Department of the Environment

About us | Contact us | Publications

Settlements Header ImageSettlements Header ImageSettlements Header Image

Publications archive - Waste and recycling

Disclaimer

Key departmental publications, e.g. annual reports, budget papers and program guidelines are available in our online archive.

Much of the material listed on these archived web pages has been superseded, or served a particular purpose at a particular time. It may contain references to activities or policies that have no current application. Many archived documents may link to web pages that have moved or no longer exist, or may refer to other documents that are no longer available.

A National Approach to Waste Tyres

Commonwealth Department of Environment, 2001

8.4 Reuse

8.4.1 Used tyres

Used (partly worn) tyres can and are reused without further treatment. Sources of used tyres include:

It could be argued that these used tyres do not fit within the definition of waste since they will continue to be used for their original purpose (as a tyre) even though they are no longer on the original vehicle. The continued ability to meet their design function is determined by safety considerations and personal taste rather than waste reduction objectives. A major sink for worn tyres is used car saleyards. The aggregate number of tyres involved is relatively small and the current informal arrangements deal with these tyres in a satisfactory way. It is considered that they do not warrant special waste policy attention.

In addition, used tyres are imported into Australia at the rate of 500,000 per year, and Australia exports approximately 350,000 used tyres annually, based on ABS figures. It has not been possible to obtain estimates of the breakdown of used tyre imports. Further, it would appear that imports of used tyres are misreported to a significant extent and even the aggregate estimates may understate the actual numbers. It is known that there is a legitimate trade in truck and bus casing imports for retreading. However, frequent comments have been received from industry and government representatives that a significant number of imported used passenger tyres have little (or no) useable tread left, do not meet Australian safety requirements or are unsuitable for retreading. Some tyres are in such poor condition that they are disposed of immediately on arrival in Australia, and anecdotal evidence suggests that the numbers are significant.

The implications for this study are that tyres with little or no residual useful life are entering the country and adding to the waste tyre management problem, but there is no robust estimate of the significance of the consequent impacts.

Overall, the reuse of tyres is a small but valuable means of ensuring that the maximum possible life is derived from the majority of tyres. Poor practices in relation to imports of tyres may be giving this aspect of the industry an undeservedly poor reputation.

8.4.2 Retreading

Of rather more importance than the direct reuse of partly worn tyres is retreading. Retreading is a general term that includes a range of technologies to replace the wearing surface of the tyre. The types of retreading are discussed in Table 8.1.

Of all the beneficial uses of waste tyres, retreading has the potential to extract the greatest value. The process of retreading involves the removal of the residual tread (which has no further value in relation to the tyre function) while retaining the full value of the casing. Casings do not wear out due to friction, as with the tread, but are subject to fatigue, which ultimately renders the casing unserviceable, and also suffer from traumatic damage due to impacts. It is of interest to note that due to the smaller diameter a passenger tyre is subject to more deflections per unit of distance and will therefore suffer fatigue failure/damage at a greater rate than does a truck or bus casing. This is one of the reasons that truck tyres tend to be able to be retreaded more often than passenger tyres.

About 450,000 truck tyres are retreaded each year and about 50 to 70% of all new truck tyres are suitable for retreading when their tread is worn to below legal limits. Prices for retreaded tyres are about 20% less than those for the cheapest new tyres though the price differential varies considerably. Many truck operators utilise a lower cost option by retreading their own casings, and this saves about 30% of the retreading cost.

About 1 million passenger tyres are retreaded each year and one of the major users is reported to be taxis.

Table 8.1 Methods used in retreading

Cold capping A pre-formed new ‘tread’ is bonded to a prepared casing. The tread can be either a strip, which is joined to the tyre, or a ‘ring’, which is stretched over the casing.
Hot capping A new ‘tread’ is remoulded by placing a prepared casing in a mould with new rubber compound. This is then heated under pressure causing the new tread to vulcanise and bond to the casing.
Remoulding Similar to hot capping but involves resurfacing the tyre from ‘bead to bead’ including a veneer on the sidewalls

All retreads fitted to vehicles are required to comply with the provisions in the Australian Standard AS 1973-1993: Pneumatic tyres passenger car, light truck and truck/bus Retreading and repair processes. However, anecdotal evidence suggests that the quality of retreads varies significantly, ranging from retreads which are to all intents and purposes of equal serviceability as a new tyre in relation to safety and life performance, through to inferior retreads perhaps on poor quality casings which do not meet AS 1973-1993.

