US2046867A - Method of and apparatus for treating concrete - Google Patents

Description

July 7, 1936. K p BlLLNER v2,046,867

METHOD 0F AND APPARATUS FOR TREATING CONCRETE A 3 n. I A i I i NVENTOR. l

ATTORNEY.

July 7, 1936. K p. BlLLNER 2,046,867

METHOD OF AND APPARATUS FOR TREATING CONCRETE- Filed April 8, 1936 2 Shee'IZS--Sheel 2 I I1:: ::::::O .."x

BY c7 ATTORNE Patented July 7, 1936 UNITED STATES METHOD F AND APPARATUS FOR TREATING CONCRETE Karl P. Billner, New York, N. Y., assignor to Vacuum Concrete Corporation, a corporation ofDelaware Application April s, 1936, serial No. 73,361

Claims.

My present invention relates to the treatment of concrete. 'I'he present application is a continuation in part of my application having the same title, filed October 5, 1935, Serial No. 43.708.

5 My objects are to provide a method and apparatus by which (l) concrete may be dried much more rapidly than heretofore (2) concrete may be treated so as to result in a substantial increase in lstrength thereof and (3) concrete will l0 be improved in texture by which considerable less volume change takes place with a resulting reduction in the formation of cracks.

My improved method is intended especially for the treatment of all concrete which can be placed in horizontal layers, such as concrete road pavements, reinforced concrete floors in buildings, concrete in dam and bridge construction and the like and the apparatus hereinafter specically described is designed for use in the treatment of concrete so placed in successive sections.

As a result of the treatment to which I subject the concrete it may be made so hard that in less than an hour after being laid a man can 25 walk upon it without leaving an imprint. Therefore the invention possesses the great practical advantage of not only strengthening and improving the texture of the concrete but also of very greatly reducing the time interval between the laying thereof and when it becomes adaptable for actual use.

While my invention as stated is intended principally for the treatment of concrete placed in horizontal layers after being laid it will be understood that the invention is not limited to such use and may be employed for the treatment of concrete shapes intended for other purposes, such as vertical walls, columns and pipes.

The product known as concrete is an artificial 40 stone created by mixing cement, sand and crushed stone or gravel or other coarse aggregates with a sufficient quantity of water to hydrate the cement and produce a plastic mass that can be molded as long as it retains its plastic consistency. After a certain interval of time and as a result of hydration the particles of cement in the mass coalesce and the whole mass becomes solid. 'I'he quantity of water required during the mixing period and during the time in which the concrete is molded is always much 'greater than the amount required for the hydration of the cement. If only the minimum amount of water necessary to hydrate the cement was used, the mixture would be so dry as to have no plasticity and it would not be possible to consolidate the cement and aggregates. The excess water above that required for hydration of the cement constitutes the gravest defect and weakening factor present in concrete. Moreover the presence of this excess water greatly prolongs the period of drying until the concrete is suitable for use.

By my present invention it becomes possible to reduce the water content in a freshly mixed concrete to a practical minimum by removing substantially all the'excess water, not required for hydration, after the concrete has been placed in the mold or is otherwise laid.

In brief, I. accomplish this result by sucking the water out of the concrete by a vacuum process and at the same time I utilize the resulting atmospheric pressure for applying 'a heavy compacting pressure to the mass. In this way I make use of a double action working simultaneously. If suction only were applied then, after a certain amount of water had been eliminated, voids would be created in the mass to thus weaken the structure. The compacting action of the atmospheric pressure compresses the mass and prevents the formation of such voids and therefore the combined double action results in a. very greatly increased strength.

In carrying out my invention, for instance in the construction of a concrete road, I first intimately mix in the ordinary manner the solid ingredients (cement, sand and aggregate) with the usual excess of water to secure plasticity and the resulting mix is placed on a roadway between the usual side forms and is spread so that its surface becomes fairly level. Then and as soon as possible after levelling the surface of the concrete is preferably covered by a fine mesh sheet of canvas or wire screen or other suitable material which will readily permit of water penetration but will prevent any considerable part of the cement or other solid particles in the concrete from passing through it.

