US3400644A - Membrane surfaced runways - Google Patents

Description

P 1968 c. M. BASKIN 3,400,644

MEMBRANE SURFACED RUNWAYS Filed June '7, 1967 l .\"VE.\ TOR. CHHRLES IVI. 5145K IN HTTOR/UE 4,

United States Patent '0 3,400,644 MEMBRANE SURFACED RUNWAYS Charles M. Baskin, 1642 A. I. du Pont Bldg, Miami, Fla. 33131 Filed June 7, 1967, Ser. No. 644,374 9 Claims. (Cl. 947) ABSTRACT OF THE DISCLOSURE This invention relates to a system of construction of combat roads and runways wherein natural soil, utilized as the base, is covered with a flexible dimensionally stable high tensile strength composite membrane as a means for deconcentrating trafiic loads. The makeup of the said membrane is:

First, a fibrous sheet or tape having a film of pressure sensitive adhesive on both surfaces.

Second, the said fibrous sheet is laid over the graded soil, and over it is spread a thin steel sheet, the pressure sensitive fibrous sheet acting as an intermediate bond between the steel sheet and the soil.

Third, the steel sheet is then, in turn, covered with a pressure sensitive adhesive fibrous sheet, the same as the one between the soil and the steel sheet, except that the film of pressure sensitive asphalt or other thermoplastic resin on the surface, exposed to t-raffic, has imbedded in it mineral particle forming a skid-resistant surface.

A special feature of this invention is the ability to build up a load deconcentrating membrane to accommodate the highest anticipated trafiic loads by laminating a number of steel sheets and interposing the above pressure sensitive sheets.

The principal features of this membrane are: high tensile strength, dimensional stability under all loads below its yield point, high flexibility, corrosion proofness, resistance to skidding and ease of maintenance.

Ever since the air arm became a primary factor in warfare, the military engineer employed various prefabricated materials and methods whereby to utilize level soil areas as runways. So far the method commonly used involves two stages. The first stage is to hastily cover the leveled soil with a light weight water-proof rubber nylon membrane. If the soil to start with is fairly dry and stable, the waterproof membrane surface Waterproofs and maintains soil stability until such time as subgrade water infilters it.

As soon .as conditions permit, the temporary runway is increased in length and properly graded to more effectively shed surface water. If at all possible, the soil is compacted and covered with a heavy rubber-nylon membrane followed by a layer of interconnected metal panels or planks, known as landing mats.

However, the utility of both the membrane and the landing mat has proven very temporary. To start with, the rubberized nylon membrane is elastic and dimensionally unstable. While the ultimate strength of the rubberized nylon membrane may be over 2000 p.s.i., which is actually twenty or more times greater than the maximum p.s.i. traffic load, its supporting value is no greater than its yield point, which is very low, since a rubberized fabric is elastic.

This deficiency in the rubberized-nylon membrane is partially supplemented'by the landing mat, but this device, being loosely jointed rigid panels that cannot deflect under a load without bending, the membrane is rapidly distorted, cut or punctured, permitting surface Water to disrupt the soil.

It must also be noted thatv the combination of rubberized ice nylon membrane and metal landing mat is very costly per unit area covered.

My invention is based primarily on the well-established fact that unstable soil or weak pavements can be made to support the heaviest traflic loads by the simple device of distributing the load over a great enough contact area. The common example would be the plain wood plank over soft soil. Without the plank a lb. pedestrian may sink instantaneously to a depth of 5" or more, While a 1" plank, covering an area of ten square feet, may support numerous passages of the same pedestrian for hours without sinking any further than $50 of an inch; the reason being that the 150 lbs. load on the plank distributes itself over an area about 70 times greater than the surface area of a pedestrians foot.

Another interesting fact about spreading or deconcentrating loads, by means of the said wooden plank, is that a plank of the same dimensions, made of concrete, would not function in the same manner because the concrete plank could not deflect in the slightest without failing.

Yet, even a wooden plank is of temporary utility insofar that where the soil is soft enough to flow under so slight a weight as one eighth of a pound per square inch, it is only a matter of time before the wooden plank too Will be submerged.

Therefore, for any given load, the lower the consistency of the soil, the greater has to be the load contact area. For example, if a load of about /a p.s.i. causes a plank covering an unstable soil area of ten square feet, to sink one-tenth of an inch within an hour, a plank covering a considerably greater surface area of unstable soil will reduce the p.s.i. load as well as rate of plank sinking into soft soil proportionately.

