US2112380A - Process of manufacturing aggregates - Google Patents

Description

March 29, 193s. C. M PRICE www PROCESS OF MANUFACTURING AGGREGATES Filed Oct. l5, 1934 2 Sheets-Sheet l INVENTOR. C// /W /r/'c e ATTORNEY.

c. M. PRucE 2,1 m@

PROCESS OF MANUFACTURING AGGREGATES Filed OCE'.. l5, 1954 2 Sheets-Shee' 2 VENTOR. pr/'c'e ATTORNEY.

Patented Mar. 1938 6 Claims.

This invention relates generally to processes for the manufacture of light-weight aggregates from natural siliceous material, and to products rev sulting from such processes. Such aggregates havel many industrial applications, including particularly theA making of hydraulic concrete.

It is a general object of the invention to provide a process of the above character which will result in a product superior in many respects to both natural and artificial aggregates heretof fore available. Among other desirable characteristics, the aggregate obtained from` my process affords extreme `lightness together with strength, and possesses an interior cellular structure with a dense, nearly impervious outer layer, so that the whole is resistant to the absorption of moisture.

It isa further object of the invention to provide a process of the above character which will make possible the manufacture of aggregates of different sizes, from the size of small sand grains to the size of large pebbles, without'the necessity of grinding or crushing after burning of the raw material, and with the individual masses smooth and rounded as to shape.

Another object of the invention is to make possible the manufacture of light-weight aggregates from natural deposits of siliceous material such as shale or diatomaceous earth. In this connection. the invention is characterized by the fact that the siliceous material which I utilize is naturally impregnated with oil or other'carboniferous matter, and this oil or carboniferous matter is made use of during the process;

A further object of the invention is to provide a superior form of concrete, having unique properties by'virtue of the use of aggregates manufactured by the present process.

Further objects of the invention will appear from the following description in which the preferred embodiment of the invention has been set forth in detail in conjunction with the accompanying drawings. l

Referring to the drawings: i

Fig. 1 is a schematic view showing the different steps taken in carrying out the preferred process 4of my invention. ,Y

Fig. 2 is a perspective view illustrating an individual mass of my aggregate after manufacture.

Fig. 3 is a cross-sectionaldetail showing the appearance of a fracture taken through the mass shown in Fig. 2.

Fig. 4 is a diagrammatic view illustrating the nature of the heat treatment which I utilize in uNrrlsD STATES PATENT, OFFICE Paocnss or MANUFACTURING AGGREGATES Carl M. Price, Berkeley, Calif., assigner to Eastman M. Markell, Berkeley, Calif.

Application October 15,

1934, Serial No. 748,309

my process, various temperature zones being noted.

Fig. 5 is a schematic view showing the different steps taken in carrying out a modification of my process, in which the heat vtreatment is divided into two steps.

Fig. 6 is a perspective view showing a fragment of diatomaceous earth after preliminary calcining in accordance with the process of Fig. 5.

Fig. 7 illustrates the fragment of Fig. 6 Ain cross-section.

The characteristics of the product resulting from my process can best be understood after a description of the process of manufacturing the same. By way of example, I shall refer to diatomaceous earth which is naturally impregnated with oil or petroleum, as a source of raw material. The extent of such natural deposits is not known, but they are found in certain` localities in California. After this natural materia] is quarried, it is subjected to crushing, as indicated at l0, and the crushed material is-then graded, as indicated at l I, invaccordance with the grade or sizeof aggregate desired for the iinal material. Assuming that it is desired to produce a medium grade aggregate, fragments within the size limitations of this grade are then subjected to the special heat treatment indicated generally at I2.

In the preferred process, I carry out the entire heat treatment in a single passage of the material 'through suitable apparatus, such as a relatively long rotary kiln. Such an apparatus has been indicated at I3 in Fig. 4. The graded diatomaceous earth fragments are introduced into the upper or entrant end of this kiln, together with a divided coating material having a` higher fusion point than the diatomaceous earth. Suitable heating means, such as a iiame of a fuel oil burner, is propagated Within the lower or discharge end of the kiln, with a draft of air and gases of combustion being maintained through the kiln to the entrant end. Adjustment of the draft serves to control thev temperature gradient 'to which the material is subjected as it progresses through the y dolomite is calcined at the temperatures utilized in the. treatment, in general it' has a` higher fusion point than that of the diatomaceous earth. It is apparent that the dolomite may be calcined magnesium and calcium carbonates, or magnesium and calcium oxides. can be used instead.

