WO2018091534A1

WO2018091534A1 - Method and arrangement for assessing the corrosion and passivation of the reinforcement while taking into account the moisture in reinforced concrete

Info

Publication number: WO2018091534A1
Application number: PCT/EP2017/079329
Authority: WO
Inventors: Ralf W. Arndt; Hans-Peter Gatz
Original assignee: Fachhochschule Erfurt
Priority date: 2016-11-16
Filing date: 2017-11-15
Publication date: 2018-05-24
Also published as: DE102016222538B3; EP3542144A1

Abstract

The invention relates to a method for determining a state of corrosion and passivation on a steel concrete component (1), in which an inert measuring electrode (3) is arranged on the surface, an electrically conductive connection to a reinforcing steel (2) is established, into which an electrical test signal is fed. A negative cathode protection current (/fc) is fed into the measuring electrode (3). On the measuring electrode (3), a corrosion measurement signal (Sl, Sl') for determining the charges, which are transported by iron ions through the outer concrete layer (1.1), and a moisture measurement signal (S2, S2') for determining the moisture of the outer concrete layer (1.1) are simultaneously measured. The corrosion measurement signal (Sl, Sl ') is compared to a predetermined limit value, when the moisture measurement signal (S2, S2 ') indicates at least one minimum measurement moisture. The invention further relates to an arrangement for carrying out the method.

Description

Method and arrangement for assessing the corrosion and passivation of the reinforcement taking into account the moisture in reinforced concrete

The invention relates to a method and an arrangement for assessing reinforced steel concrete components with respect to the corrosion and passivation of the reinforcement, taking into account the moisture.

Metal and especially steel corrosion is a common problem that causes widespread damage and causes indirect and direct costs in all industrial sectors. This applies in particular to the field of reinforcement corrosion in reinforced concrete construction.

In new buildings, the reinforcing steel is usually protected or passivated by a surrounding passivation layer against corrosion. This passivation layer is formed by the high alkalinity of the pore solution as a very thin but virtually non-porous layer around the rebar. The passivation layer prevents or inhibits the penetration of oxidizing ions down to the rebar. By reducing the pH, z. B. by carbonation or in particular by the penetration of chlorides, the passivation of this passivation layer is reduced and the passivation layer finally destroyed. As a result, the corrosion protection for the reinforcing steel is lost. For the detection of corroded and corroding reinforcement in reinforced concrete, corrosion consequential damage and the corrosion tendency of reinforced concrete, various non-destructive and non-destructive methods with limited validity are available, for example the ultrasonic echo method, the impact echo method, microwave method, inductive and / or or capacitive measuring methods, thermographic methods and radiographic methods.

Also known from the prior art are electrochemical methods, such as the electrochemical potential measuring method, in which an electrical voltage is measured between a contacted internal reinforcing steel and the outside surface of a steel-weighted concrete component, which in the present corrosion typically has more negative values than if passivation of the contacted reinforcing steel, but with a large gray area and significant uncertainty.

The document US 2012/0012470 A1 describes an arrangement with a probe, which is provided for scanning a surface of a concrete component. The arrangement includes a function generator for feeding a current into the concrete component via the probe. The function generator is designed as a reference for a potential measurement on a reinforcing steel in the concrete component. The arrangement may further comprise a current measuring device for measuring the current through the probe.

Document CH 708 249 A2 describes a method for determining the passivating properties of a metal surface in an electrolyte. The method is based on the rectification of an alternating current which passes through the metal surface into the electrolyte. The sign as well as the magnitude of the change in the DC voltage and the DC current between the metal surface and an electrode allow a conclusion on the presence of passivating conditions and thus on the corrosion behavior.

The document GB 2 224 852 A describes an apparatus and a method for monitoring the corrosion rate in a concrete component with an enclosed reinforcement material. The reinforcement material and the concrete form a corrosion half-cell. The reinforcing material is connected via a current measuring device to a probe having a first annular surface which communicates with a water-absorbing material, such as a

Sponge, is related. The sponge is moistened and moved over the surface of the concrete component, with the current being measured by the probe continuously or at discrete intervals. The voltage difference between see one of the first annular surface oppositely disposed second annular surface, which is also related to a water-absorbing material, and the reinforcing material is determined.

The disclosure DE000002335419 AI describes a method and an apparatus for measuring the corrosion or corrosion of steel reinforcements in concrete parts such as walls, ceilings and the like, wherein in a measuring range between the steel reinforcement and the surface of the concrete part by means of a patch on the surface of the concrete part, as Cathode serving electrode and a power supply connected directly to the Stahlarmierung a galvanic cell is constructed and loaded with a constant DC current, wherein the Stahlarmierung is connected as an anode, and the potential profile of the steel reinforcement is registered relative to a reference electrode over a short time before the start of the current period ,

The document WO 97/09603 describes an electrode assembly for determining the corrosion rate in reinforced concrete by means of galvanostatic pulses, comprising an active, current density-controlled counter electrode and an associated feedback electrode. On the outer surface of an enclosing adjusting electrode is arranged with associated feedback. By means of a circuit, the current fed into the electrodes is controlled so that the same current density acts on the counter electrode and on the adjusting electrode.

