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Lime
was traditionally classified as hydraulic or non-hydraulic. Hydraulic limes possess
the ability to set under water. Many of the current Standards (like British
Standards) no longer use the terminology hydraulic or non-hydraulic in the
classification of lime.
Hydraulic limes are produced
by burning limestone (calcium carbonate) containing quantities of impurities
such as silica, alumina and iron (whereas the Non-hydraulic limes contain only minor amounts
of silica, alumina and/or iron). The carbon dioxide is driven off at a
temperature in excess of 8500 C and the resultant product is calcium
oxide with calcium silicates (which give this material its hydraulic
properties). The material is sometimes also called quicklime.
Hydraulic limes made from limestone
containing silica, alumina and iron are called Natural hydraulic limes.
Artificial hydraulic limes are produced by blending powdered hydrated limes with
pozzolanic material and/or cement.
Traditionally, hydraulic limes were classified as
eminently hydraulic, moderately hydraulic and feebly hydraulic. Eminently
hydraulic lime was sometimes called Roman lime.
Non-Hydraulic limes: These are materials with high calcium content and only
minor amounts of silica, alumina and/or iron. Limestones which have a high
content of magnesium may also be classified as non hydraulic.
The main difference between Hydraulic and
Non-Hydraulic limes (Lime putty and hydrated lime) is that Hydraulic limes can
set under water via chemical reactions within the mortar, whereas Non-Hydraulic
limes can only set via Carbonation (absorbing CO2 from the
atmosphere).
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