Known such impact absorbing surfaces comprise particles of natural or synthetic rubber, such as SBR or EPDM for example, in a matrix of polymeric binder, such as polyurethane. The particles typically comprise granules or shreds of rubber.

The matrix may completely fill the spaces between the particles to give a non- porous composition, or simply coat the surfaces of the particles to cause them to adhere leaving the interstices between the particles void to give a porous product.

In many countries the impact attenuation properties of surfaces in, for example, publicly owned playgrounds are regulated by national safety standards.

Generally, the permitted impact attenuation properties of the surface are related to the height of the play equipment that the surface is beneath ie. surfaces beneath high playground apparatus will require higher impact attenuation properties than surfaces beneath lower playground apparatus. This variation of impact attenuation is achieved by varying the thickness of the surface, since the impact attenuation of a safety surface is generally proportional to thickness. Measurements using a simulated forehead fitted with accelerometers are used to determine the acceptable level of impact attenuation (Critical Fall Height) for different thickness of safety surface. Figure 1 shows a typical relationship between Critical Fall Height and thickness of a rubber bound safety-surface.

In one known method of producing such impact absorbing surfaces, tiles comprising re-cycled rubber granules/shred are manufactured using compression moulding. They are usually laminated, having a soft lower layer and a decorative stronger upper wearing layer. The tiles are laid, abutted and fixed, by adhesive or by other means, onto a flat sub-base to form a safety surface. Such tiles have a number of disadvantages.

The tiles tend to shrink and the joins between the tiles become open. In order to accommodate different fall heights, the tiles have to be stepped, i. e. the playing surface is not flat. This causes problems since children tend to trip over these steps. The alternative is that stepping is avoided by utilising the maximum thickness over the whole of the surface (such as for walkways) which is very expensive. Additionally, the tiles are not self-levelling, and cannot be laid on an uneven sub-base. Additionally still, the tiles are frequently stolen-particular in deprived areas-since they have perceived value.

Furthermore the adhesive often fails, and thus the tiles become loose.

In another known method of producing impact absorbing surfaces, rubber containing compositions of the types described above may be poured in place on a sub- base to form a sports or play surface or to form a substrate for another surface such as that provided by synthetic turf."Poured-in-place","in situ"and"wet pour"are interchangeable terms used to describe such on-site fabrication of a recreational surface comprising, usually, rubber mixed with a moisture curing pre-polymer. Such surfaces usually consist of two distinct layers. The base layer (also called a shockpad) usually comprises scrap rubber shred or granules with as little polyurethane (polyurethane is very expensive) as possible to ensure long-term integrity. The thickness of this layer is varied depending on the desired impact attenuation characteristics. The wearing course usually comprises smaller scrap rubber or coloured nascent EPDM granules (2-4mm) mixed with F-l. a greater concentration of moisture curing polyurethane to achieve the desired wearing characteristics. Such in situ systems have a number of advantages in comparison to the methods based on prefabricated tiles. For example, the surfaces can be laid on uneven sub-

bases and are"self-levelling". Also, the thickness of the surface can be adjusted to accommodate different fall heights. The area around, for example, high apparatus can be excavated to a prescribed depth such that when filled with the rubber/binder mixture the desired, enhanced, impact attenuation is attained yet the final level of this portion of the surface is the same as the surrounding areas. Furthermore, the surfaces are inherently seamless and without joins on the upper surface. Furtherstill, the finished surface is not easily stolen and, in any event, portions of the surface are of no value. However, a disadvantage is that the impact absorbing material cannot be formed to different shapes.

With conventional in situ techniques it is not possible to form legs and associated voids in the surface, and thus more resilient material must be utilised to provide a desired Critical Fall Height.

EP 1031659 discloses an in situ system in which a mould is filled with resilient composition on-site. The mould has a plurality of leg-like mould cells which ensure that void areas are left underneath the upper surface.

