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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.
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John Bukowski
Office of Asset Management, Pavements, and Construction
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Updated: 02/20/2015

United States Department of Transportation - Federal Highway Administration