Tire recycling

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Tire arm chair Tyre Arm Chair.jpg
Tire arm chair
Tires are among the most problematic sources of waste. Progress in recycling has resulted in a major reduction in dumping. Holice, hromada pneumatik (01).jpg
Tires are among the most problematic sources of waste. Progress in recycling has resulted in a major reduction in dumping.

Tire recycling, or rubber recycling, is the process of recycling waste tires that are no longer suitable for use on vehicles due to wear or irreparable damage. These tires are a challenging source of waste, due to the large volume produced, the durability of the tires, and the components in the tire that are ecologically problematic. [1]


Because tires are highly durable and non-biodegradable, they can consume valuable space in landfills. [1] If waste tires are improperly managed they may cause rubber pollution. In 1990, it was estimated that over 1 billion scrap tires were in stockpiles in the United States. As of 2015, only 67 million tires remain in stockpiles. [2] From 1994 to 2010, the European Union increased the amount of tires recycled from 25% of annual discards to nearly 95%, with roughly half of the end-of-life tires used for energy, mostly in cement manufacturing. [3] [4]

Pyrolysis and devulcanization could facilitate recycling. Aside from use as fuel, the main end use for tires remains ground crumb rubber. [2] [5] In 2017, 13% of U.S. tires removed from their primary use were sold in the used tire market. Of the tires that were scrapped, 43% were burnt as tire-derived fuel, with cement manufacturing the largest user, another 25% were used to make ground rubber, 8% were used in civil engineering projects, 17% were disposed of in landfills and 8% had other uses. [6] Globally, tire graveyards are a common environmental hazard, with significant pollutants and other challenges. For example, the Sulaibiya tire graveyard in Kuwait has had repeat highly toxic fires. [7]

Tire life cycle

The tire life cycle can be recognized through the following steps:

  1. Product developments and innovations such as improved compounds and camber tire shaping increase tire life, increments of replacement, consumer safety, and reduce tire waste.
  2. Proper manufacturing and quality of delivery reduces waste at production.
  3. Direct distribution through retailers, reduces inventory time and ensures that the life span and the safety of the products are explained to customers.
  4. Consumers' use and maintenance choices like tire rotation and alignment affect tire wear and safety of operation.
  5. Manufacturers and retailers set policies on return, retread, and replacement to reduce the waste generated from tires and assume responsibility for taking the 'tire to its grave' or to its reincarnation.
  6. Recycling tires by developing strategies that combust or process waste into new products, creates viable businesses, and fulfilling public policies. [8]
Tires in a natural area after Hurricane Katrina created debris. Tires left in landfills and other waste retention areas are likely to enter the environment during flooding or other extreme weather events. Debris left on the refuge in the wake of hurricane Katrina.jpg
Tires in a natural area after Hurricane Katrina created debris. Tires left in landfills and other waste retention areas are likely to enter the environment during flooding or other extreme weather events.

Landfill disposal

Tires are not desired at landfills, due to their large volumes and 75% void space. [9] Tires can trap methane gases, causing them to become buoyant, or bubble to the surface. This 'bubbling' effect can damage landfill liners that have been installed to help keep landfill contaminants from polluting local surface and ground water. [8] The EU Landfill Directive prohibits the disposal of used tires in landfill. [10]

Shredded tires are now being used in landfills, replacing other construction materials, for a lightweight back-fill in gas venting systems, leachate collection systems, and operational liners. Shredded tire material may also be used to cap, close, or daily cover landfill sites. [11] Scrap tires as a back-fill and cover material are also more cost-effective, since tires can be shredded on-site instead of hauling in other fill materials.

Used tires in foreground waiting to be shredded and shredded tires in background. Tires and shredded.JPG
Used tires in foreground waiting to be shredded and shredded tires in background.

Tire stockpiles create a great health and safety risk. Tire fires can easily occur, burning for long periods, up to a month and also creating substantial pollution in the air and ground. Recycling helps to reduce the number of tires in storage. An additional health risk, tire piles provide harborage for vermin and a breeding ground for mosquitoes that may carry diseases. Illegal dumping of scrap tires pollutes ravines, woods, deserts, and empty lots; which has led many states to pass scrap tire regulations requiring proper management. Tire amnesty day events, in which community members can deposit a limited number of waste tires free of charge, can be funded by state scrap tire programs, helping decrease illegal dumping and improper storage of scrap tires.

