Pozzolans are effective at lowering the mortar’s heat of hydration, which
improves its workability and durability. It also resists both sulfate and alkali-silica
reactions, which makes it beneficial to use in large concrete projects
such as bridges and dams
There are five major sources of pozzolan. Naturally occurring pozzolan deposits,
an ashlike product of volcanic activity, can be found in Europe and
the Middle East, among other regions. This type of pozzolan is very suitable
for use in concrete in wet conditions. Pozzolan also can be derived
from fired and crushed clay, such as bricks, and this variety is more durable
than volcanic pozzolan. Furnace slag from industrial processes such
manufacturing steel can also take the form of a pozzolan, and this type is
currently used as a concrete admixture. Another type is organic ash, produced
by burning coal or lime, but it is weaker than the other varieties and
is generally not suitable for brick-and-mortar construction. Finally, some
pozzolans have been produced by crushing rock and sand, and these have
been used in mortars throughout history but are not commonly used today
(Gibbons 1997).
Most pozzolans are plentiful and, because current uses for them are limited,
they represent a potential source of inexpensive construction material.
Some pozzolans can be processed into a material with characteristics
similar to Portland cement, so it is feasible that a significant portion of
cement in a concrete mixture may be replaced by pozzolan. This study explored
the properties of concrete mixes after the addition of various
pozzolan specimens.