GB2204801A

GB2204801A - Artificial playing surfaces

Info

Publication number: GB2204801A
Application number: GB08808091A
Authority: GB
Inventors: Henry John Busby Bird
Original assignee: ANGLIAN SPORTSTURF Ltd
Current assignee: ANGLIAN SPORTSTURF Ltd
Priority date: 1987-04-15
Filing date: 1988-04-07
Publication date: 1988-11-23
Anticipated expiration: 2008-04-07
Also published as: GB2204801B; GB8808091D0; GB8709054D0

Abstract

An artificial playing surface comprises a plastics grass layer (5), a free-draining stone sub-base (2) and therebetween a base (3) comprising a hard porous material containing bindable crushed rock, the base (3) having elongate slits (4) filled with granular free-draining material penetrating to the sub-base (2). The hard porous material may contain 5-10% clay, while the granular material filling the lists may be sand or grit. A shock pad of rubber or plastics material may be located between the plastics grass layer (5) and the base (3). <IMAGE>

Description

ARTIFICIAL PLAYING SURFACE The present invention relates to artificial playing surfaces. More particularly, but not exclusively, it relates to surfaces of the type having a layer of plastics grass or artificial turf laid onto a base.

Artificial surfaces are used, for example as football pitches but problems have been experienced with injuries caused by the hardness of the surface, which also causes problems with the bounce of the ball and jarring of the players legs.

Such pitches comprise generally a sub-base, approximately 150 mm thick of freely draining stone, below which are located drains. Above the sub-base is a 40 mm layer of Bitmac, which is also permeable to water. Above this is a shock-pad of rubber or the like in order to provide at least a degree of give to the surface. The artificial turf is laid on top of this pad. Apart from its hardness, Bitmac is an ideal finishing surface for the base since it can be laid reasonably easily with a good degree of levelness, e.g. +3 mm over the surface.

Because of this hardness problem, attempts have been made to substitute the Bitmac with a dynamic base. A final layer of sand has been laid, and this does give.

However, sand suffers from two defects. One is that the sand will move over the lifetime of the pitch. This problem can be overcome by dividing the site into cells, although this obviously increases the difficulties of laying the pitch. However another so far insoluble problem is footmarking. Where a pitch is used for sports, there are many occasions when a player's foot comes down heavily and this will leave a mark in the sand base.

Before the advent of artificial turf pitches, a (RT M) hard porous material known as Redgrator Driplay was used to construct playing surfaces. Such material comprises bindable crushed rock, e.g. limestone or granite possibly containing clays in an optional amount of 5-10% by weight.

Chemical analysis of Redgrai which is a distinctive reddish-brown coloured material with suitable binding properties, shows that it is dolomitic limestone of composition: Calcium Oxide (CaO) 30% Magnesium Oxide- (MgO) 20% Insoluble silicates + SiO2 3% Mixed Iron Oxides (R203) 1.5% Loss on ignition (LOI) 46% The material is crushed to have the following range of particle sizes: BS Test Sieve Accum % 5.00 mm 95 - 100 3.35 mm 85 - 95 2.36 mm 60 - 90 1.18 mm 35 - 65 300 um 20 - 40 150 um 10 - 30 75 um 5 - 20 The material can be spread like sand over the area of the surface, then watered and rolled, upon which it hardens, although not to the same degree as Bitmac.

Pitches made of this material were initially successful but it was found that after a number of years, the fines in the material are washed from the surface to form an impervious layer some 1-1 inches (25-40 mm) below. Heavy rain, or in some cases any rain, therefore rapidly flooded the pitch, which could not drain, and the pitch became (RT) unplayable. For this reason, Redgrakand similar materials are no longer favoured.

It has now been found that the drainage problems of such materials can be overcome and therefore they can be used as a base for artificial playing surfaces. They are easy to lay, have more give than Bitmac and do not suffer the disadvantages of sand.

