Recycled tire rubber feedstocks are size reduced passenger and truck tires that have been processed into raw materials meeting established specifications, for use in a variety of manufacturing and industrial processes. California has a well developed infrastructure for processing discarded whole tires. Tire processors typically first inspect incoming loads of discarded tires to sort out those suitable for reuse. Tires are then run through a series of automated grinders and separation devices to reduce them in size and to remove wire and fiber in varying degrees, to produce the rubber feedstocks described below.
Tire-derived aggregate is size reduced tires used to replace conventional light weight fill or other aggregates in a variety of civil engineering applications. It is defined in two types. Type “A” is comprised of shreds typically about 3 inches or smaller, and is used as drainage material, in septic systems, as vibration dampening layers under light rail tracks, and in landfill gas or leachate collection systems. Type “B” is comprised of shreds of 6-12 inches, and is typically used as light weight fill in embankments, behind retaining walls, or for road sections during slide repairs. The Tire-Derived Aggregate web page has additional information.
Ground rubber is made from whole tires, and is typically larger than 1/4- 3/4-inch in size, with up to 99.9 percent wire and fiber removed. Ground rubber is used in a variety of applications including loosefill playground surface nuggets, landscape covering and a variety of applications. Ground rubber is also used as equestrian arena surfacing.
Buffings are thin pieces of tire rubber produced by buffing the tread of a tire, most often a truck tire, during the retreading production process. Buffings are used extensively in pour-in-place playground systems, bonded landscape surfaces, molded rubber products, and landscape rubber bark.
Whole tires are size-reduced into shreds, typically of 1-3 inches, for sale as “tire-derived fuel” (TDF) to cement kilns in California. Several cement kilns in California also use whole tires as tire-derived fuel. TDF is also exported to Asia and other parts of the world where it is used in pulp and paper mills, cement kilns, steel mills and other industrial boilers.
Crumb rubber, 1/4-inch or smaller, is made by size reducing the whole tires through additional granulators and classifiers. The size reduction process includes further reducing contaminants to meet specification of end use products. Ambient crumb rubber is processed at room temperature, while cryogenic crumb rubber is first frozen to very low temperature prior to grinding, producing clean, small particles with different physical characteristics than ambient crumb rubber. Crumb rubber is used in rubberized asphalt concrete, paving applications, and a variety of other tire-derived products including synthetic turf infill and molded rubber products. Very fine crumb rubber of 80-200 mesh is now being used in a wider range of established and new products, and holds the promise to open up new tire recycling markets.
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