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Admixtures
A material other than water, aggregate, cement,
used as an ingredient of concrete or mortar
added to the batch immediately before or
during mixing.
There are two kinds of admixtures: Chemical
admixtures and Mineral admixtures.
Mineral Admixtures
Pozzolanic (Low-calcium FA)
-Cementitious (Granulated iron blast-furnace
slag)
-Both pozzolanic and cementitious (Hihgcalcium
FA)
-Natural materials (Volcanic Ash)
-By-product Material
Pozzolans (Definition)
Siliceous or siliceous and aluminous materials
which in themselves possess little or no
cementitious value but will, in finely divided
form and in the presence of moisture, chemical
react with Ca(OH)2 at ordinary temperatures to
form compounds possessing cementitious
properties.
The Pozzolanic Reaction
Pozzolanic Reaction
CH+S+aq CSH
Portland Cement Hydration
C3S + aq CSH + CH
The pozzolanic reaction is slow, so the rate of the
strength development and the heat of hydration
associated with this reaction are low. It may be noted
that the pozzolanic reactions can be accelerated by
temperature.