HK1133920B - Method and sensor for determining the passivating properties of a mixture containing at least two components, which are cement and water - Google Patents

Description

Method and sensor for determining the passivation properties of a mixture containing at least two components, namely cement and water

Technical Field

The invention relates to a method for determining the passivating properties of a mixture containing at least two components, namely cement and water. The invention also relates to a method that indirectly allows checking the filling of a conduit (for example a cannula) with the above-mentioned mixture. The invention further relates to a sensor for carrying out said method.

Background

Tendons for the construction of suspension and guyed structures (such as suspension bridges, cable-stayed bridges, stadium tops, buildings, communication towers, post-tensioned bridges, shell structures for reactors, etc.) comprise a plurality of strands, wires or rods (hereinafter referred to only as strands, but without limitation) embedded in a medium made of a material capable of hardening, such as a mixture of cement and water (cement paste), hereinafter referred to as "mixture". The tendons are connected to the structure by means of anchoring devices. The tendon also includes a tube, i.e., the casing, into which the strands of the tendon are introduced before the mixture is poured into the casing to completely fill the casing. The use of the mixture fill ensures that the tendon strands are in contact with the alkaline pore solution of the mixture along their entire length. Passivation of the strands and thus deep/long-term corrosion protection of the steel is achieved.

However, incomplete filling of the mixture presents problems. This results in areas on the steel strand which are not passivated in a protective manner, since condensed water is formed and reacts with CO in the air₂This can lead to corrosion, a rapid reduction in cross-sectional area and, in extreme cases, failure of the tendons. Furthermore, chloride contamination of the mixture or chloride contact with the tendons from the surface of the structure can compromise the passivation properties of the mixture and thus lead to corrosion. In some cases, it may even lead to structural collapse.

Because implantation is so important, great efforts have been made to develop this process, use materials, and order of operations. If done correctly, it can be ensured that the sleeve is completely filled with the mixture. Nevertheless, there is some uncertainty as to whether an error has occurred during mixing and injection of the mixture. Epitaxial measurements (extensive measurements) are often used to eliminate this uncertainty and to eliminate faulty operations. For example, a hole is drilled in the anchoring zone and the fillability is evaluated visually. An alternative approach is to use a transparent cover, which allows visual inspection of tendon fillability during and after the setting process at the accessible location. In addition, in individual cases, the filling of the tendons is checked at several points using radar.

However, most of these measurements cannot be performed until after successful injection and considerable time, effort and investment is required in the measurements. For these methods, there are some unreachable locations. However, the initial setting of the mixture during injection severely limits the time to complete the operation.

It is therefore important to have information about the possible under-filling of the mixture used at all important locations already during the injection operation. Only in this case a higher degree of filling can be achieved by additional measurements.

It has been proposed to make this control possible by means of a filled sensor which detects wetting of the sensor by the mixture, as described in JP 2000230915.

However, the filling of the tendons with the mixture is not sufficient in every case to ensure protection against corrosion. Therefore, even if the tendons are completely filled with the mixture, corrosion attack may occur. This may occur, for example, if blast furnace cement with trace amounts of alkalinity or mixed water contaminated with chlorides is used. In some circumstances, even optimal quality control cannot avoid such a situation. Chlorides can also penetrate successively into the casing through the leak sites in the concrete and can cause corrosion when the chlorides have a sufficiently high concentration.

Disclosure of Invention

It is therefore an object of the present invention to provide a method and a device for checking the complete filling of the tendon with the mixture, thereby ensuring the corrosion protection of the steel cord strand.

This object is achieved according to the invention by the features mentioned in claim 1.

The main object of the present invention is to detect the filling of the tendons in the critical areas by determining the possible wetting of the electrodes with a mixture having passivating properties. Excessively low pH values (pH values associated with alkalinity), excessively high chloride content, the presence of other aggressive substances or the presence of bleeding water can be easily detected. This is achieved by performing passivation measurements on the reference steel surface.

An advantage of the invention is that by performing a simple passivation measurement within the critical area in which the sensor is installed, it can already be determined during the injection operation whether the pipe is filled with the passivation mixture or not. In this manner, corrosion may already occur during implantation. The passivation measurement makes it possible to verify that the pH of the mixture and its chloride content allow the passivation of the prestressed steel. Thus, the overall corrosion protection with respect to the filling properties and the mixture composition can be verified. The sensors have a simple structure and can be integrated in all critical areas of the tendon with minimal effort.

Drawings

The invention will be better understood from the following description, given by way of non-limiting example, with reference to the accompanying drawings.

Figure 1A shows a front view of a sensor for detecting the filling of a use mixture and the passivating properties of the mixture,

figure 1B shows a side view of a sensor for detecting the filling of a use mixture and the passivating properties of the mixture,

figure 2 shows the sensor after it has been integrated within the anchor,

figure 3 shows the sensor after it has been integrated in the casing,

figure 4 shows a measurement setup for passivation measurement,

figure 5 shows an example of the measurement of passivation measurements for different mixture materials,

figure 6 shows an example of the measurement of passivation measurements over time T for different pH values,

figure 7 shows an example of passivation measurements over time T for different chloride contents in the mixture,

fig. 8 shows the measurement data of fig. 6 and 7 over time T.