In this invention, the place of the plank is taken by a membrane, the primary characteristic of which is that it is dimensionally stable under anticipated loads and especially has a high yield point and is non-elastic. By covering the whole area with such membrane, and reducing the possibility of excessive sag, by anchoring it along the edges, a surface load on the membrane is automatically diffused over the whole area covered by the membrane.

I find that sheet steel is the most suitable material for fabrication of a surface membrane for distribution of loads over runways and roads. Sheet steel is non-elastic and is dimensionally stable under loads below its yield point. Also, for any mechanical strength required, sheet steel is lower in cost and weight per unit area covered than any other material.

According to this invention, the first stage in constructing a combat runway consists of covering the leveled soil area with an asphaltic sheet or tape. The said asphaltic sheet is essentially a fibrous mat or fabric impregnated with a thermoplastic resin, having a softening point range of 110 F. to 210 F. and coated on one or both sides with a pressure sensitive film of a thermoplastic resin, specifically asphalt, having a softening point range of 90 F. to F.

The reason for such wide variation in consistency of both saturant and pressure sensitive coating is the variation in atmospheric temperatures in construction areas. In frigid zones, both saturant and coating have to be considerably softer than in tropical or subtropical areas. A thermoplastic like asphalt is very susceptible to temperature change. A rolled-up fibrous sheet saturated with an asphalt of 210 F. softening point becomes so brittle at temperatures below 40 F. that it virtually disintegrates upon unrolling.

It is also to be noted that the asphalt sheet or tape, I employ, differs entirely in composition and manner of functioning from standard asphalt coated rolled roofing felt wherein the saturant is always of considerably lower softening point than the coating and requires an extraneous adhesive such as heat liquified asphalt to cement the sheets to a roof-deck and to each other.

By saturating the paper sheet, known to the trade as felt, with a high softening point asphalt, it increases materially its strength, and by coating the so saturated sheet with a soft tacky asphalt, the sheet then becomes selfadhering under pressure.

It is to be noted that in many instances, the fibrous mat or fabric in the said asphalt sheet can be low cost paper felt as in standard rolled roofing. However, for long service and critical installations, I employ a fibrous mat or fabric, impregnated with a thermosetting or thermoplastic resin with a thin coating on one or both surfaces of pressure senstive resin.

An added feature of this invention is where I produce the said pressure sensitive film by slightly wetting one or both surfaces of the said fibrous sheet with a high boiling point solvent. This automatically forms a pressure sensitive film by surface blending with the high softening point asphalt.

Since the coating on the bituminous membrane, in this invention, is a soft and tacky asphalt, no such readily available parting agent like stone dust or fine sand can be used, as this would prevent subsequent adhesion. Therefore, the parting agent I employ is a porous paper that has been impregnated with a fatty acid, such as stearic or palmitic, or high melting point paraffin. These substances are insoluble in bitumen and are low enough in cost for the waxed paper to be wasted. This, however, does not preclude the use of a film of synthetic parting agents, such as Teflon or silicone. It is to be noted that the parting agent is in many instances nothing more than an insurance that no trouble will be encountered in unwinding the rolled-up or folded-up pressure sensitive membrane. In most instances, the pressure sensitive resin, I employ, is low enough in softening point to part under moderate pull without the need of a parting agent.

The above described asphaltic sheet is laid over the leveled soil with a slight overlap to form an impervious seal. The asphaltic sheet is, in turn, covered with a series of steel sheets, which automatically adhere to the pressure sensitive asphalt sheet.

Therefore, the pressure sensitive asphalt membrane surface Waterproofs the soil and holds the individual steel sheets in place, which otherwise would tend to shift about.

It is also to be noted that the above described sheet steel membrane is considered flexible only if a strip of it rolled half Way around a twelve inch diameter core reverse back to its original state without permanent distortion. In other words, this invention uses a flexible metal membrane as distinct from a metal plate which can only bend under a load.

The next step is to produce a skid-resistant surface over the steel steet. This is accomplished in this invention in two ways. On runways for temporary and moderate load service, I cover the sheet steel membrane with the same pressure sensitive asphalt membrane bonding the steel sheets to the soil. The exposed pressure sensitive surface is, in turn, covered with gritty mineral particles such as coarse sand or fine gravel, making the build-up membrane skid-resistant.