In some instances I have also 4positionedthe burner ilameat the upper end of the kiln, with a draft maintained toward the lower discharge end, although the results obtained have not been as favorable as with the burner at the discharge diatomaceous earth. While the material is progressing through the preliminary heating zone A, there is a general increase in temperature, with a release of some of the lighter hydrocarbon iractions. In the transitional or intermediate heating zone B there is an ignition of the voiatilized hydrocarbon fractions, Awith a relatively rapid rise in temperature. In the next zone C, which is termed the cell-forming zone for reasons to be presently explained, the material is subjected to the highest temperature attained in the kiln. In the last zone D the temperature of the material is permitted tov fall before the material is discharged.

Curve I4, plotted against the temperature scale T, illustrates a typical temperature gradient for passage of the material through the kiln. It will be noted that the transition between zones A and B occurs at a temperature of about 1500 F., and that the temperature increases in zone B to about 2000 F. In zone C the temperatures range from about 2000 to 2150 F.

- mite, the dolomite adheres to and forms a coat- The effect upon the material being treated in the kiln i3 is as followsz-As the material enters Azone B it becomes putty-like or plastic, and as it is being tumbled and intermixed with the doloing over the surfaces of each of the fragments. This coating not only prevents the fragments of diatomaceous earth from clinging together, butV also serves as a sealing medium, thus producing an outer shell foreach fragment which is largely impervious to the passage of gases. As the coated fragments of diatomaceous earth now pass into the high temperature burning zone C, there is a further softening accompanied by a final breakdown of the remaining carboniferous matter. 'Ihe resulting formation of gases within the masses causes the masses to be puffed with respect to size, and causes the interior oi the masses to assume a cellular structure. The coating material plays a part in this pulling, because the sealing action tends to prevent the escape of gas through the outer shell, although the outer shell is still suillciently vplastic to permit stretching to accommodate the enlarged size. The rolling action imparted to the masses whilethey are in putty-like form causes a rounding ofthe shapes to produce pebble-like forms, and also aids in producing smooth-textured surfaces. In the last zone D there is a drop in temperature. to permit the masses to set before their discharge. I

After delivery from the kiln i3, the cooled mavspongy or cellular interior I1.

- ariaaao, before its use, or that a synthetic mixture of pores be maintained enclosed within the outer shells of the masses. A typicalvmass i8, resulting from my procesais shown inlig. 2. It will be noted that this mass ispebbie-like in form and that the surfaces are rounded and relatively smooth. Referring to Fig. 3, the outerv shell or envelope is designated at It and surrounds the While the surface of the mass is oi' smooth texture. no glazing is apparent, .because the coating material utilized l isnotofsuchacharacterastopermitglazing or fiuxing at the temperatures utilizedin burning.

When using dolomite as a coating medium I have found that there is some chemical combination between the silica of the diatomaceous earth and the calcium of the dolomite, to form calcium silicate or silicates in the outer shell. In addition to the attributes previously mentioned, the shell is resistant to the action of acids and alkalis.

The advantages of lmy aggregate will be apparent from the preceding description. The strength aiforded is many times that of natural quarried diatomaceous earth, and at the same time extreme lightness is afforded. Concrete made with the use of myA aggregate also has many desirable characteristics. Aside from affording extreme lightness together with strength, it can be utilized as an insulating medium with respect to conduction of heat and transmission of sound. Because of the rounded ,contour of the masses, plasticity or fluidity of the concrete mix is increased, compared vwith mixes utilizing lightweightnatural or artificial aggregates, such as cinders. Likewise, as compared withV aggregates such as cinders which require crushing to the size desired, 'a lesser amount of water is required to produce a workable mixture. Since the surfaces Aof the aggregate are not glazed, a good bond is also afforded with the surrounding matrix, thus affording a high degree of strength.

Concrete formed by the use of my aggregate is also relatively resistant to climatic conditions and to corrosion by chemicals. This is for the reason that my aggregate is not subject to corrosion or disintegration by acids or other chemicals to which the concrete mix may be subjected, and because, since the aggregate masses will not absorb any appreciable amount of water, the concrete will not be subject to bursting upon freezing.

Where utmost lightness is desired, it is evident that concrete may be made by the use of my aggregate to the exclusion of all other conventional aggregates such as sand and the like. This is for the reason that my aggregate can be made over a wide range of sizes, including a size commensurate with ilne sand, and -sizes of oneinch or more in diameter. However, if extreme lightness is not desired, or is unnecessary, it is possible to utilize varying quantities of my aggregate, together with other natural aggregates, such as sand, in accordance with particular conditions or requirements.