This screen therefore will act as a very line sieve permitting water to pass through but preventing the passage of solid particles in the concrete. Owing to the relatively large area under treatment the velocity of the water passing through the screen is so slow that gravity plays a part in preventing any but the very smallest solid particles from reaching said screen.

0n top of this screen, if used, is placed a cover made either exible and yielding such as a rubber mat or of rigid material such as metal. The

.Y bottom face of this cover is preferably provided with a series of closely adjacent narrow grooves or corrugations leading to transverse channels of larger cross section which latter in turn connect with outlets to which the suction or vacuum is applied. Preferably the corrugations or grooves and channels lust referred to do not extend all the way to the sides and ends of the cover so that areas are provided all around the edges of the cover to form, under atmospheric pressure, a continuous seal, to prevent the entrance of air into the space to which suction is applied. Instead of providing the cover with longitudinal grooves and transverse channels as explained the underside of the cover may be formed with closely spaced knobs which, if the cover is made of rubber or other exible material, may be molded therewith. The interstices between these knobs will permit water to flow between the screen and cover to the outlets therefrom as hereafter explained, provision being made to seal the cover all around against the entrance of air.

Instead. I may use a cover with a smooth bottom surface and interpose a double screen between the cover and the concrete. The lower element of this double screen will be of iine mesh so as to act as a sieve as explained and the upper element will be of coarse mesh to provide tortuous channels through which the water may flow. For convenience in handling the two sections will be preferably secured together as by spot lwelding.

If the grooves in the bottom of the covei are suillciently fine and especially if the flow of water through the same is sumciently slow it may not be necessary to make use of an interposed screen or sieve. The latter, however, is preferably employed as it results in a more certain operation, especially when a very powerful suction is used resulting in a more rapid flow of the water than when more moderate degrees of suction are utilized.

From the 'several larger channels above referred to a pipe leads to a vacuum tank of sufncient capacity to hold the water removed from the concrete and this vacuum tank in turn is connected to a suitable vacuum or suction pump capable of creating and maintaining the required degree of suction under conditions of practice.

The elements of the apparatus being assembled with the screen and cover on the levelled upper surface of the freshly laid concrete and with the edges thereof sealed against the passage of air. a vacuum or suction is created when the pump is put in motion, thus creating a substantially uniform suction over the entire surface of the concrete under treatment.

In referring here to a vacuum I do not of course refer to -a perfect or Torricellian vacuum since that would be impossible under rough conditions of actual practice. I have, however, found it feasible to create a vacuum between the concrete and the cover corresponding to a vertical column of 27 inches of mercury by which I mean ninety per cent of a perfect vacuum. Such a high vacuum results in a relatively rapid operation of sucking the water out but as I will later explain lower degrees of suction may be employed, especially when the time element is not importantV or where relatively thin layers of concrete undergo treatment.

A great number of channels of small cross sectional area are formed between the wire screen if used and the ne corrugations referred to on the underside of the cover. As the vacuum increases these channels serve to lead on the water which is sucked out of the concrete and this water i'iows into the large transverse channels from which it passes through a hose or pipe connections into the vacuum tank where it is trapped without interfering with the continued operation of the pump. 6

As stated above, I have found it feasible to obtain a vacuum under the cover as high as 27 inches of mercury and this with a mass of concrete of more than one cubic yard per batch. A vacuum of this order under the cover creates a 10 high air pressure on the top, equal to nearly one ton per square foot in the assumed case. It will therefore be seen that the concrete is subjected to a very intense compression and consolidation while the water is being sucked out of it. This 15 compression compacts the mass so that concrete made in this manner will have a greater density and strength than that of concrete made by methods previously known to the art, so far as I am advised. 20

Although I prefer to make use of a very powerful suction of fifteen inches or more of mercury, so as to secure the rapid removal of water and concurrently obtain a high degree of compression, it will be understood that my invention may 25 be carried out by the use of less powerful suctions although at a sacrifice of time and with the production of a concrete of less strength than when the maximum practicable degree of suction 1s employed.

