GB2136470A - Paving slabs - Google Patents

Abstract

Concrete paving slabs can be economically and substantially reinforced by incorporating on one face a layer of reinforced cement, preferably fibre reinforced cement. Glass fibre reinforced cement may be used and may be present on one or both faces of the slab. Economies may be achieved by distributing the reinforced cement in a pattern corresponding to areas of expected high stress when the slab is laid and e.g. a vehicle drives over it.

Description

SPECIFICATION Paving slabs This invention relates to paving slabs.

Paving slabs are used in very large quantities by local authorities to construct pavements. They consist generally of a cast slab of fine concrete 50 mm or 63 mm thick and a convenient length and breadth e.g. 90 cm by 60 cm.

Such slabs are usually laid on the ground in a regular pattern, preferably with the interposition of a layer of sand or the like material to even out bumps and seat the slabs firmly on the ground.

A disadvantage of such slabs is that they are not very strong transversely. In particular, if a road vehicle mounts the pavement, there is a tendency for the slabs to crack.

It is uneconomic to manufacture slabs, which are used in enormous quantities, out of stronger materials e.g. reinforced concrete for normal purposes.

I have now found that the transverse strength of paving slabs can be very substantially improved at very small additional cost by providing one or more both major faces of the slab with reinforcement in the form of a layer of stronger material, in particular fibre reinforced cement.

Thus -according to a first feature of the present invention there is provided a paving slab formed of concrete and having on at least one major face a reinforcing layer of reinforced cement.

The reinforcement may take a variety of forms. A reinforcing metal mesh can work, but is not preferred. It is particularly preferred to form the surface layer of fibre reinforced cement. Here, the term fibre reinforced cement is to be construed broadly as covering any cementitious mixture which includes reinforcing fibres. The most commonly used fibre for strengthening set cementitious mixtures is glass fibre, but other inorganic reinforcing fibres may be used if desired.

Preferably both sides of the paving slab have such a reinforced cement surface.

I have found that particular advantage is to be gained by concentrating the reinforcement along certain lines which correspond generally to areas of high stress when the slab is transversely loaded. For a rectangular slab, these lines approximate to the two diagonals of the slab and the two lines which run parallel to the sides of the slab and which bisect it. Thus for a paving slab of conventional aspect ratio, viewed with its longer sides horizontal, a desirable pattern for thickening the application of the reinforcing cement layer is that of a pair of superimposed crosses, similar in shape to the superimposed crosses at St. George and St. Andrew on a Union Jack. The thickening of the reinforcement may alternatively be achieved by simply applying successive layers with different contours to give a maximum reinforcement thickness at the centre of the slab.

The exact distribution of reinforcement will vary depending upon the desired use of the slabs and the economic considerations governing their manufacture. One or both major faces may have overall layers of reinforced cement and/or one or both faces may incorporate patterned reinforcements as just described.

A simple mode of manufacture of slabs in accordance with the present invention is to cast into slab moulds first a fibre reinforced cementitious composition and then concrete optionally followed by a final application of fibre reinforced cementitious composition. The composition may be applied as a pre-mix or a spray, both mechanically or by hand. The material cast into the mould may be subjected to tamping or vibration or rolling to remove air bubbles and ensure the production of an integrated slab of high strength. Alternatively, vacuum de-watering of the concrete, with or without the application of pressure over the entire surface, e.g. of 7MN/m2 or more, may be employed as part of the manufacturing process.

If desired, one or both major faces of the slab may be provided with an ornamental finish, either a contoured finish or e.g. by the application of particulate material to give a decorative or other desired finish, e.g. a nonslip finish.

The following example will serve to illustrate the invention.

Slab moulds 600 mm by 600 mm by 50 mm deep were taken. Into each there was first sprayed a thin layer, e.g. 3 mm or 6 mm thick of a glass fibre reinforced cement composition. The composition was formed by mixing three parts by volume of cement, one part by volume of silica sand and one part by volume of water in a conventional cement mixer, 5% by weight of the mix of chopped glass fibre rovings being added at the end of mixing. After spraying this composition to the appropriate depth, the layer was hand rolled to remove any air bubbles.

On to the 3 or 6 mm thick layer of unset glass reinforced cement composition in the mould there was added a fine concrete mix consisting of by volume one part cement, two parts sand, four parts crushed gravel aggregate and water to give the desired consistency. In some cases the mould was not quite filled and a further 6 or 3 mm layer of glass fibre reinforced cementitious composition was sprayed to complete the filling of the mould.

The moulds were then placed on a vibrating table and vibrated to remove air bubbles and then transported to a convenient holding location until the slabs had set.

After setting the slabs were removed from the mould and left outside to cure for 28 days.

After 28 days the slabs were subjected to transverse strength tests in accordance with the procedures and the apparatus described in British Standard 368/1971. All of the slab types performed well, transverse strengths in excess of 28 KiloNewtons being obtained in some cases. It was furthermore observed that the slabs in accordance with the present invention could be loaded repeatedly up to near their elastic limit without undergoing plastic failure.

Claims (6)

1. A paving slab formed of concrete and having on at least one major face a reinforcing surface layer of reinforced cement.

2. A paving slab according to claim 1 wherein the surface layer is of fibre reinforced cement.

3. A paving slab according to claim 2 wherein both major faces have reinforcing surface layers of fibre reinforced cement.

4. A paving slab according to any one of claims 1 to 3 wherein the distribution of the or each layer of fibre reinforced cement varies across one or more faces of the slab.

5. A paving slab according to claim 4 which is rectangular in shape and wherein the amount of fibre reinforced cement is increased along the diagonals of the slab shape and/or along lines bisecting the shape and parallel to its sides.

6. A paving slab substantially as hereinbefore described with reference to the foregoing specific example.