Ground granulated blast furnace slag (GGBFS)

The ground granulated blast furnace slag (GGBFS) is a by-product of iron manufacturing which when added to concrete improves its properties such as workability, strength and durability. This material is obtained by the heating of iron ore, limestone and coke at a temperature about 1500 degree Celsius. The process is carried out in a blast furnace. The formation of GGBFS is not direct. The by-product of iron manufacturing is a molten slag and molten iron. The molten slag consists of alumina and silica, also with the certain amount of oxides. This slag is later granulated by cooling it. For this, it is allowed to pass through a high-pressure water jet. This result in quenching of the particles which results in granules of size lesser than 5mm in diameter. The main constituents of blast furnace slag are CaO, SiO2, Al2O3 and MgO. These are the minerals that are found in most of the cementitious substances. The particles are further dried and ground in a rotating ball mill to form a fine powder, known as ground granulated blast furnace slag cement. Now different methods can be employed to perform the main process called as the quenching.

Applications & Benefits of GGBFS:

In concrete:

The incorporation of ground granulated blast furnace slag in concrete manufacture gains many advantages which are mentioned below:

  • GGBFS in concrete increases the strength and durability of the concrete structure.
  • It reduces voids in concrete hence reducing permeability
  • GGBFS gives a workable mix.
  • It possesses good pumpable and compaction characteristics.
  • The structure made of GGBFS constituents help in increasing sulphate attack resistance.
  • The penetration of chloride can be decreased.
  • The heat of hydration is less compared to conventional mix hydration.
  • The alkali-silica reaction is resisted highly.
  • These make the concrete more chemically stable.
  • Gives good surface finish and improves aesthetics.
  • The color is more even and light.
  • Lower chances of efflorescence.
  • The maintenance and repair cost of structures are reduced thus increasing the life cycle of concrete structures.
  • Unlike cement, GGBFS does not produce carbon dioxide, sulphur dioxide or nitrogen oxides.

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