US1906301A - Method of preparing paving material - Google Patents

Description

Patented May 2, 1933 GLENN H. ALVEY, OF SAN ANTONIO, TEXAS, ASSIGNOR TO UVALDE ROCK ASPHALT COMPANY, OF SAN ANTONIO, TEXAS, A CORPORATION OF TEXAS METHOD OF PREPARING PAVING MATERIAL No Drawing.

This invention relates to a new and improved rock asphalt pavingmaterial' and -method of preparing the same, and more particularly to such a, paving materlal ncluding as an ingredlent lnnestone containing substantially no bitumen. 2

Limestone rock asphalt or rock asphalt occurs in nature and is found in scattered deposits in different parts of the world. It

comprises a pure limestone base of a porous, fossiliferous character, mostly shell, more or less thoroughly and intimately impregnated with asphalt. The asphalt in thisrock is approximately pure and, due to the porous character of thelimestone, the lighter distillates of the bitumen have passed. off in the ages since its formation, leaving a hard bitumen. The said too]: asphalt, as it is found in the United States,'is particularly adapted to withstand wear of traflic and weather conditions when properly prepared and installed in place. I I

In consideration of my invention it must be recognized that limestone rock asphalt is a natural product and differs widely in physical analysis from an artificial asphalt paving material or a sandstone rock asphalt, which have approximately the same chemicalv analysis. This difference betweenthe limestone rock asphalt and the artificial paving material or the sandstone rock asphalt is clearly indicated in the fact that the asphalt is contained within each particle in the former material, and is a coating on the outside of each particle in the two'latter materials.

In the construction ofasphalt pavements or surfacing, it has been found advisable to'so govern the penetration of the asphaltic content by means of fluxing or hardening agents, that the finished product falls within certain specified limits calculated to enable the material to provide satisfactory service within the range of the temperature extremes contemplated during the life of the pavement. In the construction of pavements or surfacing with limestone rockasphalt, it has been found that the material may be installed either hot or cold, but with either process it, is necessary to introduce from petroleum. This fact is true when the impregnating Application filed October 13, 1930. Serial No. 488,556.

a fluxing agent to increase the penetration of the asphalt content so as to softenthe asphalt andthereby prevent cracking, as the natural state ofthe asphalt is too-hard and brittle to perform satisfactory service unless softened with asphaltic oils or various commercial fluxes. These oils contain a sufficient amount of solvents to enable 1 them to amalgamate with the hard native asphalt thereby softening it to the proper consistency. The commercial fluxes have been made to amalgamate with the hard native asphalt either through the use of heat or a volatile solvent added as the two are mixed together. 7

- The results obtained with limestone rock asphalt pavements laid under the various processes used at present have been mostly good, but at the same time-thesepavements have often been too hard or brittle, and are especially subject to cracking if there is any yield whatsoever in the foundation.

Many such pavements arenot soft enough to flow under the pressure of trafiic and .high summer temperatures so I as to heal up the cracks that might develop due to rapid change in temperature or displacements in the foundations. 7 g

The pure asphaltscontained in thenative limestone rock asphalts is almost invariably a very high grade pure bitumen that hasa remarkable degree of stability and can withstand the weathering action of the elements much better than can asphalt manufactured. particularly bitumen is hard like the asphalt in the rock asphalts produced in Uvalde County, Texas. These hard native bitumens are especially useful in the manufacturefof high gradepaints, 9'0 moulding compounds, waterproofing. compounds andmineral rubber, and consequently sell for a relatively high price as; compared to asphalt derived from petroleum. Under present competitive conditions, however, it has not been commercially possible to extract the asphalt from theserock asphalts due principally to the fact that approximately ten tons of material have to .be

'paratus into two parts;

asphalt, and there remains as waste nine tons of soft porous limestone which has practically no commercial value. In other words, the one ton of pure asphalt has to bear the entire. cost incident to the mining, preparation, and handling of ten tons of rock asphalt, as well as the cost of the extraction process. On the other hand, if it were possible to provide a ready market for the waste porous limestone, the extraction of pure asphalt from rock asphalt would be entirely feasible and commercially profitable.

It is' an object of the present invention to provide a paving mixture and method of making the same, which mixture is flexible and pliable when laid and used.

' It is a further object to provide a mixture and method in which limestone rock asphalt from which the asphalt has been removed, serves as an ingredient.

s It is an additional object to provide a method and mixture which includes the removal of the natural hard bitumen from part of the rock asphalt and the substitution therefor of a softer bitumen or asphalt.

Other and further objects will appear as the description proceeds.

- In making my improved paving mixture I use fine ground waste porous limestone and a soft asphalt as the matrix of my paving mixture, to provide flexibility and pliability, and I use rock asphalt as the larger particles to give strength and long wearing qualities to the pavement made from this mixture.

