SI22559A - Sensor, device and procedure for determination of corrosion speed of metal reinforcement in reinforced concrete structures - Google Patents

Abstract

Measurement of corrosion speed of steel reinforcement in concrete by means of built-in electrical resistance sensors (1) is based upon the measurement of change of electrical resistance, which is the result of reduction in conductor thickness (11', 12') of corrosion-exposed electrically conductive elements of a sensor (1), whose material has similar corrosion properties than the steel reinforcement built into concrete (9). A device according to the invention comprises sensors (1) in the Wheatstone bridge configuration, where two electrically conductive elements (11, 12) with resistance (Rx) are exposed to corrosion and the remaining two elements (13, 14) are protected against corrosion and are representing the reference resistance (R). Thanks to the sensor's (1) design, whose elements (11, 12; 13, 14) consist preferentially of thin sheet metal or a conductive layer in the form of a printed circuit board, it minimises temperature effects and enables a high resolution when measuring changes in thickness. The structure of the sensor (1) enables also a relatively easy installation into concrete (9) and this e.g. also into hardened concrete (9) of already existing reinforced concrete works, and besides, among others, also monitoring of corrosion under cathode protection conditions, where the sensors (1) may be polarised by the protection potential. The measuring device according to the invention enables a simple measurement of all required parameters, whereas the measuring procedure itself, which is preferentially executable by using a respective software, enables the calculation of changes in thickness of conductors (11', 12') of sensor's (1) elements (11, 12) and thus the determination of corrosion speed with time. Monitoring of corrosion speed with time enables, among others, also the estimation of kind of corrosion and by this monitoring both of steady corrosion and pitting corrosion. The comparison of calculated corrosion speeds of individual sensors (1) is the basis for the estimation of current endangerment of reinforced concrete works by corrosion and for the locating of critical areas. By knowing respective basic data of a structure, the measuring results from a sensor (1) network enable also the prediction of the remaining life of a construction works.

Description

In the field of physics, the invention deals with the investigation and analysis of materials based on the determination of physical or chemical properties, in particular the determination of the resistance of the material to weathering and corrosion, and more specifically the measurement of corrosion rates of metal reinforcement in reinforced concrete structures.

The invention is based on the problem of how to design a sensor for determining the corrosion rate of metal reinforcement in reinforced concrete structures, which will be dimensionally large and simple for mass production as well as for safe and reliable installation of choice or in non-solid concrete already in the stage of construction reinforced concrete structures or in hardened concrete of any pre-existing reinforced concrete structure, and at the same time the sensor as such should be sensitive enough to perform single, occasional or permanent measurements with as high a precision as possible. At the same time, the object of the invention is to provide a method for measuring the corrosion rate of metal reinforcement in newly constructed or existing reinforced concrete buildings, and in this connection also a device that will allow such a process to be performed and thus to measure the corrosion rate at a large number of locations in the reinforced concrete object chosen at any one time, by providing the same temperature to the corrosion-exposed elements and reference elements in the concrete and being able to differentiate between conventional even corrosion and pit corrosion.

In order to monitor the condition of the metal reinforcement in reinforced concrete structures or to change the corrosion velocity of the steel reinforcement, a number of corrosion measurement methods have been developed, including corrosion monitoring devices. Electrochemical methods, such as e.g. potential network measurement, electrochemical linear polarization, galvanostatic pulse method, or galvanic current measurement. With these methods it is possible to measure the electrochemical parameters and to estimate the current corrosion rate. The errors in these measurements are relatively large, since the measured values are influenced by many factors, such as e.g. quality of electrical contact, electrical resistance of concrete, temperature and effective surface of active corrosion area. Given that the current corrosion activity of steel varies relatively rapidly depending on the moisture and oxygen content of the concrete, in general, even for several size classes, electrochemical methods can give very inaccurate results when evaluating for a longer period of time.

Thus, e.g. U.S. Pat. No. 4,703,255 (Strommen) describes a sensor consisting of two identical metal rods of different materials, which are spaced apart from one another by means of electrically non-conductive spacers, during the construction of a reinforced concrete object. The material of one of the bars corresponds respectively. is similar to reinforcement material. Electrical conductors are connected to the rod, which lead to a voltage meter located outside the reinforced concrete building. Regardless of the fact that this kind of sensor is intended for installation at the construction of the building and is also inapplicable for later installation in solid concrete or. Due to the measurement of the stress potentials on both bars in concrete, it is in principle possible to conclude on the corrosion rate of the reinforcement, but the accuracy of the measurement itself is influenced by many factors. Due to the dimensionality of the sensors, it is possible to incorporate a maximum number of sensors into each object, which detect the condition at only some points of the object, in which the conditions for the emergence or. corrosion progression can be very different. On the other hand, the possible effects of the materials of the electrical conductors themselves on contact with the bars, the insulation in wet concrete of at least theoretically electrically non-conductive spacers and the like, are questionable.

Further, U.S. Pat. No. 5,259,944 proposes a device comprising a voltage meter and a concrete surface in which the reinforcement is mounted, an external electrode mounted, and a centrally arranged counter electrode including two reference sensors. In doing so, they measure the polarization resistance in the observed area of the concrete, from which they then conclude on the corrosion of the reinforcement. Although measurements are also possible on existing facilities, they depend on many conditions and are therefore relatively inaccurate and unreliable.

Further, EP O 364 841 (STRABAG BAU-AG) proposes a device comprising a plurality at different depths of reinforced concrete construction of embedded anodes of material corresponding to the reinforcement material as well as a cathode of corrosion-resistant material. The anodes mentioned are connected to an available current meter by means of a non-concrete structure. The cathode can be connected to the associated anode, which is separated from it by an electrical insulator. The current meter measures the current in proportion to the corrosion of the reinforcement. Thus, it is possible to determine, in particular, if carbonation or contamination with chlorides occurs in the concrete, which in particular promotes the progress of corrosion. In such cases, the device can be used for the needs of the so-called polarization, when by supplying the appropriate electric charge or. currents in the armature seek to compensate for differences in electrical potentials, thereby halting corrosion. Sensors of this type are also intended for installation in the stage of construction of reinforced concrete construction or. object. However, the occurrence of carbonation or contamination with chlorides can also be extremely local in nature, so it does not have to occur in the area where the sensors are installed.

