US1718863A - Impact method of making pavement - Google Patents

Description

June 25, 1929. L. R. MacKENZIE IMPACT METHOD oF MAKING PAVEMENT Filed Sept. l5 1928 2 Sheets-Sheet June 25, l929 1 R. MaCKENzuE IMPACT METHOD OF MAKING PAVEMENT Filed Sept. l5, 1928 2 Sheets-Sheet 2 PATENT OFFICE.

LEON It. MACKENZIE, 0F DES MOINES, IOWA..

IMPACT METHOD 0F MAKING PAVEMENT.

Applicationled September 15, 1928. Serial No. 306,208.

'l he purpose ot my invention is to provide a method tor making a concrete pavement, which is as close in nature to hard natural stone as it is possible to secure.

lt is fthe purpose ot' all -constructors ot concrete pavement to secure a pavement having as nearly as possible the structure, durability and permanence ot hard natural stone. lt it were possihle to out slabs ot hard natural stone, .transport and lay them tor paving, this would make the ideal hard surfaced pavement. Practically and economically, it has'hecome 'necessary to crush the stone into relatively small particles, add cement, Water and ne particles, then mix together to torm concrete, and lay the concrete. rlhe concrete as ordinarily mixed and laid has many air voids and has considerahle excess Water con tent over the amount required tor complete hydration ot the cement particles.

lt is desirahle to eliminate the voids, created hy air and excess Water content, in order to leave a finished product which is as dense and homogeneous as is possihle to Secura-consistingr ot hard rocl aggregate driven into close relation with each other and properly honded or cemented together hy the cement mortar contained therein.

ln practical concrete paving construction, tor ease ot transportation and handling, it is necessary that the proportion ot mortar to stone he greater than it should he under ideal conditions. ln pavements actually huilt the mortar' in concrete is never as strongas the hard rock aggregate itself.

Various methods have heen employed tendingl toward the elemination ot excess water and the air in the plastic concrete. lll? hat 1s prohahly the most common practice involves the use ot heavy tampers applied direct to the` concrete that does up to a certain point compress the plastic mass, torcing out some excess Wat-er and air in parts ot the structure. rlhis method is successtul only to a degree tor the reason that it is in'ipossihle to make the mass homogeneous throughout. 'lhe water and air are talre'n from the upper' part ot the slah to a shallow depth hutr they are `not sulticiently removed trom the lower part of the hody.

Various methods tor vibrating and agitatinfr the concrete have heen heretofore used, and by them a better result has heen obtained than hy heavy tamping alone.

So tar as l know none ot these methods, however, have resulted in a concrete slah of ment or the like, which viill he tree trom nu merous disadvantages to which methods herctot'ore used have heen suhyect.

Another purpose 1s to provide such a metlr ,nasa l od hy Which there may he constructed a concrete pavement with a minimum amount ot mortar content and a maximum amount ot hard rock aggregate, properly compressed, so as to malte as nearly as possihle a synthetic roclr having` the homogeneous nature ot a monolithic hard roclr slah.

lt is a turt-her purpose ot my invention to provide such a process, vvhich is mechanical, more rapid and more economical in operation than those heretotore employed.

Particularly it is my purpose to provide such a method involving the use ot direct vertical impacts imposed upon suitahle grids or the like and thus conveyed'to the plastic concrete tor uniitormly condensing the con-n crete in the shortest possible time and with the greatest mechanical etliciency and tor thus effecting' more completely than has ever hetore heen done the removal ot excess water and air voids troni the completed mass.

ltior the purpose ot illustrating a practical means t'or practisingr my method, l have shown drawings accompanying this applica tion. in which:

Figure l is a perspective vievv ot a section ot pavement on which are grids and an im pacting machine with vvhich my invention may he practised.

Figure 2 is a sectional view through the impacting machine.

Figure 3 is a vertical, sectional view oit the unhalanced, overvveightcd vertical piston and connected parts ot the impacting machine taken on the line 3-3 ot liip'ure 2; and

Figure d is a horizontal sectional view taken on the line le-4l ot lligure 2.

l shall now describe somewhat in detail the steps employed in the practice ot my method.

l tirst mix concrete as usual. except that on account ot the greater torce of the impact to which the product is to he subjected and the direct vertical nature ot the impact and the consequent complete subjection ot the entire mass to the action of the repeated impacts, l am ahle to use suhstanti ally less ot the cement mortar and a greater proportion ot coarse hard rock aggregate, than have hitherto beenl generally used in making concrete pavement.

For instance, I su gest a concrete mixture of substantially di erent proportions than has heretofore been used and standardized for such purpose. Standardized concrete mixes all carry a volume of mortar 1n terms of percentage of volume of-stone aggregate considerably in excess of 50%, whereas in the mix I will use in m method, the volume of mortar in terms of percentage of the volume of stone aggregate can be less than 50%, 1n the completed pavement. The cement, fine .and coarse aggregate in proper portions are mixed with the addition of water in the usual way under prevailing standard requirements.

