AU712740B2 - Improvements in artificial surfaces - Google Patents

Description

WO 96/32174 PCT/AU96/00219 1 IMPROVEMENTS IN ARTIFICIAL SURFACES FIELD OF INVENTION The present invention relates to an improved artificial surface and to processes for producing same. The artificial surface has particular application as a weatherproof track for sporting and recreational events, such as horse racing and other equestrian events, and childrens playgrounds.

BACKGROUND

ART

In the horse racing industry, without question, turf is the optimum surface for horse racing. However, as the industry continues to expand, turf cannot consistently be expected to perform as a constant training medium. The vagaries of climate, long term wear and tear through training on the surface and the latent cost of maintaining such a surface, provides racing administrators many problems.

The construction of roads across racing tracks so as to allow vehicles access to vehicle parking space within the perimeter of the race track also presents many problems, not the least of which is the gradual deterioration and hardening of the road surface. After prolonged use, such road surfaces may present hazards to horses and jockeys alike.

In the past, and at present, solutions to the age old dilemma of turf track deterioration seem to be made by reverting to traditional surfaces such as sand, cinders and, to a lesser degree, woodchip.

Sand and cinders drain well but can harden and cause abrasive injuries to horses in training. Varying depths of the material through age and use render the tracks dangerous and the users vulnerable to injury.

This includes jockeys as well as horses in circumstances when particles are thrown up by the horses galloping action. These types of tracks require constant daily servicing to replenish and level the circuit but they are the best that are available currently.

Woodchip was once a very popular surface for horse racing tracks but due to its initial high installation cost and the fundamental requirement of constant irrigation to keep the fabric pliable, it brought about its own downfall through rot and surface deterioration.

Recently, a new and revolutionary style of training track was introduced into Australia. This was the "Equitrack", a French product that utilised oils, bitumens and polymers in various proportions to form a track surface that was expected to solve all the needs of the horse racing industry. It was very expensive to install, had a very limited life span and had a high cost in ongoing maintenance. The Australian Jockey Club, after having the facility for only two years, has ordered its removal, and is presently considering the idea of regressing to a sand track in its stead.

It is an object of the present invention to overcome or substantially ameliorate the disadvantages of the prior art.

SUMMARY OF THE INVENTION 0: According to the invention, there is provided an artificial surface comprising a cold mixture of rubber and a polymer modified bitumen emulsion, mixed in a proportion and laid under a controlled downward pressure sufficient :0 20 to produce a water permeable and flexible surface facilitated by air pockets in the laid surface.

Preferably, the artificial surface includes aggregate and filler material.

It is preferred that a catalyst is also present in the mixture.

The aggregate may be basalt and the filler may be cement dust. The catalyst may be water.

Preferably, the rubber and polymer modified bitumen emulsion are in a proportion of 5:1.

Preferably, the rubber is derived from shredded tyres.

According to another aspect of the invention, there is provided a method for producing an artificial surface comprising cold mixing rubber with a 2/09/99 polymer modified bitumen emulsion in a proportion sufficient to produce a water permeable and flexible surface facilitated by air pockets in the surface when laid, and thereafter laying the surface under a sufficient controlled downward pressure to produce said air pockets.

DESCRIPTION OF PREFERRED EMBODIMENT In order that the invention may be more readily understood and put into practical effect, reference will be made to the accompanying examples of methods for producing artificial surfaces and the surfaces thereby produced.

EXAMPLE 1 Recycled and reconstituted rubber is cold mixed with a standard polymer modified bitumen emulsion in a 5:1 ratio at ambient temperature in a o:0: slurry machine for about five minutes. Additional polymer corresponding to the polymer used in the polymer modified bitumen emulsion is added to the 1 mixture in an amount of about 15% of the total polymer concentration.

15 Variation of the amount of polymer used in the mixture will vary the hardness of the surface.

After cold mixing, the compounded mixture is forced through a screeding board by an internal auger which exerts downward pressure on the mixture whilst distributing and laying the mixture onto an impervious base to 20 the specific depth required. A possible pressure to be applied so as to force the material through the screed is between 20 to 50 kilos per square meter.

Similar laying results can be obtained by using a standard road paving machine which operates on corresponding principles. For racetracks the depth can vary from between 60 mm to 100 mm depending upon the specific requirements.

The surface of the present invention may be tailored for specific applications by varying the amount of polymer in the mixture.

Racetracks and trotting tracks require a firm surface, so the components are mixed at the highest ratio i.e. using 15% polymer. Greyhound tracks require a softer surface so, accordingly, the polymer is altered to a mix with only 10% polymer. Childrens playgrounds are softer 2/09/99 WO 96/32174 PCT/AU96/00219 4 still so a mix is used with less than 8% polymer, but walkways for stables, etc. are hardened even more than the 15% by coating the surface with an ethyl vinyl acetate polymer from a suitable sprayer machine (which is purpose built for high temperature spraying) in a mix of 5% of the total emulsion used in the preparation of the surface.