The present invention overcomes many of the difficulties and problems encountered in the above-described prior art. In particular, the present invention combines the advantages associated with in situ methods, principally the advantages of a seamless, mechanically stable structure, with the capability to incorporate legs and void regions into the surface structure and thus reduce greatly the material requirements and costs of the surface. Additionally, the present invention facilitates very convenient preparation of areas having enhanced impact attenuation properties.

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According to a first aspect of the invention there is provided an impact absorbing tile comprising a resilient composition and having an impact absorbing upper

surface and a plurality of upper surface supports which are configured so as to leave void areas underneath the upper surface which are not filled by resilient composition; in which: the upper surface comprises a plurality of indentations.

The provision of the indentations enables convenient and stable vertical stacking for areas which require greater levels of impact attenuation. As will be apparent when the skilled reader scrutinises the second aspect of the invention, the tiles are covered in situ with composition which is settable to providing a finishing layer of resilient composition. The indentations provide a further advantage in this respect since they are filled with the settable composition and thus provide a mechanical lock between the tile and the resilient composition. The tiles are convenient and cheap to produce by way of mass manufacture.

The indentations may be shaped to receive the upper surface supports of another impact absorbing tile thereby permitting stacking of the tiles.

The indentations may permit mechanical locking of a resilient composition overlaying the tile. u} The tiles may further comprise one or more locking portions shaped to engage another impact absorbing tile or tiles, thereby permitting a locked coplanar arrangement of tiles.

The tiles may further comprise one or more recess portions shaped to receive another impact absorbing tile or tiles, thereby permitting a locked coplanar arrangement of tiles. It is possible to provide tiles which have one or more locking portions and one or more recess portions. The interlocking permitted by the present invention increases the structural integrity of the ultimately produced surface.

The cross sectional area of the bottom of an upper surface support may be less than the cross sectional area of the top of an upper surface support. The upper surface supports may taper from top to bottom. The upper surface supports may be substantially frusto-pyramidal or frusto-conical.

The tile may comprise areas containing rows and columns of upper surface supports.

The upper surface supports may be disposed directly underneath the indentations.

The indentations may comprise a plurality of grooves formed in the upper surface. The plurality of grooves may form a cross-hatched pattern in the upper surface.

The upper surface may comprise a number of discrete raised portions. The raised portions may be disposed directly above the void areas.

The indentations may comprise one or more side walls downwardly depending from the upper surface, which one or more side walls are vertical or substantially vertical.

The resilient composition may comprise particles of a resilient material contained in a binder matrix. The binder matrix may be a polymer such a polyurethane.

The particles may comprise rubber.

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According to a second aspect of the invention there is provided a method for making a recreational surface comprising the steps of :

positioning a plurality of tiles according to the first aspect of the invention on a sub-base; pouring a composition over said plurality of tiles which composition is settable to provide a resilient composition; allowing the composition to set to provide a resilient composition.

In this way a recreational surface having the structural advantages associated with in situ systems can be produced which utilises a minimum of resilient composition on site due to the legs of the tile, and the associated void regions in the surface.

The step of positioning the plurality of tiles comprises providing a first layer of tiles, and stacking a second layer on the first layer by locating upper surface supports on tiles comprising the second layer in indentation of tiles in the first layer. Additional layers may be utilised as required. The indentations on the tiles provide very stable stacking of tiles.

According to a third aspect of the invention there is provided a recreational surface comprising a plurality of tiles according to the first aspect of the invention overlaid by a resilient composition. The recreational surface may comprise a first layer of tiles and a second layer of tiles stacked thereon by locating upper surface supports of tiles in the second layer in indentations of tiles in the first layer.

Tiles, surfaces and methods in accordance with the invention will now be described with reference to the accompanying drawings, in which: ,., .

