Pozzolan
Pozzolans are added to cement to increase set strength and reduce cement use.
Pozzolanic materials must be used in concrete in powder form, although lumps of hard material can be used as aggregate.
Upto 30% of portland cement may be replaced by pozzolan. Use of a waste material pozzolan such as flyash can reduce the cost of concrete.
Pozzolanic cement mixes take longer to achieve full strength.
A simple way to grind lump pozzolans is to put them in a cement mixer with a brick.
Fly ash is available as class C and class F. Only class F should be used for cement mortar mixes. This improves the strength and durability of the mortar, though both plain and pozzolanic mortars have life advantages and disadvantages under different conditions, so it does not always lead to improved life.
Concrete made with pozzolan has lower pH, and can corrode metalwork buried in it. Hence it is necessary to sleeve any metal pipework buried in the slab.
List of Pozzolans
- Fly ash
- Coal ash
- Volcanic ash
- Silica fume
- Slag
- Brick dust
- Tile & crockery dust
- Clinker
- Some clays
- Cannabis fibre