A device and method for indoor quantitative calibration of corrosion rate of steel bars under stress

Abstract

The present invention discloses an indoor quantitative calibration device and method for the corrosion rate of steel bars under stress. The device comprises: a loading device and a testing device; the loading device comprises a loading frame, a first nut, a first disc spring, a second nut and a second disc spring; the testing device comprises a signal reader, a water tank and an inclined bracket, a water tank water inlet and a water tank drain arranged inside the water tank; the signal reader is used to connect a steel wire of the same material as the steel bar to be tested. The method comprises: S1, installing the device; S2, injecting a calcium hydroxide solution containing sodium chloride into the water tank through the water inlet; S3, accelerating the corrosion of the steel bar and steel wire to be tested; S4, calibrating the steel bar corrosion rate using the change in frequency before and after the steel wire is rusted. The method of the present invention fully considers the influencing factors such as the charge transfer resistance of the interface between the steel wire and the concrete, the concrete resistance and the film resistance of the steel wire passivation film to improve the test accuracy.

Description

Technical Field

[0001] The invention belongs to the technical field of nondestructive testing of steel bar corrosion rate in structural durability testing, and specifically relates to an indoor quantitative calibration device and method for steel bar corrosion rate under continuous tension and compression loads. Background Art

[0002] Steel bar corrosion is the primary cause of premature destruction of concrete structures. Concrete cracks and peels, bearing capacity decreases, and the durability of reinforced concrete structures deteriorates rapidly, which may even cause engineering safety accidents and have caused huge economic losses. Accurate and effective detection of steel bar corrosion can not only prevent the occurrence of engineering accidents, but also provide an important basis for structural durability assessment and remaining service life prediction. Steel bar corrosion detection methods are mainly divided into damage detection and non-destructive detection methods. Since damage detection can cause great damage to the structure, it is generally used for detection under very serious steel bar corrosion, and the structure has been significantly damaged. At present, it is rarely used in actual engineering to detect the degree of steel bar corrosion. In order to avoid excessive damage to the structure during detection, people have gradually studied and developed non-destructive detection technology for steel bar corrosion in engineering practice. Steel bar corrosion non-destructive detection technology is divided into active wired type and passive wireless type. The use of passive wireless type will not be affected by these external factors. The main advantage of passive wireless type is that it can realize long-term monitoring of concrete structure without external power supply, with few interference factors, reliable performance and good economic effect.

[0003] Chinese patents CN101246116A and CN103852488A provide two wireless sensors for monitoring steel corrosion in concrete. However, the application of both sensors is based on the quantitative relationship between the steel wire rust breakage and the steel bar corrosion rate. They are only applicable to on-site detection and cannot be applied to indoor quantitative calibration experiments.

[0004] Currently, there is still a lack of a method that can be used more accurately to calibrate the corrosion rate of steel bars indoors when the steel bars are under stress. Summary of the invention

[0005] In view of the above technical problems, in order to develop a passive wireless non-destructive quantitative technology for steel bar corrosion rate, the present invention provides an indoor quantitative calibration device and method for steel bar corrosion rate under stress. The method of the present invention fully considers the influencing factors such as the charge transfer resistance of the interface between steel wire and concrete, the concrete resistance and the film resistance of the steel wire passivation film to improve the test accuracy.

[0006] The technical solution provided by the present invention is as follows:

[0007] In a first aspect, the present invention provides an indoor quantitative calibration device for corrosion rate of steel bars under stress, comprising:

[0008] Loading devices and testing devices;

[0009] The loading device includes a loading frame, a first nut, a first disc spring, a second nut and a second disc spring. Holes are reserved on opposite sides of the loading frame for installing steel bars. The first disc spring and the first nut form a group, and are used to load and fix one end of the steel bar near the outside of the loading frame. The second disc spring and the second nut form a group, and are used to load and fix one end of the steel bar near the inside of the loading frame.

[0010] The testing device comprises a signal reader, a water tank, and an inclined bracket, a water tank water inlet and a water tank drain outlet arranged inside the water tank; the signal reader is used to connect a steel wire of the same material as the steel bar to be tested, and the inclined bracket is used to place the testing device.

[0011] Furthermore, the loading frame is a square frame, and the loading of multiple steel bars is achieved by adding holes.

