US1500451A - Composite pavement and method oe pboducino same - Google Patents

Description

July 8, 1924. 1,500,451 w. 5. HACKER COMPOSITE PAVEMENT AND METHOD OF PRODUCING S AME Filed Nov. 26, 1920 INVENTOR.

ATTORNEY Patented July 8, i924.

WILLIAM E. HACKER, OF LOS ANGELES, CALIFORNIA.

COMPOSITE PAVEMENT AND METHOD OF PRODUCING SAHE.

- Application filed November 26, 1920. Serial No. 426,439.

To all whom it may concern:

Be it known that I, WILLIAM E. HACKER, a citizen of the United States, residing at Los Angeles, in the county of Los Angeles and State of California, have invented new and useful Improvements in Composite Pavements and Methods of Producing Same,

of which the following is a specification.

' in bitumen as to effectually seal it against entrance of moisture, and of such plasticity and toughness that it will effectually protect the largerparticles of mineral matter forming the main body of the avement from the wear and abrasion of tra c.

The pavements which have come the nearest to \having all of these characteristics have been those of the bituminous concrete type composed of a well graded mineral aggregate consisting of particles of crushed stone, gravel or slag varying from a maximum size, havin a' diameter of approximately one-half t e depth of the completed wearing surface section to an extremely fine powder, the several sizes being combined in such amounts as to make a mineral aggregate of maximum density or one containing a minimum'of voids, this mineral aggregatebeing combined with suflicient bituminous cement to coat all the particles of aggregate and fill the few remaining voids, the mixture being then spread and compressed upon a suitable foundation.

A pavement mixture made by this method is not only dense but also is relatively stable under traffic due to the interlocking of the largest sized particles of mineral aggregate with the intermediate sized particles. However, it was found necessary to waterproof the upper surface of thepavement by applying hot bituminous cement in a thin layer and rolling into same either sand or fine stone chips forming what is known as a flushcoat mat or finish. It was then found that as soon as this flushcoat mat was worn off by trafiic, the upper faces of the larger stones exposed to. traflic, soon became shattered or abraded also that water was not only absorbed by such stones, but also worked its way into the mixture, around the sides of such stones causing early raveling and disintegration of the mixture under traflic.

It was, therefore, necessary in the practical, commercial, laying of such avements, to increase the proportion of the t ier aggregate or mortar element to such an' extent,

that during the rolling of the hot mixture at time of laying, also when under traflic in hot weather, this excess of mortar would be forced by such pressure to the surface and,

to a certain extent at least, protect the larger sized particles of aggregate. Natur ll however, only a small portion ofsuch e cessmortar would find its way to the immediate surface of the pavement. Therefore an excessive amount of such mortar remained in the body and lower portion of the pavement section, holding the larger particles of aggregate apart and thus reducing the stability of the pavement due to more or less preventing the interlocking of'the particles of aggregate. In other words, it became a matter of individual judgment in the construction of each street to what extent stability should be sacrificed to obtain resistance to abrasion and entrance, of moisture and vice versa.

This compromise was necessary, due to the structure of the wearing section, the structure being homogeneous and of uniform physical characteristics throughout its entire depth. a

The resent invention overcomes this difficulty by producing a structure which is not homogeneous throughout its depth, but, on the contrary, isrelatively plastic at its immediate upper surface and fora slight depth below the surface, the remainder of the body of the pavement being relatively so stable as to prevent displacement of the structure or any portion thereof under traffic.

In the practical construction of bituminous concrete pavements the above-mentioned defects have been recognized, but as the commercial loss due to raveling and disintegration of mixture caused by abrasion and. entrance of moisture from above has been greater than from any other cause,

coarse aggregate bituminous concrete mixture and before same has become thoroughly compacted or chilled there was superposed thereon a fine aggregate bituminous mortar mixture, rich in bituminous content, the two dissimilar mixtures being rolled, blending the upper fine aggregate mixture with the upper portion of the coarser bituminous concrete mixture. This combination accomplished its object of waterproofing of surface and also protected the surfaces of the uppermost coarse particles of the bitumi-' nous concrete mixture from abrasion by traific. However, the practice in such cases did not increase the stability of the pavement structure as a whole and under present day modern trafiic conditions an increase of stability is not only desirable, but an extremely important essential.

