US2289248A - Method of treating concrete - Google Patents

Description

July 7, 1942. R. E. DAVIS METHOD OF TREATING CONCRETE "Filed June 5, 1940 2 sheegsshet 1 v4 W y www/wg Jul 7, 1942. R. E. DAVIS 2,289,248

" METHOD OF TREATING CONCRETE Filed June 5; 1940 2 Sheets-Sheet 2 Patented July 7, 1942 lVIETHOD F TREATING CONCRETE Raymond E. Davis, Berkeley, Calif., assignor to Kalman Floor Company, Inc., New York, N. Y., a corporation of Delaware Application June 5, 1940, Serial No. 338,992

7 Claims.

The present invention relates to methods of and apparatus for laying and. finishing concrete floors and particularly to methods of and apparatus for applying topping courses upon suitable base or supporting structures such as previously prepared concrete slabs.

It has been conventional practice for a number of years past, in the erection of numerous types of buildings, such as warehouses, terminals, schools, hospitals, and stores, to provide concrete floors of special nature, each such floor comprising two separately formed superimposed courses or layers, a heavy supporting slab of any ordinary concrete mixture having sufficient strength and placed in the usual manner, and a topping course or layer of harder and more wear-resisting nature, of maximum density, even texture, and superior appearance. This relatively thin or topping course is made of the most suitable ingredients which can be obtained for the purpose and great care is exercised in preparing the mix, spreading it over the supporting slab and working it in a finished condition. In the usual case, the topping layer is between one-fourth inch and two inches in thickness, the maximum size of the coarse aggregate particles being kept low in view of the thinness of the layer and precautions being taken to insure that the topping coat has maximum density as, when maximum density is realized, maximum durability and resistance to wear are also obtained.

The ideal condition of maximum density and durability has been mainly soughtby two principal methods. In accordance with the first method, a relatively dry mix is used, the watercement ratio being kept quite low so that the resulting mix is harsh and crumbly rather than of free flowing character. After the mix is spread upon the supporting slab, it is screeded, floated, and finally surface finished by hand troweling. Due to its dryness, however, many voids are present in the mix as it is originally deposited and also because of its dryness these voids are not by any means wholly eliminated during the subsequent operations of screeding, floating and hand-troweling. As a result, the finished topping course is somewhat porous and hence considerably less durable than it should be.

A second method of creating and finishing such a topping course involves the use of a concrete which has initially a relatively high water-cement ratio, suificient water being added not only to efiect full hydration of the cement used but also to make the mix readily flowable. A mix of this consistency will, when screeded, contain few, if

any, voids but on the other hand has the disadvantage of cotnaining an excessive amount of water, preventing early finishing of a topping course so formed. It has, however, been additionally suggested that the large excess of water which the topping course or layer contains after having been spread and screeded may be quickly removed artificially, as with the assistance of a vacuum, or by placing upon the surface of the concrete layer some material which will draw the water therefrom by capillary attraction. One method of removing excess water from a freshly deposited layer of concrete, which has been used with great success, involves the application to the surface of such a layer of a cloth or cloth-like element upon the upper surface of which in turn is spread a layer of absorbent material, for instance cement, dry sand, or a mixture of cement and dry sand. In a relatively short time a large proportion of the excess water contained in the topping course is. drawn upwardly into the layer of absorbent material above it and eventually the cloth and absorbent material resting thereon are removed, thus leaving the topping course intact but with a substantially less quantity of contained water. Before the concrete of the topping layer has any chance to set, however, its surface is rendered smooth and hard by troweling. After final curing, the floor is ready for use. This process results in a generally satisfactory product but, as now to be explained, may be improved upon. Thus, when the water is rapidly withdrawn by the placement upon the upper surface of the. topping layer of a body of absorbent material, it leaves voids between certain of the solid particles of the concrete, which voids eventually become filled with air and cause the topping course to be somewhat porous. Even the operations of floating andtroweling do not effectively cause these voids to be filled and hence the full strength and durability of the concrete course is not developed.

