Playground surface enhancement   

This invention relates to enhancements to areas of ground where children play. The invention relates to minimising the risk of bodily damage as a result of impact with the enhanced playground surface, and in particular the invention relates to improvement by resurfacing of existing playground surfaces.

“Playground” describes an area either indoors or outdoors where people; especially but not solely children play; optionally using playground apparatus such as slides and swings. For the purpose of this document the term also covers areas where games or physical exercises are carried out.

Disclaimer: This specification does not, of course, imply that an injury cannot be incurred when a playground surface has been enhanced according to the details given herein.

Some relevant test standards, the contents of which are hereby imported by way of reference, as prescribed by the American Society for Test Methods are:

ASTM F1292-04 “Standard specification for Impact Attenuation of Surfacing Mats within the Use Zone of Playground Equipment”, for establishing minimum standards specifically for playgrounds,

ASTM E303-98 “Standard test method for measuring Surface Frictional Properties using the British Pendulum Tester”, which relates to the effective grip that a person running over a surface would obtain by contact with the surface, and

ASTM F1951-99 “Determination of Accessiblity of Surface Systems Under and Around Playground Equipments”, which establishes minimum characteristics for those factors that determine accessibility.

ASTM F 2479—Guide for Specification, Purchase, Installation and Maintenance of Poured-in-Place Playground Surfacing. which covers information with regard to the design, manufacture, installation, and maintenance of poured-in-place playground surfaces.

The inventors produce modular, mutually edge-attachable and fusible mats made of a resilient material (usually a vinyl material: polyvinyl chloride plus one or more plasticisers) for use on playgrounds, among other applications. When the inventors supply a playground to be installed at an empty area, they usually lay a draining surface made of gravel or the like upon the existing ground or into an excavated, drained depression. The gravel surface is made flat and then a loose mesh of rubber fragments held together with a permeating coating of a latex is laid down, the resilience of which contributes to the final impact properties, and then an array of the modular mats that are described in this application is placed on top, welded together, and attached to the ground at the perimeter. All steps contribute in predictable ways to a final amount of resilience as required by a relevant Standard, or simply by common sense.

There have been a number of instances where a “poured-in-place” playground that was previously made by an alternative process involving the mixing and then distribution of components including resilient materials at the site has required remediation. Perhaps the need is recognised after the surface has sustained surface damage over time and become unsafe, or because the surface has deteriorated, or because the surface is found to not meet the relevant Standards (see above). Sometimes this event arises as a result of a defect in curing. The present invention is intended to provide materials and a method to upgrade such a playground. The inventors understand that the term “poured-in-place” is not a trade mark but is a generic term in the relevant field of activity.

The object of this invention may be stated as to provide an improved surface for a playground, or at least to provide the public with a useful choice. Alternatively, the object is to at least cut down the rate of accidents such as long bone or skull injuries that occur to children in playgrounds; at least those that result from impact with unduly hard surfaces.

In a first broad aspect, the invention provides a remediated playground for children based on an original playground surface having an inadequate capability for absorbtion of impact energy, hence presenting a risk of injury to users; the playground comprising the original playground surface remediated by addition of an overlying surface comprised of a plurality of mutually adherent modular, manufactured tiles made from a resilient composition selected from the range of natural rubber, synthetic rubber and a plastics material; the plastics material including polyvinyl chloride; each tile having when in use an upper surface, a lower surface, and outer edges; the plurality of tiles collectively having a perimeter, the remediated playground surface having acceptable characteristics in terms of absorbtion of impact energy when tested by an approved test method.

Optionally the plasticised polyvinyl chloride composition is a recycled material

In a first related aspect, the invention provides a tile for a remediated playground as previously described in this section wherein the resilient nature of each tile owing in the first instance to its composition is enhanced by inclusion of a plurality of supported voids beneath the upper surface so that upon impact the upper surface is capable of being temporarily deformed into at least one void, having the effect of increasing the acceptable characteristics in terms of absorbtion of impact energy as compared to a tile having no voids; the or each tile having predictable characteristics in relation to absorbtion of impact energy applied to the upper surface.

In a dependent aspect each mat comprising the array of modular playground mats is cast in a mould having an internal shape that causes the inclusion of complementary interlocking shapes around the perimeter of the mat, so that any one mat may be joined along at least one edge to at least one adjoining mat.

Preferably the or each tile has predictable characteristics in relation to absorbtion of impact energy by the upper surface, and has known characteristics in relation to surface friction of the upper surface, so that the characteristics in terms of absorbtion of impact energy of the remediated playground may be predicted.