Figure 1 shows the relationship between critical fall height and recreational surface thickness;

Figure 2 shows (a) a recreational surface having a single layer of input absorbing tiles and (b) a recreational surface having a double layer of tiles; Figure 3 shows (a) an impact absorbing tile, (b) a double layer arrangement of tiles and (g3 a cross section along the line A-At of (b); Figure 4 is a cross-sectional view of a second embodiment of a recreational surface; Figure 5 is plan view of a portion of the tile of the second embodiment; Figure 6 shows (a) a plan view of a tile of the second embodiment and (b) a cross-sectional view of a recreational surface comprising the file of Figure 6a (the upper portion of the tile only is shown); Figure 7 shows a stacking of two files of the second embodiment.

Figure 8 shows (a) a plan view of a third embodiment of the tile and (b) a cross section along the line A-A'of (a); and Figure 9 shows (a) a plan view of four tiles of the third embodiment in a locked coplanar arrangement and (b) a cross section along the line A-A'of (a).

Figure 2 (a) shows a recreational surface of the present invention comprising a prefabricated tile 10 positioned on a sub-base 12 and overlaid by a resilient composition 14. It will be understood that the surface comprises further tiles which, for presentational purposes, are not shown in Figure 2 (a).

The tile 10 comprises an impact absorbing upper surface 16 having a plurality of indentations 18, and a plurality of upper surface supports 20 which are in contact with the sub-base 12.

The upper surface 16 of the tile 10 is overlaid by the resilient composition 14.

The resilient composition 14 can be any composition used for in situ applications, typically comprising rubber (in the form of shreds or granules) mixed with binder such as a moisture curing pre-polymer, usually polyurethane. Usually, the resilient composition is of the "wearing course"type, ie. relatively small rubber granules (typically ca. 2 to 4mm) mixed with a relatively large concentration of moisture curing polyurethane.

Figure 2 (b) shows a two layer embodiment of the present invention which comprises two layers of tiles 22,24 positioned on a sub-base 12. The uppermost tile 24 is overlaid by the resilient composition 14. The stacking of uppermost tile 24 onto lowermost tile 22 is greatly facilitated by locating the upper surface supports 26 of uppermost tile 24 in the indentations 28 of lowermost tile 22, which indentations 28 are shaped so as to receive said upper surface supports 26. The indentations have a further advantage in that they provide mechanical locking of the tiles to the resilient composition 14. It is possible to incorporate grooves into the upper surface of the tiles to further enhance the mechanical locking.

The use of a second layer provides enhanced impact attenuation. The use of further layers is within the scope of the invention. Again, it is understood that the

recreational surface comprises further tiles which, for presentational purposes, are not shown in Figure 2 (b).

Figure 3 (a) shows an impact absorbing tile 30 of the present invention having rows and columns of indentations 32. The tile 30 has locking portions 34 and recess portions 36. The locking portions 34 are shaped so as to engage recess portions on other tiles. In this way, a stable, locked coplanar arrangement of tiles is produced. Such an arrangement of tiles 38 is shown in Figure 3 (b). Also shown in Figure 3 (b) is an upper tile 40 stacked on top of the coplanar arrangement of tiles 38 by locating the upper surface supports (not shown) of the upper tile 40 in indentations 42 of the tiles 38. Figure 3 (C) offers a cross-sectional view of this stacked arrangement along the line A-A1, showing the upper surface supports 44 of the upper tile 40 and the upper supports 46 of the tiles 38.

The upper surface supports provide advantageous compressibility properties.

This has the effect that a recreational surface of the present invention can absorb more energy than would a solid (but otherwise equivalent) recreational surface of the type well known in the prior art. It is believed that this is because the recreational surface is acting somewhat in the manner of a spring mattress, ie. the shockpad portion of the surface is supported by a series of"legs", each of which is relatively compressible and springy. The impact attenuation properties of a surface are proportional to the amount the shockpad (and wearing course) deforms without bottoming out. Bottoming out occurs when the system cannot deform further, i. e. at its limit of compressibility. In this instance the kinetic energy of the impacting headform is transmitted directly to the non-deforming sub-base. The deformation is proportional to the thickness of the shockpad and inversely proportional to the cross-sectional area of the deforming shockpad. The stress pattern is conical, with the apex at the point of impact. Legs greatly decrease the cross-sectional area in the stress cone and facilitate greater deformation.