While market acceptance is a major barrier (at least in the case of passenger tyres) to an enhanced rate of retreading, consultation with industry representatives suggest that the greatest constraint is the availability of suitable casings. Currently approximately 70% of truck tyres are suitable for retreading while only 15 to 20% of passenger tyres are suitable for retreading. The significant difference in the rates of retreading is due to differences in design and maintenance — truck tyres constitute a substantial proportion of the costs of operating a truck fleet and tend to be maintained to a much higher level than are passenger tyres.

While developments in tyre manufacturing technology have resulted in improvements in the life of tyres, the life of the casing appears to have followed the opposite trend, with evidence suggesting casing life is decreasing. Industry representatives have suggested that ‘cheap’ imported tyres are not generally suitable for retreading. It should also be noted that, increasingly, some locally produced tyres have also been identified as unsuitable for retreading.

Moreover, a number of older car models are fitted with tyres of dimensions that are no longer widely used on more recently produced vehicles. Casings of a size suitable for retreading on these older models (a major market for retreads) are consequently generated at much lower rates.

The type of retreading varies widely from region to region, as does the price, depending on the type and cost of tyre casings available, the capacity (both volume and type) of excisting retreading facilities and the demand for certain tyre types42.

There seems to be a marked difference between the acceptance of truck retreads and passenger retreads by both customers and the tyre and transport industries. It has been remarked that the truck industry would find it difficult to survive without the availability of retreads - truck tyre casings are imported to meet the demand. Some new tyre dealers actually offer a guaranteed buy back price for the casing at the end of a tyre's tread life.

On the other hand, passenger tyre retreads have limited acceptance. The uncertainty associated with retread quality suggests that the buyer would need to be ‘knowledgeable’, and this is a major reason why fleet owners have a high representation in the retread market. Tyre manufacturers have expressed concerns about their brand remaining on retreaded tyres in view of the association of their name with a possibly inferior product over which they have no control and the possibility of product liability implications.

8.5 Recycling

For tyres, recycling is the use of the materials in the waste tyres for different purposes, which may be, but are not necessarily, tyres themselves.

It is the very characteristics of rubber that makes it so suitable for use in tyres (strength, flexibility, chemical stability and durability) that is the source of much of the difficulties in recycling waste tyres. Rubber is vulcanised during manufacture and this process is effective in making rubber relatively inert and difficult to bond or combine with other substances.

For the purposes of this report the recycling practices have been structured along the lines of the preliminary process used to break the tyre down into an end or intermediate product. There is no particular objective basis for the approach adopted other than for convenience and other authors have adopted different structures. Figure 8.2 illustrates the range of recycling practices including energy recovery which is discussed in Section 8.6.

Recycling and energy recovery processes

Figure 8.2 Recycling and energy recovery processes

8.5.1 Crumbing

Crumbing is the production of fine powder, granules or larger particles of rubber mostly associated with careful separation of the rubber from the steel and fabric components. The distinction between shredding and crumbing for larger particles is largely arbitrary. In this study, crumb is defined as rubber that is used as a raw material in subsequent product manufacture. Direct application of shredded rubber was discussed in Part I.8.2.2.

Several means of producing crumb have been developed including wet and dry grinding, high-pressure water sprays and freezing followed by crushing. Review of the literature and discussions with industry representatives point to several other new crumbing processes and it appears that this is quite an active area of research and development as part of continual attempts to improve the economics. In addition to dedicated crumbing processes a significant source of crumb is from retread ‘buffings’ — rubber removed from the tyre cases to prepare them for retreading or during finishing of the tyres after the retreads are applied. There are significant variations in the properties of rubber crumb sourced from each of these processes and, within limits, the properties can be tailored for specific end uses.

