US1767830A - Paving material and method of preparing such material - Google Patents

Description

Patented June 24, 1930 UNITED STATES PA-TENT OFFICE GLENN n. ALVEY AND'ERNEST A; YOUNG, or sAN ANTONIO, 'rnxas, ASSIGNOR 'ro UVALDE ROCK TEXAS I ASPHALT COMPANY, OF SAN ANTONIO, TEXAS, A CORPORATION 01' PAVING MATERIAL AND METHOD OF PNEIARING SUCH MATERIAL Io Drawing.

This invention relates to a new and improved paving material and to a method of preparing such a material. It relates more particularly to the preparation of a material from natural rock asphalt and to such material which is adapted to be spread and compacted in a cold state.

The preferred basic material for use in our method to produce our product is a natural rock asphalt such as the Uvalde rock asphalt found in Uvalde County, Texas, althou h other generally similar materials may e used. This Uvalde rock asphalt consists of a comparatively porous, shell limestone impregnated naturally with asphalt which thoroughly fills the pores and minute cavities in the rock.

This rock asphalt has long been used as a material for floors or pavements, but the general methods of using it have involved heating and have required a considerable preparation plant adjacent to the work, as the prepared mass solidifies or tends to cake and set when it becomes cold, even if not compacted.

Several cold mixing processes have been developed and used in one of which the crushed rock asphalt is mixed cold with a natural oil containing both a solvent for'the asphalt in the rock and additional asphalt which serves as a flux. In another later method the rock asphalt is first treated with a solvent such as gasoline or kerosene and is then treated with a normally adhesive flux such as asphalt oil which is preferably heated.

While such processes produce a mixture in which the rock asphalt is not heated and which can be laid cold, the mixture tends to set or cake as the volatile solvents evaporate and cannot be transported successfully for to delay the evaporation of the solvent by applying porous. limestone finely crushed and- =;-I nixed with the asphalt rock. Even in this case, however, the major portion of the volatile content evaporates in a comparatively short timeand when transported by rail, the continued jars incident to such travel, cause the mass to cake or set and it ferred to above.

Application filed April 2, 1928. Serial No. 266,868.

must be broken up with pick axes or similar tools before removal from the cars. This adds very greatly to the expense and these methods are therefore not commercially practical for producing a mix to be used at any considerable distance from the mixing plant.

Our present invention is in the nature of ter may be acidified, if desired. A further of relativelyfeature lies in the addition larger sizes of crushed asphalt rock to the balanced mix of rock. These larger pieces may be added before or after the treatment with the oil.

It is an object of the present invention to provide a new and improved paving material or the like and method of preparing the same.

It is an additional object to provide such a material which may be mixed and handled without the application of heat and which may be handled and transported without serious caking.

It is a further object to provide a method and mixture in which the tendency to set is retarded by elements present in the mixture and in whlch the retardation of the set may be controlled b the amount and relation of the elements 0 the mixture.

It is also an object to provide a paving material which will be relatively soft'when first laid and which gradually becomes harder through a period of weeks or months.

prior application,

The basic element in our improved paving material is a natural rock asphalt such as the Uvalde rock asphaltwhich has been re- This material consists of a relatively soft, porous shell limestone thoroughly impregnated with asphalt or bitumen in its natural state. The asphalt forms from gravity varyin abouteight 'th twelve per cent of thetotal material as commercially used.- The asphalt rock is pulverized or crushed preferably with a swing hammer type of crusher,