[0012] Furthermore, by compressing the first disc spring, fixing the first nut, and keeping the second disc spring in a relaxed state, a tensile load is applied to the steel bar.

[0013] Furthermore, by compressing the second disc spring, fixing the second nut, and keeping the first disc spring in a relaxed state, a compressive load is applied by the steel bar.

[0014] Furthermore, the signal reader is a modified LC oscillator circuit composed of a first induction coil circuit and a second induction coil circuit; wherein the first induction coil circuit is formed by connecting the first induction coil with an oscilloscope; the second induction coil circuit is formed by connecting the second induction coil, a capacitor C 1 and capacitor C 2 The branches are connected in parallel; capacitor C 2 The branch is capacitor C 2 It is connected in series with the steel wire circuit to be tested.

[0015] This circuit is a modified LC oscillation circuit that takes into account the concrete resistance and the film resistance of the steel wire passivation film. It uses the frequency change of the oscillation circuit before and after the steel wire, which is made of the same material as the steel bar, is corroded to detect the steel bar corrosion rate.

[0016] In a second aspect, the present invention provides a method for calibrating corrosion rate using the indoor quantitative calibration device for corrosion rate of steel bars under stress state described in the first aspect, comprising the following steps:

[0017] S1, set the load on the steel bar to be tested and install it on the loading device, place it on the inclined bracket, and connect the steel wire of the same material as the steel bar to be tested to the signal reader through a wire;

[0018] S2, injecting a calcium hydroxide solution containing sodium chloride into the water tank through the water inlet so that the loading device and the steel wire are immersed, simulating the steel bar corrosion environment;

[0019] S3, regularly opening the drain port of the water tank to discharge the corrosive solution in the water tank, and utilizing the dry-wet cycle, water injection and drainage cycle to accelerate the corrosion of the steel bars and steel wires to be tested;

[0020] S4, by recording the frequency of the signal reader, the steel bar corrosion rate is calibrated using the change in frequency before and after the steel wire is rusted.

[0021] Furthermore, in step S1, the method for setting the loading load is: setting the loading load by setting the preload force of the disc spring.

[0022] Further, the step S4 comprises the following steps:

[0023] S41, recording the frequency value of the signal reader;

[0024] S42, converting the frequency value into the resistance of the steel bar to be tested using a frequency calculation formula;

[0025] S43, converted to corrosion rate through resistance.

[0026] Furthermore, in step S42, the frequency calculation formula of the signal reader is:

[0027]

[0028] Where f is the frequency of the signal reader, C 1 , C 2 is the reader capacitance, C d is the double layer capacitance, R w is the wire resistance, R t is the charge transfer resistance of the interface between steel wire and concrete, R m is the concrete resistance, R f is the film resistance of the steel wire passivation film, L 2 is the inductance of the induction coil connected to the steel wire circuit to be tested;

[0029] The resistance of the steel bar to be tested is:

[0030]

[0031] Among them, R S is the steel resistance, D S is the diameter of the steel bar, L S is the length of the steel bar, R w is the wire resistance, D w is the wire diameter, L w is the wire length.

[0032] Furthermore, in step S43, the method of converting the resistance into the corrosion rate is:

[0033]

[0034] Among them, ρ is the steel corrosion rate, R S0 is the initial resistance of the steel bar, R S1 is the resistance of the steel bar after corrosion.

[0035] The present invention has the following beneficial effects:

[0036] The present invention provides a device and method for indoor quantitative calibration of steel bar corrosion rate that can apply both pressure and tension. The device of the present invention includes a loading device and a testing device. The loading device can apply loads in the form of tension and compression, and can test multiple steel bars to be tested at one time, thereby realizing indoor quantitative calibration of steel bar corrosion rate under tension and compression loads, and can be widely used in the field of civil engineering.

