AU3780700A - Concrete crack control device - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): CORKJOINT (AUST) PTY LTD A.C.N. 002 724 138 Invention Title: CONCRETE CRACK CONTROL DEVICE es.

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The following statement is a full description of this invention, including the best method of performing it known to me/us: 2 CONCRETE CRACK CONTROL DEVICE The present invention relates to concrete crack control devices and in particular concerns an elongate device adapted to be inserted into a freshly laid concrete slab to establish a path along which inherent cracking associated with curing, drying and shrinkage is focused.

Use of such devices prevents random cracking or crazing in at least the surface portion of a concrete slab. Such cracking or crazing would be considered unsightly and unacceptable in large slabs and may give rise to moisture problems and long term corrosion of reinforcing steel in the slab.

*9 **o One known approach to the control of cracking in *concrete slabs is the utilisation of a product known as 15 "Zipcap" manufactured and marketed since 1973 by :°•oee Greenstreak Plastic Products in USA and publicised in their product literature.

The Zipcap product comprises a generally T-shaped .product in cross section having a vertical leg terminating in an arrow head shape and also incorporating, at approximately the midpoint, transversely directed arms which extend integrally from the leg on opposite sides of the leg. Installation of the product comprises using a bar with a sawing motion to part the aggregate in the concrete 25 to a depth equal to the length of the leg and then inserting the product into the preformed slot also using a sawing motion until the horizontal top arms of the T-shaped product are placed flush with the concrete slab surface.

The horizontal arms of the T-shaped product are designed to be peeled away from the vertical leg portion and removed and final trowling of the concrete slab then takes place.

As the concrete cures, shrinkage stress-cracking will occur at the vertical weakened plane created by the Zipcap product rather than at random locations in the slab.

\\GHSYDNT1\users\Speci\300 399\350 399\38160.doc 3 Another known approach is that described in patent specification AU-B-14241/83 (patent 567093) to D C Underwood. The Underwood approach is to use an elongate strip having an integral laterally extending rib defining convex and concave opposite surfaces, the strip being adapted to be inserted itself into the concrete slab, typically with a sawing motion, until the upper edge is adjacent or below the surface of the concrete slab. An optional plastic capping piece is installed on the upper edge of the product and adapted to accommodate the upper edge of the metal product below the surface of the concrete, yet the plastic finishing strip is flush with the surface of the concrete.

The present invention is aimed at new and useful 15 alternatives to known proposals.

:°oooo :....According to the present invention, there is provided a concrete crack control strip of elongate form, the strip .'.having first and second legs arranged to extend from edges S. of the strip which in use define top and bottom edges towards an intermediate portion and at the intermediate portion an integrally formed lateral arm extends to one side only of the strip, the lateral arm extending at about degrees from the legs and shaped and dimensioned to provide stiffening of the strip whereby it may be inserted S" 25 with a sawing action into a poured concrete slab and the lateral arm functions to stabilise the strip in the inserted position and substantially obviate sinking of the strip when installed in the slab.

Preferably the strip is integrally formed by rolling from metal strip so as to have an uniform cross-sectional shape so that the lateral arm is formed by two portions of the material in face to face juxtaposition extending at substantially 90 degrees to the leg portions.

Preferably the leg portions are coplanar.

It has been found that embodiments of the invention function most effectively since they are anchored in an \\GHSYDNT\uers\Speci\300 399\350 399\38160.doc 4 uncured new concrete slab and function to control shrinkage cracking.

The dimensions of the strip between the top and bottom surfaces are suitably chosen to the particular application.

Typically the strip will be approximately 50mm and thereby suit a slab of up to 200mm in depth and it has been found that strip metal of approximately Imm thickness is very effective and can be roll formed and a typical length of the lateral arm is Although a preferred embodiment of the invention utilises metal such as mild steel, a variety of materials could be used and if desired instead of roll forming other manufacturing techniques could be adopted such as extrusion.

15 For illustrative purposes only an embodiment of the eooo invention will be described with reference to the accompanying drawing Figure 1 which is a cross sectional view through a control strip.

*The control strip illustrated comprises an upper leg 10, a lower leg 11 and a lateral arm 12, the product being integrally formed by roll forming from steel strip such as zinc coated steel strip having a thickness of the order of Imm. The lateral arm is formed from upper and lower 9999 portions 14 and 15 brought into face to face contact and S" 25 leaving the tip of the arm with a curved nose. The drawing is schematic and shows a relatively large radius of curvature at corners 16 and 17 but in practice it is found that a tighter radius return is provided with no appreciable gap at this intermediate zone.

The length of the leg portions can be varied to suit the application although typically the length of the arm of around 5mm will suit a wide range of strips for different concrete thicknesses.

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Claims (8)

1. 2. A control strip as claimed in claim 1 and wherein the strip is of uniform cross-sectional shape.
2. 3. A control strip as claimed in claim 1 or claim 2, wherein the strip is integrally formed by rolling from metal strip with the lateral arm formed by two portions in 20 face to face juxtaposition and extending at substantially 900 to the leg portions.
3. 4. A control strip as claimed in any one of the preceding claims, wherein the leg portions are coplanar.
4. 5. A control strip as claimed in any one of the preceding claims wherein the strip is approximately 50mm wide and is of metal of approximate thickness imm and the lateral arm projects approximately 5mm from the legs.
5. 6. A control strip as claimed in any one of the preceding claims wherein the strip is formed from zinc-coated mild steel.
6. 7. A control strip substantially as herein described with reference to the accompanying drawing.
7. 8. A concrete slab having a crack control joint formed with the use of a control strip as claimed in any one of the preceding claims and wherein an edge of the control \\GHSYDNT1\users\Speci\300 399\350 399\38160.doc 6 strip is at or close to the surface of the concrete slab and extends substantially vertically downwardly.
8. 9. A concrete slab as claimed in claim 8 and wherein the concrete slab has the control strip extending approximately a quarter of the distance through the depth of the slab. A method of forming a concrete slab comprising pouring a concrete slab, compacting and surface finishing the slab and establishing a crack control joint along a desired line by working a control strip as claimed in any one of the claims 1 to 7 into the slab and allowing the concrete slab to cure. .o Dated this 2nd day of May 2000 CORKJOINT (AUST) PTY LTD By their Patent Attorneys GRIFFITH HACK \\GHSYDNT1\users\Speci\300 399\350 399\38160.doc