Improved use of re-purposed types for creating a roadway

Abstract

Disclosed is a method of forming the base of a roadway. The method comprises the steps of providing a generally planar ground surface 10 and placing over that surface a lower geotextile sheet or layer 20. Tyre cylinders 30 are placed upon the lower geotextile which are formed by removing the side walls from vehicle tyres with the cylinders being laid radially on the geotextile layer. The cylinders and the surround of the cylinders are filled with a composition 40 comprising an aggregate. A further upper geotextile sheet or layer 50 is placed upon the surface before laying a running surface 62 for traffic upon the upper geotextile layer, wherein the lowest layer of the running surface for traffic is a hot lay tar macadam. The upper geotextile layer may be formed of a thermoplastic or may comprise polyethylene or polypropylene. Also disclosed is a base of a roadway formed from the above method.

Description

Approximately 55 million waste tyres are created in the UK each year. The walls of the tyres may be detached and partly reused, for example by breaking down into 'crumb' for subsequent incorporation into other products or combusted to produce energy. This leaves the tyre treads, or more correctly the cylinders, here termed tyre cylinders left after a used tyre has had its tyre walls removed. These are not permitted for use in landfill and are difficult to recycle as they represent a composite of rubber, fabric and steel. It is therefore desirable that alternative uses of these cylinders may be found. Numerous uses of such waste tyres are known, for example they may be used to form the basis, when attached together, to form a road base, such as disclosed in US 5846021. The use of the tyre cylinders to form a road base is also disclosed in WO 2006 / 078485. The use of the tyre walls may also be used for a similar purpose such as disclosed in US 6457912. There are also very many disclosures for the use of used tyres to form walls, embankments and other such structures. In the first phase of such use the simple ability to find an alternative re-purpose of such waste material was sufficient and such road bases were readily adopted for forest roads, industrial areas and similar places were a quick and durable road base was required. However, now that a supply chain for recycled tyre components has been established there is a need to provide better engineering solutions so that a higher volume of waste tyre material may be effectively used. To achieve this methods of use conforming to conventional road construction techniques and requirements is needed. A number of problems can arise from the straightforward laying of tyres to form structures. One of the principal problems is that it is difficult to fill the structure of the tyre effectively and therefore irregular voids can be created and these can often fill with water which may stagnate and the underlying structure may be irregular. This is partly overcome by the use of tyre cylinders but these also present challenges. One problematic aspect of road construction is that on higher speed roads not only 5 must the road be resistant to abrasion and whether but also a very consistent and even surface must be created to avoid undue vibration and with it driver fatigue, vehicle maintenance and for the road constructor and maintainer additional maintenance. In addition, new forms of tyre are becoming increasingly prevalent. Whilst current 10 market penetration may be of only a few percent a few percent of 55 million still represents a very considerable amount of material. There is an ongoing need for improved use of tyre waste to facilitate the effective repurposing of used tyres. The present invention The present invention in its various aspects is as set out in the appended claims. The present invention provides a method of forming the base of a roadway, the method comprising the steps: a. providing a generally planar ground surface; b. placing over said surface an optional, lower, geotextile sheet or layer; c. placing upon said lower geotextile a plurality of tyre cylinders, being the product of vehicle tyres from which the side walls have been removed; d. wherein the tyre cylinders are laid radially on said ground or geotextile surface; e. infilling said tyre cylinders and surround with a composition comprising an aggregate; optionally compacting said aggregate; f. optionally repeating steps c, d and e; g. placing over said surface a further, upper, geotextile sheet or layer; h. laying a running surface for traffic over said upper geotextile; wherein: the lowest layer of the running surface for traffic is a hot lay tar macadam. As disclosed in the background section, the use of tyre cylinders for the production of a roadway base is known, however such use is generally being for utility roads and, were more widely used, for example in the United States, finished with a concrete surface. It being no accident that the predominant product in the US is produced under the mechanical concrete (RTM) brand. However, high quality roads in Europe generally use a hot lay tar macadam and these can give problems if used with tyre waste as heated tyre waste can produce toxic gases. For example, sulphur used in vulcanizing rubber can give rise to the evolution of sulphur compounds and hot tyres produce various mixes including hydrocarbons, including plasticiser elements which give some degree of volatiles. The use of hot lay tar macadam over tyre waste is therefore uncommon. In the present invention, a geotextile is placed over said tyre waste and this provides an insulating layer to stop or reduce the tyres from being unduly heated up. When laying macadam on a road the lowest layer of macadam, called the base course, is typically in the order of between 10 and 15 centimetres thick. This therefore carries a large amount of heat energy and effective insulation by the geotextile can be achieved. Whilst placing a layer of aggregate over the tyre waste would be an alternative solution this gives the disadvantage that the underlying stability due to the tyres is lost as the effective upper layer is simply a thin layer of aggregate which can readily break up and give rise to potholes et cetera. The present invention therefore enables the use of tyre waste as an effective base for a road in conjunction with hot lay tar macadam. In the present invention, the upper geotextile sheet or layer is preferably formed of a thermoplastic and has a glass transition / melting temperature of less than 170 degrees centigrade. Hot lay tar macadam is typically laid at a temperature between 130 and 166 degrees centigrade and the use of a geotextile with said glass transition temperature (or melting point depending upon what is the correct scientific measure for a given polymer type), has the very beneficial effect that at the temperature and pressure (bearing in mind that a 10 centimetre layer of tar macadam produces a 240 kilograms a square metre pressure) causes the geotextile to bond or at least conform to the tyre waste (which as previously mentioned is preferably in the form of tyre cylinders) and therefore produces a much more stable at road base structure. That this is beneficial is evident from the prior art were the great difficulty and expense of connecting tyre waste laterally (see US 584 6021) by means of nuts and bolts is considered worthwhile. An equally strong if not stronger bonding by producing a layer of geotextile which is effectively melt bonded onto the tyre waste is far more effective and durable. In terms of the present invention the running layer is therefore preferably a layer of hot lay tar macadam of greater than 2cm up to 25cm laid in a single pass. As will be appreciated this is more preferably in the range 5 to 20 centimetres most preferably in the range 10 to 15 centimetres. Typically further layers will be added subsequently but it is this first layer which is the most important for the present invention. For the purposes of the present invention then the running layer is referred to as tar macadam, which may be referred to as tarmac, asphalt, blacktop, pavement (US), asphalt (or asphaltic) concrete, bituminous asphalt concrete, and bituminous mixture. However, the common essential feature is that the material comprises a hot melt bituminous mixture in conjunction with stone aggregate. Stone aggregate is a general term for mixed stone particles which are typically admixed with other materials in construction work. Particulate sizes range from millimetres two centimetres and are commonly known in the industry. The term aggregate