave loss coefficient of each area of ​​the lightweight foam concrete.

[0063] When the ultrasonic signal loses serious moisture inside the lightweight foam concrete, resulting in more obvious shrinkage and holes and cracks, the ultrasonic signal is scattered or absorbed more seriously in the lightweight foam concrete, and the signal loss of the ultrasonic signal in the process of penetrating the lightweight foam concrete becomes more and more serious. The greater the degree of change in the signal amplitude peak, the stronger the sound wave loss coefficient, that is, the greater the absolute value of the difference between all signal amplitude peaks of the ultrasonic signal in the lightweight foam concrete area and the previous signal amplitude peak, the greater the slope of the fitting curve at each signal amplitude peak of the ultrasonic signal.

[0064] The worse the anti-cracking creep performance of lightweight foam concrete is, the smaller the internal stress relaxation of lightweight foam concrete is. In the process of testing the anti-cracking creep performance of lightweight foam concrete using the constant load method, it is easier for moisture to migrate in the pores or cracks inside the lightweight foam concrete under the action of external force. When the ultrasonic signal propagates in the lightweight foam concrete, the moisture in the pores or cracks inside the lightweight foam concrete will enhance the scattering and rebound of the ultrasonic signal, making the propagation delay of the ultrasonic signal longer and the energy distortion of the ultrasonic signal more significant.

[0065] The schematic diagram of the ultrasonic signal propagation time interval in each cycle in the lightweight foam concrete area is shown in Figure 5 As shown, in Figure 5 In the process, the propagation delay of the ultrasonic signal is enhanced due to the migration and diffusion of water in the pores or cracks inside the lightweight foam concrete, which enhances the scattering and rebound effects, making the propagation time of each cycle of the ultrasonic signal gradually increase; the frequency domain schematic diagram of the ultrasonic signal of each cycle in the lightweight foam concrete area is shown in Figure 6 shown.

[0066] Based on the above analysis, for the ultrasonic signal of each period in each area of ​​the lightweight foam concrete, the time from the emission to the reception of the ultrasonic signal is used as the propagation time interval of the ultrasonic signal, and the time-frequency conversion algorithm is used to obtain the frequency domain signal of the ultrasonic signal of each period in each area of ​​the lightweight foam concrete. The Hilbert transform is used to extract the envelopes of the frequency domain signal of the ultrasonic signal of each period in each area of ​​the lightweight foam concrete, and the energy of each frequency in each envelope of the frequency domain signal of the ultrasonic signal of each period in each area of ​​the lightweight foam concrete is used as a sequence composed of the energies of each frequency in the frequency domain signal of the ultrasonic signal of each period in each area of ​​the lightweight foam concrete in the positive order of the frequency as the sound wave frequency domain energy sequence of each envelope of the frequency domain signal of the ultrasonic signal of each period in each area of ​​the lightweight foam concrete; wherein, Fourier transform and Hilbert transform are both well-known technologies and will not be described in detail in this embodiment.

[0067] Furthermore, in order to reflect the severity of the situation in which moisture inside the lightweight foam concrete migrates in the pores or cracks, the acoustic distortion coefficient of the ultrasonic signal in each period of each region of the lightweight foam concrete is obtained based on the distance between the acoustic frequency domain energy sequences, the difference between the energy of the frequency domain signals of the ultrasonic signal, and the difference between the propagation time intervals of each period of the ultrasonic signal. The acquisition method is as follows: for the ultrasonic signal of each period of each region of the lightweight foam concrete, the cumulative result of the DTW distance between the acoustic frequency domain energy sequences of all frequency domain signals of the ultrasonic signal except the fundamental frequency envelope is calculated as the first cumulative value, the absolute value of the difference between the propagation time interval of the ultrasonic signal and the ultrasonic signal of the previous adjacent period is calculated as the second difference absolute value; the cumulative result of the absolute value of the difference between the energy of the fundamental frequency of the ultrasonic signal and the maximum signal energy of all other frequency domain signals is calculated as the second cumulative value.

[0068] Calculate the result of an exponential function with a natural constant as the base and the absolute value of the second difference as the exponent, calculate the product of the first accumulated value and the calculated result as the second product, and use the ratio of the second product to the second accumulated value as the sound wave distortion coefficient of the ultrasonic signal of each area of ​​the lightweight foam concrete in each period. The DTW distance is a well-known technology and will not be described in detail in this embodiment.

