WO2000068168A1

WO2000068168A1 - Method

Info

Publication number: WO2000068168A1
Application number: PCT/GB2000/001596
Authority: WO
Inventors: John Bruce Miller
Original assignee: John Bruce Miller
Priority date: 1999-05-05
Filing date: 2000-05-05
Publication date: 2000-11-16
Also published as: JP2002544412A; GB2365421A; GB0128868D0; AU4585100A; GB9910209D0; GB2365421B

Abstract

A method of electrochemical treatment of building material (1) includes mounting on the material (1) an anode network (5) and spraying electrolytic material (11) onto the material (1) and the network (5) and leading wetting liquid via porous, distributing hoses (6) to a gap between the material (1) and the network (5). The method may include heating in the region of the electrode (5) in order to improve the efficiency of the electrochemical treatment, the power for the heating being supplied from a source (12) separate from the power source (7) for producing the electrochemical treatment.

Description

METHOD

This invention relates to a method of electrochemical treatment of building material.

Recent years have seen the development and application of high-powered electrochemical treatments for reinforced concrete and similar building materials. There are currently two main commercially available methods. One is aimed at halting corrosion of embedded steel in chloride- contaminated concrete and is known variously as desalination, chloride extraction, salt removal, chloride removal, chloride neutralisation, and dechlorination. The other is aimed at restoring alkalinity to concretes which have lost the ability to protect embedded steel owing to the neutralisation of the alkalinity of the cement paste by absorption of carbon dioxide from the atmosphere (called carbonation) . This latter method is known as realkalisation or repassivation.

The most popular way of applying either of these methods is to mount a temporary anode on the surface of the concrete to be treated, using the existing embedded steel as a cathode. The temporary anode is then embedded in an electrolytic material, for example a mass of wet cellulose, usually made from recirculated newsprint to which water containing appropriate electrolytic substances is added. The wet cellulose is normally sprayed onto the anode and the surface of the concrete. A steady direct electric current is then applied between the anode and the cathode, which results in chloride extraction or realkalisation. Variations of these methods exist which entail the use of prefabricated anodes of various descriptions, and/or the use of alternative anode materials and/or alternative electrolytic materials.

Common to most of the methods of application, and particularly to the cellulose fibre technique described above, is that the mass of electrolytic material tends to dry out, especially in hot and/or windy weather and thus the efficiency of the treatment process decreases. Practice has shown that keeping the electrolytic material wet by covering with plastics sheeting, or spraying on more water or electrolyte solution, or using external perforated sprinkler hoses is only partially successful. Furthermore, when many of the electrolytic materials now in use dry on the surface, a water repellent crust is formed which makes it extremely difficult to re-wet using surface applications of moisture. It will be appreciated that, as the electrolytic material dries, the efficiency of the treatment rapidly falls off, leading to protracted treatment times or to the complete removal and renewal of the anode system with its electrolytic mass.

According to the present invention, there is provided a method of electrochemical treatment of building material, including providing at said material an electrode and electrolytic material in contact with each other, and with said electrolytic material in contact with said building material, and leading wetting liquid to inwards of the outside surface of said electrolytic material.

Owing to the present invention, it is possible to improve the efficiency of the electrochemical treatment.

The wetting liquid may be water, or water containing appropriate electrolytic substances.

The electrode itself may or may not contact the building material and may be an anode or a cathode. In a preferred embodiment, the electrolytic material is kept moist from the inside by the constant application of small amounts of moisture in the region of the electrode using a flexible porous tube mounted on supports for the anode and embedded in the electrolytic mass together with the anode and its supports.

In order that the invention may be clearly and completely disclosed, reference will now be made, by way of example, to the accompanying drawings, in which:-

Figure 1 is a fragmentary front view of a treatment arrangement attached to a surface of a steel-reinforced concrete wall,

Figure 2 is a partly diagrammatic, fragmentary vertical section through the wall and the arrangement, Figure 3 is a view similar to Figure 1 of a modified version of the arrangement, and

Figure 4 is a view similar to Figure 1 of another modified version of the arrangement. The drawings show schematically an installation for the high-powered treatment of the reinforced concrete wall 1 which contains embedded steel reinforcement 2. Distance pieces 4 in the form of battens are fixed to the surface 3 of the wall 1 and support a temporary anode network 5 and porous hoses 6, so that a gap exists between the wall 1 and the network 5. There may be a plurality of such networks 5 of a standard size distributed over the surface of the wall 1 to be treated, but only one is shown for ease of illustration. The anode network 5 is connected to a d.c. electric source 7 also connected to the reinforcement 2 which acts as a cathode. The hoses 6 are connected via T- pieces 8 to a supply conduit 9 common to the hoses 6 for supplying a wetting liquid, in this case water. By means of a spray gun 10, wet electrolytic material 11 may be sprayed onto the treatment arrangement 4 to 6 to embed the treatment arrangement 4 to 6 in the wet electrolytic material and to cover with that material the surface 3 in the region of the arrangement 4 to 6. Depending upon the hose layout desired, the items 8 may instead be Y- or X- pieces.

