US2997281A - Manufacture of concrete structures - Google Patents

Description

Aug. 22, 1961 W. F. REMINGTON ET AL MANUFACTURE OF CONCRETE STRUCTURES Filed April 10, 1958 INVENTORS WILL/AM F REM/N67 ON ($'NNE7H D. SYLVESTER ATTORNEVS United States Patent f 2,997,281 MANUFACTURE OF CONCRETE STRUCTURES William F. Remington and Kenneth D. Sylvester, Long Beach, Calif., assignors to Ben C. Ger-wick, Inc., San Francisco, Calif., a corporation of California Filed Apr. 10, 1958, Ser. No. 727,627 Claims. (Cl. 259-141) This invention relates to concrete structures and objects and their manufacture, and more particularly relates to means for providing such structures and objects with smooth, unmarked exterior surfaces.

In the forming of many prestressed or precast concrete objects, such as I and T girders and beams, octagonal concrete piling and the like, it is necessary to use mold forms having downwardly directed return surfaces. One difficulty with forms of this type is a tendency for pockets of water and air to collect adjacent the return surfaces during the curing of the concrete material. Apparently the water, being less dense than the other materials in the concrete mix, tends to rise much as air bubbles rise until it is trapped within the concrete mix at the mold surface. Adjacent upper exposed openings of the mold, these water pockets create no problem since the mix can be agitated and smoothed by hand to provide an unmarked outer surface. However, in the areas adjacent the return surfaces of the mold, evaporation and escape of the water leave unsightly pock mocks on the outer surfaces of the concrete. A further problem is these deformations are only discovered when the mold form is removed. In prestressed concrete structures, these pock marks are particularly objectionable in that they detract from a desired thickness of concrete over the reinforcing steel and prestressing strands extending through the concrete. Accordingly, grout filling of the pock marks and depressions is not a satisfactory solution to the problem.

In general, it is an object of the present invention to provide improved prestressed or precast concrete objects by which pock marks and holes due to the collection of water and air adjacent return surfaces of a mold are virtually eliminated.

Another object of the invention is to provide means of the character described which is inexpensive and easily adapted to existing manufacturing procedures.

Other objects and advantages of the invention will appear from the following description and from the drawings in which:

FIGURE 1 is a view in perspective of a device useful in carrying out the invention;

FIGURE 2 is a view in section and in elevation illustrating the use of the device of FIGURE 1, for example, in conjunction with the manufacture of octagonal piling;

FIGURE 3 is a detail view along the line 3-3 of FIGURE 1;

FIGURE 3A is a like view along the lines 3A3A of FIGURE 3; and

FIGURES 4A, B and C are a diagrammatic representation, in sequence, illustrating the method of the invention.

In general, We have found that a virtually complete elimination of the water pockets and air bubbles normally trapped in concrete structures can be accomplished during their manufacture by means of an extremely rapid to and fro agitation to produce a channeling action within the zone of entrapment. Preferably, such agitation is accomplished by means of an elongated substantially planar agitating member reciprocating, for example, at the rate of the order of about 800 oscillations per minute. Specifically we have found that the water pockets and air bubbles normally forming adjacent upper retinn surfaces of concrete forms and the like can be disintegrated Patented Aug. 22, 1961 and removed by such agitation occurring substantially in the plane of the return surface. We have also found that best results are obtained if the concrete is allowed to remain quiescent prior to agitation for a period ranging from about 10 to 20 minutes, so that the agitation takes place when the concrete is in a stiff, partially cured state.