The document AT 71 224 B describes a method for continuous or discrete-time monitoring of the effectiveness of repairs on reinforced concrete components, which have been damaged by corrosion of the reinforcement material. A series of spot measurements of the electrical potential of the reinforcement material relative to a first reference electrode is detected by moving the first reference electrode on the surface of the concrete component. Further, a second reference electrode of lead is implanted in the concrete mass below a surface zone. It is the electric potential of the second Re- determined reference electrode against the reinforcing material and observed the time course.

The invention is based on the object to provide a method for assessing the corrosion and the passivation capacity of a passivation layer on the reinforcement in reinforced concrete, with a reliable detection of active corrosion, passive corrosion in insufficient moisture or incipient corrosion at sufficient humidity and characterization current and future passivation behavior of the reinforcement. The invention is further based on the object of specifying a method for assessing the moisture content of a steel-reinforced concrete component in order to assess the actual progress of ions.

Furthermore, the invention is based on the object to provide an arrangement for carrying out such methods.

The object is achieved in terms of the method according to the invention by the features specified in claim 1. With regard to the arrangement, the invention is achieved by the features specified in claim 5.

Advantageous embodiments of the invention are the subject of the dependent claims.

In a method for evaluating the corrosion state and for determining the passivation capability of a passivation layer of a steel reinforcement of a reinforced concrete component, an inert measuring electrode is arranged on the surface of the reinforced concrete component. By means of a rebar connection, an electrically conductive connection to the reinforcing steel is produced, via which an electrical test voltage is fed. The reinforcement connection may be introduced through a contact opening in the outer concrete layer between the reinforcing steel and the surface of the reinforced concrete component. It is possible to have such a contact opening by drilling, whipping or other known from the prior art Abtragsverfahren in the reinforced concrete component contribute. Furthermore, reinforced concrete components can be produced, in which such a contact opening is already provided.

At the measuring electrode, a corrosion measurement signal is measured as the voltage between the measuring electrode and the rebar connection contacting the reinforcing steel. The corrosion measurement signal is determined by the charges which can break through the passivation layer. The number of charges transported through the passivation layer of ions is a measure of the passivation capacity of the passivation layer around the reinforcing steel. With reduced passivation capability, the passivation layer has a number of imperfections or voids that are permeable to ions. Thereby, a large number of charges corresponding to the number of ions, for example, iron ions passing through the passivation layer are measured. With sufficient passivation capacity, however, this number of charges is very low to low.

A negative cathode protection voltage is applied to the measuring electrode via an ohmic series resistor, which voltage is generated by a cathode protection voltage source designed as a loadable constant voltage source. If the measuring electrode is placed on the reinforced concrete component, then a negative cathode protection current is fed in via the ohmic series resistor. As a result, the course of the corrosion measurement signal, which is generated by the charge pressure or the pressure of freely movable ions in the passivation layer around the reinforcing steel, is stabilized. The cathode protection current fed into the measuring electrode via the ohmic series resistor counteracts the pressure of the freely mobile ions, in particular the iron ions dissolved from the reinforcing steel by the anodic partial process of corrosion. This creates a small stress on the passivation layer, which defines a fixed operating point for the measurement of freely mobile ions. Thus, drifting or floating of measured values of the corrosion measurement signal is avoided and the reliability of the measurement is improved. The cathode protection current fed into the measuring electrode is thus an essential basis for the detection tion of the corrosion measurement signal as well as all other parameters of the method.

Under the influence of the injected cathode protection current, an asymptotically decaying corrosion measurement signal is measured, which has a maximum initial value at the beginning of the feed-in of the cathode protection current. In this case, the reinforcing steel with the surrounding passivation layer acts like an electrode of an electrolytic capacitor. The asymptotically evanescent corrosion measurement signal is caused by the charging process on this electrolytic capacitor under the influence of the injected cathodic protection current, the maximum initial value being determined by the properties of the electrolytic capacitor electrode and the dielectric material around the reinforcing steel. Thus, the initial value of the corrosion measurement signal may be compared to at least one predetermined limit to determine the passivation capability of the passivation layer. For example, an initial value of the corrosion measurement signal above a predetermined threshold may be evaluated as sufficient passivation capability. By comparison with a plurality of predetermined limit values, gradations can be made in the evaluation of the passivation capacity. In a preferred embodiment of the method, a predetermined threshold of zero millivolts is used. If the initial value of the corrosion measurement signal is above this preferred limit, the corrosion state is determined as active corrosion and / or defective passivation. If the initial value of the corrosion measurement signal is below this preferred limit, no active corrosion and / or sufficient passivation is determined.