Due to a number of advantages, electrical resistive sensors, including modified versions with improved temperature compensation and resolution, have been largely implemented in industrial methods and corrosion monitoring devices.

Thus, in U.S. Pat. No. 4,703,253 (Strommen), it is proposed that the same arms of the material from which the reinforcement is made be incorporated into the concrete already in the loop during the construction of the object. Unlike the rest of the arm, one of the arms is protected against corrosion. As the latter limb eventually corrodes over time - presumably at about the same speed as the reinforcement itself - it increases its electrical resistance by reducing the cross-section, which can be compared by measuring the resistance of the reference, anti-corrosion arm. This sensor is also relatively large in size because it is preferably made of reinforced steel 6 12 mm in diameter in the form of an elongated loop of length from 90 cm to 6 m and is therefore suitable for maximum installation solely in the stage of construction of reinforced concrete construction or. object. Even in such cases, in some buildings, such as, for example, bridges, tunnels, nuclear power plants or radioactive waste landfills, because of the density of reinforcement, where the raster often does not exceed 100 x 100 mm, the possibility of installing such sensors is very limited. In this case, too, it is necessary to consider the possibility of installing only a relatively small number of sensors in the object, which again allows rather inaccurate monitoring of corrosion over a larger surface and only in some locations on the object, while the actual conditions and conditions for the emergence and progression corrosion in different areas of reinforced concrete structures can vary greatly.

4.

As mentioned earlier, a size sensor of this type is suitable only for installation in concrete during the construction of new structures with a previously defined method for monitoring the corrosion of reinforcement in concrete. However, given the dimensions of the sensor, it is difficult to ensure the same temperature of the corrosion-exposed elements and the reference, anti-corrosion protection elements in the concrete during use. Resistors of long sensors may be unevenly exposed to corrosion in concrete, so the measured values give only a rough average of corrosion activities. Due to their relatively large dimensions, the sensitivity of these sensors to extremely local corrosion (pit corrosion) is also quite limited.

For more complex reinforced concrete structures (viaducts, bridges, tunnels, load-bearing structures in industry, nuclear power plants, radioactive waste landfills), the load-bearing steel reinforcement grid is relatively dense (in any case less than 100 x 200 mm) and the diameter of reinforcing bars is relatively large (usually ranging from 25 to 40 mm), which makes it practically impossible to install larger sensors. It is also not possible to install sensors of such large dimensions in solid concrete of old, already existing structures.

Further, US 6,282,671 proposes a sensor consisting of a hollow stem, on which two e.g. by means of a thread, against each other, a movable flange, between which is inserted a series of alternately arranged electrically conductive rings and electrical insulators, each of said rings connected via an appropriate electrical conductor to a measuring instrument arranged outside the object. Before installing the sensor in concrete, a hole is inserted into which a stem with said rings and insulators is inserted. After tightening the nut or threaded bushing, the rings open and thus contact the well wall in the concrete. The sensor is undoubtedly also embedded in solid concrete of pre-existing reinforced concrete structures. At the same time, it is extremely complex to manufacture, and at the same time, use is associated with a relatively high probability of failure or other complications. The plurality of electrical conductors inside the stem are, on the one hand, bound by the space constraints arising from the diameter of the stem or the stem. the diameter of the hole itself, but on the other hand, a pair of wires must be counted for each ring. To measure corrosion rates at greater depths, the length of the stem is relatively large, and so is the number of rings and wires. The risk of any of the wires being damaged during insertion of the sensor into the well or later in the process of measuring corrosion is therefore extremely high. One of the further disadvantages of such sensors is that they are suitable for installation in appropriate wells in hardened concrete of already existing structures, but not for installation in still uncured concrete during the construction phase of the building itself.

Sensors must be relatively small in order to be installed in fresh concrete with a dense screen of reinforcement. This is even more important for construction in hardened concrete, since proper geometry is essential for good physical and electrochemical contact with hardened concrete. The geometry of the blades must also allow for installation at any depth. The corrosion properties of the sensor material must be identical to, or at least very similar to, the corrosion properties of reinforcing steel, and the other embedded materials must be durable in concrete. The dimensions of the electrical conductors must ensure adequate resolution of the measurement of thickness changes and at the same time a sufficient lifetime of the sensor. The sensor must be sensitive to local corrosion (pit corrosion), and the measurement procedure itself must be able to distinguish between even and pit corrosion. The measurement procedure must also ensure that the change in sensor thickness, corrosion velocity and the elimination of temperature influence are adequately calculated.

The requirements described above have been met by a new flat sensor design where the metal elements of the sensor are fabricated by a photochemical process. Given that the metal layer is not made by evaporation but from sheet metal, the corrosion sensitivity is very similar to that of reinforcement due to the unchanged crystal structure. The geometry of the electrical conductor in each element (width to height ratio) provides an adequate response to even and pitting corrosion. The design of the sensor allows to ensure temperature balance, or to compensate for temperature changes. The parasite resistance (contacts, electrical conductors) is also minimal. The design also allows the sensor to be easily installed in fresh or hardened concrete at the selected location and depth. A sufficient length of electrical conductor, or its electrical resistance, allows for high measurement resolution. The associated measuring system (bipolar current generator) ensures that sensor elements are not polarized during the measurement process to the extent that this would affect the corrosion process. Appropriate software makes it easy to calculate the change in thickness of electrical conductors and additional analysis to calculate corrosion velocity and estimate the type of corrosion.

Since the long flat conductor cannot technologically be shaped into a suitable shape on a small surface, it is possible to choose a suitable thin sheet or foil (150 to 270 pm thick) with similar corrosion properties to the material whose corrosion rate is to be measured (steel reinforcement). By laminating the sheet metal onto the substrate (glass fiber reinforced epoxy laminate), it is possible to construct a rigid load-bearing structure based on the future conductors of the corrosion-exposed and reference resistances of the ER sensor. ER sensor sensors are designed to be precisely machined by etching, just like printed circuits in electronics. The shape of the resistors of the preferred sensor design provides a sufficiently large corrosion-exposed surface, and the small external dimensions allow the installation of ER sensors in a 75 mm bore in concrete of old structures at any distance from the surface in the concrete overlay and between the steel reinforcement. The sensor design, in accordance with a further embodiment, permits installation during reinforcement with a 100 x 100 mm screen.