although other types of crushers may be used. Such a crusher has been found to crush and pulverize the material in such manner that the sizes as the come from the crusher are so roportioned as to furnish a mixture which as a substantial minimum of voids. Such a mixture is known as a. balanced mix and affords a compact pavement or the like substantially impfervious to watelera more exact y 'fluxing agent which has a relatively high gravity in the Baum scale and which contains a relatively high percentage of volatileconstituents evaporatmg below 325 F. Thisv Baum oil1s one preferably having a from twenty to forty de- This oi may be a parafiine, semiasphaltic or asphaltic base oil. This type of flux differs materiall from those used in revious methods of uxin rock asphalt, as in such revious methods t e fiuxing agents have ha a much lower Baumvgravity and have had a comparatively small content of atmosphericall volatile constituents. Oils hav been use which have been topped or from which a considerable portion of the volatiles have been removed. In other processes a mixture of a small proportion of light volatile oil and a large proportion of heavy oil or flux have been used, and in some cases the light oil and heavy oil have been applied in successive steps. In all such met ods, however, the volatiles have consisted of ve light oils such as kerosene or gasoline whic evaporate rapidly and at points well below 325 F. It will be understood that the material sets up and cakes as soon as the volatiles are evaporated and in prior methods these volatiles have evaporated rather quickly since they have been ofa highly volatile nature.

.The fluxing agent which we consider the most staisfacto for our volatile content evaporated very materially We have found the best 'rebelow 325 F. sults are obtained with a natural oil which contains from ten to forty per cent of volatile constituents, the distillation or boiling points of which vary more or less uniformly urpose contains a number of vo atile fractions which volafrom 60 F. to 325 F. The exact percentage will depend upon the length of time which it is desired to delay the final setting of the material. If such an oil is not available as a natural product, it may be manufactured synthetically by the combination of the desired percentages of a heavy base and volatiles having boiling points throughout the desired temperature range.

The pavement made from such a mixture when originally compressed and rolled into place, will still be fairly soft although ada ted to sup ort and carry traffic. It will gradually hard sn as the higher boiling fractions evaporatae slowly and this hardenin and final setting may extend over a perio of weeks or months, de ending upon the quantity and character 0 the volatiles and the temperatures and traflic conditions. Such a road surface is highly desirable where it is laid upon foundations which have not finally settled or upon frozen or partly frozen ground, as it will adjust itself to the movements or changes of its supporting foundation without cracking.

As an additional feature, whenthe material must be transported a considerable dis tance before being used or when the weather is so hot as to cause-rapid evaporation, we find it desirable to add water to the mixture.

As a further means of delaying the final setting up of the mix, the water which was added may be somewhat acidified with acids formin carbon dioxide bycombination with the car onates in the asphalt rock. This carbon dioxide is heavier than air and tends to remain in the voids in the material and thus dela evaporation of the volatiles and slow up t e setting of the material. If the water-is acidified with hydrochloric acid it will also form calcium chloride b combination with thecalcium in the roc calcium chloride is hygroscopic and therefore holds' the Water in the mixture, thus serving as an additional element in delaying the set of the material.

A further element which we may incorporate in our paving material consists in a crushed rock which is harder than the limestone rock asphalt. This crushed rock may be a rock such as tra 'rock or hard limestone and is preferab y screened so as to eliminate the smaller particles. We have found that the most satisfactory results will be obtained by'using a one-size crushed trap rock substantially the same size as the larger portions of the rock asphalt aggregate. In laying pavements of ordinary thickness, this size would be from one-fourth to one-half inch. The crushed hard rock when added to the crushed rock asphalt serves to unbalance the total mixture; that is, it will give to the total mixture a preponderance of larger aggregate sothat the smaller aggregate and and, this fine particles present will not be suflicient to fill up all voids in the mixture. This fact tends to retard the set of the material as it will cause the particles to be largely separated by air spaces.

When the material is laid and compacted, however, the hard rock will be forced into the particles of rock asphalt and these particleswill be further crushed so that a solid and compact pavement will result. It is essential to the durability and long life of the pavement that the barren rock used for unbalancing the mixture, thereby creating air pockets, be a rock that is hard and tough. As previously stated, the mixture-is unbalanced and consequently the paving contains unfilled spaces which are planes of weakness. The initial rolling or com ression, and later the continual pounding o traflic will cause an internal crushing action as the excess arge size aggregate is rubbed together. If the rock asphalt particles are crushed, no damage is done as each rock asphalt particle is impregnated throughout with bitumen. On the other hand, if the barren rock is crushed, the paving will disintegrate sooner or later as there will be no coating of asphalt on the crushed particles to cement them toether. Therefore, the barren rock must be arder and tougher than the asphalt rock. It was the discovery of this rinciple that made possible the use of an un alanced mix .ture for the purpose of having air pockets help prevent the mixture from setting up. The hard rock which extends throu hout the paving gives a surface which is e cient in preventing skidding.