The magnitude of the drop in the corrosion measurement signal is determined by the passivation capability of the passivation layer. The steeper the corrosion measurement signal drops, the fewer defects or imperfections the passivation layer has. Thus, in addition, a measure of the steepness of the drop of the corrosion measurement signal, for example the drop or the negative rise of a straight line by the initial value and a second value of the corrosive onsmesssignals at a predetermined time interval from the initial value or the time constant of a fitted exponential decay, are used for the evaluation of Passivierungsvermögens the passivation layer.

The asymptotic drop of the corrosion measurement signal is determined by the ohmic series resistor, via which the cathode protection current is fed into the electrode. This series resistor can be chosen differently depending on the measurement task.

Simultaneously with the corrosion measurement signal, a moisture measurement signal is measured which determines the moisture in the passivation layer. Only in the case of sufficient moisture in the passivation layer are differences in the passivation capability detectable by the corrosion measurement signal. In particular, too little moisture prevents the transport of ions through the passivation layer, regardless of the actual passivation capability. As a result, such a measurement can erroneously simulate a passivation that is actually absent as a pseudopassivation measurement.

In the method according to the invention, the corrosion measurement signal is compared with at least one predetermined limit value if the moisture measurement signal indicates at least one minimum measurement moisture detected as sufficient for a reliable measurement. In this way, a faulty determination and / or interpretation of the passivation state of the passivation layer is avoided in the case of an insufficient moisture of the passivation layer for the measurement.

For example, an inadequate passivation state can be determined by the corrosion measurement signal assuming a positive maximum initial value when the cathode protection current is switched on and / or when the measurement electrode is placed on it, and then decaying in the manner of a decaying exponential function. An insufficient passivation state or the presence of corrosion of the reinforcing steel can alternatively or supportively also be determined by evaluating the time course of the corrosion measurement signal. examples For example, the time period during which the corrosion measurement signal is positive can be determined, and / or the time constant of the decaying exponential function can be estimated and / or the rise or fall of the corrosion measurement signal can be determined. Advantageously, a more accurate and reliable measurement of the corrosion state, the passivation state and the expected course of corrosion in a reinforced concrete component is thus possible. Furthermore, it is possible to derive a statement about the passivation state from the amplitude value and the asymptotic decay, that is to say the profile of the difference between the peak value and the asymptote, taking into account the injected protective current.

In one embodiment of the method, the cathode protection current fed into the measuring electrode is measured as a protective current measuring signal. This cathode protection current is a measure of the external electron input required to prevent the partial processes of corrosion of the reinforcing steel.

As a result, the required current intensity for a cathode protection current can be determined in an advantageous manner, which continuously improves or maintains the passivation state of a reinforced concrete component affected or threatened by corrosion. It can also be determined whether a cathodic protection current can still be used meaningfully or whether other measures such. B. Repair are needed.

In one embodiment of the method, the cathode protection current is taken from a loadable voltage source via a selectable or variable ohmic resistor, which outputs a cathode protection voltage of minus 400 millivolts. By changing this ohmic bias resistor, the injected cathode protection current can be changed, with an increase in the current intensity of the negative injected cathode protection current resulting in a reduction of the corrosion measurement signal. Thus, for each value of the corrosion measurement signal which is below a predetermined limit value, for example for each negative value of the corrosion measurement signal, a current intensity of the negative injected cathode protection current can be assigned. Each the higher the passivating power of the passivation layer, the better. Thus, it is advantageously possible to obtain a further statement about the quality of the passivation layer from the measurement of the cathode protection current. For example, from this it is possible to determine the porosity or the inner bond of the passivation layer, ie the enforcement with imperfections or imperfections which are permeable to ions.

In one embodiment of the method, the test voltage is formed as a square wave signal having an upper voltage value of 400 millivolts during the active or high phase, a lower voltage value of 0 millivolts during the inactive or low phase and a period length of 0.1 second. By means of such a rectangular test voltage, the charge pressure or the ion pressure, which acts on the iron ions dissolved from the reinforcing steel, conditioned. The passivation layer causes a change in the test voltage, in particular a reduction in the amplitude, from the viewpoint of moisture. The reduced by the passage through the passivation layer amplitude of the test voltage is also detected as a test signal. The higher the humidity of the passivation layer, the less the

Amplitude of the test voltage reduced by the passivation layer. A perfectly dry passivation layer can be considered approximately insulating and alters the test signal. High humidity results in a test signal that is at or slightly above 400 millivolts. A water-proof passivation layer can be considered as a good electrolytic conductor, thus minimizing the amplitude of the test voltage, finding a test signal that is at or slightly below the upper amplitude value of the test voltage of 400 millivolts. A passivation layer with a sufficient moisture for the readability of the corrosion measurement signal has a

Test signal that is above 385 millivolts and at or below 400 millivolts. By comparing the test signal with a predetermined test signal limit of 385 millivolts, it is thus possible to check whether a valid, evaluable corrosion measurement signal can be measured. Analogously, other predetermined test signal threshold values for other upper voltage values of legal be determined corner-shaped test voltages. It should be noted that above a maximum test voltage, an electrical breakdown of the passivation layer can occur comparable to the electrical breakdown at a reverse-biased diode.