The purpose of the present invention is to provide an improved method for laying and finishing concrete floors, particularly the topping courses of floors, and an improved apparatus for accomplishing most readily the desired objects. More specifically stated, it is my purpose to provide a method of laying topping courses upon previously prepared floor slabs which is less costly to practice than prior methods in that it saves time in the application of the topping course and saves labor in that less troweling is required, and which also results in a superior product, i. c., a topping course which is denser and hence more durable than those which have been or may be constructed by other methods, which bonds with the supporting base in a manner heretofore not realized and which, when completed, has less tendency to check while in use. My improved method, and the novel apparatus by the aid of which it is carried out, will be hereinafter described in detail, but in general terms the invention may be said to comprise an improvement in that method of laying toppings which involves the deposition in a layer of a body of wet cementitious material which, after having been thus deposited, is rendered relatively dry by the application to its upper surface of a removable water absorbent covering which, after having absorbed from the wet cementitious material the desired amount of water, is removed. After application of the covering it is compacted to increase its efficiency as an absorbent material. jected to the pressure, while in place on the surface of the cementitious layer, of an instrument vibrating at high frequency, which instrument may be the one which is used to compact the absorbent material, so that the underlying body of cementitious material may be vibrated while the overlying layer of granular material is being compacted. Such instrument includes a member upon which is mounted a rapidly rotating eccentric element, the eccentric element being revolved about an axis at such velocity that the member upon which it is mounted will vibrate at a frequenc of 5,000 vibrations per minute, or even more rapidly, the amplitude of vibratory movement, however, being very small, for instanc in the neighborhood of five hundredths of an inch. By moving this vibrating plate over the surface of the absorbent ma terial, this material of course is pressed downwardly and is more tightly compacted and ur ed against the surface of the wet topping layer so that the process of removal of the excess water of the topping layer by capillary attraction is facilitated.

One great advantage which flows from the use of th vibratory tool is that it vibrates at high frequency each area of the topping course over which it passes, all the way to the bottom of the course, thus effecting the upward movement of excess water from all portions of the course, the rate of water withdrawal from between the bottom grains of the topping course being, under the influence of the vibratory tool, the same as that which obtains at the top. Not only is the rate of removal of excess water increased or augmented by the use of high frequency vibration and dewatering more fully and completely accomplished, in the manner specified, but the solid particles of the concrete are continually being rearranged by vibratory action as the water removal pro ceeds, the voids which would ordinarily be left as the water passes upwardly being collapsed so that few, if any, voids will remain in the material after the process has been completed. In the practice of the improved process, involving the use of the vibratory tool above briefiy described, for mixes of the usual proportions of cement to fine and coarse aggregate, the water-cement ratio of a topping layer which has been poured wet may be reduced in a very short period of time, for instance ten or fifteen minutes, to as low a value as .25 by weight. In practicing th invention the vibratory tool will be passed over the entire surface of the absorbent drying layer at least once, preferably several times. After this operation has been completed, the drying layer will be removed.

Preferably also it is sub- 1 The surface of the topping layer after removal of the drier and reduction of the water-cement ratio of the entire layer to a very low figure, will be too dry to be brought to a plane surface by an ordinary disc fioat machine of the type heretofore commonly employed. I have, however, provided a novel and improved method of and machine for reducing the surface to a true plane, this machine including the well-known rotating disc element but likewise including means for effecting vibration of this disc as it rotates, at very high frequency, for instance a frequency of 5,000 or more vibrations per minute. In operation the rotating and vibrating disc will simultaneously produce the customary smoothing action and also a high frequency kneading action which imparts to the semi-solid topping layer a plastic condition depressing the high areas of the surface of the topping layer, elevating the low areas and further compacting the topping until voids are substantially eliminated and maximum density is secured. If the topping layer has a water-cement ratio that is properly low only a very small amount of very stiff paste will be brought to the surface by the use of the rotating and vibrating disc, just enough to facilitate final hand troweling which may immediately follow. One or two hand troweling operations will be quite sufficient to give the topping layer its necessary hard smooth finish and after this has been accomplished the floor will, after curing, be ready for use. It is of the greatest advantage that the novel surface treatment after water extraction brings to the surface only a thin film of very stiff cement-sand paste, as final troweling may immediately be accomplished when this is the case and the finished surface, after hardening will offer the maximum resistance to wear and will exhibit the minimum tendency towards checking. Vibration, if not preceded by water extraction so as to produce a topping of very low water-cement ratio, would cause an excessive amount of paste of high watercement ratio to be brought to the surface, thus necessitating much troweling over an extended 3 period.