The object of the present invention is to produce a product combining not only all of the advantages of the pavements de-. scribed above, but also one possessing this desirable greater stability. The manner in which this greater stability is obtained is by using for the lower portion of the pavement, a bituminous concrete mixture preferably composed of particles of aggregate varying in sizefrom those whose diameter is approximately one-half of the depth of the wearing surface section to fine dust which will pass a screen having 200 meshes per lineal inch. The amounts of each size used may be predetermined or not, and preferably are such as to produce a mineral aggregate having not more than 18% of voids. Y I have found that it is possible, by the use of a plastic, bituminous mortar upper portion, to obtain greater stability in a bituminous concrete pavement than has been obtainable under former practice, above referred to.

The manner in which I produce the structure, possessing the above desired characteristics is by:

(a) Laying a coarse aggregate bituminous concrete mixture so proportioned as to contain less fine aggregate and less bituminous cement than would be permissible if this bituminous concrete mixture formed a complete pavement wearing section, that is, by using a mineral aggregate having a relatively small percentage of voids, using a comparatively small proportion of fines, and using an amount of bitumen and fines combined not more than substantially that amount required to fill the spaces otherwise existing between the coarser particles, and thus producing a structure possessing the essential stability.

(6) Superposing upon the above described bituminous concrete mixture a fine aggregate bituminous mortar. richer in bituminous content than would be permissible if this bituminous mortar should form the For convenience in describing the product of my invention and the method of producing said product I submit the accom panying diagram, in which the portion let tered A represents a foundation which may be of any type of foundation or base either natural or prepared, preferably of a plastic rather than of a rigid character and which is of suflicient structural strength to support the weight of trafiic to which the pavement may be subjected.

The portion lettered B represents a dense stable bituminous concrete mixture and the portion lettered a relatively fine aggregate mortar mixture, rich in bi tuminous content.

. The portion lettered D represents the portion intervening between portions B and C formed b the mixture C pressing into mixture thus forming the serrated, non-cleavage line hereinafter and more particularly described.

The bituminous concrete mixture consists of particles of mineral aggregate of various sizes mixed preferably hot with hot bituminous cement of appropriate consistency. The mineral aggregate may consist of crushed rock, crushed or uncrushed gravel or slag or any other suitable equivalent material. The bituminous cement/may beprodueed from asphaltic or coal tar materials.-

I first spread this bituminous concrete mixture B upon the foundation A in a loose layer of uniform depth approximately equal to the desired depth of the completed pavement section.

I then spread the rich bituminous motor mixture G in a comparatively thin layer, over the bituminous concrete mixture B and then compact the whole structure by rolling, tamping or other suitable means of compression, so that the resulting product consists of a bituminous concrete mixture of great denseness and stability with its upper surface sealed by the plastic and relatively unstable fine aggregate mortar mixture.

In producing .the coarse aggregate bituminous concrete mixture B, I prefer to use a mineral aggregate consisting of particles varying in size from those whose diameter is approximately one-half the depth of the wearing surface section to fine dust Per cent. Passing a screen opening of not more than of the depth of completed pavement and retained on 1}" round opening screen 40-70 Passing 1} round opening screen, re-

. tained on a #4 mesh sieve 10-25 Passing #4 mesh retained on #10 mesh sieve 5-15 Passing mesh sieve -28 The amount of the aggregate which will I pass a #10 mesh sieve shall preferably be within the above stated limits and preferably be that amount which will reduce the voids in the total aggregate to less than 18% of its total volume.

The amount of bituminous cement used will naturally vary with the purity of the bituminous cement used and with the fineness and surface area of the mineral aggregate used and shall be sufficient to coat all the particles of mineral aggregate and pro:

duce a mixture containing from 4 to 8% by weight of bitumen soluble in cold carbon bisulphide.

The fine aggregate mixture shown as layer C in the diagram, shall consist of either sand, fine crushed rock, crushed or uncrushed gravel, slag or equivalent mineral matter, all of which will pass a. #4 mesh or finer sieve mixed preferably while hot with hot bituminuous cement of appropriate consistency, prepared from asphalt or coal tar materials, in such proportions that the resulting mixture will preferably contain from 8 to 17% of the customary methods, the coarse aggregate mixture is spread on the grade or foundation by means of shovels or forks, and rakes or other appropriate .means in a layer of uniform thickness approximately. equal to the desired depth of the completed wearing surface section. Before this mixture has become too much chilled, or full compacted, the fine aggregate mixture is spread in a comparatively thin layer over the coarse mixture B and the two layers compacted by rolling, tamping or equivalent means of compression.