According to the present invention there is provided an artificial playing surface comprising a layer of plastics grass, a free-draining sub-base and therebetween a base comprising a hard porous material containing bindable crushed rock material, said hard porous material having elongate slits filled with granular freedraining material penetrating to the sub-base.

The hard porous material is for example (RTM) Redgrak It may contain 5-10% clay or clay type material.

The granular material filling the slits is preferably sand or grit.

Preferably the slits are disposed at substantially regular intervals, advantageously at a spacing of between 150 mm and 1 m, preferably 200 mm.

The slits may be 10-20, preferably 13 mm wide and 75 to 125, preferably 100 mm deep.

A shock pad of rubber or plastics material or a geotextile membrane may be interposed between the plastics grass and the base.

An embodiment of the present invention will now be more particularly described by way of example and with reference to the drawing, the single Figure of which is a schematic cross-section through a surface embodying the invention.

Referring now to the drawing, the surface comprises substantially conventional drains 1 surmounted by a sub-base 2, 150 mm thick, of stone. This is free draining to allow surface water to pass through to the drains.

Above the sub-base is a 50 mm thick layer of Redgralor material of similar constitution 3. Cut through this layer are a series of slits 4 at 200 mm centres. The slits are up to 100 mm deep to penetrate to the freedraining sub-base 2. The slits are 13 mm wide and are filled with sand or grit whic allows passage of surface water, even when the Redgr Litself has become impervious.

Above the Redgratlayer 3 is a conventional layer of plastics grass 5. Optionally, a rubber shock-pad or geotextile membrane may be interposed between the grass and the RedgriaLlayer.

In order to lay the surface, the drainage and sub-base are laid conventionally followed by spreading the particulate Redgra)material. This is then watered and rolled and slits are dug along the length of the surface. The plastics grass can then be unrolled on the top.

Machines are available, such as sand groovers or sand placement machines, which can dig a number of these slits and fill them with sand or grit in one comparatively easy operation. A Sand Groover is provided with five or seven rotary blade cutters and works at between 0.5 to 2 mph (1 to 4 km/h). The sand or grit is fed from a hopper at a rate in the region of 0.25 tonnes per minute to the just formed grooves. The groover may be towed behind a tractor with a power take-off.

The artificial playing surface is firm, much firmer than sand, but not as hard as Bitmac. Because of the presence of the slits, it is free-draining. The surface is stable and maintains its level, and also does not mark. The slits may be spaced more widely, in which case they are preferably wider themselves. For example the spacing may be 0.5 to 1 m, and the slit width may be 18 mm.

Claims

CLAIMS:

1. An artificial playing surface comprising a layer of plastics grass, a free-draining sub-base and therebetween a base comprising a hard porous material containing bindable crushed rock material, said hard porous material having elongate slits filled with granular free-draining material penetrating to the sub-base.

2. A surface as claimed in claim 1, wherein the hard porous material contains 5-10% clay.

3. A surface as claimed in either claim 1 or claim 2, wherein the granular material filling the slits is sand or grit.

4. A surface as claimed in any one of the preceding claims, wherein the slits are disposed at substantially regular intervals.

5. A surface as claimed in claim 4, wherein the slits are spaced by between 150 mm and 1 m.

6. A surface as claimed in claim 5, wherein the slits are spaced at 200 mm centres.

7. A surface as claimed in any one of the preceding claims, wherein each of the slits is 10-20 mm wide.

8. A surface as claimed in claim 7, wherein the slits are 13 mm wide.

9. A surface as claimed in any one of the preceding claims, wherein each of the slits is between 75-125 mm deep.

10. A surface as claimed in claim 9, wherein each of the slits is 100 mm deep.

11. A surface as claimed in any one of the preceding claims, wherein a shock pad of rubber or plastics material is interposed between the plastics grass and the base.

12. An artificial playing surface substantially as described herein with reference to the accompanying drawing.