US 1729884 A
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Oct. l, 1929. v L, R, MMKENZIE 1,729,884
METHOD OF MAKING A WEAR COURSE FOR PAVEMENTS Filed Aug. 6, 1928 25 retention of the same.
Patented oa. 1, `192e LEON n. MAGRENZIE, or Das MOINES, Iowa METHOD OF MAKING A WEAR COURSE FOR PAVEMENTS Application, air-,d August 6,1928. serial No. 297,634
The purpose of my invention is to provide a simple and effective method for making a wear course for pavements.
My pavement is of the type which retains its plasticity by reason of the fact that it has a substantial content of asphalt, bitumin, or
other suitable material. Such pavement when t of substantial thickness has ordinarily move- `ment within itself when subjected to trafficand temperature conditions. This is' true,
even though it have a suabstantial rock aggregate content.
It is well'known that during the summer months when the air temperature is quite high that asphaltic materials, from -which the wear course of a pavement is ordinarily formed,
are subjected to easy displacement due to traiiic upon. the wear course. l
The asphaltic materials during thehigh temperature of the summer months are comparativelyl soft or pliable and due to traffic thereon are very quickly and easily displaced.
lt is further well knownthat'asphalticmaterials have a greater affinity for heat and the It thus follows that the heat whichis absorbed within `the pavement will giveto the pavement a temperature greater or higher than Athe air temperature.
rlhe degree of heat within the pavement is retained for a considerable length 0f time after the suns heat rays have been absorbed,
and it is my object t0 providea pavement that will eliminate the movement ofthe phaltic material within itself. s. It is therefore more particularly my purpose to provide a method for constructing. such 'a pavement whereby any substantial movement vwithin the body of the pavement 40' itself is eliminated.
Especially, it is my purpose to provide a method for making such a pavement having near the location therein at which such movement is ordinarily noticeable, a substantially horizontal binding mesh anchoring means and forcing rock aggregate, into the interstices of the anchoring means, a portion of the rock being of such size that upon compression of the pavement some of the rock will enter and project through all of the openings `of the an- 50 choring means. llt is quite generally recognized that for almost all sorts of pavement bases, and es ecially for the repair of worn concrete an brick pavement, the vmost eiiicient and generally I satisfactory top or wear course'is of asphaltic or bituminous or other material which retains its plasticity during a relatively long life.
Heretofore as explained in my Patent Number 1,707,939, issued April 2, 1929, the use of such material for a wear course has been in the face of certain Well recognized difficulties and defects.
The asphaltic or bituminous material is hard to keep in place. It tends to shift or roll and form humps and hollows. On a crowned road and especially under heavy traffic in warm Weather, it tends to flow toward the low sides of the road, so that in time it will be much thicker at the sides of the roadv than in the trac lanes. Where high or'low spots or .humps and hollows are formed,'the top course may ultimately form small holes, and water gets into the holesvor seeps under the to .course and greatly increases the rapidity wit '15 which the pavement Wear course deteriorates .and disintegrates. v
The diiicultiesy experiencedl on account of' the movement ofasphaltic or bituminous top courses have greatly increased during recent years on account of the universal use of motor vehicles. lThe stopping and starting of motor vehicles and the heavy impact from them tends to pull or push the upper surface ofthe plastic wear course for moving it out of its original formation in the manner already referred to.
While highway engineers have for years i recognized the evils in the movement of plastic wear courses, theyhave not been able to solve 00- conditions. Therefore, even though the lower part of the wear course may be anchored to the base, it is found that the upper part of such course has movement with relation to the lower part of the course with the resultant formation of high and low spots and flow toward the lower portions of the highway.
My experiments have shown me that there is a normal axis of movement of such wear courses within themselves. with certain asphaltic materials commonly in use, this axis of movement begins at about an inch from the bottom of the course. At an inch and a half from the bottom, it can be studied, and at from two inches and up, it is very noticeable.
In a two inch top course, even though the lower part of the course be anchored to the base, there will be movement in the material of the top course itself in that portion, which is for instance more than an inch above the bottom.
Efforts have also been made to cure the diiiculty by using chemical ingredients for Y hardening the lastic material, but they have had only indi lerent success.
It has been found that it is desirable to use a plastic top course of asphaltic or bituminous material, which does not have such normal movement within itself. When a wear'- course is laid thin enough so that it does not have such movement within itself, it becomes too thin for practical use. This is due to the fact that asphaltic materials have in' them volatile oils. which are drawn out by hot weather, leaving a coke-like substance, which quickly disintegrates and pulverizes under traflic.
`Therefore in order to secure suicient longevity and wearing quality, it is necessary to use a top'course so thick that it has movement within itself.
By the process of my present invention,
f I am able to provide anasphaltic or bituminous wear course in which this movement within the body of material itself is eliminated or so nearly eliminated as to be negligible for practical purposes.
For purposes of illustration, I have filed Figure 1 1s a perspective view partly in For instance,-
section showing a lower layer, a metal reinforcing, and an upper layer, used in the practice of my process for making improved pavement.
Figure 2 is a vertical, sectional view through a portion of such pavement, illustratiing. at the left-hand part of the gure the complete avement .when first laid, and in the right-hand part of the figure the pavementafterit lhas been rolled or otherwise compressed.'
- Figure 3 shows a perspective view of a section of the foraminous reinforcementI which may be used in the practice of-my method.
In carrping out my method, as by way of example, lay upon worn-out concrete pavement or other pavement to be re-surfaced or upon any suitable base, such as waterbound macadam, rolled gravel, concrete or bituminous mixtures, a lower layer of asphaltic or bituminous mixture, containing standard materials and having therein fine sands and angular rock or stone, by way of example, sized from one fourth to one and one-fourth inches in their greatest dimensions.