On the more permanent and heavier duty runways, I employ a modified sheet or tape, the modification being that the core of the sheet or tape is a fibrous mat or fabric impregnated or coated with either a thermosetting resin or a high softening point thermoplastic resin; the so treated sheet or mat has a film of a pressure sensitive adhesive on the under surface, while the surface exposed to trafiic has a film of thermosetting resin within which is imbedded gritty skid-resistant mineral matter.

The accompanying drawing shows as follows:

FIGURE 1 is a cross sectional view of a pressure sensi- 4 Y L tive asphalt sheet wherein 1 is granular skid-resistant surfacing. 2 represents a film of asphalt or other suitable resin within which the said granules are imbedded. 3 is a fibrous sheet impregnated with a high softening point asphalt. 4 is a pressure sensitive film. 5 is a parting agent in the form of an easily removable sheet.

FIGURE 2 is a cross section of a pressure sensitive asphalt sheet with parting agent sheet 5 over pressure sensitive film 4 adhering to asphalt impregnated fibrous sheet 3 and a second pressure sensitive film 4.

FIGURE 3 illustrates the component parts of the membrane built up over a soil road bed and/or over any base or pavement structure. 1 is a skid-resistant granular surface. 6 is a pressure sensitive fibrous sheet. 7 is a steel sheet forming the core of the membrane. 8 is a fibrous sheet that is pressure sensitive on both sides. 9 represents the soil road bed.

FIGURE 4 is a more detailed view of steel sheet 7 with overlap margins 10, precoated with a film of high softening point thermoplastic resin.

FIGURE 5 shows steel sheets 7 joined by precoated overlap margin.

FIGURE 6 shows steel sheets 7 having been joined by interlocking.

Having thus described my invention, what I claim is:

1. A flexible high bearing capacity runway or road, composed of graded soil over which is laid a Waterproof fibrous sheet, a flexible steel sheet over the said fibrous sheet, a second waterproof fibrous sheet over the said flexible steel sheet, and a layer of mineral particles partially imbedded and attached to the said second fibrous sheet.

2. A flexible high bearing capacity runway, as in claim 1, wherein the said fibrous sheet has on both its surfaces a film of pressure sensitive resin so it adheres simultaneously to the soil under it and to the said steel sheet over it.

3. A flexible high bearing capacity runway, as in claim 2, wherein the second waterproof fibrous sheet has a pressure sensitive film on both surfaces; one of these films serves to attach the fibrous sheet to the said steel sheet; and the other pressure sensitive film serves to hold the said mineral particles in place.

4. A flexible high bearing capacity runway, as in claim 3, wherein the said mineral particles on the exposed surface of the second fibrous sheet are held in a film of thermosetting resin.

5. A flexible high bearing capacity membrane reinforcing over roads and runways, composed of a multiplicity of flexible steel sheets laminated by interposing between said steel sheets a fibrous sheet, having a pressure sensitive film on both of its surfaces, the top-most steel sheet having attached to it a fibrous sheet with a skid-resistant surfacing of mineral particles.

6. A flexible high bearing capacity membrane reinforcing over roads and runways, as in claim 5, wherein the fibrous sheets between the said steel sheets is impregnated with a high softening point asphalt and made pressure sensitive by film of asphalt having a lower softening point than the asphalt within the said fibrous sheet.

7. A flexible high bearing capacity membrane reinforcing, as in claim 6, wherein the top-most fibrous sheet has been impregnated with a thermosetting resin, one side of the said fibrous sheet being made pressure sensitive by a film of thermoplastic resin, while the other side of the said fibrous sheet has been made skid-resistant by imbedding mineral particles in a film of thermosetting resin.

8. A flexible high bearing capacity membrane reinforcing, as in claim 7, wherein the top-most pressure sensitive sheet has been impregnated with rubber, one side of the said fibrous sheet having been made pressure sensitive by a film coating of thermoplastic resin, while 5 the other side of the said fibrous sheet having been made skid-resistant by im bedding mineral particles in a film of thermosetting resin.

9. A flexible high bearing capacity membrane, as in claim 8, wherein the said steel sheets are joined securely by coating the overlap edge of the steel sheets with a high softening point thermoplastic resin and activating the said coating of thermoplastic resin by application of surface heat.

References Cited UNITED STATES PATENTS Maranville 94-7 X Bowes 947 Raskin 947 X Salyer et a1 947 X NILE C. BYERS, 111., Primary Examiner.

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