RJA 2013 August-Reclaimed

Rubber Journal Asia Reclaimed Rubber

The rubber road to growth A number of studies have suggested several

Asphalt rubber is a growth market, according to a US tyre recycling firm executive. Jeffrey Kendall, CEO of Liberty Tire Recycling, said that the recycled rubber market has sprung up amidst a weak economy and that asphalt rubber can loosen up the purse strings. He said that an overall acceptability for use of asphalt rubber has been spreading throughout the US and Canada over the years, and thus shows growth potential in the recycling market.

Tyre maker Bridgestone Americas has also shown support in diverting used tyres for rubber asphalt in roads.

Last year, it launched the “Spent Tire Program”, which ensures that for every one tyre sold, a spent tyre is sent to facilities that offer options for valuable use, and asphalt rubber is one option that, the company says, has a strong added value.

sustainable and practical uses for used tyrederived rubber, with the conclusion that these discarded tyres, or at least a large percentage of them, are prevented from making their way into landfills or being burnt. Recovered rubber has found several applications, with increased campaigns for more products with recycled content (except for manufacturing new tyres), says Angelica Buan in this report.

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n end-of-life tyre (ELT) study undertaken by US-based World Business Council for Sustainable Development (WBCSD) (an association made up of member company CEO’s or their representatives) estimates that the global quantity for ELTs is 1 billion/year, with one passenger tyre/person discarded each year in the developed world.

ELT recovery can divert around 4 billion used tyres from being sent to landfills and stockpiles worldwide. Recovered ELTs can augment raw/virgin materials to provide costeffective and sustainable energy for several Industries. Tyre derived fuel (TDF) is a key output for recovered ELTs and is mainly used in cement kilns (as a supplementary fuel), thermal power stations, pulp and paper mills, steel mills and industrial boilers.

Tyres are a higher source of energy compared to most solid fuels, states WBCSD, adding that reused tyres can also be used for civil engineering projects, to replace ground or crumb rubber that is also used in rubber roads.

The US and Japan are the major users for TDF from ELTs, and energy recovery is about equal to material recovery in Western Europe and the US, the report said.

Bridgestone Americas’s tyre recycling programme can benefit rubber asphalt schemes

Over 280 million scrap tyres/year are generated in the US, of which, more than 60 million are placed in stockpiles, according to the South Carolina-based Clemenson University, Department of Civil Engineering. The university says that between 500 and 2,000 scrap tyres can be used in each mile of a pavement.

RTR can also be used to modify the properties of the asphalt in highway construction. For instance, size-reduced RTR can be used either as part of the asphalt rubber binder seal coat, cap seal spray or joint and crack sealant, or as an aggregate substitution (rubber modified asphalt concrete).

But asphalt rubber’s limitations include being temperature sensitive. Also, it cannot be applied in cold or extreme hot weather. The recommended temperature for concrete pavement surface for the material to adhere well is between 85 to 145°F. According to the US-based Rubberized Asphalt Foundation (RAF), new standard specifications have been developed that allow the use of RTR to make the PG 76-22 asphalt that meets temperature requirements and traffic flow. The research foundation says that RTR binders can

A smooth driving opportunity iscarded rubber tyres have found applications in the engineering sector. Asphalt rubber, according to the US Environmental Protection Agency (EPA) website, is the largest single market for recycled rubber tyres (RTR), using approximately 12 million tyres.

Countries such as the US, Australia, UK, China, Brazil, Spain and Germany have started building rubber roads using asphalt rubber. It is made by crumbling used tyre rubber, which is then added to bitumen and ground stone.

This technique renders a quieter road, bringing down traffic noise by 25%, and features shorter braking distance.

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Rubber Journal Asia Reclaimed Rubber be used in place of polymer-modified binders, such as SBS, and achieve the same performance-graded results.

The RTR material is relatively cost effective compared to a polymer binder, and is not subject to chemical production variations and issues with supply/demand.

