Utilization of Recycled Materials in Illinois Highway Construction
- As iron production is to blast furnace slag, so pig iron manufacturing is to steel slag. Impurities (carbon monoxide, silicon, liquid oxides, etc.) are removed from molten steel in a basic oxygen or electric arc furnace, and combined with the fluxing agents to form steel. Depending on the stage of production, three types of steel slag are produced: furnace (or tap) slag, raker slag, ladle (or synthetic) slag, and pit (or cleanout) slag. Ladle slag, which contains high amounts of synthetic fluxing agents, is characteristically different than furnace slag-primary source of steel slag aggregate product-and is not deemed suitable for aggregate usage (1, 10).
- Physical Properties:
- The cooling rates and chemical composition of steel slag production affect physical characteristics, such as density, porosity, and particle size. In general, processed (i.e. crushed) steel slag is more angular, more dense and harder than comparable natural aggregates (9).
- Engineering Value:
- Steel slag has sufficient material properties including favorable frictional properties, high stability, and resistance to stripping and rutting. On the other hand, steel slag may contain amounts of calcium or magnesium oxides, which will hydrate-leading to rapid short-term and long-term expansion, respectively. Also, though normally mildly alkaline, steel slag may be potentially harmful to aluminum or galvanized metals (1, 9, 10).
- Present Application:
- Since 1975, steel slag has been available as an aggregate in pavement materials. It is acceptable only as a coarse aggregate for use in high-type bituminous concrete mixes and seal coats. However, the characteristics of steel slag in HMA have caused some quality control problems. Currently, a self-testing producer control program has been added to the specifications regarding bituminous concrete mixes.
- Quantity Used:
- 195,000 tons (2001 MISTIC estimate).
- Economic Impact:
- In 2001, the Department spent approximately $3,160,000 toward its recycling.