Detailed Description

Referring to the drawings (fig. 3), there can be seen tendons 100, the tendons 100 being used to construct pre-stressed, suspended and guyed structures (these structures not shown), such as suspension bridges, cable-stayed bridges, stadium tops, buildings, communication towers, post-tensioned bridges, reactor containment structures, etc.

The tendon 100 comprises a plurality of strands 10, said strands 10 being embedded in a medium consisting of a material capable of hardening, for example a mixture 11 containing at least two components, such as cement and water. This mixture 11 is called cement paste. Each tendon 100 comprises a plurality of strands 10 made of steel.

The tendon 100 also comprises a tube, such as a casing 12, wherein the strands 10 of the tendon 100 are introduced into said casing 12 before the mixture 11 is poured into the casing 12 in order to completely fill the hollow spaces 110 between the individual strands and/or between the strands and the casing 12. The sleeve 12 has a wall which can be used as a mould and can be considered to constitute a conduit.

The filling mixture, i.e. the basic pore solution that ensures that the strands contact the mixture 11 along their entire length.

The invention relates to a method for determining the passivation properties of a mixture 11. The method for determining the passivating properties of a mixture 11 containing at least two components, cement and water, comprises the steps of:

taking three elements, each made of conductive material, these elements being called first electrode 2, second electrode 4 and third electrode 5,

-fixing at least one of the three electrodes on a support 3 so that:

they are electrically insulated from each other, and

the mixture 11 is able to come into contact with at least one predetermined face on each electrode, these faces being referred to as first face 20, second face 40 and third face 50,

-selecting said first electrode 2 and said third electrode 5 and between these two electrodes:

applying a direct current (called first direct current) with a predetermined polarity (called first polarity) for a predetermined duration D1 (called first duration D1), resulting in an electrolytic reaction on the third electrode 5, and then

-selecting the second electrode 4 and the third electrode 5, and

measuring the voltage V between the two electrodes during said first predetermined duration D1, an

Storing a measure of the variation of the voltage V during the first predetermined duration D1.

Comparing the variation of the voltage V between the second electrode 4 and the third electrode 5 during the first predetermined duration D1 with predetermined data defining at least whether the mixture 11 has passivating properties, and

at least determining whether the mixture 11 has such passivating properties.

The electrolytic reaction at the third electrode 5 is an anode reaction.

The invention also relates to a sensor 1 designed to implement the invention. This sensor 1 has three elements, each made of an electrically conductive material, called first electrode 2, second electrode 4 and third electrode 5, and at least one of the three electrodes is fixed on a support 3 in such a way as to electrically insulate the elements from each other.

A second electrode 4 made of an electrically conductive material and a third electrode 5 made of steel are mounted inside the electrically conductive first electrode 2 made of a tubular part using an electrically insulating material as a support 3. The first electrode 2, the second electrode 4 and the third electrode 5 are electrically connected by means of a multi-core cable 6.

The first electrode 2 and the second electrode 4 are desirably composed of stainless steel. Materials used as electrically insulating material are, for example, polytetrafluoroethylene, polyethylene or epoxy resin.

As shown in fig. 2, the sensor 1 may be integrated within an anchoring device (anchor) 16. As shown, the force distribution ring 7 is clamped between the pad 9 and the anchor head 8. The sensor 1 is integrated in this force distribution ring 7. The sensor 1 is ideally mounted in the force distribution ring 7 by means of screws. The force distribution ring 7 has a large hole in which the strands are spaced apart and the mixture 11 must be used to encase these strands.

The force distribution ring 7 has a wall which can be regarded as constituting a conduit into which the mixture 11 can be injected so as to completely fill the hollow space between the strands and the distribution ring 7.

As shown in fig. 3, the sensor 1 may be installed at a position within the sleeve 12 where the vent pipe 14 is fixed, and installed such that the mixture 11 contacts the sensor 1. Preferably, the sensor 1 is integrated within the ventilation tube 14 so that it does not block the discharge of air. Alternatively, however, the sensor may be mounted in a similar tube that is not used for ventilation.

The steps of comparing the variation of the voltage V between the second electrode 4 and the third electrode 5 during the first predetermined duration D1 with predetermined data defining at least whether the mixture 11 has passivation properties and determining at least whether the mixture 11 has such passivation properties at least comprise:

a) it is checked whether the difference between the maximum voltage value of the first predetermined duration D1 and the voltage value at the first predetermined instant T1 of the first predetermined duration D1, i.e. the first voltage difference V1, exceeds the first predetermined voltage value.