Tire storage and recycling are sometimes linked with illegal activities and lack of environmental awareness. [12]


Although tires are usually burnt, not recycled, efforts are continuing to find value. Tires can be reclaimed into, among other things, the hot melt asphalt, typically as crumb rubber modifier—recycled asphalt pavement (CRM—RAP), [13] [14] and as an aggregate in Portland cement concrete [15] Efforts have been made to use recycled tires as raw material for new tires, but such tires may integrate recycled materials no more than 5% by weight, and tires that contain recycled material are inferior to new tires, [5] suffering from reduced tread life and lower traction. [16] Tires have also been cut up and used in garden beds as bark mulch to hold in the water and to prevent weeds from growing. Some "green" buildings, both private and public, have been made from old tires.

Pyrolysis can be used to reprocess the tires into fuel gas, oils, solid residue (char), and low-grade carbon black, which cannot be used in tire manufacture. A pyrolysis method which produces activated carbon and high-grade carbon black has been suggested. [17]

Cement manufacturing

Used tires being fed mid-kiln to a pair of long cement kilns LDWisconsinTireInject.jpg
Used tires being fed mid-kiln to a pair of long cement kilns

Old tires can be used as an alternative fuel in the manufacturing of Portland cement, a key ingredient in concrete. Whole tires are commonly introduced into cement kilns, by rolling them into the upper end of a preheater kiln, or by dropping them through a slot midway along a long wet kiln. In either case, the high gas temperatures (1000–1200 °C) cause almost instantaneous, complete and smokeless combustion of the tire. Alternatively, tires are chopped into 5–10 mm chips, in which form they can be injected into a precalciner combustion chamber. Some iron input is required in manufacturing cement, so the iron content of steel-belted tires is beneficial to the process. [18]

Tire-derived products

Shredded tires Shredded tires.JPG
Shredded tires
Tires can be shredded into small blocks for fuel with a tire shredder Double Shaft Tire Shredder.jpg
Tires can be shredded into small blocks for fuel with a tire shredder
Closeup of shredded tires Shredded tires2.JPG
Closeup of shredded tires
1 ton bags of crumb rubber Tire Crumb.JPG
1 ton bags of crumb rubber

Tires can be reused in many ways, although most used tires are burnt for their fuel value. [19] In a 2003 report cited by the U.S. EPA, it is stated that markets ("both recycling and beneficial use") existed for 80.4% of scrap tires, about 233 million tires per year. Assuming 22.5 pounds (10.2 kg) per tire, the 2003 report predicts a total weight of about 2.62 million tonnes (2,580,000 long tons; 2,890,000 short tons) from tires. [20]

New products derived from waste tires generate more economic activity than combustion or other low multiplier production, while reducing waste stream without generating excessive pollution and emissions from recycling operations. [8]

Tire pyrolysis

The pyrolysis method for recycling used tires is a technique which heats whole or shredded tires in a reactor vessel containing an oxygen-free atmosphere. In the reactor, the rubber is softened after which the rubber polymers break down into smaller molecules. These smaller molecules eventually vaporize and exit from the reactor. These vapors can be burned directly to produce power or condensed into an oily type liquid, generally used as a fuel. Some molecules are too small to condense. They remain as a gas which can be burned as fuel. The minerals that were part of the tire, about 40% by weight, are removed as solid ashes. When performed properly, the tire pyrolysis process is a clean operation and produces little emissions or waste; however, concerns about air pollution due to incomplete combustion as is the case with tire fires has been documented. [22]

The properties of the gas, liquid, and solid output are determined by the type of feed-stock used and the process conditions. For instance whole tires contain fibers and steel. Shredded tires have most of the steel and sometimes most of the fiber removed. Processes can be either batch or continuous. The energy required to drive the decomposition of the rubber include using directly fired fuel (like a gas oven), electrical induction (like an electrically heated oven) or by microwaves (like a microwave oven). Sometimes a catalyst is used to accelerate the decomposition. The choice of feed-stock and process can affect the value of the finished products.

