Utilization of Recycled Materials in Illinois Highway Construction
- Glass is formed by supercooling a molten mixture of sand (silicon dioxide), soda ash (sodium carbonate), and/or limestone to form a rigid physical state. Glass aggregate is a product of recycled mixed glass from manufacturing and postconsumer waste (1).
- Physical Properties:
- Glass aggregate, also known as glass cullet, is 100 percent crushed material that is generally angular, flat and elongated in shape. This fragmented material comes in color or colorless forms. The size varies depending on the chemical composition and method of production (1).
- Engineering Value:
- When glass is properly crushed, this material exhibits coefficient of permeability similar to coarse sand. Also, the high angularity of this material, compared to rounded sand, may enhance the stability of asphalt mixes. In general, glass is known for its heat retention properties, which can help decrease the depth of frost penetration (1).
- Potential Application:
- Glass aggregate has been investigated by many state DOTs including New York, Washington, and Pennsylvania.
New York DOT uses a limited amount of this material in embankments and bituminous concrete base and binder courses. This is a non-surface mix material because of concerns that it could result in injury claim liability. New York has experienced problems with stripping asphalt binder not adhering to aggregate that may be controlled by adding an anti-stripping agent, which in turn adds costs.
Since the 1960s, Washington DOT has used a portion of glass aggregate in bituminous concrete pavements. This aggregate material is also used in backfill for foundations, pipe bedding, and other applications not subject to heavy repeated loading. Washington State has not utilized this material on any recent projects.
Pennsylvania DOT also allows a portion of this material in nonstructural fills and drainage applications, while experimentation with this material in bituminous concrete has yielded results similar to New York's. (16, 17)
- Department Concern:
- Glass aggregate presents problems in both bituminous concrete and PCC pavements. In concrete pavements, this material is problematic due to the deleterious alkali-silica reaction with the cement paste. In bituminous pavements, this material bonds poorly to the asphalt, which results in stripping and raveling problems. In general, waste glass contains impurities such as ceramics, ferrous metal, paper, plastic, and mixed colored cullet; processing and specifications may limit associated problems.