Reinforcing or carrier element for structural material

Reinforcing or carrier elements for plaster are used as electrodes in electro-osmotic dehumidification installations. The elements comprise a carrier body constituted by a flexible net having a surface of synthetic resin in contact with the plaster and the net has filamentary carrier materials incorporated therein. The synthetic resin is a conductive, essentially ion-free thermosetting resin of macromolecular structure, preferably an at least partially cross-linked acrylate polymer having a high surface roughness and containing a small amount of a plasticizer, and forms either the matrix or a coating of the flexible net. The filamentary carrier materials may be carbon or metal filaments. In the use of the dehumidification installation, a voltage alternating between a positive and a negative potential is conducted between the cathode and the anode, the time interval of the positive potential exceeding that of the negative potential.

The present invention relates to a reinforcing or carrier element for 
structural material, more particularly an electrode for an electro-osmotic 
dehumidification installation wherein the structural material is plaster 
or the like carried by the element. 
Reinforcing or carrier elements consisting of rod-shaped or net- or 
grid-like structures for structural materials are known. For example, 
structural steel mats or grids have been used for reinforced concrete 
bodies and fine metal grids have been used as reinforcing carriers for 
plaster and the like facings. For such use, the fine metal grids are 
frequently coated with burned ceramic masses to assure better adhesion of 
the plaster or mortar. One of the disadvantages of such metallic carrier 
grids is their exposure to corrosion. When such grids are arranged in 
zones of different pH-values, galvanic elements are frequently produced, 
creating electric fields leading to a destruction of the structural body 
and an attraction of humidity from the ground into the structural body. 
Such disadvantageous effects are encountered particularly when such 
plaster carrier grids are used in the renovation of old historical 
buildings whose walls are to be dried out. Therefore, it has often become 
necessary to build in electrodes of electro-osmotically operating 
dehumidification installations in addition to the plaster carrier grids to 
obtain the required dehumidification of the structural body. 
Various methods for drying building walls are in use today. A research 
report of the Austrian Institute for Structural Research (Verlag 
Strassenbau, Chemie und Technik Verlagsgesellschaft mbH, Heidelberg, 1967) 
distinguishes the following: measures to be taken in connection with the 
plasterwork, airing methods, dehumidification bodies, incorporation of 
sealing layers, filling the pores, electro-osmotic and other methods. This 
invention belongs to the art of electro-osmotic methods and, therefore, 
the theoretical foundations thereof, as outlined in the report, will be 
outlined hereinbelow. 
The electro-osmotic methods make use of the phenomenon of electro-osmosis 
to brake the humidity rising in the capillaries of masonry walls and to 
press it downwardly. Polarization occurs at the interface between water 
and a solid material, producing a negative charge on the surface of the 
solid material and a positive charge on the liquid drops. These electric 
charges (polarization) are normally not noticed but they cause a movement 
of the charged particles in an electric field, the solid material 
particles (as far as they are mobile) moving to the anode (this being also 
known as electrophoresis) while the liquid particles, especially if the 
solid material particles cannot readily move, tend to move to the cathode. 
Since water always contains salts, it is conductive so that galvanic 
elements can be created by a suitable selection of the electrode materials 
to effect the electro-osmotic phenomena. The disadvantages include 
corrosion and a limited operating life of the electrodes while the 
installation has the advantage of requiring no maintenance. 
In the active methods, an outside electric current supply is used to create 
the electric field between the electrodes. While this could also lead to 
corrosion, this problem has been overcome by using graphite or 
electrically conductive synthetic resins. 
Various arrangements and compositions of electrodes have been disclosed in 
German patent Nos. 2,722,985 and 2,603,135 as well as Published German 
Patent Applications Nos. 2,703,813 and 2,706,193. Published German Patent 
Application No. 2,706,172 proposes electrodes with additional films 
designed to prevent corrosion. 
As has been disclosed in Published German Patent Application No. 2,705,814 
and German patent No. 2,503,670, the upper limit of the voltage applied in 
the active method in dependence on the composition of the masonry and the 
salt content of the water is set by the decomposition voltage since an 
electrolysis would generate gases by the decomposition of the water, which 
destroy the structural parts, for example the plaster, into which the 
electrodes are built. It is pointed out in Published German Patent 
Application No. 2,705,814 that generated oxyhydrogen gas may even 
constitute a danger of explosion so that an upper limit of 2.8 V is 
required. On the other hand, it would be desirable to increase the 
electric field by an increase in the applied voltage to improve the 
desired effect. This is particularly required in old or very thick masonry 
walls, or where the pressure of the rising humidity is considerable. 