India and overseas, but the longer service life the technique renders makes its use cost-effective.

The IRB, together with the Kerala Highway Research Institute, has been advocating rubberisation of roads since 1974, with about 50 km of roads in various sites already rubberised to observe performance of the material.

Meanwhile, TIFAC has also been actively promoting the benefits of asphalt rubber. It says that, firstly, low regard against retreaded tyres and their products must be eliminated. Whole used tyres, which are not suitable for retreading may be used as tree guards to prevent erosion; or these can be shredded and crumbed for use as asphalt modifiers for road construction or athletic and recreational fields and as a modifier of polyurethane. Moreover, it strongly suggests that R&D activities in useful recycling and disposal of scrap tyres must be initiated by the industry and the government.

Testing it out in India he Asian civil engineering sector may not have been aggressive in implementing rubber asphalt on a larger scale but studies relating to this are underway.

In India, about 8-15% of tyre rubber crumbs are utilised in the construction and maintenance of roads, according to a rubber recycling study conducted by Delhi-based Technology Information Forecasting and Assessment Council (TIFAC).

The study recognises that crumb rubber improves the visco-elastic properties of bituminous mixes. This then renders various advantages such as improved skid resistance, better crack reflection control, increased flexibility, toughness, tenacity of road surface, reduced noise level of traffic and improved performance under extreme temperature conditions. Nonetheless, the use of crumb as asphalt modifier in India is at an experimental stage, it said.

India’s advantage is the ample local supply of reclaimed rubber and it does not need to import, says TIFAC, adding the other advantages: existing economic reforms, comparably cheap labour and the presence of highly qualified and experienced reclaimed rubber manufacturers.

The India Rubber Board (IRB) has also found, based on its study on reclaimed rubber, that rubberised bitumen (with proper blending of about 2-4% of natural rubber into the bitumen) is an excellent binder for rubble and sand.

The rubberised bitumen lowers the incidence of permanent deformation due to overloading on roads, and is found to be unaffected by changes in atmospheric temperature.

The report also indicated that the use of rubber-modified bitumen in road construction results in as much as 33% savings in repairs and maintenance. Nonetheless, the board estimates that the additional cost for construction of rubberised roads is between 15-20% more compared to bituminous roads, based on commercial trials conducted in

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Innovations in rubber recycling eanwhile, uses for scrap rubber are continually being discovered to replace new materials and prevent a supply rundown or to mitigate the high costs of availing the latter.

One technology by the German Fraunhofer Institute for Environmental, Safety and Energy Technology comes in the form of repurposing rubber residues. It recently set up RUHR Compounds that focuses on commercialising an elastomer powder modified thermoplastic (EPMT) that it has developed. The new material exhibits the desired properties for use in the manufacture of high quality products such as wheel and splashguard covers, handles, knobs and steerable casters. Three basic EPMT recipes have been developed to date.

The rubber residues, which vary in length, are granulated to 3 mm-size particles, then cooled with liquid nitrogen and ground into elastomeric powders. These are then combined to the melt-mix process with thermoplastics (such as polypropylene) and additives.

The new compounds, which can contain up to 80% residual rubber, can be processed in injection moulding and extrusion machines. Moreover, the end products containing EPMT may also be recycled when they reach the end of their useful life.

Sports shoe manufacturer Nike is collaborating with Fraunhofer for its new EPMT-based products.

Meanwhile, in the US, a team of polymer researchers from the University of Akron, with funding from the National Science Foundation, NASA and several industrial companies, has developed a new rubber recovery technology for industrial use. It uses an ultrasonic devulcanisation extruder to enable the recovery of rubber materials from tyres and rubber soles, which are difficult to reprocess due to rubber’s vulcanised or crosslinked nature.

The patented technology, which has taken 15 years to develop, devulcanises the sulphur crosslink bonds in the rubber compound, allowing the scrap rubber to be reprocessed and reused.

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India uses rubber-modified bitumen for its national roads

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