Silica Fumes For Concrete & Its characteristics

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What is the meaning of concrete additives? Concrete additives are the substances that are mixed with the mixture of cement and used at the base of a construction. This makes the base stronger and more durable. It helps to withstand the pressure exerted by the huge buildings.

There are several additives available nowadays. The best of all is the silica fumes for concrete. This additive is not naturally formed. The metals of silicon or the alloys containing silicon are heated in huge furnaces run by electricity. They produce fumes known as silica fumes or micro-silica. The particles are very fine in texture and are powdery in nature. These particles are spherical in shape. It measures about 150 Nano meters in diameter. It consists of non-crystalline silicon dioxide.

Characteristics of silica fumes for concrete

The silica fumes consist of certain characteristic features. These are the physical properties and the chemical compositions.

Physical properties –

i. The diameter of a silica fume measures about 0.1 micron to 0.2 micron.
ii. The volume of the surface area measures about 30,000m2 per kilogram.
iii. The density of a silica fume weighs about 150 to 170kg per m3.
iv. The best suitable silica fumes for concrete have a density of 550 kg per m3.

Chemical composition –

i. The main component present in the fumes of silica is the silicon dioxide.
ii. It also consists of oxides of aluminum, calcium, sodium, carbon, potassium, magnesium and Sulphur.

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The properties of silica fumes for concrete

The silica fumes are also rich in some defined properties. These properties are as follows –

a. The fresh silica fumes for concrete and its properties:

i. The silica fumes can turn sticky if it is used too much. This will decrease the ability of the concrete to work.
ii. The silica fumes do not cause any difficulty if it is used 15 percent more in the cement mixture. This will not cause any difficulty in working.
iii. It requires more quantity of water because of the larger surface area when compared to normal concrete.

b. The properties of hardened silica fumes used along with concrete:

There has been a remarkable rise in the compressive strength when the silica fumes are used along with concrete.

How durable is the silica fumes used with concrete mixture?

The fumes form a protective layer against the attack of sulphate. This is done by:

1. It restricts the sulphate ions from entering by decreasing the permeability of the concrete mixture.
2. The conversion of mono-sulphoaluminate into ettringite is checked. This is done by the consumption of chloride hydroxides during the period of pozzolanic action.

Benefits of using silica fumes

Makes the concrete more durable.

• It decreases the possibility of bleeding and segregation.
• It increases the cohesiveness when it is added to fresh concrete.
• The process of finishing becomes for effective due to lack of bleeding.
• The properties of fresh and hardened concrete are raised with the help of silica fumes when added to it.