Preferably also the or each tile has predictable characteristics in relation to friction between the upper surface and an item of footwear.

Preferably the or each tile is secured about the outer edges to adjacent tiles by a process involving welding the tile edges together with heat.

In a related aspect, the invention provides a method for joining interlocking mats, wherein each mat is welded to adjoining mats by means of a heating process that heats and liquefies the perimeters of adjoining mats, so that the adjoining mat perimeters become merged, and upon cooling the adjoining mats are welded together.

In one option, the heating process comprises the controlled application of hot air from a heating device.

In a preferred option, the heating process comprises the passage of a controlled electric current through wires laid into the array of mats along mat perimeter lines during installation, so that the adjoining mat perimeters are at least partially liquefied and become merged and upon cooling the adjoining mats are welded together.

In a second related aspect, the invention provides a perimeter enclosure for a plurality of mutually adherent modular tiles for a remediated playground as previously described in this section; the perimeter enclosure comprising an elongate beams comprised of an upper strip and a parallel lower strip side by side, and a third connecting strip opposite an open side thereby forming a rectangular groove along the length of the beam; the perimeter enclosure being capable of being fastened to a substrate, the groove having a width such that it will closely encompass and restrain an exposed edge of a modular tile, so that the tiles around the edge of the remediated playground cannot inadvertently be lifted above the height of the shared upper surface.

Preferably the open side of the elongate strip (the groove) has sufficient depth to accommodate expansion and contraction of the array of tiles in a horizontal plane, when in use.

In one option, the lower strip extends further from the base in a direction towards the groove than the upper strip, so that, when in use, the lower strip may conveniently be fastened to a substrate.

In another option, the upper strip extends further from the base away from the groove than the lower strip, so that, when in use, the extended upper strip protects the corner between the upper strip and the joining strip from damage.

In a dependent aspect, the upper strip is made with an inherent bias or natural curvature tending, when in use, to force said upper strip down against the tile surface, and said upper strip is terminated at each side with a sloping edge.

In a second broad aspect the invention provides a method for providing a remediated playground as previously described in this section; the method comprising the steps of (a) repairing the original surface so that the surface is flat and has consistent properties at least in terms of impact attenuation; (b) laying an array of prefabricated modular mats on the topmost surface; (c) adhering the mats together by their edges, and (d) affixing the array of mats to the perimeter of the playground by means of the perimeter enclosure.

Preferably the method includes provision of resilient preferred underlying materials as required overall or at particular positions for repair of the original surface before being covered by the array of mats, so that the original surface is made flat and has substantially even characteristics in terms of absorbtion of impact energy.

Preferably the method includes the steps of assessing the existing impact attenuative properties of the original surface, and more preferably assessing the impact attenuative properties of the surface after remediation by means of an accepted Standard test Method, before the remediated playground is accepted for use by children.

The description of the invention to be provided herein is given purely by way of example and is not to be taken in any way as limiting the scope or extent of the invention.

Throughout this specification unless the text requires otherwise, the word “comprise” and variations such as “comprising” or “comprises” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

FIG. 1: is a diagram showing in perspective an underside view of a remediation type mat, to be used as a module, showing the “supported voids”.

FIG. 2: is a cross-sectional diagram showing how the perimeter of the playground surface may be finished against the surrounding soil.

FIG. 3: is a cross-sectional diagram showing a way to finish a perimeter of the playground surface against a hard perimeter.

FIG. 4: is a diagram showing a cross-section of an edging extrusion.

FIG. 5: is a diagram showing a cross-section of another edging extrusion, with a fastener.

FIG. 6: is a cross-section of the FIG. 5 extrusion in use, nailed or otherwise fastened to a concrete foundation.

FIG. 7: graphically shows the before and after remediation impact properties of two remediated sites (playgrounds) in terms of their impact resistance.

A typical application for the present invention takes an existing playground surface which will fail or is likely to fail to meet various criteria including (a) that shock (impact attenuation) behaviour of the surface should pass the minimum standard test, (b) the surface should be complete and unbroken, (c) and the surface should be not slippery and should have a “grip” according to the relevant standard test, currently as previously described in the Background. The invention proceeds to cover that existing playground surface, flattened or built up if necessary, with a factory-made surface comprised of modular mats which are constructed so as to inherently provide the required characteristics. The underlying intention is to at least cut down the rate of accidents such as long bone or skull injuries that occur to children in playgrounds; at least those that result from impact with unduly hard surfaces.

