Method of porous building materials' electrochemical treatment

The invention relates to a process for the electrochemical treatment of porous building materials, in particular electro-osmic drying to remove water from saturated porous building materials such as concrete, gypsum, bricks, certain types of stones and many insulating materials having a capillary porous system. These porous systems can often be filled with water, especially where the materials are in contact with a moisture source such as a moist soil or the like. In many cases, prolonged continuation of conditions in which the building material is saturated with moisture will cause undesirable environments and / or conditions for material disintegration.

The known processes for drying saturated, porous materials have proved to be unsatisfactory. One traditional way is to use a combination of heating and ventilation. However, these processes are not only very slow, but also use large amounts of energy. In addition, there is an additional risk, such as Π O A. OVC <i £ deformation and / or cracking of the structure.

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Another known technique for removing water from porous materials is electroosmosis. It is known that capillary walls in most conventional building materials are coated with an electrically charged film of adsorbed water, sometimes referred to as an electric bilayer. It has been found that if such a body is exposed to an electric field, part of the so-called bilayer will tend to

migration. A certain amount of free liquid in the pores is drained by this process, which may result in a marked decrease in the internal moisture content of the porous body.

Regardless of the theoretical attractiveness of the electroosmotic process, its use in practice has serious drawbacks. One reason is the extremely low efficiency achieved by conventional systems. In this regard, the use of an electrical charge for a wall of porous building material involves the use of electrodes supplied in / or into the porous material fitted and connected through the material to the ground electrode. When the electrodes are polarized, the water molecules migrate towards the negative electrode. However, after a period of operation of the system, the electrodes are coated with continuous gaseous films, typically hydrogen gas on the cathode, and in other cases with oxide, sulfide or other films, forming electrochemical reactions on the electrode surfaces. These films have a very high electrical resistance, which leads to the breakdown of the electrical characteristics of the system and results in low operating efficiency.

Another important problem associated with conventional electroosmics is the fact that positively charged system electrodes are subject to high levels of electrolytic corrosion. Where electrodes are installed specifically for this purpose, such corrosion initially results in reduced system efficiency and ultimately complete electrical

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- 3 breaks at the electrode. In many cases, however, it is desirable to use reinforcing steel as a positive electrode. In such cases, severe corrosion of the positive electrode can severely degrade the structure itself.

It has been proposed to use high frequency pulses of rapidly alternating asymmetric signal shapes to achieve electroosmos. However, such a procedure is considered to be completely impractical because the extremely high cycling speed causes a considerable load of performance and high radiation high-frequency radiation.

The method of the invention provides a new and improved system and process for performing electroosmic drying of porous structures to avoid problems that typically arise from electrode polarization and concomitant loss of operating efficiency and / or system degradation, or possibly the structure itself. The invention is particularly important for foundation walls and similar constructions. For example, it is important for reducing fluid in pop in large basement walls. Other structures in which the method of the invention can be successfully used are water tanks, retaining walls, decking, structural columns, and so on, i.e., in conjunction with any construction of concrete or other porous building material exposed to water and is subject to degradation from capillary capillary action.

It is also useful to use certain aspects of the invention

in the implementation of reinforced concrete, which has become acidic by carbonization.

An exemplary embodiment of the invention is shown in the drawing, in which Fig. 1 is a diagram of an idealized voltage-time curve of the electro-osmotic system; Figs. 2 and 3 are characteristic partial cross-sections in connection with superstructure; Figs. characteristic partial cross-sections in connection with underground structures such as foundations, and Fig. 7 is a simplified voltage-time cycle of the reference voltage cycle when used to control the operation of the electroosmic system ,,

FIG. 2 shows a reinforced concrete wall 10, which may be a reinforced concrete retaining wall or the like, which is exposed to a source of moisture and is likely to be saturated with water in the pores. It is a concrete wall with internal reinforcement of bars of conventional type 11.

For use of the electro-ossic drying of the wall 10, it is advantageous to use the metal of the internal reinforcement in the system as a positive electrode or anode. For the complete connection of the circuit to the negative electrode, in the described system it is advantageous to use an electrolytic mortar plaster or other suitable porous conductive plaster 12 applied to the outer face of the wall 10. Typically, the conductive mortar plaster 12 will have an electrode 13 embedded therein. which may be in the form of a wire grid or the like

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- The negative and positive electrodes are conductor 6. a controlled voltage source 14 is connected to provide controlled voltages to the system as described below.

The voltages are applied to the electrodes E1, 13 as shown in FIG. 1 by a graphical representation of the voltage-time curve of one operating cycle with two main phases. In the first major phase, a DC voltage pulse 17 is applied to the electrodes E1, 13, with the internal electrode E1 a radiating anode or a positive electrode, and the electrode 11n with the outer face of the wall 10 forming a cathode or a negative electrode. 7 In the second major part of the operating cycle, the voltage reverses to voltage pulse 18j so that the electrodes E1, reverse polarity and become a cathode or anode.