To determine the corrosion rates of steel and to detect the carbonation / penetration of chlorides, the sensors are installed at different depths (with a cover layer of concrete from 5 to 50 mm, or up to the depth of the steel reinforcement). To detect the beginnings of contamination and degradation of concrete, and thereby initiate corrosion processes, the sensors should be installed closer to the surface.

In the foregoing, the invention relates primarily to a corrosion rate sensor for metal reinforcement in reinforced concrete structures based on the determination of the resistance of at least one electrically conductive element in corrosion and the corrosion of an electrically conductive element with respect to the reference resistance of at least one electrically reinforced concrete, but corrosion protected conductive element.

The sensor according to the invention comprises at least one electrically non-conductive load-bearing plate on which at least one highly flattened, corrosion-exposed electrically conductive element is mounted with a zigzag conductor of extremely small cross-section and a relatively large resistance, with respect to the surface available at all times, of sufficiently high resistance. as well as at least one substantially flattened, corrosion-protected electrically conductive reference element with a zig-zag cross-section of an extremely small cross-section and, with respect to each available surface, of extremely long length corresponding to a high reference resistance, the material of said electrically conductive elements identical to, or at least approximately equivalent to, the material in the concrete of the reinforcement and, wherever available, the elements are connected to the electrical circuit.

The carrier plate is preferably a relatively rigid plate of relatively small dimensions, which is provided with openings for receiving the electrically conductive lot and, if necessary, the conductor cable of the sensor cable and may conveniently consist of laminated glass epoxy material. The conductor of the electrically conductive element mounted on the electrically non-conductive plate is advantageous, in particular, thanks to the simplest method of construction, designed with a profile or profile. a cross-section in the form of a trapezoid that is narrowed in the direction away from said plate. Said conductor for each electrically conductive sensor board mounted on the electrically conductive element preferably consists of cold-formed metal material which is identical, or at least approximately, to the material in the concrete of the available reinforcement. Thus, said conductor of the electrically conductive element mounted on an electrically non-conductive plate most preferably consists of a photochemically treated metal sheet or other metallic material which is electroplated, vaporized or otherwise applied directly to the surface of the support plate and which is identical or. its composition at least approximately corresponds to the material in the concrete of the available reinforcement.

According to a preferred embodiment of the sensor according to the invention, such sensor comprises a corrosion-resistant pair of non-shielded electrically conductive elements with a corrosion-dependent variable resistance, as well as an electrically coupled pair of anti-corrosion protected reference elements with a reference resistance. In this connection, the two pairs of adjacent and interconnected elements can be electrically connected via the Wheatston jumper and in such a connection can be connected to the available external electrical circuit through the connecting cables. Each of said elements can be electrically connected in each area within the area of the electrically conductive lot, which is available in the corresponding opening in the electrically non-conductive support plate, thus obtaining generally non-separable electrical contacts. Two of the element contacts mentioned are intended to be connected to the conductor of the electrical cable to connect the sensor to the available electrical circuit, one of them being provided in the corrosion zone of the exposed elements and the remaining contact in the corrosion protection zone of the protected elements.

In one possible embodiment of the sensor according to the invention, all electrically conductive elements are arranged on the same side of the electrically non-conductive support plate. In a further embodiment of the sensor according to the invention, it is contemplated that the electrically conductive variable-resistivity elements exposed to corrosion are arranged on one side of the electrically non-conductive support plate, and the electrically conductive reference elements with the corrosion-resistant non-exposed reference element are available they are arranged on the opposite side of that tailored carrier plate.

Furthermore, electrically conductive reference elements and other electrically conductive parts, including in the area of the support plate, are each provided with conductors of electrical cables, but in any case, with the exception of corrosion-exposed elements with resistance varying over time depending on corrosion, are electrically conductive coated. protective layer.

The insulating protective layer available at all times is available as a solid or plastic layer of electrically conductive or poorly conductive material. Furthermore, in the case of the sensor according to the invention, the corrosion-exposed elements in the position of installation in the concrete are always facing the outer surface of the reinforced concrete element. In a further version of the sensor according to the invention, the exposed corrosion-exposed elements are cathodically shielded at each time, with sensors connecting terminals available at each time interval, at which corrosion velocity measurements are carried out at desired intervals, using a connector to contact the elements. variable and reference resistances on the sensors are short-circuited, and the electrical contacts of this connector are connected to the available conductor, which is in electrical contact with the steel armature ie a cathode embedded in concrete, the aforementioned connector being disconnected or otherwise engaged during the measurement of corrosion rates.

The invention also provides a device for determining the corrosion rate of metal reinforcement in reinforced concrete structures based on the determination of the resistance of at least one electrically conductive element in corrosion and the corrosion of the electrically conductive element, with respect to the reference resistance of at least one electrically conductive but also corrosion protected electrically conductive element. Such an apparatus according to the invention comprises at least an electrical resistance meter which is electrically connectable to the number of sensors selected by the electrical cables according to the previously described characteristics. The device comprises a finite and predetermined number of sensors installed at different locations and at different depths, or in corresponding wells in the hardened concrete of an existing pre-existing reinforced concrete structure or in non-hardened concrete of a pre-fabricated reinforced concrete object, with electrically conductive elements exposed to corrosion. with resistance arranged on the side of the sensor support plate facing the outer surface of the reinforced concrete object. The sensors of the device according to the invention are arranged in the concrete so that they run at least substantially parallel to the reinforcement embedded in the concrete.

The device according to a preferred embodiment of the invention is battery-powered and contains a current generator and a suitable combination of voltage preamps, the current generator being adapted to provide a constant source of the bipolar electric current selected in two directions, while the voltage preamps are provided to amplify the voltage drop at sensor and voltage differences to a readable level with a hand-held voltmeter.

Furthermore, a variant of the device which is connected to the electrical circuit of the already existing cathodic protection of the reinforcement in the concrete of the existing reinforced concrete object and adapted to measure the change in corrosion resistance of the exposed elements after preliminary shutdown for cathodic protection of the intended electrical circuit is also provided.