Furthermore, an increase in the applied voltage will considerably increase 
the speed of the drying effect. 
It is accordingly a primary object of the invention to provide a 
reinforcing or carrier element of the first-indicated type, which may be 
used in regions of different and/or changing pH-values and which make 
possible an intimate connection with the surrounding structural materials. 
It is another object of the present invention to use such reinforcing or 
carrier elements as electrodes for dehumidification installations 
operating on the basis of electro-osmosis. 
The above and other objects are accomplished according to this invention 
with a reinforcing or carrier element for structural material, which 
comprises a carrier body constituted by a flexible net having a surface of 
synthetic resin in contact with the structural material, the net having 
filamentary carrier materials incorporated therein. The synthetic resin is 
preferably a conductive, essentially ion-free thermosetting resin of 
macromolecular structure, for example an acrylate, and may either form the 
matrix of the flexible net or a coating thereof. The filamentary carrier 
materials are preferably conductive filaments of carbon or metal, which 
preferably are silver-coated. 
The unexpected advantages of the invention include the fact that it 
provides a chemically neutral reinforcing or carrier element for 
structural material, which may be built into structural bodies regardless 
of various prevailing pH-values. They furthermore avoid creating electric 
fields by electrochemical decomposition so that they may be used in the 
renovation of old historical buildings whose structural bodies are very 
humid. At the same time, they may be used as electrodes for 
dehumidification installations based on electro-osmotic principles. Such 
net-like electrodes are particularly useful for building an electric field 
over large areas, the intimate connection between the carrier net and the 
surrounding structural materials additionally assuring an intensive 
building of the field over a long operating time. Even subsequent settling 
of the structural materials and/or the structural body do not interfere 
with the intensive building of the field. If some of the filaments of the 
net are broken, electric current supply remains assured by parallel 
filaments supplying power to the installation so that the electric field 
continues to function. At the same time, no disturbances can be created by 
electrolytic decompositions or hydrogen depositions on the anode even when 
the reinforcing or carrier elements of the invention are used in 
installations of large area and at higher operating voltages because at 
least the entire surface of the net consists of a conductive synthetic 
resin. The flexibility of the net assures a full adaptation thereof to 
different environments, such as different ground or structural body 
levels. This advantage is noted especially when the reinforcing or carrier 
elements of the present invention are used in the renovation of very humid 
structural bodies. Since the coating of the net with the conductive 
synthetic resin causes a uniform voltage discharge over the entire area of 
the electrode, an electro-kinetic effect, for example electro-osmosis, 
over a large area is obtained.

Referring now to the drawing and first to FIG. 1, there is shown a 
reinforcing or carrier element for structural material, such as plaster or 
the like, comprising carrier body 1 constituted by flexible net 2. In the 
illustrated embodiment net 2 comprises electric power supply conductor 3 
as an integral part thereof and this conductor is constituted by band 4 
consisting of a plurality of flexible wires 7 embedded in synthetic resin 
9. As shown, the net is band-shaped and extends in a longitudinal 
direction indicated by arrow 5 and electric power supply conductor 3 
extends in this direction centrally between respective longitudinal edges 
6 of the band-shaped net. The flexible wires may be metal filaments 8 
which may be silver-coated. The use of titanium wires will assure good 
conductivity while keeping the potential differential between the surface 
of metal filaments 8 and surrounding synthetic resin 9 low. If the 
potential differential is low, no electromotive force and, therefore, no 
current flow will be created between the different materials, i.e. the 
silver-coated or titanium wire 8 and the synthetic resin 9. Accordingly, 
the metal will not be decomposed, particularly metals whose own potential 
is more negative, so that no ions will go into solution in the surrounding 
synthetic resin. The resin will remain ion-free. If desired, carbon 
filaments preferably coated with silver may also be used in the electric 
power supply conductor instead of the metal filaments. 
The illustrated electric power supply conductor enables this carrier 
element to be uniformly supplied with electric current when used as an 
electrode and such electrodes may be built in subsequently to produce 
electric fields in building bodies to provide barriers against the spread 
of humidity. The use of preferably silver-coated carbon filaments or metal 
filaments, such as titanium filaments, in the electric power supply 
conductor increases not only the strength of the net but also its 
conductivity. The central arrangement of the electric power supply 
conductor assures the uniform supply of current to all parts of the 
band-shaped net and enables damaged net parts to be readily bridged. 