The T-, Y-, or X-pieces 8 incorporate valves suitable for the regulation of the water supply to each of the porous hoses 6. The conduit 9 is a hose or pipe connected to the water mains. The ends of the hoses 6 further from the conduit 9 are plugged by any suitable method, such as crimping and gluing, bending back and tying, inserting objects or the like. Alternatively, plugging can be avoided by running excess lengths such that the length of the hose exceeds its effective length as described later. The porous hoses 6 are of internal diameter of preferably 10mm or less. Larger diameters can of course be used, but smaller diameters are preferred since they allow closer and easier bending without collapsing around features of high curvature, such as the corners of columns, architectural ornamentation, window openings and the like. The porous hoses should preferably be designed to work up to pressures in excess of 20 bars (2 MPa) . There are a number of types of porous hose on the market. The most common types are designed to work at pressures of up to 5 bars or so, and are meant for horticultural purposes, such as soaker hoses which are used on the surface of soil to ease the watering of plants, or buried in order to keep the root zones of plants moist. Though these types of hoses can be used, they are not ideal since their porosity is such that water regulation is difficult because these types tend to deliver water at rates which are in excess of those necessary to keep the electrolytic material correctly moistened, and indeed might often result in the material being loosened and falling off. The types of hoses designed to work at higher pressures are much more suitable, since their being designed for higher working pressures results in easier regulation, at ordinary mains pressures, of the low flow rates of water necessary to replace that lost by evaporation and drainage from the electrolytic mass.

An example of a very suitable commercially available porous hose is manufactured by Itep International in Gap, France and is called by them Microporex 6/11. The hose has an inner diameter of 6mm, an outer diameter of 11mm, and a working pressure of up to 60 bars (6 MPa) . When used at normal water main pressures of 1 to 7 bars, this hose allows easy regulation of low flow rates of water over lengths approaching 20m. The effective length of the horticultural type of hose under similar conditions is shorter, and correct regulation is more difficult, since these hoses tend to deliver too much water at one end, and too little at the other end of the effective length.

The effective lengths of the hoses 6 are limited by their diameters. The larger the diameter, the greater the effective length becomes, i.e. before pressure loss results in too little water transport through the walls of the far ends of the hoses. Using the Microporex 6/11 hose mentioned above, the effective length approaches 20m, which appears to be an eminently suitable length for the following reasons :

1. It is commensurate with the largest surfaces normally treated in one operation.

2. It avoids unnecessary cutting of the hoses, since smaller surfaces can be covered by bending the hose down to and running it along the next lower level, where it is abutted, but not necessarily hydraulically joined, to the next hose.

3. 20m lengths are easily handled, installed, re-used and stored.

4. Water distribution is sufficiently homogeneous.

The hoses are installed by any suitable means. Often they can be intertwined through, or tied to, the meshes of the temporary anode network 5, or fastened to the battens 4 affixed to the anode network 5 or fastened directly to the concrete surface 3 by any convenient means. For maximum efficiency, the hoses 6 should lie between the anode network 5 and the concrete surface 3, since this is the zone which it is important to keep wet. Since any drying of the outer surface zone of the electrolytic mass tends to produce a crust which aids in reducing evaporation, and advantageously thus also the amount of replacement moisture required to maintain conductivity of the inner part of the electrolytic material, the hoses 6 should not normally be installed between the anode network 5 and the outer surface of the electrolytic material.

The flow rate of replacement moisture required is, of course, dependent on the evaporation rate, which in itself is highly variable since it in turn depends heavily upon weather conditions, and on the nature and smoothness of the outer surface of the electrolytic mass. In addition, moisture can be absorbed by the concrete itself depending on the dryness of the concrete surface to be treated. In practice, the supply should be adjusted until the flow rate is observed to keep the material below the hose in question and above the next one down sufficiently wet. There are several ways to judge whether the material is sufficiently wet. One is to observe the current passing between the anode and the cathode. This current responds to the water flow by increasing with increasing flow up to a maximum after which no further increase in water flow is necessary or desirable. Another way is to observe the drainage from the material. This should be slight, for example no more than a few drips per minute from each linear metre at the bottom edge of the installation, or no more than a few drips per minute from each square metre of downwards-facing horizontal surface. The amount of moisture needed may be between 0.1 and 5 litres per minute per square metre of the concrete surface being treated.

On vertical surfaces, the vertical distance between the hoses depends upon the permeability of the electrolytic mass. For a cellulose fibre mass, the vertical distance is usually between one and three metres, depending on the exact source of fibre and the density of the sprayed material . For horizontal surfaces, the distance between tubes may be between 0.5 and lm.

Should the electrochemical method in use require re- wetting using a solution of electrolyte instead of water, then the mains water supply may be replaced by supply lines containing the appropriate solution using conventional pumping or header tank techniques.

It has been found in practice that the method of moistening described above with reference to the drawings saves expensive and difficult, often unsuccessful, external moistening operations. It also cuts down the amount of water or electrolyte solution used since run-off is minimal, and by the same token is far less messy since excesses are eliminated. Most importantly, the constant moistening of the inner zone between the anode and the concrete surface results in optimal treatment conditions for the electrochemical process in question. This gives the best result in the least time, and thus at lowest cost.