The process of making rubber crumb is quite capital intensive. Indicative up-front costs are up to $8 per tyre of annual capacity, and the economies of scale demand an operation processing a substantial number of tyres (no less than say 50,000 to 100,000 per year). The process is also energy and labour intensive and generates noise and dust. The problems associated with crumbing waste tyres have been summarised as43:

Nevertheless, there are substantial quantities of rubber crumb produced in Australia, and recent investments have resulted in significant increases in capacity. This trend is projected to continue into 2001, with further investments in NSW and Queensland. In addition, a Chinese delegation has shown interest in establishing a plant in Australia to make ultra-fine rubber crumb for which there is reported to be considerable demand world-wide, with a projected capacity of 1.5 million tyres per year.

Rubber crumb is traded internationally and Australia both imports and exports crumb. The current applications of rubber crumb in Australia and potential markets are listed in Table 8.2 and are discussed in more detail below.

Table 8.2 Application and market potential of rubber crumb in Australia

Application Current market Potential market Barriers/issues
Roads Australia uses approximately 1,000t of crumb in roads each year. The potential market for rubber crumb in roads is in the order of several hundred thousand tonnes per year, which significantly exceeds the available waste tyre supply. As an aggregate, rubber competes with crushed rock that is less costly to produce and transport.
Roads that use substantial proportions of rubber are reported to have extended life but cost over twice as much.
Rubber is reported to increase emissions if excisting road materials are reused during resurfacing.
Despite numerous studies it is likely that significant testing work over several years would be required before rubber would be used for road making in all States and Territories in Australia.
Moulded products There is a wide range of products made from rubber and synthetics where rubber crumb could be used. The market potential is significant in the order of several million tonnes. Crumb must compete with other readily available fillers.
Markets demand consistent quality and security of supply.
Paving products
Use of rubber crumb in paving products, athletic tracks and equestrian arenas is increasing. Availability of consistent quality cost competitive crumb.
Competition from excisting products.
New rubber products Rubber crumb is added to rubber compound and subsequently into tyres and other rubber products. At 2% addition to new tyres the potential annual consumption is about 4,000 tonnes.
Consumption in other rubber products is of a similar magnitude.
Competition from natural and synthetic rubber, which have superior quality and security of supply.
Adhesives Tile adhesive is reputedly one of the biggest users of rubber crumb, which is currently sourced from retread ‘buffings’. No data have been obtained on this area. This is an excisting market and it is not clear how it would be influenced by the expansion of the crumb industry.
Loose Predominantly ‘soft fall’ material in playgrounds. Mulches, composting aids, aggregate absorption media, explosive stemming and drainage material. Availability of suitable crumb and knowledge of applications.

The market value of crumb is determined by its size and purity. As a general rule, the costs of production for rubber crumb increase with decreasing particle size and increasing purity (removal of metal and fabric). Subsequent applications have varying requirements for size and purity.

Within each of the markets for rubber crumb products there are excisting and potential competing products. Market penetration is limited due to factors such as price and market acceptance of reprocessed products. The ability of the Australian market to use the number of waste tyres generated annually is considered to be limited. In no country, with the exception of the special case of India, has the number of tyres used for rubber crumb yet exceeded 20% of the total waste tyre volume, though this should not be considered an inherent limitation. The current crumb market in Australia is only a few percent but has been described as ‘immature’ and based on international trends and current developments there is significant scope for expansion.

A wide variety of moulded products can be manufactured from rubber crumb including, mats, paving products, athletic tracks, posts and pipes. To make the products the crumb is bonded using a material such as polyurethane. In many applications much of the physical strength of the product comes from the bonding agent and the crumb acts just as filler. As vulcanised rubber is essentially inert, rubber crumb is referred to as ‘dead filler’ and does not contribute directly to the physical properties of the product. As a rule of thumb, the effect of adding an additional 1% of crumb is to weaken the product strength by 1%. The bonds between rubber crumb and other materials or objects (including other rubber crumb particles) are essentially physical rather than chemical in nature and this limits their strength. According to the CSIRO44 the inability to bond rubber crumb to other products restricts the range of applications to low value products where strength requirements are not critical.

