This application is based upon and claims priority to Chinese Patent Application No. 202210574972.6, filed on May 25, 2022, the entire contents of which are incorporated herein by reference.
The present invention belongs to the technical field of nondestructive testing, and particularly relates to an evaluation method for corrosion damage evolution of underwater concrete structures.
Underwater concrete structures (such as bridge piers, dams and underwater concrete pipes) are usually built as important load-bearing members in concrete constructions. They suffer from various damage due to the complex service environment, especially the long-term physical erosion and chemical corrosion of water. These water erosion and corrosion can induce damage to underwater concrete structures, resulting in the degradation of their local mechanical properties. These kinds of damage may become a major factor that affects structures' safety, applicability, and durability. In this regard, it is significant to develop an evaluation method for corrosion damage evolution of underwater concrete structures.
At present, acoustic imaging-based methods and optical imaging-based methods are generally adopted to evaluate the damage of underwater concrete structures. Among them, the optical imaging-based methods mainly include artificial diving photography, underwater photographing robot, etc., and the acoustic imaging-based methods include acoustic emission, sonar, etc. However, these methods have the following limitations: (1) the measured data is susceptible to water quality; (2) the underwater flow situation is complicated, and sometimes the measurement equipment cannot be well placed at the predetermined position; (3) the equipment is expensive and measurement is time-consuming; and (4) it is difficult to detect the global damage and internal damage of structures. These limitations make these methods difficult to apply to evaluate the corrosion damage of underwater concrete structures.
In recent years, a time reversal method based on stress waves is widely used in the damage evaluation of concrete structures because of its self-adapting spatial, temporal focusing characteristics, high signal-to-noise ratio, and suitability for heterogeneous materials. The results show that the time reversal method based on stress waves can be used to identify and locate the damage in concrete structures, but the feasibility of applying the time reversal method based on stress waves to evaluate the corrosion damage of underwater concrete structures still lacks proof.
In view of this, the present invention provides an evaluation method for corrosion damage evolution of underwater concrete structures in order to solve the technical problems mentioned above. The present invention belongs to the field of nondestructive testing of underwater concrete structures, especially related to the corrosion damage caused by hydrochloric acid to underwater concrete structures, which provides a feasible method for corrosion damage evolution of underwater concrete structures based on the time reversal of stress waves.
The technical solution of the present invention is as follows:
The evaluation method for corrosion damage evolution of underwater concrete structures includes:
In the formulas, CI is the corrosion index, DI0 is the damage index of concrete in the water-immersed state, DI′ is the damage index of concrete in the corrosion state, LRF is the loss rate of concrete compressive strength, Fcp0 is the compressive strength of concrete in the water-immersed state, F′cp is the compressive strength of concrete in the corrosion state, LRE is the loss rate of concrete elastic modulus, Ec0 is the elastic modulus of concrete in the water-immersed state, and E′c is the elastic modulus of concrete in the corrosion state; and
δCE=CI−LRF (4)
δCE=CI−LRE (5)
In the formulas, δCF is the absolute error between the corrosion index and the loss rate of concrete compressive strength, CI is the corrosion index, LRF is the loss rate of concrete compressive strength, δCE is the absolute error between the corrosion index and the loss rate of concrete elastic modulus, and LRE is the loss rate of concrete elastic modulus.
Preferably, a method for obtaining the damage index of concrete by performing the time reversal test on the concrete beam specimen includes:
V
B(r,ω)=kA(ω)kB(ω)G(r,ω)VA(W) (6)
the expression of the response signals in time domain is formula (7),
In the formula, r is a distance from A to B, kA is an electromechanical coupling coefficient of the sensor {circle around (5)} at A, kB is an electromechanical coupling coefficient of the sensor {circle around (6)} at B, and G(r, ω) is a transfer function from the sensor {circle around (5)} at A to the sensor {circle around (6)} at B; VB(t) is the response signal received by the sensor {circle around (6)} at B;
the expression of the reversed signal in frequency domain is formula (9),
{circumflex over (V)}
B(r,ω)=k*A(ω)k*B(ω)G*(r,ω)V*A(ω)eiωt (9)
the expression of the reversed signal in time domain is formula (10),
In the formulas, V*B is a phase conjugation of VB, * is a complex conjugation operator, T is a sampling duration, and r is the distance from A to B;
{circumflex over (V)}
A(r,ω)=kA(ω)k*A(ω)kB(ω)k*B(ω)G(r,ω)G*(r,ω)V*A(ω)eiωT (11)
the expression of the focused signal in time domain is formula (12);
{tilde over (V)}
A(r,ω)={circumflex over (V)}*A(r,ω)eiωT (13)
In the formula, {circumflex over (V)}*A is a phase conjugation of {circumflex over (V)}A, and * is the complex conjugation operator; and
the expression of the reconstructed signal in time domain is formula (14);
N
A(t)=VA(t)/max(VA(t))
Ñ
A(t)={tilde over (V)}A(t)/max({tilde over (V)}A(t)) (15)
In the formulas, VA(t) is the excitation signal, {tilde over (V)}A is the reconstructed signal, NA is the normalized excitation signal, and ÑA is the normalized reconstructed signal; and
In the formula, DI is the damage index, t0 and t1 are start time and end time of a signal comparison interval separately, NA(t) is the normalized excitation signal, and NA(t) is the normalized reconstructed signal.
