A byproduct of electric-arc furnaces producing silicon and ferrosilicon metal, with particles roughly 100 times finer than cement grains. At 5 to 10 percent of the cementitious content it packs the gaps between cement particles and reacts strongly as a pozzolan, helping push strength past 10,000 psi and cutting chloride penetration. Bridge decks, parking garages and high-rise columns use it, but the mix is sticky, bleeds almost nothing and cracks easily if the surface dries before curing starts.
Silica fume deck tomorrow, so get the foggers and the evap retarder on the truck, that mix won't give you any bleed water.
Finishers describe it as gummy: the time between floating and cracking is short, and it punishes anyone who waits for bleed water.
Also heard as
- microsilica
- condensed silica fume
Related terms
SCM
Supplementary cementitious material: fly ash, slag cement or silica fume used alongside portland cement in a mix.
HRWR
High-range water reducer, the superplasticizer that makes concrete flow without adding water.
Plastic shrinkage cracking
Cracks that open in fresh concrete before it sets, when the surface dries faster than bleed water replaces it.
Evaporation retarder
A film-forming liquid sprayed on fresh concrete to slow moisture loss between finishing passes.