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Ground granulated blastfurnace slag (GGBS or GGBFS) is obtained by quenching molten iron blast furnace slag (a by-product of iron and steel making) in water or stream, to produce a glassy granular product that is then dried and ground into a fine powder.

GGBS is used to make durable concrete structures in combination with ordinary Portland cement and/or other pozzolanic materials. GGBS has been widely used in Europe, and increasingly in the United States and in Asia (particularly in Japan and Singapore) for its superiority in concrete durability, extending the lifespan of buildings from fifty years to a hundred years.

Two major uses of GGBS are in the production of quality-improved slag cement, namely Portland Blastfurnace cement (PBFC) and High Slag Blastfurnace cement (HSBFC), with GGBS content ranging typically from 30-70%; and in the production of ready-mixed or site-batched durable concrete.

Concrete made with GGBS cement sets more slowly than concrete made with ordinary Portland cement depending on the amount of GGBS in the cementitious material, but also continues to gain strength for longer in production conditions. This results in lower heat of hydration and lower temperature rises, and makes avoiding cold joints easier, but may also affect construction schedules where quick setting is required.

Use of GGBS significantly reduces the risk of damages caused by Alkali-silica Reaction (ASR), provides higher resistance to chloride ingress, reducing the risk of reinforcement corrosion, and provides higher resistance to attacks by sulphate and other chemicals.

GGBS substitutes Portland cement by 30-70%. Manufacturing of Portland cement is a major contributor of greenhouse gases, responsible for about 5% of all global carbon dioxide emissions. By comparison, manufacturing of GGBS requires less than a fifth the energy and produces less than a tenth of the carbon dioxide emissions.

U.S. Federal Highway Administration. Ground Granulated Blast-Furnace Slag. Retrieved on January 24, 2007.

Civil and Marine Company. Frequently Asked Questions. Retrieved on January 24, 2007.

EnGro Corporation Ltd.. Ground Granulated Blastfurnace Slag (GGBS). Retrieved on January 24, 2007.