10-04-2017, 08:16 PM
SILICA FUME CONCRETE
INTRODUCTION
Silica fume is also referred to as micro silica or condensed silica fume but the term silica fume has been generally accepted
The addition of ultra fine particles in concrete improves strength of concrete
The optimum proportion of silica fume is found in between 20% and 25% by weight of concrete
Silica Fume when react with calcium hydroxide on hydration of cement produces calcium siicate hydrate which has good binding properties.
CHARACTERISTICS OF SILICA FUME
1 Physical Properties
Diameter is about 0.1 to 0.2
Surface area about 30,000 m /kg
Density varies from 150 to 700 kg/m
When its density is about 550 kg/m it is the best suited as concrete additive
2 Chemical Composition
Contains more than 90 percent silicon dioxide
Other constituents are carbon, sulphur and oxides of aluminium, iron, calcium, magnesium, sodium and potassium
PROPERTIES OF SILICA FUME CONCRETE
1 Properties of Fresh Concrete
Too much silica fumes cause the concrete to become sticky and thus reduces the workability
Silica fume addition up to 15% by weight of cement does not result in any loss of workability
Silica fume concrete, due to larger surface area of fine particle requires higher water content for same workability than ordinary concrete
DURABILITY OF SILICA FUME CONCRETE
Resistance to Chemical Attack
Silica fume checks sulphate attack by
Being very fine, it reduces permeability and the entry of sulphate ions.
By consuming the calcium hydroxide in course of pozzolanic action, it checks conversion of mono-sulphoaluminate into ettringite.
ADVANTAGES
Silica fume improves the properties of fresh and hardened concrete
Fresh concrete made with silica fume is more cohesive
Silica fume reduces segregation and bleeding
Silica fume improves the durability of concrete
Lack of bleeding allows a more efficient finishing process
CONCLUSION
The use of silica fume give rise to an increase in the fresh as well as hardened properties of concrete, with less cement and a concrete having better resistance for freezing and thawing than ordinary concrete
Durability is improved through significant improvement in resistance to chemical attack. The chief reasons for this are reduced permeability and reduced levels of calcium hydroxide
Reinforcement corrosion is vastly reduced due to improved permeability, increased resistivity and improved tensile strength.