During the first or main part of the cycle, the voltage pulse 17 causes the current to flow in the direction in which the electro-osmotic drying occurs. A second voltage pulse 18 of opposite polarity is applied periodically to prevent or reduce to an acceptable level the formation of gaseous or other insulating films on the electrodes E1, 13 and / or the formation of corrosion products.

For electro - os - matic drying, the mains power must be in the correct direction throughout the cycle. Therefore, the power consumption during the first cycle of the voltage pulse 17 should be at least twice the power consumption during the second part of the voltage pulse cycle 18. The power consumption during the

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in fact, the first part of the cycle should be maximized with respect to the power consumption during the second part of the cycle, avoiding the achievement of a ratio such that undesirable gaseous film formation and / or excessive formation of corrosion products is avoided. Typical experience shows that power sizes from two to ten times are effective, but in certain cases, the sizes may be clearly higher than those indicated. In a given setup, these sizes can be optimized by using an oscilloscope so that circuit power can be monitored during startup.

A microprocessor may be used to continuously optimize cycle periods to derive optimal operating performance. Generally, the voltage pulse ΐχ of the first cycle portion will be the same as the voltage pulse 18 of the second cycle portion. Likewise, the power input for each part of the cycle will be a function of the pulse duration and the power input will be a function of the pulse duration.

In the typical case of the structure to which the method may be applied, shown in Fig. 2, the structure itself may have a considerable capacitance. Thus, the method of the invention provides a controlled voltage change from positive to negative and vice versa. Such a controlled change takes into account the loss of any capacitive charge and substantially prevents radiation of radio frequency interference.

The magnitude of the voltage pulses 17, 18 will normally be at least 20 volts DC. Theoretically it is possible

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use lower voltages. However, the time required to carry out any apparent degree of drying may become disproportionate. At the upper end of the range is a maximum of 40 volts DC. The theoretical peak limit can be much higher than 40 volts. However, as the voltage value increases, safety considerations are becoming increasingly prominent. In this sense, a voltage range of 20-40 volts DC is preferred for typical commercial systems. Desirably, the transition from positive to negative, and vice versa, is controlled so that it does not run faster than about S volts per second, so that the transition periods 19, 20 of Figure 2 from + 40 volts to -40 volts or vice versa would approach approximately 10 seconds or more. If necessary, these sections can be empirically shortened, but should be sufficiently controlled so as to avoid substantial radio frequency interference and / or loss of capacitive charge.

The repetition rate of the duty cycle can be varied considerably. However, it is desirable to use this only in the positive direction, that is, the direction in which the electroosmotic displacement of water is effective. In the present system, cycling is controlled by monitoring the passivity / non-passivity state of the steel reinforcement within the concrete. This is achieved by casting a reference half-cell into the concrete, for example lead - lead oxide, me &lt;5 - cupric sulphate, silver - silver chloride, etc.

The half-element is located inside the concrete, in the area close to (between 10 - 20 mm) of steel reinforcement, or the inserted electrodes if the porous material has no reinforcement in it. According to well known relationships, the potential of the half-cell is a reflection of the smuggled / depassivated state of the inner steel. According to one aspect of the invention, if the semiconductor potential shows that steel is depasivating, the controlled transition potential reverses as previously mentioned and the deposited potential is maintained until the semiconductor potential indicates a sufficiently passivated state of the steel, after which the aforementioned controlled transition reapplies positive potential.

In certain circumstances, the initial state of the building material may be such that controlling the process by exclusively comparing it to the passivated or depressed state of the inner steel would not be effective. In such cases, the suppressed control is used so that the total energy (voltage x time) applied in the positive direction, i.e. in the direction in which the electroosmotic drying is effective, is at least twice the energy applied in the opposite direction. In a typical situation, there are relatively extraordinary circumstances in which control of the electrode of the half-cell has to be suppressed relatively time and improve with the progress of treatment. The system can return to control by the half-electrode electrode again.

The time required to achieve the desired level of efficacy

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drying of the structure is a function of many variables, including the size of the structure and the rate at which the structure absorbs water from the environment. In one case, a large, strong base of one power plant was dried from a moisture level of 100% (full saturation) to about SO% (considerably dry) over a period of about nine months using voltage pulses plus / minus 40 volts DC for

The basement wall of a house with a wall thickness of about 300 m / m can reduce humidity from about 100% to about 77% over a two month period by applying plus / minus 40 volts direct current. Such a process may control itself in the sense that at moisture levels below 80% the continuity of the water column in the pores becomes uncertain. In such cases, the electro-oscillating effect tends to end due to lack of circuit continuity.