An arrangement for carrying out a method for determining a corrosion state on a reinforced concrete component comprises an inert measuring electrode with coupling fluid provided for the arrangement on the surface of a reinforced concrete component, a reinforcement connection intended for the electrical connection to a reinforcing steel in the reinforced concrete component, one for the generation and feeding of a Test signal provided in the reinforcement connection test signal source, a provided for the supply of a cathode protection current in the measuring electrode cathode protection current source, a measuring device and an evaluation unit.

The measuring device is designed to determine a corrosion measurement signal which measures charges of ions which are released from the reinforcing steel and pass through an outer steel cement interface and are collected at the measuring electrode. Devices for measuring charges of ions are known in the art, for example from devices for determining a pH above an electrochemical potential.

The measuring device is further designed such that a value of a moisture measurement signal is determined simultaneously with the value of the corrosion measurement signal. The corrosion measurement signal is determined by the capacitance of a measuring field between the measuring electrode and a section of the reinforcing steel opposite the measuring electrode. The measuring field comprises the passivation layer and the outer concrete layer surrounding the reinforcing steel. The capacitance of this measurement field can be modeled as a capacitance of an electrolytic capacitor, wherein an electrolytic capacitor electrode is formed by the reinforcing steel surrounded by the passivation layer. Since this electrolytic capacitor does not have any moisture protection, the moisture changes in the region of the passivation Layer the dielectric and thus also the capacity of the electrolytic capacitor. Thus conclusions on the moisture in the region of the passivation layer are possible from the measurement of the capacitance of the electrolytic capacitor. Devices and methods for measuring the capacitance of electrolytic capacitors are known from the prior art, for example from commercially available digital multimeters.

The corrosion measurement signal describes the different states of the passivation layer, which depending on the passivation capability can be described as an insulator or as an insulator with defects or as an active voltage-generating iron oxidation process.

The measuring device is further configured such that a protection current measuring signal is simultaneously determined for the corrosion measurement signal and the moisture measurement signal, which measures the cathode protection current fed by the cathode protection current source into the measurement electrode. Devices for measuring a current are known from the prior art, for example from commercially available digital multimeters.

The evaluation unit can be connected to the measuring device and designed so that the corrosion measurement signal, the moisture measurement signal and the protective current measurement signal can be evaluated and optionally graphically displayed.

With the arrangement according to the invention, the corrosion state on a reinforced concrete component can be determined reliably, quickly and with little effort. In particular, by means of a single arrangement, a stable measured value can be obtained for different degrees of moisture of a tested reinforced concrete component, since a reduced ion mobility resulting from a lack of moisture is determined and taken into account in the evaluation of the corrosion measurement signal. In one embodiment of the arrangement, the measuring electrode is made of an inert material, e.g. As graphite, manufactured. Measuring electrodes made of graphite are chemically so resistant that they can be regarded as inert with good approximation, and have a very good conductivity. They are also inexpensive to produce.

In one embodiment of the arrangement, the measuring device comprises at least one analog-to-digital converter and outputs digital measuring signals. Digital measuring signals are particularly easy to evaluate.

In one embodiment of the arrangement, digital measurement signals are transmitted via a telecommunications protocol to at least one mobile telephone. For example, an e-mail or a short message service such as the short message service (SMS) can be used as the telecommunications protocol. Advantageously, a test engineer can be informed of measurements even when he is not on site.

In one embodiment of the arrangement, the test signal source and / or the cathode protection current source are / is battery powered. Advantageously, this eliminates the problem of an external reference or reference ground and the problem of a protective conductor or grounding. In addition, such an embodiment is transportable and independently used outdoors or on construction sites.

In one embodiment of the arrangement, the battery supply of the test signal source and / or the cathode protection current source takes place by means of high-capacity accumulators. Advantageously, a sufficiently long service life of the arrangement can thereby be achieved with a low weight and thus good transportability of the arrangement. For example, can be achieved with lithium-based batteries over 100 hours of operation. In one embodiment of the arrangement, the evaluation unit is designed as a notebook or as a netbook. For notebooks or netbooks, for example, compared to a digital signal processor, programs for evaluating measuring signals can be developed with little effort or available commercially available programs can be adapted. In addition, notebooks or netbooks are easily transportable and can be operated for a sufficiently long period for a measurement independent of the electrical network. Furthermore, notebooks have standardized outputs, for example universal serial bus (USB) outputs, with which electrical measuring devices, for example constant voltage sources or measuring devices in the form of digital multimeters, can be fed without significantly impairing the operating life of a notebook.