It may be said in general that the removal of the excess water should be completed beore the concrete begins to set. If water is being removed and if compression is being applied when concrete begins to set and during setting the result- 35 ing product is not so strong as when the excess water is removed and the pressure released before setting because it is important that the concrete should be undisturbed during setting. The setting of the concrete depends upon many conditions but it ordinarily commences between one and two hours after laying according to the season. Therefore it is important that the suction should be at least of such value as to remove excess water prior to setting.

Obviously the thickness of the concrete is a factor to be considered in placing a, minimum value on the degree of suction used, since the .excess water can be removed from a layer of concrete one inch thick in less time than from a 50 layer 8 inches' thick. I have found, for example, that in treating a concrete road 8 inches in thickness a suction as low as 8 inches of mercury (26.7% of perfect vacuum) will remove the excess water prior to the commencement of set- 55 ting although the reduced pressure (approximately 575 pounds per square foot) will result in a product of less strength and density than when higher suctions and pressure are used.

Theoretically the time required to remove the G0 excess water is proportional to the thickness of the concrete, assuming equal degree of suction and conversely the suction is proportional to the thickness of the concrete, assuming equal times. In other words, the removal of excess water from 65 a layer one inch thick in the same time that excess water is removed from a layer 8 inches thick with a suction of 8 inches of mercury would mean the employment of a suction of 1.0 inch of mercury, resulting in a pressure of 72 pounds 70 per square foot.

In some of the claims which are hereafter presented I will define my invention broadly as utilizing a suction of 1.0 inch of mercury or more per inch of thickness since as explained this will 75 be equivalent in point of time to a suction of 8 inches of mercury for concrete 8 inches thick. Although aseggplained such low auctions may be used and will involve the spirit of my invention it is by all means preferable to use suctions as powerful as can be conveniently obtained since in this way the operation is much'quicker and the greater pressure obtained results in superior strength. f

It will be observed that the space in which the partial vacuum is created is of minimum size and comprises only the combined cubical contents of the water channels formed on the under side of the plate or cover. It is thus readily possible with a pump of relatively small capacity to create a high partial vacuum within this space; as a matter of ,fact this small suction space need only be large enough to permit the ready flow of the removed water which moves out of the suction space in a direction parallel to the face of the concrete.

In order that my invention may be better understood, attention is directed to the accompanying drawings forming a part of this speciflcation and in which Figure 1 is a side elevation, partly in section taken on the line I-I of Fig. 3, showing a section of a concrete road under treatment, the cover being illustratedas a rubber or flexible mat extending substantially the distance between the sides of the mold.

Figure 2 is a plan view showing the under side of said mat.

Figure 3 is a cross section taken on the line 3-3 of Figure 2 on an enlarged scale illustrating particularly an arrangement for sealing the edges of the coven' and showing more clearly the screen and fine grooving. l

Figure 4 is a longitudinal section at right angles to Figure 3.

Figure 5 is a diagrammatic'view showing how a plurality of covers may be used simultaneously to permit a larger area of concrete to be treated or to allow covers of reduced size and weight to be employed so as to make handling thereof easier and also permitting a continuous process to be carried on, as will be explained.

Figure 6 is a plan view of rigid metal cover or plate and Y Figure 7 is a side view thereof.

Except as hereafter stated, like parts are indicated by the same numerals.

Referring first to the arrangement of Figures l to 4 inclusive, I-I represent side molds such as are now used for the construction of concrete roads. Between these molds, a mass of concrete 2 is laid and levelled off in any suitable way. This concrete mass in order that it may be made plastic contains the usual large excess of water, and when laid extends some distance above the tops of the side molds I-I. In other words, the illustration of Figure 1 shows the concrete mass after it has been treated so as to bepressed down substantially level with the top of the molds I-I.

