DE102016222538B3 - Method and arrangement for assessing the corrosion and passivation of the reinforcement taking into account the moisture in reinforced concrete - Google Patents

Abstract

The invention relates to a method for determining a state of corrosion and passivation on a reinforced concrete component (1), in which an inert measuring electrode (3) is superficially arranged, an electrically conductive connection to a reinforcing steel (2) is produced, into which an electrical test signal is fed becomes. In the measuring electrode (3), a negative cathode protection current (Ik) is fed. At the measuring electrode (3) are simultaneously a corrosion measurement signal (S1, S1 ') 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 content of the outer concrete layer (1.1) measured. The corrosion measurement signal (S1, S1 ') is compared with a predetermined limit value when the moisture measurement signal (S2, S2') indicates at least a minimum measurement humidity. In addition, the invention relates to an arrangement for carrying out the method.

Description

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.

Further known from the prior art are electrochemical methods such as the electrochemical potential measuring method, in which an electrical voltage between a contacted internal reinforcing steel and the outer surface of a steel-reinforced concrete component is measured, which in the present corrosion typically more negative values than in the present 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.

The 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 method for monitoring the rate of corrosion in a concrete component with an enclosed reinforcement material. The reinforcement material and the concrete form a corrosion half-cell. The reinforcement material is connected via a current meter to a probe having a first annular surface which is covered with a water-absorbing material, for example a sponge. 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 difference in tension between a second annular surface opposing the first annular surface, which is also covered with a water-absorbing material, and the reinforcing material is determined.

The publication DE000002335419 A1 describes a method and an apparatus for measuring the corrosion or corrosion hazard 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 an attached to the surface of the concrete part, serving as the cathode electrode and a power supply is connected directly to the steel reinforcement, a galvanic cell is constructed and loaded with a constant direct current, wherein the Stahlarmierung is connected as an anode, and the potential profile of the Stahlarmierung is registered relative to a reference electrode over a short time before turning on the current period.

The document WO 97/09603 A1 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 such that the same current density acts on the counterelectrode 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 reinforcing 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. The electrical potential of the second reference electrode relative to the reinforcement material is determined and its time course observed.

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 introduce such a contact opening in the reinforced concrete component by boring, impacting or other known from the prior art Abtragsverfahren. 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 reinforcing 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 capability 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.

At the measuring electrode, a negative cathode protection voltage is applied via an ohmic resistor, which 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 of the corrosion measurement signal as well as of all other measured variables 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 injection of the Cathode protection current has. 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 threshold 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 fall of the corrosion measurement signal, such as the slope of a line through the initial value and a second value of the corrosion measurement signal at a predetermined time interval from the initial value or the time constant of a fitted exponential decay, may be used to evaluate the passivation capability the passivation layer are used.

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 pseudo passivation 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 insufficient 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 measuring 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. 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 is also possible to determine whether a cathodic protection current can still be usefully used or if 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. The lower this current is, the better the passivation capability of the passivation layer is formed. 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 penetration 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 passivation layer moisture, the less the amplitude of the test voltage is 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 sufficient humidity 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. In an analogous manner, other predetermined test signal threshold values for other upper voltage values of rectangular test voltages can be determined. 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 has no moisture protection, the moisture in the region of the passivation layer changes the dielectric and thus also the capacitance of the electrolytic capacitor. Thus, from the measurement of the capacitance of the electrolytic capacitor conclusions possible on the moisture in the area of the passivation layer. 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 short message service (SMS) may 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, such as Universal Serial Bus (USB) outputs, which can be used to power electrical meters, such as constant voltage sources or digital multimeter-type meters, without appreciably affecting the 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 displaying 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 measuring signals are known from the prior art, for example as magnetic Hard disks or as solid state disk (SSD) called semiconductor memory known.

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 from the prior 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). 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:

1 schematically a reinforced concrete component with contacted reinforcing steel and measuring electrode,

2 schematically the structure of a test signal source,

3 and 4 schematically the structure of a cathode protection current source as well

5 schematically a measurement record with time course of a corrosion measurement signal, a humidity measurement signal and a protective current measuring signal.

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

1 schematically shows a reinforced concrete component 1 in which a reinforcing steel 2 is enclosed, extending along a longitudinal direction of the reinforced concrete component 1 extends. On the outer surface of the reinforced concrete component 1 is an inert measuring electrode 3 arranged. The measuring electrode 3 can be made of graphite, for example. The measuring electrode 3 can be fixed, for example, as a rod electrode, or even spatially, for example, as a wheel electrode, be formed.

