US3434401A - Sealing strips for concrete slabs - Google Patents

Description

March 25, 1969 J. L... KIEWIT SEALING STRIPS FOR CONCRETE SLABS 0 i. a 2 o m w F Filed June 20, 1967 A T TOR/V5 Y5 March 25, 1969 J. L. KlEWlT SEALING STRIPS FOR CONCRETE SLABS Filed June 20. 1967 lNl/E/VTOR JACK L. K/EW/T A TTORNE Y5 United States Fatent C i 3,434,401 SEALING STRIPS FOR CONCRETE SLABS Jack L. Kiewit, Fort Collins, Colo., assignor to the United States of America as represented by the Secretary of the Interior Continuation-impart of application Ser. No. 542,698, Apr. 14, 1966. This application June 20, 1967, Ser. No. 653,310

Int. Cl. E01c 11/10 US. Cl. 94-18 Claims ABSTRACT OF THE DISCLOSURE A combination waterstop and weakened plane forming strip composed of (a) two closely adjacent sheets of flexible material (e.g. rubber) joined together along one edge to form a slot therebetween and (b) a flange projecting from each of the outer faces of the slot-defining sheets to anchor the strip between adjacent concrete sections which result from cracking of the slab.

This application is a continuation-in-part of application Ser. No. 542,698 filed Apr. 14, 1966, and now abandoned. The invention resulted from work done by the Bureau of Reclamation of the Department of the Interior, and the domestic title to the invention is in the Government. It relates to the field of constructing watertight monolithic structures such as roads and canals.

Control of the inherent cracking in concrete-type structures is of paramount importance, particularly in water conveying structures such as canals, since water leakage through the cracks of subjacent earth and surrounding property presents obvious problems such as water loss, washing out of the earth support or damage to the structure when the water freezes. One present cracking control method involves casting these structures as a plurality of relatively small slabs with contraction joints therebetween to prevent random cracking wherein it is only necessary to establish Water seals at each joint. An article on pages 74-79 of the autumn 1952 edition of Rubber Development discusses a water seal, known as a waterstop strip in the art, for such jointed structures. Likewise US. Patent No. 2,400,493 shows a waterstop for contraction joints. Although cracking is avoided by this meth- 0d, the cost of casting many separate slabs and forming the contraction joints therebetween is cost prohibitive in large water-conveying structures. As a result, it has been far more economical to cast these structures as a monolothic slab that will inherently crack at predetermined locations, and then attempt to prevent water leakage through these cracks. This has previously been done by forming grooves on the surface as the material such as concrete was placed, and filling the grooves with a mastic substance. Since each groove creates a plane of weakness in the concrete slab, later rupturing occurs at one or more of the grooves rather than elsewhere, and the mastic material therein fills the resultant crack. However this system has proved unsatisfactory in that the mastic material tends to slowly deteriorate when exposed to the sun and atmosphere in, for example, an empty canal. Further, under substantial Water pressure the mastic tends to extrude through the cracks even at widths less than inch. Disbonding of the mastic from the groove surfaces has also occurred.

A further elfort to prevent water leakage through cracked concrete slabs involves casting specially shaped waterstop strips into the uncured slab during placing of the concrete. These elements are shaped so as to form weakened planes along the slab so that cracking will occur at the location of these waterstops rather than elsewhere,

3,434,401 Patented Mar. 25, 1969 the waterstops then functioning to prevent water leakage through the cracks. Note US. Patent No. 3,023,681 in this respect. However, this waterstop strip has not always been found to be watertight. It appears that the anchoring flanges of the waterstop, each imbedded in the concrete slab on opposite sides of the crack, tend to become distorted with further widening of the crack thereby allowing water to pass between the flanges and the concrete. Furthermore, ditficulties have been encountered in placing this waterstop strip into uncured material such as concrete, and incorrect placement of this strip has been observed to cause spalling of concrete from the surface thereof at the location of the weakened planes.