The flexible net preferably has a mesh size adapted to the structural 
material reinforced and carried thereby and the mesh width is preferably 
about 5 mm if the carrier element is used for plaster. This will enable 
the plaster to be placed on the carrier element without damage thereto. 
FIG. 2 shows flexible net 11 comprising carrier body 10. Strands 12 to 14 
of net 11 consist of synthetic resin 15 which is a conductive, essentially 
ion-free thermosetting resin of macromolecular structure. The preferred 
synthetic resin is an at least partially cross-linked acrylate polymer 
having a high surface roughness and containing a small amount of a 
plasticizer. A useful synthetic resin for the purposes of the present 
invention has been disclosed in my Austrian patent No. 313,588 whose 
disclosure is incorporated herein by way of reference. It is of advantage 
to use a synthetic resin doped with an oxygen-reducing metal, such as 
titanium or boron. When a net comprised of such a doped synthetic resin is 
used as an anode in an electro-osmotic dehumidification installation, 
oxidation of the anode and its concurrent loss of activity is avoided. The 
high surface roughness of the synthetic resin has the advantage of 
providing good adhesion between the carrier body and the structural 
material, such as plaster, carried thereby and surrounding it. 
Incorporating a small amount of plasticizer in the synthetic resin assures 
that the synthetic resin matrix or coating does not shrink so that this 
adhesion is maintained. Thus, good contact is maintained for a long time 
between the carrier element and the surrounding structural material when 
such carrier elements are used as electrodes in dehumidification 
installations. This effect is further enhanced with the use of the doped 
synthetic resins which avoid the fouling of the anode during operation. 
If the synthetic resin wherein the filamentary carrier material 20 is 
embedded is a semi-conductor containing a relatively small amount of 
carbon particles freely floating in the synthetic resin, the electrical 
charges are carried by electrons and holes, in contrast to so-called ion 
semi-conductors wherein the charges are carried by the substance. Such 
reinforcing or carrier elements have a particularly good conductivity 
under the temperature conditions prevailing in buildings. Since the carbon 
particles, which enhance the conductivity of these semi-conductors, need 
not form a skeleton for the carrier element, small amounts of carbon 
suffice, which reduces the brittleness of such synthetic resin structures. 
To increase the mechanical strength of the net as a carrier element for 
structural material and to increase the conductivity of the net for use as 
an electrode, metal or carbon filaments 16 and 17 are incorporated in 
synthetic resin matrix 15 of the net so that the surface of the flexible 
net in contact with the structural material it carries, such as plaster or 
the like (not shown), consists of the synthetic resin. 
In the embodiment of FIG. 2, strand 14 of net 11 constitutes electric power 
supply conductor 18, the mechanical resistance and electrical conductivity 
of the conductor being enhanced by incorporated carbon or metal filaments 
16, 17 shown to carry silver coating 19. If desired, the conductivity of 
the entire net may be enhanced by coating all filaments embedded in the 
synthetic resin of the net with silver whereby the electric field will be 
made stronger over the entire area of the net. 
It is within the scope of this invention to use any conductive synthetic 
resin for the manufacture of flexible net 11, which is highly elastic and 
may be readily bent without snapping back to its original shape, i.e. 
which is shape-retaining. This considerably improves the adaptability of 
the carrier element and enables the structural material to be readily 
applied thereto so that the entire assembly may conform to various surface 
configurations of structural bodies on which it is mounted as a facing. 
The entire net may then be coated with synthetic resin 15, as has been 
shown by way of example at the intersection of strands 12 and 14 of net 
11. Carbon or metal filaments 16, 17 serve not only to enhance the 
electrical properties of the carrier body but filamentary carrier material 
20 constituted by these filaments also reinforces the flexible net. While 
any suitable material may be used for filamentary carrier materials 20, 
carbon and metal filaments are preferred because, for the preferred use as 
an electrode in electro-osmotic dehumidification installations, such 
filaments combine good conductivity with high strength. 
FIG. 3 shows an enlarged cross section of strand 13 of net 11. As shown, 
metal filaments 16 and carbon filaments 17 are embedded in synthetic resin 
matrix 15, the carbon filaments having silver coatings 19. As also shown, 
freely floating and randomly distributed carbon particles 21 are 
distributed throughout the synthetic resin matrix, this arrangement being 
possible because the synthetic resin has semi-conductor properties and the 
carbon is not required to provide a conductor system but merely serves to 
increase the conductivity. 
