ELECTROCHEMICAL MEASUREMENT SYSTEM AND METHOD FOR MONITORING A CONCRETE STRUCTURE

Abstract

An electrochemical measurement system for monitoring a concrete structure having a reinforcement bar, including: at least six electrodes to contact the concrete structure's surface, including at least two emitting electrodes to inject electrical signals into the structure and at least four receiving electrodes combined in pairs, each pair receiving electrical signals, originating from an explored zone of the structure located beneath an axis connecting the electrode pairs with its depth depending on the distance between the two electrodes in the pair; an acquisition module to (i) control the electrodes and (ii) acquire and store in a memory the electrical signals; a processing module to calculate, for the electrical signals, induced polarization potential response value(s) and one apparent resistivity value; from these values, process output characteristic(s) of each explored zone; an image reconstruction module to generate an image of the distribution of the output characteristic(s) in the explored zones.

Claims

1.-18. (canceled)

19. An electrochemical measurement system for monitoring a concrete structure comprising a reinforcement bar, said system comprising: at least six electrodes configured to be placed in contact with a surface of the concrete structure and arranged in a predefined spatial configuration; comprising: at least two emitting electrodes configured to inject a plurality of electrical signals into the concrete structure; at least four receiving electrodes configured to be combined in pairs; wherein each pair of electrodes receives a plurality of electrical signals, originating from an explored zone of the concrete structure; an acquisition module configured (i) to control the emitting electrodes and receiving electrodes, and (ii) to acquire and store in a memory the plurality of electrical signals; a processing module configured to: calculate apparent resistivity values and apparent chargeability values for each plurality of electrical signals; receive a model comprising a geometric disposition of the reinforcement bar in the concrete structure, initial values of resistivity and chargeability for the reinforcement bar volumes and initial values of resistivity and chargeability for the concrete volumes; perform inversion using the model, the apparent resistivity values and the apparent chargeability values so as to obtain the inversed resistivity values and the inversed chargeability values, and from these values, process at least one output characteristic of the concrete structure associated to each explored zone from which the plurality of signals originates; wherein one output characteristic of the concrete structure is the corrosion rate of the reinforcement bar; and an image reconstruction module configured to generate an image of the distribution of the output characteristics of the concrete structure in the explored zones.

20. The system according to claim 19, wherein the corrosion rate value is obtained from the induced polarization potential response value corrected by the apparent resistivity value.

21. The system according to claim 19, wherein the processing module is configured to obtain a distribution of the polarization resistance from the apparent resistivity then to obtain the corrosion rate.

22. The system according to claim 19, wherein in one predefined spatial configuration the electrodes are disposed inline.

23. The system according to claim 19, wherein the image generated represents the distribution of the at least one output characteristic of the concrete structure for an in-depth section of the concrete structure below the aligned electrodes.

24. The system according to claim 19, wherein the at least one output characteristic of the concrete structure is at least one of: cracking, crazing, blistering, delamination, chalking, air void, corrosion, water content or a transport characteristic selected from the group comprising permeability, diffusivity or porosity.

25. The system according to claim 19, wherein the processing module is further configured to estimate a self-potential and/or electrical impedance value.

26. The system according to claim 19, wherein each of the electrodes of the system is configurable to take the role of an injection electrode or a receiving electrode.

27. The system according to claim 26, wherein the configuration of the electrodes is pre-programmed and/or reprogrammable.

28. The system according to claim 19, wherein the plurality of electrical signals is acquired from the multiple pairs of receiving electrodes sequentially or simultaneously.

29. The system according to claim 19, wherein the injected plurality of electrical signals is configured to perform a galvanostatic pulse method or a time-domain induced polarization method.

30. The system according to claim 19, wherein the electrodes are electrically connected to the concrete structure via an electrically conductive fluid deposited on the surface of the concrete.

31. The system according to claim 19, further comprising a robotic module configured to move the system with respect to the concrete surface.

32. The system according to claim 31, being configured to iterate a measurement routine for monitoring a region of the concrete structure, said routine comprising: a displacement phase wherein the robotic module moves the system according to a predefined pitch; a measurement phase wherein the acquisition module acquires a plurality of electrical signals and stores the signals together with information related to the location of the electrodes at the time of acquisition of each signal.

33. The system according to claim 32, wherein the image reconstruction module is configured to generate a tridimensional image of the explored zones or region of the concrete structure using the stored signals and the information related to the location of the electrodes at the time of acquisition of each signal.

