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www.tecnologos.it/.../numero_010/concrete.asp
La historia de la puzolana es un buen ejemplo de como
la humanidad olvida y redescubre ciclicamente cosas
que nunca debió olvidar.
Short History of Concrete
by Umberto Barbisan e Matteo Guardini
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The oldest known form of concrete is to be found in
the Middle East and it dates back to 5600 BC; the Egyptians
(XXVI Century BC) used mixed with straw to bind dried
bricks, gypsum and lime mortars in stone masonry (in
particular for the construction of pyramids).
The Greeks living in Crete and Cyprus used lime mortars
as well (Eight Century BC), whereas Babylonians and
Syrians used bitumen to construct stone and brick masonries.
The Ancient Greeks, similarly, used calcined limestone,
while the Romans made the first concrete: mixed lime
putty with brick dust or volcanic ash. They used it
with stone to construct roadways, buildings and aqueducts.
The Romans used pozzolana, a particular type of sand
from Pozzuoli, near the volcano Vesuvio (Southern Italy),
to construct buildings of crucial importance, such as
the Pantheon or the Colosseo.
- Pantheon J. Durm, Handbuch der Architektur, Stoccarda,
1905.
Pozzolana is an uncommon kind of sand which reacts
chemically with lime and water, becoming a rocklike
mass; furthermore, it is siliceous and aluminous and
it reacts with calcium hydroxide to form compounds with
cementation properties.
The domed Pantheon, constructed in the Second Century
AD, is one of the structural masterpieces of Roman time:
it has a sophisticated structure with a large number
of voids, niches and small vaulted spaces aimed at reducing
its weight; in particular the dome shows a thicker structure
at its base, whereas its thickness tends to diminish
gradually, according to the increased height of the
dome (in other words, the dome thickness is inversely
proportional to its height).
Pliny reported a mortar of lime and sand (one part of
lime to four parts of sand), and Marco Vitruvio Pollione
(First Century BC) reported a mixture of pozzolana and
lime (two parts of pozzolana to one part of lime) and
we have also an essay of him as regards the properties
of concrete.
The name concrete comes from the Latin concretus, which
means to grow together.
During the Middle Ages the quality of cementing materials
deteriorated: lime and pozzolana were no longer used;
they were reintroduced in the thirteen and fourteen
centuries.
By the Fifteenth Century, Venetian constructors used
the black lime of Abetone – an area near Vicenza
(Northern Italy) - which is similar to pozzolana.
In 1499 Fra Giocondo used the pozzolana sand in the
mortar of the pier of the Pont de Notre Dame in Paris.
In 1779 B. Higging was granted a patent for hydraulic
cement used for exterior plastering.
In 1793 J. Smeaton found that the calcination of limestone
containing clay produced a kind of lime that hardened
under water; Smeaton used hydraulic lime to construct
the Eddystone Lighthouse in Cornwall.
- The Eddystone Lighthouse in
Cornwall by the interpretation of M. G. Sganzin,
Nuovo corso completo di pubbliche costruzioni, Venezia,
1849.
In 1796 James Parker patented a special type of natural
hydraulic cement – called Roman Cement –
obtained through the calcination of nodules of impure
limestone containing clay. A similar process was used
in France in 1802.
In 1812 L. Vicat prepared an artificial hydraulic lime
by calcining artificial mixtures of limestone and clay.
In 1818 natural cement was produced in the United States
and M. de Saint Leger was granted patents for hydraulic
cement. In 1822 J. Frost launched an artificial hydraulic
lime called British Cement.
The year 1824 is of paramount importance in the history
of concrete: in 1824 J. Aspdin improved the so called
Portland Cement – named after the high quality
stones quarried at Portland, in England - by burning
together a mixture of chalk and clay until carbon dioxide
was driven off; Aspdin’s cement was an immediate
success.
In 1828 I. K. Brunel was the first architect who used
Portland Cement for the constriction of the Thames Tunnel,
whereas in Germany systematic tests of the compressive
and tensile strength of cement began in 1836.
J. L. Lambot built in Southern France, in 1848, a small
concrete boat (later he reinforced his boats with iron
bars and wire mesh) and in the 1890s the Italian C.
Gabellini began to build concrete ships as well.
Notas :
1) El cemento puzolánico CP-40 debe contener
un promedio de 70% puzolana y 30% cal, siendo su finura
similar a la del cemento portland.
Ver pistas de tierra batida
Ver fichero PFD de la investigación de Murat.(en
francés)
Mortero de Cal
Horno de Cal
Puzolana
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