It is possible to utilise a variety of upper surface support configurations, such as frusto-pyramidal, a frusto-conical configuration, or, indeed, more complicated geometrical shapes.

Typical dimensions for an upper surface support might comprise a width, length and depth of around 4 to 5cm. However, it is understood that these values are representative only. A design consideration is that although longer legs increase the deformation for a given head impact, the legs become mechanically unstable, buckling above a critical aspect ratio of leg length/cross sectional area of leg. This ratio is dependent on the material used. It should be noted that when tiles are stacked the upper surface of the lower tile provides a stabilising membrane before criticality of aspect ratio is realised, therefore facilitating increased leg length without having to increase the leg cross-sectional area.

An advantage of the present invention is the ease with which recreational surfaces having areas of enhanced impact attenuation can be produced. A first layer of tiles is laid on the sub-base, and an additional layer (or layers) of tiles are disposed in the indentations of the first layer in the regions requiring enhanced impact attenuation (such as the areas surrounding high play equipment). An in situ settable safety surface composition is laid over the top of the shockpads, filling the indentations on the upper surfaces of the tiles and the surrounding areas. The in situ safety surface composition is allowed to cure. In this way, a recreational surface is provided which does not have seams : rather, the tiles and in situ resilient composition form a coherent mass.

If the area of enhanced impact attenuation is produced by positioning a selective second layer of tiles on top of a base layer of tiles, then the pouring of in situ settable composition can be controlled to produce a gentle slope leading to the area of enhanced impact attenuation. Alternatively, a uniformly flat surface can be produced,

although additional quantities of in situ settable composition would be required.

Alternatively, still, it is possible to use a sub-base of uneven depth, ie. to excavate deeper in the region corresponding to an area of enhanced impact attenuation. In this way, a selective layer of tiles can be positioned below the main layer of tiles, and a flat surface can be produced using a minimum of iii situ settable composition.

Figure 4 shows in cross-section a second embodiment of a recreational surface comprising an impact absorbing tile 50 and a layer of resilient composition 52.

The impact absorbing tile 50 comprises an impact absorbing upper surface 54 having a plurality of indentations 56, and a plurality of upper surface supports 58 which are in contact with a sub-base (not shown).

In this second embodiment, the indentations 56 comprise a series of grooves formed in the upper surface 54. The upper surface 54 comprises a number of discrete raised portions 60. Figure 5 shows, in plan, the grooves 56 and raised portions 60. The positions of the upper surface supports 58 are shown by dotted lines in Figure 5. As shown in Figure 4, the walls 56a, 56b of the indentations 56 (which are also the walls of the raised portions 60) are vertical. This is an important consideration because a conical (or sloped) section can tend to cause the wearing course to lift or separate if the tile begins to shrink. The present design ensures that the stress associated with tile shrinkage is distributed evenly over the entire tile/wearing course interface and eliminates any upward or separating force vectors that would be produced by conical or otherwise sloping sides.

Thus vertical or near vertical (at an angle of greater than about 85'from the horizontal) walls are preferred.

- Thus, the file has raised (male) members arranged rather like square checkers on a checker board. The arrangement redistributes the mass of the tile from over the legs

to the area between the legs and provides a thick, durable connection between the upper surface supports.

The wearing course forms female cavities around these raised (erect) male members 60, which act rather like lugs.

The grooves can be conveniently formed by milling slots into the mould die.

Conveniently, the grooves form a cross-hatched pattern such as that shown in Figure 5.

The grooves can form two mutually perpendicular sets, i. e. the grooves can comprise one series which extend in an x direction and another set which extend in the y direction.