At the interface between the rebar 2 and the outer concrete layer 1.1 is one compared to the outer concrete layer 1.1 very thin, but with good passivating power practically non-porous passivation layer 2.1 educated. An intact passivation layer 2.1 with good passivating effect causes the corrosion protection for the reinforcing steel 2 by preventing or greatly reducing the diffusion of ions and thus the anodic and cathodic sub-process of corrosion.

In the longitudinal direction of the reinforced concrete component 1 and to the measuring electrode 3 is spaced in the reinforced concrete component 1 a contact opening 4 introduced, in which an outer layer of concrete 1.1 so far removed is that the reinforcing steel 2 is accessible. A contact opening 4 can be destructive and with small diameter, for example by drilling or localized impact of the outer concrete layer 1.1 getting produced. By means of one in the contact opening 4 arranged electrically conductive rebar connection 5 is the rebar 2 electrically coupled. Alternatively to introducing a contact opening 4 can the reinforced concrete component 1 an outward, electrically with the inner reinforcing steel 2 having connected contact access, at which the rebar connection 5 is coupled.

A measuring device 6 is electrically between the rebar connection 5 on the one hand and the measuring electrode 3 on the other hand connected. 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 with an evaluation unit 7 so connected that by the measuring device 6 provided measurement signals S1, S2, S3, S1 ', S2', S3 'on the evaluation unit 7 are available as digital, ie time-sampled and amplitude-discretized values. Alternatively, the measured values can also be determined by the measuring device 6 be sent via a telecommunications protocol, for example by e-mail or short message to a mobile phone.

For example, the evaluation unit 7 be designed as a computer, as a notebook or as a netbook to which a Universal Serial Bus (USB) port, an analog-to-digital converter is connected. By means of such an analog-to-digital converter, an analog measured value of a measuring signal S1, S2, S3, S1 ', S2', S3 'generated by the measuring device 6 is converted into a digital signal, that of an evaluation program on the evaluation 7 is evaluable. The evaluation program can be an evaluation unit designed as a computer, notebook or netbook 7 For example, the commercially available program "Realview" from Abacom be used. As an evaluation program, however, other programs or software products can be used, with which digital signals recorded, whose timing graphed and such digital signals can be stored.

With the rebar connection 5 is also a test signal source 8th electrically connected, the one electrical test signal in the reinforcing steel 2 feeds.

The structure of the test signal source 8th is described below on the basis of 2 explained in more detail.

The test signal source 8th includes 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 via the electronically switchable switch 8.2 with the non-inverting input of an operational amplifier 8th .5 connected. The electronically switchable switch 8.2 is operated by a square wave signal coming from the square wave source 8.3 is generated. Preferably, the square wave signal has a frequency of 10 Hertz, that is a period length of 100 Milliseconds, up.

The output of the operational amplifier 8.5 is fed back to the inverting input, giving the operational amplifier 8.5 works as an impedance converter. This ensures that the test signal at the output 8.6 the test signal source 8th regardless of the load on the first constant voltage source 8.1 set test voltage U _p . 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. Low power amplifiers are known in the art.

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

Thus, the test signal source generates 8th at the exit 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 or passivation layer 2.1 between the rebar 2 and the concrete of the outer concrete layer 1.1 of the reinforced concrete component 1 in a characteristic way to the measuring electrode 3 on the surface of the reinforced concrete component 1 ,

With the measuring electrode 3 is also a cathode protection current source 9 electrically connected, the a cathode protection current in the measuring electrode 3 feeds. The structure of the cathode protection current source 9 is described below on the basis of 3 explained in more detail.

The cathode protection current source 9 includes a second constant voltage source 9.1 , each with a first end of at least two series resistors 9.2 connected to 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 also includes a selector switch 9.3 that the exit 9.4 selectable with the second end of exactly one series resistor 9.2 combines. Thus, the output 9.4 the cathode protection current source 9 with a selectable ohmic resistor with the second constant voltage source 9.1 connectable. Will this output 9.4 with the measuring electrode 3 on a reinforced concrete component 1 connected, which has sufficient humidity for ion transport, so can by means of the selectable Vorwiderstands 9.2 one through the measuring electrode 3 driven current can be adjusted. The cathode protection current source 9 thus acts approximately as a power source with a via the resistor 9.2 adjustable current.