The historical issue of tire pyrolysis has been the solid mineral stream, which accounts for about 40% of the output. The steel can be removed from the solid stream with magnets for recycling. The remaining solid material, often referred to as "char", has had little or no value other than possibly as a low grade carbon fuel. Char is the destroyed remains of the original carbon black used to reinforce and provide abrasion resistance to the tire. The solid stream also includes the minerals used in rubber manufacturing. This high volume component of tire pyrolysis is a major impediment, although this theme continues to be a source of innovation.

Cryogenic recycling

NASA Stennis Space Center worked on cryogenic recycling of tires, in 1995. Cryopolymers (95-557-24).jpeg
NASA Stennis Space Center worked on cryogenic recycling of tires, in 1995.

Tires can be frozen using cryogens, or super-cold fluids, then broken down and made into a material called "crumb," which can be used in asphalt road beds, agricultural hoses, and truck bed liners.


Three boys are on a tire swing Three Boys on a Tire Swing.JPG
Three boys are on a tire swing
Car tires as seats in Thailand. Car tires as seats in Thailand.JPG
Car tires as seats in Thailand.
Tire art Tire art.JPG
Tire art
Tires recycled into water tanks on roof. Cherchen, Xinjiang. Tires recycled into water tanks on roof. Cherchen, Xinjiang.jpg
Tires recycled into water tanks on roof. Cherchen, Xinjiang.

Aside from recycling old tires, the old tire can be put to a new use.

Old tires are sometimes converted into a swing for play. The innovative use allows for an easy way to find a purpose for an existing old tire not suitable for road use. [23]

Used tires are also employed as exercise equipment for athletic programs such as American football. [24] One classic conditioning drill that hones players' speed and agility is the "Tire Run" where tires are laid out side by side, with each tire on the left a few inches ahead of the tire on the right in a zigzag pattern. Athletes then run through the tire pattern by stepping in the center of each tire. The drill forces athletes to lift their feet above the ground higher than normal to avoid tripping. [25] Other athletic uses include tire flipping (tractor or large truck tires typically used) or for upper cardio conditioning by hitting a tire repetitively with a sledge hammer. [26]

Re-purposed tires can also be harnessed as an affordable alternative building material used in the framework of rammed Earth thermal mass dwellings. [27] This is beneficial across scales of production such as individually sustainable housing. [28]

Rows of stacks of tires are often used as barriers in motor racing circuits as a method of dissipating kinetic energy over a longer period of time during a crash, comparatively to striking a less malleable material such as a concrete or steel wall.

Many cattle farmers re-purpose old tractor tires as water troughs for their cattle by placing them over natural springs or by piping stream water into them. These tires contain the water and allow it to pool for the cattle without any additional interaction from the farmer. Most farmers also include a drainage pipe near the top or in the center of the tire so excess water can drain off to prevent overflow and erosion around the outside of the tire where the cattle would be. [29]

Repurposing as an elastic base for multipurpurposes uses, such as holding advertisement boards, static or swinging. This is an application still under development and at a prototype stage. [30]

Tire repurposed as an elastic base uses. Prototype Nr.2, Variant Nr.1: Mid-body axle swing sign. Lisbon, Portugal. Tire repurposed as an elastic base for multipurpose uses.jpg
Tire repurposed as an elastic base uses. Prototype Nr.2, Variant Nr.1: Mid-body axle swing sign. Lisbon, Portugal.

Environmental concerns

Due to their heavy metal and other pollutant content, tires pose a risk for the leaching of toxins into the groundwater when placed in wet soils. Research has shown that very little leaching occurs when shredded tires are used as light fill material; however, limitations have been put on use of this material; each site should be individually assessed determining if this product is appropriate for given conditions. [9]

For both above and below water table applications, the preponderance of evidence shows that TDA (tire derived aggregate, or shredded tires) will not cause primary drinking water standards to be exceeded for metals. Moreover, TDA is unlikely to increase levels of metals with primary drinking water standards above naturally occurring background levels. [31]

See also

Tire repurposed as elastic base. Prototype Nr.1, Variant Nr. 1: Three faced stand/support. Lisbon, Portugal. Tire repurposed as flexible base.jpg
Tire repurposed as elastic base. Prototype Nr.1, Variant Nr. 1: Three faced stand/support. Lisbon, Portugal.