This concrete mix is then laid on the subgrade in the ordinary way.

My method may be em loyed wlth or without the use of added sur acing stone.

If surfacin stone is not used, an equivalent amount o coarse material of similar size is incorporated into the concrete mixture as it goes into the mixer drum. The concrete surface is struck or leveled in the usual way after being placed on the prepared sub-grade.

If surfacing stone is used, there is placed on the plastic concrete after being leveled and before it is hardened a covering of hard crushed stone of the kind acceptable in standard specifications having a maximum size of from one to three inches or preferably one to two and one-half inches, which will make'a surface layer substantially one inch thick when impacted into the solid mass.

I then lay grids or impact conveying units on the top stone or the prepared surface of the concrete. These units, in sections, are fitted together to furnish a supporting semi-rigid surface on which the impacting machines can be moved freely from place to place. Likewise they serve the function of conveying the impact to the top stone and/or to the plastic concrete. They also serve as a restraining medium for maintaining the surface being impacted in substantially uniformly level position, instead of permitting parts to be pressed down while other parts bulge up. They likewise serve a function in that they hold the conc-rete in place between successive impacts by their own weight and the weight imposed upon them, so that upon the return or upward stroke of the impacting machine, the

` plastic material will not return to its condition as it existed before the previous impact.

The next step in the practice of the method involves placing the impact machine upon Lthe units and freely and independently moving it longitudinally of the pavement and also diagonally in both directions across the pavement slab and operating it for imparting to the plastic concrete the successive direct downward impacts by which the ultimate desirable result is attained.

I shall now described an apparatus which ma be used in the `practice of my method an shall then explain some of the important features and advantages of 'the apparatus and method.

The impact conveyin units employed may be such-as those descri d in my co-pendin a plication, filed September 8, 1928, Seria Generally they arev composed of light metal, such as aluminum, or gum wood or other light material or a combination of metal and wood. They ma have a series of pro rly spaced cleats, in icated in the drawings the reference numeral 10,0ftruesurfaces. eirup r and lower surfaces normally rest in para lel horizontal planes. The cleats of each unit are held in place therein by the rods 12 extending through the cleats the full length of the unit. The ends of the rods are threaded to receive nuts 14, which are used with lock washers 16. The nuts are thus adjustable for keeping the rods taut and holding the units to shape while allowing sullicient flexibility for properly carryin out my method. Metal or Wood spacing bloc s 18 are arranged on the rods 12 between the successive cleats 10.

The units may be made with the cleats running longitudinally of the pavement, with the tie rods arranged transversely as explained in my co-pending application.

'lhe drawings here are simply illustrative. Other forms of units may be used. It is important that the area bearing on the pavement be at least twice the area of the openings which permit the escape of air and excess water from the concrete. Such opcnin s also provide free visual observation of te mass worked 'upon and the condition thereof.

The impacting machine comprises a frame 19 supported on rollers and/or wheels 22, adapted to travel freely and independently over the rids. On the frame is a vertically reciproca le device such for instance as the piston 28 forming part of an internal combustion engine having the cylinder 30, fly wheels 32 and other usual operative mechanisms. The engine is in balance, as per standard construction, except for the weight of the piston which is preferably more than double that of the ordinary piston for an engine of similar bore and horse power, (see Figures 2, 3 and 4).

The frame 19 has the handles 34 by which an operator may `move the machine from place to place. The throttle control 36 is accessible for controlling fuel feed from the handles for thus regulating the speed of the piston and consequently controlling the force of the impact.

The impacting desired may be secured by means of a vertically reciprocating member, other than the engine piston, driven from the engine or by a. separate motor of the electric l I a mobile frame and produce downward vertical impacts through the frame and through the units to the concrete.

l shall now refer in greater detail to some of the steps of the method and to its advantages.

After the impacting of each section of pavement covered by the units has been carried out, the units are lifted and moved forward from one-half to three-quarters of their length and relaid without in any way disturbing the concrete surface previously established. The rear parts of the units then rest on port ions o l the concrete that have been impacted and the front portions on unnnpacted concrete.

lhe impacting operation is repeated on the units as thus advanced. 'l`his cycle of operation is carried on for all the pavement laid.

After the impacting has been completed and the units advanced, the impacted concrete is left with shallow mortar ridges on the surface. These mortar ridges are then leveled and smoothed out and the mortar evenly distributed over the entire pavement surface.

'.ll he pavement surface is then finished by belts, floats or the like in the usual manner for concrete pavements.

