Ordinary high CO2 emissions arising from OPC manufacture

Ordinary
Portland cement (OPC) has traditionally been used as the binder material in
concrete.
Global production of cement has grown very rapidly in recent years. Concrete is the most widely used construction material in
the world, with current consumption of 1 m3 per person per year.
After fossil fuels and land-use change, it is the third-largest source of
anthropogenic emissions of carbon dioxide. However
OPC has high embodied energy, with carbon dioxide equivalent (CO2-e), the
measure used to compare the emissions from various greenhouse gases based upon
their global warming potential, ranging from 0.66 to 0.82 kg of CO2
emitted for every kilogram manufactured. The contribution of the production of
OPC is approximately 5–7% of global anthropogenic CO2 emissions. The
key causes of high CO2 emissions arising from OPC manufacture have
been attributed to: (i) calcination of limestone, one of the key ingredients,
which leads to formation and release of CO2; and (ii) high energy consumption
during manufacturing, including heating raw materials within a rotating kiln at
temperatures greater than 14000C.

 

Global warming
is caused by the emission of excessive green house gases into the atmosphere by
human activities and carbon dioxide is responsible for about 65% of global
warming. Therefore, the impact of cement production on the environment has
created a significant challenge to concrete industries in the future. As a
result, it is necessary to find a new concrete material to replace traditional
Portland cement concrete, which is environmentally stressful, yet provides an
effective building material.

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Alternative
cements to OPC have been proposed to reduce greenhouse gas emissions. Blended
cements, comprising OPC that has been partly substituted by supplementary
cementitious materials (SCCs), are used as binders for concrete. Common SCCs
include fly ash, a fine waste residue that is collected from the emissions
liberated by coal burning power stations, and silica fume, a waste by product of the
production of elemental silicon or ferrosilicon alloys.
An alternative cementitious binder, termed ”geopolymer”, comprising of an
alkali-activated fly ash, has been considered as a substitute for OPC.

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