Method and Apparatus for Removing Ice from Paved Surfaces

TECHNICAL FIELD This invention resides in the fields of micro-wave heating

and the removal of ice from surfaces. BACKGROUND ART

Considerable time and expense are utilized to free paved roads, airport runways and walks from ice in cold climates. Ex- pendable materials which are destructive to pavements and mach ^" -

i ery alike are used in large quantities, and when removed with the partially melted ice and snow, often require special dumping areas for various reasons. An example of such materials is the salt spread on many road surfaces which, when thrown up against wheel wells, metal flooring, frames and running gear of road ve¬ hicles result in accelerated rust and thus greatly reduce the life of vehicles. Another example is the use ^' of considerable quantities of urea on airport runways, requiring high acquisition, storage

and disposal costs, and in addition result in very disagreeable odors when the ice melts.

Various schemes have been proposed to better solve this

problem of ice removal which must be accomplished to allow the safe use of streets, highways, intersections, walks and airport runways. Proposals include that of Mouatt in U.S. patent 3, 964, 183 in which he concentrates an intense beam of visible light onto

the interface of a coating of ice, snow or frost and the top sur¬ face of a pavement adequate to raise the temperature of the inter-

facial zone to the melting point of water so as to free the icy coat- ing from the pavement and then quickly remove the ice, so freed, by other apparatus before it re-freezes . As inventor Mouatt notes, infra-red radiation, has also been used to attempt to remove ice from pavements .. Mechanical means used alone, as he infers, fail to completely clean the surface of ice because of the adhesive forces between ice and other common materials which exceed the internal cohesive strength of ice itself. The infra-red radiation method failed because of the need to supply the heat of fusion to the entire thickness of ice coupled with the insulating effect of the standing water so formed above the remaining thickness of ice. In a different field, micro- ave energy is proposed for use in U. S. patent to Puschner 3 , 443, 051 to develop thermal wedge forms in rock to split the rock. Inventor Stone in U. S. patent 3, 601, 448 uses two micro-wave generators spaced apart from one another and directed at concrete or rock to produce spaced heat zones to ex- pand the material s o as to place high tensile forces on the unheated material between the heat patterns . In U. S. patent 4, 175, 885, inven¬ tor Jeppson discloses a method of producing a composite pavement in which a 915 M-Hz micro-wave generator and wave guides are pass ed

very slowly over a cement concrete pavement with the additional use

of hot gas to heat the concrete to the depth of about 6 inches s o as to

drive off moisture and use the hot concrete to lower the vis cosity of a thermoplastic s ealer for maximum penetration of sealer into the

interceces of the concrete. However, the surface of concrete can be damaged with spalling when heat is applied. D IS C L O S U R E O F I N VE N T I O N

This invention is a way of removing ice and snow from a pave¬ ment having a carbonaceous top surface by passing over such carbon¬

aceous top surface a 915 M-Hz micro-wave generator with wave guide to raise the temperature of the carbonaceous surface sufficient¬ ly to weaken or melt the ice at the interface of the ice and carbonac¬ eous surface s o that the ice may be s craped off the carbonaceous surface and removed therefrom. Concrete pavements are prepared

for this process of ice removal when dry by covering it first with a tightly adhering layer of an adhesive sealer containing a continuous heat conducting and reflecting material, an intermediate layer of heat insulating material and a top layer of a wear resistant material containing a micro-wave absorptive carbonaceous material. Asphalt materials, being carbonaceous , do not require the application of these coatings . When a concrete pavement so prepared or an asphalt

pavement has been coated with ice, a 915 M-Hz micro-wave genera¬

tor with wave guide is passed over the ice, the micro- waves at this

frequency pass through the ice, the carbonaceous material of the pavement becomes heated thereby, the interface between the ice and ice -coated pavement is melted by conduction with the micro-wave

heated surface of the pavement, and the ice, so freed from the pavement, ^-' is scraped off the pavement without damaging the pave- . ment. Thus this invention provides an efficient way to remove ice and snow from pavement without the use of disposable chemicals to melt the ice and without the excessive use of energy. BRIEF DESCRIPTION OF DRAWINGS

In the drawings, Figure 1 is a cross -section of concrete pavement coated so as to facilitate or allow the removal of ice from it by micro-wave energy according to my invention.

Figure 2 is a perspective of a device for removing ice and snow from the carbonaceous surface of a pavement according to my invention. BEST MODE FOR CARRYING OUT THE INVENTION

In the sectional view of Figure 1, a concrete pavement 1 has been prepared for the winter by a three layer top coat applied thereto. Before application of the top coat, the pavement is cleaned so as to provide ^" a clean, dry, dust-free surface for strongly adhering each layer to the pavement and to each other.

The first layer 2 of the coating to be applied to the concrete pavement is an epoxy containing aluminum ^' flakes and/or powdered aluminum. The aluminum is used to reflect the heat from the micro¬ waves generated in the top layer 4 and to insure a relatively even

temperature cf. the concrete pavement 1 during heating of the coat- ing for ice removal.

