Silica fume, also known as microsilica, (CAS number 69012-64-2, EINECS number 273-761-1) is an amorphous (non-crystalline) polymorph of silicon dioxide, silica.
However, the production process, particle characteristics and fields of application of fumed silica are all different from those of silica fume.
The first testing of silica fume in Portland-cement-based concretes was carried out in 1952.
The biggest drawback to exploring the properties of silica fume was a lack of material with which to experiment.
Early research used an expensive additive called fumed silica, an amorphous form of silica made by combustion of silicon tetrachloride in a hydrogen-oxygen flame.
Silica fume on the other hand, is a very fine pozzolanic, amorphous material, a by-product of the production of elemental silicon or ferrosilicon alloys in electric arc furnaces.
Before the late 1960s in Europe and the mid-1970s in the United States, silica fumes were simply vented into the atmosphere.
With the implementation of tougher environmental laws during the mid-1970s, silicon smelters began to collect the silica fume and search for its applications.
The early work done in Norway received most of the attention, since it had shown that Portland cement-based-concretes containing silica fumes had very high strengths and low porosities.
Since then the research and development of silica fume made it one of the world’s most valuable and versatile admixtures for concrete and cementitous products.
Silica fume is an ultrafine material with spherical particles less than 1 μm in diameter, the average being about 0.15 μm.
This makes it approximately 100 times smaller than the average cement particle..