Preferably:

before applying said first direct current with a first predetermined polarity between the first electrode 2 and the third electrode 5 for a first period of a first predetermined duration D1,

another direct current (referred to as second direct current) having a predetermined polarity (referred to as second polarity) opposite to the first polarity is applied between the first electrode 2 and the third electrode 5 for a predetermined duration D2 (referred to as second duration D2),

when the voltage V between the second electrode 4 and the third electrode 5 has been measured during said first predetermined duration D1,

measuring the voltage V between the second electrode 4 and the third electrode 5 during said second predetermined duration D2 and then storing these voltage values,

when comparing the variation of the voltage V between the second electrode 4 and the third electrode 5 during the first predetermined duration D1 with predetermined data defining at least whether the mixture has passivation properties and determining at least whether the mixture 11 has such passivation properties,

the variation of the voltage V between the second electrode 4 and the third electrode 5 during said second predetermined duration D2 is also compared.

In this example, the step of selecting the first electrode 2 and the third electrode 5 and applying a first direct current between the two electrodes and then applying a second direct current comprises using a first direct current and a second direct current having the following characteristics:

the first predetermined polarity is opposite to the second predetermined polarity,

the first duration D1 is equal to the second duration D2.

In a preferred mode:

-the first predetermined duration D1 is ten seconds (10s), and/or

The second predetermined duration D2 is ten seconds (10 s).

What occurs during the first predetermined duration D1 is an anodic polarization state, and what occurs during the second predetermined duration D2 is a cathodic polarization state.

Preferably, the step of comparing the variation of the voltage V between the second electrode 4 and the third electrode 5 during the first predetermined duration D1 and the second predetermined duration D2 with predetermined data defining at least whether the mixture 11 has passivation characteristics and determining at least whether the mixture 11 has such passivation characteristics comprises:

-a) checking whether the difference (called first voltage difference V1) between the maximum voltage value of the first predetermined duration D1 and the voltage value at a predetermined instant T1 (called first instant T1) of the first predetermined duration D1 exceeds the first predetermined voltage value, and

-b) checking whether the difference (called second voltage difference V2) between the maximum voltage value of the first predetermined duration D1 and the voltage value at the predetermined instant T2 (called second instant T2) of the second predetermined duration D2 is within a first predetermined range, and

-c) checking whether the difference (called third voltage difference V3) between the voltage value at the predetermined instant T3 (called third instant T3) of the first predetermined duration D1 and the voltage value V at the predetermined instant T4 (called fourth instant T4) of the second predetermined duration D2 is within a second predetermined range.

At least one of these two cases is preferably satisfied:

-at least one of the first predetermined instant T1 and the fourth predetermined instant T4 is between ten percent and one hundred percent of the value of the first predetermined duration D1, and

-at least one of the second predetermined instant T2 and the third predetermined instant T3 is between ten percent and one hundred percent of the value of the second predetermined duration D2.

The first predetermined duration D1 has a value between one second and thirty seconds and/or the second predetermined duration D2 has a value between one second and thirty seconds.

At least one of these two cases is preferably satisfied:

-at least one of the first predetermined instant T1 and the fourth predetermined instant T4 is equal to ninety percent of the value of the first predetermined duration D1, and

-at least one of the second predetermined instant T2 and the third predetermined instant T3 is equal to ninety percent of the value of the second predetermined duration D2.

According to the invention, for selecting the first electrode 2 and the third electrode 5 and between these two electrodes

Applying a first direct current with a first predetermined polarity for a first predetermined duration D1, and thereafter

A step of applying a second direct current with a second polarity opposite to the first polarity for a second predetermined duration D2:

a first direct current of two and five milliamperes per square centimeter (2.5 mA/cm) current density flowing from the third electrode 5²) And is and

a second direct current of two and five milliamperes per square centimeter (2.5 mA/cm) in a current density flowing from the first electrode 2²)。

Preferably, for the step of comparing the variation of the voltage V between the second electrode 4 and the third electrode 5 with predetermined data at least determining whether the mixture has passivation properties, when:

-the first voltage difference V1 maximum value is fifty millivolts (50mV) (first predetermined voltage value),

-the second voltage difference V2 is one point eight volts to two point three volts (1.8V-2.3V) (a first predetermined range), and

-the third voltage difference V3 is one point eight volts to two point three volts (1.8V-2.3V) (second predetermined range),

the conclusion is that the mixture 11 has passivating properties at least in the vicinity of the three electrodes.

It is easy to understand that the method of the invention also indirectly allows to check the filling of the bushing with the above-mentioned mixture at least in the vicinity of the three electrodes.

In the step of comparing the variation of the voltage V between the second electrode 4 and the third electrode 5 with predetermined data defining at least whether the mixture 11 has passivation properties, when

Fourth second and fourth second for at least a first predetermined duration D1 and a second predetermined duration D2

At least the potential between the ninth second of the first predetermined duration D1 and the second predetermined duration D2 varies by more than six millivolts (6mV),

the conclusion is that the third electrode 5 is in contact with a mixture 11 of hardened cement and water (instead of merely a bleeding slurry), i.e. a liquid emerging from the mixture 11 of water and cement.

Preferably, taking three elements, each made of conductive material, these elements being said first electrode 2, second electrode 4 and third electrode 5, each of these three electrodes having at least one face 20, 40, 50, the above step comprising the operation of selecting three elements each made of steel.