is used herein. Whilst the definition of hot lay tar macadam is known in the art if the definition is required then it is a tar macadam or asphalt with an in use laying temperature in the range 275°F (135°C) and 330°F (166°C). The geotextile of the present invention preferably comprises polyethylene or polypropylene, or mixtures thereof. These materials are both readily available, durable, waterproof, good insulators and become plastic / melt at the required temperature. The preferred material is polypropylene or high-density polyethylene when laying a thick base course, such as 15 centimetres or greater. It is found that under high temperature and pressure a polymer melting point around 160 degrees centigrade is beneficial so is to provide bonding without fluid flow. The preferred material is low density polyethylene when laying a thin base course, a base course of between 5 and 10 centimetres. It is found that under low temperature and pressure then adequate bonding / melting is more readily achieved with low density polyethylene with a melting point around 130 degrees centigrade. When laying, i.e. utilising the method of the present invention in cold weather, cold weather being at a temperature of less than five degrees centigrade then the use of low-density polyethylene is generally preferred. When laying, i.e. utilising the method of the present invention in hot weather, hot weather being as a temperature of greater than around 20 degrees centigrade then the use of high-density polyethylene or polypropylene is generally preferred. The geotextile for use in the present invention, for the upper layer may preferably be a nonwoven. Nonwovens come in many forms but essentially a nonwoven is a form of felt in which fibres are laid randomly to form a mat. The advantage of a nonwoven is that it gives better thermal insulation and therefore less heat is passed through to the underlying tyre waste thus more readily avoiding the problem of gaseous evolution from a tyre waste. The preferred thickness of the geotextile for use in the present invention, in the upper layer is between 3 and 20 millimetres in thickness. More preferably between 4 and 10 millimetres in thickness. This is particularly so in the case of a nonwoven as this can give very effective insulation. The upper geotextile may preferably also comprise particulate carbon. A high surface area particular carbon suitable for the absorption of gases is preferred. The particulate carbon serves to absorb gases which may be evolved, such as from the rubber / plastics component of the tyre cylinders and thus provides increased safety and environmental protection. It should be appreciated that whilst the benefits of the present invention require that the upper geotextile is laid in direct contact with the tyre waste, i.e. the tyre cylinders, it may be possible to have a thin layer of other material present, such as sand however this is not generally desirable as it can be unclear whether any let alone sufficient bonding takes place between geotextile and tyre waste. Some layer of material above the geotextile such as sand, though preferably no thicker than one or two centimetres, particularly if dry sand is used may still be suitable particularly if a thick base layer of tarmac is laid as the melting / bonding of the geotextile can still take place to any protruding upper edges of the tyre cylinders. This layer is most preferably absent. In the present invention the tyre cylinders may be joined by means of nails filed by email gone through the walls of the tyre cylinders where they abut so as to join the tyre cylinders. This is a highly effective means for joining the tyre cylinders and does not require the drilling of any holes and the metal reinforcement of the tyre cylinders, as an inherent feature of the construction of a radial tyre tread which is the predominant form of tyre used acts to retain the nails in place. In the present invention the tyre cylinders may be secured to the planar ground surface by means of staples, not shown in the diagrams, which loop over the top of one or more of the tyre cylinders and penetrate through any geotextile layer or layers, through the aggregate, if the aggregate is present at the point of attaching the staples and into the planar ground surface. This improves the efficiency of road construction and the regularity of placement as the tyre cylinders do not move around during placement of the aggregate into the tyre cylinders to form the road base. It is also advantageous in that the staples can act to secure the geotextile layers, particularly the upper geotextile layer 50 so as to stop it being disturbed, such as blown away while awaiting the laying of the running surface for traffic over the previous layers. Drawings The present invention is illustrated by means of the following schematic drawings in which like features are designated with like numerals. The figures provide: figure 1 shows a vertical’s cross section through a base of the roadway of the, and formed by the method, of the present invention; and figure 2 shows a vertical cross section showing an intermediate stage of the method of the present invention were the hot lay tarmac is being placed upon the foundation layers of the present invention. The features of the drawings are listed as follows: 10 a generally planar ground surface; 20 optional, lower, geotextile sheet or layer; 30 a tyre cylinder, being the product of vehicle tyres from which the side walls have been removed; similar visual indications represent further instances; 30a a tyre cylinder, being the product of vehicle tyres from which the side walls have been removed, a plan view juxtaposed for ease of interpretation; 40 infill composition comprising an aggregate; 50 upper, geotextile sheet or layer; 52 melting / deforming upper geotextile sheet or layer; 54 deformed / melted upper geotextile sheet or layer; 56 bonding of upper geotextile sheet or layer with tyre cylinder; 60 running surface for traffic; and 62 laying a lowest layer of a hot lay tar macadam as part o or being the running surface for traffic over said upper geotextile. Detailed description Figure 1 shows a cross-section of a road base 100 and the present invention as created by the method of the present invention. The ground for the road base is typically prepared using conventional means to provide a planar ground surface 10 with some degree of stability upon which a road can be constructed. Upon this is placed a first geotextile layer 20. Whilst this is optional it reduces the potential for subsequent layers to admixed with the ground layer and thus undermine the road over time. Upon the lower layers are placed a plurality of tyre cylinders (30) preferably abutting, most preferably alternating so that one tyre will typically touch six other tyres on the outer radius of each cylinder. This layer is then infilled with an infill composition 40 comprising a stone aggregate such as mixed stone between one and 10 millimetre in size. This aggregate is then optionally rolled or compacted to consolidate the aggregate. The upper edges of the tyre cylinders 30 (cf 56) should protrude above or be as an equal height to, very less advantageously slightly below, the upper level of the aggregate. An upper geotextile layer 50 is then laid over the upper edges of the tyre cylinders and therefore also over the infill composition. The road surface is then completed by provision of an upper tar macadam layer or layers 60. The base layer of which being a hot lay tar macadam. The steps of the method of the present invention are as described above with figure 2 illustrating the underlying mechanism of the present invention. In this figure the base layers 20, 30, 40, 50 are placed over the ground 10. A hot lay tar macadam base layer 62 is then rolled out (i.e. poured / pushed out, and preferably compacted by rolling) over the upper geotextile layer as shown by the arrow. As the hot lay tar macadam, being hot, such as at the 150 degrees centigrade advances over the upper geotextile layer the geotextile layer 50 starts to melt / deform 52 typically becomes more compact 54 and acts to bind to the tyre cylinders 56 thus securing the tyre cylinders in place. This securing may be by means of an actual melt bond but simple deformation of the geotextile layer so as to conform to the circle of the cylinder and is in itself sufficient to give some degree of additional integrity to the role structure. During this process the upper geotextile layer serves to insulate the tyre cylinders from excessive heat thus minimising the evolution of any gaseous component from the rubber materials.

