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Publication numberUS3377462 A
Publication typeGrant
Publication dateApr 9, 1968
Filing dateJan 5, 1965
Priority dateSep 16, 1963
Publication numberUS 3377462 A, US 3377462A, US-A-3377462, US3377462 A, US3377462A
InventorsHerbert Pferschy
Original AssigneeHerbert Pferschy
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Device for heating surfaces subject to strong mechanical stresses or considerably varying atmospheric conditions
US 3377462 A
Abstract  available in
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

April 9, 1968 H. PFERSCHY 3,377,462


conductive concrete tube a n, l i l penings mffffifi" IIIIXH foundatlon April 1968 H. PFERSCHY 3,377,462


faultcurrent protective circuits switch transformer metalsheathing' I protective conductor heating cable fault currenttrip ground connection United States Patent DEVICE FOR HEATING SURFACES SUBJECT TO STRONG MECHANICAL STRESSES OR CONSIDERABLY VARYING ATMOSPHERIC CONDITIONS Herbert Pferschy, Radetzkystrasse 23, Dornbirn, Austria Filed Jan. 5, 1965, Ser. No. 423,876 Claims priority, application Austria, Sept. 16, 1963, 7,407/63, 7,408/63, 7,409/63 4 Claims. (Cl. 219-213) The invention relates to a device for heating surfaces subject to strong mechanical stresses or considerably varying atmospheric conditions such as roads, airport runways, bridges and other traffic areas, using electric resistance heating elements.

The invention will be explained hereinafter with reference to the accompanying drawing in which FIG. 1 shows a fragmentary perspective view of a portion of a traffic area to be heated; and

FIGURE 2 shows a diagram of a fault-current protective circuit.

It has been proposed to use the heat developed by electric current in resistance elements to heat trailic areas such as roads, bridges, runways, parkings, and the like. This has been achieved by providing heating cables and grids in the pavement; these have, however, the disadvantage of a non-uniform release of heat.

It is an object of the present invention to provide a device ensuring uniform and homogeneous heating and to design the heating element such that the surface releasing the heat is large compared to the cross section of the heating element.

According to the invention this is achieved by providing laminar electric resistance elements.

A particularly favorable type of laminar heating element is shown in FIG. 1 and consists of an electrically conductive concrete layer, since in this instance the heating element is at the same time supporting the traffic area. Since the set concrete normally used has a very high electric resistivity, it is necessary to add admixtures ensuring a satisfactory conductivity for the heating even after the concrete has set, or to achieve a suflicient humidification of the concrete.

A satisfactory, substantially electrolytic conductivity can be achieved in the concrete by suitable chemical admixtures such as salts, for instance NaCl, or acids, for instance hydrochloric acid. The chemical admixtures mentioned above can be introduced into the concrete using, for instance, a system of tubes embedded in the concrete layer and provided with numerous openings through which the chemical admixtures are discharged in liquid state. In this case it is recommended to seal the concrete layer with a coat inhibiting evaporation.

Another possibility of obtaining a satisfactory conductivity, this time a substantially electrical (metallic) conductivity, in the concrete consists in incorporating particles of metals and/or conductive ores. By way of example this can be done by pre-compressing, as in the prepact process, a bed consisting of grit and filling then under pressure the cavities with cement or cement mortar. In stead of cement other bin-ding agents can be used, e.g., magnesia.

When a concrete layer rendered conductive is used as a heating element as mentioned above, connecting electrodes are required to feed the heating current. The shape and arrangement of the connecting electrodes can be varied. By way of example, plate electrodes are appropriate, the electrode plates being applied to the surface of the concrete layer, e.g., to its lateral faces and/or are embedded in the said concrete layer. Instead of plate electrodes, bar-shaped electrodes or wires serving as electrodes can be used which are incorporated in the conductive concrete layer. Moreover, wire grids, wire gauzes or metal foils can be used as electrodes and applied to the concrete layer or embedded therein. The arrangement of the electrodes can be conceived such that the heating current flows substantially parallel to the plane of the trafiic area being heated or transversely of the same, thus from top to bottom or inversely.