In the accompanying drawings the several steps of th method just above described are diagrammatically illustrated insofar as it is possible to do so, and one of the implements or tools which are employed is shown in detail. It will be appreciated by one skilled in the art that the method may be varied in minor respects without departure from the invention and likewise that the design and arrangement of the component elements of the implement shown may be varied to suit conditions, also without departure from the invention.

In the drawings:

Figure l is a perspective view of portion of a cement fioor showing the supporting slab, topping course, superposed layer of drier, and two of the implements employed in the practice of the process;

Figure 2 is a plan view of one of the implements, this machine being utilized to compact the layer of absorbent material and impart vibrations to the topping layer underlying the same;

Figure 3 is a section on line 3-3 of Figure 2;

Figure 4 is an enlarged side elevation of the free end of the handle of the machine, showing the driving motor; and

Figure 5 is a section on line 5-5 of Figure 2.

Referring first to Figure l. The supporting slab of concrete, which may be plain or reinforced, is indicated at l0 and the topping course resting directly upon the upper surface of the slab l0 and having been placed in such position after the slab I has sufficiently hardened to form an ad quate support. It is, of course, highly essential that the topping course I l bond as firmly as possible with the upper surface of the supporting slab l0 and hence the upper surface of slab I0 is prepared in known manner just before the deposition of the topping course upon it. After the topping course, which has been prepared with a relatively high water-cement ratio so' as to be easily workable, as previously explained, has been spread over the surface of the slab In, it is screeded in the usual manner so that its upper surface is approximately at its final level. Promptly thereafter a layer of fabric, for instance burlap, portion of which layer is indicated at I2 in Figure 1, is laid upon the surface of the freshly deposited topping layer and after this has been done a layer of absorbent material, as indicated at [3, is spread over the fabric layer l2, the absorbent layer [3 comprising either cement, dry sand, or a mixture of dry sand and cement. After this has been done, a tool or implement such as shown more particularly in Figures 2 to 5, inclusive, of the drawings is passed over the surface of the granular material comprising the absorbent layer i3. This tool or implement comprises essentially a pan-like member [5 which includes a flat bottom plate It of generally rectangular form and upwardly extending and outwardly inclined flanges ll. Extending transversely of the major axis of this pan-like member, and suitably secured upon the upper surface thereof are four parallel braces l8 and these braces in turn serve as mounts or supports for four aligned bearings l9, these bearings being preferably of the ball or roller type. Rotatably supported in the bearings i9 is the elongated shaft 29 which shaft is provided with eccentric portions 2| and 22. Rapid rotation of shaft results in movement of the eccentric portions 2i and 22 rapidly about the axis of the shaft, causing vibration of the entire pan structure upon which the shaft is mounted.

Rotation of shaft 20 is effected by means of an electric motor 25 rigidly connected to the handle member 23 by means of a bracket 2?. The motor shaft is horizontally disposed and aligned with this shaft and preferably connected thereto through a universal coupling is a pulley 28 rotatably sup-ported wholly or in part upon the bracket member 29 rigid with handle 26. Centrally mounted upon the shaft 20 is a second pulley member 30 the pulleys 28 and 3f] being preferably provided with V-shaped grooves to receive a V-belt 3| of endless type which passes over or around both pulleys, the intermediate reaches of the V-belt passing through the handle 26 which is made hollow in order that this may be accomplished. Idler rolls 32 at the lower end of the handle and idler rolls 33 at the upper end thereof function as belt guides.