Upon the'upper surface of the mass 2 is preferably placed a screen 3 made of ne mesh or canvas or other suitable material which will permit water to pass through it but will not allow solid particles from the cement mass to do so.

On the screen 3 is placed a cover l which in these gures is preferably yielding or flexible. A thick rubber mat may therefore be employed for this purpose. By making the cover -flexible it will yield somewhat to irregularities in the surface of the concrete.

wise but this particular arrangementvis unimportant.

Connected with the groove i is a pipe 1, this connection beingpreferably made by using a mat 9 made preferably of rubber laid on top of the cover 4` and having a groove therein coinciding with the groove or slot 8 in said cover.

The mat 9 will be held rmly in place by atmospheric pressure when suction is created beneath the cover. 'I'he pipe 1 is connected to the mat 9 in any suitable way, with an air tight joint,

as by means of a. rubber suction cup 8 which normallyv has the shape shown in dotted lines in Figure 3 but under the effect of vacuum will be collapsed to the shape shown in full lines in Figures 3 and 4. If more than one cross channel 6 is used, each will be connected by suitable piping to the pipe 1. The latter leads to a vacuum tank I0 of sufficient capacity to hold the water removed by the vacuum from the section of concrete under treatment. A motor driven vacuum pump I2 `of any suitable type is connected by a flexible hose I I with the vacuum tank III as shown in Figure 1.

Any suitable arrangement may be employed for properly sealing the sides and end edges of the cover 4 to prevent loss of vacuum at these points. For example, the cover may be provided at its under side adjacent the edges with very ne serrations, indicated by I3 which under. the atmospheric pressure will be embedded in the concrete to thereby constitute eifective seals. It will be noted in Figure 3 that the screen 3 and grooves 5 occupied the area circumscribed by the seals I3.

The operation is of course obvious. When the pump I2 (Figure 1) is started it creates a suction under the cover, drawing out excess water from the concrete, which water flows through the groove 5 to the channel orchannels 6 and thence to the vacuum tank Il). `It will be noted that the ilow through grooves and channel is parallel to the surface of the concrete, thus permitting the vacuum space above the concrete to be made of minimum size.

Simultaneously the resultant atmospheric pressure will cause the cover 4 to powerfully compact the concrete so as to result in greatly increased strength and improved texture thereof.

With the arrangement of Figures 6 and rI a metal cover I9 is used, suitably stiiened by cast ribs 20 so as to reduce weight. The edges of such cover are provided with the line sealing serrations I3 shown in Figures 2 and 3 to prevent the entrance of air although other sealing arrangements may be used. IOtherwise the arrangement is the same as with Figures 1 to 4. When the rigid cover is used as in Figures 6 and '7 a very smooth upper surface will be formed on the concrete as will be understood and also with this arrangement, if it is desired, the cover may be given a curve or crown to impart this shape to the resulting road bed.

With the arrangement of Figure 5 I show how a plurality of covers may be used, four of which are here represented by the numerals I5, I6, I1,

and Il. Ihessmaybeeithertherubbercovers of Figures l to 4, or ruid metal 6 and 'l and eaelx may be sealed around the edges in the way above described. This particular amusement oi.' multiple covers enables me to carry on the method practically as a continuous operation in the f manner.

Assumethattherearefourcoversasshown in Figure 5 andthattheecmcreteinprocessofbeing levelled is progressing in a direction to the left beyond the cover Il. Then the four covers will be placed in position as shown and subiected to suction for a period of say twenty minutes. Thereupon the cover Il will be removed and placed in position at the left. Suction will then be applied again for a period of say nve minutes. Thereupon the cover l1 will be removed and placed on the left of cover is and the suction thereupon again applied for say five minutes. In this way it will be seen that eventually the suction period for all,the covers will extend for twenty minutes or whatever time may be desired, whereas. the individual covers will be handled at shorter intervals, depending upon the number used. This therefore will permit a practically continuous process to be performed.

