Concrete Carbonation Depth Detection Method and System

Abstract

The present invention discloses a method and system for detecting the carbonation depth of concrete, belonging to the technical field of concrete detection in civil engineering. Rayleigh waves are adopted, and the particles vibrate in an elliptical shape. Rayleigh waves can propagate far and have a large detectable range. A transducer is installed on any surface of the concrete test block, and the carbonation of the concrete can be detected through the detection device, with convenient and fast operation. By observing the spectra of the excitation signal and the received signal through an oscilloscope and calculating the correlation coefficient, it can be detected whether the concrete at the current depth has carbonated. Then, by changing the excitation frequency and repeating the above steps, it can be detected whether the concrete at any depth L has carbonated, that is, the carbonation depth.

Description

Technical Field

[0001] The present invention belongs to the technical field of civil engineering concrete detection, and particularly relates to a method and system for detecting the carbonation depth of concrete. Background Art

[0002] During the service life of concrete, CO2 gas in the air penetrates into the concrete and reacts with its alkaline substances (Ca(OH)2) to form carbonate (CaCO3) and water, and the process of reducing the alkalinity of concrete is called concrete carbonation, and this process is the concrete carbonation.

[0003] When the PH < 9, the passivation film of the steel bar is damaged and rusted. Since the volume of rust is 2 to 4 times larger than that of the steel bar, the generated expansion stress causes the concrete to crack internally and destroys the bond between the steel bar and the concrete.

[0004] Therefore, it is necessary to detect the carbonation depth of concrete to prevent the carbonation depth from exceeding the thickness of the steel bar protection layer.

[0005] However, the existing carbonation detection method is a destructive method. It mainly uses an impact drill to punch holes on the surface of the tested component, clears the powder in the drill hole, sprays ethanol phenolphthalein solution in the hole, and the thickness of the surface non-discoloring concrete measured with a vernier caliper is the carbonation depth of the concrete. For details, see the industry standard for measuring carbonation depth values (JGJ / T 23 - 2001).

[0006] Patent CN202110593045.4 discloses a non-linear ultrasonic detection method and detection system applicable to concrete carbonation. This patent uses longitudinal waves for detection, and the propagation distance of longitudinal waves is limited, and the detection range is small.

[0007] During detection, PZT piezoelectric ceramic chips need to be respectively arranged on two opposite surfaces of the concrete test block, so there are certain requirements for the shape of the concrete test block.

[0008] And this patent can only detect whether the concrete test block has carbonated and cannot detect the carbonation depth. Summary of the Invention

[0009] The present invention provides a method and system for detecting the carbonation depth of concrete to solve the technical problems raised in the background art.

[0010] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0011] A method for detecting the carbonation depth of concrete includes the following steps:

[0012] S1. Place two transducers perpendicular to the surface of the concrete test block to be detected, and respectively excite and receive Rayleigh waves;

[0013] The waveform of the transducer excitation signal is as follows:

[0014] ;

[0015] Among them, N is the number of sine wave periods, f is the excitation frequency, and t is time; adjust the excitation frequency f, and calculate the wavelength λ = c / f of the Rayleigh wave according to the known Rayleigh wave velocity c.

[0016] S2. Perform Fourier transform on x(t) to obtain the excitation signal spectrum X(f), record the received signal as y(t), and perform Fourier transform on y(t) to obtain the received signal spectrum Y(f).

[0017] When the concrete has not carbonized, the pores in the concrete and the Rayleigh wave scatter, and there are obvious differences between the received signal spectrum and the excitation signal spectrum, and the correlation coefficient of the two spectral waveforms is small.

[0018] When the concrete carbonizes, the pores in the concrete are filled with carbides, the pore diameter is further reduced, the Rayleigh wave scattering phenomenon weakens, the difference between the received signal spectrum and the excitation signal spectrum decreases, and the correlation coefficient increases.

[0019] The correlation coefficient is calculated as:

[0020] ;

[0021] Among them, Cov(X,Y) is the covariance of X and Y, Var[X] is the variance of X, and Var[Y] is the variance of Y.

[0022] When the r value is greater than or equal to the correlation coefficient, it is determined that the concrete at the current depth L has carbonized.

[0023] S3. Change the excitation frequency f, repeat S1-2, and determine whether the concrete at any depth L has carbonized.

[0024] As a further preference of the present invention, in S1, the influence depth of the Rayleigh wave is concentrated within the range of 1 / 3 wavelength, so the influence depth L = λ / 3 is calculated.