The lower end of the handle is provided with laterally offset brackets 35 the ends of which are pivotally supported upon shaft 20, or are in any other suitable manner pivotally attached to the pan-like portion of the implement. To the motor casing is attached a handle member 36 by means of which the entire implement may be moved about and a suitable electrical connection to a source of power will of course be employed to supply the motor with electrical energy. If desired, weights may be placed upon the pan-like portion of the implement to cause it to hear more heavily upon the drying material, four such per minute or even higher.

weights being indicated in dotted lines at 38 in Figure 2 and one being shown in full lines in Figure 5. It will be observed that each of the bracing members [8 is provided with two upwardly extending spindles IS. The weights 38 are provided with circular apertures to receive the spindles l8 but these apertures are lined with sponge rubber, as indicated at 39, and likewise the undersurface of each Weight 38 is provided, at least under the portions thereof which overlie the members 18, with layers 40 of sponge rubber. Hence, by means of such weights, the total downward pressure upon the drying substance may be increased as desired but by reason of the inclusion of the yielding material intermediate the weights and the pan, these weights do not vibrate with the pan under the influence of the eccentric device, at least to the extent that the pan vibrates.

In the practice of the invention the implement just described is moved one or more times over the drier immediately after the application of the absorbent material, and at the end of this time it is removed, together with the fabric layer I2 and the cement or sand. By reason of the conjoint action of the drier and the implement described, vibrating at high frequency, the excess water is removed from the topping layer and the surface of the layer, after removal of the fabric, appears to be quite dry. It may not be successfully smoothed by hand operated trowels nor by the use of the ordinary rotary float, but must be acted upon by some such implement as is indicated at 05 in Figure 1. The details of construction of this implement are fully described and set forth in my copending application, Serial No. 338,991, filed June 5, 1940, and it is only here necessary to state that the lower portion of the instrument, indicated at 45, comprises a rotatable disc with cylindrical upwardly projecting peripheral flange and that the machine or implement includes means for simultaneously rotating this disc and effecting its vertical vibration at high frequency, for instance at a frequency of 5,000 vibrations The amplitude of vibration is small, for instance approximately .05 inch. The implement is moved back and forth over the entire surface until such surface is rendered smooth. It functions to depress elevations and raise low areas; to further densify the topping layer as an entirety, and to render the surface suitably plastic for troweling. While in operation it causes a slight amount of paste to pass upwardly to the surface of the topping layer and without causing segregation, just enough to facilitate hand troweling, which is the final step of the process.

The method described is less costly and may be carried out more rapidly than previous methods. Likewise the topping course which is the ultimate product of the method is denser and more wearresisting than topping courses produced by any previously practiced methods. Labor is saved, one or two simple hand trowelings being all that is necessary as a final step in the method.

In certain instances the step of subjecting a plastic mass of concrete to high frequency vibration may be beneficially employed in the fabrication of concrete bodies other than the relatively thin topping courses for the manufacture of which the method and machine have been primarily evolved. The rotating and vibrating disc of the implement 45, for instance, is an implement of general application in the concrete art and might be used directly upon the surface of a freshly poured concrete slab which has or has not been dewatered. Other beneficial modifications of the process will be readily apparent to one skilled in the art.

The complete method calls for two applications of a vibratory implement but, within the import of the invention as set forth in the appended claims, one of these applications may be dispensed with and appreciable benefits be still realized. Thus, while I prefer to effect the withdrawal of excess water from the freshly poured topping course with the aid of both the absorbent material and vibratory implement, such excess water may be withdrawn without the aid of the vibratory implement, although not as satisfactorily.