The cellar wall often does not have steel reinforcement. In such a case, the electrode elements need to be implanted into the wall. A preferred model for such electrodes is to place each electrode 0.5 m each in a horizontal row about half the height of the cellar wall. Usually it is necessary or necessary to drill so that the electrodes can be deeply embedded in the wall. It is recommended that the primary and reverse voltage pulses have the same magnitude. However, this is not known to be critical and it is found that one of the stresses may be of a different magnitude than the other. In such cases, in order to achieve a predetermined primary pulse power input as compared to the reverse pulse power input, the deposition time of the lower voltage pulse would have to be sufficiently extended to maintain the desired power rate proportionality.

FIG. 2 shows a voltage source 14 which is connected to the monitoring electrodes E1-2. The electrode E1 is connected directly to the steel reinforcement or other intermediate electrode within the concrete mass, while the electrode E2 represents a half-cell of a predetermined composition, preferably lead-lead oxide, due to its relatively low cost.

A positive stress is applied to the reinforcement rod 11 to produce electroosmotic activity within the concrete wall 10. As this electroosmotic activity continues, the reinforcement bars gradually polarize to the point where the corrosion of the reinforcement bar is promoted. As the reinforcement bar L1 gradually polarizes, gradually varying voltages develop between the electrodes E1, E2. The specific voltage level is a function of the half-cell composition. However, the outline of the voltage-time reference voltage half-cell-reinforcement bar (Fig. 7), referred to herein as the reference voltage, is quite distinct and can be used to control voltage reversal, preferably using simple microprocessor circuits.

Thus, as seen in FIG. 7, when it is fed. . · -

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A positive voltage pulse to the electrodes through the external voltage source 14, the reference voltage first increases very gradually, but then rapidly until it reaches a maximum. The reference voltage 60 remains relatively stable for a while before starting to decrease as shown in FIG. 7 »

If the reference voltage begins to drop during a positive voltage pulse from the external voltage source 14, it turns out that the steel becomes depasivated to such an extent that corrosion is a problem. This implies using the inverted reference voltage to initiate the inverted voltage pulse from the external voltage source 16

Reversing the external voltage causes a relatively sharp drop in the reference voltage 61, as seen in Figure 7, until the reference voltage reaches a negative value. Shortly thereafter, the negative reference voltage 62 shown in FIG. 7 is implied. This fact that the steel reinforcement becomes depolarized is stable in ux, hence the reC t kw-V passivated. Thus, a stable negative voltage can be used to restart the positive voltage pulse 17 from the external voltage source 14. This cycle of operations is repeated during the drying process

The duration of the pulses controlled by the semiconductor electrode may vary over a very wide range, depending on factors such as moisture content, electrical conductivity, and the amount and type of oxidizing and reducing substances in the electrode.

- 12 concrete. Typically, the positive impulse can extend up to one hour or even the whole day before the steel reinforcement is polarized to such an extent that corrosion becomes a problem, which can be controlled automatically by monitoring the half-cell voltage.

Under certain conditions, automatic control, only in accordance with the voltages indicated between the electrodes E1, E2, would produce anomalous results. Where the amount of energy transmitted during the positive pulse is not sufficiently greater than the energy transmitted during the negative pulse, the underlying treatment objectives will be substantially impaired. When the positive applied energy is less than half of the energy during the negative pulse in the half-cell electrode control, the half-cell electrode control is suppressed by program control such that in any case the positive voltage multiplied by its duration is at least twice the negative voltage multiplied by duration.

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Typical circumstances in which automatic control can be suppressed are: concrete or other porous building materials contain large amounts of redox substances, problem of poisoning of the half-cell due to the presence of harmful substances, molds or bacteria, disturbing electrical conditions are applied to the reinforcement bars, certain types of earthing systems, or in the half-cell control system, will cause an error due to short circuit, open circuit, and so on.

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In each of the above circumstances, the process should be controlled by a backup suppression control to ensure that the positive energy will be at least about twice as large as the supplied negative energy.

The conditions under which the automatic control of the half-cell electrode must be suppressed are eliminated during drying. Accordingly, normally, automatic control when monitoring the semiconductor electrode system becomes possible at some point very soon from the beginning of the entire drying process. The method of the invention can be applied to saturated structures in many specific ways. For example, in FIG. 3 is an overhead wall 25 which is accessible from both sides on one side and is provided with a porous electrolytic inalloy material 20 with an embedded electrode 27. Connected to the electrode 27 and the conductive surface 28 is a programmed voltage source 11 using the conductive surface 28 as the anode and the embedded electrode 27 as the cathode. Upon activation of the system, the electroosmotic migration of water to the mortar material 26 has a sufficiently porous structure to allow easy drying by evaporation as moisture enters the wall itself.