This layer is referably about one and onequarter inches t ick when fluffed to the contour of the highway. The thickness, of
' course, may vary somewhat depending upon the materials used and upon the hei ht of the normal vaxisof movement in suc terial. It should be of such thickness that its top will not be much above the height where movement in a body of plastic top course begins within itself.
The base upon which the pavement is laid is indicated at 10, the lower layer of plastic material' is indicated at A, and the rock therein by the lreference numeral 12.
The greatest dimension of`a portion of the rockA should be greater than the thickness of the layer after the layer has been finally rolled.
Asphaltic mix or bituminous mix or natural rock asphalt maybe used for the purpose.
Where hot asphalt is used, and wherever the process will permit, this `lower` layer A should be iufed while hot andimmediately there should be placed thereon sheets of exanded metal or other binding mesh anchormg means, such as indicated at 14. The sections thereof should be locked at their ends in any suitable way for making a continuous mat of this reinforcing.
Immediately a second layler B is imposed` e lower layer A ower layer or may varysome- The product thus far completed is then -subjected to pressure, as for instance by being rolled by heavy rollers. Thispressure compacts and compresses the material, which is porous, and forces therefrom the air in its voids, and adjusts the rock, and in particular forces the rock from above and below the reinforcing downwardly and upwardly into and partially through the interstices of the reinforcing.
The size of the openings in the mesh may be for example six to twelve inches long dimensions, and three to six inches short dimensions (inside measurements). The mesh should be such with relation to the stone that several stone may enter the interstices and become fixed therein andv can not have much lateral movement Without coming int contact with the metal. l
There is thus provided a solid mass in which the lower layer, upper layer and reinforcing are thoroughly tied or anchored'to-k stone 'content for effectively meeting abrasion and wear, which stone content is thoroughly keyed to the semi-rigid metal mesh and thus serves to anchor and hold the body of material against any movement within itself.
Any tendency of the upper part ofthe body of material to move would be resistedby the engagement ofthe stone in the interstices of metal with the strands of the metal.
It should perhaps be mentioned that the reinforcing material should be in a plane parallelto the top surface of the Wear course and should not project either upwardly or downwardly any substantial distance above or below the top of the bottom layer A, so that it will not interfere with the raking and fluffing of the top layer.
1t must be laid after the bottom layer A has been laid, so it will not interfere with the placing and flufling of that layer.\..`
It is possible that my method be practiced with well known and generally available materials and equipment.
In myvclaims, I intend by the use-of the terms asphalt or bitumin or their adjectival derivative-s to include any plastic paving material suitable for such a pavement and normally having movement within itself under t-raflic and temperature conditions.
In any reference to reinforcing, I intend to cover any Iforan'iinous material adaptable to the purpose.
I claim as my invention: l. A method of making a bitumlnous pavement comprising the superposmg of one layer of asphaltic material upon another, -with a semi-rigidbinding mesh anchoring element placed between them, and compressing the mass, and thereby forcing into and partially through the meshes of the anchoring element rock aggregate, a substantial portion of which is of a maximum size greater than the thickness of either layer when the layers are finally compressed. f l
2. A method of making a bituminous pavement, comprising placing upon a suitable base a layerof asphaltic material containing a large content of rock aggregate, a substantial portion of which is of a largest dimen-` sion slightly greater than the thickness `of the layer after final compression of such layer, the
placing upon said layer of afsemirigid substantially continuous binding mesh anchoring means, placing upon s uch anchoring means and lower layer an upper layer. of asphaltic material, having a large content of rock aggregate, a vsubstantial portion of which aggrcgate has a largest dimension slightly greateinthan the'thickness of the upper layer when such layer is finally compressed, and subjecting said pavement to pressure for thereby compressing both layers and forcing members of the rock aggregate into and partially through Athe interstices of the anchor.
3. A method of making a bitummous pavement comprisingplacmg upon a smtable base a layer of asphaltic material containing a large content of rock aggregate, a substantial portion of which is of a largest d1mension slightly greater than the thickness o f the layer afterlinal compression of such layer,
4thepl'acing upon said layer of a semirigid substantially continuous blnding mesh anchoring means, placing upon such v anchoring means and lower layer an upper .layer of asphaltic materlal, and subjecting said pave- `ment to pressure for thereby compressing both layers and forcing members of the rock aggregate into and partially through the inf -terstices of the anchoring means.
4. A method of making a bituminous pavement comprising placing upon a suitable base" a layer of asphaltic material, the placing upon said layer of a semirigid substantially continuous binding mesh anchoring means, placing upon suchV anchoring means and lower Alayer .an upper layer of asphaltic material having a largecontent of rock aggregate, a substantial portion of which aggregate has a largest dimension slightly greater thanthe thickness of the upper layer when such layer is finally compressed, and subjecting said pavement to pressure forthereby compressing both layers'and forcing members of the rock aggregate in'to and partially through the in terstices of the anchoring means.
5. A method of making a bituminous ave'- i ment comprising placing a layer of asp altic material upon a base, placing a semirigid binding mesh anchoring means upon said I. 5 layer, superposing a second layer of as haltic material upon the anchoring means an lower layer and compressing the layers and forcing `into the meshes of the anchoring means rock aggregate of such size relative to the layers and the meshes that upon final compression of the pavement some of the rock will enter all the meshes and proiectntherethrough into both layers. v
LEON R. MACKENZIE.