34. An assembly comprising at least two electrochemical measurement systems for monitoring a concrete structure comprising a reinforcement bar, wherein the at least two systems are mechanically coupled so as to form a longitudinal series of electrodes or multiple parallel lines of electrodes; each system comprising: at least six electrodes configured to be placed in contact with a surface of the concrete structure and arranged in a predefined spatial configuration; comprising: at least two emitting electrodes configured to inject a plurality of electrical signals into the concrete structure; at least four receiving electrodes configured to be combined in pairs; wherein each pair of electrodes receives a plurality of electrical signals, originating from an explored zone of the concrete structure; wherein the emitting electrodes and the receiving electrodes are disposed inline; an acquisition module configured (i) to control the emitting electrodes and receiving electrodes, and (ii) to acquire and store in a memory the plurality of electrical signals; a processing module configured to: calculate apparent resistivity values and apparent chargeability values for each plurality of electrical signals; receive a model comprising a geometric disposition of the reinforcement bar in the concrete structure, initial values of resistivity and chargeability for the reinforcement bar volumes and initial values of resistivity and chargeability for the concrete volumes; perform inversion using the model, the apparent resistivity values and the apparent chargeability values so as to obtain the inversed resistivity values and the inversed chargeability values, and from these values, process at least one output characteristic of the concrete structure associated to each explored zone from which the plurality of signals originates; wherein one output characteristic of the concrete structure is the corrosion rate of the reinforcement bar; and an image reconstruction module configured to generate an image of the distribution of the output characteristics of the concrete structure in the explored zones, which is an in-depth section of the concrete structure below the aligned electrodes.

35. A method for monitoring a concrete structure comprising a reinforcement bar, said method comprising the following steps: receiving a plurality of electrical signals, originating from an explored zone of the concrete structure, acquired using electrochemical measurement system comprising at least six electrodes; receiving a model comprising a geometric disposition of the reinforcement bar in the concrete structure, initial values of resistivity and chargeability for the reinforcement bar volumes and initial values of resistivity and chargeability for the concrete volumes; using the model to calculate for each plurality of electrical signals at least one induced polarization potential response value and one apparent resistivity value, and from these values, process at least one output characteristic of the concrete structure associated to each explored zone from which the plurality of signals originates; wherein one output characteristic of the concrete structure is the corrosion rate of the reinforcement bar; and generating an image of the distribution of the output characteristics of the concrete structure in the explored zones.

36. The method according to claim 35, further comprising obtaining a distribution of the polarization resistance from the apparent resistivity then to obtain the corrosion rate.

Description

DESCRIPTION OF THE DRAWINGS

[0098] The following detailed description will be better understood when read in conjunction with the drawings. For the purpose of illustrating, the system is shown in the preferred embodiments. It should be understood, however that the application is not limited to the precise arrangements, structures, features, embodiments, and aspect shown. The drawings are not drawn to scale and are not intended to limit the scope of the claims to the embodiments depicted. Accordingly, it should be understood that where features mentioned in the appended claims are followed by reference signs, such signs are included solely for the purpose of enhancing the intelligibility of the claims and are in no way limiting on the scope of the claims.

[0099] Features and advantages of the invention will become apparent from the following description of embodiments of a system, this description being given merely by way of example and with reference to the appended drawings in which:

[0100] FIG. 1 is a schematic representation of a concrete structure on which is placed the system of the invention according to a first embodiment.

[0101] FIG. 2 is a schematic representation of a concrete structure comprising reinforcement bars on which is placed the system of the invention according to a first embodiment.

[0102] FIG. 3 is a cross section of the concrete structure and the system of FIG. 2.

[0103] FIG. 4 is a schematic representation of a robotic module comprising a system having the electrodes disposed in a linear predefined spatial configuration.

[0104] FIG. 5 is an example of a plot of the current as a function of time.

[0105] FIG. 6 is an example of a plot of the potential difference as a function of time.

[0106] FIG. 7 is an example of a plot of the average and normalized value of the potential difference as a function of time, calculated from the ten potential difference slots shown in FIG. 6.

[0107] FIG. 8 is an example of a plot of the imaginary impedance as a function of the real impedance as a function of the frequency.

[0108] FIG. 9 is an example of a plot of the impedance modulus and the phase shift as a function of the frequency.

[0109] FIG. 10 is an illustration of the explored zone in a specific configuration of electrodes.

[0110] FIG. 11 is an illustration of the reconstructed image of a sample when inversion method is run with (top) or without (bottom) decoupled inversion. Resistivity in the sample is shown in a grey scale, with values ranging from 1.5 Ohm.Math.m (light grey) to 300 Ohm.Math.m (dark grey).

[0111] While various embodiments have been described and illustrated, the detailed description is not to be construed as being limited hereto. Various modifications can be made to the embodiments by those skilled in the art without departing from the true spirit and scope of the disclosure as defined by the claims.