Therefore, if 5 kg of emulsion is used in mixing, 250 grams of the e.v.a. polymer is required to coat, seal and further harden the surface. This is done by heating the e.v.a. polymer to a temperature of 200 0 C then spraying it upon the top surface using, in small areas, a spray bar and, in larger areas, a suitable sprayer machine. Surface hardening can also be provided by using the exact same method as described above but substituting the standard polymer modified bitumen plus 15% extra polymer for the e.v.a. polymer. In some cases, this may be necessary for specific racetracks.

The factor that is consistent with all such mixes is the "honeycomb" effect created by mixing then laying without excessive downward pressure.

This generates air pockets critical for water permeation or percolation and drainage and reflex properties and makes the artificial surface of the invention sympathetic to users. Should too much pressure be exerted in laying the artificial surface, it is likely that the mixture will compound and loose the above mentioned attractive properties.

Once the artificial surface is laid, it may be held in place by erecting on either side thereof special barriers. These barriers are initially made in moulds using the same proportions of mix 5:1 plus 1 of sand or crusher dust, and the moulds are 160 mm high x 120 mm wide. The barriers are permitted to cure for approximately 48 hours, then removed from the moulds in 5 metre lengths, transported to the site of the laid artificial surface and joined together and to the surface by direct heat and a small amount of bitumen. The barriers may be coloured and may be of variable height as desired.

WO 96/32174 PCT/AU96/00219 When the track surface is formally laid in its full dimension, it may be sealed with a polymer modified bitumen emulsion. If the base upon which the surface is laid needs to be made impervious to water penetration, the aforementioned emulsion can be sprayed in such an amount that it bleeds through to the base, thus forming a seal on the base whilst binding the surface. The extra amount of emulsion needed for this exercise is 10% of the specific mix. For instance, if 1 kg is used in the mix, an extra 100 grams is needed for the bleed process.

Curing of the surface material in normal temperatures takes about 48 hours for a standard 90 mm thick surface, but surfaces that are above or below the 90 mm thickness level will take proportionally longer or shorter time to cure.

When curing is complete, the surface is then coloured as desired with a high grade ultraviolet protective acrylic paint that is sprayed onto the surface. This cures within 24 hours depending upon the ambient temperature.

In some cases, a top coat of coloured material is sprinkled loosely over the finished surface to a depth of approximately 60 mm.

The aforementioned surface is useful in racetracks but could also be used for other applications, e.g. playgrounds, equestrian arenas, etc.

EXAMPLE 2 In order to produce a thinner and harder surface that retains water permeable and flexible properties, nine parts of recycled rubber are hot mixed with one part of e.v.a. polymer modified bitumen emulsion in a drum plant at 200 0 C. The resultant heated mixture is then pushed through a screed for laying. The screed determines the depth of the surface which is typically about 60 mm for athletic tracks, trotting tracks and horse walkways.

WO 96/32174 PCT/AU96/00219 6 EXAMPLE 3 A particularly preferred artificial surface of the invention is prepared according to the following method. The artificial surface is useful as part of a road for vehicles crossing a horse racing track.

Prior to laying the said artificial surface, a road base across a horse racing track is prepared. The road base is compacted, hardened and stabilised so as to withstand the constant pressure of both equine and vehicular traffic thereon and to be consistent and durable. The road base should be made according to known industry specifications, comprise a depth of about 150 mm, and be cambered or angled downwardly to one or more drainage systems, such as a spoon drain, sump, pipe or garden. In some instances, a cambered road base of concrete or like material may be used.

The road base may be sealed with conventional prime seal, such as a hot bitumen spray, and then may be re-primed with a polymer modified sealing material to produce a membrane over the road base that is both waterproof and flexible. The membrane is then permitted to cure for 24 to 48 hours depending upon ambient weather conditions.

The membrane over the road base acts as a waterproof seal and protects the road base from erosion. It also facilitates the rapid flow of water in the direction of the cambered surface to the sides of the road base where the water may be drained from the road base by established drainage sumps and the like.

A layer of aggregate of particle size between about 7 and 10 mm may cover the membrane sealed road base.

The combination of road base, membrane and aggregate provide a long term, stable foundation for further layers to be applied thereon.

The artificial surface of the invention is then applied over the aggregate layer which provides a high surface area for bonding of the artificial surface.

WO 96/32174 PCT/AU96/00219 7 The artificial surface is produced by cold, dry mixing in a "PAVESEAL" (trade mark) mixing machine (used for road making) a combination of about 32.8% w/w recycled, reconstituted or new rubber (of mesh size about 7 to 16), about 32.8% w/w mineral aggregate (of up to 7 mm diameter) such as basalt, sand or crusher dust. Added to this mixture is about 4.8% w/w filler, such as cement dust and fly ash, about 2.6% w/w catalyst, such as water, and about 27% w/w polymer modified bitumen emulsion.

The use of mineral aggregate, filler and water catalyst in the making the artificial surface of the present example is preferred and may affect the flowing capabilities and chemistry of the mixture, as well as the final hardness of the surface.