Fig. 4 shows a measurement setup for passivation measurement. Current is applied between the first electrode 2 and the third electrode 5 by means of a power source 18, such as a battery or a galvanostat. The voltage V between the third electrode 5 and the second electrode 4 is measured using a voltage measuring device 19, for example a voltmeter.

This measurement of various media in contact with the sensor 1 is shown in fig. 5. The voltage V (volts) between the second electrode 4 and the third electrode 5 is shown on the horizontal axis and the current density CD (mA/cm) flowing out of the third electrode 5 is shown on the vertical axis²)。

For filling the hollow space 120 with the mixture 11 of the basic type (curve "e") which is passivated against chloride, the maximum voltage is achieved by the amount of current, the generation of which limits the maximum voltage. In this example, which is composed of stainless steel, an increase in the third electrode 5 above 0.5 volts compared to the second electrode 4 indicates effective passivation.

If a dilute bleed (curve "f") is used to fill the hollow space 120, the increase in the measurable voltage V under current flow is significantly lower. The value did not exceed 0.5 volts. This indicates that corrosion is caused by too low alkalinity.

In the example of filling the hollow space 120 with tap water, even an absolute negative voltage V (curve "g") is measured. This indicates strong corrosion of the strand steel.

The process shown in fig. 5 shows the disadvantage that the oxygen content in the mixture 11 and the passivation quality of the second electrode 4 influence the potential measurement from the third electrode 5 to the stainless steel electrode 4.

Furthermore, the presence of a passivating film on the third electrode 5 due to previous exposure to a passivating environment may lead to misleading results, i.e. indicative of passivity even in aggressive environments.

These problems are overcome by the above method, as shown in fig. 6 for different pH values.

As before, by cathodic polarization (by-2.5 mA/cm)²Is applied with a second direct current having a second polarity for a second predetermined duration D2, e.g. 10 seconds) to remove the possibility ofA passivation film formed on the third surface 50 of the third electrode 5.

By applying an anodic current (passing +2.5 mA/cm) between the third electrode 5 and the first electrode 2²Is applied with a first direct current having a first predetermined polarity opposite to the second polarity for a first predetermined duration D1, e.g. 10 seconds), thereby generating a new passivation film on the third surface 50 of the third electrode 5.

During the measurement, the basicity changes due to the hydrogen and oxygen generated on the third surface 50 of the third electrode 5. This effect can be minimized if the amount of charge is equal during the cathodic and anodic polarization.

This is five mA/cm with negative two spots in cathode polarization²(-2.5mA/cm²) Lasting ten seconds and anodically polarized at five mA/cm in positive two points²(+2.5mA/cm²) For ten seconds. Thus, repeated measurements result in minimal interference with the pH of the mixture 11.

Fig. 6 shows the electrochemical process that takes place on the third surface 50 of the third electrode 5. Starting from the undefined third surface 50 with possible oxide and passivation film coating, the cathodic polarization (first curve portion CP1) reduces all residual protective passivation film.

If the pH is sufficiently high and the chloride content is sufficiently low, the subsequent anodic polarization will lead to the formation of a protective passivation film (second curve portion CP 2). This is the case at a pH equal to or higher than 12(pH12, pH 13).

If the pH of the mixture 11 is too low (e.g., pH11) or the chloride content is too high, a passivation film is formed (third curve portion CP 3); however, the subsequent polarization may cause partial failure of the passivation film, resulting in corrosion activation and potential reduction (fourth curve portion CP 4).

If the pH of the mixture 11 is very low (e.g., pH7), a passivation film is not formed at all (fifth curve portion CP 5).

The decision about corrosion activation may be based on a potential difference between the second electrode 4 and the third electrode 5. Although the second electrode 4 is not a stable reference electrode with a well defined potential value, the passivation measurement is very reliable. This is due to the fact that the decision on corrosion activation may be based on a potential decrease between the third curve portion CP3 and the fourth curve portion CP4 during anodizing and/or on a difference between the first curve portion CP1 and the fifth curve portion CP 5.

Because the decision about corrosion activation is based on the difference between the two potential readings, possible errors related to the second electrode 4 can be eliminated.

In addition, the process shown in FIG. 6 uses hydrogen generation during cathodic polarization (first curve portion CP1) and/or oxygen generation during anodic polarization (second curve portion CP2) to determine the potential effect of the second electrode 4 and to eliminate the effect of a reduction in resistance potential within the mixture 11.

Since the potential difference between the generation of oxygen and hydrogen in the alkaline mixture 11 is roughly about two volts, the difference between these two potentials can be used as a criterion to assess the wetting of the third electrode 5 with the mixture 11 having passivating properties.