ILLUSTRATIVE EMBODIMENTS OF THE INVENTION

[0112] As shown in FIG. 1, the electrochemical measurement system S for monitoring a concrete structure Cs, according to the first embodiment, comprises six electrodes Ei configured to be placed in contact with a surface of the concrete structure which are placed on a surface of a concrete structure Cs.

[0113] In this embodiment, the system S further comprises an acquisition module Ma configured to control the electrodes Ei so as to inject a plurality of electrical signals I in the concrete structure and to acquire from it a plurality of electrical signals Si which are stored in a memory.

[0114] The system S comprises also a processing module Mp for processing the acquired signal so as to extract information on the characteristic of the concrete structure Cs and an image reconstruction module Mi for showing such information.

[0115] As shown in FIG. 2, the electrodes Ei are aligned, equally spaced and fixed on a mechanical structure. In order to monitor the corrosion rate of the rebars R of the concrete structure Cs, the system S is placed on the concrete structure surface in proximity of the rebars.

[0116] FIG. 3 shows the system according to the first embodiment, comprising two emitting electrodes A and B configured to inject a plurality of electrical signals I into the concrete structure, represented by the lines of current flow. In this configuration, the emitting electrodes are disposed each on one end of the mechanical structure.

[0117] The four receiving electrodes P1, P2, P3 and P4 are fixed along the mechanical structure between the emitting electrodes A and B.

[0118] The acquisition module is configured to control the plurality of electrical signals I injected into the concrete structure using the emitting electrodes A and B. The acquisition module is configured to combine the receiving electrodes P1, P2, P3 and P4 in pairs, using all the possible combinations (i.e. P1-P2, P1-P3, P1-P4, P2-P3, P2-P4, P3-P4), so as to measure from each pair of electrodes a plurality of electrical signals (S12, S13, S14, S23, S24, S34), originating from one explored zone of the concrete structure. The explored zone is located beneath the axis connecting the electrodes in the pair at a depth depending on the distance between the two electrodes in the pair.

[0119] This embodiment is particularly advantageous as it allows to recovery information on the concrete structure beneath the system which allows the reconstruction of a bidimensional (2D) image of an in-depth section of the concrete structure.

[0120] FIG. 4 shows a second embodiment of the invention where the system S comprises a robotic module Rm.

[0121] According to this second embodiment, the system S is mechanically fixed on a track-driven robotic module Rm configured to move the system with respect to the concrete surface. The continuous track and the road wheel of the robotic module are configured to move of concrete structures having various surface geometries disposed from the horizontal to the vertical direction.

[0122] The system S in this embodiment comprises aligned electrodes Ei, equally spaced and fixed on a mechanical structure as for the embodiment shown in FIG. 2.

[0123] The system S further comprises an articulated arm on which is mechanically and removably fixed, through a holding arm, the mechanical structure on which are fixed the electrodes. The articulated arm comprises a support element, connecting the robotic module Rm to the holding arm. The holding arm is pivotably fixed to the support element so that the position of the mechanical structure on which are fixed the electrodes may be modified between a measurement position, where the electrodes must be in contact with the concrete structure to allow acquisition of electric signals from the concrete, and a movement position, where the electrodes must be raised so as to easily displace the robotic module.

EXAMPLES

[0124] The present invention is further illustrated by the following examples.

Example 1

[0125] Experiments were performed in laboratory on a CEM I mortar sample (52×34×13 cm, w/c=0.4) with one carbon steel rebar (60 cm, Φ=12 mm, cover depth=4 cm), with constant relative humidity and temperature. The carbon steel rebar was in passive conditions.

[0126] Measurements were performed in time-domain using four stainless steel electrodes in Wenner configuration; the two outer emitting electrodes (A, B) were used for the injection of a current of 100 μA and the two inner receiving electrodes (P1, P2) for measuring the potential difference. The interelectrode spacing was 15 cm (i.e. 45 cm between the two emitting electrodes) in order to ensure that the entire rebar is polarized.

[0127] The experimental protocol consists of performing ten current square wave, as follow: [0128] injection of 100 μA on electrode A during a time period of 30 s; [0129] no injection during a time period of 30 s; [0130] injection of −100 μA on electrode A during a time period of 30 s; [0131] no injection during a time period of 30 s.

[0132] FIG. 5 presents the evolution of the current with time and FIG. 6 presents the evolution of the potential difference with time when performing the measurements.

[0133] The continuous derivation of the self-potential is observed, as visible in FIG. 6 where the baseline of the potential difference constantly decreases during time.

[0134] An average and normalized value of the potential difference obtained for the ten slots is then calculated during the charge, as shown in FIG. 7. A curve fitting based on the Randles circuit—R(CR)—is finally used to determine the concrete resistance, the polarization resistance and the double layer capacitance, using Equations. 5-8.