FIGS. 4 and 5 show two installations with different arrangements of the 
reinforcing or carrier elements of this invention on structural bodies 
constituted, for example, by a brick or reinforced concrete wall. 
In the embodiment of FIG. 4, two flexible nets 24 and 25 are mounted on a 
surface of structural body 22, being affixed thereto by suitable fastening 
means 27, such as synthetic resin studs. The two nets constitute a cathode 
and an anode, respectively, of voltage supply 31 for an electro-osmotic or 
electro-kinetic dehumidification installation 37 for the structural body, 
the two nets being arranged one above the other in a vertical direction. 
The voltage supply comprises direct current source 30 having positive pole 
28 and negative pole 29, and lower net 25 is connected to the negative 
pole while upper net 24 is connected to the positive pole of the direct 
current source. After these connections have been made, plaster or the 
like is applied as the structural material to the two nets to cover the 
surface of structural body 22. The structural material is applied in a 
sufficient thickness to embed nets 24 and 25 entirely therein, i.e. so 
that the nets lie below surface 34 of the structural material layer. Net 
25 constituting cathode 36 is arranged in foundation 39, the soil in the 
range of the cathode preferably having been replaced by a porous, 
water-permeable layer capable of permitting water to be removed from 
around the foundation. The vertically superimposed arrangement of the two 
electrodes on the outside of structural body 22 provides an effective 
horizontal barrier against the rise of humidity 38 from the foundation of 
the structural body. Since the anode is arranged above the cathode and the 
humidity within the structural body travels in the direction of the 
cathode, the humidity cannot rise from the foundation, as symbolically 
shown by arrows 43. The electric field generated between the electrodes is 
indicated by field lines 42. 
In the embodiment of FIG. 5, wherein like parts operating in a like manner 
are designated by the same reference numerals as in FIG. 4, the 
considerable thickness of structural body 23 makes it desirable to mount 
carrier element 24 constituting anode 35 on the interior surface of the 
structural body facing the inside of the building while carrier element 25 
constituting cathode 36 is mounted on the exterior surface facing the 
atmosphere. As in the embodiment of FIG. 4, the cathode is mounted in the 
foundation and an intensive electric field 41 is generated when the 
electrodes are connected to direct electric current source 30, which is 
schematically indicated by field lines 42. 
To avoid a depolarization of the anode and a concomitant weakening of the 
conductivity, which would decrease the strength of the electric field 
generated between the electrodes, pole reversal switching member 44 is 
associated with direct electric current source 30 and is arranged between 
upper net 24, i.e. the anode, and the direct current source. This 
switching member has the result of periodically and in short intervals 
reversing the polarity of electro-kinetic installation 37. In this manner, 
a voltage alternating between a positive and a negative potential is 
conducted between cathode 36 and anode 35. As a result, the ions in the 
electric field cannot be deposited and depolarization is avoided. The high 
conductivity in the structural body prevents salt ions traveling between 
the electrodes from being deposited and the large current flow assures 
building of a very intensive electric field, causing a correspondingly 
strong flow of water in the direction of the cathode, i.e. out of the 
structural body. 
The use of like electrodes avoids the disadvantages of an electrolytic 
decomposition on the basis of potential differentials in the structure. 
Furthermore, the installation may be operated with relatively low voltages 
since the switch effecting a reversal of the polarity will prevent 
electrolytic depositions on the anode. 
It is also possible to arrange the two electrodes at two different levels 
relative to foundation 39 and to ground them together whereby the natural 
potential differential is balanced and a horizontal barrier is produced to 
prevent the humidity from migrating beyond the level of the electrodes. 
Since the synthetic resin of the reinforcing or carrier element of the 
present invention preferably has a high surface roughness and low 
shrinkage, the adhesion of the plaster to the synthetic resin element will 
remain strong for a long time, thus avoiding any collection of humidity 
and concomitant corrosion in the range of the electrodes while assuring a 
high conductivity. 
FIG. 6 shows voltage supply circuit 45 for anode 46 and cathode 47 
constituted, respectively, by nets 48 and 49 of the present invention. 
This circuit comprises transformer 50, direct current smoothing diode 51, 
polarity reversal switching member 52 and timing member 53. The switching 
member has electric pulse switch 55 arranged parallel to smoothing diode 
51 of rectifier circuit 54. The switch is constituted by transistor 56 and 
has input 59 connected to negative pole 58 of direct current source 60 
constituted by transformer 50 and output 61 connected to transmission line 
62 leading to anode 46. Transistor 56 serving as closing contact for the 
pulse switch is actuated by timing member 53. The timing member enables 
the transistor to permit passage of the current for a predetermined time 
interval. Diode 57 associated with polarity reversal switching member 52 
assures voltage passage only when a negative potential is applied to 
output 58 of transformer 50. 