In the arrangement of FIG. 4, the substructure is formed by a base wall 30 with a system of reinforcing bars 31,

14 which are connected to a power source 14 generating a programmed voltage. The ground 33 is driven by one or more grounding electrodes 32 adjacent to, but not touching, the wall 30, and the grounding electrodes 32 are connected to the negative side of the voltage generating source 14 to serve as negative electrode means. In the illustrated embodiment, the grounding electrode system 32 is provided. located on the side of the wall 30 which is furthest from the reinforcing bar system 31, so that the effect of the electroosmosis reaches the maximum. construction volume zciio

In the foundation wall structure of FIG. 5, the wall 40 is without internal reinforcement. In such cases, elongated holes 41 are inserted into the wall at an obliquely downward direction into which the electrodes 42 are inserted. The voltage source 14 is connected by a positive messenger to the inserted electrodes 42 and negative to the ground electrodes 43 in the form and an electrode gap of 0.5 m has proved satisfactory.

In the construction of FIG. 6, the concrete wall 50, which may be, for example, a cellar or retaining wall, is free on one side 51 and contacts the ground 52 on the other side 53. ' For such an arrangement it is suitable to apply^T.. ' . ’

The outer surface of the wall 51 is an electrolytic mortar material 54 and provided with a cast electrode grid 51, or may be, for example, in the form of a wire mesh. Source 14 gene-

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The programmed voltage is connected with its positive pole to the plaster cast electrode 55 and the negative messenger to the ground electrode system 56 driven into the ground.

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It can be seen that the arrangement of FIG. 6 differs from that of FIG. 3 in that the connections to the voltage source 14 are reversed. Fig. 6 shows the electroosmotic migration of water particles in the direction of the surrounding earth. In this sense, it should be understood that the references in Figs. 2-6 to a refer to the polarity of the main voltage pulse 17 as shown in Fig. 1.

The process according to the invention represents a distinct advantage over the known methods of drying concrete structures and other structures of porous materials which are completely or almost completely saturated with water. Although electroosmotic processes are well known, their non-measurement context has not been accomplished because of the practical difficulties associated with developing insulating gaseous films, especially at the cathode, and burning the corrosion products at the anode. In the case of an insulating gaseous film, the process quickly becomes ineffective as the resistance value increases with the formation of the gaseous film. In the case of the formation of corrosion products, in addition to introducing considerable resistance or breaking the electrical continuity, the dried structure may be seriously damaged by weakening the internal reinforcement and / or by cracking of surrounding material due to internal pressures due to expansion of the corrosion products.

Using the method of the invention, controlled cyclic polarity reversal of the energy pulses serves to prevent the formation of unwanted gaseous films and corrosion products while at the same time allowing energy flow in the network so that electroosmotic processes can advance forward with remarkable efficiency levels and without making structural integrity.

The process according to the invention is of course applicable not only for the electroosmotic drying of porous building materials, but also for the realization of concrete by electrochemical processes. In the case of realization drying, it is desirable to cause the electrolytic migration of hydroxyl ions from one area of ​​the existing concrete structure to another area that has been colored and thereby acidified to the extent that serious corrosion of the internal reinforcement structure may be imminent. Restoration of reinforced concrete structures that have reached an undesired degree of carbonization can be accomplished by applying voltage between spaced electrodes, one of which is located within a relatively carbonated area of ​​concrete and the other is located within a relatively uncharged area of ​​that concrete, or is embedded within deposited layers of electrolyte material that is rich in hydroxyl ions. Depending on the specific shape of the dried structure, the reinforcement bars may be exposed

- 17 depacification or gaseous film coating. In any case, the controlled drying method of the invention, including controlled burning of the applied voltage, can be used with great advantage in protecting the inner steel reinforcement against corrosion and / or improving the efficiency of the operation.

In the method according to the invention, the polarity change is performed in all cases according to the controlled change so that radio frequency radiation interference and / or intrinsic cepacitance of the structure is efficiently discharged in accordance with its discharging rate so that polarity changes do not involve unnecessary energy consumption to overcome opposite residual stresses.

A particular advantage is the process control by monitoring the half-cell voltage, so that at each stage of the process there may be a tendency to polarize, depressivize and be subject to corrosion in the internal steel reinforcement or embedded electrodes where the reinforcement and applied voltage are not inverted.

and the inverted voltage pulse is maintained until a satisfactory passivity state is restored. This procedure makes it possible to achieve optimum efficiencies to the extent that a positive or augmenting pulse of electric energy can be maintained to the greatest extent possible and periods of inverted polarity can be minimized.