Field of the Invention

[0001] The present invention generally finds application in monitoring of physicochemical properties of materials, and particularly relates to a system for detecting and monitoring chloride ion concentration and pH in concrete structures.

[0002] The invention also relates to a method for detecting and monitoring chloride ion concentration and pH in such structures.

Background art

[0003] In the field of building, concrete degradation caused by the presence of chloride ions and pH reduction at the interface with the metallic reinforcement in concrete is known to be monitored.

[0004] Systems have been developed for monitoring chloride ion concentration and pH, which are based on core sampling, high-pressure concrete extraction, or acid/water concrete extraction.

[0005] A first drawback of these processes is that they are highly invasive and necessarily involve destruction of the concrete sample being tested.

[0006] As a result these processes are hardly implemented on-site and cannot be continuously iterated, therefore they cannot provide real-time concentration values.

[0007] A further drawback is that the equipment for these processes is particularly expensive and do not allow quick testing of concrete structures.

[0008] In view of at least partially obviating these drawbacks, methods and systems have been developed, which allow quick, non-destructive chloride ion and pH detection by detection and processing of the redox potentials of the chemical species being monitored in concrete structures.

[0009] A system for on-site concrete structure monitoring is known from Anal. Chem. 2006 78, 3179-3185, which uses a device comprising Ag/AgCI and lr/lrO ₂ electrodes for detecting chloride ions and pH.

[0010] The electrodes are placed in respective housings previously formed in the concrete structure, a counter-electrode being also placed in a hole formed in the structure and buried in a conductive liquid. The detected potential values are later used to calculate chloride ion concentration and pH using the known Nernst formula.

[0011] A limit of this device is that it provides excessively approximate chloride ion concentration and pH measurements, as it does not account for all input variables of the Nernst formula.

[0012] Therefore, the use of such device is limited to very stable and controlled temperature conditions, to avoid possibly considerable alterations of the electric quantities monitored by the electrodes.

[0013] A further drawback of this known system is that the level of conductive liquid in contact with the counter-electrode decreases with time due to normal leakage occurring in the structure, and this may considerably alter ion concentration and pH measurements.

[0014] This drawback may cause oxidation of the counter-electrode and inevitably lead with time to its degradation.

Disclosure of the invention

[0015] A general object of the present invention is to obviate the above drawbacks, by providing a method and a system for detecting and monitoring chloride ions and pH in concrete structures, that are highly efficient and relatively cost-effective.

[0016] A particular object of the present invention is to provide a detection and monitoring method that can be used on-site and provide very accurate real-time results.

[0017] A particular object of the present invention is to provide a detection and monitoring method that do not involve destruction of the sample being tested.

[0018] Another object of the present invention is to provide a detection and monitoring method and system that provide real-time concentration values with high accuracy and sensitivity.

[0019] A further object of the present invention is to provide an automatic system for detecting and monitoring chloride ion concentration and pH. [0020] The above mentioned objects, as well as others to be better explained hereafter, are fulfilled by a system for detecting and monitoring chloride ions and pH in concrete structures as defined in claim 1 .

[0021 ] In a further aspect, the invention relates to a method of detecting and monitoring chloride ions and pH in concrete structures as defined in claim 7.

[0022] Advantageous embodiments of the invention are obtained in accordance with the dependent claims.

Brief Description of the Drawings

[0023] Further features and advantages of the invention will be more apparent from the detailed description of a preferred, non-exclusive embodiment of a system and method for detecting and monitoring chloride ion concentration and pH in concrete structures according to the invention, which are described as a non-limiting example with the help of the annexed drawings, in which:

FIG. 1 is a first general schematic view of the detection system of the invention, installed in a concrete structure to be monitored;

FIG. 2 is a first enlarged detail of Fig. 3;

FIG. 3 is a second enlarged detail of Fig. 1 ;

FIG. 4 is an implementation diagram of the system of Fig. 1 ;

Fig. 5 is a block diagram of the chloride ion concentration and pH detection method of the invention.

Detailed description of a preferred embodiment

[0024] Referring to the above figures, there is shown a system for detecting and monitoring chloride ion concentration and pH, which can be used with a building structure S made of reinforced concrete or structural concrete, possibly comprising lithoidal materials or concrete mixes, generally designated by numeral 1 .

[0025] With the detection of chloride ion concentration and pH, concrete reinforcement corrosion may be monitored and prevented, and the carbonation degree of the material may be measured.

[0026] The system 1 may be used both on consolidated concrete structures and on relatively fresh concrete castings for new structures.

[0027] As shown in FIGS. 1 and 2, the system 1 of the present invention comprises at least one first electrode 2, embedded in the structure S, for detecting chloride ions and at least one second electrode 3, also buried in the structure S, for detecting the pH.

[0028] A first electrode 2 may have an active Ag/AgCI part, which is designed to contact the structure S, and a conductive part 5, which is electrically connected to the active part 4 and projects from the structure S.

[0029] The active part 4 may be formed by an anodization process using hydrochloric acid HCI as the electrolyte solution.

