What is the purpose of silica fume in concrete?

Condensed silica fume is a very fine, amorphous, and reactive mineral admixture. It reacts readily with the calcium hydroxide, which is produced during Portland cement hydration. Silica addition refines pore structure and produces concrete of improved mechanical strength.

What is the effect of silica fume on concrete workability?

The results of this research indicate that as the proportion of silica fume increased, the workability of concrete decreased but its short-term mechanical properties such as 28-day compressive strength and secant modulus improved.

What is silica fume admixture?

Silica fume is a mineral admixture, composed of submicron particles (100 to 150 times smaller than a grain of cement) of amorphous silicon dioxide. Silica fume powder is gray to off-white in color, and is available in several product forms and packaging options.

What do silica fumes do?

When silica fume is added to concrete, initially it remains inert. Its small particle size which is 100 times finer than ordinary portland cement complements the finess modulus of concrete and provides a ball-bearing effect, which improves thixotropic behavior, in effect modifying concrete viscosity.

Is silica fume pozzolanic material?

Silica fume, a by-product of the ferrosilicon industry, is a highly pozzolanic material that is used to enhance mechanical and durability properties of concrete. It may be added directly to concrete as an individual ingredient or in a blend of portland cement and silica fume.

Why does silica make concrete stronger?

Because the microsilica particles are so small they disperse among and separate the cement particles. The resulting fine, uniform matrix can give markedly higher compressive, flexural, and bond strength.

How does silica influence cement production?

Silica fume accelerates the hydration of 3CaO·SiO2 (C3S), reduces the amount of calcium hydroxide by reacting with it, and slightly lowers the (1.5 – 2.0)CaO·SiO2·nH2O (C – S – H) ratio of the C – S – H formed by hydration. Silica fume is considered a good model for reactive pozzolans used in concrete.

What is the difference between silica fume and fumed silica?

Fumed silica and silica fumed are two different terms for two substance. They are both silica dioxide. On some occasions people confused with them. They have different derivations, technical characteristics, and applications, then the price is different.

What is the difference between silica fume and microsilica?

Silica fume consists primarily of amorphous (non-crystalline) silicon dioxide(SiO2). Concrete containing silica fume can have very high strength and can be very durable. Micro Silica Fume or Microsilica is finer particle than Cement. It is produced by some chemical processing of the ash.

Why does silica fume increase concrete strength?

Silica fume reacts with calcium hydroxide produced by cement hydration reactions and produces more calcium silicate hydrate, which continues to add strength to the concrete matrix. When smaller quantities of silica fume are used as a replacement for portland cement, water demand may not increase.

How does silica fume react to concrete?

Why is silica fume not used in concrete?

Silica fume has a very high specific surface and acts as a reactive pozzolan. Normally, silica fume is used in small amounts compared to other pozzolanic materials. Its homogeneous dispersion in concrete is problematic. This inhomogeneity may cause a ball bearing effect and localized problems.

What is silica fume densification?

Silica fume is only densified to increase the bulk density, which makes it more economical for truck transportation. The densification involves a form of electrostatic attraction which forms loose agglomerations of particles which can be re-dispersed during the concrete mixing.

What is condcondensed silica fume?

Condensed silica fume is a very fine, amorphous, and reactive mineral admixture. It reacts readily with the calcium hydroxide, which is produced during Portland cement hydration. Silica addition refines pore structure and produces concrete of improved mechanical strength.

What is the difference between densified and undensified concrete?

The densification involves a form of electrostatic attraction which forms loose agglomerations of particles which can be re-dispersed during the concrete mixing. In fact undensified, densified and even slurried silica fume are all available on the market as concrete additives.