Such an arrangement is depicted in Figure 5, although, in principle, the sets of grooves do not have to be mutually perpendicular.

The recreational surface of the second embodiment can be produced using the techniques and materials described above. Representative depths for the grooves are 0.5 to 2cm, although these values are not limiting ones.

Figure 6 (a) shows a tile 70 of the second embodiment. The tile 70 has grooves 72 formed therein, which act as indentations to receive upper surface supports (not shown) of another tile and permit mechanical locking of a resilient composition used as an in-situ material. The tile 70 comprises seven rows and seven columns of internal discrete raised portions 74 of one size. Around the periphery of the tile 70 are thirty-two discrete raised positions 76 which are of smaller sizes than the internal discrete raised portions 74. The numbers of raised portions used are representative only, and are not limiting. A preferred tile size is 60 x 60 x 7.5 cm, although, once again, this specification should not be regarded as being a limiting one.

Figure 6b shows a recreational surface 78 comprising the tile 70 overlaid with a resilient composition 80. Only the uppermost portion of the tile 70 is shown in Fig. 6b, although it is understood that the tile 70 comprises a plurality of upper surface supports. Figure 7 shows a stacking of two tiles 70 of the second embodiment.

The upper surface supports 82 of the tiles 70 are shown.

In a conventional tile design, the files might typically be edge glued such that all the tiles form a large aggregate tile. Such an arrangement tends to shrink as a single unit. Such an aggregate tile is not stuck to the sub-base or the wearing course. If it therefore quite likely that a large gap will be formed under the wearing course along one of the edges of the aggregate tile and the area will fail catastrophically. This will be exacerbated during cold wet weather when the coefficient of friction of the various interfaces is greatly reduced. If the tiles are not edge glued they will tend to move around (depending on foot traffic) and form gaps. This will result in wearing course failure.

It is an advantage of the present invention that the indentations provide mechanical locking of the resilient composition which forms the wearing course. Tile to tile adhesion is retained, since the edges of adjoining tiles tend to shrink at the same rate, and thus a shear force is not imposed. It should be noted that the wearing course is typically anchored to the sub-base adjoining the tiles, and it too will tend to shrink. Thus, the wearing course is held in tension over the area. The wearing course cannot move laterally and its position over the surface of the tiles remains constant with the mechanical locking between wearing course and tiles being retained.

A recreational surface will also be subject to shear stresses produced by shrinkage of the thickness of a tile. However, the tile of the present invention can be produced so as to be relatively soft resulting in the shear stress on each tab being negligible.

Figure 8 shows a further embodiment of a tile 90, which shares many of the features of the second embodiment shown in Figures 4 and 5. Identical numerals are used to denote such shared features, which include grooves 56 and raised portions 60. The tile 90 comprises overhanging ledges 92,94 on two sides of the tile 90. The remaining two sides of the tile comprise edges 96,98 which have top surfaces 96a, 98a, which, conveniently, are at the level of the bottom of the grooves 56. The level of the top surfaces 96a, 98a of the edges 96,98 is substantially at the level of the undersides of the edge ledges 92,94. This permits co-planar locking of tiles 90, as shown in Figure 9. The provision of notches 100 in corners of the tile 90 permits co-planar locking of four mutually adjoining tiles. Alternatively, it may be possible to utilise tiles in which ledges are only formed by lateral extension of raised portions 60.

The tiles can be prefabricated using mass manufacture techniques.

Any suitable resilient composition might be utilised: typically, scrap rubber shred or granules together with a relatively small quantity of a binder such as polyurethane is used.

The thickness of the tile can be varied depending on the desired impact attenuation characteristics. Tiles can be produced by moulding processes. The tiles might wholly comprise resilient material, or, alternatively, a suitable mould (such as a plastic or paper mould) might comprise part of the tile itself. Such moulds are disclosed in EP 1031659.