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FLY ASH-BASED GEOPOLYMER CONCRETE
By
K. VINAY RAJ Guide Y.M. MANJUNATH LECTURER
CONTENTS:
INTRODUCTION
DEFINATION
CONSTITUENTS OF GEOPOLYMER CONCRETE
MIXING AND COMPACTION
CURING PROCESS
FACTORS AFFECTING THE COMPRESSIVE STRENGTH OF CONCRETE
SULPHATE RESISTANCE
ADVANTAGES AND APPLICATION
CONCLUSION
INTRODUCTION To reduce the emission of greenhouse gas from cement industry.
7%of annual global warming is due cement indutry.
To reduce the use of portland cement.
Geopolymer technology is an alternative to the portland cement.
GEOPOLYMER CONCRETE
DEFINATION
The source material reacts with alkaline liquid to form the geopolymer paste that binds the coarse and fine aggregates, together to form the geopolymer concrete.
There is no use of portland cement.
CONSTITUENTS OF GEOPOLYMER CONCRETE
•
Low-calcium fly ash
•
Alkaline liquid
•
Super plasticizer
Low-calcium fly ash
Low-calcium fly ash is obtained from coal-burning power station. •
•Low-calcium
fly ash can be successfully used in geopolymer concrete when it consists of silicon and aluminum oxides about 80% by mass. •Iron
oxide content usually range from 10 to 20% by mass. •Calcium
oxide content must be less than 5%.
Alkaline liquid is a combination of sodium silicate solution and sodium hydroxide solution. Alkaline liquid should to prepared by mixing both the solution together at least 24 hours prior to use.
superplasticizer
Naphthalene based superplasticizer is used. Superplasticizer are used to improve the workability.
Mixing and compaction of Geopolymer concrete
The fly ash and the aggregates are mixed together for 3 min.
The alkaline liquid was mixed with super plasticiser.
The fresh concrete can be handled up to 120 min.
The fresh concrete can cast and compacted by the usual method used in the case of portland cement concrete.
Pan Mixer Used in the Manufacture of Geopolymer Concrete
Addition of Liquid Component
Fresh Geopolymer Concrete Ready for Placing
Slump Measurement of Fresh Geopolymer Concrete
Curing of geopolymer concrete
Heat-curing is generally recommended.
Heat curing substantially assists the chemical reaction in the geopolymer paste. Heat curing is done at the temperature of 60 degree C for 24 hours. Then air curing is continued for 28 days at the temperature of 23-25 degree C. Both curing time and curing temperature influence the compressive strength.
Factors affecting the compressive strength (a) Longer curing time improves the polymerisation reaction resulting in higher compressive strength. (b) Use of superplasticizer upto 2% by mass of fly ash will not affect the compressive strength. (c) The liquid to fly ash ratio by mass must be 0.35.
(d) Compressive strength does not varies with the age of concrete.
Sulphate resistance When the fly ash-based GPC specimens were soaked in 5% concentration of sodium sulphate solution it has been observed that there is no damage to the surface of specimens.
It was found that after 24 weeks exposure, GPC did not show any sign of sulphate attack or degradation in compressive strength and other properties.
ADVANTAGES
Reduce the emission of carbon dioxide to the atmosphere.
The cost of fly ash is low.
Econamic
Sulphate resistance.
Application
Geopolymer concrete are used in the manufacture of precast railway sleeper, sewer pipes, wall panels etc.
Geopolymer concrete are used in marine structure.
Conclusion:
Geopolymer concrete is good alternative to portland cement concrete.
Reduces the emission of CO2 to the atmosphere from cement industries.
Fly ash –based geopolymer concrete shows excellent resistance to sulfate attack and good acid resistance therefore it is used in marine structure.
References:
Davidovits, J (1988) "Soft Mineralogy and Geopolymers",
Proceedings of the of Geopolymer 88 International Conference, the Université de Technologie, Compiègne, France.
Davidovits, J (1994) "High-Alkali Cements for 21st Century Concretes. in Concrete Technology, Past, Present and Future”