The use of a vibrating plate or smoothing implement for surfacing purposes, however, is essential if a smooth, level surface is to be obtained, since the material which is to be surfaced is too dry to be surfaced Without the aid of an implement which is not equipped with a vibratory unit. In fact, the superiority of the process over those which have preceded it largely results from the fact that the concrete just prior to surfacing, is of the lowest possible water-cement ratio, so dry that only by the application of a vibratory implement of the kind here described can a very thin film of very stiff paste be actually brought to the surface, barely enough for final hand troweling; and further that through the action of the vibratory implement the surface is not only brought to a plane but the underlying topping is brought to a condition of maximum density. It is also clear that it is immaterial whether the surfacing step of the process, just prior to final troweling, be practiced upon concrete which has been mixed with a low water-cement ratio or concrete mixed with a high Water content and then dried or dewatered. Surfacing with the aid of the vibratory tool is not necessary when the water-cement ratio of the concrete of the customary topping mix is greater than about 0.35, but when the watercement ratio is substantially less than this the tool is highly useful and, for very dry concretes, say having a water-cement ratio of less than 0.30, the tool is essential.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. The method of forming a concrete fioor slab or the like which comprises depositing in a layer a body of wet cementitious material, applying to the surface of such layer a water penetrable sheet and thereafter covering said sheet with a layer of material in granular form, subjecting the layer of granular material to pressure and vibration by pressing against all areas thereof an implement the work-engaging surface of which is vibrating at high frequency, and thereafter removing the sheet and the compacted layer of granular material.

2. The method of forming a concrete floor slab or the like which comprises depositing a layer of wet cementitious material, applying to the surface of such layer a sheet of textile fabric, covering said sheet with a layer of cement, subjecting the layer of cement to pressure and vibration by pressing against all areas thereof an implement the Work-engaging surface of which is vibrating at high frequency, and thereafter removing the sheet and the compacted layer of granular material.

3. The method of forming a concrete floor slab or the like which comprises depositing a layer of Wet cementitious material, applying to the surface of such layer a sheet of textile fabric, covering said sheet with a layer of cement, subjecting the layer of cement to pressure and vibration by pressing against all areas thereof an implement the work-engaging surface of which is vibrating at high frequency, the magnitude and duration of the pressure being such that the passage of the desired quantity of water to the cement layer from the wet cementitious material, and closure of all voids in such cementitious material, is effected, and thereafter removing the sheet and the compacted body of cement.

4. The method of forming a concrete floor slab or the like which comprises depositing in a layer a body of wet cementitious material, applying to the surface of such layer a water penetrable sheet and thereafter covering said sheet with a layer of material in granular form, compacting the layer of granular material to increase its capacity to withdraw water from the underlying cementitious material, removing said sheet and granular material after the water cement ratio of the cementitious material has been reduced and the cementitious material has been rendered relatively dry and stiff, and finally levelling and smoothing the surface by passing over each area thereof a surfacing implement vibrating at high frequency.

5. The method of forming a concrete floor slab or the like which comprises depositing in a layer a body of wet cementitious material, applying to the surface of such cementitious layer a water penetrable sheet, covering said sheet with a layer of granular material, passing over and pressing against the layer of granular material an implement the work-engaging surface of which is vibrating at high frequency, removing said sheet and granular material after the water cement ratio of the cementitious material has been reduced to such an extent that its surface cannot be levelled by horizontally working the particles of the uppermost stratum thereof, and thereafter smoothing and levelling the surface by moving over each area thereof a surfacing implement having a work-engaging surface vibrating at high frequency.

6. The method of forming a concrete floor slab or the like which comprises depositing in a layer a body of wet cementitious material, applying to the surface of such layer a removable water absorbent covering, lightly pressing a vibrating implement against all areas of said covering While it is so positioned, and thereafter removing the covering and the water which it has absorbed.

7. The method of forming a concrete floor slab or the like which comprises depositing in a layer a body of wet cementitious material, applying to the surface of such layer a water penetrable sheet and thereafter covering said sheet with a layer of material in granular form, compacting the layer of granular material to increase its capacity to withdraw water from the underlying cementitious material by capillary action and, after the desired amount of water has been withdrawn, removing the said sheet and granular material.

RAYMOND E. DAVIS.

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