Slag cement, or ground granulated blast-furnace slag (GGBFS), has been used in concrete projects in the United States for over a century. Earlier usage of slag cement in Europe and elsewhere demonstrates that long-term performance is enhanced in many ways. In general, high quality slag cements are hydraulic cements consisting primarily of hydraulic calcium silicates (see ASTM C 989 for specifications).

Slag cement is commonly found in ready-mixed concrete, precast concrete, masonry, soil cement and high temperature resistant building products. While there are many applications and benefits of slag cement, a few are highlighted below and detailed information sheets are located here.

Slag cement, often called “ground granulated blast-furnace slag” (GGBFS), is one of the most consistent cementitious materials used in concrete. It is actually a byproduct of iron production. When the iron is processed using a blast furnace, slag and iron both collect at the bottom of the furnace.

The molten slag is either air cooled or water quenched, depending on its use. It can then be stored and shipped for further processing into slag cement. The slag is pulverized and ground into particles that are somewhat smaller than Portland cement particles; typically between 0.045″ and 0.002″ in size.

Slag cement, often called “ground granulated blast-furnace slag” (GGBFS), is one of the most consistent cementitious materials used in concrete. It is actually a byproduct of iron production. When the iron is processed using a blast furnace, slag and iron both collect at the bottom of the furnace. The molten slag must first be separated from the molten iron. The separated slag, which now consists of glassy granules, can be further processed to create GGBFS.

Ground granulated blast-furnace slag (S95) is used as a separate cementitious material in concrete for producing high-strength, high-quality concrete with low heat evolution and improved durability. In this article, we will discuss some important properties of GGBFS that make it useful in concrete for both precast and ready mixed concrete applications.

Properties of Slag Cement

The following are the important properties of ground granulated blast-furniture slag (GGBFS) that make it useful in concrete:

Hydration rate

When added to a concrete mix, ground granulated blast-furnace slag (GGBFS) acts as a partial replacement for Portland cement. This reduces the

Slag cement, often called “ground granulated blast-furnace slag” (GGBFS), is one of the most consistent cementitious materials used in concrete. It is actually a byproduct of iron production. When the iron is processed using a blast furnace, slag and iron both collect at the bottom of the furnace. The molten slag must first be separated from the molten iron. The molten slag is then either air-cooled or water-quenched, the latter process causes it to granulate.

Slag cement, often called ground granulated blast-furnace slag (GGBFS), is one of the most consistent cementitious materials used in concrete. It is actually a byproduct of iron production. When the iron is processed using a blast furnace, slag and iron both collect at the bottom of the furnace.

The molten slag is either air cooled or water quenched, depending on the application. Air cooling produces a granular material that is then processed into a fine powder. Water quenching produces a glassy material that can also be ground into a fine powder.

Slag cement usually comes in a very finely ground powder form and can be added to concrete in percentages that range from 15% to 70%. Because of its cementitious characteristics, slag cement helps improve strength, permeability resistance and durability of concrete. The type of admixture used depends on the desired set time and strength of the hardened concrete. For example:

High Range Water Reducers (HRWRs) increase workability without increasing water content (and therefore overall strength). HRWRs are often used with slag cements as they can help maintain workability for extended periods of time with reduced bleeding or segregation issues commonly associated with slags.

Slag cement, often called “ground granulated blast-furnace slag” (GGBFS), is one of the most consistent cementitious materials used in concrete. It is actually a byproduct of iron production. When the iron is processed using a blast furnace, slag and iron both collect at the bottom of the furnace. The molten slag must first be separated from the molten iron.

The molten slag is then either air-cooled or water-quenched to produce a glassy granular product that is then dried and ground into a fine powder known as GGBFS. The physical properties of this material are similar to those of Portland cement, but there are many additional benefits when it is used in concrete.