The subject of the invention is also a method of determining the corrosion rate of a metal reinforcement in reinforced concrete structures on the basis of determining the resistance of at least one electrically conductive element in the concrete and the corrosion of the reference resistance of at least one also of the electrically conductive shielded concrete in the concrete. In this connection, sensors connected to the measuring device in accordance with the above described characteristics shall also be installed either in uncured concrete or in the corresponding holes in the hardened concrete of the already existing reinforced concrete object in accordance with the above described characteristics, so that the exposed electrically conductive elements are exposed to the corrosion. surface of the concrete and run at least approximately parallel to the reinforcement. Thereafter, in the case of installation in the hardened concrete of said borehole, it is filled with concrete, the structure of which corresponds to the same place before the borehole is made available to the concrete, and electrically connected outside the concrete to the connecting cable within the said measuring device. The process of the invention comprises steps

i) determining the voltage difference between the two branches, namely, the first branch where the drop across the two branches is measured, and the second, where the difference of the drop between the corrosion variable resistance and the reference resistance is measured, sending a constant current of a certain value passing through the circuit the two branches are identical, which is done by the formulas u = («, + *) j

Δ1 / = (ί, - / ί) ί

Δί / _ AT?

In ~ 2R + LR tsR

2u

-m

AU

In _R ^^ _R

S-AS l-u

S ii) detecting the change in the cross-sectional area of the resistor by the formulas

c Λ ( (R Ί 1 R , R Δ5 - S 1 = S = S i - = - t R + & R) _{R +} ² R k l-u J <1-M 7

iii) determining the conductor thickness reduction factor for the corrosion of electrically conductive elements exposed by the formula

AKJ er means d, - the difference in the amount of - the thickness (d = c _Nekor -) d ₂ - the difference in the width of d>

d 'by measuring the geometry of the corroded and non-corroded sensor specimens for each series of sensors, by examining the cross-section of the conductors of corrosion-exposed elements on a metallographic microscope and by examining the surface on a line electron microscope, taking into account the method of fabrication of the sheet, in particular e.g. in the case of cold rolling and the corresponding cold-deformed microstructure similar to that of reinforcing steel, whereby crystalline grains are flattened and therefore exposed to corrosion by the sensor conductors corrode more rapidly in width than in height or. thickness;

iv) determination of the surface of the trapezoidal profile of conductors of corrosion-exposed electrically conductive sensor elements by the formulas e (a + b \ ^S ° ~ T ~ sin /? = - x sin β

AS = S _o - S,

C sin β - - d

AS ₌ (a + b) c | (α + ά-4χ) _ _d _ (a + b) cl sin /? J

2 ^kx · Δ5 = (a + b ~) c - (a + b- 4x) (c - J,) = 4 ^ (cd,) + <i, (e + i.) Sin p

4d

2 · Δ5 = J, (a + b) + - (c-d ^ sin /?

where, taking into account the thickness reduction factor:

d ₂ = A-dj 4d

2-AS = - (c-dj) + dda + b) sin p ₌ )! </, (A + b) sin p sin /? <son /?

and where a is the shorter side of the trapezoidal profile of the conductors of the elements on the corrosion exposed side, b the longer side of the trapezoidal profile of the conductors of the elements on the corrosion exposed side, c the height of the trapezoidal profile d the oblique side of the trapezoidal profile di the difference in height d _{2 the} difference in width β as between pages d and b and at the same time

% represents the ratio d ₂ x = sin β

v) determining the difference in height or the thickness of the corrosion conductors of the electrically conductive sensing elements of the formulas d, =

sin /?

32-Δ5-Λ sin /?

where, given that:

Δ5 = 5

2u i? «

4Ac son /?

+ a + b ± '

4Ac son /?

x2 32-S

2u son /?

8A son /?

based on the observed voltage difference given by the formula

AU and vi) based on the change in thickness of the individual sensor (1) within the said device also a step of determining the type of corrosion.

The invention will now be explained in further detail by way of example examples and in connection with the accompanying drawing showing

FIG. 1 is an example embodiment in perspective of an illustrated sensorium according to the invention,

FIG. 2 shows electrically conductive parts belonging to the lower surface of the sensor according to FIG. 1;

FIG. 3 is a sensor according to FIG. 1 in the installed state and in the longitudinal section in the plane III - III according to FIG. 1;

FIG. 4 is a schematic illustration of a design of a sensorium as part of a device according to the invention;

FIG. 5 is a further variant of the sensorium of FIG. 4 as belonging to the device according to the invention;

FIG. 6 is a schematic view of geometric starting points for determining the corrosion rate; and FIG. 7 is a graphical representation of the thickness reduction of the electrically conductive portion of the sensor.

In FIG. 1 is an exemplary sensor 1 according to the invention, which basically consists of an electrically non-conductive support plate 90 and four electrically conductive elements 11, 12, 13, 14, which are electrically connected in a manner which will be explained in more detail below.

The carrier plate 10 is preferably made of an electrically insulating epoxy laminate. Each of the aforementioned electrically conductive elements 11, 12, 13, 14 preferably consists of a material corresponding to the material from which the reinforcement of the reinforced concrete structure is derived, which is intended to measure the corrosion rate. Each of said elements 11, 12, 13, 14 exhibits a certain electrical resistance, with two elements 11, 12 having corrosion resistance R _x and the remaining two elements 13, 14 with R resistance being protected against corrosion. Typically, the sensor according to the invention is that each of said electrically conductive elements 11, 12, 13, 14 is designed as a flat element with respect to the width of the extremely small thickness, whilst taking into account the long-range possibilities given each time. Thanks to this design of the elements 11, 12, 13, 14, the electrical resistance R or. R _x can be relatively high, but at the same time the reduction in thickness as a result of corrosion has a considerable effect on the change in resistance, which on such a basis is then certainly easier to measure with high accuracy.

The corrosion rate measuring device according to the invention consists of a corresponding number of basic measuring sensors 1, each sensor 1 consisting of four extremely thin and flat electrically conductive elements 11, 12, 13, 14, which are electrically connected to the Wheatston bridge and are two electrically conductive elements 11, 12 are exposed to corrosion and represent variable resistance R, while the remaining two elements 13, 14 which represent reference resistance R are protected against corrosion.

