US2078485A - Composite highway beam construction - Google Patents

Description

April 27, 1937. A, w N -1 coMPosiTE HIGHWAY BEAM CONSTRUCTION Filed Feb. 15, 1954 Patented Apr. 27, 1937 UNITED STATES PATENT orFicE COMPOSITE HIGHWAY BEAM CONSTRUCTION 1 Claim.

The object of my invention is to provide a composite highway beam construction, having the advantages of concrete for a supporting base and of bitumen for a travel surface.

It is a further object to provide such a construction in which the concrete base and the asphalt top layer are each provided with properly located reinforcement and are suitably bonded together so as to afford a homogeneous composite beam.

Another object is to provide a load-distributive wearing course of asphalt and steel adapted to be bonded to a pavement base of plain concrete, reinforced concrete, brick or other new pavement material, said load distributive action to'be de rived from the action of the perforated steel plate in providing a means for the superimposed load to be spread over a greater pavement surface than heretofore possible, thereby dissipating the destructive action of impact and vibration.

Another purpose of my present invention is to provide a wear course adapted for use on a suitable base and composed of asphalt having embedded therein perforated steel plate in the form of sections continuously connected together to secure maximum load distributive effect by joints allowing enough play to take care of ordinary expansion and contraction.

With these and other objects in view, my invention consists in the construction, arrangement and combination of the various parts of my construction, whereby the objects contemplated are attained, as hereinafter more fully set forth, pointed out in my claim, and illustrated in the accompanying drawing, in which:

Figure 1 is a perspective view of a piece of highway construction embodying'my invention, parts being broken away and parts being shown in section.

Figures 2 and 3 are plan views illustrating different ways of securing together the sections of reinforcing for the bitumen or asphaltlayer.

Figure 4 is a vertical, sectional view of a specimen of such reinforcing illustrating another type of joint; and

Figures 5 and 6 are diagrammatic views for illustrating the imposition-of loads upon the completed structure.

In the construction of paved roads, concrete has many advantages, particularly for the pavement base laid upon a prepared dirt surface, On the other hand, asphalt (or bitumen) has many advantages-for instance in the elimination of noise and vibration, but asphalt has distinct disadvantages, such as its tendency to creep, particularly when not laid upon a hard artificial base.

At the present time, the general practice is to lay concrete with reinforcing, if used at all, at or near the top of the slab.

In the practice of the present invention, I lay a concrete base course, which may be for instance four inches thick. In this, preferably about one and one-fourth inches above the sub-grade is laid a wire mesh reinforcement, preferably of about 58 pounds weight. I preferably select concrete having a strength of 3500 pounds per square inch at 28 days.

As shown in Figure 1, the slab of concrete is indicated .at Ill and the reinforcing at I2.

It will be understood that the specifications given are simply illustrative.

The finish is rough. When the concrete has attained sufficient strength, say after about seven days, a tack coat I4 of asphalt emulsion or cutback is applied at the rate of about one-sixth of a gallon per square yard.

While this coat is still tacky, a first or lower coat of asphalt or bitumen, indicated at IE, is laid over the tack coat. I preferably make this asphalt coat about three-eighths of an inch maximum, in order to give it maximum clear thickness of one-fourth inch. This coat I6 is smoothed to proper crown and elevation.

Then there is laid thereon perforated steel plates I8. These plates may be eight feet by eighteen feet in case of eighteen foot rural highways.

The successive plates are preferably locked together in some suitable way. For instance in Figure 2, I have shown the plates joined together by means of notches having narrow necks 22 and corresponding tongues 25.

In Figure 3, I have shown the plates spotwelded together as at 26.

In Figure 4, I have shown indicated at 28.

Over the plates is laid another course of asphalt. Mineral asphalt, such as natural rock asphalt ground to specification may be employed.

The top course is rolled with a roller of weight limited perhaps to five or six tons. The top course of asphalt may be of the same thickness as the lower course I6 or may differ in thickness.

The sheets I8 shown in Figures 1 and 2, I80. shown in Figure 3 or lBb shown in Figure 4, preferably have holes 32 regularly spaced to eliminate about one-third of the area and weight of the steel. Preferably the holes are from to inch in diameter.

There is produced by this construction what is in effect a composite beam of reinforced concrete and reinforced asphalt. The provision of the tack course on the rough partly cured concrete affords a certain and efficient bond.

By providing the concrete base with the reinforcement in its lower portion and part of the reinforcing in the asphalt, you have a beam reinforced for tensile stresses in both the upper and lower fibers.

In Figures '5 and 6, I have illustrated the manthe plates beveled as ner in which the reinforcing strengthens the composite beam.

