US1807116A - Method of compacting, finishing, and curing concrete pavements - Google Patents

Description

Patented May 26, 1931 UN'ETEETJD STATES PATEN QFFICIE PERCY A. HIPZPLE, OF ATLANTA, G ORGIA No Drawing.

,which consists in filling up the minute cavities or superficial pores of the pavement by means of the action of a fine spray of liquid directed against the surface thereof. The material with which the cavities or superficial pores are thus filled may be the fine skim of pure wet cement which normally accumulates on the surface of newly laid concrete, or it ing of concrete pavements and involves the forced removal of entrapped air and the displacement of excess water from the concrete mass by the injection of solid matter into the interior of the mass.

The purpose of this invention is to provide: a means which will effectively eliminate the surplus water, that is now left in concrete pavement slabs, after various commercial machines, now in use for compacting and finishing concrete pavement, have become ineffective; a means whereby the water content of the fresh pavement slab is reduced until only moisture remains in the amount that is ideal for effective and uniform cementing action; a means whereby the entire body of the pavement is more thoroughly compacted and solidified; a means whereby all pores both superficial and internal are thoroughly filled with durable solid particles of materials of elemental similarity to the concrete aggregate; a means whereby the pavement surface is so compacted and solidi lied that it will resist the evaporation of moisture, that remains in the fresh finished slab for the purpose of hydration of the cement therein, thereby increasing and extending the efiective time of curing; a means whereby the pavement surface is so compacted and solidified that the surface is effectively sealed against entry of outside moisture during the Application filed August 26, 1929. Serial No. 388,636.

entire life of the pavement thus eliminating the subsequent damage caused by expansion stresses and by freezing and thawing action that are set up within the pavement by the entry of moisture or water after the pavement is cured; and-a means whereby the mortar of the pavement surface is so effectively compacted and solidified that it will better re- Sist the abrasion and wear and tear of traflic.

t has been a well known fact for years that in mixing and placing concrete for pavement slabs, it has been necessary to use a greater amount of water, in the process of mixing the concrete than the ideal amount which should be present in the completed,

fresh pavement slab for the purpose of hydrating the cement therein, and in all commercial processes, of my knowledge, for compacting concrete pavement, the compacting is done by the application of various tools to the surface of the plastic concrete slab. All of these tools deliver pressure to the surface by various means; some having a tamping action, some, pressing and troweling and some vibrating and pressing.

Any of these commercial means above described cease to affect the concrete mass, as soon as the larger aggregate particles in the concrete make firm contact with one another and form stress columns or arches from the top to the bottom of the mass. During the period of these operations in which the stress columns and arches are formed, the'finishing or compacting equipment exerts a direct influence on the entire mass of concrete and in t llS operation quite a bit of the surplus'water and surplus mortar is displaced to the surface of the slab. I

As soon as thestress columns and arches form in the mass the existing machines for compacting and finishing concrete slabs are rendered ineffective in the further elimination of surplus Water and entrapped air that yet remains within the concrete mass. This is due to the fact that unpacked formations of mortar remain within the mass and these formations are protected by the column and arching action of the coarser aggregate particles which column and arching action prevents further agitation of the unpacked mortar and prevents the forced expulsion of the remaining surplus water by these means.

Agitation, effected by the compacting or troweling action of the present commercial machines having ceased, the retained water is slowly released by the settling of the finer particles in the concrete mass. These finer particles come to rest one against the other and have a tendency to free the water and force it toward the surface of the slab. In the present existing methods of operation the removal of this slowly draining water, from the pavement surface, necessitates several operations of belting and reworking over periods of time; and these operations cannot remove all the free water that remains near the surface of the slab.

The settling together of these finer particles effects the same column and arch action among these finer particles as has previously occurred among the larger particles of coarser aggregate, and in consequence, when the pavement is considered finished by the now existing methods the interior of the concrete slab yet is honey combed with voids, each of which voids is a receptacle for a globuleof water and this condition especially exists in the upper portion of the new pavement slab.

The belting operations, carried on for the purpose of removing the water that is accumulated on the surface, causes a quick rush of water which adversely effects the natural action of the fine cement particles that are present in or near the surface; and the globules of water that may remain in the small interior voids act to disturb the fine cement particles and retard their natural action.

I will herewith show that the finely pulverized impalpable' particles of cement, which particles 1 will call cement flour, really prove to be the active constituent of the cement; the coarser grains of cement being practically inert filler and also being vehicles for distribution of the cement flour throughout the mass. At the instant of contact with moisture this cement fiour immediately attaches itself to the coarser particles of cementor to the surface of any sand or stone with which it may make contact. The interior of these coarser particles of cement and the interior of the concrete aggregates, being dry, they absorb moisture and in the process of this absorption the moistened cement flour is drawn into the capillaries of the coarser and more rugged materials. This establishes the relationship which later effects the cement bond throughout the entire mass.

