ES2917622A1 - Method and measurement of corrosion speed in reinforced concrete (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Corrosion speed measurement in reinforced concrete structures with a preparation phase and a measurement phase that comprise: apply a current pulse of 1 second between the armor and two counter -electrodes, internal and external; Verify that δ vss </p> in two interior electrodes is opposite; Verify that kxce </p> and k <p> ce </p> are in an admitted range; Apply short pulses, doubling ice </p> to a minimum polarization of 5 mv; Increase ice </p> to determine an i1 </st> for a polarization close to 20 mv; apply for 10 seconds i1 </st> between armor and internal counter -electrode; interrupt the current 200 microseconds; Determine effective polarization (epol) and optimize the value of ice </p> for 10 <= epol </p> <= 20 mv, increasing or reducing Ice </p> 5%; Determine and </p> repeatedly adjusting i <subs. ce </p>, to obtain an ou </p> of optimal polarization; Apply i2 </p>, interrupt the current and determine the definitive value of epol </p>. (Machine-translation by Google Translate, not legally binding)

Description

DESCRIPTION

METHOD AND SENSOR FOR MEASUREMENT OF THE CORROSION SPEED IN

REINFORCED CONCRETE

OBJECT OF THE INVENTION

The present invention refers to a method and a sensor for measuring the rate of corrosion in reinforced concrete that allows said rate to be known accurately by reliably applying the in situ polarization resistance method, and avoiding excessive and irreversible polarization. of the armor.

An object of the present invention is the corrosion rate measurement method that allows correct control and regulation of the current applied in the polarization resistance method.

Another object of the present invention is the sensor for measuring the rate of corrosion in reinforced concrete structures, designed to generate a controlled current that allows the temporary polarization of the reinforced concrete reinforcement, allowing to know the rate of corrosion of the same. . In addition, this new sensor allows the electrical resistivity of the concrete to be determined simultaneously during the measurement.

BACKGROUND OF THE INVENTION

Reinforced concrete is one of the most used materials when building structures due to its good performance in terms of durability and mechanical stress. However, reinforcement corrosion is one of the main causes that reduce the life expectancy of reinforced concrete structures.

In order to tackle this problem, the EHE-08 Structural Concrete Instruction requires the inclusion of an inspection and maintenance plan in the project to ensure that the performance level of the structure does not decrease during its useful life below certain minimum levels. . Inspections should be included in this maintenance strategy. Periodic techniques to assess the state of the structure and detect in advance any risk of pathology.

Undoubtedly, one of the inspection strategies of greatest interest is mapping the corrosion rate of the reinforcements, since this parameter allows the quantification of the corrosive process in a non-destructive way. To perform this task, portable corrosimeters are used, based on the application of electrochemical techniques.

One of the most widely used methods for quantifying the rate of corrosion in situ is based on a galvanostatic pulse measurement system through sensorized confinement of the applied signal.

This device is based on the linear polarization resistance method, RP, proposed by Stern and Geary. In this case, a single current pulse (AI) is used to try to cause a low (10-20 mV) bias (AV) to the armature around its corrosion potential ( E C0RR). In this way, the value of RP is obtained from the quotient

where EP0Les the effective polarization recorded in the potential-time response of the steel-concrete system, that is, the potential applied to the reinforcement once the effect of the ohmic drop (AEn) has been discounted from the maximum polarization reached (E ^max ):

AEa = AI x Rn

^Epol = Emax — ^AEn

Where Rn is the electrical resistance of the concrete.

Figure 1 shows an example of the potential-time response of a steel-concrete system when a bias current is applied for a predetermined time and the current is switched off, producing the ohmic drop and the decrease in the effective bias voltage.

Figure 2 shows a sensorized confinement system of the state of the art, which comprises an internal annular counter electrode and an external annular counter electrode.

The objective of the confinement system is to delimit the electric field generated between the armature and the internal annular counter electrode when applying a current pulse. Yo EC. This is achieved by applying a countercurrent 1XCE between the armature and an external annular counter electrode. The value of 1XCE it is adjusted during the measurement so that the limit of the confined area is located between the external and internal counter electrode. This adjustment operation is performed by measuring a potential difference (AFSS) between two Cu/Cu electrodes. ^two SW ⁴ located between both counter electrodes, taking into account that confinement is considered optimal when AVSS~ 0mV

The corrosion rate, expressed as corrosion density ( ^{i COrr} ), results from applying:

B.

lc0RR = R^S

The constant B can adopt values, according to the bibliography, between 13 and 52 mV, depending on whether they are structures with active or passive reinforcement, respectively, although in unknown systems an average value of 26 mV is considered. On the other hand, S is the steel area on which the measurement is made, whose value corresponds to the lateral surface of the reinforcement located under the confinement system, in a projected area with a diameter equal to the diameter of the circumference that passes through the perpendicular bisector between the Cu/Cu electrodes ^two SW ⁴ for the V ^ss control of Figure 2).