In a further preferred form, the emulsion includes 17.5% w/w latex and the mixing is done at an ambient temperature of about 250C. Also, the polymer may be e.v.a. or SBS.

The above preferred formula may be altered to provide artificial surfaces that vary in their degree of hardness. The mixing may also be conducted hot, rather than cold, depending on the required use. If the weather temperature is significantly outside the ambient range, variations may be made to the quantity of components used in the formula at the site of production. The length of mixing time is also dependent on such conditions.

The mixing machine has a calibrated continuous external flow means and a means for constantly monitoring the concentrations of the mixed components during the external flow. The various concentrations and overall density of the mixture are monitored constantly whilst the mixture is poured out of the machine and the mixture can be regulated according to these factors if required.

The monitoring thus helps to calibrate either an increase or decrease in the quantities of components and the speed of pouring. The flow box of WO 96/32174 PCT/AU96/00219 8 the mixing machine from which the mixture is poured is at a height that can be adjusted according to the specific requirements.

The mixture comprising a preferred artificial surface of the invention is laid over the aggregate in an even distribution at a depth of between about 65 mm and 100 mm to provide optimal impact absorption and water permeability. The layer is then allowed to air cure for about 40 minutes depending on weather conditions, before it is subject to controlled downward pressure by hydraulic vibrating and rolling machinery. The application of downward pressure must be of such a magnitude as to form a tightly gripped, water permeable and shock absorbent mat over the road base foundation. The rolling of heavy machinery assists in the binding of the rubber and other components of the artificial surface.

During the curing and rolling process, some of the artificial surface layer may "break" due to evaporation. This "breaking" phenomenon, which is common in bitumen road making, is theorised to reduce the amount of emulsion which is involved in direct bonding to the rubber.

The extremities of the artificial surface layer may be further sealed to prevent physical deterioration thereof by spraying with a hot bitumen spray or by building retaining walls.

The artificial surface of this example has the following properties and advantages over prior art surfaces:- 1) Unprecedented high level drainage 2) High stress absorption 3) High post yield resistance 4) Superior anti-strip properties High tensile strength 6) High resistance to temperature extremes 7) High resistance to ultra violet radiation and oxidation 8) Low maintenance 9) Extended track longevity WO 96/32174 PCT/AU96/00219 9 1 0) True in all weather surfaces 11) Environmentally friendly and uses recycled materials 12) Virtually soundless when in use 13) Dust and insect free surface 14) A surface that does not require any watering or chemical treatments The artificial surface layer may be overlaid by an overcushion surface of laterally serrated rubber shavings of between about 20 mm and 80 mm maximum width depending on requirements of use. The shavings are randomly cut top and bottom to provide a maximum coefficient of friction.

This overcushion surface of rubber shavings forms a helpful interlocking protective matrix over the artificial surface layer whilst permitting a high rate of air and water percolation therethrough under all weather conditions.

It also compliments the shock absorbing properties of the artificial surface.

The overcushion surface and/or the artificial surface may be coated and coloured by a coloured surface coating material that inhibits ultraviolet radiation induced damage to the surfaces, strengthens the rubber component of the surfaces, and provides a seal against oxidation of the emulsion and other components. Coating may be carried out over small to large areas by variously sized spray machines. The coating material also compliments the impact absorbing properties of the surfaces, can flex and bend with minimal flaking or peeling, and retains its colour over time and wide ranging weather conditions.

The coating adds weight to the surfaces, thereby reducing wind and rain caused scattering of the rubber shavings, and provides a colour appearance that may blend aesthetically with the surrounding environment.

In general, the artificial surface of the present invention has advantageous qualities that include water permeability, high resistance to temperature extremes, high resistance to ultraviolet rays and oxidation, WO 96/32174 PCT/AU96/00219 high stress and shock absorption and recovery post yield, high tensile strength, and superior anti-strip properties.

Various modifications may be made in details of design and construction without departing from the scope or ambit of the invention.

Claims (6)

1. An artificial surface comprising a cold mixture of rubber and a polymer modified bitumen emulsion, mixed in a proportion and laid under a controlled downward pressure sufficient to produce a water permeable and flexible surface facilitated by air pockets in the laid surface.

2. The artificial surface of claim 1 and including aggregate and filler material.

3. The artificial surface of claim 2 and including a catalyst.

4. The artificial surface of claim 2 wherein the aggregate is basalt and the filler is cement dust. e* The artificial surface of claim 3 wherein the catalyst is water.

6. The artificial surface of claim 1 wherein the rubber is derived from shredded tyres.

7. A method for producing an artificial surface comprising cold mixing rubber with a polymer modified bitumen emulsion in a proportion sufficient to produce a water permeable and flexible surface facilitated by air pockets in the surface when laid, and thereafter laying the surface under a sufficient controlled downward pressure to produce said air pockets. Dated this 2nd day of September, 1999 PROTRAK AUSTRALIA PTY LIMITED Patent Attorney for the Applicant PETER MAXWELL ASSOCIATES