Shamrock Mining & Metals

Shamrock Natural Pozzolan, unlike cement, contains almost no lime, yet
it needs the lime to start reacting as a cement. The cement provides the
lime. Once the cement starts to hydrate with the addition of water, it
forms a matrix of crystals, which tie together the particles of sand and
aggregate. It also starts to produce an excess of lime that has not been
needed in the reaction. This “free lime” is needed for the Pozzolan to
start its reaction. The Pozzolan does not show any significant activity
immediately, but it reacts when the volume of “free-lime” is sufficient for
Pozzolan to start acting like a cement.

This delay in reaction by Pozzolan is of vital importance to producing
high quality and durable concrete, because part of the cementitious
binder does not react immediately. The rate of strength growth in the
early hours after placing is reduced – so the concrete stiffens more
slowly allowing more time for working and compaction and more time to
mix and place more concrete without the risk of cold joints.