At the moment of complete saturation this cement flour forms a jelly-like substance which readily attaches itself to the surface of the coarser particles of cement but this ellylike substance is found to be repellant to the presence of additional moisture or free water an'das long as free surplus water is present in the concrete mass the cement flour remains inactive and is removed from the surface of the coarser materials by the film of water which inserts itself between. Hence it is seen that after a pavement is finished by the existing methods, the surplus water that yet remains within the slab retards the natural cementing action of the cement flour and holds it in suspension until the said surplus water has passed from the slab either by drainage or evaporation. The water content of the slab must, therefore, be reduced in volume until only moisture exists before complete and effective cementing action is started, and after the cementing action is started 7 it is desira le to maintain a uniformity of moisture within theslab until the cement is thoroughly set and the concrete is cured.

Present day standards require that 85% of the entire volume of cement used in con-} crete work, must be ground fine enough to pass a 200 mesh sieve, the said sieve having 40,000 mesh openings per square inch. In the process of grinding the cement to this fineness quite a percentage of 300 to 400 mesh impalpable cement flour is produced and I have authority for the statement that an increase of fineness in the cement from 85% to 95% passing the 200 mesh sieve will increase the strength of the concrete 49% in all concrete wherein the cement used was ground to a fineness where 95% would pass the 200 mesh sieve. The authoritative conclusions drawn as to the cause of this extra developed strength being that the longer grinding of the cement, to produce the extra 10% of 200 mesh particles, would thereby produce a greater amount" of impalpable cement flour;

which extra cement flour increases the strength of the cement. I have authority for the statement that cement will not set and harden if all the particles smaller than the 200 mesh including the in'ipalpable flour are removed therefrom; the coarser particles being only inert fillerand vehicles of distribution for the vitally-necessary liner particles; therefore it is my purpose to correct existing conditions that tend to neutralize the proper action of any portion of the cement flour, in the operation of compacting and finishing concrete pavements.

lVhereas the strength that may be developed in concrete slabs being dependent upon the presence of this impalpable cement flour in the concrete mass anv agency which prevents the even distribution of this impalp able cement throughout the concrete slab or which retards its coalescence and colloidal action must necessarily-retard or prevent the development of the maximum strength in the concrete slab.

- Coalescence of the impalpable cement flour must take place and the saidflour must form a colloidal or jelly-like paste free from disturbing influence of surplus Water before these particles will crystallize and start their cementing action. This paste must evenly coat the surface, of the coarser grains of cement, and the entire surface of the sand and stone aggregate; and at the same time it must be freed from the disturbing effect of any surplus water that may be present in the mass, before fully effective cementing action can be started and attained.

The facts above cited prove that moisture,

and not free water, is the effective agency of hydration of the cement in a concrete mass, and every commercial method, now in use, causes damaging formations of free water in the upper portion of concrete pavement slabs, without providing an efiecti-ve means for its complete removal and expulsion from the slab.

I have discovered that, after the existing commercial machines for compacting and finishing concrete pavements, have ceased to function, and during the period of natural settling of the liner particles in the concrete mass, the presence of free water in the upper portion of the concrete slab, causes the mortar of the upper portion to be extremely plastic; and that itis practicable to shoot finely divided solids, into and through the surface of this plastic mortar, with such force that they will penetrate deeply into the interior of the plastic mortar and displace the remaining water to the surface of the fresh laid pavement slab.

lVith the application of sufficient force to solid particles of the proper size, my herein described method becomes operative immediately after the present commercial machines have ceased the operation of com par-ting, or pressing and troweling the surface, of the fresh concrete slab.

As soon as these machines cease operation, and while the surface is water soaked and plastic, and without the lapse of time necessary for the a pearance of the watersheen, as required in the process described in my above mentioned Patent No. 1,175,088; the operation of my present improved method begins. The operation of the method is as follows: A blast of sand, or a blast of finely d' ided solid particles of stone or other material that may become a lasting and elemental part of the concrete slab, is directed at the surface of ti e fresh laid concrete slab; the actuating force being compressed air or other suitable means. 7

In this operation the force of the compressed blast or other applied power is great enough to impel the solid particles through space, at and against the surface of the fresh concrete, with such momentum that the flying particles will penetrate, to the extreme depth of plastic buoyancy, into the interior of the concrete slab; and should their flight be arrested by inert particles in the plastic mass, will impart their momentum to the obstructing particles,

The multiplicity of impelled solid particles enter the fresh concrete surface and spend their forces in the manner of so many wedges being driven into the mass. As each individual particle comes to rest it displaces its volume, of Water, air or plastic mortar, which is forced upward, and each succeeding particle in turn does likewise until all the surplus water and entrapped air is driven out of the mass and replaced With embedded solid particles to the' very top of the concrete slab. In this manner the elimination of the surplus water is followed from the deep interior of the fresh concrete slab to the very surface, with a positive means to assure its expulsion. I

The impact of these impelled solids, and the friction engendered in entering and passing through the plastic and buoyant mortar, set up intermittent waves of hydrostatic pressure that cause the fine cement in the concrete mass to better penetrate and fill the capillaries in the surface of all the stone, sand and other aggregate in the concrete mass, as well as coating with cement, the

surface of the impelled solids; which solids come to rest in the interior of the slab and remain as a part of the structure.