As a loose material rubber crumb has a number of applications and it is here that the distinction between crumb and shred becomes blurred. Applications include:

As the requirements for particle size and purity of loose crumb are generally lower than is the case for other applications, this represents a lower cost application for waste rubber. Total use of loose rubber crumb in Australia is unknown though proposals have been put forward in all of the areas listed above.

One of the relatively recent applications in Australia is explosive stemming on mine sites and in quarries45. Trials of rubber crumb have been described as very promising, both technically and economically. The potential for rubber crumb consumption is considerable. As an example, one mine quoted that it consumes in the order of 6,500 tonnes of stemming material per year. Savings could be achieved if the rubber is sourced from waste tyres generated on the mine site though the processing equipment would then need to be brought to the mine. On the financial side, it is understood that this application would require a ‘gate fee’ of the order of $2.50 per tyre to make it competitive with the use of aggregate as a stemming agent. The down side is that the rubber crumb cannot be reused and essentially ends up being landfill in the mine, albeit in a widely dispersed manner and at very low overall concentrations.

The potential applications of rubber crumb in road construction include:

As a fill material, rubber has the advantage that it is lightweight which can reduce the costs of some civil structures particularly on slopes. The occurrence of fires in a number of such applications in the US has prompted concern over this application. Investigation of the fires suggests that while the tyres ultimately provided the fuel they were unlikely to be the source of ignition.

The use of rubber asphalt has been shown in tests to result in an increased economic life by a factor of two or more due to a number of reasons such as reduction in the occurrence of cracking, bleeding and ageing. The surface is also apparently more skid resistant and less noisy. The improved performance comes at a cost penalty multiple of two or three due not only to the higher cost of rubber crumb but also to increases in process time and new practices that are less suited to excisting road making and repair equipment and outside the current experience of operators. Some of the techniques are patented and attract royalties, at least in the US. There are also concerns with increased emissions of air pollutants at the time when the road is refurbished by recycling the surface.

Crumb can be used in asphalt in, so called, wet or dry methods. It should be noted that these general terms cover a range of similar and proprietary processes, and various terminologies are used by different authors. In the wet method fine crumb is mixed with the asphalt prior to mixing with the aggregate. Here the crumb acts as a binder with the asphalt. In the dry method crumb of large and small sizes is blended with the hot aggregate just before it is blended with the asphalt. Here the crumb acts both as a binder (small particles) and as a flexible aggregate (large particles).

Crack seals and repair membranes utilise the flexibility of rubber to provide improved road maintenance performance.

In the US, some States have mandated minimum levels of waste tyre use in road works though there have been delays in implementing this due to legal challenges from the road construction industry. Despite this, considerable quantities of rubber crumb are used in US roads.

It is considered that there is significant scope for expansion in the use of rubber crumb in roads in Australia. Total usage of rubber crumb in roads is estimated to be in excess of 1,000 tonnes per year. Victoria reports that approximately 15% of new road surfaces use bitumen containing combined rubber (approximately 300 lane kilometres out of a total of 2,000 lane km) representing approximately 600 tonnes of crumbed rubber.

Australia's sealed road network is over 320,000 km long, all of which needs periodic maintenance and repair and replacement. It is recognised however that the bulk of this network is ‘spray seal’ bitumen, a process not suited to the inclusion of rubber. The rates of application of rubber crumb in different uses are listed in Table 8.3. No direct statistics on the quantity of road works could be found, but a rough estimate of 5% replacement of roads per year (equivalent to a 20 year life) equates to over 700,000 tonnes of rubber, which is several times larger than the available waste tyre rubber supply.

As a further example, the lane widening as part of the proposed national highway project46 (ignoring town bypasses) represents approximately 4,500 lane km of new road. At a 3% addition the potential consumption of crumb is 80,000 tonnes or nearly 10 million tyres.