[0037] The method of the present invention can fully consider the factors affecting the corrosion rate of steel bars, such as the charge transfer resistance of the interface between the steel wire and concrete, the concrete resistance and the film resistance of the steel wire passivation film, and can obtain a more accurate calculation result through relevant calculations. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a loading device diagram of a device for quantitatively calibrating corrosion rate of steel bars under stress;

[0039] Figure 2 A diagram of a test device for indoor quantitative calibration of corrosion rate of steel bars under stress;

[0040] Figure 3 It is a schematic diagram of a signal reader of an indoor quantitative calibration device for corrosion rate of steel bars under stress;

[0041] Figure numerals: 1-first nut, 2-first disc spring, 3-loading frame, 4-second disc spring, 5-second nut, 6-steel bar to be tested, 7-steel wire of the same material as the steel bar to be tested, 8-signal reader, 9-water trough, 10-tilted bracket, 11-water trough water inlet, 12-water trough drain outlet. DETAILED DESCRIPTION

[0042] The content of the present invention is further described below in conjunction with specific embodiments, but the content of the present invention is not limited thereto.

[0043] Example 1

[0044] like Figure 1 , 2 A device for indoor quantitative calibration of corrosion rate of steel bars under stress is shown, comprising:

[0045] Loading devices and testing devices;

[0046] The loading device includes a loading frame 3, a first nut 1, a first disc spring 2, a second nut 5 and a second disc spring 4. Holes are reserved on opposite sides of the loading frame for installing steel bars; the first disc spring 2 and the first nut 1 are a group, used to load and fix one end of the steel bar near the outside of the loading frame; the second disc spring 4 and the second nut 5 are a group, used to load and fix one end of the steel bar near the inside of the loading frame;

[0047] The testing device includes a signal reader 8, a water tank 9, and an inclined bracket 10, a water tank water inlet 11 and a water tank drain outlet 12 arranged inside the water tank; the signal reader 8 is used to connect a steel wire 7 of the same material as the steel bar to be tested, and the inclined bracket 10 is used to place the testing device.

[0048] As a specific embodiment, the loading frame is a square frame, and the loading of multiple steel bars is achieved by adding holes.

[0049] As a specific embodiment, the steel bar to be tested is provided with threads to facilitate connection with a nut.

[0050] As a specific embodiment, the first disc spring 2 is compressed, the first nut 1 is fixed, and the second disc spring 4 is kept in a relaxed state, and a tensile load is applied by the steel bar.

[0051] As a specific embodiment, the second disc spring 4 is compressed, the second nut 5 is fixed, and the first disc spring is kept in a relaxed state, and the pressure load is applied by the steel bar.

[0052] For example, when loading tension, loosen the second nut 5 to release the internal force of the second disc spring 4, use a torque wrench to tighten the first nut 1, apply pressure to the first disc spring 2, and the reaction force of the first disc spring 2 generates tension on the steel bar 6 to be tested. Observe the torque value of the torque wrench to control the size of the tension value. When the loading force reaches the test requirements, tighten the first nut 1.

[0053] For example, when loading pressure, loosen the first nut 1 to release the internal force of the first disc spring 2, tighten the second nut 5 using a torque wrench, apply pressure to the second disc spring 4, and the reaction force of the second disc spring 4 generates pressure on the steel bar 6 to be tested. Observe the torque value of the torque wrench to control the pressure value. When the loading force reaches the test requirements, tighten the second nut 5.

[0054] As a specific embodiment, the signal reader is a modified LC oscillation circuit composed of a first induction coil circuit and a second induction coil circuit; wherein the first induction coil circuit is composed of a first induction coil L 1 Connected with an oscilloscope; the second induction coil circuit is formed by the second induction coil L 2 , capacitor C 1 and capacitor C 2 The branches are connected in parallel; capacitor C2 The branch is capacitor C 2 The steel wire circuit to be tested is connected in series with the steel wire circuit to be tested; the steel wire circuit to be tested is connected after the steel wire to be tested is connected, and the charge transfer resistance R of the interface between the steel wire and the concrete t The double layer capacitance C d After being connected in parallel with the concrete resistance R m , the film resistance R of the steel wire passivation film f In series, and then with the steel wire resistance R w in parallel.

