The present invention relates to an anti-spalling edging, in particular, though not exclusively for concrete.

Concrete is strong in compression, but weak in tension. Small sections are liable to fail in shear. The result is that edges of concrete slabs are liable to spall, that is the edge is liable to crack away, generally at angle.

The problem can be relieved to an extent by a flat steel edging, with may form part of a joint allowing contraction of the slabs on setting and thermal expansion. Flat steel strip can become bent away from the concrete, thus the original problem is not really solved. The steel strip can be reinforced against such bending away by provision of an in-turned edge or return level with the top of the slab. This protects the edge of the slab, but loading, deflections and impact can allow the free edge of the return to lift. This gives rise to another set of problems. In turn the free edge can be turned down and provided with cut-outs for its anchoring in the slab.

Again there is a problem, in that the down-turn has a radius of curvature at its abutment with the top surface of the concrete, which creates yet another potential spalling site.

The object of the present invention is to provide an improved anti-spalling edging

According to the invention there is provided an anti-spalling edging comprising:

• a metal strip adapted for concrete to be cast against,

• a return along a top edge of the strip, • a down-turn from the edge of the return spaced from the strip,

• cut-outs in the down-turn for anchoring it in the concrete; wherein: • the cut-outs are so arranged as to provide faces, extending through the return and generally in the direction of the edging, against which faces the concrete abuts when cast level with the outer surface of the return.

Whilst it is envisaged that anti-spalling advantage could be obtained if the faces were non-planar, such as being S or W shaped when viewed in plan, preferably the faces are flat and face directly away from a bend connecting the metal strip to the return.

Preferably, in the direction of the edging, the transverse faces predominate compared with fingers of the down-turn extending down between the cut-outs.

Whilst it could be envisaged that the fingers are not joined at their distal ends, we prefer to join them at their distal ends to stabilise them during installation and casting of the concrete. Members joining the fingers are important for holding the finger from drawing upwards of the concrete.

Normally the metal strip will be of steel galvanised before or after punching of its cut-outs. However, it can also be of stainless steel, mild steel or plastics materials.

As in the preferred embodiment, a pair of anti-spalling edgings will normally be provided as a "joint" between two sections of concrete slab, the two metal strips abutting with the returns extending in opposite directions on laying of the concrete and separating on curing. The joint will normally include dowels extending into the two sections of the slab, for vertical load transfer in use; the dowels may be any type of dowels and indeed are optional. Furthermore, a single anti-spalling edging may be used, particularly at an edge.

To help understanding of the invention, a specific embodiment thereof will now be described by way of example and with reference to the accompanying drawings, in which:

Figure 1 is cross-sectional view of a joint including two anti-spalling edgings in accordance with the invention and

Figure 2 is a perspective view of the joint. Referring to the drawings, a joint 1 including a pair of anti-spalling edgings 2,3. Both have:

• metal strips 21 ,31 , the first being deep and the second being shallow, • returns 22,32 along the top edges of the strips, facing in opposite directions from the central plane P of the joint,

• down-turns 23,33 extending down from the edges of the returns,

• cut-outs 24,34 in the returns,

• the cut-outs defining: • edges 25,35 in the returns which face outwards from the plane P,

• fingers 26,36 of the down-turns extending down between the edges, the fingers being narrow and the edges being wide,

• connections 27,37 at the bottom of the fingers.

The two anti-spalling edgings are lightly connected together with frangible fixings 5, below the level of the connections.

The deep metal strip 21 extends to or close to the base of the slab into which the joint is to be laid. It has a return 28 and up-stand 29 for stiffening it. These features are both optional and may be used separately. The shallow strip 31 also has a return 38, which is angled slightly away from the top return 32. The return 38 has a series of apertures 39. As shown these are of a similar size to the cut-outs 34, but they can be either large or more usually smaller. Beneath the return 38, the deep strip has flat plate dowels 6 welded to it at punched cut-outs 7. On the shallow strip side, the dowels are enclosed in sleeves 8, which allow the dowel to withdraw from the slab portion in which they extend. The dowels are not essential to the working of the invention, and embodiments can be envisaged without dowels.

To install the joint, it is set up to form the edge of a slab portion S2, that is with the top of the return at the intended finished height of the slab. It can be temporarily secured by means that form no part of this invention. The slab portion is laid. Once it has cured to a green state, the temporary securement is removed and the portion S3 of the slab on the second side is laid. During laying, the concrete forms against the edges 25,35 in a manner that is not prone to spalling. The concrete is able to rise against the underside of the returns, since air can flow out at the edges. Further air escape cut-outs 10 can be provided in the returns 22,32.

As an alternative to sequential laying of the slab portions on opposite side of the joint means, again conventional, for holding the joint can be left set into the slab and both portions laid without the first setting off to green state first.

On full curing, the fingers 26,36 and the connections 27,37 firmly hold the down-turns in the concrete. Thus the returns 22,32 and indeed the strips 21,31 at the top of the slab are held against the concrete. The strips pull apart from each other and the fixings 5 break.

However, the slab portions are restrained from vertical movement by the dowels 6, which are known in themselves.