Sensor 1 with such conductive elements 11, 12, 13, 14 forming electrical resistors R, R _{x is} , in principle, practicable in at least two ways, either by means of only one electrically conductive panel 10 (Fig. 1), which parts 11, 12, 13, 14 are mounted bilaterally, or by means of said non-conductive plate 10 and another additional electrically non-conductive plate 10 '(Fig. 5) such that the insulated parts 13,14 are inserted between said plates 10 , 10 '.

Thus, for example, at sensor 1 of FIG. 1 shows corrosion-exposed parts 11, 12 representing resistors R _x arranged on the upper side of electrically non-conductive, in particular laminate support plates 10, while the remaining conductive parts 13,14 representing reference resistors R and shown separately in FIG. 2, are located on the underside of the carrier plate 10. The parts 11, 12, 13, 14 forming the electrical resistors R and R _x are connected to the Wheatston bridge with corresponding lots 3 through the corresponding holes 2 such that in FIG. 1 shows the contacts A, B, C, D, E and F in the resistors R _x associated with the contacts in FIG. 2 denoted by A ', B', C ', D', E 'and F' and belong to resistors R.

Sensor 1 is in the built-in state, namely either already in the construction phase of the building or afterwards incorporated in concrete 9, shown in FIG. 3. On the upper side, in the present case, of the two-layer insulating panel 10, resistors R _{x are} formed from the conductive elements 11,12. Plate 10 provides openings 2 for soldering, which are filled with electrically conductive lot 3 during assembly of sensor 1. On the underside of electrically non-conductive plate 10 there are electrically conductive elements 13, 14 forming the reference resistors R. In other words, there is a lot 3, which also contains a conductor 4 of the connecting cable 5. On the upper side of the panel 10, all the surfaces intended for soldering, including the lots 3, are coated with an anti-corrosion protective layer 6 of epoxy resin. Also, on the underside of panel 10, the entire surface of the elements 13,14, and thus the resistors R, including lots 3 and non-insulated portions of the conductors 4, is protected by a suitably thick epoxy resin layer 6.

With sensor 1 constructed in this way, it is possible to calculate with external dimensions, not including the connecting cable 5, approximately 50 x 30 x 3 mm, with the total corrosion exposed surface of the two resistors R _x measuring approximately 7.5 cm ² .

A further version of the sensor is shown in FIG. 5. The flat electrically conductive elements 11, 12, 13, 14 forming the resistors R _x and R of sensor 1 are fabricated on the insulating panel 10 of glass-epoxy laminate one-sided. Only the parts 13, 14, which represent the reference resistors R, are also corrosion-protected on the upper side of the side with an additional layer 7, which in this case consists of a glass epoxy laminate. Contacts A, B, C, D, E and F for soldering the connecting cable 5 and the associated part of the connecting cable 5 are coated with a protective layer 6, which in this case consists of a permanently elastic sealant. In this case, the external dimensions of sensor 1 without the connection cable 5 are, for example, 87 x 53 x 3.5 mm. This version of the sensor 1, compared to the previous one, is a simplification, especially in the view of even simpler construction, with a slight increase in the external dimensions at the same resistances R _x and R.

The following will describe in more detail the use or usage. installation of sensors 1.

When installing sensors 1 in fresh concrete during the construction of the respective reinforced concrete structure or. the construction of the new facility, the sensors are fixed to the desired location before concreting. For the purpose of determining the corrosion rates of steel and detecting the carbonation / penetration of chlorides, the sensors are installed at different depths (with a cover layer of concrete from 5 to 50 mm, or up to the depth of the steel reinforcement position). They can be fastened to the surface of reinforcement bars or to special supports, which provide a reasonable distance from the outer surface of the concrete. In this case, the active resistors R _x must always be facing the outer surface of the concrete 9. The cables of the 5 sensors 1 must be routed through the appropriate connectors into a metal hermetic box at the point where we will later have access to the measuring connection and then concreting.

Non-destructive detection of the position and depth of the steel reinforcement (eg by the swirling method) is initially performed when the sensors 1 are installed in the hardened concrete of the existing reinforced concrete structure of the already constructed object, and then holes are drilled at selected locations with a 75 mm diameter crown to the desired depth. The drilled cylinders of concrete can be inspected and analyzed for the content of corrosive ions (chlorides, sulphates) by depth and the pH of the concrete in the depth where the sensors are to be installed. The new covering concrete is preferably made with the same content of corrosive additives as those analyzed on the drilled cylinders. at the depth where the sensors will be placed. Align the bottom of the wells and glue the sensors 1 to the bottom of the wells available at the back. The connection cables of the 5 sensors 1 with suitable connectors are routed in an airtight metal box at an accessible location. Each hole above the sensors 1 is filled with new concrete, whose structure and properties should be as close as possible to the old concrete.

When the steel-concrete object is cathodically shielded, resistors R, R _{x of} sensors 1 must be electrically connected to the cathodically shielded steel armature. In this case, the active resistors R _{x of} sensor 1 are also cathodically protected. To the connection connectors of sensors 1, at which corrosion velocity measurements are performed at desired intervals, a connector is used to connect the terminals (in Fig. 1 marked A, B, C, D, E, F) connecting the resistors R _x and The R on sensors 1 is short-circuited, and the electrical contacts of this connector are connected to the available conductor, which is in electrical contact with the steel armature (cathode). At the time of corrosion velocity measurements on sensors 1, the aforementioned connector is disconnected, and after measurements, it is switched on again.

Electrically conductive elements 11, 12, 13, 14 and thus resistors R, R _{x of} sensor 1 preferably consist of a sheet whose composition is identical or at least approximately equivalent to that of the reinforcement, and are further preferably made by a photochemical process, therefore, the cross sections of the conductors of the elements 11 , 12, 13, 14 are not rectangular but trapezoidal in shape. Given the selected thickness of the sheet (150 to 270 μπι) and the cross-sectional shape of the resistor conductor R, R _x, we must also take into account the thickness reduction factor, which depends on the degree of deformation of the crystalline grains of the resist material. Because the sensors 1 have specific corrosion properties due to their shape, a method of determining or detecting the corrosion is also designed according to the invention. for determining the corrosion rate based on the design of the sensors 1 described above and also the adequate device at which these sensors 1 are used.