[0055] Example 2

[0056] The method for calibrating the corrosion rate using the indoor quantitative calibration device for corrosion rate of steel bars under stress state described in Example 1 comprises the following steps:

[0057] S1, set the load on the steel bar to be tested and install it on the loading device, and place it on the inclined bracket; connect the steel wire of the same material as the steel bar to be tested to the signal reader through a wire;

[0058] S2, injecting a calcium hydroxide solution containing sodium chloride into the water tank through the water inlet so that the loading device and the steel wire are immersed, simulating the steel bar corrosion environment;

[0059] S3, regularly opening the drain port of the water tank to discharge the corrosive solution in the water tank, and utilizing the dry-wet cycle, water injection and drainage cycle to accelerate the corrosion of the steel bars and steel wires to be tested;

[0060] S4, by recording the frequency of the signal reader, the steel bar corrosion rate is calibrated using the change in frequency before and after the steel wire is rusted.

[0061] Furthermore, in step S1, the method for setting the loading load is: setting the loading load by setting the preload force of the disc spring.

[0062] Further, the step S4 comprises the following steps:

[0063] S41, recording the frequency value of the signal reader;

[0064] S42, converting the frequency value into the resistance of the steel bar to be tested using a frequency calculation formula;

[0065] S43, converted to corrosion rate through resistance.

[0066] Furthermore, in step S42, the frequency calculation formula of the signal reader is:

[0067]

[0068] Where f is the frequency of the signal reader, C 1 , C 2 is the reader capacitance, Cd is the double layer capacitance, R w is the wire resistance, R t is the charge transfer resistance of the interface between steel wire and concrete, R m is the concrete resistance, R f is the film resistance of the steel wire passivation film, L 2 It is the inductance of the induction coil connected to the steel wire circuit to be tested.

[0069] The resistance of the steel bar to be tested is:

[0070]

[0071] Among them, R S is the steel resistance, D S is the diameter of the steel bar, L S is the length of the steel bar, R w is the wire resistance, D w is the wire diameter, L w is the wire length.

[0072] Furthermore, in step S43, the method of converting the resistance into the corrosion rate is:

[0073]

[0074] Among them, ρ is the steel corrosion rate, R S0 is the initial resistance of the steel bar, R S1 is the resistance of the steel bar after corrosion.

[0075] The following is explained in conjunction with specific embodiments:

[0076] The length of the steel bar to be tested is 500 mm, and the bearing capacity of the steel bar to be tested is directly measured by the tensile testing machine.

[0077] The steel bar 6 to be tested together with the entire loading device is placed on the inclined bracket 10 in the water tank 9; a steel wire 7 of the same material as the steel bar is placed in the water tank 9 and connected to the signal reader 8 through a wire; a calcium hydroxide solution containing sodium chloride is injected into the water tank 9 through the water injection port 11, the pH value of the calcium hydroxide solution is 12.5, and the mass fraction of sodium chloride is 2.4%, simulating the steel bar corrosion environment; the drain port 12 is opened regularly to discharge the corrosive solution in the water tank, and the dry-wet cycle is used, with a water injection and drainage cycle of 12 hours to accelerate the corrosion of the steel bar 6 and the steel wire 7 to be tested.

[0078] like Figure 3 As shown, L 1 is the induction coil of the circuit in the signal reader, L 2It is the induction coil of the resistance circuit of the steel wire to be tested. The working principle of the signal reader 8 is the LC oscillation circuit. The changes in resistance and capacitance of the oscillation circuit before and after the steel wire 7 is rusted are used to induce changes in the electrical signal. The signal of the signal reader 8 is recorded to calibrate the corrosion rate of the steel bar 6 to be tested.

[0079] An indoor test was conducted using an indoor quantitative calibration device and method for corrosion rate of steel bars under stress. It was found that when the steel wire 7 was not corroded, the resonant frequency of the signal reader 8 was 498kHz; when the steel wire 7 was rusted and broken, the resonant frequency of the signal reader 8 was 705kHz. The resonant frequency changed significantly, and the degree of corrosion of the steel wire could be detected. The corrosion rate of steel bars 6 of different specifications to be tested was quantitatively calibrated indoors when steel wires 7 of different specifications were rusted and broken, and the results were shown in Table 1.

[0080] Table 1 Corrosion rate test data

[0081]

[0082]

[0083] The method of this embodiment records the signal change of the signal reader 8 to determine whether the steel wire 7 is rusted and broken, thereby obtaining the corrosion rate of the steel bar 6 to be tested. The method of the present invention can be effectively used for indoor quantitative calibration of steel bar corrosion rate under tensile and compressive loads.