[0069] It should be noted that when the phenomenon of water migration in holes or cracks in lightweight foam concrete due to internal stress relaxation is more serious, the scattering and rebound of the ultrasonic signal inside the lightweight foam concrete will be stronger, the difference between the frequency domain signals of the ultrasonic signal will be smaller, the propagation delay of the ultrasonic signal will be longer, the difference between the fundamental frequency energy of the ultrasonic signal and the maximum signal energy of the remaining frequency domain signals will be smaller, and the sound wave distortion coefficient will be higher, that is, the cumulative result of the DTW distance between the sound wave frequency domain energy sequences corresponding to all signal envelopes of the ultrasonic signal except the fundamental frequency envelope will be larger, the difference in the propagation time interval corresponding to each cycle and the previous cycle will be larger, and the cumulative result of the absolute value of the difference between the fundamental frequency energy corresponding to the ultrasonic signal and the maximum signal energy of all other frequency domain signals in the cycle will be smaller.

[0070] When the anti-crack creep performance of lightweight foam concrete is worse, the internal stress relaxation of lightweight foam concrete is smaller, and moisture is more easily lost through the holes or cracks inside the lightweight foam concrete, which makes the sound wave loss coefficient of the ultrasonic signal during the propagation inside the lightweight foam concrete stronger, the sound wave distortion coefficient of the ultrasonic signal is higher, and the frequency domain energy of each period of the ultrasonic signal is more chaotic.

[0071] Furthermore, in order to reflect the moisture loss of lightweight foam concrete, based on the uncertainty of the energy of the frequency domain signal of the acoustic wave loss coefficient, the acoustic wave distortion coefficient and the ultrasonic signal, the acoustic wave scattering rebound significance value of each area of ​​the lightweight foam concrete is obtained. The acquisition method is: for the ultrasonic signal of each period of each area of ​​the lightweight foam concrete, the Shannon entropy of the maximum energy of all frequency domain signals of the ultrasonic signal is calculated, the sum of the acoustic wave distortion coefficient of the ultrasonic signal and the Shannon entropy is calculated as the second sum, the sum of all the second sums of each area of ​​the lightweight foam concrete is calculated, and the product of the acoustic wave loss coefficient of each area of ​​the lightweight foam concrete and the sum result is used as the acoustic wave scattering rebound significance value of each area of ​​the lightweight foam concrete.

[0072] It should be noted that when the anti-crack creep performance of lightweight foam concrete is worse, the scattering and rebound of the ultrasonic signal due to the loss of water in the lightweight foam concrete will become more significant. The more significant the water loss is, that is, the stronger the amplitude loss of the ultrasonic signal is, the higher the sound wave distortion coefficient in each period is, and the greater the Shannon entropy of the maximum energy corresponding to all frequency domain signals of the ultrasonic signal in each period is.

[0073] At this point, the acoustic wave scattering rebound significance value of each area of ​​the lightweight foam concrete can be obtained through the above method to reflect the water loss situation.

[0074] Step S3, based on the significant value of the acoustic wave scattering rebound, obtain each loss path and the loss direction of the loss path in the regional window of each area; based on the difference between the significant values ​​of the acoustic wave scattering rebound and the number of areas passed by the loss path in the regional window, obtain the diffusion degree of each loss path in the regional window of each area of ​​the lightweight foam concrete; based on the difference and similarity between the significant values ​​of the acoustic wave scattering rebound, obtain the diffusion non-uniformity coefficient of each area of ​​the lightweight foam concrete; based on the diffusion degree and the diffusion non-uniformity coefficient, obtain the anti-crack creep factor of each area of ​​the lightweight foam concrete.

[0075] Evaluating the anti-crack creep performance of lightweight foam concrete only by the significant value of acoustic wave scattering rebound in each area of ​​lightweight foam concrete still has the following disadvantages: the significant value of acoustic wave scattering rebound is used to reflect the water loss in each area of ​​lightweight foam concrete. There is a lack of synergistic analysis of water loss between various areas of lightweight foam concrete, which makes it impossible to accurately measure the overall water loss of lightweight foam concrete. The test results of the anti-crack creep performance of lightweight foam concrete may be affected by abnormal water loss in individual areas.