I have now developed an improved combination Waterstop-weakened plane forming strip which is composed of (a) two closely adjacent flexible sheets joined together along an edge to define a slot therebetween, and (b) a flange projecting from each of the outer faces of the slotdefining sheets. A weakened plane is formed in the cured slab by the embedded sheets which extend in one direction through almost the entire width and in another direction through a major portion of the thickness of the slab. After cracking occurs in the slab along the sheets, the flanges secure the strip to the concrete sections on side of the crack. As water leaks from one surface of the slab through the crack, it is received and held by the slot defined by the sheets. Hydraulic pressure within the slot urges the sheets and flanges into firm engagement with the concrete sections thereby effecting a watertight seal.

It is therefore an object of this invention to provide a combination waterstop and weakened plane forming strip which will eflect a watertight seal in the induced cracks even under the high water pressures exerted within a water-conveying structure such as a canal.

Another object is to provide a strip that can be readily placed into uncured concrete.

Further objects and advantages of the present invention will be obvious from the following detailed description of the device taken in conjunction with the drawings in which:

FIG. 1 is a side view of the combination waterstopweakened plane forming strip of the present invention.

FIG. 1a is a perspective view of the strip.

FIG. 2 is a cross-section of the strip as it is being installed in fresh concrete.

FIG. 3 is a cross-section of the strip in a concrete slab immediately after placement.

FIG. 4 is a cross-section of the strip in a concrete slab after cracking.

FIG. 5 is a perspective view of the strip in a concrete slab after cracking.

FIG. 6 is a cross-section of the strip in a cracked concrete slab with water under a hydrostatic head bearing against the concrete and strip.

FIG. 7 is a fragmentary cross-section of an alternate embodiment of the strip.

FIG. 8 is a fragmentary cross-sectional view of another embodiment.

Referring to FIGS. 1 and 1a, numeral 1 designates the combination waterstop-weakened plane forming strip of the present invention which strip is basically composed of adjacent flexible sheets 2 and 3 joined together along their lower edges in a pointed configuration 4 to define a slot 5 therebetween. Flanges 2a and 3a project from sheets 2 and 3, respectively, each flange being centrally disposed between the upper edge and opposing lower edge of its respective sheet. After strip 1 is embedded into the uncured concrete slab, sheets 2 and 3 cause a weakened plane in the cured concrete which results in a crack at the strips location. Anchoring flanges 2a and 3a secure the strip 1 between the two sections of the slab that result from rupturing. At the extremities of the flanges 2a and 3a are bulb-shaped protuberances 2b and 312, respectively, which act as anchoring and sealing means for the strip. A height of about 2 /2 inches for the sheets 2 and 3 and a total anchoring arm member length of about 1%. inches from bulb to bulb are suitable for the purposes of this invention in a 4 /2 inch concrete slab. Depending upon the thickness and composition of the slab to be sealed, the dimensions and proportions of the strip may obviously be modified. Any flexible material which is inert to water and concrete, and is otherwise suitable to exposure, as for example various polyvinyl chloride plastics, rubbers or other elastomers, can be used to make the strip. If the materials of construction are flexible enough, strip 1 will take on a collapsed shape rather than the rigid configuration shown in FIGS. 1 and la.

As shown in FIG. 2 the shape of the strip is such that a plurality of parallel metal bars 6 may be used to readily insert the strip into the uncured concrete. Vibration of the blades during placement of the strip further eases entry into the concrete and insures consolidation of the concrete around the lower portions of the strip, especially around the bulbs 2b and 3b. Other installation procedures can obviously be used.

Referring to FIG. 3, when the strip is initially installed in fresh concrete, adjacent faces of sheets 2 and 3 are pressed into contact as a result of forces exerted by surrounding concrete. The resultant narrow shape of the strip is such as to cause a substantially weakened plane in the hard concrete.

Upon hardening and/or drying of the concrete slab, contraction occurs placing the slab in tension. This is relieved by rupture or cracking in the slab at the weakened plane as shown in cross-section in FIG. 4 and in perspective in FIG. 5. As the crack opens up, its width may approximate inch on the average, but under some circumstances, could be as great as inch. Although the segments 7 and 8 of the slab move apart, little, if any, stress develops tending to pull the embedded bulbs 2b and 3b from the concrete. Entry of foreign matter such as sand or gravel into the slot between sheets 2 and 3 or into the depths of the crack is impeded by the lip 9 protruding from sheet 3 in the direction of sheet 2.