[0025] As a further preference of the present invention, for concrete with the same mix ratio, perform carbonization detection of S1-2, calculate the correlation coefficient as a reference value, and when the detected correlation coefficient is significantly less than the reference value, it is determined that the concrete at the current depth L has not carbonized.

[0026] The concrete carbonization depth detection system includes: a concrete test block to be detected, transducers, and a detection device; the two transducers respectively excite and receive Rayleigh waves, are fixed on the surface of the concrete test block to be detected, are provided with an excitation probe and a receiving probe at the upper end, and are connected to the detection device through a wiring harness.

[0027] The detection device includes: a signal generator, a high-voltage amplifier, a voltage amplifier, and an oscilloscope; the signal generator is used to generate an excitation signal to form an incident wave; the input end of the high-voltage amplifier is connected to the signal generator, and the output end is connected to the excitation probe; the high-voltage amplifier is used to amplify the energy of the incident wave and transmit it to the surface of the concrete specimen to be detected through the excitation probe; the input end of the voltage amplifier is connected to the oscilloscope, and the output end is connected to the receiving probe; the receiving probe is used to receive the vibration wave after transmission in the concrete specimen to be detected, and the voltage amplifier is used to amplify the energy of the vibration wave to generate a received signal; the oscilloscope is connected to the output ends of the signal generator, the high-voltage amplifier, and the voltage amplifier; the oscilloscope is used to display the spectra of the excitation signal and the received signal.

[0028] As a further preference of the present invention, the detection device can detect the carbonation depth of concrete specimens placed underwater or above water.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] The present invention uses Rayleigh waves, and the mass points vibrate elliptically. Rayleigh waves can propagate far and have a large detection range. A transducer is installed on any surface of the concrete specimen, and the carbonation of the concrete can be detected through the detection device, which is convenient and fast to operate. By observing the spectra of the excitation signal and the received signal on the oscilloscope and calculating the correlation coefficient r, it can be detected whether the concrete at the current depth L has carbonated. Then, by changing the excitation frequency and repeating the above steps, it can be detected whether the concrete at any depth L has carbonated, that is, the carbonation depth. Description of the Drawings

[0031] Figure 1 It is a schematic diagram of the concrete carbonation depth detection system;

[0032] Figure 2 It is a schematic diagram of the influence depth of Rayleigh waves;

[0033] Figure 3 It is the spectra of the excitation signal and the received signal of non-carbonated concrete;

[0034] Figure 4 It is the spectra of the excitation signal and the received signal of carbonated concrete;

[0035] In the figure, 1 is the concrete specimen to be detected, 2 is the signal generator, 3 is the high-voltage amplifier, 4 is the voltage amplifier, 5 is the oscilloscope, 6 is the excitation probe, and 7 is the receiving probe. Detailed Embodiments

[0036] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0037] All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0038] A method for detecting the carbonation depth of concrete includes the following steps:

[0039] S1. Place two transducers perpendicular to the surface of the concrete test block to be detected, and respectively excite and receive Rayleigh waves;

[0040] The waveform of the transducer excitation signal is:

[0041] ;

[0042] where N is the number of sine wave cycles, f is the excitation frequency, and t is time; adjust the excitation frequency f, and calculate the wavelength λ = c / f of the Rayleigh wave according to the known Rayleigh wave velocity c.

[0043] S2. Perform Fourier transform on x(t) to obtain the excitation signal spectrum X(f), record the received signal as y(t), perform Fourier transform on y(t), and obtain the received signal spectrum Y(f);

[0044] As Figure 3 shown, the dotted line in the figure represents the received signal spectrum, and the solid line represents the excitation signal spectrum.

[0045] When the concrete has not carbonated, the pores in the concrete and the Rayleigh waves are scattered, and there are obvious differences between the received signal spectrum and the excitation signal spectrum, and the correlation coefficient of the two spectrum waveforms is small;

[0046] As Figure 4 shown, the dotted line in the figure represents the received signal spectrum, and the solid line represents the excitation signal spectrum.

[0047] When the concrete has carbonated, the pores in the concrete are filled with carbonated substances, the pore diameter is further reduced, the Rayleigh wave scattering phenomenon is weakened, the difference between the received signal spectrum and the excitation signal spectrum is reduced, and the correlation coefficient increases;

[0048] The correlation coefficient is calculated as:

[0049] ;

[0050] Among them, Cov(X,Y) is the covariance of X and Y, Var[X] is the variance of X, and Var[Y] is the variance of Y; when the r value is greater than or equal to the correlation coefficient, it is determined that the concrete at the current depth L has carbonized.

[0051] S3. Change the excitation frequency f, repeat S1-2, and determine whether the concrete at any depth L has carbonized.