[0076] When the area where the moisture loss of lightweight foam concrete is more serious is closer to the edge of the lightweight foam concrete, the shrinkage and drying inside the area is more significant, and the stress inside the lightweight foam concrete at the corresponding position of the area is more concentrated, resulting in severe squeezing of the pore walls inside the lightweight foam concrete, so that the holes or creep cracks inside the lightweight foam concrete are further expanded, making it easier for moisture to migrate through the holes or creep cracks, aggravating the moisture loss inside the lightweight foam concrete and reducing the performance of the lightweight foam concrete.

[0077] Based on the above analysis, for each area of ​​lightweight foam concrete, a regional window is constructed with each area as the center, and the size of the regional window is 11 11. The unit of the regional window side length is the number of regional side lengths. The acoustic scattering rebound significance values ​​of all regions in the regional window are taken as input, and the OTSU method is used to obtain the segmentation threshold. All regions with acoustic scattering rebound significance values ​​greater than the segmentation threshold are recorded as significant loss regions.

[0078] Further, for the regional window of each region, the center point of the region with the smallest significant value of acoustic wave scattering rebound in the regional window is connected with the center point of all other significant loss regions, and each connecting line is used as each loss path of the regional window of each region, and the direction of the center point of the region with the smallest significant value of acoustic wave scattering rebound and the center point of all other significant loss regions is the loss direction of each loss path. Among them, the OTSU method is a well-known technology and will not be described in detail in this embodiment.

[0079] Furthermore, in order to reflect the degree of migration and diffusion of moisture through the pores or creep cracks inside the lightweight foam concrete, based on the difference between the significant values ​​of sound wave scattering rebound and the number of areas passed by the loss path in the regional window, the diffusion degree of each loss path in the regional window of each area of ​​the lightweight foam concrete is obtained. The acquisition method is: for the regional window of each area of ​​the lightweight foam concrete, the absolute value of the difference between the significant value of sound wave scattering rebound of each area on each loss path and the next area along the loss direction is calculated as the third absolute value of the difference, the cumulative result of all the third absolute values ​​of the difference on the loss path is calculated, and the calculation result of an exponential function with a natural constant as the base and the cumulative result as the exponent is calculated, and the product of the number of areas passed by each loss path in the regional window and the calculation result is used as the diffusion degree of each loss path in the regional window of each area of ​​the lightweight foam concrete.

[0080] When the anti-crack creep performance of lightweight foam concrete is worse, the moisture loss inside the lightweight foam concrete is more serious, the moisture is easier to migrate and diffuse through the holes or creep cracks inside the lightweight foam concrete, the moisture diffusion range is larger, the moisture loss in each area along the loss direction is more serious, the diffusion degree is greater, that is, the longer the moisture loss path is, the greater the cumulative difference between the corresponding sound wave scattering rebound significance values ​​of each area on the loss path and the next area along the loss direction.

[0081] The worse the anti-crack creep performance of lightweight foam concrete is, the more serious the stress concentration inside the lightweight foam concrete is, which leads to the aggravation of the uneven shrinkage and drying of the lightweight foam concrete, and then the more significant differences in the internal moisture migration and diffusion between different areas of the lightweight foam concrete.

[0082] The sequence of the acoustic wave scattering rebound significance values ​​of all areas on each loss path in the corresponding regional window of any area in the lightweight foam concrete in the order of loss direction is taken as the water loss sequence of each loss path in each area.

[0083] Based on the above analysis, in order to reflect the significant differences in the moisture migration and diffusion conditions between various regions inside the lightweight foam concrete, based on the differences and similarities between the significant values ​​of sound wave scattering rebound, the diffusion non-uniformity coefficient of each region of the lightweight foam concrete is obtained. The acquisition method is: for each region of the lightweight foam concrete, the absolute value accumulation result of the difference between the significant values ​​of sound wave scattering rebound of the region and all regions of its eight neighborhoods is calculated as the third accumulated value, the accumulation result of the cosine similarity between the moisture loss sequences of all loss paths in the regional window of the region is calculated as the fourth accumulated value, the sum of the fourth accumulated value and the preset parameter adjustment factor is calculated as the third sum, and the ratio of the third accumulated value to the third sum is used as the diffusion non-uniformity coefficient of each region of the lightweight foam concrete.