Referring to FIG. 6, if water 10 under a hydrostatic head such as that encountered in concrete-lined canals is present on the upper surface of the cracked slab, the water penetrates the slot 5. It also penetrates somewhat between the strip and the concrete until it approaches the embedded bulb-shaped protuberances. Simultaneously, water pressure in the slot 5 pushes the sheets 2 and 3 outwardly, this force being transmitted to the protuberances 2b and 312 by way of flanges 2a and 3a. The transmitted forces act to press the protuberances into firm contact with the concrete and thereby effect a watertight seal. Further, as a result of the tapered, curved shape of the flanges, they are also pressed into sealing engagement with the concrete by the water pressure. Thus, the greater the hydrostatic head, the greater the force exerted by the bulbs and flanges against the concrete, and the greater the sealing power of the strip.

FIG. 7 shows an alternate embodiment of strip 1 wherein water sealing mastic 11 such as US. Bureau of Reclamation specification material, Sealing Compound, Rubberized, Cold Application, Ready Mixed, for Joints in Concrete Canal Lining, has been molded onto a part of the bulb portions to further enhance the water-sealing capabilities of the strip. Instead of employing this molding technique, the mastic could be lightly coated on the bulb prior to installation.

Referring to FIG. 8, another alternative embodiment of strip 1 is shown wherein only sheet 2 extends above its anchoring flange into the upper section of the slab. In this arrangement the total amount of material required to fabricate the strip is reduced, while the strip still functions effectively to form a weakened plane substantially throughout the height of the concrete slab. This modification can also include a dirt-impeding lip 9 protruding from sheet 2 or 3 near the point where sheet 3 terminates.

Other advantages of the strip as a result of its configuration are as follows: (a) Positive placement of the strip at the desired location in the concrete slab is facilitated. However, the sealing system will tolerate, without impairment of function, moderate displacement, twisting or distortion of the strip from its intended position in the concrete. (b) Formation of air voids at the critical water sealing point is eliminated or minimized during installation in the fresh concrete, thus promoting a tight seal. (c) The strip is so designed to maintain an effective seal between slab segments even after abnormally large relative vertical movement has occurred between segments.

While the particular strip herein described is well adapted to carry out the objects of the present invention, it is to be understood that various modifications and changes may be made all coming within the scope of the following claims.

What is claimed is:

1. A combination water stop and weakened plane forming flexible strip adapted to be placed in an uncured concrete slab to cause a crack to form along the strip in the hardened slab, and then prevent water from leaking through the crack comprising? (a) two sheets of flexible material, each of said sheets having first and second faces, each of said sheets having first and second opposing edges: said first faces being closely adjacent one another, and said sheets being joined together along only one of said opposing edges so that said sheets define a slot therebetween; and

(b) flanges projecting from each of said second faces of said sheets, the width of each flange tapering from its inner end to its outer end, at least one of said sheets having a flange projecting from its second face in an area centrally disposed between its first and second opposing edges; said flanges having a bulb-shaped protuberance at the outer end portion thereof whereat the flange is at its narrowest width, said protuberances cooperating with said sheets and said tapered flanges to effectively prevent water under high pressure from leaking through the crack in the slab at the strip when the water is present in said slot.

2. The strip of claim 1 wherein the sides of each flange defining the tapered shape are curved.

3. The strip of claim 2 wherein the curved sides of each flange are concave with respect to said flange.

4. The strip of claim 3 further including a lip on one of said sheets adjacent the open end of said slot, said lip protruding in the direction of the adjacent sheet so that foreign matter such as sand and gravel is impeded from entering said slot after the crack has formed at the strip.

5. The strip of claim 4 wherein the strip is composed of an elastomer.

References Cited UNITED STATES PATENTS 1,806,275 5/ 1931 Adler 9418 1,965,403 7/1934 Alvey 94-18 2,245,633 6/1941 Wolfe 94--18 X 2,431,385 11/1947 Fischer 94l8 2,695,513 11/1954 Williams 9418 X 2,937,065 5/1960 Harza 94l8 X NILE C. BYERS, JR., Primary Examiner.

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