IMPROVEMENTS IN PAVING SLABS

Abstract: A concrete paving slab comprises an upper face and a lower face, the lower face having a plurality of spacing members (9) embedded therein, each spacing member comprising a generally planar portion (1, 4) resting against the face, a first portion (2, 5) extending generally normally to the planar portion and located within the slab, and a second portion (3, 6) extending generally normally to the planar portion outwardly of the slab.

Description: IMPROVEMENTS IN PAVING SLABS Field of the Invention This invention relates to improvements in paving slabs and the like. Background to the Invention Concrete paving slabs are typically formed either by casting a liquid concrete mix in a horizontal mould or by pressing a relatively dry mix. The "dry" process produces finished slabs more quickly, but the appearance of the slabs is less satisfactory than the wet cast slabs, which can yield textured or exposed-stone finishes, for example. In the production of wet cast slabs, after the concrete has set sufficiently to al- low removal from the mould, it is necessary to space the slabs from each other while the concrete cures and gains strength, to allow air to carry away moisture, and this is usually done with the slabs arranged upright. The slabs are then packed, again vertically, on pallets for transport, and again some form of spacing is necessary, in this case to prevent damage to the decorative surface of the slabs by abrasion by the adjacent slab. Spacing during transport is typically achieved by means of sheets of paper or card, and the positioning of these between the slabs adds to the cost, in terms of labour and materials, as well as presenting a waste disposal problem at the location where the slabs are to be used. Environmental considerations result in a cost to end user in disposing of the separating sheets. Although the "dry" process relies on mechanical pressing to provide a slab which can be handled, curing is still necessary, and protection during subsequent handling is also required. Summary of the Invention According to the invention there is provided a concrete paving slab comprising an upper face and a lower face, the lower face having a plurality of spacing members embedded therein, each spacing member comprising a generally planar portion resting against the face, a first portion extending generally normally to the planar portion and located within the slab, and a second portion extending generally normally to the planar portion outwardly of the slab. Preferably, at least the first portion of each spacing member is shaped such that the width thereof in at least one plane normal to the planar portion is least adjacent to the planar portion so as to anchor said portion in the slab, in the case of the first portion and to anchor the slab in the concrete on which the slab is laid in use, in the case of the second portion. More preferably, at least the first portion of each spacing member increases in size in two dimensions away from the planar portion. For example, a frusto-conical shape may be adopted. The planar portion is suitably in the form of a disc, which may, for example, be a few millimetres thick, for example 1 to 5 mm. The invention also provides a spacing member for use in the manufacture of paving slabs, comprising a generally planar portion having a first portion extending generally normally thereto on one side thereof and a second portion extending generally normally thereto on the opposite side thereof. Another aspect of the invention comprises a method of manufacturing paving slabs or the like, comprising casting a hardenable mix in a mould, locating in the mix before the mix has hardened a plurality of spacing members in accordance with the invention, such that the first portions thereof are embedded in the mix and the planar por- tions rest on or in the surface thereof, and then allowing or causing the mix to harden. The casting may be achieved by pouring a liquid mix into the mould, or pressing a mixture having a high proportion of solids and just sufficient liquid to permit hardening to take place. The spacing members embedded in the slabs allow the slabs to be readily stacked one against another vertically during storage and transport without the risk of the surface of one slab causing damage to the adjacent slab, and, where appropriate, permits the flow of air around the slabs while they are curing or drying. A further advantage of the spacing members is that they help to anchor the slabs more firmly to the bed on which they are typically laid (usually a sand and cement mortar), increasing the strength of the resultant paving. Conventional slabs rely solely on surface roughness of the undersides of the slabs to bond them to the bed, and this bond is generally weak, allowing the slabs to separate more readily from the bed. Yet another advantage of the invention is that the spacing members, by providing a gap between adjacent slabs, improve the safety and convenience of handling the slabs. The gap permits individual slabs to be lifted more easily, at the same time ensuring that fingers do not become trapped between adjacent slabs. The planar portions ensure that the spacing members can be readily located manually in the concrete or other hardenable material in the moulds, to an accurately predetermined and consistent depth, ensuring that the slabs stack next to each other tidily for transport and storage, and that there is no risk of the spacing members being inserted too deeply in the slabs, giving rise to risk of marred appearance of the surface if the members break through the surface, and also to the risk of local weakening of the slabs. The spacing members may be formed of plastics material, for example being formed in a simple two-part injection mould. Recycled plastics materials may be used in their manufacture, the appearance of the spacing members being unimportant as they will be buried in the bed beneath the slabs, in use, and so the spacing members will not add significantly to the costs of the slabs, while possibly permitting savings in the use of other packaging materials as well as reducing the number of damaged slabs which might need to be replaced. The plastics material is preferably a resiliently compressible or de- formable material, so that when the slabs are positioned one against another an individual spacing member does not cause excessive localised pressure leading to the risk of breakage of the slab; the member will deform until the other members contact the slab as well to share the load. Brief Description of the Drawings In the drawings, which illustrate exemplary embodiments of the invention: Figure 1 is a perspective view of a spacing member according to one embodiment of the invention; Figure 2 is a perspective view of a spacing member according to a second embodiment; and Figure 3 is a view of a slab casting mould illustrating the casting of a slab with spacing members as shown in Figure 1 embedded therein. Detailed Description of the Illustrated Embodiments Referring first to Figure 1 , the spacing member comprises a unitary plastics moulding having a central disc 1 with a pair of frusto-conical portions 2 and 3 extending generally normally to the disc 1 on each side thereof, with the widest parts of the portions 2 and 3 furthest from the disc 1 and the narrowest parts arranged centrally on the respective faces of the disc. In use, the spacing member has one of the portions 2 or 3 embedded in the slab while still in the mould and before the concrete has set, the disc 1 resting on the surface of the concrete, as hereinafter described with reference to Figure 3. The other frusto-conical portion extends from the rear face of the finished slab, ena- bling the slabs to rest one against another in the upright position with only the spacing members contacting the next slab, thereby avoiding the risk of damage to the slab. When the slab is laid in position on a mortar or other bed , the projecting frusto- conicai portion 3 becomes embedded in the mortar, keying the slab to the mortar and increasing stability of the resultant paved surface. Each of the frusto-conical portions 2 and 3 has a domed end 2a and 3a respectively to minimise the contact area with the adjacent slab in a stack, thereby minimising the risk of abrasion, for example by grit between the portion 3 and the adjacent slab surface. Figure 2 shows an alternative arrangement, in which the central disc 4 has respective truncated triangular members 5 and 6 extending from the centre of each face of the disc 4, with the widest parts of the truncated triangles furthest from the disc. The outward ends of the members 5 and 6 are radiused to minimise the contact area with adjacent slabs in a stack, for the reasons set out hereinbefore with reference to Figure 1. The use of this embodiment is identical to that described with reference to Figure 1. Figure 3 illustrates the moulding of the slab, with four spacing members in accordance with Figure 1 in position in the surface which is to become the rear face of the slab, in use. The rectangular mould 7 is first treated with a suitable release agent in conventional manner and the wet concrete mix 8 is then poured into the mould. The spacing members 9 are then pushed into the wet mix 8, each at a position space in- wardly from the corners, until the disc portion lies on the surface of the concrete. The slab is allowed to harden to a strength sufficient to permit removal from the mould, and is then stacked upright, with the spacing members spacing the slab from the next adjacent slab, allowing the circulation of air around the slabs as they cure to their final strength. The slabs are then packed upright on pallets for transport to the site where they are to be used, the relatively soft plastics spacing members 9 serving to protect the upper surfaces of the slabs from damage due to abrasion by adjacent slabs during the transporting operation; any relative movement of one slab to another tending at worst to result in abrasion of the spacing member rather than the slab surface. Although the invention has been described with reference to concrete paving slabs, it will be appreciated that the spacing members can be used with other types of surfacing member, especially, but not exclusively, those produced by cold-cure casting methods.