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

Is the measuring electrode 3 above an active corrosion site 10 at the rebar 2 arranged so engages that of the cathode protection current source 9 into the measuring electrode 3 fed, by selecting the Vorwiderstands 9.2 adjustable cathode protection current I _K active in the corrosion process and thus influences the corrosion measurement signal, provided the outer concrete layer 1.1 has a sufficient minimum measuring 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 moisture in the passivation layer 2.1 ,

By adjusting the cathode protection current I _K , that of the cathode protection current source 9 is discharged, the inventive method is therefore suitable, different degrees of moisture of examined reinforced concrete components 1 To compensate and thus moisture-independent comparable measured values to capture, as long as a certain, for a minimum conductivity of the outer concrete layer 1.1 and the passivation layer 2.1 indispensable minimum humidity is given. Such a minimum moisture can be achieved by a known from the prior art humidification of the surface of the reinforced concrete component 1 always achieve, so that the process is universally applicable in principle.

When used on a reinforced concrete component 1 with unknown humidity that of the cathode protection current source 9 delivered cathode protection current I _{K set} so that a predetermined ion mobility is achieved, which corresponds to a predetermined nominal reference humidity range. The achieved ion mobility can be read from the measurement signal S2, which is from the measuring device 6 is won. 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 ,

The following is based on an in 5 schematically illustrated Messschriebs 11 the extraction of the measurement signals S1, S2 and S3 explained in more detail. The measurement record 11 represents along a time axis t a first measurement duration T with measurement signals S1, S2 and S3 and a second measurement duration T 'with measurement signals S1', S2 'and S3'. The first measurement duration T corresponds to a measurement on a reinforced concrete component 1 with existing corrosion, so with inadequate passivation. The second measurement period T 'corresponds to a measurement on a reinforced concrete component 1 without corrosion, so with sufficient passivation.

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

A good passivation represents a barrier to the passage of iron ions. In the detection of the corrosion measurement signal S1, S1 'be by means of the measuring device 6 the electric charges of iron ions that covers the passivation layer 2.1 pass. These charges form an associated size with the iron ions. Many iron ions pass through the passivation layer 2.1 and then through the outer concrete layer 1.1 , so many loads are free. 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 S1, S1 'indicates the measured voltage, which is a measure of the number of charges and thus of the number of iron ions, which is the passivation layer 2.1 and the outer concrete layer 1.1 pass through and from the measuring electrode 3 to be picked up.

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 from the inert measuring electrode 3 is formed, and a second electrode made of reinforcing steel 2 is formed. Thus, the whole of the measuring electrode can be 3 , the passivation layer 2.1 , the outer concrete layer 1.1 and via the rebar connection 5 contacted reinforcing steel 2 as an electrolytic capacitor, whose capacity depends on the moisture in the concrete layer 1.1 , in particular 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 sufficient. For example, a humidity sufficient for the evaluation of the corrosion measurement signal may be assumed to be at one of the first constant voltage source 8.1 the test signal source 8th delivered test voltage of +400 millivolts a humidity measurement signal S2, S2 'of at least +385 millivolts is measured. Particularly preferably, a moisture sufficient for the evaluation of the corrosion measurement signal is assumed if a moisture measurement signal S2, S2 'of at least +390 millivolts is measured. Thus, in case of insufficient moisture, the reinforced concrete component 1 moistened, for example, be sprayed with water. After a short wait, the externally applied water is in the outer concrete layer 1.1 and further into the passivation layer 2.1 penetrated and it can be carried out a new measurement. If necessary, this procedure is repeated until a reliable measurement with sufficient humidity can be made.

Furthermore, the measurement record 11 the protection current measurement signal S3, S3 ', that of the cathode protection current source 9 fed cathode protection current I _K indicates. 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 a corresponding to the external electron demand cathode protection current I _K.

LIST OF REFERENCE NUMBERS

1

 Reinforced concrete component

1.1

outer concrete layer

2

 rebar

2.1

passivation

3

 measuring electrode

4

 contact opening

5

 rebar connection

6

 measuring device

7

 evaluation

8th

 test signal source

8.1

first constant voltage source

8.2

electronically switchable switch

8.3

Square wave generator

8.4

Pull-down resistor

8.5

operational amplifiers

8.6

output

9

 Cathodic protection current source

9.1

second constant voltage source

9.2

resistors

9.2 '

potentiometer

9.3

selector switch

9.4

output

10

active corrosion site

11

measurement plot

U _p

Test voltage

U _K

constant voltage

I _K

Cathodic protection current

R _PD

Pull-down resistance

S1, S1 '