Claims

1. A method of forming the base of a roadway, the method comprising the steps: a. providing a generally planar ground surface;b. placing over said surface an optional, lower, geotextile sheet or layer;c. placing upon said lower geotextile a plurality of tyre cylinders, being the product of vehicle tyres from which the side walls have been removed;d. wherein the tyre cylinders are laid radially on said ground or geotextile surface;e. infilling said tyre cylinders and surround with a composition comprising an aggregate; optionally compacting said aggregate;f. optionally repeating steps c, d and e;g. placing over said surface a further, upper, geotextile sheet or layer;h. laying a running surface for traffic over said upper geotextile;wherein:the lowest layer of the running surface for traffic is a hot lay tar macadam.

2. The method of claim 1 wherein said upper geotextile sheet or layer is formed of a thermoplastic and has a glass transition temperature of less than 160 degrees centigrade.

3. The method of claim 1 or claim 2 wherein said upper geotextile sheet comprises polyethylene or polypropylene.

4. The method of claim you will three wherein said upper geotextile sheet comprises polyethylene.

5. The method of claim 4 wherein said upper geotextile sheet comprises low density polyethylene.

6. the method of any preceding claim wherein said upper geotextile sheet is a nonwoven.

7. The method of any preceding claim wherein said upper geotextile sheet is between 3 and 20 millimetres in thickness.

8. The method of claim you will seven wherein said upper geotextile sheet is between four and 10 millimetres in thickness.

9. The base of a roadway formed by the method of any preceding claim.

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