As shown in the cross-sectional elevation diagram in FIG. 2, the invention comprises a new playground surface, comprised of modular pre-constructed interlocking playground mats 201 (underside shown in FIG. 1) made of a resilient material also having a specific, inherently resilient, open, shaped structure, placed upon a layer of a geotechinical textile 205, which in turn is placed on the existing “poured-in-place” material 206. As necessary, the surface of the original playground 206 is built up or is flattened so that it forms a consistently flat surface. In the event that the original surface is rock-hard it may be necessary to first cover it with a resilient layer such as a “poured-in-place” layer.

Mats according to the invention are each a modular unit, and for example each mat is 20 inches square. Mats may be delivered already made up in (for example) 2×2 modules at the factory or by a distributor. Mats are generally cast from a polyvinyl chloride (vinyl; PVC) composition including plasticisers, filler, and pigments as is known in the art. By way of a non-limiting example, one composition is: plasticiser 4.4%, fillers 25.1%, stabilisers 1.5%, polyvinyl chloride 66.8%, and pigments 2.1%. The composition of the mats should, when appropriately tested, provide a Shore hardness of about 86 Shore, for a desired balance between durability and desired friction.

A particular structure is favoured although the Example shown here is but one way to provide supported voids beneath a flat (or perhaps sculpted for grip, or perforated) upper surface. A perspective drawing of a portion 100 of the underside of a mat is shown in FIG. 1, showing how the supported voids into which the upper surface of the mat may be deformed by impact during use, are created. The scale of this example is such that the centres of the legs 102 are spaced apart on a 1.5 inch matrix. Each leg has a number of feet 103 which carry the static weight of the mats and any loads placed on the mats. Each set of four legs surrounds an area 101 with transverse bars 105 that help stop the legs deviating from straight, and which bear some load. Each area 101 is perforated so that the top side comprises groups of partially rectangular holes 104 in sets of 4 and spaced apart on a rectangular array at 1.5 inch spacings. Mounds or dimples are moulded into the top surface and in combination with the hole perimeters, assist to a small extent in providing friction. When in use, some dirt and some sand may collect under each set of holes but this does not detract from performance until a lot of sand has collected in which maintenance is required. The holes also admit water which should be drained away. Mats are held together around their edges at least by interlocking lugs and sockets (not shown here except as rectangles 202). Welding and gluing may also be used to create sheets of mats. It will be appreciated that the cavity construction together with the inherent resilience of the plasticised vinyl, allows such mats to meet or exceed the required impact or shock behaviour characteristics. Note that a solid block of the PVC material would have much less resilience than the formed shapes of the mats, and due allowance should be made for hardening caused by cold weather or by loss of plasticiser.

FIG. 2 is a sectional elevation diagram through an edge 200 of a playground, surrounded by grassed soil, after remediation. 201, 201 are individual mats and 202 is one interlocking lug helping to bond the edges of those mats together. The edge of the playground substrate 206 (the poured-in-place material), which may be much thinner than shown in this diagram, is demarcated in this example by a buried wall 207A, of concrete (reinforcing steel not shown) or perhaps of wood. 207 is an example base of concrete, for containing the resilient poured-in-place material 206. 208 is a screw, spike, pin or other fastener used to attach the mats along the top of the buried wall. An optional layer of geotechnical cloth to be placed between the tiles and the existing poured-in-place material is shown as the dotted lines 205. FIG. 2 shows a preferred way (provided as a non-limiting example) to merge the playground surface with the surrounding grass 203 so that a user cannot trip over a projecting surface is to slope the mats (e.g. mat 201A) down into the surrounding earth 204, and allow grass 203 to grow on top of the earth around the perimeter. Beam 209, shown in section, helps to hold the free edges of the mats together.

There may not be any surrounding grass or soil. For that case, FIG. 3 is a sectional elevation diagram through an edge of a playground, surrounded by a hard permanent surface 211 such as asphalt or concrete, after remediation.