In one embodiment, the arrangement comprises a display device which is provided for the display of digital measurement signals. Such a display device can be formed by a display and a computer on which runs a commercially available computer program for displaying measured values. For example, the computer program RealView from ABACOM-Ingenieurgesellschaft GbR is known from the prior art for the representation of measured values.

In one embodiment, the arrangement comprises a data memory which is provided for the storage of digital measurement signals. Data memories for digital measurement signals are known from the prior art, for example as magnetic hard disks or as solid-state disk (SSD) designated semiconductor memory.

In one embodiment, the arrangement comprises a transmission device, which is provided for the transmission of digital measurement signals by means of a telecommunications protocol to at least one mobile telephone. Such transmission devices are known in the art, for example as modems for the transmission of mobile radio protocols such as Long Term Evolution (LTE) or Long Term Evolution Advanced (LTE Advanced) known. Advantageously, the detected corrosion measurement signal and the detected moisture measurement signal can thus be transmitted and evaluated independently of the measurement location.

Embodiments of the invention are explained in more detail below with reference to drawings.

Show:

Figure 1 schematically a reinforced concrete component with contacted

Rebar and measuring electrode,

FIG. 2 schematically shows the structure of a test signal source,

Figure 3 and Figure 4 schematically shows the structure of a Kathodenschutzstrom- source and

FIG. 5 schematically shows a measurement record with the time course of a

Corrosion measurement signal, a humidity measurement signal and a protection current measurement signal.

Corresponding parts are provided in all figures with the same reference numerals.

FIG. 1 schematically shows a reinforced concrete component 1, in which a reinforcing steel 2 is enclosed, which extends along a longitudinal direction of the reinforced concrete component 1. On the outer surface of the reinforced concrete component 1, an inert measuring electrode 3 is arranged. The measuring electrode 3 may be made of graphite, for example. The measuring electrode 3 may be stationary, for example as a rod electrode, or may be designed to be movable, for example as a wheel electrode. At the interface between the reinforcing steel 2 and the outer concrete layer 1.1 is compared to the outer concrete layer 1.1 very thin, but with good passivation virtually pore-free passivation layer 2.1 is formed. An intact Passivierungsschicht 2.1 with good passivation effect corrosion protection for the reinforcing steel 2 by preventing the diffusion of ions and thus the anodic and cathodic sub-process of corrosion or greatly reduced.

Spaced in the longitudinal direction of the reinforced concrete component 1 and the measuring electrode 3 is in the reinforced concrete component 1, a contact opening 4 is introduced, in which an outer concrete layer 1.1 is removed so far that the reinforcing steel 2 is accessible. A contact opening 4 can be manufactured destructive and small diameter, for example by drilling or localized impact of the outer concrete layer 1.1. By means of an arranged in the contact opening 4 electrically conductive reinforcement connection 5 of the reinforcing steel 2 is electrically coupled. As an alternative to introducing a contact opening 4, the reinforced concrete component 1 may have an outwardly guided contact access, which is electrically connected to the inner reinforcing steel 2, to which the reinforcement connection 5 is coupled.

A measuring device 6 is electrically connected between the reinforcement connection 5 on the one hand and the measuring electrode 3 on the other hand. The measuring device 6 determines measurement signals S1, S2, S3, S1 ', S2 \ S3' in a manner which will be described in more detail below.

The measuring device 6 is connected to an evaluation unit 7 such that the measurement signals S1, S2, S3, S1 ', S2', S3 'provided by the measuring device 6 are available on the evaluation unit 7 as digital, ie time-sampled and amplitude-discretized values. Alternatively, the measured values can also be sent by the measuring device 6 via a telecommunications protocol, for example by e-mail or short message, to a mobile telephone. For example, the evaluation unit 7 can be embodied as a computer, as a notebook or as a netbook, to which an analog-to-digital converter is connected via a universal serial bus (USB) connection. By means of such an analog-to-digital converter, an analog measurement value of a measurement signal S 1, S 2, S 3, S 1 ', S 2', S 3 'provided by the measuring device 6 can be converted into a digital signal which is generated by an evaluation program the evaluation unit 7 is evaluated. For example, the commercially available program "Realview" from Abacom can be used as an evaluation program for an evaluation unit 7 embodied as a computer, notebook or netbook, but other programs or software products with which digital signals are recorded can also be used as an evaluation program represented and such digital signals can be stored.

Furthermore, a test signal source 8, which feeds an electrical test signal into the reinforcing steel 2, is electrically connected to the reinforcement connection 5. The construction of the test signal source 8 will be explained in more detail below with reference to FIG.