Table 8.3 Quantity of rubber used in different road applications

Application Rate of rubber use
Asphalt rubber crack sealant 0.2 kg rubber /kg
Asphalt rubber seal coat 0.6 kg rubber/m2
Asphalt rubber stress absorbing membrane interlayers 0.6 kg rubber/m2
Rubber modified asphalt 3% to 20%

Moving away from road applications, rubber crumb can be added to new rubber compound, which is the starting point for all rubber products. There are a plethora of compound recipes made up of mixes of natural and synthetic rubber and various additives and fillers. Several different compounds may be used in any one product. Rubber crumb replaces some of the natural or synthetic rubber and can both improve handling and some properties, such as wear resistance, while reducing others, such as strength. A few percent is routinely added to many compounds used in new tyres and retreads. In the US, Continental General Tire uses up to 6% of crumb in new passenger tyres47 , and one US car manufacturer is reported to be making a car with tyres that contain 25% recycled content. With surface modification (as discussed below) it is potentially possible to use even higher proportions in tyres and other rubber products. Given that the market for rubber in Australia is of the order of 150,000 to 200,000 tonnes annually the scope for use of rubber crumb in ‘new’ rubber products is considerable.

8.5.2 Devulcanisation and surface treatment

In view of the limitations on end uses of rubber crumb, because of its low bonding strength, considerable effort has gone into developing chemical processes which reverse (in part at least) the vulcanisation of rubber, which is referred to as reclaiming, or in some way modify the surface of the rubber so that it is more easily bonded to other substances. Some of the major techniques that are available are listed in Table 8.4.

Table 8.4 Summary of de-vulcanisation and surface treatment processes

Devulcanisation Devulcanisation is reported to be both energy intensive and utilises a range of chemicals that could harm the environment.
CSIRO process CSIRO have developed a technique that allows the surface of rubber crumb to be modified so as to make it compatible with virtually any other substance.
CSIRO are currently working with a number of companies to complete a demonstration trial and commercialise the process.
TyreRecycle The process has been available for a number of years in the US and also in one plant in Australia. The process involves coating the rubber crumb with latex, which improves its adhesion to other materials.
Gas phase halogenation US company Composite Particles has developed a gas phase halogenation process to oxidise the rubber surface which makes crumb suitable for a limited number of alternative applications.

Numerous other processes have been reported that use a variety of thermal, chemical and even microwave techniques to devulcanise rubber but few if any are used commercially.

Devulcanisation is not new. Prior to World War II it was widely practised, even by the major tyre companies. However, due to rubber shortages during the war, the subsequent development of synthetic rubber and competition from plastics for traditional markets, the economics of devulcanisation changed drastically such that it is now carried out in appreciable quantities only in India48.

Since the recent commercial failure of an operation using a US proprietary process for surface treatment, there are currently no commercial examples of the use of this technology in Australia. However, CSIRO has been active in developing new products and processes and report that they have successfully addressed technological questions in regard to strength and other characteristics. They have joined EcoRecycle in developing markets.

The market for devulcanised and surface treated rubber is complementary to the market for rubber crumb, as overviewed above, and has the potential to increase the quantity of crumb that can be incorporated into products without adversely affecting properties.

8.5.3 Pyrolysis

Pyrolysis involves heating the tyre (usually shredded) in the absence of oxygen. The resulting thermal decomposition of tyres produces:

The gas from the process is generated in sufficient quantities to meet the heating requirements for pyrolysis and little or no external energy is needed.

Markets exist for all of the products of pyrolysis but product quality limits the potential commercial values, as outlined in Table 8.5. Though there are reports of a number of pyrolysis plants operating around the world (none of which are in Australia), apparently none have been particularly successful and the economics of pyrolysis appear to be marginal. Further development is occurring which may shift the economics in the future to bring down costs and improve quality so as to be competitive with similar products made from virgin materials.