DESCRIPTION OF THE INVENTION

The invention relates to a dynamic (DIN) or controlled polarization measurement method. The invention is based, on the one hand, on the application of modified galvanostatic pulses, dynamically adjusting the current applied by an internal counter electrode for the development of the measurement with real control of the polarization, so that the polarization of the armature embedded inside a structure occurs at adequate levels, both to reliably apply the in situ polarization resistance method and to avoid excessive and irreversible polarization of the reinforcement.

On the other hand, an additional control system of the current applied to an external counter electrode is included to avoid recurring situations of non-confinement that occur with the use of the methods of the state of the art.

In the method of the invention, the corrosion density measurement ( ^{í COrr} ) is based on the linear polarization resistance method, which is only reliably applicable if the effective polarization ( E P0L ) of the reinforcement is between 10 and 20 mV. Too high a polarization could cause irreversible damage to the embedded reinforcement, while a lower polarization leads to considerable errors in the value of the calculated corrosion density. Consequently, the value of ICE must be adapted according to the type of steel-concrete system studied.

For this reason, the method of the invention is developed as an improvement of the measurement methods of the state of the art, in particular, the method defined in patent ES2024268 (hereinafter EST method) for the regulation and control of the value of 1 CE, in order to guarantee adequate polarization of the armature embedded in the structure.

The proposed method, hereinafter referred to as the DIN method, is applied to reinforced concrete structures to assess the state of the embedded reinforcement. The method of the invention comprises a preparation phase and a measurement phase.

In the preparation phase, the response of the sensor is checked and the starting parameters for the next measurement phase are established. The preparation phase comprises the steps of applying a current pulse of approximately 1 second between the armature and an internal counter electrode ( I CE), and then applying a current pulse of approximately 1 second between the armature and an external counter electrode ( I XCE).

Next, it is verified that the potential difference value (AFss) between electrodes, preferably Cu ² SO ⁴ , located on both sides of a midline between the internal and external counter electrodes, is opposite, that is, AFSS CE = - AV ^s5 X ^ce . Also, it is verified that the KXCE and KCE factors are within a range of admissible values, which is obtained through previous calibrations. KXCE and K ^ce are defined as:

^{AV ss_xce}

K x c e

EC

to ^

K ^{ss_ce _}

^{ec ec}

Next, a set of short pulses are applied in which the ICE current is successively doubled until an armature bias of at least 5 mV is achieved.

The resulting current ( 1 CE) is then increased proportionally to determine the optimum current to be applied (/x) to achieve a bias close to 20 mV.

In the measurement phase, the corrosion measurement is carried out, also including a regulation stage of the applied current to ensure adequate polarization of the armature.

The measurement phase comprises the steps of: applying a current ICE = for 10 seconds. The current is then interrupted for 200 microseconds and the effective bias ( E P0L) is determined. For this, EP0L is defined as the effective polarization recorded in the potential-time response of the steel-concrete system, that is, the potential applied to the reinforcement once the effect of the ohmic drop ( AE n) has been discounted from the maximum polarization reached ( E MAX):

^Epol = Emax — ^AEn

Next, an optimization of the ICE value is performed to ensure that 10 < Epol < 20 mV. To do this, the ICE value is increased (if EP0L< 10 mV) or reduced if ( EP0L> 20 mV) by 5%.

Every second, EP0L is determined again by the process described above and the value of ICE is reset. This process is carried out repeatedly for a period of 15 seconds, which is considered long enough to achieve an adequate current value (/2) for which 10 < EP0L < 20 mV.

After said current optimization period, ICE = I ² is maintained for the rest of the polarization time, at which point the pulse is finally interrupted and the final value of EP0L is obtained.

Throughout the measurement process, the value of XCE is varied to ensure that AFSS « 0 mV. To do this, during current optimization, the 1XCE is increased or decreased by the same percentage as ICE. In addition, to avoid situations of inadequate confinement, it is imposed at all times that I ^xce > I ^ce .