During the actual application of the blast of impelled solids the plastic mortar is penetrated with such high frequency that it fairly boils upward under the intensity of this blast and as long as surplus Water remains in the mortar the mortar remains plastic and tends to level-itself off at the surface such as any fluid would do. lVhen enough sand or other solid material has been shot into the concrete slab to displace the volume of surplus water and entrapped air the surface immediately becomes firm and of gritty texture, due to the fact that the progress of the solidifying action was outward from the interior and that the surface itself at the final period of the operation will resist impact of the ini- -pelled solids,

The sizes of the impelled solids may be varied in accordance with the depth of the slab, and the impact forces desired. The impelled solids may be of especially select and durable material to increase the Wear resistance of the pavement surface, since it is :manifest that with the completion of the pavement by this process, the surface will be loaded with this material.

The'volume of the solids that may be impelled into and become a part of the concrete slab. is in direct proportion to the volume of water and entrapped air that may remain in the slab after the existing conr mercial methods, have ceased their effect.

This is a very small amount in relation to the entire mass of the pavement itself, but very important in that it displaces damaging water and consequent voids and replaces same with solid durable materials.

In actual practice I have found that there is a uniformity of displacement which is effected by my process over the entire slab of any given mixture of concrete and the completion of the operation of this process over any fresh slab of concrete, leaves the surface as true and uniform of contour as it existed before the solids were applied; only adding a gritty texture at the very top.

To meet any argument, that may be raised, that the extra amount of solid materials, inipelled into the concrete slab by this process, might reduce the cement ratio of the finished slab I- have found it practicable to blast under low pressure, a coating mixture of pure cement and water fluid over the fresh concrete surface immediately before the application of the compacting blast of impelled solids. This mixture can be varied, though one part cement to one and one half parts water seems to be the ideal consistency, and a calculated amount of this mixture of pure cement and water may be applied to the fresh concrete surface, to compensate for the subsequent reduction of the cement ratio. If desired, this cement fluid may be mixed with the solid particles and impelled by the same force, at the same time.

The operation of my process efiects and accomplishes all the desirable results above set forth in the description of the purpose of my invention, far beyond the effective range of methods and equipment now available for this purpose. 1

I find that the outward passing of the surplus water, which in present commercial methods of operation is uninterrupted in its tendency to wash the surface during the belting operation, is, in my method, changed in direction by the force of each impelled solid that enters the slab. This change of direction, at high frequency under the blast of impelled solids, frees all the cement flour from the exuding water and causes the cement flour to remain in the pavement, in close contact with the solids therein. I

I find that this process, effectively reduces the water content of the fresh concrete slab, until only moisture remains in the amount that is ideal for effective and uniform cementing action; and I find that in displacing the surplus water with solid materials, of elemental similarity to the concrete aggregate and in so doing, having alternated the flow of exuding water at high frequency and retained the cement flour for normal action in the surface of the slab; I have produced a pavement surface, of such density, that the subsequent passage of moisture through the surface is greatly prevented.

This density of surface tends to retard the escape of the moisture remaining within the slab, for the purpose of hydration of the cement therein, thus slowing down and prolonging the period of curing.

This density of surface also protects the which consists in initially compacting the freshly laid mass by external pressure upon the surface thereof, and then internally compacting the mass and expelling air and excess water from the interior of the mass by in jecting into the body of the mass particles of material of elemental similarity to the concrete aggregate.

2. The process of indurating concrete which consists in initially compacting the freshly laid mass by external pressure upon the surface thereof, and then internally compacting the mass and expelling air and excess water from the interior of the mass by injecting thereinto, at a high velocity, particles of material of elemental similarity to the concrete aggregate.

3. The process of indurating concrete which consists in partially compacting the solids in the mass thereby producing a top layer of buoyant water ladened plastic mortar, and then impelling finely divided particles of material of elemental similarity to the concrete aggregate through the layer of plastic mortar and into the main body of v the mass by means of an air blast.

4. The process of indurating concrete which consists in partially compacting the solids in the mass thereby producing a top layer of buoyant water ladened plastic mortar, then impelling solid material through said layer of plastic mortar into the interibr of the mass, and then applying to-said mass a low pressure blast of pure cement mixed with water to compensate for the reduction of cement ratio in the original concrete mix effected by the injection of said solid particles into said mass.

5. The process of indurating concrete which consists in subjecting the plastic, freshly laid concrete mass to a blast of finely divided solid particles which become an elemental part of the mass, the force of said blast being sufficient to cause the solid particles to penetrate into the interior of the concrete mass whereby their momentum will be transmitted to suspended particles originally incorporated in the mass effecting an internal compacting action upon the interior of the mass and displacing therefrom entrapped air and surplus water. i

6. The process of indurating concrete which consists in subjecting the interior of the freshly laid concrete mass to hydrostatic impulses of high frequency and intensity, said impulses being engendered in the hydrated plastic mortar of the mass by the impact forces of finely divided solids impelled against the surface of the fresh concrete with sufiicient momentum to cause their penetration into the interior of the mass, whereby internal pressure created Within the mass causes the fine cement particles originally incorporated in the concrete to better penetrate the capillaries therein and adhere to the surfaces of the aggregate in the concrete.

PERCY A. HIPPLE.