[0030] In order to obtain a compact and uniform Ag/AgCI layer, anodization will be carried out on a platinum gauze, not shown, which is wrapped around one end 6 of a silver wire 7 having a length close to about 1 cm.

[0031 ] The conductive part 5 may be formed as a copper braid 8, which is joined to the opposite end 9 of the silver wire 7.

[0032] The copper braid 8 may have a length of about 1 0 cm and will be covered by a rubber or plastic sheath, not shown, for electric insulation.

[0033] Conveniently, the first electrode 2 will be covered by a layer 1 0 of a two-component insulating resin at the connection between the copper braid 8 and the end 9 of the silver wire 7.

[0034] The second electrode 3 may also comprise an active lr/lrO ₂ part, designed to contact the structure S, and a conductive part 1 2 projecting from the structure S.

[0035] Here, the active part 1 1 of the second electrode 3 may be formed by immersing an iridium wire 1 3 in calcium carbonate heated to a temperature of about 700 °C in a muffle for about 60 minutes.

[0036] The iridium wire 1 3 may have a length of about 1 cm and once again the conductive part 1 2 of the second electrode 3 may be formed as a copper braid 8, having a length of about 20 cm.

[0037] The second conductive part 12 may be electrically insulated by covering the second electrode 3 with an epoxy resin.

[0038] The system 1 also comprises a metal counter-electrode 15 which can be located in contact with the structure S proximate to the first electrode 2 and the second electrode 3.

[0039] In a preferred embodiment, the first electrode 2, the second electrode 3 and the counter-electrode 1 5 may be held within respective housing holes 1 6, 1 7, 1 8 formed in the structure S to be monitored.

[0040] Particularly, the housing holes 1 6, 1 7 of the first electrode 2 and the second electrode 3 may have a small diameter, e.g. about 5mm, and may have equal or different depths h-i , h ₂ depending on whether monitoring has to be performed on a particular area of the concrete or throughout the thickness of the casting G.

[0041 ] Furthermore, the housing holes 1 6, 17 of the first electrode 2 and the second electrode 3 may be located at substantially the same distance from the housing hole 1 8 of the counter-electrode 1 5.

[0042] Conveniently, once the first electrode 2 and the second electrode 3 have been introduced into their respective housing, the cavities 1 9, 20 of the holes 1 6, 1 7 may be filled with liquid plaster L.

[0043] The outer edges 21 , 22 of the holes 1 6, 1 7 will be preferably covered with a sealing resin R to waterproof the electrodes 2, 3.

[0044] The counter-electrode 1 5 will be also introduced into a corresponding housing hole 1 8 and will be bonded to the structure as by an appropriate rubber cement M distributed on the bottom wall 23 of the hole 1 8.

[0045] In a preferred embodiment, the system 1 may further comprise a cleaning circuit 24 for cleaning the housing hole 1 8 of the counter-electrode 1 5, in which a cleaning liquid P is pumped to remove drilling debris from the hole 1 8.

[0046] Furthermore, an appropriate feeding circuit 25 is provided in which a conductive liquid C is pumped for at least partially drowning the counter- electrode 1 5 when the latter is introduced into the housing hole 18 that was previously cleared with the washing liquid P.

[0047] As the hole 1 8 is filled with the conductive liquid C, constant and uniform electric continuity will be ensured between the counter-electrode 15 and the structure S to be monitored. [0048] The washing circuit 24 and the feeding circuit 25 may comprise respective metering pumps 26, 27, which are adapted to promote controlled feeding of the cleaning liquid P or the conductive liquid C from respective reservoirs 24', 25' into the hole 1 8 that houses the counter-electrode 1 5.

[0049] The system 1 further has microprocessor means 28, or data logger, comprising a measuring unit 29 for detecting electric voltages V-i , V ₂ between each first electrode 2 and the counter-electrode 15, and between each second electrode 3 and the counter-electrode 1 5.

[0050] The measuring unit 29 may comprise a digital voltmeter 30 having first inputs 31 connected with the electrodes 2, 3 and with the counter- electrode 1 5 for detecting real-time values of such electric voltages V-i , V ₂ .

[0051 ] The microprocessor means 28 also comprise a processing unit 32, which is adapted to calculate the chloride ion concentration and pH values from the electric voltage values Vi , V ₂ that have been measured by the measuring unit 29.

[0052] Particularly, the microprocessor means 28 may comprise a storage area 33 containing a computer program A having a series of instructions for calculating chloride ion concentration and pH using the known Nernst formula, i.e. :

V _x = Vo + (RT _x /nF) In (C _ox / C _red )

where V _x is the electric voltage as measured between the first electrode 2 or the second electrode 3 and the counter-electrode 1 5, V ₀ is the standard reduction potential, T _x is the Kelvin temperature, C _ox and C _re d are the concentrations of the oxidized and reduced species of chloride ions or hydrogen ions respectively.

[0053] Preferably, the microprocessor means 28 may comprise a control unit 34 having outputs 35 connected to the metering pumps 26, 27 in the cleaning circuit 24 and the conductive liquid C feeding circuit 25 for controlling actuation and batch operation thereof.