Table 8.5 Market potential for some of the major products from pyrolysis

Product Market potential Barriers
Carbon Black Carbon black is used in a wide variety of applications - one of the major users is the rubber industry. Tyres contain approximately 20% carbon black. The tyre industry in Australia consumes approximately 10,000 tonnes of carbon black which could be supplied from processing 40% to 50% of the waste tyres generated. The value of carbon is determined by the purity and VOC content. Achieving the necessary quality standards at a competitive price is a limiting factor.
Oil Pyrolysis oil is similar to diesel and can be used as a fuel. It is reported to be of value to the chemical industry because of its high aromatic content.
Steel There is a large market for recyclable steel and the quantity routinely traded in Australia greatly exceeds the amount that could be produced from processing waste tyres. The steel scrap from tyres contains a number of other metals which affect recycled steel quality. The ‘residuals’ present in tyre steel are likely to limit its value and saleability.

8.6 Energy recovery

Tyres have a relatively high specific energy content (slightly higher, when the steel is removed, than coal), which makes them a valuable fuel source. Worldwide, energy recovery makes up one of the largest end uses of waste tyres, particularly in the US. Tests suggest that the use of waste tyres as a substitute for coal results in lower emissions of oxides of nitrogen and sulphur, as well as greenhouse gases. Concerns regarding dioxins and furans need to be addressed by attention to furnace design and operation. In cement kilns (the only significant use of tyres as fuel in Australia), the long residence times and high temperatures are effective in reducing the organic compounds to carbon dioxide and water and any potentially harmful non-volatile residual materials are encapsulated in the cement product. In addition, the steel in tyres displaces the iron that is added as part of the standard cement product.

The energy recovery options and potential levels of use for waste tyres in Australia are listed in Table 8.6.

Currently approximately 14,000 tonnes of tyres are burnt in cement kilns in Victoria and 11,000 tonnes in Queensland, equivalent to a total of over 3 million EPU per year. Cement industry representatives indicate that they see considerable potential for further applications for fuel from waste tyres. There is potential for three other cement plants to use tyres for energy and mineral recovery, bringing the total potential use of waste tyres by the cement industry to 75,000 tonnes per year or approximately 8 million EPU. The main requirements for further developments to proceed are:

The competition for tyre derived fuel (TDF) comes from other fuels: energy requirements in cement kilns are currently met by fossil fuels (coal or natural gas). The burning of 11,000 tonnes of tyres annually as in Gladstone displaces a slightly higher quantity of coal, say 12,000 tonnes. At a price for delivery of coal to the plant of $25 per tonne, the annual avoided cost is $300,000. Operating costs are increased due to labour and maintenance requirements, and vary according to plant — use of tyres decreases productivity of a cement plant by 5—15 per cent. According to the cement industry, a cement plant needs to receive, on average, in the order of $0.80—$1.20 per tyre (EPU) at the gate for a feasible resource recovery operation. This is within the range of landfill gate fees for shredded tyres.

The cost for modifying the Geelong plant was reported to be $2.6 million in 1993 dollars, which at today's prices would be over $3 million. The cement industry estimate that there is an additional $0.5 million upfront cost for trials and consultation.

A quick analysis suggests that total ‘income’ for an assumed throughput of 1.7 million tyres is $1.7 million (assuming a gate fee of $1 per tyre) plus $300,000 for avoided fuel costs, or a total of $2 million. The income has to cover the cost of capital, provide for depreciation and pay the additional operating and maintenance costs. For a plant with an expected life of ten years, the capital and depreciation charges are estimated to be somewhat less than $1 million per year.

In summary, the use of TDF in cement kilns appears to be an environmentally benign approach to the management of waste tyres (see section 6.4.3 above) and has the advantage of leaving no residue. The cement industry has the capacity to consume a substantial proportion of all the waste tyres generated in Australia. From an economic perspective, TDF appears to be competitive with landfill disposal costs, though Corbett (1999) notes the difference in effective gate fees between Victoria and Queensland.

There seem limited opportunities for costs to be reduced below the estimates given here, since the technology is well established. TDF is unlikely to become more attractive in the future unless there are increases in the real costs of the fuels that it displaces.

