A pozzolan collected by electrostatic precipitators or baghouses at coal-burning power plants, made of glassy spherical particles that help concrete pump and finish. Class F ash, low in calcium, reacts slowly and is the standard choice for fighting alkali-silica reaction and sulfate attack; Class C ash carries more calcium and has some self-cementing ability. Dosages of 15 to 25 percent of the cementitious content bring lower heat, lower permeability and higher long-term strength.
That load's 20 percent fly ash and it's 50 degrees out, so it's going to sit there forever before you can get the pans on.
Ash with high unburned carbon soaks up air-entraining admixture, so a sudden drop in air content is often an ash problem, not a plant mistake.
Also heard as
- ash
- Class F ash
- Class C ash
- pulverized fuel ash
Related terms
SCM
Supplementary cementitious material: fly ash, slag cement or silica fume used alongside portland cement in a mix.
ASR
Alkali-silica reaction, a slow internal reaction between cement alkalis and certain aggregates that cracks concrete.
Air entrainment
Deliberately building billions of microscopic air bubbles into concrete so it survives freezing and thawing.
Slag cement
Ground granulated blast-furnace slag, an ironmaking byproduct that replaces part of the portland cement in a mix.