[0084] It should be noted that when the anti-cracking creep performance of lightweight foam concrete is worse, the moisture migration and diffusion conditions between different regions due to the uneven shrinkage and drying inside the lightweight foam concrete are more significant, the moisture loss conditions on different moisture loss paths in the region are more inconsistent, the difference in the significant values ​​of sound wave scattering rebound in various regions within the neighborhood of lightweight foam concrete is greater, and the diffusion unevenness coefficient is stronger, that is, the greater the cumulative result of the absolute value of the difference in the significant values ​​of sound wave scattering rebound corresponding to all regions within the neighborhood, the smaller the cumulative result of the cosine similarity between the moisture loss sequences corresponding to all loss paths in the region.

[0085] When the anti-crack creep performance of lightweight foam concrete is worse, the water loss caused by the migration and diffusion of water inside the lightweight foam concrete is more serious, and the unevenness of the water migration and diffusion is more significant.

[0086] Furthermore, in order to reflect the anti-cracking creep performance of lightweight foam concrete, the anti-cracking creep factor of each region of lightweight foam concrete is obtained based on the diffusion degree and the diffusion unevenness coefficient. The calculation method is: for each region of lightweight foam concrete, the normalized result of the inverse of the product of the cumulative result of the diffusion degree of all loss paths in the regional window of the calculation region and the regional diffusion unevenness coefficient is used as the anti-cracking creep factor of each region of lightweight foam concrete.

[0087] It should be noted that when the anti-cracking creep performance of lightweight foam concrete is worse, the moisture inside the lightweight foam concrete is easier to migrate and diffuse through the holes or creep cracks caused by drying shrinkage or stress extrusion, the stronger the degree of diffusion of moisture in the holes or creep cracks to the edge of the lightweight foam concrete, the more uneven the diffusion and migration of moisture inside the lightweight foam concrete, and the smaller the anti-cracking creep factor of the lightweight foam concrete at the corresponding position in the region, that is, the greater the cumulative result of the diffusion degree of all loss paths in the region, and the stronger the regional diffusion unevenness coefficient.

[0088] At this point, the anti-cracking creep factor of each area in the lightweight foam concrete can be obtained by the above method.

[0089] Step S4, testing the anti-crack creep performance of the lightweight foam concrete based on the anti-crack creep factor.

[0090] The overall anti-cracking creep property of lightweight foam concrete is obtained by taking the average value of the anti-cracking creep factor of all areas of lightweight foam concrete. The implementers can directly test the anti-cracking creep performance of lightweight foam concrete based on the anti-cracking creep factor, or use it as a basis to establish a mechanical numerical theoretical model of lightweight foam concrete for indirect testing.

[0091] Specifically, a preset anti-crack creep threshold of lightweight foam concrete is set. For each area of ​​lightweight foam concrete, when the anti-crack creep factor is greater than or equal to the preset anti-crack creep threshold, it is considered that the holes or creep cracks generated inside the lightweight foam concrete are relatively slight, and the condition of large-scale water loss through the holes or creep cracks is relatively slight. The smaller the internal stress relaxation of the lightweight foam concrete, the qualified anti-crack creep performance; when the anti-crack creep factor is less than the preset anti-crack creep threshold, it is considered that the internal stress relaxation of the lightweight foam concrete is large, the water loss in the holes and creep cracks generated during the drying shrinkage process is serious, and the anti-crack creep performance is unqualified; the larger the preset anti-crack creep threshold of lightweight foam concrete, the higher the requirements for the anti-crack creep performance of lightweight foam concrete. In this embodiment, the preset anti-crack creep threshold of lightweight foam concrete is 0.7, and the implementer can set the preset anti-crack creep threshold of lightweight foam concrete according to actual conditions.

[0092] At this point, a method for testing the anti-crack creep performance of lightweight foam concrete can be achieved through the above method.