In preparing this composition I pulverize the limestone rock asphalt t0 the proper and predetermined size suitable for the work for which the paving mixture is being made. Ordinarily I would crush the rock asphalt and down, using a swing hammer pulverizer or other crushing equipment that would tend to cause the large and small particles to be in such proportions as to form what is generally known as a balanced grading. I then separate this pulverized rock asphalt by the use of screens or other ap- (1) relatively fine material and (2) relatively coarse'material. The relatively fine material (comprising from 20 to 50% of the whole when pulverized 4 and down) will be of such size that 95% will pass a 20 mesh screen; The relatively coarse material comprising approximately 40 to 80% of the whole, will be of such size that 95% will be retained on-a 40 mesh screen.

I then take the relatively fine material and extract the pure hard asphalt from it by means of a suitable solvent or combination of solvents in conjunction with the proper equipment designed for that purpose. After the extraction there remains a finely porous limestone due to the fact that the asphalt which formerly occupied these pores has been removed.

I next incorporate in this finely porous limestone a relatively soft asphalt in sufficient quantity to fill all the voids or pores and to provide a thin film of asphalt on the surface. There are several ways in which this may be done, namely (1) by heating until fluid the soft asphalt; (2) by cutting back the soft asphalt with a solvent; or (3) emulsifying the asphalt in water and mixing same with the porous limestone. I prefer the emulsion process as there is no danger of overheating, and it is much cheaper than the use of solvents My next step is to add the relatively coarse rock asphalt to this fine porous material which has been treated with soft asphalt and mix the two thoroughly together.

Finally,for thepurpose of coating the rockasphalt particles, I add an additional quantity of soft asphalt which has been emulsified with water or, if preferred, which has been cut back with a solvent. In some cases I may use a commercial fiux or even an asphaltic base flux oil. Except in the case of the emulsified asphalt,.I also add a small quantity of water so as to prevent the mixture from setting up and getting hard before it is used. I

If I want a non-skid paving mixture I add approximately 20% of finely crushed trap rock or other sharp rock harder than the rock asphalt. I

Owing to the fact that there are so many variables in this mixture it is practically impossible to set even approximate limits to the amounts of each ingredient used, or to give the exact mixing procedure, but in order that one familiar with the art of making asphalt paving mixture may manufacture a product such as herein described, I give below one formula which has proven successful Solid ingredients 80% porous limestone from which hard asphalt has been extracted (100% passing 40 mesh) 1 50% limestone rock asphalt (100% passing 4 and retained on 40 mesh); v

20% trap rock (100% passing A and retained on 40 mesh). 1

- U Liquid ingredients Asphalt emulsion (50% water and 50% soft asphalt) being in amount of 8% of the solid ingredients. I

Order 0 f mixing put in the emulsion until the whole has become a homogeneous mass.

The material thus prepared will form a pavement or asphalt surface that has a high stability, excellent wearing ualities, and comparatively high degree of fexibility and pliability. It will be noted that the principal and very important difference between this composition and the rock asphalt mixtures generally in use now is that the cementing medium of the latter is an amalgamation of the pure native bitumen and roadoil or fiux whereas the cementing medium of the former is almost entirely the soft asphalt which was introduced into the fine porous limestone. This is true because there will be a relatively small amount of the soft as phalt that will amalgamate with the hard native asphalt inasmuch as there are relaquantity of soft asphalt to coat the coarser rock asphalt material.

5. The process for the manufacture of a rock asphalt paving mixture which comprises crushing rock asphalt, separating the finely crushed material from the coarser material, removing the natural asphalt from the finely crushed material, adding to the finely crushed material after extraction of tively few surfaces of-contact between the two asphalts, whereas in mixture designed according to present day practice the asphaltic oil or flux is intimately in contact with the native bitumen and it is heated or solvents are used so as to force an amalgamation of the two.

I contemplate such changes and modifica- V tions of my mixture and the method of preparing it as may come within the spirit and scope of the appended claims.

I claim:

1. The process for the manufacture of a rock asphalt paving mixture which comprises crushing rock asphalt, removing the natural asphalt from a portion of the crushed material, and adding a soft asphalt asa binder.

2. The process for the manufacture of a rock asphalt paving mixture which comprises crushing rock asphalt, removing the natural asphalt from a portion of the crushed material, and adding a soft asphalt in an emulsion with water as a binder.

3. The process for the manufacture of a rock asphalt paving mixture which comprises crushing rock asphalt, separating the finely crushed material from the coarser material, removing the natural asphalt from the finely crushed material, adding to the finely crushed material after extraction of the natural asphalt a soft asphalt in an emulsion with water to form a binder, and finally adding tothe mix the coarser rock asphalt material.

4:. The process for the manufacture of a rock asphalt paving mixture which comprises crushing rock asphalt, separating the.

finely crushed material from the coarser material, removing the natural asphalt from the finely crushed material, adding to the finely crushed material after extraction of the natural asphalt a soft asphalt in an emulsion with water to form a binder, adding to the mix the coarser rock asphalt material, and finally adding an additional