Properties and tests on cement
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Properties of cement
Concrete is a compound material made from sand, gravel
and cement. The cement is a mixture of various minerals which when
mixed with water, hydrate and rapidly become hard binding the sand and
gravel into a solid mass. The oldest known surviving concrete is to
be found in the former Yugoslavia and was thought to have been laid in
5,600 BC using red lime as the cement.
The first major concrete users were the Egyptians in
around 2,500 BC and the Romans from 300 BC The Romans found that by
mixing a pink sand-like material which they obtained from Pozzuoli
with their normal lime-based concretes they obtained a far stronger
material.
The pink sand turned out to be fine volcanic ash and they
had inadvertently produced the first 'pozzolanic' cement. Pozzolana is
any siliceous or siliceous and aluminous material which possesses
little or no cementitious value in itself but will, if finely divided
and mixed with water, chemically react with calcium hydroxide to form
compounds with cementitious properties. |
The Romans made many developments in concrete technology
including the use of lightweight Aggregates as in the roof of the
Pantheon, and embedded reinforcement in the form of bronze bars,
although the difference in thermal expansion between the two materials
produced problems of spalling. It is from the Roman words 'caementum'
meaning a rough stone or chipping and 'concretus' meaning grown
together or compounded, that we have obtained the names for these two
now common materials.
Test on cement
Strength of concrete in the hardened state is usually
measured by the COMPRESSIVE STRENGTH
using the Compression Test.
