US1999152A

US1999152A - Covering foe

Info

Publication number: US1999152A
Authority: US
Publication date: 1935-04-23
Anticipated expiration: 1952-04-23

Description

D. FINLEY Aplrfi 23, 1935.

COVERING FOR CURING CONCRETE Filed June 1, 1951 INVENTOR 22/5? F/IVZ. E)

///.5' ATTORNEY Patented Apr. 23, 1935 .ITED STATES PATENT OFFICE 9 Parafline Companies, Inc.,

San Francisco,

Calif, a corporation of Delaware Application June 1,1931, Serial No. 54111,,M6

4 Claims.

My invention relates to a covering to be used on concrete during the curing or drying state to preserve the desired moisture content.

It is among the objects of my invention to 5 provide a covering that will maintain a body of concrete in a moist state during the drying or curing process and supply Water in addition to that in the original mix where it is desirable or necessary.

Another object of the invention is the provisio of a covering that is in convenient form for use, and that is capable of repeated use.

A further object of the invention is to provide a covering that will improve the surface quality of concrete by preventing chilling of the surface by evaporation of moisture therefrom.

Referring to the drawing:

Figure 1 is a section taken through the covering material of my invention, illustrating in section a portion of a wet'concrete slab over which the covering is laid.

Figure 2 is a view similar to Figure 1, but showing a variant construction which is particularly applicable to floor slabs of buildings; and

Figure 3 is a similar view, on reduced scale, showing another variant form of construction.

In terms of broad inclusion, the covering for curing concrete embodying my invention comprises an integrally formed sheet having a water absorbent base layer over which is secured a layer of material impervious to the passage of moisture. This covering sheet is laid on the finished concrete surface in a moist or wet condition; it being held in place by any suitable means, so that the edges of the covering are sealed to prevent the escape of moisture. The covering prevents any material evaporation of moisture from the concrete and the moist base, supplies additional water needed for curing, and thus develops practically the ultimate strength obtainable by complete water curing. Preferably the covering sheet is raised slightly above the surface of the concrete, so that a water space is provided for excess water to pool under the absorbent base layer.

In the preferred form of my invention the water absorbent base layer comprises a fibrous sheet, such as rag "felt, and the moisture impervious layer comprises a coating of a cold cementing compound, such as paint. The use of a cold cementing compound in the waterproof layer is highly desirable, because it may be applied by simple operations, such as by brushing or spraying and without the requirement that heat be used. In this .way the preparing of the curing material for use, or its manufacture, avoids the use of special machinery of complicated nature involving heated machine elements, supply tanks for holding the molten product, and the like which are necessary in the application of hot cementing compounds, such as bitumen.

For use in buildings, or in other locations where workmen are moving about, the covering employed is preferably one embodying a protective surface layer comprising a tough and preferably waterproof membrane-such a membrane as to kraft paper, or a metallic membrane of metal foil, for instance. This tough surface permits light tramc over the covering when laid in place, and therefore does not interrupt the operations of other workmen. The top surface membrane 15 also aids in the cure of the concrete by assisting the paint layer in the retention of the added water held by the absorbent base. When made of a waterproof material the top surface membrane may conveniently alone serve as the moisture 20 impervious layer. In this case the membrane may be secured over the base sheet by stitching,

' stapling, or other means providing a mechanical tie.

The color of the top surface of the covering 5 may also assist materially in controlling curing temperatures. If the covering is to be used in a comparatively cool climate it may be desirable to use a black colored top surface to absorb the maximum amount of heat; or, if it is to be used in an excessively hot climate, the top surface may be suitably colored to reflect heat and thus keep the concrete at a lower temperature than would otherwise obtain. As the ultimate strength is a function of curing temperature it is thus possible to improve the jquality of concrete in areas of climatic extremes. It is to be noted further that, by preventing evaporation from the surface of the concrete, the covering prevents localized chilling of the surface by evaporation of moisture therefrom, which is a frequent cause of surface cracking.

In terms of greater detail, and referring particularly to Figure 1, the covering for curing concreteJembodying my invention comprises a water absorbent layer 2 preferably. a sheet of fibrous material, such as a rag felt having a weightv preferably of between 15 to '75 pounds per 480 sq. ft. It is to be noted however that other ma terials may be employed in the water absorbent layer 2; the important thing being, of course, that the material exhibits water-holding properties.

A moisture impervious layer 3 of a cold cementing compound is coated on the upperv side of the sheet 2. unitary covering is thenlaid, preferably in a wet condition on a concrete slab 4 to preserve the moisture content during the curing period.