Parameters can then be calculated that allow the corrosion density to be determined, in particular at least one of:

i) the ohmic resistance ( Rn):

n _ ( E

k-n ^max - E ^pol )

⁼ }

l2

ii) the resistance to polarization ( RP ):

iii) the corrosion density ( ^{í Corr} ):

0.026

ÍC0RR = ( f í ; 7 s ) x 10

Where S is the steel area on which the measurement is made, whose value corresponds to the lateral surface of the reinforcement located under the confinement system, in a projected area with a diameter equal to that of the circumference that passes through the perpendicular bisector between the Cu/Cu electrodes ^two SW ⁴ for the control of V ^ss of Figure 2.

The DIN method incorporates as a novelty with respect to the previous EST method, a current balance control that guarantees that IXCE > Yo EC. The previous EST method did not limit this fact, which produced a high percentage of erroneous measurements due to the incorrect confinement that occurs by allowing an uncontrolled decrease in the value of ¡XCE.

Thus, a reliable and non-destructive method for measuring the rate of corrosion in situ in reinforced concrete is proposed. Its main advantage lies in the inclusion of a regulation and control protocol for the applied current. In this way, the polarization of the armature occurs at adequate levels, both to reliably apply the polarization resistance method and to avoid excessive and irreversible polarization of the armatures.

The DIN method has advantages for both periodic inspection and continuous monitoring of the state of structures.

The invention also relates to a sensor for the simultaneous measurement of the rate of corrosion of the reinforcement and the electrical resistivity of the concrete.

The sensor of the invention comprises: two electrodes connected to a measuring device and two counter electrodes, an internal counter electrode and an external counter electrode, connected to power sources.

The measuring device comprises a DC voltage source, controlled by a D/A converter, with voltage/current converters, which allow increasing ranges of DC polarization intensity, powered by a set of rechargeable batteries via external power supply. The processing unit controls the D/A converters, which in turn give rise to the controlled voltage sources and the potentiostatic circuits that are connected through a connector for the galvanostat and a connector for the potentiostat.

Likewise, it comprises a processing unit configured to carry out the phases and steps of the method of the invention. The processing unit may be connected to a display and a data input unit.

The sensor of the invention comprises electrodes made of non-polarizable material, preferably titanium or stainless steel, instead of Cu/Cu ² SO ⁴ electrodes, which are described in patent ES2024268. The sensor described in ES2024268 is designed for on-site inspection of structures, that is, to be implemented by an operator periodically and punctually on the concrete surface of the different points of the structure to be evaluated. Thus, sensor maintenance tasks are carried out before each inspection with full guarantee, especially the review of the two Cu/Cu ² SO ⁴ electrodes used for AFSS measurement and control.

Titanium or stainless steel electrodes, on the other hand, are cheaper, more durable and more reliable because they do not require maintenance. By using titanium or stainless steel electrodes, the sensor of the invention can be reliably implemented for continuous and long-term monitoring of structures, allowing permanent installation of the sensor on the surface and even embedded in structural structures. new run. This would allow to optimize the inspection and control operations of structures.

Likewise, the sensor of the invention can be used at the same time to determine the resistivity of concrete by the infinite disk-bar method. Concrete resistivity is a parameter of great interest when interpreting the corrosion parameters recorded by the sensor.

To do this, after applying the corrosion measurement phase described above, a measurement of the electrical resistance between the internal counter electrode of the sensor and the armature would be made. The resistivity value (p) is obtained by applying the formula:

p = K x R

where K is a constant whose value depends on the concrete cover, the diameter of the bar and the diameter of the internal counter electrode.

The sensor described in ES2024268 required an additional sensor to determine the resistivity. The sensor of the invention supposes, therefore, a technological simplification that makes the monitoring of structures more efficient.

DESCRIPTION OF THE DRAWINGS

To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, according to a preferred example of its practical embodiment, a set of drawings is attached as an integral part of said description. where, by way of illustration and not limitation, the following has been represented:

Figure 1.- Potential-time response of a steel-concrete system to which an anodic galvanostatic pulse is applied. At the final interruption of the current, the ohmic drop (AE ^q ) and the effective polarization (E ^pol ) are determined.

Figure 2. Scheme of the sensor of the state of the art to measure in situ the rate of corrosion of reinforcements: a) Bottom view where the reference electrode (RE), the external counter electrode (XCE), the internal counter electrode (CE) are represented , the electrodes S1 and S2 for the control of the confined area through the AVSS measurement and the LM line that defines the effective polarization area during the measurement. b) Sectional view where the effective polarization area achieved during the measurement by means of the confinement system is represented.