The s econd or intermediate layer 3 is a rigid foamed phenol¬

ic sheet tightly adhered to the bottom layer 2 by a coating of epoxy.

The purpos e of the s econd layer 3 is to provide another heat-insul-

ating layer between the concrete pavement 1 and the top layer 4 of

the coating, greatly limiting conductance of heat from the top layer

4 to the bottom layer 2 s o as to retain the heat in the top layer 4

for conductance into the interface of ice and coating 12.

The third or top layer 4 of the coating applied to the concrete

pavement 1 is a mixture of epoxy and graphite in a proportion of

about 95% epoxy to 5% graphite. This thin layer is highly conductive

and being graphite -filled will totally abs orb or attenuate the micro¬

waves and put the heat on the top surface in order to instantly re ¬

leas e the hard ice by melting the interface 12 without warming the

remaining thicknes s of the coating. Heat s o generated in the top layer 4 is readily transferred to the interface 12 of ice 13 in contact there¬

with becaus e of the high conductivity of both graphite and epoxy. Because ice is a poor conductor of heat, a relatively thin layer of

graphited epoxy is required to quickly melt the interface 12 s o as to

free the ice from the coated pavement 1 . A small proportion of

relatively fine silica or similar material may be included in this

top layer 4 of the coating to improve strength, rigidity, wear re ¬

sistance and skid resistance. Thes e qualities are des irable to pro¬

tect the coating, giving it a longer life.

Since asphalt pavements are not brittle as is the cas e with

concrete, but are elastic, such a surface does not require the pro¬ tection from heat with the epoxy and aluminum flake coating 2 and/or the intermediate phenolic sheet layer 3 applied to the concrete pave-

ent 1. Likewise, since asphalt pavements are carbonaceous , the top layer 4 of epoxy and graphite as applied to concrete pavements

1 is not required. Thus the asphalt pavement does not require special treatment to practice my invention.

An essential of my invention is to use the ability of micro- waves of relatively high frequency at about 900 megacycles to read¬ ily pass through ice without melting the ice to be absorbed by car¬ bonaceous materials such as graphite or asphalt. This is in contrast with the effect of the much lower frequency, 24-27 megacycle -micro¬ waves, as used in a domestic micro- wave oven which will readily melt an ice cube wrapped in clear plastic wrap placed therein. Since the 900 range megacycle micro-waves will pass through ice to be

absorbed by the carbonaceous materials, no energy is required to raise the temperature of the layer- of ice through the heat of fusion to transform it to water. Since much less energy is required to melt the interface 12 between the carbonaceous surface and the layer of ice 13 than to melt the entire layer of ice 12, not only is power saved, but, as the micro-wave generator wave guide 8 is pas sed over the ice -coated pavement 1 at a much higher velocity than would be required to melt the ice 13, the ice 13 s o freed is lifted and

removed by the scraper blade 10. Since very little ice is converted

to* water at the interface 12 than if the ice were melted, the pave ¬ ment so freed of ice will provide a much safer surface. It will be

appreciated that if the ice is melted, it is much more likely that

s ome of the water s o formed will re-freeze on the cold pavement before it can be removed therefrom. It can als o be recognized that uncoated pavements are very porous and therefore will be wetted

by water to a much greater extent than epoxy sealed pavemfent. As noted above under " Background Art", micro-waves can be us ed to

fracture concrete pavements . The coating des cribed above and used on concrete pavements 1 in the practice of my invention effectively protects the pavements s o coated from fracturing by the application of micro-waves especially at the high speed with which the icro.- •wave generator 8 may be passed over the coated pavement 1. This

high speed of ice removal is particularly needed where airport run¬ ways are in need of ice removal. Since the concrete pavement is sealed from water by the coating, it will experience a greatly ex¬ tended pavement life.

As seen in Figure 2, a preferred embodiment of a machine utilizing the principles of my invention consists of a truck 5 having

a snowplow 6 carried by the front of the truck 5, an electric power

plant 7 mounted on the truck bed connected to a micro-wave gen¬ erator and wave guide 8 mounted on the rear of the truck by ad¬ justable arms 9 with a s craper blade 10. A suitable micro-wave generator for this purpose is an RCA 8684 magnetron which is

capable of generating useful continuous RF power of 30 kilowatts

at 915 M-Hz. Mechanical ice-splitting blades 11 along the face of the scraper blade 10 as seen in Figure 1 assist in breaking up the

ice 13 as it is freed from the coated pavement 1. Because of the mas s of the ice layer 13, it is essential that the s craper blade 10 be placed closely behind the micro -wave generator and wave guide 8 so that as soon as the ice 13 is freed, it will be fractured and pushed into a windrow along the downstream end of the scraper 10. Thus the way of removing ice from pavements according to this invention can be performed by passing the truck. 5 with associated equipment over the ice -coated pavement 1 at a speed such that as the interface 12 of ice 13 and pavement surface is melted by the micro-wave gen¬ erator and wave guide 8, the scraper blade 10 following the micro-

wave generator and wave guide 8 will remove the ice coating 13 from the pavement 1.