The device according to the invention consists of a plurality of sensors 1 which are electrically connected via a connecting cable 5 with associated connectors to a suitable instrument for measuring the change in electrical resistance. The device is e.g. battery-powered, contains a current generator and a combination of voltage preamps. The current generator provides a constant current source that is selected (100 μΑ or 50 mA) and switched on in two directions (bipolar). Voltage preamplifiers amplify the voltage drop across the sensor and the voltage difference to a readable level by a hand-held voltmeter.

In an alternative embodiment of a device that allows the corrosion rate to be measured in cathodically shielded objects, the active resistors R _{x of} sensors 1 are also cathodically protected. Sensor 1 connector terminals, at which corrosion velocity measurements are performed at desired intervals, are connected to a connector, by means of which terminals A, B, C, D, E, F connect the resistors R _x and R on sensors 1 to be short-circuited. and the electrical contacts of this connector are connected to the available conductor, which is in electrical contact with the steel armature, ie the cathode.

At the time of corrosion velocity measurements on sensors 1, the aforementioned connector is disconnected, and after measurements, it is switched on again.

In the system, the voltage difference between the two branches is measured, the first (which measures the fall across the two branches) is denoted by U, and the second (which measures the difference of the fall between R _x and R) by AU. We send a constant current of values from 10 to 50 mA through the circuit (Fig. 4). Keep in mind that the flow through the two branches is the same, so the following applies:

l / = (*, + *) £ (1) fu = (r _x -r) -.

(2)

The resistance R _x represents the sum of the original resistance and the change in FR, that is, R _x = R + FR, and we divide the two equations into each other:

The change in resistance corresponds to

Followed by:

where it is

FU _ FR U ~ 2R + FR

FR

2u

-m

AU

U

FS

S-FS

2u l-u _ξ * 1

S (3) (4) (5) (6) (7)

The change in the cross-sectional area of the resistor conductor can be written as:

z With λ f R Ί R <R FS - S 1 = S 1 = s ¹ - ~ - R + FR) R + ² “R and (i +. ² “) k l-u) 7

(8)

FS = S \ and we get

2u '+ u j (9).

Due to the method of manufacture, e.g. cold rolling, cold deformed microstructure, similar to reinforcing steel. The crystal grains are flattened, which is why the conductors 1Γ, 12 'of the resistor R _{x of the} resistive sensorium 1 corrode faster in width (d ₂ ) than in height (dQ of the resistor conductor R _{x of the} sensorium 1. In order to be able to estimate the actual change as accurately as possible of thickness (di) it is possible to introduce a factor of reduction of thickness A. The factor of reduction of thickness of conductor 1Γ, 12 'of resistance is determined as

(10) d, - height difference - thickness (c ?, = c _{nave) r} - c _cor ) d ₂ - width difference

The thickness reduction factor A is determined by measuring the geometry of the corroded and non-corroded samples of the sensorium 1 and must be determined for each series of sensors 1 by inspection of the cross-section of conductors 1Γ, 12 'corrosion of exposed elements 11, 12 of resistance R _x on a metallographic microscope and examination surfaces on a line electron microscope.

The cross-section of conductor 11 'of one of the corrosion-exposed elements 11, 12 of sensor 1 with resistor R _x , which is designed in the form of a trapezoid, is shown in FIG. 6. The following is a sequence of determining the corrosion rate, which is preferably carried out using appropriate software. The terms used are as follows:

a - shorter side of the trapezoid on the corrosion exposed side b - longer side of the trapezoid on the corrosion exposed side c - height of the trapezoid d - oblique side of the trapezoid

6? I - difference in height - thickness d2 - difference in width β - angle between sides d and b x - delineate sin Z?

OD

The trapezoidal surface is calculated as follows:

_s ^ (a + b] c

Surface change:

sin β = - x sin β a + b - 4x 2 (c - d,) (12) (13)

Δ5 = S _o - S, son of Z? = - d (14) (15)> x =

Δ5 = · (a + b) ci (a + b - 4x) (a + b) c | _{O +} 6- ^4rf · sin /?

· AS = (a + b) c - (a + b- 4x) (c - d _l ) 4d = - ^ (cd>) + d, (a + b) sin /?

We solve the equation:

4d

2- LS = d ^ a + b) + -— (c -d _t ) sin β (16) (Π)

Considering the thickness reduction factor, we can write d ₂ = A · d, (18)

4d

2LS = - ^ - (cd _x ) + d _x (a + b) sin /?

4JJ, son /?

(19) (c - J,) + J, (a + b)

4A, ₂ (4Ac

-d * - - + a + b sin> 3 ^ sin /?

I

4Ac </, + 2-AS = 0 (20) d, = sin /?

+ a + b ± JI + a + b

32-Δ5-Λ sin /? J son /?

8J son /?

(21)

Noting that:

AS = S

2u ϊ + ΰ we get:

(22) d, =

4Ac sin β + a + b ± '

4Ac

--Ha + b sinfi j

32-S

2 «, ΐ + κ sin /?

whereby

8A son /?

(23)

AU

In (24).

Example 1 (sensor test, result analysis)

Sensors 1 and steel reinforcement were embedded in concrete specimens 9. Concrete specimens 9 were exposed to carbonation and cyclic corrosion exposures (wetting with the presence of chlorides / drying). The thickness reduction graph of elements 11, 12 of sensor 1 is shown in the diagram in FIG. 7, which clearly confirms the high measuring resolution of the sensors 1 according to the invention. The results were also compared with the results of the corrosion rate calculation of the steel reinforcement by the gravimetric method.

After corrosion of the conductor of one resistor R _x, further measurement of corrosion velocity is no longer possible, and a sudden significant decrease in the thickness of sensor 1 implies the detection of pit corrosion.

With the form of flat electrically conductive elements 11, 12, 13, 14 for the formation of resistors R _x , R, greater electrical resistance is achieved, thanks to the arrangement of the corrosion-exposed and reference resistors R _x , R in the immediate vicinity of each other, the temperature compensation of the Wheatston bridge is achieved . These measures result in high measurement resolution compared to the sensors known so far and a good comparison of the measured corrosion velocities with the corrosion velocities of the steel reinforcement in concrete.

Due to the shape and construction, the outer dimensions of the sensors 1 according to the invention are relatively small, but on the other hand the corrosion-exposed surface is relatively large.