An important feature of the impacts produced in the practice of this method lies in the fact that they are at all times delivered direct and vertical and in a downward direction without loss by being diverted to other directions or being dissipated for other purposes. Another important feature of these impacts is the fact that no part of the impact is lost as is the case with ordinary concrete pavement finishing machines in the use of which. due to the fact that the weight of the tamping devices is carried upon the side forms or curbing, only a small part of the impact created by such machines is actually exerted upon the concrete itself. 'llhese other types of concrete pavement tamping and fm'- ishing machines actually act as a bridge over the concrete and furnish no sustained pressure or Weight to the mass after each successive blow is imparted. hence the action on the concrete is on the surface only and for the depth of the blow given.

@till another important feature of this method is the flexibility of operation. lndividual batches of concret-e constituting the plastic mass vary somewhat in consistency and general makeup. For that reason different areas of the pavement surface will require longer and more vigorous treatment to bring them to the same condition as other parts of the surface more easily worked. llt will thus be seen that the impact machine must be readily movable on and independently of the grids or conveying units for comparatively short distances in all directions as the condition of the plastic material may require, and it must be possible to apply the variable impact force over a limited area for a long or short time as conditions may require.

A further important feature is the factthat the impact force may be greatly increased or decreased at will by merely increasing and decreasing the speed of the reciproeating member. Such variation is required by the variations in different batches of concrete in different parts of the pavement mass.

lhus an important feature of the impact process is the ability to apply variable impact forces readily over any .limited areas for variable lengths of time as the variations in the concrete may require.

Un account of the flexibility of the process, ll insure certainty and uniformity in its practice.

'llhe weight of the impact machine operating over the grids, together with the subjecting of the concrete to the successive vertical impacts of the machine will condense to its full depth nthe mass of concrete and if top stone is used will force it into the mass.

ll find that there are substantial advantages in using a vertically reciprocating impact machine over a vibrating machine of the rotary type using 11n-balanced fly wheels oi the like.

l`he use of the vertical stroke machine has less tendency to cause the units to travel longitudinally and. laterally on the concrete. 'lhis is true because it gives the full force of the stroke in a direct line instead of having a glancing or shoving action. ll thus effect an economy of power.

l find that the result of removing surplus `water and air is more quickly and thoroughly secured by the vertical impacts than by ros tary vibration machines. ln part this is due to the fact that there is a tendency on the part of rotary machines to push the grids horizontally from their proper place. Con sequently the units to some extent tend to pull the top surface ol the concrete mass horizontally. This tends to pull the component parts of the pavement apart and counteracts that condensing and packing of the mass, which is the prin'iary object in view. Such tendencies are avoided by my method.

l? or the same reason, there is less tendency for the vertical stroke machine to rock the grids and thus cause inequalities in the surfaceof the concrete pavement.

rlhe. result, which it is desired to accomplish is the elimination of the air voids and excess Water in the. concrete mixture, thereby condensing the mass and at the same time maintaining a true surface contour. 1With the successive impacts, the air is forced out, and the excess water comes to the surface and flows off between the cleats or througli the openings of the units. 'lhe compression of the layei of concrete is accomplished much more quickly with a vertical stroke machine.

I find that the vertical typef, impact machine can be of less'ibulk and weight and still secure a better condensing result in quicker v time.

Furthermore, because of the direct and heavier stroke delivered by the impact machine than is procurable with the rotary or vibrating type of machine, fewer blows are 4necessary and there'is an economy in wear `tion of the machine, and is thus im osed through the gridsto the concrete, there 1s not only an increase in the speed of operation, but

also there is insured delivery of the entire im- .pact force'developed. This force is sufficient in amount to eliminate excess water and air voids, not only from the upper portions of the pavement mass, but from the entire lower` part thereof, so that when the product is com- -pleted by this method, the lower part of the pavement mass as well as the upper part becomes a homogeneous structure with a maximum of hard rock aggregate and a minimum of mortar.

-By using the method here employed, less mortar is put into the mix originally than it has been commercially possible to successfully operate with heretofore, and I find that there is produced bymy method a monolithic structure inwhich the rock aggregate particles are crowded so closely together that there is between them only a film of the binding mortar or cement.- v

There is thus attained the effect of a monolith of stone particles closely crowded together land bonded by thin layers of cement mortar into a slab, approaching as nearly as possible in its composition and strength and wearing qualities, high grade natural stone in its original condition.

In addition to the fact that the impact method eliminates more excess water and air voids throughout the mass than other methods and devices have heretofore been able to eliminate, I `find that the impact method causes a change in the physical action of the cement used in the concrete. Portland cement is made from limestone, clay and certain other materials. The material is burned, fused, and then ground very fine with the addition of a small amount of gypsum,',which is for regulating the setting time or hardening time required for the cement,

v after it is mixed with water. Cement is thus dehydrated and when mixed with water will the physical and chemical structure of the cement particles.