In this version, the perimeter is finished with a novel elongated plastic edging or extrusion 210 (examples shown in detail as a U-shaped cross-section in FIG. 4 and in FIG. 5) that is pushed on to the edges of the outermost mat 201A which may optionally be curved downwards as shown. A preferred material is polyvinyl chloride or other plastics material; perhaps a mixture of a plastics with an elastomeric polymer. Use of materials safe for children is of course advisable. The material should be tough, flexible, weather-resistant and sunlight-resistant so that it has a good service life. The perimeter enclosure may be described as an elongate beam comprised of an upper strip and a parallel lower strip side by side, with a third connecting strip opposite an open side thereby forming a rectangular groove along the beam, as shown in FIGS. 4, 5 and 6. The perimeter enclosure is capable of being fastened to a substrate whereupon the groove has dimensions such that it will closely encompass an exposed edge of a modular tile and then restrain the encompassed tile, The plastics edging may be nailed down, such as by corrosion-resistant nail or other fastener 208 through the mat 201A, and into a substrate such as the wooden rail 209 which surrounds the playground area. The extrusion has the effect of providing a neat border around the mats, fixing the periphery of the mats in relation to the ground surface, and preventing the edges from being lifted up. It must be realised that the extrusions shown in FIGS. 4 and 5 are but two versions of a possible range. The space 401 fits tightly around a perimeter or a cut edge of a standard tile after any projecting lugs of the perimeter mat are cut off. FIG. 5 shows an improved version with an extra leaf 512 which serves to protect an underlying peripheral rim of (for example) concrete, and protects the otherwise exposed outer corner of the extrusion. Note that the edges 411 and 512 which are the exposed edges are preferably chamfered. Also, the die through which the extrusion is formed may include a curve or bend (see FIG. 5 such as the line of 512 as compared to the line of 411) ensuring that the extrusion tends to hold the inserted tile around space 401. The lower part 413 typically extends further than part 411. Preferably a series of drainage holes 514 is provided along the extrusion to release any collected water. Typical sizes for extrusions according to the invention are: about 0.125 inches (3 mm) thick. FIG. 4 shows a cross section with a shorter upper limb 210, finished off at a tangent 411, a longer lower limb 413 (here, 1.75 inches (45 mm) that is used for nailing or pinning on to deeper structures, and a rising portion 414. The inside height of the space 401 is slightly larger than the height of a standard plastics tile as moulded. In this example the space A is seven eighths of an inch (22.23 mm) in height. The inventor has noted that free material such as sand or small stones near the edge of an area of tiles may find their way under the tiles, lifting the edges and causing a raised object that people can trip over. Also, people may be able to vandalise an area of mats by lifting them up from around the edges. This extrusion is capable of coping with dimension changes over time caused by thermal expansion or by loss of plasticiser or the like.

The slight bend that is shown in the upper surface of FIG. 3 is optional.

In FIG. 6 details of the FIG. 5 extrusion placed against a concrete perimeter are shown. The concrete has been made with a rebate large enough to accommodate the extrusion; in this example about 1 inch (25.4 mm) deep and 1.65 inches (42 mm) wide. This section shows two concrete nails as example fasteners (208, 208) that are used in sufficient numbers along the edge to restrain the extrusion and keep it in line. The extrusion is fixed in place first, and then the modular tiles 201 are cut to size and inserted into the slot 401. The poured-in-place material will be located to the right of the concrete perimeter, underlying the array of resilient playground tiles. It will be noted that the perimeter is inevitably not as “soft” as is the majority of the playground surface.

The remediation process comprises the following steps: 1. Test the impact absorption capacity of the existing surface in critical areas and replace any deficient areas either by inserting shock pads, or by supplementing, or increasing the existing depth of the “poured-in-place” surface with a newly formulated poured-in-place composition. It is appreciated that some operators may not do an initial test but the results will show whether the tiles will be sufficient on their own or whether further resilient surface such as a shock pad or a poured-in-place layer is needed. 2. Make the existing surface (which will become the surface under the cloth layer 205) flat and preferably also level, by filling in gaps with a resilient material having similar properties to those of the remainder of the existing surface. This becomes the substrate. 3. Prepare an edging (as described above, according to whether there is soil or a hard surface bounding the playground) by means of which the new modular mats will be restrained and the edge will be finished and protected. Within the playground area, the interlocked mats are usually not downwardly attached to the underlying substrate. 4. Lay a geotextile fabric 205—preferably comprised of felted hard-wearing and ultra-violet and environmentally resistant material typically made of glass fibre—over the substrate. Where there is existing equipment, such as posts supporting swings, the geotextile fabric is cut so as to surround the posts. Step 4 is optional. 5. Lay down mats 201 as supplied. They may be provided pre-welded; for example in sets of four—as 40 inch squares. Where there is existing equipment, such as posts supporting swings, the mats are cut so as to surround the posts. A hot-air gun is helpful to heat and soften the mats which can then be cut with a knife. 6. The mats are attached to each other by means of their complementary lugs and pockets and are preferably sealed together, so that a continuous surface is formed over the entire playground. A glue can be used to seal the mats together, but a more preferred method includes passing permanently embedded horizontal wires along the perimeter of each mat about half way between the upper and the lower surfaces, then putting the wires under tension, which wires may later be used for permanent restraint. As a step during installation, a controlled electric current is passed along the wires for a period of time in order to melt the surrounding plastic and hence to weld the mats together. That preferred welding method is preferred over use of a glue, because it has been noted that the plasticiser from within the mat material tends to invade the glue over time and soften the glue so that it comes away from the body of the tiles. 7. Verify (on-site) that the finished surface meets the Critical Fall Height Requirements as outlined in the current ASTM F1292-04 or in other relevant, accepted standard tests. 8. Optionally, further tests may be applied to check that the friction provided by the finished surface (such as between a person\'s shoes and the mat surface) meets or exceeds the requirements of, for example, ASTM E303-98. This is a predictable aspect of each tile.