The reinforcing in the lower part of the concrete takes care of the load indicated by the arrow in Figure 5, and the reinforcing in the upper part of the asphalt takes care of the loads indicated by the arrows in Figure 6.

The provision of the plate between two layers of asphalt affords an efiective load distributing agent.

I'he wear course in itself has great advantages. While the steel plate alone would sustain only a light load, yet when assembled in the asphalt wear course, it distributes the load, as I believe has never before been done. I thus provide an asphalt wear course which when supported on and especially when bonded to a base, will carry a load never before possible with an asphalt course of such thickness, distributing the superimposed load over a greater pavement area, and will thus dissipate the destructive action of impact and vibration, while also giving maximum resistance to wear.

This reinforced asphalt wear course is peculiarly adapted for air fields, factory floors, resurfacing old pavements and the like.

In the finished beam, the reinforcing is where it belongs-to-wit,--the top and bottom of the composite beam.

A pavement of this kind has all of the nonskid advantages of asphalt, which is preferably proportioned with aggregates, so as to afford a maximum resistance to wear.

A pavement of this kind can be repaired inexpensively and easily. The total cost makes it possible to build a very economical pavement. The asphalt course with its perforated steel reinforcing can be used for repair purposes on other bases, such as old brick or concrete pavement.

It will be observed that I prefer a perforated steel plate for the reinforcing of the asphalt wear course.

For practical handling, the plates must be in sections. In order to secure the maximum functioning of the steel plate for load distributive purposes, it is necessary that the sections be properly connected together. For this connection, I prefer the type of joint shown in Figure 4 in which the respective plates are beveled, so asto leave a smooth connection. The asphalt itself extending through the holes 32 in the beveled portions serves to anchor the successive plates to each other. At the same time, enough slippage is allowed to take care of expansion and contraction.

When the type of joint shown in Figure 2 is employed, it is desirable in many instances to allow some play as indicated by the spaces 23 of that figure.

The type of joint shown in Figure 3 is particularly convenient when cuts are made in the pavement for utility service, such as gas, electricity and so forth. When a section of pavement has been taken out, it can be readily replaced and the removed sections of steel welded to the permanently placed sections for maintaining the steel continuity required for maximum load distributive effect.

The inadequacy of the present day methods of highway construction to stand up under the increasing strain of modern traffic is suggested by the constant addition of laws regulating limiting load per unit, load per wheel, load per size of tire, length of vehicle, and distance between axles and so forth. The main factor in the early failure of roads built under present practices is the concentration of heavy loads, severe shocks, and vibration over small area of highway.

The use of the steel sheets as contemplated in my present construction affords such a distribution of the load as will take care of much of the difiiculty which I have just mentioned.

Asphalt is generally considered to be the best wearing course, providing it can be made to stay placed.

Concrete highways are subject to cracks which collect moisture, which inturn freezes and then expands and causes larger cracks.

The structure of the present device retains all the strength and rigidity of concrete and combines with it the benefits of an asphalt wear course, which is held properly in place by the steel plate.

The steel plate not only holds the asphalt in place but distributes the load and thus protects the entire beam from the concentration of load and shock and vibration mentioned above.

I have thus produced a pavement utilizing the qualities of a concrete base, embodied in a composite beam with an asphalt wear course in such an arrangement that the concrete is protected from the disintegration that ordinarily results from concentrative shock and from expansion and contraction and subject to moisture.

It will be seen by the construction here defined that I have a wear course usable with new or resurfaced pavement, capable of bridging weak spots in the base material, and of preventing additional damage to the old base.

Depressions in an old base may be brought to a proper grade and contour for the wear course by patches of asphalt or suitable material.

The increased strength and wearing quality of a pavement of this kind is so great that there can be a substantial saving of materials used, due to the fact that the entire beam can be made much thinner than is otherwise the case. 7 applies tothe building of the complete new pavement. Even in the case where a wear course is placed on old pavement, sheet asphalt is ordinarily put on to a thickness of one and one-half to two and one-half inches, whereas this wear course can be laid at a thickness of approximately five-eighths to one inch.

Modifications may be made in the pavement as above explained, and it is my purpose to cover by my claim any variations in construction or use of mechanical equivalents, which may be reasonably included within its scope.

By the term asphalt in the claim, I desire to include material containing bitumen in any form combined in any state with other materials. This would include mineral asphalt, native asphalt, natural rock asphalt, and asphalt combined with other materials and common emulsions and cutbacks.

I claim as my invention:

A roadway structure, comprising a lower or base layer of concrete, a tack or bonding course thereabove, an upper relatively thin asphalt course, and perforated metal plate embedded in the structure above the concrete and not directly bonded to the concrete, said plate composed of sections connected together by joints adapted to allow play to take care of expansion andcontraction.

ANSEL W. DUNHAM.

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