Introduction:
Geopolymer cement is made from
aluminium and silicon, instead of calcium and silicon. The sources of aluminium
in nature are not present as carbonates and therefore, when made active for use
as cement, do not release vast quantities of CO2. The most readily available
raw materials containing aluminium and silicon are fly ash and slag – these are
the materials that Zeobond uses to create its low carbon emission binder.
Difference between
OPC and geopolymer cement:
The main process difference between OPC and geopolymer cement is that OPC relies on a high-energy manufacturing process that imparts high potential energy to the material via calcination. This means the activated material will react readily with a low energy material such as water. On the other hand, geopolymer cement uses very low energy materials, like fly ashes, slags and other industrial wastes and a small amount of high chemical energy materials (alkali hydroxides) to bring about reaction only at the surfaces of particles to act as a glue.
Research:
Much of the drive behind research
carried out in academic institutions involves the development of geopolymers as
a potential large-scale replacement for concrete produced from Portland
cement.This is due to geopolymers’ lower carbon dioxide production emissions,
greater chemical and thermal resistance and better mechanical properties at
both ambient and extreme conditions. On the other side, industry has
implemented geopolymer binders in advanced high-tech composites and ceramics
for heat- and fire-resistant applications, up to 1200 °C. There is some debate
as to whether geopolymer cement has lower CO2 emissions compared to
Portland cement. Calcination of limestone in production of Portland cement is
responsible for CO2 emissions (one ton of cement produced releases
one ton of CO2), while some processes of formation of lime also
release CO2. Mainly it is the ratio of CO2 reduction that
is under debate, and it is process-dependent.
Production:
Geopolymers are generally formed by
reaction of an aluminosilicate powder with an alkaline silicate solution at
roughly ambient conditions. Metakaolin is a commonly used starting material for
laboratory synthesis of geopolymers, and is generated by thermal activation of
kaolinite clay. Geopolymers can also be made from sources of pozzolanic
materials, such as lavaor fly ashfrom
coal. Most studies on geopolymers have been carried out using natural or
industrial waste sources of metakaolin and other aluminosilicates. Industrial
and high-tech applications rely on more expensive and sophisticated siliceous
raw materials.
Geopolymers are a type of inorganic
polymer that can be formed at room temperature by using industrial waste or
by-products as source materials to form a solid binder that looks like and
performs a similar function to OPC. Geopolymer binder can be used in
applications to fully or partially replace OPC with environmental and technical
benefits,
 |
including an 80 - 90% reduction in CO2 emissions and improved resistance to fire and aggressive chemicals.
Corrosion
resistance:
The corrosion resistance of
geo-polymer concrete is similar to this property of geo-polymer cement.
Geo-polymer concreted has been excellent properties within both acid and
saltenvironments since limestone has not used as a material in concrete. It is
especially suitable for tough environmental conditions. The geo-polymer
concrete can be become bend when it is insea water environment. This can be
useful in marine environments and on islands short of freshwater; in contrast
Portland cement concrete is impossible in sea water.Two grades of AAFG
concretes were prepared for this investigation. G54 represents aGeopolymer
concrete synthesised at high temperature (12 hours at 70°C) whereas G71
wasachieved at ambient. They were used in resistance of corrosion in Fly Ash
based Geo-polymer concrete research by X. J. Song, M. Marosszeky, M.
Brungs, R. Munn.As can be seen in Figure 11, the binder in the normal PC55 concrete
shows significantdegradation the aggregate becoming exposed after only 4 weeks
in 10% sulphuric acid. Bycontrast, Geo-polymer concrete cubes, G71 and G54,
remained structurally intact in the sameacidic environments after 56 days,
though some very fine localised cracks were observed.