Preferably, a method for determining the excitation signal VA(t) includes:
The expression of a 5-cycle sine function modulated by a Hanning window is formula (17),
modulated signals with different central frequencies are modulated from 0-10 MHz at an interval of 10 kHz, the modulated signals with different central frequencies are input to the sensor {circle around (5)} at A on the concrete beam specimen separately, and the response signals are received by the sensor {circle around (6)} at B, the modulated signal with the largest amplitude of the response signal is selected as the excitation signal VA(t).
Preferably, the compressive strength of concrete in the water-immersed state is obtained with formula (18), and the elastic modulus of concrete in the water-immersed state is obtained with formula (19);
In the formulas, Fcp is the compressive strength of the concrete cube specimen, Fmax is a failure load, A is a loading area of the specimen, Ec is the elastic modulus of the concrete cube specimen, Fa is a load when stress is ⅔Fcp, F0 is a load when the stress is ⅓Fcp, L is a measuring scale distance of the concrete cube specimen, and Δ is a deformation of the concrete cube specimen loaded from F0 to Fa.
Preferably, a method for preparing the concrete specimens includes:
performing anti-corrosion, insulation and waterproof treatment on a pair of sensors;
building a formwork of the concrete specimens;
placing sensors at predetermined positions in the formwork of the concrete beam specimen; and
pouring concrete, and completing maintenance according to standards.
Compared with the existing technology, the evaluation method for the corrosion damage evolution of underwater concrete structures provided by the present invention has advantages that the method is not easily affected by water quality, the sensor arrangement is simple, the integrity damage of underwater concrete structures can be detected, and the corrosion evolution process can be evaluated without damaging underwater concrete structures, and the method is practical and worth popularizing.
In order to describe the examples and the technical solutions of the present invention, accompanying drawings required by the examples are briefly introduced below. Obviously, the accompanying drawings in the following description are only partial examples of the present invention, and a person of ordinary skill in the art can be able to derive other accompanying drawings from these accompanying drawings without creative efforts. According to the examples of the present invention, corrosion evolution of underwater concrete structures is evaluated by taking corrosion damage caused by immersing C30 concrete specimens in a hydrochloric acid solution with pH=1 as an example.