[0135] Considering that all the injected current polarizes the rebar, the results obtained from the fitting are: [0136] R.sub.Ω=13.8Ω, i.e. ρ.sub.Ω=13 Ω.Math.m considering k=2πa; [0137] C.sub.dl=0.037 F; [0138] R.sub.p=158Ω.

[0139] To convert the polarization resistance R.sub.p in current corrosion I.sub.corr, the Stern-Geary relation was used (see Eq. 3), with a B value of 0.052 V (passive conditions), obtaining a value of I.sub.corr equal to 329 μA.

[0140] The corrosion current I.sub.corr was then converted in corrosion rate in term of penetration rate using the following equation:

[00007]$\begin{array}{cc}{v}_{\mathrm{corr}}=\frac{I_{\mathrm{corr}}M}{nA\rho F}& \left(\mathrm{Eq}.14\right)\end{array}$

[0141] where M is the molar mass of iron (g/mol), n is the number of electrons exchanged in the reaction (n=2), A is the geometrical surface of the rebar (cm.sup.2), ρ is the density of steel (g/cm.sup.3) and F is the Faraday constant (96485 C/mol).

[0142] Here, considering that the entire rebar embedded in the concrete is polarized, the geometrical area is 196 cm.sup.2. Hence, applying equation 14 the corrosion rate is 19.7 μm/year.

[0143] However, this result does not represent the real corrosion rate as only a part of the applied current will polarize the rebar. To determine the polarizing current, the plurality of signal must be inverted.

Example 2

[0144] Experiments were performed in laboratory on a CEM I mortar sample (52×34×13 cm, w/c=0.4) with one carbon steel rebar (60 cm, Φ=12 mm, cover depth=4 cm), with constant relative humidity and temperature. The carbon steel rebar was in passive conditions.

[0145] Measurements were performed in frequency-domain using four stainless steel electrodes in Wenner configuration; the two outer emitting electrodes were used for the injection of 100 μA RMS (alternating current) and the two inner receiving electrodes for measuring the potential difference. The interelectrode spacing was 15 cm in order to ensure that the entire rebar is polarized.

[0146] The frequencies range from 10 Hz to approximately 10.sup.−3 Hz (3.6 mHz). Measurement at each frequency was realized three times and the mean value was reported.

[0147] Results are presented as Nyquist plot (FIG. 8), showing the imaginary part of the impedance as a function of the real part of the impedance, and as Bode plot (FIG. 9) showing the modulus of the impedance and the phase shift as a function of the frequency.

[0148] An electrical equivalent circuit (EEC) was used to fit the experimental results. For this example, the selected EEC was R(QR). Considering that all the current polarizes the rebar, the results are: [0149] R.sub.Ω=12.4Ω; [0150] Q=0.035 F; [0151] α=0.94; [0152] R.sub.p=166Ω.

[0153] To convert the polarization resistance R.sub.p in current corrosion I.sub.corr, the Stern-Geary relation was used (Eq. 3), with a B value of 0.052 V (passive conditions), obtaining 313 μA.

[0154] The corrosion current I.sub.corr was then converted in corrosion rate in term of penetration rate using the equation 14, considering that the entire rebar embedded in the concrete is polarized, the geometrical area is 196 cm.sup.2 so as to obtain a corrosion rate of 18.8 μm/year.

[0155] However, this result does not represent the real corrosion rate as only a part of the applied current will polarize the rebar. To determine the polarizing current, the distribution of the current has to be modeled considering several parameters, especially the resistivity of the concrete and the cover depth.

Example 3

[0156] Acquired signals from example 2 were used to reconstruct an image of the distribution of concrete and rebar.

[0157] In a first reconstruction, a standard smoothness-constrained inversion is run, yielding bottom image of FIG. 11. Although a low resistivity structure is identified (in light grey), it is not accurately located.

[0158] In a second reconstruction, decoupled inversion has been used. In the starting model, concrete has a resistivity of 200 Ohm.Math.m and rebar has a resistivity of 1.7 Ohm.Math.m (low corrosion conditions). Image obtained is shown on top of FIG. 11. A structure of low resistivity is identified and very precisely located.

REFERENCES

[0159] A and B—emitting electrodes; [0160] Cs—concrete structure; [0161] Ei—electrodes; [0162] Ma—acquisition module; [0163] P1, P2, P3, P4—receiving electrodes; [0164] Mi—image reconstruction module; [0165] Mp—processing module [0166] R—reinforcement bar; [0167] Rm—robotic module; [0168] S—electrochemical measurement system;