US1637993A - Means for maturing and stabilizing road structures - Google Patents

Description

g s. E. FINLEY MEANS FOR MATURING AND STABILIZING ROAD STRUCTURES Filed June 23, 1926 Patented Aug. 2,1927. UNITED j STATE;

PATENT OFFICE;

SAM EVERETT Fm, OF ATLANTA, GEQBGIA."

mnms ron ma'runme AND s'rammzme non) s'ria ue'runns;

Application filed June as, 1920. Serial in. 118,048.

The invention relates to a novel apparatus for maturing and stabilizing road structures, including those made of mineral aggregate and bituminous binding material, which comprises means for subjectingthe body of the road structure to a series of zone, whereby voids between alternatively varying pressures progressively applied in adirection substantially normal to the road surface and-in parallel mixed with the aggregate throughout the.

.of alternately varying peripheral face of each rib curved transroad structure, fixing the aggregate as a consolidated mass enveloped and united in a matrix of the binder; these operations and results being effected, preferably, by

having continuous s aced relation and eights, with the a novel type of roller circumferential ribs in versely.

In the accompanying drawings,

Fig. 1 is a partial side elevation of a typical road roller having the new form of roller element applied thereto.

Fig. 2 is a front elevation partly in section, of the roller element.

In constructing roadways and thelike, of mineral aggregate and bituminous hinder, the ultimate desideratum is to obtain a road structure in which the mineral aggregate elements are firmly interlocked, with the larger elements at the bottom and the smaller elements grading off toward the top surface of the road in which the finest aggregate is disposed as the wearing surface, this densified and compacted body of graded aggregate being firmly imbedded in a matrix of bituminousbindeii SucliTroad structure is ideal, in that it is substantially homogeneous and uniform throughout, is water and weatherproof, and, while it is sulficiently resilient to provide a perfect rolling surface for vehicular traflic, it is inherently stable, against the shoving, rollm and scouring effects of such traflic, an altogether approximates a condition of permanen ce and durabilityunder all conditions of use. All road engineers have striven to attam these hlghly desirable characteri'sticsin finished roads and it has longbeen an estab-' lished canon of practice to cover the prepared subgrade of a road bed with mineral aggregate varying in sizes from the largest to the smallest from the bottom upward.

and then gregate cation of" the binding medium thereto; means of a heavy roller, usually with a compact the layer ofmineral agsmooth cylindricalsurface, or,;in some cases,

with an interrupted cylindrical surface;

either before or after the applisuch, for example, as would/be formed by a ser1es of independently mounted disks, or by a unitary cylinder havingcircumferential ribs of uniform height spaced at intervals laterally of the roller surface. These various types ofrollers, as heretofore employed; have proven ineffective, however, to produce a road structure in which all of the elements of the aggregate are compressed into a dense, compacted, interlocked and substantially uniform mass, for the reason that the pressure applied by the roller is normal to the surface of the road,-so that' the movement of the aggregate'elements is downward and in the direction of movement of the roller, due to the action of the curved surface of the roller shoving elements of the aggregate near the top of the layer ahead of it.

The present invention is designed to effect a thorough kneadin elements of the roa structure, during the compacting operation,

ment of the roller, so that the elementsare and rubbing of the by initially causing a movement of the elements downwardly,-

firmly interlocked, the larger sizesof the aggregate being forced toward the bottom and the smaller sizes being worked toward the top, after which the compacted 'str'uc5 ture is subjected to maximum pressure applied in parallel zones over the entire surface, thereby producing a substantiallyv homogeneous"mass,

practically proofagainst relativecmovement in any direction. To produce these results, the preferred instrumentalityis that illustrated inthe drawin s,

the elements of which are in whichl represents the body of-the rolling element of a power roller, which may have a weight of ten tons,

but which wei ht may bevvaried according .to the particu ar type of road being constructed The peripheral surface of the roller element 1 is provided with a series of circumferential ridges or ribs 2 and 3 sepasurfaces of the ribs are [unifor'ml peripherally and transversely, as indicated rated by intervening spaces, these ribs or ridges, .which should be continuous, alteron the drawings by the surfaces 4 and 5. It will be seen,therefore, that any part of the contact area of the roller -1 is curved in every direction; that is to say, no straight line, however short, would contact this surface at morethan one point, with the result that the material of the road surface, which is engaged by these contact surfaces of the ribs, is subjected -to alternating varying. pressures in a direction substantially normal to the road surface and in parallel spaced zones and to simultaneously imposed oppositely disposed lateral pressures in each zone,

as well asto pressure imposed by the for-- ward rolling movement of the surface of each rib. This efiects a distinct rubbing, kneading andcompressing' action'upon all of the elements of the road structure to force the latter into most intimate interlocking engagementwith a minimum of voids between the aggregate elements.