[0054] Thus, the hole 1 8 that houses the counter-electrode 1 5 may be automatically cleaned and later filled with the conductive liquid C at regular intervals since installation of the system 1 in the structure S. [0055] Furthermore, the processor means 28 may comprise cable or radio communication means, and GSM location means for transmitting and receiving data from a remote station designed for multiple systems installed on various structures, not shown.

[0056] The system 1 may possibly comprise level sensors, also not shown, which are connected to the electronic control unit 34 and are adapted to detect the amount of conductive liquid C in the hole 1 8 that houses the counter-electrode 15.

[0057] When the level of the conductive liquid C is lower than a predetermined threshold value, the control unit 34 will actuate the corresponding metering pump 27 to restore the level of the conductive liquid C.

[0058] In a peculiar aspect of the invention, the system 1 comprises at least one pair of thermocouples 36, 37.

[0059] The first thermocouple 36 is at a first location Si of the structure S near the first electrode 2 and/or the second electrode 3.

[0060] The second thermocouple 37 is at a second location S2 in contact with the structure S proximate to the counter-electrode 1 5.

[0061 ] The thermocouples 36, 37 will be connected to second inputs 38 of the measuring unit 29, for detecting corresponding instantaneous temperatures Ti, T ₂ at the first location Si and the second location S2.

[0062] As best shown in FIG. 1 , the first location Si and the second location S ₂ may be provided by forming respective holes 39, 40 in the structure S for housing the thermocouples 36, 37.

[0063] Advantageously, the thermocouples 36, 37 are connected to the microprocessor means 28 such that the computer program A installed in the storage area 33 of the control unit 34 may calculate chloride ion concentration and pH values using the above Nernst formula, in which the temperature value T _x is replaced by the instantaneous value T-i , T ₂ as measured by the thermocouples 36, 37.

[0064] Conveniently, a kit 41 may be provided, comprising a first container 42 and a second container 43, which contain all the components of the system 1 of the invention.

[0065] Particularly, the first container 42 may contain microprocessor means 28, the electrodes 2, 3 and the counter-electrode 15, whereas the second container 43 will be designed to accommodate the reservoirs 24', 25' and the metering pumps 26, 27 associated with the washing circuit 24 and the feeding circuit 25.

[0066] The method of operation of the device is shown in the diagram of FIG. 3 and comprises steps for detection and monitoring of chloride ion concentration and pH in concrete structures or the like.

[0067] The method comprises a step of a) providing at least one first electrode 2 for detecting chloride ions in a structure S and a step of b) providing at least one second electrode 3 for detecting pH as described above.

[0068] In step c) the first electrode 2 and the second electrode 3 are embedded in the concrete structure S before or after concrete casting G.

[0069] The first electrode 2 and the second electrode 3 may be introduced into respective housing holes 1 6, 1 7 formed at different locations in the structure S. Furthermore, these housing holes 1 6, 1 7 may have equal or different depths h-i , h ₂ .

[0070] The next steps are d) providing a metal counter-electrode 1 5 and e) positioning the counter-electrode 15 in contact with the structure S near the first electrode 2 and second electrode 3.

[0071 ] The counter-electrode 1 5 may be also inserted in a respective housing hole 1 8 formed in the structure S, which may be later filled with a conductive liquid C to ensure constant electric continuity between the counter-electrode 15 and the structure S to be monitored.

[0072] The next step is f) measuring the electric voltages V-i , V ₂ between the counter-electrode 1 5 and the first electrode 2 and the second electrode 3 respectively, preferably using a digital voltmeter 30.

[0073] The next step is g) calculating the chloride ion concentration and pH values from such measured electric voltages V-i , V ₂ . Such calculation will be made by the microprocessor means 28 and will be preceded by a step of h) positioning at least two thermocouples 36, 37, one of which at a first location Si in the structure S near the first electrode 2 and/or the second electrode 3, and the other at a second location S ₂ in contact with the structure S proximate to the counter-electrode 1 5.

[0074] In step i) respective instantaneous temperatures T-i, T ₂ will be detected by the thermocouples 36, 37 such that the calculated concentrations may account for these measured temperature values ^~ T\ T ₂ .

[0075] Preferably, the microprocessor means 28 will be configured to repeat the calculation step g) at predetermined time intervals to determine a time curve of chloride ion concentration and pH in the structure.

[0076] The microprocessor means 28 will perform the calculation step g) using the Nernst formula in which the variables V _x and T _x are replaced by the corresponding electric potentials V-i, V ₂ and the instantaneous temperatures Ti, T ₂ as detected by the voltmeter 30 and the thermocouples 36, 37 respectively.

[0077] The method and system of the invention are susceptible to a number of changes or variants, within the inventive concept disclosed in the appended claims. All the details thereof may be replaced by other technically equivalent parts, and the materials may vary depending on different needs, without departure from the scope of the invention.

[0078] While the method and system have been described with particular reference to the accompanying figures, the numerals referred to in the disclosure and claims are only used for the sake of a better intelligibility of the invention and shall not be intended to limit the claimed scope in any manner.