8.7 Whole tyres

Whole tyres or tyres that are split or processed in some way have a wide variety of uses ranging from artificial reefs to water tanks. The current uses in Australia and potential markets include:

Increasingly, Australian governments are discouraging some of the more traditional forms of whole tyre applications, or are taking more direct action such as imposing bans or licence and approval requirements. A major reason why such applications have lost favour is that in the past they have often been carried out with little controls. There have been unfortunate experiences with environmental impacts (in relation to mosquitoes and risk of fires), increased erosion or disturbance of stream flows, or the structures have collapsed and loose tyres have become a problem by being washed away.

More recent developments of properly engineered structures using waste tyres offer the prospect for a much more valued use of tyres, which meets engineering standards and environmental requirements at competitive cost levels. An example is the civil engineering applications developed by Ecoflex49 that involve removing one wall of the waste tyre, thus creating a container which is then filled with gravel or other material.

The market at the moment is estimated to be of the order of 200,000 tyres per year. There is considerable potential for using waste tyres in applications such as retaining walls, road base, and as void formers and reinforcing in concrete floor slabs for buildings. Based on current levels of construction activity alone, the last-named process could take the major part of all waste tyres generated in Australia.

The system has the advantage that, unlike TDF and rubber crumb applications, capital costs are low. The equipment costs approximately $10,000 and is easily transported. This is an attractive feature for small remote communities without sufficient tyres to justify major investments or which cannot generate economies of scale. The system could be applied to accumulated waste tyre stockpiles in their area by perhaps sharing the equipment with neighbouring councils.

The analysis summarised by Robinson (2000) suggests that the environmental impacts on a whole-of-life basis are much less than for competing materials. The process uses the entire tyre, leaving no residue. On the economics side, products are claimed to be price competitive with more traditional materials and construction methods to the extent that waste tyres have positive value in absolute terms not just relative to landfill gate fees. There remains the issue of flammability of tyres and this may be of concern in some applications.

A major barrier appears to be conservatism and related poor knowledge in respect to new solutions on the part of engineers and purchasing officers. This observation applies more widely to a number of other products made from waste tyres.

8.8 Discussion

At present, there is insufficient demand for products made from waste tyres using excisting or emerging technologies to divert the greater part of waste tyres from landfill and inappropriate disposal. The causes are both supply-side and demand-side related or, perhaps more accurately, arise from the interaction between supply and demand.

On the supply side, there are limitations of a mainly technological nature to certain recycling options. Strength and other performance characteristics of rubber crumb restrict the range of products made from crumb. There are many competing products in view of the non-exacting strength requirements, and the costs associated with crumbing tyres (as well as the costs of collection, transport and materials handling) make it difficult to get significant market share. In the retread industry, there are reports that a constraint is the availability of good quality casings in the sizes demanded by the market.

There is also the ‘cost’ of supply. Most end users are actually paid for accepting waste tyres (or arrange the collection of tyres directly). The price that can be charged is determined in a market situation by the cheapest management option, which is generally disposal to landfill (or even cheaper, in the case of certain operators, for illegal disposal). Accordingly, landfill gate fees set the price structure within which end-users of waste tyres are forced to operate.

Both recycling and energy applications are capital intensive. One of the risks faced by these investors in these facilities is the difficulty in gaining access to a constant supply of waste tyres. If investment in high-value use of waste tyres is to be promoted then this risk must be managed by arrangements that provide an acceptable level of assurance for the supply of tyres.

On the demand side, a major hurdle to increased sales is market conceptions regarding the quality of goods made from waste tyres. Nowhere is this more apparent than with tyre retreads for passenger vehicles where there has been a significant decline in market share. The price of recycled goods is also a major barrier in very competitive markets. Some opportunities are limited due to the relatively small size of the Australian market and, while there is the potential for exports, production generally needs to be established for the home market to provide a solid base before moving to sell offshore.

Of all the end-uses for tyres, only for tyre derived fuel have schemes been set up which utilise a large proportion of the Australia-wide total. Currently these schemes operate within the cement industry in two States, but there are prospects for extension to other areas. But even the cement industry, in Queensland, has apparently needed to induce an increase in landfill gate fees so as to be able to accept waste at charges that make the operation commercially viable.