Based on the example shown, the following criteria can be used to determine the presence of the passivating mixture 11 on the surface of the sensor 1:

a) after a predetermined time elapses between the maximum potential during anodic polarization (the second curve portion CP2, the third curve portion CP3, the fifth curve portion CP5) and the maximum potential during anodic polarization (the second curve portion CP2, the fourth curve portion CP4, the fifth curve portion CP5) (T1: for example nine seconds) may not exceed a certain value (for example 50mV),

b) after a predetermined time elapses between the maximum potential during anodic polarization (the second curve portion CP2, the third curve portion CP3, the fifth curve portion CP5) and the cathode polarization (the first curve portion CP1) (T2: for example nine seconds) must be within a certain range (for example 1.8-2.3 volts),

c) after a predetermined time elapses during the anodic polarization (the second curve portion CP2, the third curve portion CP3, the fifth curve portion CP5) (T3: e.g., 9 seconds) and the elapse of a predetermined time (first curve portion CP1) during cathode polarization (T4: e.g., nine seconds) must be within a certain range (e.g., 1.8-2.3 volts).

The above-mentioned cases "a", "b" and "c" make it possible to eliminate the effect of possible potential fluctuations of the second electrode 4.

Furthermore, it may also influence the measurement, taking into account the reduction of the resistance potential in the mixture 11. Studying various parameters, it has been shown that the most reliable determination of the wetting of the sensor 1 with the mixture 11 having passivating properties can be achieved by a combination of the cases "a" and "b". However, the use of the case "c" or "a" alone can also determine the wetting of the surface of the sensor 1 with the mixture 11 having passivating properties.

In fig. 7, corresponding measurements of a typical mixture 11 with different chloride contents are shown. The difference between the maximum potential and the potential after nine seconds within the anodic polarisation is zero for 0.1% and 0.2% Cl- (chloride), which confirms the passivating properties of the mixture 11.

In contrast, for 0.4% Cl- (chloride), this difference is about 700 to 50mV, confirming corrosion activation.

Determining the difference between the maximum potential within the anodic polarization and the potential after a predetermined time (first curve portion CP1) (e.g., nine seconds) during the cathodic polarization allows for determining the reduction in the resistance potential within the mixture 11.

Since the resistance potential decrease increases, once the mixture 11 begins to set, monitoring the potential decrease over time can be used to determine whether the sensor 1 is in contact with a hardened mixture 11 having passivating properties or only with a bleeding paste having passivating properties.

This procedure requires measuring the decrease in electrical resistance potential within the mixture 11 after at least twenty-four hours after the mixture 11 is injected within the casing 12.

If the reading indicates the presence of bleeding, the problem can no longer be corrected. Thus, while it is still possible to correct the situation by additional injections, it is most helpful if the determination about the presence of bleeding can be made on the basis of direct measurements after the injection of the mixture 11.

The present invention makes it possible to make such a determination using the relevant electrochemical process. Not only can the residual oxide layer be removed during cathodic polarization, hydrogen can also be generated and the pH of the mixture 11 increased.

On the other hand, the anodic polarization causes not only the generation of a passivation film but also the generation of oxygen and lowers the pH of the mixture 11. The potential for oxygen and hydrogen generation is dependent on pH according to nernst equation.

As a result, the potential changes with increasing polarization time during both anodic and cathodic polarization. Since the rate of change of pH is determined by the applied current density CD, the potential change should always be consistent for all tests.

However, the pH change is affected not only by the amount of hydroxide or hydrogen ions generated, but also by their accumulation in front of the third electrode 5. As a result, if the mixture 11 having the passivation property is in contact with the third electrode 5, the pH value may be rapidly changed.

On the other hand, if the bleeding slurry contacts the third electrode 5, the convection and large diffusion rate in the liquid will prevent the accumulation of hydroxyl or hydrogen ions. Therefore, the change in pH will be small and the change in potential will be small. Thus, monitoring the potential over time allows to determine the accumulation of reaction products (hydroxide or hydrogen ions) in contact with the third electrode 5.

This effect is shown in fig. 8, where the results for fig. 5, pH thirteen (pH13), and fig. 7, 0% Cl- (chloride) are compared. When the maximum value is reached, the potential in the electrolyte at pH thirteen (pH13) remains more or less constant, while a continuous increase is observed for the mixture 11 at 0% Cl- (chloride).

In the given measurement case, if the mixture 11 with passivating properties is in contact with the third electrode 5, the potential increase during the second fourteen and twenty seconds of anodic polarization should be at least 6 mV. This effect increases with the hardening of the mixture 11, since the transport of the reaction products (hydroxide ions during cathodic polarization and hydrogen ions during anodic polarization) in the solid mixture becomes slower.

This same effect can be used in the following studies for determining the pH value at the third electrode 5. During anodic polarization, the alkalinity of the mixture 11 in contact with the third electrode 5 will decrease as the polarization progresses. At a constant anode polarization current, the change in pH will occur more quickly when the initial pH is lower because there are fewer neutralizing hydroxide ions. Therefore, in a low pH environment, the potential drop over time will be greater. If the pH in the mixture 11 is high, the same current over time produces a smaller pH change and a smaller potential change is measured.

This procedure allows to determine the pH value before the third electrode 5, as long as the diffusivity of the hydrogen ions and the neutralized hydroxide ions generated in the mixture 11 is constant over time or known. If the current is applied such that the total charge is zero after all tests, the introduced pH change can be compensated.

