Glass accounts for 7 percent of the garbage produced in the United States by weight, according to the U.S. Environmental Protection Agency (see References 1). Unlike some materials, glass can be repeatedly recycled without losing its quality or strength, so glass manufacturers use crushed, recycled glass, called cullet, to reduce their production costs for glass items of many descriptions (see References 2).
Of all the glass recycled, 90 percent goes to the container industry to make bottles and jars. Container manufacturing requires high-quality cullet that is free of contamination with different colors of glass and nonglass materials, such as bottle caps and labels (see References 1, page 8). Container manufacturers realize savings of up to 5 percent for each 10 percent of a glass batch that uncontaminated cullet replaces. Recycled glass also melts at a lower temperature than virgin glass, saving energy as well as wear and tear on furnaces (see References 1).
The fiberglass industry uses relatively small amounts of post-consumer recycled glass. Compared to the container industry, fiberglass manufacturers realize smaller savings when using recycled material, with cost reductions of about 3 percent for every 10 percent substitution with cullet (see References 1). Structural fiberglass requires high-quality cullet, putting it in direct competition with container manufacturers, while lower-quality cullet can be used in fiberglass insulation (see References 2).
Aggregate and Glasphalt
Low-quality cullet with mixed glass colors and high contamination levels can also be used in concrete and glasphalt and as construction fill, replacing gravel. Glasphalt, a mixture of 10 to 20 percent cullet with asphalt, is suitable for roads with speed limits under 40 mph but offers poor tire grip at higher speeds. As an aggregate material, crushed glass has many of the same properties as gravel, so demand is largely dependent on gravel and cullet prices. (See References 1, page 11)
Many other products contain small amounts of post-consumer recycled glass. Industrial applications include using glass fines, or very small fragments, as a sandblasting medium or a flux. The abrasive nature of glass fines also makes them suited to match tips (see References 1). Many glass-bead manufacturers use cullet, as do art-glass and decorative-tile producers. Reflective beads used on roadways to increase driver safety may also include recycled glass (see References 2).
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