Annex
BACKGROUND INFORMATION
The Cementitious Slag Makers Association (CSMS)
is a Trade Association, which was formed in 1985 to promote the
use of ggbs in the UK.
Ground granulated blastfurnance slag (ggbs)
is a by-product from the blast-furnaces used to make iron. These
are fed with a mixture of iron-ore, coke and limestone. The iron
ore is reduced to iron and the remaining materials form a slag
that floats on top of the iron. This slag is periodically tapped
off as a molten liquid and if it is to be used for the manufacture
of ggbs, it has to be rapidly quenched in large volumes of water.
The quenching, optimises the cementitious properties and produces
granules similar to a coarse sand. This "granulated"
slag is then dried and ground to a fine powder.
The member companies of the CSMA operate five
Works, located across England and Wales, which dry and grind the
slag (an energy intensive process). These Works currently produce
some 1.5 million tonnes of ggbs each year. UK cement production
is about 12 million tonnes per year.
The main use of ggbs is in the Construction
Industry, as a replacement for part of the cement content of concrete.
Concrete made with ggbs shows many advantages. Of particular note,
is its increased durability in many applications.
Ggbs typically replaces 50 per cent of the Portland
cement in a concrete mix, on an approximately weight-for-weight
basis. The replacement level can be altered to optimise the technical
properties and in some applications may be as high as seventy
per cent.
Carbon dioxide emission, related to the production
of ggbs, is about seventy kg/ tonne of ggbs, compared with about
1,000 kg/ tonne for cement. Encouragement of the use of ggbs as
a replacement for cement offers substantial opportunities for
reducing UK carbon dioxide emissions. Current ggbs production
of 1.5 mt/year reduces UK carbon dioxide emissions by some 1.5
mt/year.
November 1999
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