GEOPOLYMER CEMENT

                     USER- FRIENDLY     GEOPOLYMER CEMENT

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’.

Prepared by……………

P.RAMARAJAN
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