Another variation of this process consists in substituting rock asphalt for the hard barren rock, which rock asphalt has been crushed and screened to a uniform size so that when it is added to the mixture it will cause said mixture to be unbalanced, thereby creating air pockets which help prevent the mixture from setting up. There will be no disintegration of the pavement due to the internal crushing of the large size aggregate by rollin or by traflic for the reason that each particle of rock asphalt that is crushed will be permeated and coated with natural bitumen.

We have found that a very material difference may be made in the rate of set of the material, not only by varying the quantities of the several elements, but also by varyin the order in which the elements are mixe together. asphalt may first have added thereto the flux and water thoroughly mixed together. In this case the flux is merely thinned or emulsified by the water and its action therefore retarded since it is rendered less sticky. The action will be further retarded if the water is first added to the rock asphalt which is thusthoroughly wetted with the v one-half to two per cent or covering roofs.

For example, the crushed rock water before the flux is applied. The asphalt rock will not be permeated by the flux until the water has largely evaporated as the oil will not penetrate through the water.

Another manner in which the materials may be mixed is by ap lying the oil or flux to the crushed rock asphalt, then wetting the crushed hard rock or larger pieces of rock asphalt with water and mixing the damp rock with the treated rock asphalt. The dampness of the rock prevents-1t from be ing immediately coated with the solvent and flux and serves to separate the particles of rock as halt and to retard the set. If desired, the rock asphalt and hard rock may be mixed together and' the fluxand water may be added in the form of an emulsion. In some cases where long delay of set is desired, it may be found advisable to wet both the rock as halt and rock before applying the flux an mixing the mass together.

It will be apparent therefore that our materials may be mixed together in a variety of ways and that the method and order of mixture may be adapted to the particular needs-of the temperatures present and the length of transportation. These elements will preferably be so adjusted that when the material is' spread out in a thin layer on the surface being covered, the lightest part of the volatile constituents and any water present will be sufiiciently evaporated in a short time, such as one-half hour, so that the material may be compacted by a heavy steam roller or the like and formed into a dense water-proof surface.

While the several elements of our mixture may be widely varied in proportion, the mixture will generally cons1st of from ten time and the distance required for to thirty-three per cent of hard rock, where hard rock is used, from sixty to ninety per cent rock asphalt, and from cent flux; and, where water is used, from more of water.

While our material is particularly adapted for paving purposes in aving streets and roadways, it W111 be un erstood that it is also capable of many other uses. For example, it may be used to pave sidewalks or floors in buildings and may also be used in In view of its impermeability, it has also proved of value incovering the for holding liquid. The material is also efficient in dampening vibrations and is therefore particularly useful in bridge coverings,

industrial flooring, railroad platforms and crossings, and engine foundations.

While we have given by way of example, certain preferred methods of mixing and preferred proportions, our invention is capable of wide modification, and we con template such changes and modifications as bottoms of reservoirs or chambers one to five per come withiii .the spirit and scope of the ap ended claims.

position which comprises providlng a e claim:

1. The method of preparing a paving composition which comprises crushing rock a halt, and treating said rock asphalt with a ux and with water acidified with an acid combining with the rock to form carbon dioxide. 2. The method of preparing a paving composition which comprises crushing rock halt, andtreating said rock asphalt witha ux and with water acidified with an acid combining with the rock to form carbon dioxide and calcium chloride.

3. The method of preparing a pavin composition which comprises crushing roc asphalt, and treating said rock asphalt with a flux com rising a heavy oil, and with water acidi ed with an acid adapted to combine with the rock to forma heavy gas.

4. The method of preparing a paving cal;-

" anced mix of crushed natural rock asphalt and adding to said mix a flux, and crushe rock asphalt in larger sizes adapted to unbalance the mix.

Signed at San Antonio, Texas, this 17th day of March, 1928. v

' Y GLENN H. ALVEY.

ERNEST A. YOUNG.