some of the fastest growing human impact. The
one tonne of cement produces 1.25 tonnes of CO2 comes
from two sources. First the limestone which is burned to make cement
is more than twice the density of water and has to be heated to 1,450
degrees C, which uses a lot of fossil fuel, about .75 tonnes per tonne
of cement. Second to the energy load to heat the limestone, the stone
itself is composed of calcium and carbon. To
make cement the extremely
stable carbon, the living part of the creatures whose remains make up
the limestone, has to be made into CO2.
In this way we have made two sources of very stable fossilised carbon into
a huge amount of CO2.
In doing this for the last 100 years we have produced a
global construction sector which is now entirely client to the cement
industry. Through legislation cement has become a monopoly material
throughout the world, and for increasingly minor structures. Not only
has cement dominated the legislative and codified areas of
construction, it has dominated education in the professions and trades
too. Most engineers know nothing of any other form of
construction, and as we are driven by an increasingly style oriented
architecture the results are ever heavier burdens of pollution.
Other misconceptions about cement include its
longevity. Not only has concrete cancer been identified as a big
killer of concrete structures, users also destroy buildings with the
same lack of concern over their consumerist values as with all other
forms of consumption and waste. The difference is that cement has such
a high burden of embedded energy that is not justified by a short
life of even a hundred years. So much
modern building is destroyed through internal
faults or changes in use or fashion.