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Pozzolana is a natural or artificial material containing silica in a reactive form.
Roman builders used volcanic tuff found near Pozzuoli village near Mount
Visuvius in Italy. Tuff is a deposit of
volcanic ash that has formed a crust-like layer over the underlying land.
This volcanic tuff or ash is mostly siliceous in nature and acquired the name
of Pozzolona on the name of village Pozzuoli.
Subsequently, the term came to be applied to any other natural/artificial
material having nearly the same composition as that of volcanic tuff or ash
found at Pozzuoli.
Pozzolanas are materials
which, though not having cementing
properties in them, will combine chemically with Portland cement in presence of
water to form strong cementing material.
ASTM C 618-78 describes Pozzolana as a
siliceous or siliceous and aluminous material which in itself possesses little
or no cementitious value but will, in finely divided form and in presence of
moisture, chemically react with calcium hydroxide at ordinary temperatures to
form compounds possessing cementitious properties.
Pozzolana materials include power-station
fly ash ( ash precipitated electrostatically from the exhaust fumes of coal fired
power stations, also called pulverized fuel ash), burnt clays, ash from burnt
plant material and siliceous earths, volcanic ash etc
ASTM Standard C 595-79
describes Portland Pozzolonic Cement (PPC) as Type IP for general concrete
construction & Type P for use when high strengths at early ages are not
required. It limits pozzolana content to between 15 and 40% of the weight of
PPC.
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