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What is the difference between slag cement and slag aggregate?

Slag cement is the hydraulic cement that results when molton slag from an iron blast furnace is rapidly quenched with water, dried and ground to a fine powder.  The rapid quenching ("granulation") "freezes" slag cement in a glassy state and imparts cementitious properties to the product when ground finely. 

Blast furnace slag aggregate comes in two forms: 

  • Air cooled blast furnace slag, results when molten slag from a blast furnace slag cools slowly by ambient air (as opposed to rapid quenching), and is processed through a screening and crushing plant for use principally as a construction aggregate. Air cooled slag is not cementitious.
  • Pelletized or expanded slag results when molten slag is quickly cooled using water or steam.  It produces a lightweight aggregate that can be used for concrete masonry, lightweight fill, or can be ground into a cementitious product.

For more information on slag aggregates, visit the National Slag Association's website.