In the example shown, the determination as to the passivation properties of the mixture 11 is based on ten seconds of anodic polarization. Alternatively, the anodic polarization may instead be continued until corrosion activation occurs and a potential decrease is observed. This effect occurs because the pH will decrease over time due to the generation of hydrogen ions in the anodic polarization. Thus, the ratio between chloride and hydroxide ions will decrease over time and activation will occur. This process allows quantitative information to be obtained about the passivation properties of the mixture 11 rather than just pass/fail information. A more detailed analysis of the chloride content can be made based on this process.

The use of the sensor 1 can thus result in a total assurance of corrosion protection for the tendon. The sensor 1 can be simply integrated in the anchorage and in all important areas within the sleeve 12 and allows, by means of a simple passivation measurement, to check the filling during the step of injecting the anti-corrosive mixture 11.

Thus, in case of defects or errors, the steps can be carried out directly during injection and the mixture 11 can be replaced again. In contrast to alternative methods, such as monitoring by radar or visual inspection, the fillability of the casing 12 is checked directly during injection. In this regard and in addition to this, direct monitoring of the preservative effectiveness of the mixture 11 using the sensor 1 may be the first time. This measurement is so fast and uncomplicated that it can be performed at the completion of the injection. Therefore, if necessary, the step may be performed before setting the mixture 11.

Different variations of this process may be considered. For example, each sensor 1 may be equipped with a measuring device that continuously measures the passivation properties and transmits the data to a central station at the infusion pump. So that a technician can monitor the position of the leading end of the mixture 11 within the casing 12 during injection.

Furthermore, there is the possibility of transmitting these data via a wireless network to an independent station which performs a recording of the complete injection operation for the construction worker.

The passivation measurements shown can also be performed manually using a simple battery and voltmeter. So that a simple current pulse having a predetermined duration can be used.

This can be generated by interruption of the current. With this simple battery-driven device, measurements can also be performed at the same time based on the current and the voltage V. So that the measurement of the grouting mixture and the corrosion protection effect can be achieved in one operation.

Furthermore, there is the possibility of running the electrical connections of all sensors 1 or of selected sensors 1 into a central measuring box and using them in later monitoring measurements. The design also allows other methods to be applied, such as impedance spectroscopy, galvanostatic pulse measurements, determination of linear polarization resistance and potential, and corrosion current measurements.

Furthermore, in the example of connection to a tendon, as is the case in fig. 2, for example, measurements can be made directly on the tendon 10. Thus, the sensor 1 not only allows for full and direct quality control during the injection operation, but also provides the possibility of long term corrosion monitoring of the tendon 10.

Thus, the sensor 1 can be directly integrated in the overall monitoring system of the structure. The voltage V between the second electrode 4 and the third electrode 5 can thus be taken as a function of time. As the corrosion begins, the voltage V will decrease. Alternatively, the current between the third electrode 5 and the ring 2 may be measured as a function of time. Conclusions about the onset of corrosion and the uniform rate of corrosion can be drawn analogously when the current is increased. Furthermore, the voltage between the strand 10 and the second electrode 4 can be measured.

In addition, the sensor 1 can be used to determine the effectiveness of cathodic protection on the tendon in terms of potential distribution. The polarization of the strands 10 can be determined by measuring the electrical potential between the second electrode 4 and the strands 10. At the same time, the cathodic current density on the third electrode 5 can be determined, allowing the level of cathodic protection to be evaluated. This possibility is particularly relevant for electrically insulated tendons.

The invention is of course not limited to the embodiments shown and described. The sensor 1 may thus comprise further electrodes so that passivation measurements may be performed on the individual electrodes.

Instead of the first electrode 2, any other third electrode 5 in the sensor 1 may be used. Instead of a contact with the first electrode 2 or the second electrode 4, a contact with a concrete reinforcing structure may also be used. This is possible because the reinforcing structure typically contacts the bolster, anchor head and strands. Further, the first electrode 2 and the second electrode 4 may be combined in one electrode. This is very possible if the surface of the combined electrode is large. Thus, a reinforcing structure or strand or anchor head may be suitable as a combined electrode in this application.

The materials of the second electrode 4, the third electrode 5 and the first electrode 2 must have electrical conductivity. Thus, copper, graphite, carbon fiber reinforced plastic, plastic filled with any conductive material, or any other metal may be used instead of, for example, stainless steel. For passivation measurements, it is critical that the third electrode 5 consists of an iron-based material, and that the iron-based material has a passivation behavior as similar as possible to the strands. It is obvious to use steel or to use prestressed steel strands. However, the use of iron is also conceivable.

The material of the third electrode 5 may be any electrically conductive material if the detection of the presence of a mixture 11 with passivating properties, rather than a bleed, or the determination of the pH value of the later stage is the only relevant information. For anodic polarization, inert or passivating materials are preferred, such as gold, platinum, graphite, titanium, tantalum, and the like. There is no limit as to the geometry of the electrodes. May have any shape as shown in fig. 1. It is important to note that it does not have to be planar in shape.