On the other hand, there are prospects for growth in the case of rubber crumb, particularly in road making applications. More recent developments appear to have an even greater potential to absorb large numbers of tyres, notably civil engineering applications and use in mine blasting. However, cost pressures and highly competitive end markets suggest that further developments will be needed in one or more of the areas of technology, marketing and institutional arrangements.

There is also promise from the more high technology applications, such as pyrolysis and chemical treatment of the rubber from waste tyres to give it better adhesive properties and therefore greater strength. These are areas that are subject to considerable interest and R&D activity, and it is difficult to forecast with any confidence their future place in managing waste tyres. However, the potential is there for them to absorb a large proportion of the waste tyres generated in Australia, if technological and cost barriers can be overcome (or if economic factors such as a rise in the price of crude oil make their competitors more expensive).

Table 8.6 Options for energy recovery from waste tyres in Australia

Application Current market Potential market Barriers/issues
Cement kilns Approximately 14,000 tonnes/year are consumed in Victoria in cement kilns. The total consumed in Queensland cement kilns in 1999 was 600 tonnes, currently 11,000 tonnes/year and forecast to rise to 30,000 tonnes/year by 2003. Tyres are used as a fuel substitute for coal and natural gas. Between 5 and 7 GJ of energy are used in the kiln for each tonne of cement produced depending on the type. Tyres can be substituted for 15% of the fuel used. Australia produces approximately 7 Mt of cement per year meaning that 10 million tyres can be consumed which is 60% of the total. Resource security.
Overcoming implementation hurdles and approvals at a State level.
Capital cost of $3 million to install feeding and handling works.
Other co-firing
(use of tyres in conjunction with another form of fuel)
A pulp mill in Tasmania has investigated using tyres as fuel in its boilers. The total annual Tasmanian supply of waste tyres could be consumed in only 2-3 months of operation.
A number of studies have been conducted around the world on the co-combustion of coal and tyres and the co-gasification of coal and tyres where the tyres apparently have favourable impacts on the process.
The combustion processes that can be used are limited to those that can burn the tyre without resulting in increased pollution and waste.
Some types of boilers such as coal-fired power stations cannot use tyres because the metal in the tyres causes accretions.
Direct firing A number of tyre powered options have been investigated by various proponents but there are no examples in operation . The energy content of all waste tyres generated each year is equivalent to about 2 weeks of the operation of a typical coal fired power station. Resource security.
Other uses preferred.
Small in comparison to other fuels, that is limited economies of scale.
Blast Furnaces Not currently used. No strong prospects. The zinc in the tyres caused significant operational issues.

9 Findings of Part I

In spite of the deficiencies in the information available, the message from Part I is quite clear. Waste tyres do constitute a ‘problem’ and there is considerable room for improvement in the practices associated with waste tyres and expansion of the markets and uses of products derived from waste tyres. The problem is not directly due to the physical and chemical nature of waste tyres. Rather the problem arises from the failure to recover value from the resource to an adequate extent, as well as the high levels of inappropriate disposal which pose the greatest threats to the environment.

Though it is not a prerequisite or an absolute requirement, improvements in the availability and quality of data and periodic reporting of this data to the general public and the tyre and rubber industry would improve decision-making and policy development.

Part II of the report assesses a range of options that deal with specific aspects of the waste tyre problem identified in Part I, using the information presented there as a basis for evaluation.

 


41 The shelf life of tyres is in fact limited and tyres suffer degradation and embrittlement with age even if not in use, so that after several years they are no longer suitable for ‘new’ tyre applications.

42Personal communication

43Sive (1996) as reported in Corbett (1999).

44Personal communication with CSIRO.

45Stemming is the material that is placed on top of explosives in drilled blast holes to contain and direct the explosion. Blasting occurs regularly in many mines and quarries and involves drilling a series of holes into the material to be removed which are subsequently filled with explosives, ‘stemmed’ and then detonated to break up the material before removal by earth-moving equipment.

46BTCE (1997).

47Continental General Tire (1999).

48 After Snyder (1998) and IRRDB.

49see Robinson (2000).