Microsilica, also known as silica fume, results from the reduction of quartz in an electric arc furnace. It consists of tiny spherical particles that are 100 times finer than cement grains. Concrete containing microsilica has several improved properties, including the highest possible strength even rivaling steel, weight savings for construction, very low permeability that reduces water penetration by 90%, and excellent resistance to frost, road salts, acids, and other chemicals. It also provides greater corrosion resistance of steel reinforcement by reducing permeability and electrical conductivity in concrete, as well as improved resistance to chloride penetration and carbonation due to its high alkalinity. Additional benefits are stronger bonding to reinforcement, high abrasion resistance, and maintained strength even at

1. Some properties of concrete using microsilica
What is micro-silica or silica fume?
Micro-silica (silica fume) results from the reduction of quartz (SiO2) by carbon in the electric arc furnace. Part of
the only partially reduced quartz evaporates as SiO and is re-oxidized to SiO2, when it comes in contact with
oxygen in a cooler part of the furnace. This SiO2 condenses in tiny microscopic spherical particles as amorphous
silicon dioxide with average grain size of 0.1 micron. Micro-silica particles are thus about 100 times finer than a
grain of cement.
Properties of concrete using microsilica or silica fume?
1. Highest strength
By the reaction cement-superplasticizer-microsilica, strengths hitherto never achieved are possible.
Extremely strong concrete using microsilica ca almost reach the strength of steel.
2. Weight saving
Possibilityfor tall building have been improved, not only because of the high strength of microsilica concrete but
also because of weight saving.
3. Permeability to water
An additional of 10% microsilica and superplasticizer reduces the permeability to one tenth.
4. Resistance to frost and road salt
Microsilica improves the chemical resistance to sulphates,chlorides,(road salt),alkali-reative aggregates, acids,
carbon dioxide (carbonation), sulphur dioxide and nitrous gases. Resistance to freeze-thaw with road salts are
greatly improved.
5. Corrosion resistance
For steel to rust, for importantconditions mustbe fulfilled. There must be: an electrolytic cell in which there is an
anode where ions go into solution and electrons are released;an electrical conductor,in this case the reinforcing
steel,which transports the electrons from the anode to cathode; the cathode where the electrons are used up in
the presence ofacid and dampness;and an electrolyte, the dampness ofthe concrete which allows ions to move
between cathode and anode. It is the reactions at the cathode which control the speed of rusting. Thus when
neither acid nor water can diffuse to the steel, rusting cannot occur. By reduction of the permeability and of the
electrical conductivity through the combination of calcium hydroxide, microsilica improves the rust resistance of
steel in concrete.
6. Chloride penetration and carbonation
The high alkalinityof cementprotects the reinforcing steel naturallyagainst rust. The pH value if cement paste is
about 12.5 and thus passiveness the steel so that even in the presence of acid and damp it cannot rust. The
action of carbon dioxide from the air reduces the alkalinity continuouslyby neutralizing the lime. If the carbonated
region reaches the steel it begins to rust. With chlorides,whether from road saltor seawater,rusting begin athigh
PH value and even at a high rate. The consequence are known. But if carbonation is stopped and the entry of
chlorides is made difficult, the reinforcement corrosion can be prevented.
7. Bond with reinforcement
With increasing microsilica content the bond strength between concrete and steel improves.

2. 8. Abrasion resistance
High abrasion resistance is needed for many applications. The property can be greatly improve by the use of
microsilica.
9. Temperature resistance
Combination ofthe free substances,cement,microsilica and superplasticizer can produce materials of very high
strength. Surprisingly, the compressive strength is maintained even above 400 Celsius degrees.