It is evident that my process is capable of various modifications, within the spirit of the present invention. For example, it is possible to carry out the heat treatment in two separate steps, with the coating operation being carried out before the second heat treatment. A process of this character is indicated in Fig. 5. Thus, after crushing and grading, the diatomaceous earth is subjected to calcining, as indicated at I2a. After the calcining operation the material is subjected to coating at I 2b, with dolomite or like material, after which it is subjected to burning. as indicated at 12e.

The calcining can be carried out in an inclined rotary kiln, in which temperatures ranging from 300 to 700 F. are maintained. As the fragments become heated, combustible hydrocarbon vapors are evolved from the oil or other carboniferous matter, and the vapors can be collected as discharged from the kiln and utilized to advantage. By virtue of such calcining treatment, the fragments are'caused to have an. outer calcined shell or envelope of appreciable thickness, from which substantially all carboniferous matter has been removed. 'Ihis shell surrounds an inner blackened core containing considerable carboniferous matter but having no greater porosity than the original quarried material.

In Fig. 6 there is shown a typical fragment i8 after the calcining treatment referred to above. Fig. 7 shows the calcined envelope i9 surrounding the inner core 2|. The envelope I 9 is whitish in color and may vary from 1,4m to 1/,4 of an inch in thickness. The inner core 2| is black in color, as compared with the color of the surrounding freshly quarried fragments, and shows no signs of pufliing or sintering from the heat treatment.

The coating step, after calcining, can be conveniently carried out by introducing the calcined fragments into a rotary treater or tumbler together with a slurry of the dolomite or like divided material. After such treatment it is desirable to permit the fragments to dry in order to avoid the introduction of excessive moisture into the subsequent part of the heat treatment.

The burning after coating can be carried out in a separate rotary kiln in which the material is elevated to a temperature of about 2150 F. The action here is substantially the same as with the process previously described, in that a breakdown of the inner carboniferous matter occurs, with the result that gases thereby formed cause the masses to be puffed with respect to size. Here again, the coating tends to seal the outer shells of the masses, to prevent escape of gas, and also prevents the masses from sticking together.

While it is possible to utilize the second outlined process with results practically the same as the simplified process described with reference to Figs. l and 4, it is obvious that heat treatment in a single rotary kiln has the advantages of simplicity and cheapness of manufacture.

This application is a continuation in part of subject-matter disclosed in my co-pending application Ser. No. 708,649, filed January 27, 1934.

I claim:

1. In a method of manufacturing a light- Weight aggregate, characterized by the use of a rotary kiln, introducing into one end of the kiln fragments of naturally formed siliceous material containing carboniferous matter, simultaneously introducing into the kiln a divided material having a fusion point higher than the fusion point of the siliceous material, and causing the temperavture of treatment for the material progressing 2. In a method of manufacturing a light- 4weight aggregate, characterized by the use of a the divided material to effect substantial sealing of the surfaces of the fragments.

3. In a method of manufacturing a light-weight aggregate, characterized by the use of a rotary kiln through which the material being treated is caused to progress, introducing into the kiln fragments of naturally formed siliceous material containing carboniferous matter, likewise introducing into the kiln a divided material containing calcium and magnesium, causing the kiln to be fired in such a manner that the fragments in their passage through the kiln are gradually heated to a burning temperature, as represented by about 2150 Fahrenheit, the fragments, before being heated to such temperature, passing through an intermediate temperature zone in which they become softened and pick up the divided material to effect substantial sealing of the surfaces of the fragments, there being a chemical reaction between the silica of first-named material and the calcium content of the divided material.

`4. In a method of manufacturing a lightweight aggregate, burning fragments of naturally formed siliceous material containing carboniferous matter, while the fragments are coated with a non-combustible divided material having a fusion point higher than that of the material forming the fragments and serving to seal the surfaces of the fragments.

5. In a method of manufacturing a lightweight aggregate from fragments of naturally formed siliceous material, applying to the fragments a coating of divided material consisting mainly of magnesium and calcium, said material having a fusion point higher than that of the material forming the fragments and serving to seal the surfaces of the same, and burning the fragments to cause puing of the same to form a cellular interior structure with a dense, irnpervious outer shell.

6. In a method of manufacturing a lightweight aggregate, burning fragments of naturally formed diatomaceous earth containing carboniferous matter, while the outer surfaces of the fragments are sealed with a powdered material containing calcium and magnesium, whereby the fragments are vesiculated, and causing continuous rolling motion of the fragments during such burning, whereby the fragments are reshaped to form pebble-like bodies.

CARL M. PRICE.

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