[0084] The above description is only a preferred specific implementation manner of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention should be included in the scope of protection of the invention.

Claims

1. A method for indoor quantitative calibration of corrosion rate of steel bars under stress, characterized in that: The method is implemented based on a corrosion rate indoor quantitative calibration device, which includes a loading device and a testing device; The loading device comprises a loading frame, a first nut, a first disc spring, a second nut and a second disc spring. Holes are reserved on opposite sides of the loading frame for installing steel bars. The first disc spring and the first nut form a group, and are used to load and fix one end of the steel bar near the outside of the loading frame. The second disc spring and the second nut form a group, and are used to load and fix one end of the steel bar near the inside of the loading frame. The loading frame is a square frame, and multiple steel bars can be loaded by adding holes. The loading device applies a tensile load to the steel bar by compressing the first disc spring, fixing the first nut, and keeping the second disc spring in a relaxed state; and applies a compressive load to the steel bar by compressing the second disc spring, fixing the second nut, and keeping the first disc spring in a relaxed state. The testing device comprises a signal reader, a water tank, and an inclined bracket, a water tank water inlet, and a water tank drain outlet arranged inside the water tank; the signal reader is used to connect a steel wire of the same material as the steel bar to be tested, and the inclined bracket is used to place the testing device; The signal reader is used to detect the frequency change of the oscillation circuit of the steel wire with the same material as the steel bar before and after corrosion, and is a modified LC oscillation circuit composed of a first induction coil circuit and a second induction coil circuit; wherein the first induction coil circuit is formed by connecting the first induction coil and the oscilloscope; the second induction coil circuit is formed by connecting the second induction coil, the capacitor C 1 and capacitor C 2 branches are connected in parallel; capacitor C 2 routing capacitors C 2 is formed in series with the steel wire circuit to be tested; the steel wire circuit to be tested is connected after the steel wire to be tested is connected, and the charge transfer resistance of the interface between the steel wire and the concrete R t Double layer capacitance C d After parallel connection with concrete resistance R m , the film resistance of the steel wire passivation film R f In series, and then with the steel wire resistance R w in parallel; The calibration method includes the following steps: S1, set the load on the steel bar to be tested and install it on the loading device, and place it on the inclined bracket; connect the steel wire of the same material as the steel bar to be tested to the signal reader through a wire; S2, injecting a calcium hydroxide solution containing sodium chloride into the water tank through the water inlet so that the loading device and the steel wire are immersed, simulating the steel bar corrosion environment; S3, regularly opening the drain port of the water tank to discharge the corrosive solution in the water tank, and utilizing the dry-wet cycle, water injection and drainage cycle to accelerate the corrosion of the steel bars and steel wires to be tested; S4, by recording the frequency of the signal reader, the steel bar corrosion rate is calibrated using the change in frequency before and after the steel wire is rusted; The frequency calculation formula of the signal reader is: in, f is the frequency of the signal reader, C 1. C 2 is the reader capacitance, C d is the double layer capacitance, R w is the wire resistance, R t is the charge transfer resistance at the interface between steel wire and concrete, R m is the concrete resistance, R f is the film resistance of the steel wire passivation film, L 2 is the inductance of the induction coil connected to the steel wire circuit to be tested; The resistance of the steel bar to be tested is: in, R S is the steel bar resistance, D S is the steel bar diameter, L S is the length of the steel bar, R w is the wire resistance, D w is the wire diameter, L w is the length of the steel wire; The method of converting resistance into corrosion rate is: in, ρ is the steel bar corrosion rate, R S0 is the initial resistance of the steel bar, R S1 is the resistance of the steel bar after corrosion.

2. The indoor quantitative calibration method for corrosion rate of steel bars under stress state according to claim 1 is characterized by: In the step S1, the method for setting the loading load is: setting the loading load by setting the preload force of the disc spring.

3. The indoor quantitative calibration method for corrosion rate of steel bars under stress state according to claim 1 is characterized by: The step S4 comprises the following steps: S41, recording the frequency value of the signal reader; S42, converting the frequency value into the resistance of the steel bar to be tested using a frequency calculation formula; S43, converted to corrosion rate through resistance.

Images