[0052] As Figure 2 shown, since the influence depth of Rayleigh waves is concentrated within the range of 1 / 3 wavelength, the influence depth L = λ / 3 is calculated.

[0053] It should be noted that for the carbonization detection of concrete with the same mix ratio, the correlation coefficient is calculated as a reference value. When the detected correlation coefficient is significantly less than the reference value, it is determined that the concrete at the current depth L has not carbonized.

[0054] Based on multiple tests, the reference value is taken as 0.8. When the correlation coefficient r ≤ 0.8, it is determined that the concrete at the current depth L has not carbonized.

[0055] Embodiment, please refer to the appendix Figure 1 , a concrete carbonization depth detection system, including: a concrete test block 1 to be detected, a transducer, and a detection device; the concrete test block 1 to be detected is placed underwater, and the two transducers respectively excite and receive Rayleigh waves, are fixed on the surface of the concrete test block 1 to be detected, and are provided with an excitation probe 6 and a receiving probe 7 at the upper end, and are connected to the detection device through a wiring harness.

[0056] In the above structure, the model of the excitation probe 6 is Fuji AE1045SW, and the model of the receiving probe 7 is Fuji AE1045SW.

[0057] The detection device includes: a signal generator 2, a high-voltage amplifier 3, a voltage amplifier 4, and an oscilloscope 5; the signal generator 2 is used to generate an excitation signal x(t) to form an incident wave; the input end of the high-voltage amplifier 3 is connected to the signal generator 2, and the output end is connected to the excitation probe 6; the high-voltage amplifier 3 is used to amplify the energy of the incident wave and transmit it to the surface of the concrete test block 1 to be detected through the excitation probe 6; the input end of the voltage amplifier 4 is connected to the oscilloscope 5, and the output end is connected to the receiving probe 7; the receiving probe 7 is used to receive the vibration wave after transmission in the concrete test block 1 to be detected, and the voltage amplifier 4 is used to amplify the energy of the vibration wave to generate a received signal y(t); the oscilloscope 5 is connected to the output ends of the signal generator 2, the high-voltage amplifier 3, and the voltage amplifier 4; the oscilloscope is used to display the excitation signal spectrum X(f) and the received signal spectrum Y(f).

[0058] In the above structure, the signal generator 2 is of the model Tektronix AFG31000, the high-voltage amplifier 3 is of the model Aigtek ATA4051, the voltage amplifier 4 is of the model PXPA3, and the oscilloscope 5 is of the model Tektronix MSO64.

[0059] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. Method for detecting carbonation depth of concrete, characterized in that, It includes the following steps: S1. Place two transducers perpendicular to the surface of the concrete specimen to be detected, and respectively excite and receive Rayleigh waves; The waveform of the transducer excitation signal is: ； Where, N is the number of sine wave periods, f is the excitation frequency, and t is the time; adjust the excitation frequency f, and calculate the wavelength λ = c / f of the Rayleigh wave according to the known Rayleigh wave velocity c; S2. Perform Fourier transform on x(t) to obtain the excitation signal spectrum X(f), record the received signal as y(t), perform Fourier transform on y(t), and obtain the received signal spectrum Y(f); When the concrete has not carbonated, the pores in the concrete and the Rayleigh waves scatter, and there are obvious differences between the received signal spectrum and the excitation signal spectrum, and the correlation coefficient of the waveforms of the two spectra is small; When the concrete carbonates, the pores in the concrete are filled with carbides, the pore diameter is further reduced, the Rayleigh wave scattering phenomenon weakens, the difference between the received signal spectrum and the excitation signal spectrum decreases, and the correlation coefficient increases; The correlation coefficient is calculated as: ； Where, Cov(X,Y) is the covariance of X and Y, Var[X] is the variance of X, and Var[Y] is the variance of Y; When the r value is greater than or equal to the correlation coefficient, it is determined that the concrete at the current depth L has carbonated; S3. Change the excitation frequency f, repeat S1-2, and determine whether the concrete at any depth L has carbonated.

2. The concrete carbonation depth detection method according to claim 1, characterized in that In S1, the influence depth of the Rayleigh wave is concentrated within the range of 1 / 3 wavelength, so the influence depth L = λ / 3 is calculated.

3. The concrete carbonation depth detection method according to claim 1, characterized in that, In S2, for the concrete with the same mix ratio, perform the carbonation detection of S1-2, calculate the correlation coefficient as the reference value, and when the detected correlation coefficient is significantly less than the reference value, it is determined that the concrete at the current depth L has not carbonated.

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