The efficiency of the electrochemical treatment can be considerably further increased by raising the temperature of the anode network and the adjacent concrete zone. This can be achieved in two ways respective examples of which are shown in Figures 3 and 4. In a first instance, shown in Figure 3, the anode network 5 itself can be utilised as a resistance element to produce heating upon the application of an electric current. This entails the connection of the extremities of the anode network to an electrical power source 12. The rating of the power source 12 is selected in dependence upon the dimensions of the anode network 5 and the desired temperature increase. The connections are to bus-bars 13 welded to respective opposite edge zones of the network 5. In a second and preferred instance, shown in Figure 4, a distributed resistance element 14 extending in parallel to the anode network 5 is electrically insulated from the network 5. The resistance element may be a proprietary heating element, or, as shown, may simply consist of a length of conventional insulated conductor. The extremities of the element 14 are connected to the electrical power source 12. The rating of the power source 12 depends upon the dimensions of the resistance element 14 and the desired temperature increase.

In both cases, the temperature is conveniently regulated by thermostatic control by thermostatic elements 15 implanted into the deposited electrolytic material 11. Alternatively, a timer control may be used so that the anode and the adjacent concrete zone are heated for fixed lengths of time.

It is important that the power source 12 used has no common electrical circuit with the power source 7 used for the electrochemical treatment as such, otherwise the two circuits will interfere with each other.

Heating the anode in this way is energy efficient in that very little heat is wasted. Energy can be further conserved by covering the electrolytic material 11 surrounding the anode network 5 by some form of thermally insulating sheeting 16.

The heating of the anode network 5 greatly accelerates the rate at which the electrochemical process proceeds. In the case of chloride extraction, for example, the time required for reductions of 70% in the concentration of chloride is shortened by a factor of 2 to 3 for a 10 to 20°C increase in temperature. The time taken for reductions of 90% in the concentration of chloride, which prior to this method was impracticably long, can now often be achieved in times associated with 70% reductions using conventional methods. In addition, when using iron-containing, in practice steel, anodes for electrochemical chloride extraction, the increased efficiency results in the extracted chloride ion causing very early rusting of the anode, which in turn causes early rust staining of the cellulose fibre. If chloride-contaminated zones in the concrete alternate with zones with little or no chloride contamination, discrete portions of the external surface of the cellulose fibre are rust-stained, thus rendering clearly visible the chloride- contaminated zones in the concrete which are otherwise difficult to find using conventional survey techniques, which include expensive sampling and chloride analysis. This visibility allows sampling and analysis to be concentrated on relevant areas, thus saving much time and expense .

Claims

1. A method of electrochemical treatment of building material (1) , including providing at said material (1) an electrode (5) and electrolytic material (11) in contact with each other, and with said electrolytic material (11) in contact with said building material (1) , characterized by leading wetting liquid to inwards of the outside surface of said electrolytic material (11) .

2. A method according to claim 1, wherein said leading comprises leading said wetting liquid to the region of said electrode (5) .

3. A method according to claim 1 or 2, and further comprising, prior to said leading, supporting said electrode (5) relative to said building material (1) by mounting means (4) provided in a gap between said electrode (5) and said building material (1) .

4. A method according to claim 3 as appended to claim 2, wherein said wetting liquid is led to said gap.

5. A method according to any preceding claim, wherein said wetting liquid led to inwards of said outside surface is distributed over said electrolytic material (11) by way of distributing means (6) .

6. A method according to claim 5 as appended to claim 3, wherein said distributing means (6) is supported on said mounting means (4) .

7. A method according to claim 5 or 6, wherein said distributing means (6) comprises a porous hose (6) .

8. A method according to any preceding claim, and further comprising heating in the region of said electrode (5) in order to improve the efficiency of said electrochemical treatment .

9. A method according to claim 8, wherein said heating is electrical heating.

10. A method according to claim 9, wherein said electrical heating comprises utilising said electrode (5) as an electrical resistance element.

11. A method according to claim 9, wherein said electrical heating is by an electrical resistance element (14) in the region of said electrode (5) .

12. A method according to claim 11, wherein said resistance element (14) is electrically insulated from said electrode (5) .

13. A method according to any one of claims 8 to 12, wherein said heating is thermostatically controlled.

14. A method according to claim 13, wherein said heating is thermostatically controlled in dependence upon temperature in said electrolytic material (11) .

15. A method according to any preceding claim, wherein said outside surface is covered by thermally insulating sheeting (16) .

16. A method according to any preceding claim, wherein said electrochemical treatment is chloride extraction and said electrode (5) is an iron-containing electrode which rusts during said electrochemical treatment.

17. A method according to claim 16, wherein the rusting of said electrode (5) results in staining of discrete portions of said electrolytic material at said outside surface.

18. A method according to claim 17, wherein the staining of said discrete portions is followed by sampling at corresponding discrete zones of said building material (1) .