GEOPOLYMER CONCRETE
General Introduction
Concrete usage around the world is second only to water. For
the production of concrete Ordinary Portland Cement (OPC) is a major material
for binding purpose. Some environmental issues are there during production of
OPC. One ton of cement production approximately liberates 0.80 – 1 ton of
carbon dioxide to the environment. In addition, more energy are required to
produce the cement next to steel.
Portland cement manufacture can cause environmental impacts
at all stages of the process. This includes emissions of air pollution in the
form of dust, gases, noise and vibration when operating machinery and during
blasting in quarries, consumption of large quantity of fossil fuel during
manufacture and release of CO2 from the raw materials during manufacture.
The CO2 associated with Portland cement
manufacture falls in to three categories:
Source 1: CO2 emission from decarbonation of lime
stone.It is fairly constant, minimum around 0.47kg CO2 per kg of
cement, maximum 0.54kg CO2 per kg of cement.
Source 2: CO2
from kiln fuel combustion, it varies with plant efficiency: efficient
precalciner plant 0.24kg CO2
per kg of cement, low efficiency wet process as high as 0.65kg CO2
per kg of cement, typical modern practices (e.g. UK) averaging around 0.30kg CO2 per kg
of cement.
Source 3: CO2
produced by vehicles in cement plants and distribution. It is almost
insignificant at 0.002 – 0.005 CO2 per kg of cement.
Total CO2
emission around the world is 0.80kg CO2 per kg of cement. Electrical
energy consumption is of the order of 90 – 150 kWh per ton of cement.
Emission of carbon di
oxide causes greenhouse effect and it is consider to an increases of global
temperature that may result in climate change. In an article scientist John Hooke,
Queensland University, Australia. He told that every day there will be an
increases of CO2 in our earth, this temperature was 4 times bigger
than the temperature produced during bomb blast in Hiroshima and Nagasaki at
Japan. 90% of global temperature goes to inside the sea. The amount of greenhouse gas emission due to
cement production is estimated to be about 1.35billion tons annually or 7% of
total greenhouse gas emission to the environment.
On the other hand,
abundant availability of fly ash worldwide creates opportunity to utilize this
by product of burning coal, as a substitute for manufacturing of concrete. When
used as a partial replacement of OPC, in the presence of water in ambient
temperature, the fly ash reacts with calcium hydroxide during hydration process
of OPC and form the calcium silicate gel (CSH).
Geo polymer
Geo polymer are material based on pure aluminosilicate
materials such as fly ash, granulated blast furnace slag obtained from
industrial waste or calcined clays like metakoline, activated with an alkali
metal hydroxide and silicate solution. The term “Geo polymer” was proposed by Davidovits(1980) due to their setting mechanism, a
polycondensation process under alkaline conditions, similar to organic polymers.
Geo polymerization is a complex multiphase exothermic
process, involving a series of dissolution – reorientation – solidification
reaction analogous to those observed in zeolite synthesis. According to T.F.Yen(Year
) geo polymers can be classified in to two major groups: pure inorganic geo polymers
and organic containing geo polymers.
Benefits of Geo polymer
The
geo polymer does not create a greenhouse gas emission since there is no
calcination step in the synthesis, thus
avoiding the release of CO2 and because of this energy efficiency,
inorganic polymer have become increasingly attractive. Additionally it is
possible to produce these products using recycled materials. In addition these
alumino silicate materials possess comparatively higher strength and are much
more resistance to chemical attack, e.g. by acids.
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Fly ash based geo polymer concrete:
The geo polymer concrete can be
formed by binding the fine and coarse aggregate with geo polymers (Fly ash and
alkaline solution). It can be used in structures instead of OPC concrete. The
manufacture of geo polymer concrete is carried out using usual concrete
technology methods.
As in case of OPC concrete, the
aggregate occupy about 75 – 80% by mass in geo polymer concrete. The silicon
and aluminium in the low calcium fly ash react with alkaline liquid that is
combination of sodium or potassium hydroxide and sodium or potassium silicate
to form the geo polymer that binds the fine, coarse aggregate and other
unreacted materials.
