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What is Slag Cement

Slag Cement Powder.jpg


Slag cement, otherwise known as “ground granulated blast furnace slag,” is a byproduct of an iron blast furnace, part of an integrated steel mill.  An iron blast furnace converts iron ore into molten pig iron (a material used subsequently in steel production)  and molten slag.  These products are tapped off separately. 


The molten slag can be processed in two ways, resulting in two different products.  If slag is deposited in pits and allowed to cool slowly, it can be mined from the pit to become “air-cooled blast furnace slag aggregate,” used in various construction applications (e.g., concrete, fill, base material, asphalt/hot mix).  Air-cooled slag aggregate is non-reactive and is a relatively low-value product.  (For more information about air-cooled slag aggregate, visit the National Slag Association.)


Granulator.jpgThe other method of post-processing blast furnace slag is to rapidly quench the molten material in a “granulator” which solidifies the slag into a glassy material with sand-like consistency. “Granulated slag,” is then dried and ground to a fine powder, at which point it becomes “slag cement.”  Slag cement is a “hydraulic cement,” which, like portland cement, chemically reacts with water and forms the “glue” that causes concrete to become a solid, durable building material.  Slag cement is a high-value product used primarily as a cement in concrete, and can replace between 20 and 80 percent of portland cement in concrete (depending on application and engineering requirements).


Click here to download information sheet on slag cement.