Due to the small dimensions, the sensors 1 according to the invention can be installed in concrete of new and old structures even during reinforcement with a relatively small dimension grid or also e.g. into small laboratory samples. The small dimensions of each sensor 1 allow the installation of more sensors 1 on smaller surfaces, and thus more efficient detection of locations of corrosion foci, or places where corrosion velocities are high. Sudden corrosion of a single corrosion-exposed resistor of a single sensor also detects pit corrosion.

Measurements can be taken continuously or at intervals. The accuracy of the measurements of the small current intensities of the electrochemical processes are not directly affected, e.g. occurs in electrochemical methods of measuring corrosion velocities.

The sensors 1 according to the invention can also be installed in objects that are cathodically shielded with active cathodic protection by electric current and corrosion velocity measurements are performed at intervals.

Claims (23)

1-M (8) (9) · iii) determining the factor (A) of reducing the conductor thickness (1Γ, 12 ') of the resistor elements (11, 12) (R _x ) by the formula 1-M (5) R = (Ό ii) to determine the change in the cross-sectional area of the resistor by the formulas AS = S 1-R + AR R ₊ ^ -R 1-M (3) AU U (5) AS S-AS 2m 1. Sensor for determining the corrosion rate of metal reinforcement in reinforced concrete structures based on the determination of resistance (R _x ) of at least one in concrete (9) embedded and corrosion exposed electrically conductive element (11, 12) with respect to the reference resistance (R) of at least one in the concrete (9) of an electrically conductive shielded element (13,14) incorporated but corroded, characterized in that it comprises at least one electrically non-conductive support plate (10) on which at least one highly flattened, corrosion-exposed electrically conductive element is mounted (11, 12) with a zigzag-shaped conductor (IT, 12 ') zigzag along the surface of the plate (10) with a distinctly small cross-section and with respect to the surface available at each time of extremely large length of correspondingly high resistance (R _x ), as well as at least one equally pronounced a flattened, corrosion-protected electrically conductive reference element (13, 14) with a zigzag guide (13 ') circled over the surface of the plate (10) , 14 ') of extremely small cross-section and with respect to the surface available at each time of extremely large length, correspondingly high reference resistance (R), the material of said electrically conductive elements (11, 12, 13, 14) being identical or at least approximately corresponding to the material in reinforced concrete reinforcement and the elements (11, 12, 13,14) available at each time are connected to the electrical circuit. 2 · AS =, ² (c - e /,) + J, (a + b) (19) sin β Δ.ΛΗ (20) and where a is the shorter side of the trapezoidal profile of the conductors (1Γ, 12 ') of the elements (11, 12) on the corrosion-exposed side, b the longer side of the trapezoidal profile of the conductors (13', 14 ') of the elements (13, 14) ) on the corrosion-exposed side, c height of trapezoidal profile d oblique side of trapezoidal profile d \ height difference - thickness di difference in width β as between sides d and b, while x represents the ratio v) determining the difference in height or thicknesses of conductors (1Γ, 12 ') of electrically conductive elements (11,12) of sensor (1) according to formulas (21) sin β 32-AS-A sin β where, given that A5 = S 2m Ϊ7μ (22) is valid: d, = 4Ac son /? + a + b ± ' 4Ac son /? 8Λ son /? sin /? </ ₂ = A · d, (18) 4J 2 · AS = J, (a + b} + (17) where, taking into account the thickness reduction factor, 2 · AS = (a + b) c - (a + b- 4x) (c - d _x ) 4J = -τ ^^ - ά _λ ) + ά _λ {α + υ} srn /> Sensor according to claim 1, characterized in that the support plate (10) is a relatively rigid plate of relatively small dimensions, which is provided with openings (2) for receiving the electrically conductive lot (3) and, if necessary, the conductor (4) of the connecting cable (5) ) sensoia (1). A sensor according to claim 2, characterized in that the support plate (10) consists of laminated glass epoxy material. 4 = ^ · (10) «1 where means J, - the difference in the amount of - the thickness (d _x = c _Nekor - c _kor) d ₂ - the difference in the width of the measuring geometry of corroded and nekorodiranih samples of sensors (1) for each of a series of sensors (1), in particular by examining the cross-section of conductors ( 11 ', 12') corrosion of exposed elements (11, 12) of resistance R _x on a metallographic microscope and examination of the surface on a line electron microscope, taking into account the method of fabrication of the sheet, in particular e.g. in the case of cold rolling and the corresponding cold-deformed microstructure similar to that of reinforcing steel, whereby the crystalline grains are flattened and therefore the conductors (1Γ, 12 ') of the resistor (R _x ) of the sensor (1) corrode faster in width (d ₂ ) as height or height. thickness (di) of resistor (R _x ) sensor (1); iv) determining the surface of the trapezoidal profile of conductors (11 ', 12') of electrically conductive elements (11, 12) of sensors (1) by the formulas sin β = - x * x = sin β {a + b) c, 4d ₂ a + b - sin / J ^S ° - 2 (12) a + b - 4x, ---- (e-d,) (13) AS = S ₀ -S, (14) sin β = - (15) (cd _x ) Sensor according to any one of the preceding claims, characterized in that the conductor (IT, 12 ', 13', 14 ') of the electrically conductive element (11) of the electrically conductive element (11, 12, 13, 14) in each case is designed with profile or. a cross-section in the form of a trapezoid, which is narrowed in the direction away from said plate (10). Sensor according to claim 4, characterized in that the conductor (IT, 12 ', 13', 14 ') of the electrically conductive element (11) of the electrically conductive element (11, 12, 13, 14) in each case consists of a cold-formed metallic material identical in composition or composition to at least approximately the material in each case in the concrete (9) of the available reinforcement. Sensor according to claim 4, characterized in that the conductor (1Γ, 12 ', 13', 14 ') of the electrically conductive element (11) of the electrically conductive element (11, 12, 13, 14) in each case consists of photochemically treated sheet metal or other metal material, whether or not electroplated, by evaporation or otherwise, applied directly to the surface of the support plate (10) and which is identical or. its composition corresponds at least approximately to the material in each case in the concrete (9) of the available reinforcement. Sensor according to one of the preceding claims, characterized in that it comprises a corrosion-resistant pair of non-shielded electrically conductive elements (11, 12) with resistance (R _x ) and an electrically coupled pair of anti-corrosion protected reference elements (13, 14) with a reference resistance (R). Sensor according to claim 7, characterized in that the two adjacent and interconnected elements (11, 12) and (13, 14) are electrically connected to each other via the Wheatston bridge and in such a connection via connecting cables (5) plugged in to any available external electrical circuit. A sensor according to claim 7 or 8, characterized in that each of the elements (11, 12; 13, 14) is electrically connected to the respective element (11, 12; 13, 14) in the region of the electrically conductive lot (3) , which is available in the corresponding opening (2) in the electrically non-conductive load-bearing plate (10), thereby making generally non-dismantling electrical contacts (A, B, C, D, E, F). A sensor according to claim 7 or 8, characterized in that two contacts (C, F) of the elements (11, 12; 13; 14) are provided for connection to the conductor (4) of the electrical cable (5) for connecting the sensor (1 ) at each available electrical circuit, one contact (C) being provided in the corrosion zone of the exposed elements (11, 12) and the remaining contact (F) in the corrosion protection zone of the protected elements (13, 14). 