Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
1999-01-14
2001-08-07
Phasge, Arun S. (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C204S600000
Reexamination Certificate
active
06270643
ABSTRACT:
The present invention relates to a method of effecting fluid flow in porous materials and relates particularly, to a method of effecting fluid flow by means of electroosmosis.
Metal reinforced concrete has widespread uses in the construction industry, for example as walls, floors, columns of a building, bridge spans or piers, and many other such applications. Steel reinforcing rods are usually employed to provide metal reinforcement of cast concrete structures, so as to provide a matrix on which the cast material can be formed. This increases the resistance to tensile stresses of the cast building element, since concrete is strong in compression but much weaker in tension.
The cast building elements are usually constructed by locating metal reinforcing rods at desired locations within the intended cast structure, between shuttering, and then pouring the cast material into a space defined by the shuttering so as to surround the metal reinforcing rods. On setting of the cast material, the metal reinforcements become rigidly embedded within the cast slabs.
Although the metal reinforcements usually remain firmly embedded within the cast structure, problems often arise with metal reinforced concrete as a result of water penetration to the metal reinforcement. Such water penetration is a source of corrosion of metal reinforcements over a period of time, and the constituents of the concrete mixture may also have an adverse effect on the metal reinforcement. This can result in failure of the cast structure which in the case of building elements, can have very serious consequences.
It has been proposed to control the water content of concrete structures by means of electroosmosis. In a porous structure such as concrete, it is known that the walls of the capillaries are covered with an electrically charged, adsorbed water film, often referred to as an electrical double layer. Electroosmosis involves subjecting such a porous body to an electric field, which causes part of the double layer to tend to migrate under the influence of the field, which in turn can cause some of the free liquid in the pulses to be carried along in this process. This can lead to a significant reduction in the internal moisture content of the porous body.
In particular, U.S. Pat. No. 5,015,351 proposes the removal of water from porous building materials by applying a controlled cyclical voltage to an electrode system to effect osmotic migration of water from an anode located within the structure to a cathode spaced from the structure but in electrical contact therewith. The cycle includes a first energy pulse in a direction to effect osmotic migration, followed by a shorter pulse of reverse polarity to counteract formation of insulating gas films. However, the process proposed in U.S. Pat. No. 5,015,351 is believed to give unsatisfactory results when used on metal reinforced concrete structures.
It has been proposed in U.S. Pat. No. 5,368,709 to control the relative humidity in concrete structures by feeding an anode with a pulse sequence generated with a first negative pulse, followed by a neutral interval or a zero voltage interval, followed by a positive pulse, accompanied by simultaneous feeding of the cathode with a corresponding pulse sequence of inverted polarity to control the humidity and the structure.
When this process is used on reinforced concrete structures, a voltage potential on the steelwork, which becomes an anode, occurs, causing rapid corrosion of the steel (Fe→Fe
2+
+2e).
Also, a fixed pulse system does not have the ability to deal with variations in the design of reinforced concrete structures. A combination of the engineering mass of a structure from the volume of concrete and the amount of steelwork inside, together with the pore size of the matrix, requires the flexibility of variable pulse frequency.
Preferred embodiments of the present invention seek to overcome the above disadvantages of the prior art.
According to an aspect of the present invention there is method of effecting fluid movement in metal reinforced porous materials, the method comprising applying a sequence of voltage pulses between spaced apart first and second electrodes having a region of the porous material therebetween, each said voltage pulse comprising a first portion in which an electroosmotically active first potential difference is applied between said first and second electrodes to effect fluid movement in said region of porous material, and a second portion in which a second potential difference of opposite polarity to said first potential difference is applied between said first and second electrodes; and applying a voltage to a metal reinforcement located at least partly in said region of porous material to make the voltage of said metal reinforcement negative with respect to the porous material adjacent thereto for at least part of said sequence of voltage pulses.
The provision of the first portion of each pulse enables fluid movement in the porous material to be effected, while the provision of the second portion at least partly counteracts the formation of gas or other insulating films at the electrodes (which leads to a deterioration in the electrical performance of the system and results in low operating efficiency) and/or the formation of corrosion products. Making the voltage of the metal reinforcement negative with respect to the porous material adjacent thereto provides the further advantage of preventing or minimising corrosion of the metal reinforcement which may otherwise occur as a result of the electroosmosis process.
Preferably, the method is a method of controlling humidity in a metal reinforced building material, and wherein said first potential difference is positive.
By making the first potential difference positive, the process can be used to effect electroosmotic reduction in the humidity internal to a metal reinforced building material. This helps to reduce the corrosive nature of the surroundings of the metal reinforcement, whilst minimising corrosion of the metal reinforcement as a result of the electroosmosis process.
In a preferred embodiment, the building material is concrete. The method may be a method of treating water in which said porous material is immersed, and in which said first potential difference is negative to effect electroosmotic movement of humidity through said porous material.
In this way, the porous material acts as a filter to remove impurities from the water.
Preferably, the method is a method of raising the pH level in said water.
Each said pulse may comprise a third portion following said second portions and in which a third potential difference having an amplitude between that of said first and second portions is applied between said electrodes.
It has been found that the provision of such a third portion has the advantage of stabilising the system prior to repetition of the first portion of each pulse.
The amplitude of each said third portion may be substantially zero. Preferably, said first and/or second portions have substantially rectangular waveforms.
The first potential difference may vary from substantially +40V to substantially −40V.
In this case, said first potential difference is substantially 80V and the voltage applied to each said electrode differs by substantially 40V from earth potential.
This gives the advantage of improving the safety of the system by minimising the variation from earth potential of the voltage at each electrode.
The second potential difference may be substantially −40V.
In a preferred embodiment, the voltage applied to the metal reinforcement is applied in the form of a series of pulses.
By making the voltage of the metal reinforcement negative with respect to the porous material adjacent thereto by means of a series of pulses, the amount of current flow and thus the power consumption of the system is minimised.
Said voltage pulses are advantageously applied to said metal reinforcement during said first portion only of each pulse.
In a preferred embodiment, each said voltage pulse has an on p
Harden Technologies Limited
Madson & Metcalf
Phasge Arun S,.
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