Utilization of Recycled Materials in Illinois Highway Construction
Ground Granulated Blast Furnace Slag
- Blast furnace slags are developed during iron production. Iron ore, as well as scrap iron, is reduced to a molten state by burning coke fuel with fluxing agents of limestone and/or dolomite. Ground Granulated Blast Furnace Slag (GGBFS) is a glassy, granular material resulting from blast furnace slag being rapidly cooled by water immersion, and pulverized to a fine, cement-like material (1, 2, 3).
- Physical Properties:
- GGBFS is a glassy, non-crystalline material varying in size depending on its chemical composition and method of production-its own production as well as that of its iron source (1).
- Engineering Value:
- When ground down to cement-sized fineness, granulated blast furnace slag is pozzolanic *; therefore, it can be used in PCC as a mineral admixture, component of blended cement, or substitute for portland cement (1, 2).
* Note: FHWA adds these notes due to the use of the word: pozzolanic, it is not used correctly here in this report done by Illinois DOT. The following statement is considered correct: "When crushed or milled to very fine cement-sized particles, ground granulated blast furnace slag (GGBFS) has cementitious properties, which make a suitable partial replacement for or additive to Portland cement."
- Present Application:
- The primary uses of GGBFS slag are as a fine aggregate substitute, mineral admixture, and component of blended cement. In blended cements, GGBFS has a low heat of hydration, which slows the chemical reaction responsible for strength gain, resulting in a gradual strengthening of the concrete. Consequently, the Department currently allows no more than 25% to be included in PCC (2, 3).
- Quantity Used:
- 530 tons (2001 MISTIC estimate).
- Economic Impact:
- The use of GGBFS as a supplementary cementitious material aided in the reduction of landfill space need, and reduced emissions and fuel consumption required for cement production.