11-M J A5 = FIG 2m Ϊ + Μ ί (ΐ ₊ Λ) A sensor according to any one of claims 1 to 10, characterized in that all electrically conductive elements (11, 12; 13; 14) are arranged on the same side of the carrier plate (10). Sensor according to any one of claims 1 to 10, characterized in that the electrically conductive elements (11, 12) with resistance (R _x ) exposed to corrosion are arranged on one side of the electrically non-conductive support plate (10). , the electrically conductive reference elements (13, 14) with resistance (R), which are not exposed to corrosion, are located on the opposite side of the bearing plate (10). Sensor according to one of Claims 1 to 12, characterized in that electrically conductive reference elements (13, 14) with corrosion resistance (R) and other electrically conductive parts including in the area of the support plate ( 10) available conductors (4) of electrical cables (5), with the exception of corrosion-exposed elements (11, 12) with resistance (R _x ) coated with an electrically non-conductive protective layer (6, 7). A sensor according to any one of claims 1 to 13, characterized in that the insulating protective layer (6, 7) available at each time is available as a solid or plastic layer of electrically conductive or poorly conductive material. Sensor according to one of Claims 1 to 14, characterized in that the corrosion-exposed elements (11, 12) in the position of incorporation into the concrete (9) are facing the outer surface of the reinforced concrete element. (16) Sensor according to one of Claims 1 to 14, characterized in that the corrosion-exposed elements (11, 12) with the resistance (R _x ) of the sensor (1) are cathodically protected, with sensory connectors ( 1), through which corrosion velocity measurements are performed at desired intervals, a connector connected by means of which the connections (A, B, C, D, E, F) of the resistance elements (11, 12; 13, 14) (R _x ) and (R) on the sensors (1) are short-circuited, and the electrical contacts of this connector are connected to the available conductor, which is in electrical contact with the steel reinforcement, ie the cathode embedded in the concrete (9), while during the corrosion measurement speed the aforementioned connector is disconnected but otherwise on. 17. Device for determining the corrosion rate of metal reinforcement in reinforced concrete structures based on the determination of resistance (R _x ) of at least one in the concrete (9) of the electrically conductive element (11, 12) installed and corroded with respect to the reference resistance (R) of at least one in the concrete (9) of the electrically conductive shielded element (13, 14) incorporated but corrosion-protected, characterized in that it comprises at least an electrical resistance meter which is electrically connected to the number of sensors (1) by electrically cables (5) claims 1 to 16. Apparatus according to claim 17, characterized in that it comprises a finite and predetermined number of sensors (1) which are installed at different locations and at different depths or in corresponding holes in the hardened concrete (9) of a pre-existing reinforced concrete object or in non-hardened concrete (9) of the fabricated reinforced concrete structure, with electrically conductive elements (11, 12) exposed to corrosion (R _x ) on each side of the support plate (10) of the sensor (1) facing the outside surface of reinforced concrete building. Apparatus according to claim 16 or 17, characterized in that the sensors (1) in the concrete (9) are so arranged that they run at least substantially parallel to the reinforcement embedded in the concrete (9). Apparatus according to one of Claims 16 to 19, characterized in that it is battery-powered and contains a current generator and a suitable combination of voltage preamps, the current generator being adapted to provide a constant source of the bipolar electric current selected in two directions, while Voltage preamplifiers designed to amplify the voltage drop across the sensor (1) and the voltage difference to a readable level by a hand-held voltmeter. Apparatus according to one of Claims 16 to 20, characterized in that it is connected to the electrical circuit of the pre-existing cathodic protection of reinforcement in concrete (9) of the existing reinforced concrete object and adapted for measuring the change in resistance (R _x ) of corrosion of exposed elements (11 , 12) after prior exclusion for cathodic protection of the intended electrical circuit. 22. A process for determining the corrosion rate of a metal reinforcement in reinforced concrete structures based on the determination of the resistance (R _x ) of at least one in the concrete (9) of the electrically conductive element (11, 12) installed and corroded with respect to the reference resistance (R) of at least one in the concrete (9) of an electrically conductive shielded element (13, 14) incorporated but corroded by incorporating sensors (1) into the measuring device according to any one of claims 17 to 21, either in uncured concrete or into the corresponding holes in the hardened concrete of the pre-existing reinforced concrete structure, so that the corrosion-exposed electrically conductive elements (11, 12) with resistance (R _x ) face the outer surface of the concrete (9) and run at least approximately parallel to the reinforcement, and then in the case Fill the holes in the hardened concrete (9) with wells, the structure of which corresponds in the same place before the wells are available to the concrete (9), outside the concrete (9). however, the live connecting cables (5) are electrically connected within the said measuring device, characterized in that it comprises the steps i) determining the voltage difference between the two branches, namely, the first branch (U), where the fall is measured on both branches, and the second (with AU), where the difference of the fall between resistances (R _x ) and (R) is measured, sends a constant current of a certain value through the circuit, which is the same through both branches, which is done by the formulas (7 = (Λ _Λ + ί) ί (1) Δ1 / = (Λ, −Λ) 7 (2) At / AR U ~ 2R + AR (3) AR 2u (23) based on the observed voltage difference given by the formula AU (24) and vi), also based on the change in thickness of the individual sensors (1) within the said device, is also a step of determining the type of corrosion.