For example, a cylindrical geometry may also be used. Furthermore, the third electrode 5 may be divided into several single electrodes located in the same area or dispersed. For example, several separate third electrodes 5 may be introduced into the same force distribution ring 7. In a single measurement, several regions can be tested. It is even possible to extend the third electrode 5 over the entire sleeve 12. This electrode may be divided into individual electrodes. This can be achieved by using wires that are insulated and introduced parallel to the pre-stressed strands. By removing the insulation in the critical areas or at regular intervals, information about the filling of the entire bushing 12 with the mixture 11 having passivating properties can be obtained in a single measurement. For example, pre-stressed strands coated with polyethylene may be used. As long as the presence of the mixture 11 is confirmed, the polyethylene must be removed before insertion into the casing 12.

The current does not have to be constant during the test. Any possible waveform may be used, such as a sine wave including a ramp wave or positive and negative half waves. However, the use of a constant voltage may make the results easier to interpret.

Since the second electrode 4 does not carry any current, its conductivity is not critical. Its sole function is to provide a stable potential during measurement. Therefore, not only the materials listed for the third electrode 5 but also an organic or inorganic semiconductor, and even a polymer-coated metal and semiconductor may be used.

Furthermore, there is the possibility of integrating a reference electrode into the sensor 1 so that absolute electrochemical potentials can be measured. In this case, a measurement of the voltage V can be made between the reference electrode and the third electrode 5. Thereby enabling an accurate determination of the pH of the mixture 11.

The invention may also be used to monitor the passivation properties and pH of other concretes or mixtures 11 used in concrete structures.

According to the invention, the potential change in the solid mixture is used to determine the alkalinity of the mixture 11 at any later point in time.

According to the invention, measuring the potential polarization resistance (potential polarization resistance) of the second electrode 4 is used to monitor the corrosion behavior over time.

Claims (16)

1. A method for determining the passivating properties of a mixture (11) containing at least two components, cement and water, comprising the steps of:

-taking three elements, each made of electrically conductive material, these elements being called first (2), second (4) and third (5) electrodes,

-fixing at least one of the three electrodes on a support (3) such that:

they are electrically insulated from each other, and

the mixture (11) being able to contact at least one predetermined face located on each electrode, these faces being called first face (20), second face (40) and third face (50),

-selecting and between said first electrode (2) and said third electrode (5)

-applying a first direct current having a first predetermined density value and a first predetermined polarity for a first predetermined duration (D1), thereby causing an electrolytic reaction on the third electrode (5), and thereafter

-selecting the second electrode (4) and the third electrode (5), and

measuring the voltage (V) between the two electrodes during said first predetermined duration (D1), and

-storing a measure of the variation of said voltage (V) during said first predetermined duration (D1),

-comparing said variation of said voltage (V) between said second electrode (4) and said third electrode (5) during said first predetermined duration (D1) with predetermined data defining at least whether the mixture (11) has passivation properties, and

-determining at least whether the mixture (11) has such passivating properties.

2. The method of claim 1, wherein: the steps of comparing said variation of said voltage (V) between said second electrode (4) and said third electrode (5) during said first predetermined duration (D1) with predetermined data defining at least whether a mixture (11) has passivation properties and determining at least whether said mixture (11) has such passivation properties comprise at least:

-a) checking whether the difference between the maximum voltage value during the first predetermined duration (D1) and the voltage value at a first predetermined instant (T1) of the first predetermined duration (D1), i.e. the first voltage difference (V1), exceeds a first predetermined voltage value.

3. The method according to claim 1, characterized in that it further comprises the steps of:

before applying the first direct current with a first predetermined polarity for a first period of a first predetermined duration (D1) between the first electrode (2) and the third electrode (5),

applying a second direct current of a second predetermined value and of a second predetermined polarity opposite to said first predetermined polarity between said first electrode (2) and said third electrode (5) for a second predetermined duration (D2),

-when the voltage (V) between the second electrode (4) and the third electrode (5) has been measured during the first predetermined duration (D1),

-measuring the voltage (V) between the second electrode (4) and the third electrode (5) during the second predetermined duration (D2) and then storing these voltage values,

-when comparing the variation of the voltage (V) between the second electrode (4) and the third electrode (5) during the first predetermined duration (D1) with predetermined data defining at least whether a mixture has passivation properties and determining at least whether the mixture (11) has such passivation properties,

-also comparing the variation of the voltage (V) between the second electrode (4) and the third electrode (5) during the second predetermined duration (D2).

4. The method of claim 3, wherein: the step of selecting the first electrode (2) and the third electrode (5) and applying a first direct current between these two electrodes and then a second direct current comprises using a first direct current and a second direct current having the following characteristics:

the first predetermined polarity is opposite to the second predetermined polarity, and

-the first predetermined duration (D1) is equal to the second predetermined duration (D2).