There are several cold cementing compounds that can be used in the waterproofing layer 3, but I have found a very satisfactory coating can be obtained by applying paint. The paint prefer.- ably used is one having decided cementitious characteristics, and, at the same time, highly moisture impervious qualities. Such a paint may 'be made by raising three hundred pounds of rosin to 450 F., and adding thereto twenty-one pounds of flaked sodium hydroxide (anhydrous) the mixture being held at 475 F. until the sodium hydroxide is all taken up. Eighty gallons of drying oil, either linseed oil, perilla oil, China-wood oil, or mixtures of one or more of these with sardine oil or soya bean oil, are then added; the drying oil being added gradually and the temperature raised to about 500 F. while the first portions are being added, and gradually allowed to drop to 400 F. as the final amounts are added.

Four pounds of red lead are then cooked in at 400 F., after which the mixture is withdrawn from the fire and ten gallons additional of the drying oil are added along with three pounds of manganese resinate. Finally, at about 225 F., one hundred and thirty-five gallons of water are added, and, when the mixture has cooled, thirtyfour hundred pounds of slate or shale dust, or equivalent filler of approximately the same specific gravity, are also added- This paint may be spread by brushes, scrapers or may, after further thinning with water, be applied by spraying. By using acold cementing compound, such as the paint above described, in the layer 3 the same maybe applied by simple operations, and without the requirement that heat be used. In this way the manufacture of the curing material is greatly facilitated.

While the above mentioned paint has been set forth as being preferably used in the waterproof ing layer 3, it has been found that other cold cementing compounds may be used. Soluble silicates may be employed, particularly as it is found that these tend to become insoluble after drying and standing for a considerable time. Rubber latex may also be used, as it is both cementitious and moisture impervious. Resin, both natural and artificial, when out back with softening oil to lessen its brittleness, may also be used in the waterproofing layer.

Preferably a second coat 5, one employing linseed oil, a varnish and a pigment, is applied over the paint last described. I have found that a satisfactory paint in the top coat 5 may be made by mixing together three and one-half pounds of raw linseed oil, seven pounds of ground shale or slate, two pounds of vamish and one pound of turpentine. To the above, dryer in suitable amounts may be added as required.

For use in buildings, or in other locations where workmen are moving about, it is highly desirable that the covering be such that persons may tread over its surface. Figure 2 shows a variant form of structure to meet with these conditions, in which a tough and preferably a waterproof membrane 6 is provided as a surface sheet over the layer 3. This tough sheet not only permits light traffic over the covering when laid, but also aids in the cure of the concrete by assisting the paint layer 3 in the retention of the added water held by the absorbent sheet 2. i

A tough fibrous sheet, such as kraft paper, is preferably used in this connection and is preferably embedded in the coating 3 of paint while the same lies still wet on the surface 'of the absorbent layer 2. The two sheets 6 and 2 are then pressed gently together by rolls, and'in their united form are passed into suitable drying racks. Finally the composite covering sheet is rolled up on winding machines and suitably packed in the rolled form for marketing.

A suitable kraft paper for this surface sheet may be one weighing thirty pounds per 2,880 sq. ft. It is obvious that heavier sheets may be used in the membrane 6 where greater resistance to traific is desirable, while lighter sheets may be used where the somewhat diminished strength of such lighter sheets does not detract from theutility of the finished product. In other words, the weight and strength of this surface sheet are proportioned to the service to be encountered, and

determined also by the cost of the finished material. Sulifite, straw, jute and other similar materials maybe used in thesheet 6. Anyof these may be made partially or highly waterproof by waxing, oiling or the like. A suitable treatment is to saturate the top sheet with China-wood oil, as this oil is highly resistant to the transmission of water or moisture thru its films. Linseed oil, vegetable waxes, fatty oils, resins, fats, waxes, and/or resins may also be used to treat the surface membrane, and may be used either as a saturant or as a coating, or both.

While the surface sheet 6 is preferably united to the absorbent layer 2 by means of the cemenas by means set forth in the above paragraph;

As a further alternate in construction, a flexible metal, such as the metal foils, may be used as the surface or traflic sheet. Figure 3 shows a metallic sheet 1 overlying and stapled to the absorbent sheet 2. The metallic surface sheet may also be applied to the layer 2 as a coating, such as by spraying or by electro-depositing.

In applying the material over a concrete slab 4, the covering sheets are preferably unrolled from suitable spindles inserted to the hollow cores of the rolls, and are wetted as they are laid over the concrete; the concrete having reached and passed a state of initial set at this time. Additional water is preferably flooded under the covering until the latter almost floats. It may be desirable to hold the covering sheet away from the surface of the concrete slab, so that a water space is provided. This may be accomplished by any suitable means, such as by a thin sprinkling of coarse sand. The spacing is preferably such as 7 to raise the water absorbent layer 2 up about an eighth of an inch above the surface of the concrete. Note Figure 3, in which the covering sheet is raised slightly off the concrete surface. When water is flooded under the covering that which is unabsorbed by the layer 2 will pool in the space provided. As the pooled water is fed to the concrete the former is replenished by the store in the felt. Thus a thinner felt, holding a lesser volume or weight of water, may be made to serve in place of a. thicker felt laid directly on the concrete. I