Figure 3.- Diagram of the galvanostatic controlled polarization method (DIN method) of the invention. A schematic graph of the potential-time response recorded in the measurement is used to represent the sequence of the various processes involved.

Figure 4.- Comparison between the claimed dynamic method (DIN) and the state-of-the-art standard method (EST): Applied current (I ^ce ) and effective polarization (E ^pol ) in active (A) and passive (P) armatures ).

PREFERRED EMBODIMENT OF THE INVENTION

The present invention relates to a method for measuring the rate of corrosion in reinforced concrete.

Figure 1 shows an example of the potential response as a function of time of a reinforced concrete structure to which an anodic galvanostatic pulse is applied, to cause a low bias, after which the current is interrupted. At that time, the ohmic drop (AE ^q ) and the effective polarization (E ^pol ) of the armature are determined. The value of E ^pol is determined by subtracting AE c from the maximum polarization reached (E ^max ):

E ^pol = E ^max &En

Figure 2 shows a bottom and sectional view of the sensor of the state of the art that allows the corrosion rate of the reinforcements to be measured in situ. The sensor of the invention comprises two titanium electrodes (3, 4) and two ring-shaped counter electrodes (1, 2), an internal counter electrode (1) and an external counter electrode (2). The counter electrodes (1, 2) are placed concentrically. The electrodes (3, 4) are placed on opposite sides of a midline (5) between both counter electrodes (1, 2).

Figure 3 shows a schematic graph of the potential response as a function of time of the controlled polarization galvanostatic method (DIN method) of the invention. The method shown in Figure 3 comprises the phases of preparation and measurement.

The preparation phase includes the stages of:

- apply a current pulse of approximately 1 second between the armature and an internal counter electrode (1) ( I CE), which corresponds to the time t0 of figure 3;

- apply a current pulse of approximately 1 second between the armature and an external counter electrode (2) ( 1 XCE);

- verify that the potential difference value (AFSS) between two electrodes (3, 4) (S1 and S2), located on both sides of a median line (5) between the internal (1) and external (2) counter electrodes, is opposite, ie Ayss CE « —^ VsS_XCE ;

- verify that the confinement factors KXCE and KCE are within an admitted range of values, obtained through previous calibrations; where:

„ _ AVSSXCE

K- ^xce _ 7

' ^ce

AV ^ss _ ^ce

KCE_1

' ^ce

- apply a set of short pulses, successively doubling the ICE current until an armature bias of 5 mV is achieved;

- proportionally increasing the resulting current ( I CE) to determine the optimal current to be applied ( I{) to achieve a polarization close to 20 mV, which corresponds to the time t1 of figure 3;

The measurement phase comprises the stages of:

- apply a current between the armature and the internal counter electrode (1) ( ICE) of value for 10 seconds;

- interrupt the current for 200 microseconds;

- determine the effective polarization ( E P0L), determining the maximum potential applied to the armature ( EMAX) and discounting the effect of the ohmic drop ( AEÜ):

E ^pol = E ^max ^In

- optimize the ICE value to achieve an optimal EP0L value, increasing the ICE value by 5% if E P0L < 10 mV or reducing it by 5% if EPOl > 20 mV;

- determine, for a period of 15 seconds, EP0L repeatedly every second, and re-adjust the value of ICE on each repetition, obtaining a suitable current value (/2) to achieve optimal polarization; - apply a current between the armature and the internal counter electrode (1) ( ICE) of value /2 during a polarization time, which corresponds to the time t2 of figure 3,

- interrupt the current;

- determine the final value of the effective polarization ( EP0L), determining the maximum potential applied to the armature ( E MAX) and discounting the effect of the ohmic drop (A£n), which corresponds to the time t 3 in the figure 3, where:

EP ^ol = E ^max &Eñ

Throughout the process, the value of 1XCE is varied to guarantee that AV ^ss ® 0mV, increasing or decreasing its value by the same percentage as I CE.

The method of the invention also includes the step of calculating the ohmic resistance (Rn), using the formula:

In = ( EMA ^x - EP0L) / /2

Also to calculate the resistance to polarization (RP), using the formula:

PR = ^Epol / I2

And calculate the corrosion density ( ^{í corr} ), using the formula:

i-coRR = 106 x 0.026 / ( RP x S)

Figure 4 shows a comparison between the dynamic method (DIN) of the invention and the standard method (EST) described in the state of the art.

Figure 4 shows the applied current ( ICE) and the effective polarization ( E P0L) in active (A) and passive (P) armatures.

