Microsilica (silica fume) and metakaolin are the two most widely used high-reactivity pozzolans. Both react with the calcium hydroxide released when cement hydrates, turning a weak by-product into extra binding gel.
Strength and permeability
Microsilica is the finer of the two and usually gives the highest compressive strength and the lowest chloride permeability, which is why it dominates in marine works, bridge decks and UHPC.
Colour and workability
Metakaolin is off-white, so it suits architectural and white concrete where grey silica fume would darken the mix. Many producers also find it easier to handle and finish.
Which should you use?
For maximum strength and durability, start with microsilica at 5–10% of binder. For light-coloured or architectural work, or where finishing matters, metakaolin at 8–15% is a strong alternative. Contact us for samples of both and run trials with your own mix.