Corrosion measuring signal, measuring signal

S2, S2 '

Humidity measurement signal, measurement signal

S3, S3 '

Protective current measuring signal, measuring signal

T

 first measurement period

T '

second measurement period

t

 timeline

Claims (10)

Method for assessing the corrosion state and for determining the passivation capacity of a passivation layer ( 2.1 ) around a rebar ( 2 ) of a reinforced concrete component ( 1 ), characterized in that - an inert measuring electrode ( 3 ) on the surface of the reinforced concrete component ( 1 ), - by means of a rebar connection ( 5 ) an electrically conductive connection to one of the reinforced concrete component ( 1 ) enclosed reinforcing steel ( 2 ), - an alternating electrical test signal by means of a test signal source ( 8th ) comprising a first constant voltage source ( 8.1 ) and a switching device ( 8.2 ) in the contacted reinforcing steel ( 2 ), - into the measuring electrode ( 3 ) from a second constant voltage source ( 9.1 ) with a constant cathode protection voltage (U _K ) via an ohmic resistor ( 9.2 . 9.2 ' ) a negative cathode protection current (I _K ) is fed, - at the measuring electrode ( 3 ) simultaneously - a corrosion measurement signal (S1, S1 ') for determining the charges of 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 ) and - the corrosion measurement signal (S1, S1 ') is compared with at least one predetermined limit value if the moisture measurement signal (S2, S2') indicates at least a minimum measurement humidity. Method according to claim 1, characterized in that the device (in 3 ) Fed cathodic protection current (I _K) to protect current measurement signal (S3, S3 ') is measured and the foreign electron supply required (for preventing the anodic and cathodic partial processes of corrosion of the reinforcing steel 2 ) is determined. Method according to claim 2, characterized in that that of the second constant voltage source ( 9.1 ) supplied to the feed of the cathode protection current (I _K ) constant cathode protection voltage (U _K ) minus 400 millivolts. Method according to one of the preceding claims, characterized in that the test signal is a square wave signal with an upper voltage value of 400 millivolts, a lower voltage value of 0 millivolts and a period length of 0.1 second. Arrangement for carrying out a method according to one of the preceding claims, comprising - one for the arrangement on the surface of a reinforced concrete component ( 1 ) provided inert measuring electrode ( 3 ), - one for electrical connection to a rebar ( 2 ) in the reinforced concrete component ( 1 ) reinforcement connection ( 5 ) - one for the generation and supply of a test signal in the reinforcement connection ( 5 ) provided test signal source ( 8th ), - one for the generation and feeding of a cathode protection current (I _K ) into the measuring electrode ( 3 ) provided cathode protection current source ( 9 ) comprising the second constant voltage source ( 9.1 ) and at least one with the second constant voltage source ( 9.1 ) connectable ohmic resistor ( 9.2 . 9.2 ' ), - a measuring device ( 6 ) for the simultaneous detection of - a corrosion measurement signal (S1, S1 ') for measuring charges of ions which are present at the measuring electrode ( 3 ) are collected, - a moisture measurement signal (S2, S2 ') for measuring a capacitance from the measuring electrode ( 3 ), one of the measuring electrode ( 3 ) opposite section of reinforcing steel ( 2 ), the passivation layer surrounding this section ( 2.1 ) and outer concrete layer ( 1.1 ) formed measuring field and - one in the measuring electrode ( 3 ) from the cathode protection current source ( 9 ) fed cathode protection current (I _K ) - and an evaluation unit ( 7 ) for evaluation with the measuring device ( 6 ) detected measurement signals (S1, S2, S3, S1 ', S2', S3 '). Arrangement according to claim 5, characterized in that the cathode protection current source ( 9 ) as a series connection of the loadable constant voltage source ( 9.1 ) and a selectable series resistor ( 9.2 ) or potentiometers ( 9.2 ' ) is trained. Arrangement according to claim 5, characterized in that the inert measuring electrode ( 3 ) is made of graphite. 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 (S1, S2, S3, S1 ', S2', S3 ') outputs. Arrangement according to one of Claims 5 to 8, characterized in that the test signal source ( 8th ) and / or the cathode protection current source ( 9 ) are battery powered / is. Arrangement according to one of Claims 8 or 9, characterized in that the arrangement has 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 ') and a transmission device provided for the transmission of digital measurement signals (S1, S2, S3, S1', S2 ', S3') by means of a telecommunications protocol.

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