As I stated above, it is possible by my invention to obtain a concrete so dense that a man may walk'on it immediately after treatment without making any imprint on the surface. In other words, concrete treated in accordance withthis invention has much greater strength than concrete made in the manner. Moreover. it is subjected to considerably less volume change and resulting formation of cracks, which unfavorable characteristics are now caused principally by the evaporation of excess water while the concrete hardens and dries out. Obviously with my invention this cannot occur, at least to the same extent since the concrete is -compacted concurrently with the removal of water.

What I claim is: l

l. The method of treating concrete which consists in placing the concrete with an excess of water to secure plasticity. then in applying to the concrete a suction of at least one inch of mercury per inch in thickne of concrete, whereby excess water will be removed from the interior thereof and'in concurrently imposing a heavy compacting pressure upon the concrete.

2. The method as recited in claim 1 wherein complementary atmospheric pressure is utilized to apply the compacting pressure.

3. The method of treating concrete which consists in placing the concrete with an excess of water to secure plasticity, then in applying to the concrete a powerful suction' of at least 15 inches of mercury, whereby excess water will be removed from the interior of the concrete and in concurrently imposing a heavy atmospheric pressure upon the concrete.

4. 'I'he method of treating concrete which consists in placing the concrete with an excess of water to secure plasticity, then in applying to the surface of the concrete a powerful suction and corresponding atmospheric pressure whereby excess water is withdrawn by suction from the interior thereof and in drawing off the removed water in a direction parallel to the surface of the concrete the suction employed being of at least one inch of mercury per inch in thickness of concrete.

5,'Tne`method of preparing concrete which consists in placing the concrete with an excess of water to secure plasticity, then in placing against the surface of the concrete a cover presenting small channels through which water may flow in a direction parallel to the surface of the concrete. then in sealing the edges of said cover against the entrance of air and in nnally applying a powerful suction between the cover and concrete whereby excess water will be removed from the interior of the concrete and the concrete will be simultaneously subjected to complementary atmospheric pressure the suction employed being of at least one inch of mercury per inch in thickness of concrete.

6. The method of treating concrete which consists in laying or casting the concrete with sumcient excess water to secure plasticity, simultaneously applying suction and compression to a prescribed area of the concrete to remove from the interior of the mass part of the excess water 20 not required for hydration, the suction employed being at least one inch of mercury per inch in thickness of the concrete, in cutting ofi' a portion of the prescribed area from further suction,

in providing for the application of equivalent suction and compression to an equivalent new area, then in again applying equivalent suction and so continuing, whereby practically a continuous process will be eiTected.

'7. Apparatus for treating concrete comprising in combination, a cover which is placed against the surface of the concrete having therein an excess of water to secure plasticity, means for sealing the edges of said cover to exclude air and means for applying between the cover and concrete a suction of at least-one inch of mercury per inch of concrete whereby excess water will be removed from the interior of the mass and comp'ement-ary atmospheric pressure imposed by said cover upon the concrete.

8. Apparatus for treating concrete comprising in combination a cover, having grooves or channels on its under face, placed against the concrete containing an excess of water to provide plasticity. means for sealing the edges of said cover to exclude air and means for applying a powerful suction to the spaces defined by said channels, whereby excess water will be removed from the interior of the mass and will flow in a direction parallel to the surface thereof and complementary atmospheric pressure will be imposed upon the cover to consolidate the mass.

9. Apparatus for treating concrete having therein suiiicient excess water to secure plasticity,

said apparatus comprising in combination a fine 5 screen or sieve placed against the concrete mass to permit substantialy free flow of water, a cover in contact with said screen, having grooves or channels on its under face, means for sealing the edges of said cover to exclude air and means for applying a powerful suction to the spaces defined by said channels whereby excess water will be removed from thc interior of the mass and will flow in a direction paralel to the surface thereof and complementary atmospheric pressure will 05 be imposed upon the cover to consolidate the mass.

l0. Apparatus as recited in claim 9 wherein the cover is made of flexible material like rubber, and

the grooves or channels are proportioned to withstand the consolidating pressure without collapsing.

KARL P. BILLNER.

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