The recycling of scrap tires may be defined under two different categories: using the scrap tires as whole or mechanically modified shapes (in crumps or shredded), chemical decomposition or separation of scrap tire contents into different materials.
Recycling as-is or after mechanical process has the advantages of directly using scrap tires without major investment. For example, scrap tires can be directly used as boat bumpers at marinas to protect ships from scratching or hitting at the side of wharf. Similarly, old tires can be placed side by side in half tire shifted pattern for slope stability or under roads for improved stability. Ripped tire pieces in large chunks can be directly used as light weight infill material at embankments. Smaller scrap tire pieces can be used as mixture in concrete as gravel substitute to improve tensile capacity or in asphalt paved roads for better traction. Smaller crumbs can be bonded together to generate walking or running mats or soft surfaces for playgrounds. Drainage around building foundations, erosion control for rainwater runoff barriers, wetland establishment, crash barriers at sides of race tracks are other uses of scrap tires without much modification.
Recycling of scrap tires at element level that includes some form of chemical decomposition or transformation is different than the mechanical process. Chemical recycling has additional advantages of obtaining well defined building blocks of a tire separately (such as steel wires, natural gas, pyrolysis oil, carbon black, charcoal etc.). The process in a way reverses the manufacturing process and obtains the elements forming a tire backwards.The materials then can be directly sold or used for energy in factories or diesel cars. Alternatively, burning scrap tires may also be included as a chemical process since long chained carbon based molecules are divided into smaller molecules and carbon forms new bounds with oxygen generating heat and carbon dioxide. Additionally, hydrogen in the molecules also forms bounds with oxygen forming water.