The test signal source 8 comprises a first constant voltage source 8.1, an electronically switchable switch 8.2, a square wave signal generator 8.3, a pull-down resistor 8.4 and an operational amplifier 8.5. The first constant voltage source 8.1 outputs a constant voltage U _p of preferably 400 millivolts and is connected via the electronically switchable switch 8.2 to the non-inverting input of an operational amplifier 8.5. The electronically switchable switch 8.2 is actuated via a square-wave signal, which is generated by the square wave signal source 8.3. The square-wave signal preferably has a frequency of 10 hertz, that is to say a period of 100 milliseconds.

The output of the operational amplifier 8.5 is fed back to the inverting input, so that the operational amplifier 8.5 operates as an impedance converter. This ensures that the test signal at the output 8.6 of the test signal source 8 regardless of load set at the first constant voltage source 8.1 Test voltage U _p outputs. To achieve larger test voltages U _p and / or a greater load capacity with an output current, the output of the operational amplifier can be supplied to a low-power amplifier. Small power amplifiers are known from the prior art.

The non-inverting input of the operational amplifier 8.5 is grounded via a pull-down resistor 8.4. Preferably, the pull-down resistor 8.4 has a pull-down resistance R _PD of 1 megohm. The pull-down resistor 8.4 causes the non-inverting input and thus also the output of the operational amplifier 8.5 to be safely at ground potential when the electronically switchable switch 8.2 is open.

Thus, the test signal source 8 generates at output 8.6 a square-wave test signal with a maximum value of 400 millivolts independent of load and a minimum value of 0 millivolts and a frequency of 10 hertz. This test signal traverses the boundary layer or passivation layer 2.1 between the reinforcing steel 2 and the concrete of the outer concrete layer 1.1 of the reinforced concrete component 1 in a characteristic manner up to the measuring electrode 3 on the surface of the reinforced concrete component 1.

Furthermore, a cathode protection current source 9, which feeds a cathode protection current into the measurement electrode 3, is electrically connected to the measurement electrode 3. The construction of the cathode protection current source 9 will be explained in more detail below with reference to FIG.

The cathode protection current source 9 comprises a second constant voltage source 9.1, which is connected to a respective first end of at least two series resistors 9.2 having different resistance values. The second constant voltage source 9.1 outputs a constant voltage U _K of preferably minus 400 millivolts. The cathode protection current source 9 further comprises a selection switch 9.3, the output 9.4 selectable with the second end exactly one Series resistor 9.2 connects. Thus, the output 9.4 of the cathode protection current source 9 can be connected to the second constant voltage source 9.1 with a selectable ohmic resistance. If this output 9.4 is connected to the measuring electrode 3 on a reinforced concrete component 1 which has sufficient moisture for an ion transport, a current strength driven by the measuring electrode 3 can be set by means of the selectable series resistor 9.2. The cathode protection current source 9 thus acts approximately as a current source with an adjustable current through the resistor 9.2 current.

FIG. 4 shows an embodiment of a cathode protection current source 9, in which the constant voltage source 9.1 is preceded by a series resistor 9.2, which results from the series connection of a potentiometer 9.2 'with a fixed series resistor 9.2. Thus, in this embodiment, a total series resistor is continuously adjustable over a range of resistance values.

If the measuring electrode 3 is arranged above an active corrosion point 10 on the reinforcing steel 2, then the cathode protection current I _K , which is fed into the measuring electrode 3 by the cathode protective current source 9 and which can be adjusted by selecting the series resistor 9. 2, actively intervenes in the corrosion process and thus influences the corrosion measuring signal, if the external one Concrete layer 1.1 has a sufficient for this purpose minimum measurement humidity and thus conductivity. The cathode protection current I _K influences the mobility of the ions, in particular the iron ions and the iron hydroxide ions, in the region of the passivation layer 2.1 in the same way as a reduction of the moisture in the passivation layer 2.1.

By adjusting the cathode protection current I _K , which is emitted by the cathode protection current source 9, the method according to the invention is therefore suitable for compensating different degrees of humidity of investigated reinforced concrete components 1 and thus for detecting comparable measured values regardless of moisture, as long as a certain minimum conductivity of the outer Clay layer 1.1 and the passivation layer 2.1 indispensable minimum measurement moisture is given. Such a minimum moisture can always be achieved by a known from the prior art humidification of the surface of the reinforced concrete component 1, so that the method is in principle universally applicable.

When applied to a reinforced concrete structure 1 of unknown humidity, the cathode protection current I _K delivered by the cathode protection current source 9 is adjusted to achieve a predetermined ion mobility corresponding to a predetermined nominal reference humidity range. The achieved ion mobility can be read from the measurement signal S2, which is obtained from the measuring device 6. The cathode protection current I _K necessary for setting the predetermined ion mobility is then at the same time a measure of the actual moisture content of the reinforced concrete component 1.