[0093] It should be noted that the above-mentioned sequence of the embodiments of the present application is only for description and does not represent the advantages and disadvantages of the embodiments. The above-mentioned specific embodiments of the present application are described. In addition, the processes depicted in the accompanying drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0094] The various embodiments in the present application are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0095] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Modifications to the technical solutions recorded in the aforementioned embodiments, or equivalent replacement of some of the technical features therein, do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A method for testing the anti-crack creep performance of lightweight foam concrete, characterized in that: The method comprises the following steps: Collect ultrasonic signals of each period in each area of ​​lightweight foam concrete; Analyze the difference between the peak values ​​of the ultrasonic signal and the slope of the peak value on the ultrasonic signal fitting curve to obtain the acoustic wave loss coefficient of each area of ​​the lightweight foam concrete; Obtain the sound wave distortion coefficient of the ultrasonic signal in each period of each area of ​​the lightweight foam concrete through the distance between the energies of each envelope of the frequency domain signal of the ultrasonic signal, the difference between the energies of the frequency domain signal of the ultrasonic signal and the difference between the propagation time intervals of each period of the ultrasonic signal; Based on the uncertainty of the acoustic wave loss coefficient, the acoustic wave distortion coefficient and the energy of the frequency domain signal of the ultrasonic signal, the significant value of the acoustic wave scattering rebound in each area of ​​the lightweight foam concrete is obtained; Based on the significant value of acoustic wave scattering rebound, each loss path and the loss direction of the loss path in the regional window of each region are obtained; Combining the difference between the significant values ​​of the acoustic wave scattering rebound and the number of regions that the loss path passes through in the regional window, the diffusion degree of each loss path in the regional window of each region of the lightweight foam concrete is obtained; The diffusion inhomogeneity coefficient of each area of ​​lightweight foam concrete is obtained by using the differences and similarities between the significant values ​​of sound wave scattering and rebound. The anti-cracking creep factor of each area of ​​the lightweight foam concrete is obtained by using the diffusion degree and the diffusion non-uniformity coefficient, and the anti-cracking creep performance of the lightweight foam concrete is tested based on the anti-cracking creep factor; The method for obtaining the acoustic wave loss coefficient is: For the ultrasonic signals of each area of ​​the lightweight foam concrete, a peak detection algorithm is used to obtain the peak value of the ultrasonic signal, a curve fitting algorithm is used to fit all the peak values ​​of the ultrasonic signal to obtain a fitting curve, and the slope of each peak value on the fitting curve is calculated; For each peak value of the ultrasonic signal in each area of ​​the lightweight foam concrete, the absolute value of the difference between the amplitude of the peak value and the previous adjacent peak value is calculated as the first absolute value of the difference, the product of the slope of the peak value on the fitting curve and the first absolute value of the difference is calculated as the first product, the sum of all the first products in the ultrasonic signal is calculated as the first sum, and the calculation result of the exponential function with the natural constant as the base and the first sum as the exponent is used as the sound wave loss coefficient of each area of ​​the lightweight foam concrete; The method for obtaining the acoustic wave distortion coefficient is: Based on the energy of each envelope of the frequency domain signal of the ultrasonic signal, obtaining the sound wave frequency domain energy sequence of each frequency domain signal of the ultrasonic signal of each period in each region of the lightweight foamed concrete; For each period of the ultrasonic signal in each area of ​​the lightweight foam concrete, the time from the emission to the reception of the ultrasonic signal is taken as the propagation time interval of the ultrasonic signal; For the ultrasonic signal of each period in each area of ​​the lightweight foam concrete, the cumulative result of the DTW distance between the sound wave frequency domain energy sequences of all frequency domain signals except the fundamental frequency envelope of the ultrasonic signal is calculated as the first cumulative value, and the absolute value of the difference between the propagation time interval of the ultrasonic signal and the ultrasonic signal of the previous adjacent period is calculated as the second absolute value of the difference; the cumulative result of the absolute value of the difference between the energy of the fundamental frequency of the ultrasonic signal and the maximum signal energy of all other frequency domain signals is calculated as the second cumulative value; Calculate the calculation result of an exponential function with a natural constant as the base and the absolute value of the second difference as the exponent, calculate the product of the first accumulated value and the calculation result as the second product, and use the ratio of the second product to the second accumulated value as the sound wave distortion coefficient of the ultrasonic signal of each area of ​​the lightweight foam concrete in each period.

2. A method for testing the anti-crack creep performance of lightweight foamed concrete as claimed in claim 1, characterized in that: The method for obtaining the acoustic wave frequency domain energy sequence is: A time-frequency conversion algorithm is used to obtain the frequency domain signal of the ultrasonic signal of each period in each area of ​​the lightweight foam concrete, and the Hilbert transform is used to extract the envelopes of the frequency domain signal of the ultrasonic signal of each period in each area of ​​the lightweight foam concrete. The energy of each frequency in each envelope of the frequency domain signal of the ultrasonic signal of each period in each area of ​​the lightweight foam concrete is sequenced in the positive order of frequency as the sound wave frequency domain energy sequence of each envelope of the frequency domain signal of the ultrasonic signal of each period in each area of ​​the lightweight foam concrete.

