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Utilization of Recycled Materials in Illinois Highway Construction

Glass Beads

Origin:

Virgin glass, in general, is a molten mixture of sand (silicon dioxide-a.k.a. silica), soda ash (sodium carbonate), and/or limestone supercooled to form a rigid solid (1). Glass beads, in particular, are a product of recycled soda-lime glass. This material's primary source is from manufacturing and postconsumer waste. At recycling centers, recovered glass is hand sorted by color (clear, amber, and green), and then crushed to customized sizes.

Physical Properties:

Glass beads are transparent, sand-sized, solid glass microspheres (3).

Engineering Value:

Glass beads can enhance the nighttime visibility of various objects through the fundamentals of retro-reflectivity-light is reflected back to its source, for instance, vehicle headlights.

Present Application:

The Department uses two types of glass beads-Type A (uncoated) and Type B (silicone coated, moisture resistant)-depending on the method of application (drop-on or intermix) and the type of pavement marking paint used (solvent-based, waterborne, or thermoplastic). Glass beads are utilized in many traffic control devices including reflective sheeting decals, pavement striping, and pavement marking tape. Essentially all traffic lines on highways contain glass beads, which improve the overall safety of nighttime highway travel. Outside the Department, glass beads are utilized in license plates, movie screens, and reflective fabrics (3, 5).

Quantity Used:

7,310 tons (2001 MISTIC estimate).

Economic Impact:

The use of glass beads, as an alternative to their disposal, has created a market for material recovery facilities specializing in waste glass recycling. Since soda-lime glass cannot be re-melted by glass manufacturers, the production of glass beads avoids the necessity of land filling (1). In 2001, the Department spent approximately $2,490,000 on glass beads.