Subsequently, the extraction of the measurement signals S 1, S 2 and S 3 is explained in more detail on the basis of a measurement record 11 shown schematically in FIG. The measuring record 11 represents along a time axis t a first measuring duration T with measuring signals S1, S2 and S3 and a second measuring duration with measuring signals S1 ', S2' and S3 '. The first measuring duration T corresponds to a measurement on a reinforced concrete component 1 with present corrosion, So with insufficient passivation. The second measurement period T "corresponds to a measurement on a reinforced concrete component 1 without corrosion, ie with sufficient passivation.

The corrosion measurement signal S 1, S 1 'evaluates the corrosion or passivation state of the reinforcing steel 2 below the measuring electrode 3 on the basis of a measured charge. If a portion of the corrosion measurement signal Sl, Sl 'at the beginning of a measurement period T, T' in the positive voltage range, so there is corrosion or insufficient passivation. This is the case with the corrosion measurement signal S1 in the region of the first measurement duration T. If a portion of the corrosion measurement signal Sl, Sl 'at the beginning of a measurement period T, T' in the negative voltage range, so there is sufficient passivation. This is the case with the corrosion measurement signal S 1 'in the region of the second measurement T 'is the case. The passivation state can also be evaluated on the time profile of the corrosion measurement signal S1, S1 ', for example at the rise or fall of the corrosion measurement signal S1, S1'.

A good passivation represents a barrier to the passage of iron ions. Upon detection of the corrosion measurement signal Sl, Sl ', the electrical charges of iron ions which pass through the passivation layer 2.1 are detected by the measuring device 6. These charges form an associated size with the iron ions. If many iron ions pass through the passivation layer 2.1 and then through the outer concrete layer 1.1, then many charges are released. The measurement of the charges is carried out according to the known from the prior art principle of measuring a pH indirectly by measuring a voltage at the inert measuring electrode 3. The corrosion measurement signal Sl, Sl 'indicates the measured voltage, which is a measure of the number of Charges and thus for the number of iron ions that pass through the passivation layer 2.1 and the outer concrete layer 1.1 and are collected by the measuring electrode 3.

The measurement record 11 also represents the moisture measurement signal S2, S2 '. The interface of the passivation layer 2.1 to the concrete layer 1.1 also acts as a dielectric between a first electrode, which is formed by the inert measuring electrode 3, and a second electrode, which is formed by the reinforcing steel 2 , Thus, the entirety of the measuring electrode 3, the passivation layer 2.1, the outer concrete layer 1.1 and the reinforcing steel 2 contacted via the reinforcement connection 5 can be modeled as an electrolytic capacitor whose capacity depends on the moisture in the concrete layer 1.1, in particular on the moisture in the passivation layer around the reinforcing steel 2, depends. The moisture measurement signal S2, S2 'corresponds to the measurement of the capacitance of an electrolytic capacitor, as known from the prior art and used for example in commercially available digital multimeters. The moisture measurement signal S2, S2 'indicates whether the moisture in the concrete layer 1.1 for a reliable measurement of the corrosion or passivation state of the reinforced concrete component 1 is sufficient. For example, a humidity sufficient for the evaluation of the corrosion measurement signal can be assumed if a moisture measurement signal S2, S2 'of at least +385 millivolts is measured at a test voltage of +400 millivolts output from the first constant voltage source 8.1 of the test signal source 8. Particularly preferably, a moisture sufficient for the evaluation of the corrosion measurement signal is assumed when a moisture measurement signal S2, S2 'of at least + 390 millivolts is measured. Thus, with insufficient moisture, the reinforced concrete component 1 moistened, for example, be sprayed with water. After a short waiting time, the externally applied water has penetrated into the outer concrete layer 1.1 and further into the passivation layer 2.1 and a new measurement can be carried out. If necessary, this procedure is repeated until a reliable measurement with sufficient humidity can be made.

Furthermore, the measurement record 11 represents the protection current measurement signal S3, S3 ', which indicates the cathode protection current I _K fed by the cathode protection current source 9. Methods for current measurement are known from the prior art and are used, for example, in commercially available digital multimeters. The protective current measuring signal S3, S3 'indicates which external electron supply is needed to prevent the anodic and cathodic sub-processes of corrosion and thus to promote the passivation. Thus, a building can be protected against progressive corrosion by feeding in a cathode protection current I _K corresponding to the external electron demand.