The advantage of this method over open pondingis, of course, that the pended water is autothe boundary of the covering are preferably weighted down by piles of dirt, or'other suitable means, so thatthe entire covering sheet is sealed down over the concrete to prevent the escape of moisture. When the cure is deemed to have been effected, in the ordinary case and with the ordinary Portland cement concrete, this will be in about ten days, the curing material is removed. The covering may be used repeatedly as its construction is such that good durability is attached toit.

n steeply inclined concrete surfaces, practically the same procedure applies except thatrthe covering may have to be secured against sliding down. On vertical walls and the like it is obvious that the covering would have to be suspended or otherwise supported in contact with the concrete mate strength of concrete is closely dependent on its moisture content at the various stages of cure, and in part on the temperature during curing, and modern specifications are frequently as much concerned with moisture content and method of curing as they are with other ratios and qualities.

To secure the highest strength and most economical combination of materials, and to obtain the complete hydration of the cement it has been the practice to keep the newly laid concrete in a wet condition by sprinkling or open ponding to insure a proper cure. In arid regions the large amounts of water needed for sprinkling or open ponding may be expensive, or not available, and on inclined or vertical surfaces sprinkling or ponding treatment is dimcult if not impossible because the water flows away by gravity. Accordingly various attempts have been made to effect a cure of concrete by means other than those requiring excess amounts of water. i

A moisture impervious covering alone has been tried, but, without means for holding additional moisture, it does not operate satisfactorily, because the moisture evaporated from the surface of the concrete condenses on the surface of the impervious covering and flows down along the unavoidable wrinkles and away from the areas where it is needed. Furthermore, such a covering when merely laid over the concrete permits some circulation of air beneath it, which circulation operates constantly to reduce the moisture content at the surface of the concrete being cured. Such a covering can not supply additional water needed for hydration.

Furthermore, merely placing a second layer of moisture absorbent material beneath the moisture impervious layer does little to correct these defects, since the dense top covering cannot be held in sufliciently intimate contact with the moisture absorbent layer to prevent circulation of air and subsequent loss of moisture.

Such separate coverings are also more expensive to apply than my unitary covering, because of the extra time. required to lay two coverings, and. becausev of the further expense involved since such coverings are so weak mechanically that they can ordinarily be used but once. In the covering of my invention the water stored in the material contributes to the complete hydration of the cement, and the improved mechanical strength of the unitary structure permits repeated use. When used on highways the material can be wetted and laid in one operation, by a machine if desired, and a practically perfect cure obtained. Even where water is so plentiful that ponding or sprinkling might be employed, the covering of my invention produces a concreteof improved and more uniform strength because of the closely controlled temperature and moisture conditions, and at a saving in expense.

As a rule highways are defective largely because of the improper curing, particularly at thev surface which spalls off under traflic. The use of the covering of my invention will prevent a repetition of such waste, since actual tests under the severest of conditions have demonstrated that when cured under my covering a concrete road slab will develop practically its full standard water cured strength. This means that a thinner slab can be used, and still developed as much strength as'those previously employed, and also will present a superior traffic surface.

These remarks apply with equal force when the curing material of my invention is used on irrigation ditches and the floor slabs of buildings.

In the latter case the effect is multiplied since,

by lightening the floor slabs in the upper stories,

the entire frame structure down to and including the foundation can also be lightened propor: tionately. It is thus feasible to save as much as of the cost of ooncretematerials used in a tall building.

In conclusion, and looking at the problem from a different angle, it is pointed out that the ultimate strength of concrete cannot be obtained by endeavoring to provide suflicient water to the mix when it is poured. When a wet mix is poured a large amount of cement is actually carried away and lost as the water runs out of the forms, and when the mix finally sets the pores that are left by the final evaporation of the excess water operate to materially weaken the concrete. In order to make up for this weakening the tendency is to add more cement. This results not only in a greater cost, but also in a more pronounced expansion and contraction with changing moisture content. This latter is highly undesirable in slabs which are not permitted free movement, such as road slabs, bridge slabs positioned between structural steel members, and stucco coats. Actually,

\the ultimate strength in concrete is obtained by use of smallproportions of cement, and in a mix which is poured in a fairly dry state. This means however that sufficient water for the complete hydration of the cement is not present in the mix, and that additional water must be fedto the slab during the curing. By use of the covering embodying my invention the ideal mix may be used, because not only is the original water used in the mix retained, but also means are pro vlded for supplying additional water if such is needed for complete hydration.

I claim:

1. The method of curing concrete which comprises overlaying the surface of the concrete with a moisture retaining material, holding the material above said surface, and flooding the space between the material and surface with water.

ing the space between the sheets and surface with water.

4. The method of curing concrete which comprises overlaying the surface of the concrete with a water absorbent sheet, apply water to saturate the sheet, and then flooding additional water over the surface of the concrete'until the sheet substantially floats.

DOZIER FINLEY.