To validate the method of the invention, a series of measurements were made on different reinforcements in the active state and in the passive state. Figure 4 compares the values of the applied current ( I CE) and the effective polarization caused ( E P0L) with the method of the invention (DIN) compared to those obtained with the method described in ES2024268 (EST) or the non-polarization method. -controlled.

It is observed how with the EST method only EP0L values close to 20 mV are achieved in the active samples. In passive samples, the EST method does not manage to sufficiently reduce the value of I CE, which is why a high polarization of the armatures is produced, which must remain after the measurement for a long period at rest to return to their initial value of potential. ( E C0RR). This would mean that the measurement of corrosion in passive reinforcements would be semi-destructive with the EST method.

On the contrary, with the method of the invention or the DIN method, the polarization is maintained in all cases close to 20 mV, for which in the passive samples the ICE value is considerably reduced compared to the active samples.

Therefore, with the DIN method, any risk of disturbing the reinforcements in the corrosion measurement is eliminated, so it can be considered a truly non-destructive method, which also avoids errors in the measurement that occur regularly with the EST method.

Claims (7)

1. Corrosion rate measurement method in reinforced concrete structures, comprising a reinforcement embedded inside, comprising a preparation phase and a measurement phase, where the preparation phase comprises the stages of: - apply a current pulse of approximately 1 second between the armature and an internal counter electrode (1) ( I CE); - apply a current pulse of approximately 1 second between the armature and an external counter electrode (2) ( 1 XCE); - verify that the potential difference value (AFSS) between two electrodes (3, 4) located, respectively, between the internal counter electrode (1) and a midline (5) between the internal (1) and external (2) counter electrodes and between the external counter electrode (2) and the midline (5), in both measurements it is opposite; - verify that the confinement factors KXCE and KCE are within an admitted range of values, obtained through previous calibrations; where:

- apply a set of short pulses, successively doubling the ICE current until an armature bias of 5 mV is achieved; - proportionally increase the resulting current ( I CE) to determine the optimum current to be applied ( I{) to achieve a polarization close to 20 mV; and the measurement phase comprises the steps of: - apply a current between the armature and the internal counter electrode (1) ( ICE) of value for 10 seconds; - interrupt the current for 200 microseconds; - determine the effective polarization ( E P0L), determining the potential applied to the armature ( E MAX) and discounting the effect of the ohmic drop ( AEa): ^Epol = Emax — ^AEn - optimize the ICE value to achieve an optimal EP0L value, increasing the ICE value by 5% if E P0L < 10 mV or reducing it by 5% if Epol > 20 mV; - determine, for a period of 15 seconds, EP0L repeatedly every second, and re-adjust the value of ICE on each repetition, obtaining a suitable current value (/2) to achieve optimal polarization; - apply a current between the armature and the internal counter electrode (1) ( ICE) of value /2 for a polarization time, - interrupt the current; - determine the definitive value of the effective polarization ( EP0L), determining the potential applied to the armature ( EMAX) and discounting the effect of the ohmic drop (A Ea): E ^pol = E ^max AEn and where the value of 1XCE is varied to guarantee that AV ^ss « 0mV, increasing or decreasing its value by the same percentage as I CE. 2. Method according to claim 1, further comprising the step of calculating the ohmic resistance (Rn), using the formula: In = ( Emax - ^Epol ) / /2 3. Method according to any of the preceding claims, further comprising the step of calculating the polarization resistance (R ^p ), using the formula: PR = ^Epol / 12 4. Method according to any of the preceding claims, further comprising the step of calculating the corrosion density ( ^{í corr} ), by means of the formula: Í-CORR = 1 °6 x 0.026 / ( RP XS) 5. Method according to any of the preceding claims, which further comprises a concrete resistivity measurement phase, after applying the corrosion measurement phase, which comprises the steps of performing a measurement of electrical resistance between the internal counter electrode (1) and the armature and calculate the resistivity value ( p) using the formula: p = K x R where K is a constant whose value depends on the concrete cover, the diameter of the bar and the diameter of the internal counter electrode (1). 6. Sensor for measuring the rate of corrosion in reinforced concrete structures comprising: - an internal counter electrode (1); - an external counter electrode (2), placed concentrically with the internal counter electrode (1), defining a midline (5) between both counter electrodes; Y - two reference electrodes (3, 4) made of non-polarizable material placed on opposite sides of the midline (5). Sensor according to claim 6, where the reference electrodes (3, 4) are made of titanium or stainless steel.