Further switch 65 is arranged between transmission line 62 leading to anode 
46 and transmission line 64 leading to cathode 57 so that, if and when 
desired, the polarity of nets 48 and 49 may be reversed, the anode 
becoming the cathode and the cathode becoming the anode. Also, current 
indicating device 66 is connected to voltage supply circuit 45 to enable 
the current flow and voltage to be read. Any suitable type of voltage 
supply circuit may be used within the scope of this invention and the 
transistor circuit may, for example, be replaced by a relay control or an 
integrated circuit in a microprocessor or the like. Thus, this type of 
voltage supply circuit has the advantage of being able to make use of 
various technologies best designed to fit the conditions under which the 
system is used. 
FIG. 7 shows a preferred form of the voltage supply curve in a method for 
the electro-osmotic movement of a polar liquid in a porous structural 
material reinforced or carried by the two electrodes of the invention. In 
this method, a voltage alternating between a positive and a negative 
potential is conducted between the cathode and anode, the time interval of 
the positive potential exceeding that of the negative potential and the 
positive potential preferably exceeding the negative potential. This 
produces the desired electro-osmotic effect while the short application of 
the negative potential eliminates any electrolytic decomposition products, 
such as undesired gases. The high concentration of the substances 
generated at the electrodes effects a rapid and preferred reversal of the 
chemical reactions while any build-up of a reversed electric field and 
thus the reversal of the electro-osmotic effect is reduced or fully 
avoided. 
The requirement of different time integrals for the positive and negative 
potentials may be met by providing different time intervals and/or 
different voltages for the positive and negative voltage portions. It is 
particularly advantageous if the alternating potential is a sinus voltage 
of an existing electric current supply net and the negative potential of 
the supplied electric current is reduced. FIG. 7 shows positive sinus 
curve 67 of a suitably down-transformed electric current obtained from an 
existing electric current supply net while negative potential portion 68 
of the sinus curve has been reduced by cutting off the voltage peak of the 
negative potential. Thus, as long as the negative potential portion of the 
original sinus curve does not exceed a predetermined voltage, no potential 
is applied to the electrodes. Only a portion of the sinus voltage 
exceeding the predetermined voltage is conducted to the cathode and anode. 
This may be readily realized by semiconductors. The sinus voltage of the 
positive potential preferably exceeds 6 V. While the use of the net 
frequency has great advantages, the method of the present invention is not 
limited to sinus voltages of 50 or 60 s.sup.-1. 
The preferred voltage time curve shown in FIG. 7 may be readily obtained 
with voltage supply circuit 45 illustrated in FIG. 6. Passage of potential 
through transistor 56 is opened by a condenser arranged in timing member 
53 only after positive potential has been applied for a certain time 
interval so that negative potential is applied to anode 46. The timing 
member is so constructed that this application of negative potential to 
transmission line 62 leading to the anode is blocked again when the 
potential is below the pre-selected voltage level. This produces the 
voltage curve shown in FIG. 7. 
For the best operation of the dehumidification system using the electrodes 
of the invention, it is preferred to arrange the electrodes at a minimal 
distance of about 10 cm along the height of the structural body. 
Furthermore, it is preferred to mount the cathode about 30 to 50 cm below 
ground level. It is of great importance for the effective operation of the 
system in connection with power supply circuit 45 to make certain that the 
charge at any point of the electrode is such that the voltage and amperage 
of the applied current produces no more than negligible amounts of oxygen, 
never reaching a level of magnitude sufficient to destroy the electrode 
elements. 
The advantage of using the reinforcing or carrier elements of the present 
invention as electrodes in electro-osmotically operating dehumidification 
installations resides not only in the increased desired effect obtained in 
a fraction of the time in which success is achieved even at high water 
pressures in old and thick building walls but also in the dependable 
avoidance of the chemical decomposition of the water leading to the 
evolution of undesired gases and the precipitation of heavy metal, which 
may lead to the destruction of the structural materials. The measured 
effective voltages of the positive portion of the alternating voltage may 
be more than 16 V. Even with such high voltages, the conductive or 
semi-conductive synthetic resin of the carrier elements is not corroded. 
Operating the disclosed system in accordance with the method of this 
invention produces an effective electro-osmotical dehumidification 
producing optimal results when the described steps are followed.