3. A method for testing the anti-crack creep performance of lightweight foamed concrete as claimed in claim 1, characterized in that: The method for obtaining the significant value of the acoustic wave scattering rebound is as follows: For the ultrasonic signal of each period in each area of ​​the lightweight foam concrete, the Shannon entropy of the maximum energy of all frequency domain signals of the ultrasonic signal is calculated, the sum of the sound wave distortion coefficient of the ultrasonic signal and the Shannon entropy is calculated as the second sum, the sum of all the second sums of each area of ​​the lightweight foam concrete is calculated, and the product of the sound wave loss coefficient of each area of ​​the lightweight foam concrete and the sum is taken as the sound wave scattering rebound significance value of each area of ​​the lightweight foam concrete.

4. A method for testing the anti-crack creep performance of lightweight foamed concrete as claimed in claim 1, characterized in that: The step of obtaining each loss path and the loss direction of each loss path in the regional window of each region includes: Construct regional windows in each area of ​​lightweight foam concrete; A threshold segmentation algorithm is used to obtain the segmentation threshold of the acoustic wave scattering rebound significance value of all regions in the regional window of each region, and the region where the acoustic wave scattering rebound significance value is greater than the segmentation threshold is regarded as a significant loss region; For the regional window of each area, the center point of the area with the smallest significant value of acoustic wave scattering rebound in the regional window is connected with the center point of all other significant loss areas, and each connecting line is used as the loss path of the regional window of each area. The direction between the center point of the area with the smallest significant value of acoustic wave scattering rebound and the center point of all other significant loss areas is the loss direction of each loss path.

5. A method for testing the anti-crack creep performance of lightweight foamed concrete as claimed in claim 4, characterized in that: The method for obtaining the diffusion degree is: For the regional window of each area of ​​the lightweight foam concrete, the absolute value of the difference between the significant value of the sound wave scattering rebound of each area on each loss path and the next area along the loss direction is calculated as the third absolute value of the difference, the cumulative result of all the third absolute values ​​of the difference on the loss path is calculated, and the calculation result of an exponential function with a natural constant as the base and the cumulative result as the exponent is calculated, and the product of the number of areas passed by each loss path in the regional window and the calculation result is taken as the diffusion degree of each loss path in the regional window of each area of ​​the lightweight foam concrete.

6. A method for testing the anti-crack creep performance of lightweight foamed concrete as claimed in claim 4, characterized in that: The method for obtaining the diffusion inhomogeneity coefficient is: The sequence of the acoustic wave scattering rebound significance values ​​of all regions on each loss path in the regional window of each region of the lightweight foam concrete is composed in the order of loss direction as the water loss sequence of each loss path in the regional window of each region of the lightweight foam concrete; For each area of ​​lightweight foam concrete, the accumulated result of the absolute value of the difference between the significant values ​​of the acoustic scattering rebound of the calculated area and all the areas of its eight neighborhoods is taken as the third accumulated value, the accumulated result of the cosine similarity between the water loss sequences of all loss paths in the area window of the calculated area is taken as the fourth accumulated value, the sum of the fourth accumulated value and the preset parameter adjustment factor is calculated as the third sum, and the ratio of the third accumulated value to the third sum is taken as the diffusion unevenness coefficient of each area of ​​lightweight foam concrete.

7. A method for testing the anti-crack creep performance of lightweight foamed concrete as claimed in claim 4, characterized in that: The method for obtaining the anti-crack creep factor is: For each area of ​​lightweight foam concrete, the normalized result of the inverse of the product of the cumulative result of the diffusion degree of all loss paths in the regional window of the calculation area and the regional diffusion unevenness coefficient is used as the anti-cracking creep factor of each area of ​​lightweight foam concrete.

8. A method for testing the anti-crack creep performance of lightweight foamed concrete as claimed in claim 1, characterized in that: The method for testing the anti-crack creep property of lightweight foam concrete based on the anti-crack creep factor includes: For each area of ​​the lightweight foam concrete, when the anti-cracking creep factor is greater than or equal to the preset anti-cracking creep threshold, the anti-cracking creep performance of the lightweight foam concrete is qualified; otherwise, the anti-cracking creep performance of the lightweight foam concrete is unqualified.

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