Referring to the drawings, FIGURE 1 illustrates one form of the device for subjecting partially cured concrete to the desired rapid to and fro agitation. As shown, the device generally comprises an elongated substantially planar blade or agitation member 10, a portable transmission housing 12, and a carrying handle 14. Preferably the blade member 10 is provided with a plurality of transversely extending slots 16 which can be interconnected by the longitudinally extending slot 18. As is further shown in FIGURES 3 and 3A the member 10 is adapted to rapid, straight line reciprocation by means of a rotating eccentric 20 engaged within a transverse slot 22 provided in the inner end 24 of the blade member. The eccentric 20 is caused to rotate about the axis of shaft 26 by means of the cone gear 28 carried by the shaft and engageable with the cooperating cone gear. 30. Rotation of the gear 30 can be accomplished in conventional manner by means of a rotating flexible cable indicated generally at 32 in FIGURE 2. As will be apparent, rotation of the cable 32 will be converted into reciprocation of the agitating member 10 by means of the cooperating gears 28, 30 and the eccentric 20.

As indicated in FIGURE 2, the agitating device is preferably balanced so that it can be easily supported by the handle 14 and positioned by the operator inwardly adjacent a return surface, such as the upper mold surface 34. The planar configuration of the blade member 10 facilitates its endwise insertion into the concrete mix, and provides a zone of agitation substantially in the plane of such return surface. Preferably, the longitudinal dimensions of the blade are such that they substantially correspond to the width dimensions of the return surfaces 34.

In carrying out the objects of the invention, concrete is poured into a suitable mold, such as the octagonal piling form 36, and allowed to remain in a quiescent state until partially set. For most concrete mixes, a curing period of about 10 to 20 minutes (usually about 15 minutes) will suflice. The blade 10 of the device can now be inserted into the concrete to disintegrate the larger pockets of air and water and to facilitate movement of such air and water to the upper exposed surface 38 of the mix. In a preferred procedure, the blade 10 is first positioned well inwardly of the return surface 34, as illustrated in FIGURE 4A. The device is now slowly moved into an outermost position in which the blade is substantially flush with the return surface, as indicated in FIGURE 40. During this operation the larger water pockets are rapidly broken up into smaller bubbles which are constrained to an upward path along the elongated slot 18 of the blade. This channeling through the blade of the agitating device results in a rapid, virtually complete elimination of the disintegrated pockets of water and air. The blade 10 can now be removed as indicated by the arrow 40 in FIGURE 4C. Thereafter the upper exposed surface of the mix, at 38, can be worked and smoothed by hand to provide an unmarked exterior surface.

As will be apparent from the above description of an exemplary procedure and embodiment, the present invention provides a simplified means of treating concrete mixes during their curing to form precast or molded objects that are virtually free of exterior deformations caused by entrapped water and air. The procedures and apparatus of the present invention are also readily adaptable to existing manufacturing operations, as the equipment required is inexpensive and permits the use of readily available sources of supply. For example, the input to the .flexible cable 32 has satisfactorily been provided in field operations with a standard /z inch drill motor operating on available power supplies. Moreover; it is significant that the entire operation can be carried out without interruption of the normal processingv of the concrete and with a minimum requirement of skilled labor.

We claim:

1. A device for eliminating air and water pockets adjacent upper return surfaces of concrete forms and the like, comprising a shaft, means imparting rapid rotation to said shaft, a rotatably mounted eccentric, an elongated substantially planar agitation member operatively engaging said eccentric, said agitation member being provided with a plurality of transversely extending slots, means imparting the rotation of said shaft to said eccentric, and means converting the rotation of said eccentric to reciprocal movements of said agitation member, whereby said agitation member may be inserted endWise into the mass of poured concrete to cause disintegration and removal of water pockets and air bubbles.

2. A device as in claim 1 wherein said means imparting rotation to the shaft comprises an elongated flexible cable.

References Cited in the file of this patent UNITED STATES PATENTS 271,810 Decker Feb. 6, 1883 565,379 Dickson Aug. 4, 1896 1,098,070 Whitney May. 26, 1914 1,911,966 Pickop May 30, 1933 1961388 Pickop June 5, 1934 2,055,514 Whiting Sept. 29, 1936 2,411,317 Day et al NOV. 19, 1946 2,424,073 Morgan July 29, 1947 2 ,614,312 Rankin t Oct. 21, 1952 2,638,655 Creskofi May 19, 1953

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