Advantages:
This is one of the primary
advantages of geopolymers over traditional cements from anenvironmental
perspective is largely associated with releasing much lower CO2
emission than Portland cement. This
is mainly due to the absence of the high-temperature calcinations step
ingeopolymersynthesis.Secondly, Geo-polymer concrete offers several economic
benefits over Portland
cementconcrete. The price of a ton of fly ash is only small fraction of the
price of a ton of Portlandcement; therefore, after allowing for the price of
the alkaline liquids required making the geo-polymer concrete, the price of
fly-ash-based geo-polymer concrete is estimated to be about 10to 30% of
Portland cement concrete. Furthermore, the very little drying shrinkage, low
creep,excellent resistance to sulphate attack, and good acid resistance offered
by the heat-cured, fly-ash-based geo-polymer concrete may yield additional
economic benefits when it isused in infrastructure application.The other factor
is geopolymer concrete offers increase resource efficiency by producingconcrete
products with longer services lives.Corrosion resistance and high strength of
geo-polymer are other factors. Geo-polymer concretestill keeps high compressive
strength after mass loss and resisting from acid attack.
Disadvantages:
Regardless of all these positive
attributes, geo-polymer concrete is finding it hard to enter themodern market
today. A main reason is because large cement companies are basically scaredthat
the profit margins go down and financial risk. Another reason, the cost of
geo-polymer ismajor factor. It is more expensive than Portland cement about 60%
per cubic meter.In the construction industries view, “green cement” has yet to
establish itself as a viable, justrecognised or proven technology.
Example 1. A mixture for the geopolymer cement of the present invention is detailed in the Example below.
First the aluminosilicate powder is prepared in mixture A.
Mixture A:
This 233g of powder is then added to
the liquid component, Mixture B.
Mixture B: 
The calcined weathered lnterbasaltic
material from Northern Ireland
is preferably a dehydroxylated lithomarge such as is found in Co. Antrim, Northern Ireland,
is calcined at
75O0C for 6 hours and then milled to a
fine powder with a median particle size of 95 microns. The calcined weathered
lnterbasaltic material from Northern Ireland
is preferably a dehydroxylated lithomarge such as is found in Co. Antrim, Northern Ireland
and has a chemical composition containing approx 35% SiO2; 25% AI2O3;
21 % Fe2O3 and 2.5% TiO2 ( average amounts). This composition is quite different from the prior art in which the
AI2O3 content is lower. This composition equates to a calculated Si:AI atomic ratio of 1.18:1.
The solution formed is mixed at slow speed until the dry ingredients are completely wetted out and then mixed at high speed with a high shear mixer for 1 minute until the mixture becomes fluid. The mixture has a working time of approximately 1 hour at 2O0C in this form however, by altering the GGBS content it is possible to vary the setting time between 10 minutes up to 2 hours. The mixture can then be cast into a mould and sealed to avoid evaporation of water during curing. It is possible to demould the specimen after 2 hours at 2O0C. In terms of oxide mole ratios, the reactant mixture contains the following oxide mole ratios; however, it must be noted that for the larger particles not all of the particle is dissolved and the reaction will only take place on the surface of the particle.
K2O/SiO2 - 0.23
SiO2/AI2O3 - 3.68
H2O/K2O - 10.76
K2O/AI2O3 - 0.83
Conclusion:
Construction and concrete industry
have been utilising a tremendous amount of resources andenergy. Therefore, they
have a responsibility to reduce environmental impacts in their activities.For
the concrete industry to contribute to the sustainable development of mankind,
it isnecessary to promote technical development for further reduction of
environmental impacts. Topromote this, it will be necessary to introduce
environmental design systems based onenvironmental performance, develop environmental
performance evaluation tools and constructsystems for their actual
application.It is obvious that the concrete sector also has to consider the
reduction of environmentalimpacts in their technologies towards the sustainable
development of human beings. The newcentury of concrete technologies is
beginning with geo-polymer concrete. It releases lower carbon dioxide than
traditional concrete. Geo-polymer offers many advantages in durability
of structure such as increase of corrosion resistance, high compressive
strength. Geo-polymer also has a high economic effect in concrete market
today.In future, national and global environmental laws in regards to C02
emissions should force thePortland cement and concreting companies to convert
to use ‘green cement’.
P.RAMARAJAN
MY PAGE:
https://www.facebook.com/civilengineerramarajan.net