I find that the use of the im act/method applied to the concrete after it las been put into place from the mixer accomplishes two purposes not heretofore accomplished in ordinary concrete paving practice.

.In the first place, it is equivalent to a remlxing action on the concrete. During the discharge of the concrete from the mixer drum and the handling process, the concrete materials tend to segregate somewhat. The application of the impact method tends to restore the original condition of the concrete \as in the drum at the end of the mixing period and before being discharged. Each cement particle in the mass is thus given ready access tothe required amount of water for hydration and the formation of the cement crystals which is necessary to the binding properties of cement mortar. Thus hydration `of a much larger ercentage of the cement particles than usual) is accomplished, and the more complete hydration of all particles is faeilitatedand increased.

In the second place, by the use of the impact method prior to,the hardening or setting process of the cement, certain changes occur in the form of the crystal, resulting in a different crystalline structure having u.

, higher cementing or binding property.

One of the results of the chemical and U5 physical changes taking place is the formation of a definite and characteristic crystalline form in much the same way as snowiakes take a definite and characteristic form. Under the impact method this crystalline 100 form is different than usually secured, and this different form is also distinctly characteristic of'impacted concrete when the hydration process is fully completed without interruption.

There thus results from the use of my method a more complete crystallization and a different and better crystallization of the cement.

Thus by the use of this method, there is se- 11o cured a better product.

1st. Because the impacted concrete is more uniformly dense and therefore stronger, because I am enabled to use a higher percentage of the strongest element, to-wit, the 115 coarse aggregate or hard stone in the mass;

2d. The density and consequently the strength of the resultant product is more uniform throughout the mass than where any other method known to me is used.

3d. The density and strength ofthe mortar consisting of cement, sand and water is also increased because of the more complete hydration and crystallization of thc cement particles and of the different crystallization. 125

I have also determined by experiment that where this method is used, the concrete not only reaches a higher ultimate strength, but it acquires a relatively high percentage of its ultimate strength at a much earlier 130 1s usable at a much earlier date than or.

dinary concrete.

By the use of the term coarse aggregate in my claims, I would include gravel pebbles, steel slag, crushed rock or other similar materials of proper size and structural qualities as ordinarily used in or adapted to meet the requirements of pavement or other concrete construction.

Nor do l desire to limit myself to the use of my method for pavei'nents, but I intend to cover it i'or any concrete slab construction, subject to abrasion or wherein the factor of dense concrete is a requisite.

ll claim as my invention:

l. A method ot making concrete pavement, comprising placing on a sub-grade a mass ot' plastic pre-mixed concrete mortar `and coarse aggregate in such proportions that the loose measured volume of coarse aggregate shall exceed by one hundred percentum or more the volume of mortar in the finished pavement, placing on the mass while still plastic a plurality of grids, subjecting each of the consequently variable portions of the mass to constant pressure and to a succession of direct downward vertical impacts, regulated as to force and as to location on the units, and for the proper length of time, to force the excess water and air from such portion throughout its full 'depth for thus forming a resultant Javement of maximum density and substantially uniform composition. 2. A method of making concrete pavement, comprising placing on a sub-grade a mass of plastic concrete mortar and coarse aggregate, and then while the mass is still plastic subjecting each consequently variable portion thereof to'continued vertically downward pressure and repeated vertically directed downward impacts regulated as to :torce and as to location and for the proper length of time to force upwardly the excess water and air from each such portion for thus forming a resultant pavement of maximum density and substantially uniform composition.

3. A met-hed of condensing concrete comprising placing on a suitable base a mass of plastic concrete, which varies in plasticity in different portions, then while the mass is still plastic, placing thereon impact conveying units wholly supported by the mass, then su jecting the units while stationary to continued pressure and to repeated impacts imparted in vertical downward direction only vand varying the location of application oi' the impacts and pressure on the conveying units,

and also varying the force, rapidity and dura-` tion of the impacts, as required by the variable plastic conditions of the various portions of the mass until the entire mass is compacted to uniform density.

4. A method of condensing concrete consisting of placing on a suitable base a mass of plastic concrete, then While the mass is still plastic, placing thereon grating members through which the mass is discernible, then placing on the grating members an impacting machine having a frame movable on thegrating members and having parts arranged to deliver vertical blows to its frame, and then operating said machine on said grating mem' bers to apply continued pressure and also to impart repeated vertical impacts through the machine frame and through said grating members, in a downward direction only, to the underlying mass,and regulating the force of said impacts and the position of the impacting machine on the grating members as required by the inherently variable plastic conditions of the various portions of the mass as disclosed through said grating members, until the entire mass is .compacted to uniform densit y LEON R. MAGKENZIE.

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