Why does silica fume increase Compressive Strength of concrete ?
Many would have done experiments in silica fume concrete which increases the compressive strength of the concrete, why does it increase the compressive strength ? what is so great about silica fume? how is it used?
let's discuss.....
What is Silica Fume ?
Silica Fume is obtained as a co-product during the production of silicon or ferrosilicon metal. It is a mineral admixture, a very fine powder of spherical particles with a surface area of 17 to 30 m2/g. It is used in a variety of cementitious concrete, grouts and mortars, refractory, applications. Silica fume powder is gray to off-white in color.
Silica fume in general is of size of 150 nm (particle diameter) which is around 100 times smaller than cement particles so when it is present in a concrete mixture it fills in the voids created by cement and sand which leads to dense mixture. Thereby creating a strong concrete mixture.
How it reacts..
When added to cement it stays inert until water is added, after that it reacts with water and cement to produce two compounds Calcium silicate hydrate (CSH) and Calcium Hydroxide (CH),
where CSH increases concrete strength by crystallization, CH acts as a filler by settling in the pores within the concrete. This type of reaction in a dense mixture not only increases the compressive strength but also the flexural strength and bond strength .
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Other advantages also include
Because of its high surface area more water is consumed for wetting the larger surface area, which reduces bleeding and segregation.
High work-ability which also due to high surface area (fineness modulus ). High cohesive workability makes it suitable for long distance pumping
This clearly shows that silica fume is a great boon to civil engineers and construction industry...
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