In order to make the technical solution of the present invention better understood and implemented by those skilled in the art, the present invention will be described in detail below with reference to
According to the evaluation method for corrosion damage evolution of underwater concrete structures, the basic steps are shown in the flow chart of
The present invention will be further described with reference to
performing anti-corrosion, insulation and waterproof treatment on a pair of sensors, with a specific operation method as shown in
after that, building a formwork of the concrete beam specimen, placing the sensors at predetermined positions A and B in the formwork, after leading out the leads {circle around (3)}, pouring concrete, and making C30 concrete specimen by selecting ordinary Portland cement with a grade of 32.5, fine aggregates are sands with particle sizes of 0.25-0.5 mm, and coarse aggregates are stones with particle sizes of 5-30 mm according to a mass ratio of 1:0.958:2.462 and a water-cement ratio of 0.38. As shown in
next, the time reversal test of stress waves is performed on the concrete beam specimen, before the test, as shown in
a process of the time reversal test is shown in
in the formula, fc is the center frequency of the modulated signal, the modulated signal is input to the sensor {circle around (5)} at A on the concrete beam specimen separately, the response signal is received by the sensor {circle around (6)} at B, a waveform diagram of the response signal in a frequency band of 60-140 kHz is shown in
V
B(r,ω)=kA(ω)kB(ω)G(r,ω)VA(ω)
the expression of the response signal in time domain follows:
In the formula, r is the distance from A to B (that is, the distance of propagation of stress waves), kA is an electromechanical coupling coefficient of the sensor {circle around (5)} at A, kB is an electromechanical coupling coefficient of the sensor {circle around (6)} at B, and G(r, ω) is the transfer function from the sensor {circle around (5)} at A to the sensor {circle around (6)} at B. The response signal obtained in the test is shown in
the expression of the reversed signal in frequency domain is:
{circumflex over (V)}
B(r,ω)=k*A(ω)k*B(ω)G*(r,ω)V*A(ω)eiωt
the expression of the reversed signal in time domain is:
In the formula, V*B is the phase conjugation of VB, * is the complex conjugation operator, T is the sampling duration, and r is the distance from A to B;
{circumflex over (V)}
A(r,ω)=kA(ω)k*A(ω)kB(ω)k*B(ω)G(r,ω)G*(r,ω)V*A(ω)eiωT
the expression of the focused signal in time domain is:
{tilde over (V)}
A(r,ω)={circumflex over (V)}*A(r,ω)eiωT
In the formula, {circumflex over (V)}*A is the phase conjugation of {circumflex over (V)}A, and * is the complex conjugation operator.
the expression of the reconstructed signal in time domain is:
N
A(t)=VA(t)/max(VA(t))
Ñ
A(t)={tilde over (V)}A(t)/max({tilde over (V)}A(t))
In the formula, VA(t) is the excitation signal, {tilde over (V)}A(t) is the reconstructed signal, NA(t) is the normalized excitation signal, and ÑA(t) is the normalized reconstructed signal; and
the normalized excitation signal and the normalized reconstructed signal are shown in
In the formula, DI is the damage index, t0 and t1 are start time and end time of the signal comparison interval separately, NA(t) is the normalized excitation signal, and ÑA(t) is the normalized reconstructed signal.
Next, the uniaxial compression test is performed on the concrete cube specimens;
in the formulas, Fcp is the compressive strength of the concrete cube specimen, Fmax is the failure load, A is the loading area of the specimen, Ec is the elastic modulus of the concrete cube specimen, Fa is the load when stress is ⅔Fcp, F0 is the load when stress is ⅓ Fcp, L is the measuring scale distance of the concrete cube specimen, and Δ is the deformation of the concrete cube specimen loaded from F0 to Fa;
in the formulas, CI is the corrosion index, DI0 is the damage index of concrete in the water-immersed state, DI′ is the damage index of concrete in the corrosion state, LRF is the loss rate of concrete compressive strength, Fcp0 is the compressive strength of concrete in the water-immersed state, F′cp is the compressive strength of concrete in the corrosion state, LRE is the loss rate of concrete elastic modulus, Ec0 is the elastic modulus of concrete in the water-immersed state, and E′c is the elastic modulus of concrete in the corrosion state.
δCE=CI−LRF
δCE=CI−LRE
in the formulas, δCF is the absolute error between the corrosion index and the loss rate of concrete compressive strength, CI is the corrosion index, LRF is the loss rate of concrete compressive strength, δCE is the absolute error between the corrosion index and the loss rate of concrete elastic modulus, and LRE is the loss rate of concrete elastic modulus.
It can be seen from Table 1 and Table 2 that the absolute error δCF between the corrosion index and the loss rate of concrete compressive strength and the absolute error δCE between the corrosion index and the loss rate of concrete elastic modulus are less than 5%, and the corrosion index can reasonably evaluate the corrosion state of concrete. The above results show that the provided method is feasible and effective for evaluating the corrosion damage evolution of underwater concrete structures.
The evaluation method for corrosion damage evolution of underwater concrete structures provided by the present invention timely and effectively represents degradation degree of mechanical properties of the underwater concrete structures caused by corrosion, provides a feasible method for realizing the corrosion damage evolution evaluation of the underwater concrete structure, and the method is practical and worth popularizing.
The examples disclosed above are only preferable specific examples of the present invention, but the examples of the present invention are not limited to the above examples, and variations readily conceivable to anyone skilled in the art all fall within the scope of protection of the present invention.
Number | Date | Country | Kind |
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202210574972.6 | May 2022 | CN | national |