If the conductivity is electrolytic (ionic), alternating current must be used as a heating current in order to prevent electrolytic decomposition as far as possible. In this instance it will also be useful to arrange the electrodes such that they can be replaced and/or cleaned, if need be.

It is possible to operate the installation with a low voltage of about 40-50 volts. Under normal conditions the heating capacity (connected load) will be about 200 var/m If the installation is very large, a use of the low voltage harmless to man and animal necessitates a large dimensioning of the feeds. It is true that this disadvantage can be overcome to a-certain degree'by providing several transformers, but it proves much more convenient to apply an operating voltage above 40-50 volts, preferably above volts. To avoid any risk in this instance, all installations of this type will be operated with highly sensitive safety circuits known in themselves, and be insulated efiiciently.

The safety circuits or safety measures considered are, e.g.: fault-current protective circuits; protective transformers or generators insulated against the ground; current reduction triggers; covering or enveloping of the insulation of the heating elements with an electrically conductive grounded material; suitable arrangement and dimensioning of the heating elements to keep the step voltage low, insulating bordering of the trafiic area; insulating surfacing, preferably consisting of wear resistant and impact resistant material. Evidently it is possible to use several of the individual safety circuits and measures indicated at the same time or to combine them with each other.

In the following, the above-mentioned safety measure of the fault-current circuit will be described in detail with reference to FIG. 2, since it is of special importance in connection with the present field of application. It is here the case of an electric safety circuit provided at the conductor inlet which disconnects the current feeds in a manner known in itself by means of the leak current occurring on damage or ground-leakage in the system, before this leak current reaches the permissable tolerance for man and animal. The upper limit of this leak current is defined by the permissable tolerance for man and domestic animal and is about 2040 milliamps. When the leak current reaches this limit, the current supply must be interrupted so rapidly that any damage to man or animal is prevented with certainty. For this, empirical values are available which were incorporated into the safety rules stipulated by law. The absolute values are not completely identical in the different countries. Since the upper limit of the reaction time is about 200 millisec., disconnection by the leak current switch must be effected at about 20- 4O milliamps within a maximum delay of 200 millisec.

The operating system of the safety switch can be chosen arbitrarily. Tests have shown that with a threephase power current connection, the above-mentioned requirements are fully met by an inductive fault-current protective switch. With this fault-current protective switch the leak current is determined by means of a totalizing current transformer. The current feeds are wound as a primary Winding around an iron core carrying a secondary winding. As long as the heating cable is not defective, the total current in the current transformer equals zero. If the heating cable becomes defective, the total current in the primary winding is no longer zero and thus a current is induced in'the secondary winding which triggers a switch via a highly sensitive relay. The sensitivity and the time of response can be adjusted in a relatively simple way. Thus, it may become necessary, if very large areas are involved, that the total area must be divided into subareas and each sub-area must be provided with a separate current supply and safety switch. Since, however, with modern materials very good insulation can be achieved, even with 100% moisture, such a measure will always remain an exception.

' With a view to the fact that the heating elements are arranged within a region of possible mechanical destruction, the safety measures must satisfy particularly rigorous conditions, but with the present state of technology this is possible without difii-culty.

What I claim is:

1. A device for heating surfaces subject to strong mechanical stresses or considerably varying atmospheric conditions, such as roads, airportrunways, bridges or other traffic areas, said device comprising a foundation layer and at least one coating covering said foundation layer, said coating comprising a heating element of :at least one layer of concrete which is uniformly electrically conductive throughout the entire layer, and means in contact with said conductive concrete layer for connecting the latter to a source of electrical energy.

2. A device as claimed in claim 1, wherein said electrically conductive concrete layer contains admixtures causing an electrolytic conductivity.

3. A device as claimed in claim 1 comprising a tubular system with numerous openings emebdded in said electrically conductive concrete layer through which a liquid rendering said concrete layer electrolytically conductive can be passed into said concrete layer.

4. A device as claimed in claim 1, including and wherein said electrically conductive layer is covered with a sealing layer inhibiting evaporation of the liquid rendering the concrete layer electrically conductive.

