Glossary of Terms and Acronyms Page 9 | 27 Cryogenics A technology for processing materials at very low temperatures. For processing rubber, liquid nitrogen, or commercial refrigeration methods are commonly used to embrittle rubber. The embrittled rubber is then processedin a hammermill or granulator to a desired product size. Cryogenic Crumb Rubber A cryogenic process includes grinding a tire and separating and freezing the smooth clean particles using liquid nitrogen or commercial refrigeration to a temperature of below – 80 degrees Celsius (-112 degrees Fahrenheit) to embrittle the rubber. The embrittled rubber is crushed in a mill to the desired particle size. Cryogenic grinding avoids heat degradation of the rubber and produces a high yield of product that is free of almost all fiber or steel, which is liberated during the process. Cryogenically Ground Rubber Rubber that results from the process of freezing scrap tire rubber or other rubber and crushing the rubber to the particle size desired. D Density Mass per unit volume of a material. (ASTM D1566 – 21, E126, E20) Density, Bulk Mass per unit volume of a material, including any voids present. (ASTM D1566 – 21) Depolymerization A process that reduces a polymer to individual elements. For rubber, this reduction permits the blending of these individual elements with other polymers. Devulcanization Destruction of the chemical crosslinks in a vulcanized rubber. (ASTM D1566 – 21) A process in which crumb rubber is subjected to treatment by heat, pressure, or the addition of softening agents to regenerate the rubber compound to its original plastic state. Chemical, thermophysical, or biological means are used to break apart the sulfur bonds found in rubber. Dry Process Paving The addition of chemically engineered tire rubber during the hot mix asphalt production process. Rubber-binder interactions, after mixing and mechanical changes in the mix, promote greater pavement resistance to both rutting and cracking. Dry process mix modification is commonly used as an alternative to polymer modification of asphalt binders and wet process modification with tire rubber.
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