Shamrock Mining & Metals

Because strength development of natural Pozzolan in concrete is
slower than that of cement, the only place where it can grow is within
the voids left in the hardened cement matrix. It plugs the gaps in the
concrete. There is a significant reduction in the number of voids found
in concrete made using natural Pozzolan. This reduction is so great,
that there is a measurable increase in the impermeability of the
concrete.

A concrete with improved impermeability will better resist attack from
chemicals and salts, which can be carried in water. By reducing the
amount of water penetrating the concrete, the salts are unable to reach
the binder and attack it. It is because of this characteristic that
throughout the world, concrete for use in marine and harsh
environments are usually specified to contain a quality assured,
chemical resistant component like natural Pozzolan.