FIG. 7 shows some test results in bar-graph form. The vertical axis 701 is the measurement of Head Injury Criteria (HIC) as outlined in ASTM F 1292-04 for a Critical Fall Height (CFH) of 8 feet. The horizontal axis 702 displays six test positions from two test sites. The drop test amounts to recording the amplitude of an impulse made by dropping a specified mass from a specified height. A better-absorbing mat provides a smaller HIC. The horizontal line at 1000 signifies the maximum HIC imposed by ASTM F1292-04 for the tested CFH, in this case, 8 feet. As shown in FIG. 7, use of the invention results in a substantial improvement of the shock behaviour of the surface, (as reduction in HIC) when tested according to ASTM F1292-04. The shock absorbtion behaviour of a number of installations has been tested before and after placement of the additional mats and the results are plotted graphically in FIG. 7. The horizontal line at 1000 is the limit set by ASTM F1292-04. Any measurement above 1000 fails the standard test as defined. At site 1, the existing surface was slightly worse than the limit, and at site 2 the existing surface was about twice as bad. In both cases, the new measurements, made after the process according to the present invention was carried out, were below the prescribed limit.

A vinyl composition has been described in particular, since the Applicant\'s products are at this time based on PVC. The invention extends to rubber compositions, which have the advantage of having less temperature-dependent properties than those of vinyl, by which we mean that a mat tested on a hot day will be substantially more resilient than if tested on a freezing day. The nibber composition may use at least some recycled rubber such as from car tyres, and it may use syiithetic rubber such as “Neoprene”. Other suitable resilient materials may be brought into use in the near future.

A foamed mat (in which the “voids” previously described are bubbles) having an unfoamed top surface could be used in place of the moulded versions described herein. However foam mats tend to be less predictable in terms of their properties at the time of manufacture, and do not allow for perforations. Hence there is no widely distributed drainage facility, which the perforated mats do have. Furthermore there is less sideways strength for use in perimeter bonding.

In the event that the original surface has no effective resilience at all, one solution is to prepare and apply a “pour-in-place” resilient composition over the surface.

Optionally, the existing pour-in-place composition can be removed to a desired depth around fall zones around equipment, and shock pads can be installed beneath the final layer of mats as described previously in this specification.

The same edging could be used in factory floors (for example) using this tiling for its ergonomic features, where tripping somebody up could result in a serious accident. It is by no means limited to outdoors uses.

The performance of the finished surface of a playground after resurfacing according to the invention can be guaranteed to the purchaser, since the properties of the finished surface are under control during manufacture of the modular mats. In contrast, there is a possibly variable composition and mixing and curing of a mixture that had been made up at a site. Each mat may be tested before shipping from the factory.

In situations where the original surface did not have enough “give” or resilience, and therefore exposed users to an increased risk of injury, the finished surface should meet the relevant standards.

Building a more resilient surface on top of an existing surface is usually preferable, in terms of sustainability and conservation of resources, to removing and disposing of the existing surface and replacing the existing surface with another.

An existing playground such as one of the type that is “poured in place” can be repaired and brought up to meet the relevant standard, so that the area is rendered safer for play than it would otherwise have been, without the complications of total removal and replacement of the resilient mass.

Further, those responsible for the playground have some defence against claims of negligence in the less likely, but still possible event of injury; particularly if the remediated playground has been certified by test against an accepted Standard.

In regard to the extrusions, their use is visually appealing and they define the tiled space. Tile edges are protected from impact damage. Tiles can\'t easily be lifted up around the edges because the edges are restrained and because there is a seal to block the ingress over time of sand or small stones. The extrusions allow some scope for shrinkage of tiles over time, before the edging has to be lifted up and moved.

Finally, it will be understood that the scope of this invention as described by way of example and/or illustrated herein is not limited to the specified embodiments. Where in the foregoing description, reference has been made to specific components or integers of the invention having known equivalents, then such equivalents are included as if individually set forth. Those of skill will appreciate that various modifications, additions, known equivalents, and substitutions are possible without departing from the scope and spirit of the invention as set forth in the following claims.