I The apparatus may be used elfectivel in preparing the mineral aggregate base 0 the road structure, after the latter is distributed on the prepared s ubgrade, by operating the roller over the surface of the aggregate layer. During the initial movements of the roller, the higher ribs 2 sink into the loose aggregate and force the latter downward and also laterally and forwardly to a slight extent, by the maximum pressure represented by the entire weight on the roller, which is distribut- .ed by the peripheral faces of the higher ribs 2. As the roller is moved back and forth over the surface of the aggregate, all'portions of the aggregate body are ultimately subjected to this maximum pressure and kneadin effect' of the ribs until the entire mass 0 the aggregate is ultimately consolidated and compacted, with the larger elements of the aggregate worked to the bottom and the smaller elements forced toward the top, so

that, when the rolling operation iscomi "pleted, all *of'the elem'entsi'of the' aggregate applied, usually in the form of asphalt of bitumen of any suitable character, andfinally a top dressing of stone chips, sand or the like, is spread over the surface, which is again subjected to a thorough .rolling by the same roller, which has the effect of kneading the binding material into the in terstices of the mineral'aggregate layer" and 'compacting the surface 0 the roadway into a dense and uniform wear resisting consistencyythat is impossible of attainment with the older types of rollers.

It is to be noted that the act-ion of this particular type of roller is distinctly "novel and the results obtained thereby are not approximated by the rollers heretofore employed for this general purpose. On first passing over the more or less loose or uncompacted aggregate, the ribs of the roller sink in the loose aggregate until all of the peripheral surfaces of the roller are in contact with the top surface of the aggregate and the pressure per square inch imposed by the roller is the least possible. The material of the aggregate is rubbed and massaged, due to the divergent diameters of the and forced into the closest possible contact.

ribs, kneaded and pushed in all directions" All bridging of the aggregate is prevented,

the fine material is rubbed into the voids and the coarse non-friable material is forced deeper into the surface, while the finer;

contact represented by the engaging peripheral surfaces of the higher ribs 2, thereby producing a maximum pressure on the road structure at these points of contact, and, as the rollingoperation is continued until the entire road surface has been treated, it is. apparent that the whole area of the road will ultimately be subjected to the maximum pressure represented by the entire weight of the roller, as distributed by the engagementthereof by the higher" ribs. A ten ton, roller of the usual cylindrical type ordinarily weighs about two hundred pounds per linear inch of roll. If the areaof contact of such a roller were less, as in the ribbed type con- .i stituting the present invention, the pressure per square inch upon the road structure would be increased indefinitely and limited only by the moduli of elasticity of the materials in contact.

' Many road and street surfaces of the mineral aggre ate asphalt binder type require long perio s in which to mature and to reach their best effectiveness. This matgri ng f process is aided by the action of trafiic; which I dition.

performs slowly and in lanes some of the functions which the instant invention produces quickly and uniformly over the full surface of the road. For example, asphalt macadam is usually compacted with a roller weighing approximately two hundred pounds per linear inch of roll and is finished by casting dry stone chips over this surface. Traific is then turned on and the dry stone gradually imbedded or worn away, while the asphalt and fine material is kneadedto the surface. This maturing by traflic occurs first in traflic lanes, while outside of these lanes the maturing is very slow. In anyca'se, ay'ear or more is usually required to bring the roadway to its best con- The machine heretofore described, and the method which it carries out, are designed to greatly accelerate the 'maturing process, while, at the same time, conserving the mineral aggregate and not wasting it in dust produced by the attrition of vehicle wheels. The same rapid maturing and stabilization is accomplished by the use of this method of machine on various other types of road construction. Among these may be included, all road ty es, depending upon a binding medium whic is'lfquid or a combination of liquids, whether these types be hot mix pavements, or those manufactured by. the application ofbituminous or other binding medium by penetration processes. In the hot mix types, the kneading, working and imbedding process, in combination with large finshing pressure per square mch, produces the most compact and most densemixture possible. Further, it decreases the perviousness to a minimum and increases the supporting power and stability of the road structure to a maximum. In the penetration types, mutually soluble combinations of liqu1d.bitumens may be used and the elimination of the less viscous bitumen is hastened by the mechanical action of the oxidation, and the more rapid release of the lighter molecules, carrying with them entrained heavy molecules, together with the working into the matrix of the more finely divided aggregate. Also, emulsions of bitumen in water are quickly broken under this roller, releasing the water and coalescing the elements of the bitumen. It will be seen, therefore, that the method herei'nbefore described and the apparatus by means of which the same is carried out, are most effective not only in preparing and compacting foundations of mineral aggregate, but are also particularly eflicacious in rapidly maturing and stabilizing the wearing surfaces of bituminous concrete roadways.

While the invention has been described with particular reference to its application in treating bituminous concrete road structures, it is to be understood that it is not limited to this specific type of road, but evidences a high degree of utility in maturing and stabilizing road structures of clay,

gravel, sand, earth, water-bound macadam and other types.

What I claim is: 1. Means for maturing and stabilizing.

composite road structures, comprising a roller having continuous circumferential ribs in s aced relation and alternatel varying heig ts on its periphery,'the perip eral face of each rib belngcurved transversely.

2. Means for maturing and stabilizing composite road structures, comprising a roller havin continuous circumferential ribs in s ace relation and alternately var in heig ts on its periphery.

I testimony whereof I afiix'm si ature. SAM EVERETT I EY.

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