While I prefer to spread the fine mixture C over the coarse mixture B before the coarse mixture B has received compression, this is not an essential point in the invention and if desired, the lower coarse mixture may be given partial compression by rolling if the fine mixture is applied at such a time and in such a-manner that the subsequent rolling of the two mixtures together will not only bind the two mixtures together, but will also, due to the kneading action of the roller, disturb the lower coarse aggregate to such an extent that the upper fine aggregate mixture is forced down into and between the uppermost stones in the coarse aggregate mixture blending the two mixtures, so that, after the completed wearing surface section has received ultimate compression, there shall not be a distinct plane of cleavage between the two mixtures,

ut on the other hand, a vertical sawed section ofthe completed wearing surface shall show, if anything, a serrated line at the upper surfaces of the uppermost coarse stones in the lower mixture.

By using the proportions of ingredients, and by following the methods described above,'thus locating the different sizes of mineral aggregate in their proper places, the resulting. product consists of a monolithic bituminous structure, the body of which consists of a bituminous concrete of great denseness and stability with its upper surface protected by the plastic and relatively unstable bituminous mortar.

The relative quantities of each of the two bituminous mixtures,'used, may and should be varied in accordance with the physical characteristics of the materials used for the coarse aggregate in the body or lower portion of the pavement wearing section, as obviously a thicker layer of the fine aggregate surface mixture is advisable, to protect a \coarse aggregate composed of soft or brittle mineral matter, than is required to protect a coarse aggregate composed of hard and tough stone, gravel, etc.

Under the ordinary conditions three (3) to five (5) parts by volume of the bituminous concrete mixture and one 1) part by volume of the bituminous mortar will give the best results.

It will be seen from the above description that the bituminous concrete mixture used for the lower portions or body of the pavement is one in which the various sized particles of aggregate are so proportioned in amount, that'if such a mixture were spread on a firm foundation and thoroughly compressedby rolling with a heavy'road roller or other equivalent means, theresult' would be an exceedingly dense stable bitu minous concrete, the upper surface of which would be relatively smooth, yet present a mosaic appearance, showing particles of coarse aggregate bound together by, but not materially protruding above the fine aggregate content of the bituminous concrete which has been forced up to the surface by the compression of the roller.

However, when the bituminous concrete mixture is spread loose by raking as described above, a large number of the larger sized particles of aggregate protrude above the mass of the mixture, and if the bituminous mortar mixture "is spread thereon before such protruding particles have been completely forced down into the body of the structure and compression is then applied ]by rolling or other means, the result will (a) Some of the bituminous mortar mixture will be forced into any and all spaces between the tops of suchvparticles as protruded above the mass of the bituminous concrete mixture.

(6) Some of the bituminous mortar mixture. will be compacted into a relatively thin layer above .the .tops of the uppermost particles of bituminous @-concrete mixture.

(0) Many vof "the uppermost particles of the bituminous concrete mixture will be embedded partially in "the finer portion of the coarse aggregate bituminous concrete mixture, and partiallyembedded in the fine aggregate bituminous mortar surface mixture, thus firmly jointing or interlocking by blending of the two mixtures together.

I have, of course, specifically disclosed the best practical embodiment of my invention I of which I am cognizant, but it is obvious that in'the future practice of the invention departure from the scope such changes may be made as do not involve of my invention as claimed. I

I claim: v 1. A unitary bituminous pavement wearing structure composed of two dissimilar bituminous mixtures, the lower being a relatively' stable coarse aggregate bituminous concrete containing relatively 'coarseand relatively fine mineral bodies and containing not more than substantially that proportion of relatively fine mineral bodies and bitumen which will fill the spaces otherwise existing between the relatively coarse bodies if compacted alone, the upper mixture being a relatively plastic fine aggregate bituminous mortar containing relatively fine' mineral bodies and containing not less than substantially that proportion of bitumen which will fill the spaces otherwise existing between the mineral bodies if compacted alone, the contiguous portions of the two mixtures being mo auf plastic fine aggregate bituminous mixture 7 containing relatively fine mineral bodies and containing not less than substantiallythat proportion of bitumen which will fill the spaces otherwise existing between the mineralbodies if compacted alone, and compacting the pavement by compression applied to the upper course and thereby forcing the contiguous )ortions of the two courses into blending at mixture with each other to produce a unitary mass.