Related Research Articles

<span class="mw-page-title-main">Tire</span> Ring-shaped covering that fits around a wheels rim

A tire or tyre is a ring-shaped component that surrounds a wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide traction on the surface over which the wheel travels. Most tires, such as those for automobiles and bicycles, are pneumatically inflated structures, which also provide a flexible cushion that absorbs shock as the tire rolls over rough features on the surface. Tires provide a footprint, called a contact patch, that is designed to match the weight of the vehicle with the bearing strength of the surface that it rolls over by providing a bearing pressure that will not deform the surface excessively.

<span class="mw-page-title-main">Waste management</span> Activities and actions required to manage waste from its source to its final disposal

Waste management or waste disposal includes the processes and actions required to manage waste from its inception to its final disposal. This includes the collection, transport, treatment, and disposal of waste, together with monitoring and regulation of the waste management process and waste-related laws, technologies, and economic mechanisms.

Thermal depolymerization (TDP) is the process of converting a polymer into a monomer or a mixture of monomers, by predominantly thermal means. It may be catalysed or un-catalysed and is distinct from other forms of depolymerisation which may rely on the use of chemicals or biological action. This process is associated with an increase in entropy.

<span class="mw-page-title-main">Asphalt concrete</span> Composite material used for paving

Asphalt concrete is a composite material commonly used to surface roads, parking lots, airports, and the core of embankment dams. Asphalt mixtures have been used in pavement construction since the beginning of the twentieth century. It consists of mineral aggregate bound together with bitumen, laid in layers, and compacted. The process was refined and enhanced by Belgian-American inventor Edward De Smedt.

<span class="mw-page-title-main">Plastic recycling</span> Processes which convert waste plastic into new items

Plastic recycling is the processing of plastic waste into other products. Recycling can reduce dependence on landfill, conserve resources and protect the environment from plastic pollution and greenhouse gas emissions. Recycling rates lag those of other recoverable materials, such as aluminium, glass and paper. Through 2015, the world produced some 6.3 billion tonnes of plastic waste, only 9% of which has been recycled, and only ~1% has been recycled more than once. Additionally, 12% was incinerated and the remaining 79% sent to landfill or to the environment including the ocean.

<span class="mw-page-title-main">Crumb rubber</span> Recycled rubber produced from scrap tires

Crumb rubber is recycled rubber produced from automotive and truck scrap tires. During the recycling process, steel and tire cord (fluff) are removed, leaving tire rubber with a granular consistency. Continued processing with a granulator or cracker mill, possibly with the aid of cryogenics or by mechanical means, reduces the size of the particles further. The particles are sized and classified based on various criteria including color. The granulate is sized by passing through a screen, the size based on a dimension or mesh. Crumb rubber is often used in artificial turf as cushioning.

<span class="mw-page-title-main">Retread</span> Re-manufacturing process for tires that replace the tread on worn tires

Retread, also known as "recap", or a "remold" is a re-manufacturing process for tires that replace the tread on worn tires. Retreading is applied to casings of spent tires that have been inspected and repaired. It preserves about 90% of the material in spent tires and the material cost is about 20% compared to manufacturing a new one.

<span class="mw-page-title-main">Tire fire</span> Events involving the combustion of tires

Tire fires are events that involve the combustion of large quantities of tires, usually waste tires, typically in locations where they are stored, dumped, or processed. They exist in two forms: as fast-burning events, leading to almost immediate loss of control, and as slow-burning pyrolysis which can continue for over a decade. They are noted for being difficult to extinguish. Such fires produce much smoke, which carries toxic chemicals from the breakdown of synthetic rubber compounds while burning.

Rubber mulch is a type of mulch used in gardens and landscaping that is made from recycled rubber, most often crumb rubber sourced from waste tires.

