cementitious slag makers association


GGBS (Ground Granulated Blast-furnace Slag) is one of the ‘greenest’ of construction materials. Its only raw material is a very specific slag that is a by-product from the blast-furnaces manufacturing iron. Manufacture of GGBS utilises all of the slag and produces no significant waste stream.

As well as the environmental benefit of utilising a by-product, GGBS replaces something that is produced by a highly energy-intensive process. By comparison with Portland cement, manufacture of GGBS requires less than a fifth the energy and produces less than a fifteenth of the carbon dioxide emissions. Further ‘green’ benefits are that manufacture of GGBS does not require the quarrying of virgin materials, and if the slag was not used as cement it might have to be disposed of to tip.

Each year, the UK uses up to two million tonnes of GGBS as cement, which:

  • Reduces carbon dioxide emissions by some two million tonnes
  • Reduces primary energy use by two thousand million kWhs
  • Saves three million tonnes of quarrying
  • Saves a potential landfill of two million tonnes

Click here to view the CSMA factsheet on GGBS and the environment.

Further information:

In 2010, the average emission by the membership of the CSMA to produce 1 tonne of GGBS was 67kg CO2e. Details of how this was calculated can be found by clicking here.

The apparent increase over the figure reported for 2007 is due to a widening of the boundaries and to the use of different conversion factors; the CO2e emissions for GGBS have not changed significantly since 2007.

Factsheet on the embodied CO2e of UK cement, additions and cementitious material clicking here.

Higgins D D, “Sustainable Concrete: How can Additions contribute?” The Institute of Concrete Technology Annual Technical Forum, March 2006. clicking here.

An Environmental Profile prepared by BRE for GGBS click here.

The effectiveness of GGBS in reducing the embodied carbon dioxide of concrete

ConcreteCO2e per cubic metre (kgCO2e/m3)CO2e as % of PC-only
DesignationTypical applicationPC concrete30% fly ash concrete50% GGBS concrete30% fly ash concrete50% GGBS concrete
GEN1 S4Trench foundations21317110880%51%
RC25/30Reinforced foundations28622815580%54%
RC28/35Suspended floors30424816981%56%
RC32/40Structural concrete33627619682%58%
NOTE: Calculations are based on:
• The typical mix designs used by BRE for the calculations of 'Ecopoints' for concrete.
• The data on embodied CO2e of UK cement, additions and cementitious material, referenced below.
• D Higgins, L Parrott & L Sear “Effects of ground granulated blastfurnace slag and pulverised-fuel ash upon the environmental impacts of concrete”. CIA Factsheet.