LIST OF REFERENCE NUMBERS

Reinforced concrete component

.1 outer concrete layer

rebar

.1 passivation layer

measuring electrode

contact opening

rebar connection

measuring device

evaluation

test signal source

.1 first constant voltage source

.2 electronically switchable switch

.3 square wave signal generator

.4 pull-down resistor

.5 operational amplifier

.6 output

Cathodic protection current source

.1 second constant voltage source

.2 series resistors

9.2 'Potentiometer

9.3 Selection switch

9.4 output

10 active corrosion site

11 measurement record

U _p test voltage

U _K constant voltage Cathodic protection current

Pull-down resistance si, sr Corrosion measurement signal, measurement signal

S2, S2 'Humidity measurement signal, measurement signal

S3, S3 'Protective current measuring signal, measuring signal

T first measurement duration

T 'second measurement period

t Timeline

Claims

PATENT APPLICATIONS

1. A method for assessing the corrosion state and for determining the passivation capacity of a passivation layer (2.1) around a reinforcing steel (2) of a reinforced concrete component (1),

characterized in that

an inert measuring electrode (3) is arranged on the surface of the reinforced concrete component (1),

an electrically conductive connection to a reinforcing steel (2) surrounded by the reinforced concrete component (1) is produced by means of a reinforcement connection (5),

an electrical test signal is fed into the contacted reinforcing steel (2) by means of a test signal source (8) comprising a first constant voltage source (8.1) and a switching device (8.2),

a negative cathode protection current (I _K ) is fed into the measuring electrode (3) from a second constant voltage source (9.1) with a constant cathode protection voltage (U _K ) via an ohmic series resistor (9.2, 9.2 '),

at the measuring electrode (3) simultaneously

a corrosion measurement signal (S 1, S 1 ') for determining the charges that are transported by iron ions through the outer concrete layer (1.1), and

a moisture measurement signal (S2, S2 ') for determining the moisture content of the outer concrete layer (1.1)

be measured and

the corrosion measurement signal (S 1, S 1 ') is compared with at least one predetermined limit value if the moisture measurement signal (S2, S2') indicates at least a minimum measurement humidity.

2. The method according to claim 1,

characterized in that the cable fed into the measuring electrode (3) is Thodenschutzstrom (I _K ) is measured as a protective current measuring signal (S3, S3 ') and from the required external electron supply to prevent the anodic and cathodic sub-processes of corrosion of the reinforcing steel (2) is determined.

3. The method according to claim 2,

characterized in that the le from the second Konstantspannungsquel- (9.1) (U _K) for feeding in the cathodic protection current (I _K) given constant cathodic protection voltage minus 400 millivolts.

4. The method according to any one of the preceding claims,

characterized in that the test signal is a square wave signal having an upper voltage value of 400 millivolts, a lower voltage value of 0 millivolts and a period length of 0.1 second.

5. Arrangement for carrying out a method according to one of the preceding claims, comprising

an inert measuring electrode (3) provided for the arrangement on the surface of a reinforced concrete component (1),

a reinforcement connection (5) provided for the electrical connection to a reinforcing steel (2) in the reinforced concrete component (1), a test signal source (8) provided for the generation and feeding of a test signal into the reinforcement connection (5),

a cathode protection current source (9) provided for generating and supplying a cathode protection current (I _K ) into the measurement electrode (3) comprising the second constant voltage source (9.1) and at least one ohmic series resistor (9.2, 9.2 ') connectable to the second constant voltage source (9.1),

a measuring device (6) for the simultaneous detection of

a corrosion measurement signal (S 1, S 1 ') for measuring charges of ions collected at the measurement electrode (3), a moisture measuring signal (S2, S2 ') for measuring a capacitance of a measuring field formed by the measuring electrode (3), a section of the reinforcing steel (2) opposite the measuring electrode (3), the passivation layer (2.1) surrounding the section and the outer concrete layer (1.1) and

a cathode protection current (I _K ) fed into the measuring electrode (3) from the cathode protection current source (9)

- And an evaluation unit (7) for evaluating the measurement with the measuring device (6) detected measuring signals (Sl, S2, S3, Sl ', S2', S3 ').

6. Arrangement according to claim 5,

characterized in that the cathode protection current source (9) as a series circuit of a loadable constant voltage source and a selectable series resistor (9.2) or potentiometer (9.2 ') is formed.

7. Arrangement according to claim 5,

characterized in that the inert measuring electrode (3) is made of graphite.

8. Arrangement according to one of claims 5 to 7,

characterized in that the measuring device (6) comprises at least one analog-to-digital converter and digital measurement signals (Sl, S2, S3, Sl ', S2', S3 ') outputs.

9. Arrangement according to one of claims 5 to 8,

characterized in that the test signal source (8) and / or the cathode protection current source (9) are battery-powered / is.

10. Arrangement according to one of claims 8 to 11,

characterized in that the arrangement comprises a display device provided for the display of digital measuring signals (S1, S2, S3, S1 ', S2', S3 '), one for the storage of digital measuring signals (S1, S2, S3, S1', S2 ', S3 ') seen data storage and a for the transmission of digital measurement signals (Sl, S2, S3, Sl ', S2', S3 ') provided by means of a telecommunications protocol transmission device comprises.