5. The method of claim 4, wherein: the steps of comparing the variation of the voltage (V) between the second electrode (4) and the third electrode (5) during the first predetermined duration (D1) and the second predetermined duration (D2) with predetermined data defining at least whether a mixture (11) has passivation properties and determining at least whether the mixture (11) has such passivation properties comprise:

-a) checking whether a first voltage difference (V1) between a maximum voltage value of the first predetermined duration (D1) and a voltage value at a first predetermined instant (T1) of the first predetermined duration (D1) exceeds a first predetermined voltage value, and/or

-b) checking whether a second voltage difference (V2) between a maximum voltage value of the first predetermined duration (D1) and a voltage value at a second predetermined instant (T2) of the second predetermined duration (D2) is within a first predetermined range, and/or

-c) checking whether a third voltage difference (V3) between the voltage value at a predetermined instant (T3) of said first predetermined duration (D1) and the voltage (V) at a fourth predetermined instant (T4) of said second predetermined duration (D2) is within a second predetermined range, said predetermined instant (T3) being called third predetermined instant (T3).

6. The method according to any of claims 3-5, wherein: at least one of the first predetermined duration (D1) and the second predetermined duration (D2) has a value between one second and thirty seconds.

7. The method according to any of claims 3-5, wherein: at least one of the first predetermined duration (D1) and the second predetermined duration (D2) is ten seconds (10 s).

8. The method of claim 5, wherein: at least one of these two conditions is satisfied:

-at least one of said first predetermined instant (T1) and said fourth predetermined instant (T4) is between ten and one hundred percent of the value of said first predetermined duration (D1), and

-at least one of said second predetermined instant (T2) and said third predetermined instant (T3) is between ten and one hundred percent of the value of said second predetermined duration (D2).

9. The method of claim 5, wherein: at least one of these two conditions is satisfied:

-at least one of said first predetermined instant (T1) and said fourth predetermined instant (T4) is equal to ninety percent of the value of said first predetermined duration (D1), and

-at least one of said second predetermined instant (T2) and said third predetermined instant (T3) is equal to ninety percent of the value of said second predetermined duration (D2).

10. A method according to any of claims 3-5, characterized in that for selecting and between said first electrode (2) and said third electrode (5)

Applying a first direct current with a first predetermined polarity for the first predetermined duration (D1), and thereafter

-a step of applying, for said second predetermined duration (D2), a second direct current having a second polarity opposite to said first polarity:

-said first direct current is such that the current density flowing from said third electrode (5) is two and five milliamperes per square centimeter (2.5 mA/cm)²) And is and

-said second direct current is such that the current density flowing from said first electrode (2) is two and five milliamperes per square centimeter (2.5 mA/cm)²)。

11. The method of claim 5, wherein: for the step of comparing the variation of said voltage (V) between said second electrode (4) and said third electrode (5) with predetermined data defining at least whether the mixture has passivation properties, when:

-the first voltage difference (V1) maximum is fifty millivolts (50mV),

-said second voltage difference (V2) is one point eight volts to two point three volts (1.8V-2.3V), and

-said third voltage difference (V3) is one point eight volts to two point three volts (1.8V-2.3V),

the conclusion is that the mixture (11) has passivating properties at least in the vicinity of the third electrode (5).

12. The method of claim 5, wherein: in the step of comparing the variation of said voltage (V) between said second electrode (4) and said third electrode (5) with predetermined data defining at least whether the mixture (11) has passivation properties or not, when

A fourth second and of at least one of the first predetermined duration (D1) and the second predetermined duration (D2)

-the change in potential between the ninth second of at least one of said first predetermined duration (D1) and said second predetermined duration (D2) is greater than six millivolts (6mV), then the conclusion is that said third electrode (5) is in contact with the mixture (11) of hardened cement and water, rather than just the bleed, i.e. the liquid emerging from the mixture (11) of water and cement.

13. The method according to any of claims 1-5, wherein: -taking three elements, each made of conductive material, these elements being said first electrode (2), said second electrode (4) and said third electrode (5), each of these three electrodes having at least one face (20, 40, 50), the above-mentioned step comprising the operation of selecting three elements, each made of steel.

14. The method according to any of claims 1-5, wherein: the potential change in the solid mixture is used to determine the alkalinity of the mixture (11) at any later point in time.

15. The method according to any of claims 1-5, wherein: measuring the potential polarization resistance of the second electrode (4) is used to monitor the corrosion behaviour over time.

16. Sensor for determining the passivating properties of a mixture (11) containing at least two components, cement and water, according to the method of any of claims 1-15, this sensor being characterized in that it has:

-three elements, each element consisting of an electrically conductive material, the elements,

having at least one predetermined face intended to come into contact with the mixture (11), called first face (20), second face (40) and third face (50),

are separately connected to electrical conductors intended to allow connection to separate devices, so that each of these three elements can have the function of a first electrode (2), a second electrode (4) and a third electrode (5), and

-a support (3) for supporting at least one of the three elements such that:

they are electrically insulated from each other, and

the mixture (11) is able to contact all the faces, namely the first face (20), the second face (40) and the third face (50).