References Cited UNITED STATES PATENTS 2,851,639 9/1958 Ford et a1. 317-2 3,121,065 2/1964 Greger et al. 252-519 3,121,825 2/1964 Abegg et al 317-2 3,166,518 1/ 1965 Barnard 252-503 2,348,365 5/ 1944 Sandenburgh 94-23 2,504,146 4/ 1950 Mossin 219-345 X 2,573,120 10/1951 Wandelt 219-345 X 2,912,555 11/1959 Jamison 219-213 X 3,047,701 7/1962 Frungel 219-213 3,168,019 2/1965 Lynn 94-23 X 3,176,116 3/1965 Lighter 219-213 X 3,193,664 7/1965 Beery 219-213 3,214,638 10/1965 Moser et al 317-27 X FOREIGN PATENTS 1,195,162 5/1959 France.

798,304 7/195'8 Great Britain.

RICHARD M. WOOD, Primary Examiner.

C. L. ALBRITTON, Assistant Examiner.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2348365 *Mar 13, 1940May 9, 1944William M PindellProtective coating for concrete pavements
US2504146 *Feb 6, 1940Apr 18, 1950Barth Mossin GeorgElectrical heating device
US2573120 *Dec 4, 1947Oct 30, 1951Wandelt Richard FHeat radiator and method of radiating heat
US2851639 *Mar 27, 1952Sep 9, 1958Mosaic Tile CompanyElectrically-conductive ceramic floortile units and floors composed of such conductive units
US2912555 *Mar 10, 1958Nov 10, 1959Jamison Frederick WDetachable ice and snow melting panels for traffic bearing surfaces
US3047701 *May 13, 1960Jul 31, 1962Frank FrungelDevice for heating a ground covering
US3121065 *Aug 3, 1960Feb 11, 1964Greger Dean FelixElectrically conductive ceramic tile
US3121825 *Oct 14, 1959Feb 18, 1964Abegg Moroni TElectrically conductive floor covering for use in explosive hazard areas
US3166518 *Dec 29, 1960Jan 19, 1965Schlumberger Well Surv CorpElectrically conductive concrete
US3168019 *Nov 16, 1961Feb 2, 1965Stanley Lynn BernardJet aircraft runway having anti-skid properties when wet
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US3193664 *Feb 20, 1961Jul 6, 1965Virgil R BeeryElectrical heating mat
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FR1195162A * Title not available
GB798304A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3626149 *Jan 2, 1970Dec 7, 1971Superior Graphite CoThermally conductive concrete with heating means
US3804543 *Sep 25, 1972Apr 16, 1974Dow Chemical CoTrafficked surfaces
US3936702 *Jan 8, 1973Feb 3, 1976Micro Devices CorporationElectrical protection means
US3995965 *Mar 31, 1976Dec 7, 1976The Raymond Lee Organization, Inc.Road surface deicing device
US4015105 *Dec 2, 1975Mar 29, 1977Bjorksten Research Laboratories, Inc.Panel electrical heating element
US4174912 *Jul 31, 1978Nov 20, 1979Electroosmosis Inc.System for heave reduction in highways due to frost or moisture in expansive clay or shale materials
US4300320 *Nov 13, 1979Nov 17, 1981Havens Steel CompanyBridge section composite and method of forming same
US4314772 *Dec 13, 1979Feb 9, 1982Lestraden Jakobus WGround heating system
US4484243 *Sep 30, 1982Nov 20, 1984General Electric CompanyProtective circuit arrangement for a sheathed heating element
US4748314 *Mar 2, 1987May 31, 1988A.R.M.I.N.E.S.Device for the rapid vaporization of a liquid
US5605418 *Sep 20, 1993Feb 25, 1997Taisei Home Engineering Kabushiki KaishaRoad snow melting system using a surface heating element
US5707171 *Sep 26, 1995Jan 13, 1998Zaleski; Peter L.Electrically conductive paving mixture and pavement system
US6825444Jan 28, 2000Nov 30, 2004Board Of Regents Of University Of NebraskaHeated bridge deck system and materials and method for constructing the same
WO2000045620A1 *Jan 28, 2000Aug 3, 2000Bing ChenHeated bridge deck system and materials and method for constructing the same
U.S. Classification219/213, 404/71
International ClassificationE01C11/26, E01C11/24
Cooperative ClassificationE01C11/265
European ClassificationE01C11/26B