. 3. A bituminous pavement wearing structure composed of two bituminous mixtures of dissimilar physical characteristics, to-wit: (a.) a relatively stable bituminous concrete mixture consisting of bitumen four to eight percent by weight and a mineral aggregate composed of particlesvarying in size from 'those whose diameter is not more than seventenths of the depth of the completed pavement structure, to those which will pass approximately, a 200 mesh sieve, theamounts of the several sizes used beingsuch-fthat the voids in the-mineral aggregate of this mix,- ture, considered by itself, are not more than eighteen percent of the volume of themineral aggregate, the weight of such aggregate which will ass a ten mesh sieve being not less than fteen percent nor more than twenty eight percent of the weight of the total mineral aggregate used "in this mixture; and I(b.) a relatively plastic bituminous mortar mixture, composed of eighty three percent to ninety two lpercent by weight of mineral aggregate, al of which will pass a' sieve having four meshes per linealinch and eight percent to seventeen percent by weight of bitumen; said bituminous mortar mixture being superposed upon the bituminous concrete mixture and compressed and the contiguous portions of the two mixtures being thereby blended to produce a unitary mass.

4. A bituminous pavement wearing structure composed of two dissimilar superposed bituminous mixtures, the lower being a relatively stable coarse aggregate bituminous concrete mixture, the mineral aggregate of which contains not more than approximately eighteen percent of voids by volume, the particlesof the aggregate being coated with cent to seventeen percent of bitumen i liyweight, the contiguous portions of the mixtures being so bonded and blended together by compression. as to produce a unitary mass.

5. A bituminous pavement wearing structure composed of two dissimilar bituminous mixtures, the first being a relatively stable coarse aggregatebituminous concrete 'xture the graded mineral aggregate of W ch contains not more than approximately eighteen percent of voids by volume, and the amount of such mineral aggregate that will pass a ten mesh screen being not more than approximately twenty-eight percent by weight, the particles of the aggregate being coated with bitumen in an amount approximatel four to eight percent'by weight, the second being arelatively plastic fine aggregate bituminous mortar containing approximately eight percent to seventeen percent of bitumen by weight, the two contiguous portions of the mixtures being so bonded and blended together by compression as. to produce a unitary mass,

6. A bituminous pavement wearing structure of the kind specified in claim 4, characterized further by the coarse aggregate bituminous concrete mixture being such that if a given volume of said mixture should be compacted by itself, the specific gravity of said compacted mixture would equal at least ninety percent of the specific gravity of the mineral aggregate used in said mixture.

7. The combination, in a bituminous pave- I ment wearing structure of, a bituminous concrete mixture, the mineral aggregate 'of which contains eighteen'percent or less of voids containing bitumen in an amount approximately four, percent to eightpercent by weights spread in a layer of substantially uniform thickness upon which layer is. spread a comparatively thin layerof a relatively rich-bituminous mortar mixture containing bitumen approximately eight to seventeen percent by weight the whole being compacted and the contiguous portions of the two mixtures blended together by compression. I 8. A bituminous pavement'wearmg structure com osed of two bituminous mixtures of dissimilar physical characteristics, towit:

(a arelatively stable bituminous concrete mixture consisting of mineral aggregate and bituminouscement comin within the following proportions by weig t:

' Per cent. Coarse aggregate which will passa screen having openings not larger thanf of the depth of the completed wearing structure. and which will be retained on 1} inch round opening screen 407O Intermediate size aggregate which will pass e; inch round opening screen and be retained on a #10 mesh sieve 15-40 Fine'aggregate which will pass a #10 mesh sieve 15-28 Bituminous cement, sufficient to coat all par-- ticles of the aggregate and produce a mixture containing 48 per cent of bitumen soluble in cold carbon bisulphide; and (b) 'a relatively plastic. bituminous mortar mixture composed of eighty three per cent to ninetytwo per cent by Wei ht of mineral aggregate, all of whlch wil pass a sieve having four meshes per lineal inch, mixed 'wit eight per cent to seventeen per cent by weight of bitumen, this latter bituminous v mortar mixture being superposed upon the previously spread bituminous concrete mixture and compressed so as to produce a bummmous pavement structure consistmg of a uniformly graded, dense, stable bituminous;

concrete mixture throughout the lower two thirds to three fourths of its depth and of a rich, plastic, bituminous mortar in the u permost one fourth to one eighth of its depth, the intervening portion being composed of large particles of the lower portion of the structure bound together .partly by some of the fine bituminous coated aggregate from the lower portion of the structure and partly by some of the plastic flexible bituminous mortar forming the surface of the pavement, thus forming a structure in which the two abovedescribed mixtures are so blended that a vertical cross section of the completed structure will not show a distinct plane of cleavage between the two mixtures.

Signed at Los Angeles, California, this 16th day of November, 1920;

, WILLIAM E. HACKER. Witnesses:

L. BELLE WEAVER, Fnnonmo'x S. LYON.

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