Claims: CLAIMS 1 . A concrete paving slab comprising an upper face and a lower face, the lower face having a plurality of spacing members embedded therein, each spacing member comprising a generally planar portion resting against the face, a first portion extending generally normally to the planar portion and located within the slab, and a second portion extending generally normally to the planar portion outwardly of the slab. 2. A concrete paving slab according to Claim 1 , wherein at least the first portion of each spacing member is shaped such that the width thereof in at least one plane normal to the planar portion is least adjacent to the planar portion so as to anchor said portion in the slab, in the case of the first portion and to anchor the slab in the concrete on which the slab is laid in use, in the case of the second portion. 3. A concrete paving slab according to Claim 2, wherein at least the first portion of each spacing member increases in size in two dimensions away from the pla- nar portion. 4. A concrete paving slab according to Claim 3, wherein at least the first portion of each spacing member has a frusto-conical shape. 5. A concrete paving slab according to any preceding claim, wherein the planar portion of each spacing member is in the form of a disc. 6. A concrete paving slab according to Claim 5, wherein the disc has a thickness of 1 to 5 mm. 7. A spacing member for use in the manufacture of paving slabs, comprising a generally planar portion having a first portion extending generally normally thereto on one side thereof and a second portion extending generally normally thereto on the opposite side thereof. 8. A method of manufacturing paving slabs or the like, comprising casting a hardenable mix in a mould, locating in the mix before the mix has hardened a plurality of spacing members according to Claim 7, such that the first portions thereof are embedded in the mix and the planar portions rest on or in the surface thereof, and then allowing or causing the mix to harden.

Inventors: PANTON MARK, PANTON, MARK
Applicants: PANTON MARK, PANTON, MARK
Application year: 2000
Main classification: B28B23
IPC codes: B28B11, B28B13, B28B23, E01C5