<span class="mw-page-title-main">Construction aggregate</span> Coarse to fine grain rock materials used in concrete

Construction aggregate, or simply aggregate, is a broad category of coarse- to medium-grained particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates are the most mined materials in the world. Aggregates are a component of composite materials such as concrete and asphalt; the aggregate serves as reinforcement to add strength to the overall composite material. Due to the relatively high hydraulic conductivity value as compared to most soils, aggregates are widely used in drainage applications such as foundation and French drains, septic drain fields, retaining wall drains, and roadside edge drains. Aggregates are also used as base material under foundations, roads, and railroads. In other words, aggregates are used as a stable foundation or road/rail base with predictable, uniform properties, or as a low-cost extender that binds with more expensive cement or asphalt to form concrete. Although most kinds of aggregate require a form of binding agent, there are types of self-binding aggregate which do not require any form of binding agent.

<span class="mw-page-title-main">Automotive shredder residue</span>

The shredding of automobiles and major household appliances is a process where a hammermill acts as a giant tree chipper by grinding the materials fed into it to fist-size pieces. The shredding of automobiles results in a mixture of ferrous metal, non-ferrous metal and shredder waste, called automotive shredder residue or automobile shredder residue (ASR). ASR consists of glass, fiber, rubber, automobile liquids, plastics and dirt. ASR is sometimes differentiated into shredder light fraction and dust. Sometimes these residual materials are called "car-fluff".

There is no national law in the United States that mandates recycling. State and local governments often introduce their own recycling requirements. In 2014, the recycling/composting rate for municipal solid waste in the U.S. was 34.6%. A number of U.S. states, including California, Connecticut, Delaware, Hawaii, Iowa, Maine, Massachusetts, Michigan, New York, Oregon, and Vermont have passed laws that establish deposits or refund values on beverage containers while other jurisdictions rely on recycling goals or landfill bans of recyclable materials.

Rubberized asphalt concrete (RAC), also known as asphalt rubber or just rubberized asphalt, is noise reducing pavement material that consists of regular asphalt concrete mixed with crumb rubber made from recycled tires. Asphalt rubber is the largest single market for ground rubber in the United States, consuming an estimated 220,000,000 pounds (100,000,000 kg), or approximately 12 million tires annually.

<span class="mw-page-title-main">Tire-derived fuel</span>

Tire-derived fuel (TDF) is composed of shredded scrap tires. Tires may be mixed with coal or other fuels, such as wood or chemical wastes, to be burned in concrete kilns, power plants, or paper mills. An EPA test program concluded that, with the exception of zinc emissions, potential emissions from TDF are not expected to be very much different from other conventional fossil fuels, as long as combustion occurs in a well-designed, well-operated and well-maintained combustion device.

<span class="mw-page-title-main">Demolition waste</span> Waste debris from destruction of buildings, roads, bridges, or other structures

Demolition waste is waste debris from destruction of buildings, roads, bridges, or other structures. Debris varies in composition, but the major components, by weight, in the US include concrete, wood products, asphalt shingles, brick and clay tile, steel, and drywall. There is the potential to recycle many elements of demolition waste.

Recycling can be carried out on various raw materials. Recycling is an important part of creating more sustainable economies, reducing the cost and environmental impact of raw materials. Not all materials are easily recycled, and processing recyclable into the correct waste stream requires considerable energy. Some particular manufactured goods are not easily separated, unless specially process therefore have unique product-based recycling processes.

Products made from a variety of materials can be recycled using a number of processes.

Micronized rubber powder (MRP) is classified as fine, dry, powdered elastomeric crumb rubber in which a significant proportion of particles are less than 100 µm and free of foreign particulates. MRP particle size distributions typically range from 180 µm to 10 µm. Narrower distributions can be achieved depending on the classification technology.

<span class="mw-page-title-main">Tire recycling in the United States</span>

Tire recycling in the United States is the disposal and reuse of waste tires.

Tire-derived aggregate (TDA) is a building material made of recycled tires, which are shredded into pieces of varying sizes. It is commonly used in construction projects because it is sustainable and lightweight, along with being less expensive than many competing available materials. In 2007, an estimated 561.6 thousand tons of TDA were produced. This accounted for about 12 percent of the total recycled tire material used. Particle sizes less than 12mm are considered crumb rubber.


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