More than 2000 years ago, Greeks and
Romans built structures that survive today that took advantage of the pozzolan-lime reaction. The Romans used a mixture of lime
and pozzolana, a fine volcanic ash, to produce a hydraulic cement (hardening
under water). Romans used pozzolana cement from Pozzuoli,
Italy near Mt. Vesuvius
to build the Appian Way, the Roman baths, the
Coliseum and Pantheon in Rome, and the Pont du Gard aqueduct in south France. Vitruvius reported a 2 parts pozzolana
to 1 part lime mixture. Animal fat, milk, and blood were used as admixtures (to
improve performance.) These structures still exist today!
Roman Gate
NATURAL
POZZOLAN
Pozzolans are present on earth's surface such as
diatomaceous earth, volcanic ash, opaline shale, pumicite, and tuff. These materials require further
processing such as calcining, grinding, drying, etc.The Aegean island
of Santorini
has natural deposits of volcanic ash (Santorin
earth.) In the United States,
volcanic tuffs and pumicites, diatomaceous earth, and
opaline shales are found
principally west of the Mississippi River in Oklahoma,
Nevada, Arizona,
and California.
Natural pozzolans have been used in dams and bridges
to lower the heat of hydration and increase resistance of concrete to sulfate
attack and control the alkali-silica reaction. Usually the pozzolanic
deposit must be in the vicinity of the project to support mining and processing
costs.
Tungurahua Volcano
in Abata,Ecuador
(Courtesy of AFP/MArtin Bernetti)
Mount St. Helens
emits plume of steam and ash. 
Popocatepetal Volcano in Mexico-volcanic ash. 
Cascades Volcano Observatory (Courtesy U.S. Geological Survey) 
The Los Angeles aqueduct (1910-1912) is comprised of portland
cement and a natural pozzolan, Rhyolite
pumicite. The Bonneville dam (1935) used portland-natural pozzolan cement.
The piers of the San Francisco-Oakland Bay Bridge have pozzolan
concrete (1935.)
ARTIFICIAL POZZOLAN
Fly ash is an
artificial pozzolan produced when pulverized coal is
burned in electric power plants. The glassy (amorphous) spherical particulates
are the active pozzolanic portion of fly ash. Fly ash
is 66-68% glass. Class F fly ash (see ASTM C 618) readily reacts with lime
(produced when portland
cement hydrates) and alkalies to form cementitious compounds. Class C fly ash also may exhibit
hydraulic (self-cementing) properties. Hungry Horse, Canyon Ferry, Palisades, Yellowtail dams all contain
portland cement-fly ash concrete.
Power plant (Courtesy
of Korean Electric Power Co. KEPCO)
Fly Ash (Courtesy of U. of Québec)
A pozzolan requires
the presence of a reactive alumino-silicate glass.
These glassy particulates must be fine enough to provide a sufficient reactive
surface area for the solid-state chemical reactions. This reactive glass reacts
with available calcium hydroxide and alkalies to
produce cementitious compounds.(calcium-silicate
hydrate gel and calcium-alumino silicates, etc.)
History of pozzolans and concrete
Information
on Pozzolans
Lassenite SR Pozzolan (Northern California, USA). See Western Pozzolan
MetaKaolin Pozzolan
Lava S.A.- Pozzolanic Rock (Milos, Greece).
see LAVA
Pagan Island
Pozzolan (Northern Mariana
Islands). see here.
More
Information on Pozzolan
Pyramids
have pozzolan?
