How microsilica works in concrete
This is to tell how microsilica works in concrete, as well as some of the practical considerations specifiers should be aware of when considering microsilica concrete.
Microsilica is a byproduct from silicon metal or ferrosilicon industries, where these metals are produced in submerged electric arc furnaces. As the molten metal is produced, a silica-based gas is emitted. This gaseous fume, as it rises, cools rapidly and forms extremely minute,Amorphous, spherical particles. The microsilica is collected in a bag house, a system for filtering the hot air and gases vented from the furnace.
30 years before, the microsilica particles were considered a Waste residue and discarded.However, during the 1950’s European researchers began to examine potential uses and investigate potential applications for microsilica, including its use in combination with portland cement.
Physical and Chemical Composition
The physical characteristics of microsilica are quite different than other concrete components.but the chemical make-up is rather similar. Microsilica is an extremely fine particulate, with average particle diameter is 0.2-0.3 μm , it is 100 times finer than cement particles.
Specific gravities of microsilica are low, about 2.2, versus 3.15 for most portland cements.Because microsilica is an extremely fine material, its raw bulk densities are very low, varying from 200 to 400 kg/m3 (9 to 25 lbs/ft3), after densified the density will be 650 kg/m3 to save freight fee.versus a dry bulk density of 1506 kg/m3 (94 lbs/ft3) for cement.
The chemical make-up of microsilica from silicon metal is almost pure amorphous nano silicon dioxide (SiO2). Table A compares a typical chemical analysis of the three common concrete constituents.