Silica Fume Concrete [why it is in concrete ]

Silica Fume is used widely as a Construction Material

It is more popular due to its finesse and its advantages. Due to its fineness, it brings more advantages to the construction industry.

It is a light-dark grey cementitious material composed of at least 85 percent ultrafine, amorphous non-crystalline spherical silicon dioxide particles.

It is a byproduct of silicon metal production or ferrosilicon alloy production.

Because of the chemical and physical properties, it is a very reactive pozzolan. Concrete containing silica fume can have very high strengths and good durability.

Further, it is a very fine material having around 1/50 the size of ordinary Portland cement. The average size of a particle varies 0.1-0.3 microns and the minimum specific surface areas are around 15000m2/kg.

Extreme fineness, large surface area and high content of amorphous silicon dioxide gives silica fume super pozzolanic properties.

Reduction of bleeding and segregation in fresh concrete, improvement of the strength and the durability of hardened concrete are some of the key advantages of the silica fume.

Low porosity with its fineness reduces permeability. In addition, the following advantages and disadvantages can be identified.

Advantages of Silica Fume

1. Segregation and Bleeding; it reduces the bleeding significantly.
2. It can be used with fly ash or blast furnace slag to develop strength at an early age.
3. Increase chloride permeability
4. Increase plastic shrinkage
5.  Improve bond strength to steel
6. Significantly reduce alkali-silica-reactivity
7. Provide excellent resistance to sulphate and seawater attacks
8. Reduce steel corrosion

Disadvantages of Silica Fume

1. Workability; due to the fineness of the material, it creates a more cohesive mix. Therefore, there is a higher water demand. However, the addition of suitable superplasticizer will reduce it.
2. Setting Time; adding a small amount (250 – 300 kg/m³) has no significant effect on the setting time. However, increasing the content may cause set retarding.
3.  It required a longer mixing time