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Definitions
& History
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Complete History of Cement
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1. Earliest
binding/cementing materials
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The simplest, and possibly the earliest, binding material used
was wet mud, and there are records of its use in ancient Egypt.
Another example of a binder from the distant past is the use of naturally
occurring bitumen by the Babylonians and Assyrians in their brick and
alabaster (gypsum plaster) constructions.
Ancient
Egyptians also used Calcined impure Gypsum.
Early Greeks & Romans mostly used cementing
material obtained by burning Limestone. Roman mortar was very
hard & superior due to thorough mixing & long continuous ramming.
Lime is often considered as the "First Cement” of the
mankind.
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2. Naturally
obtained Hydraulic Cement
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Hydraulic Cement: Around 1000 BC, the ancient Greeks
were the first to learn the beneficial effects of mixing lime with fine
volcanic ash (may be, as a result of some lucky accident).
Ash can be thought of as naturally calcined rock,
having silicon in a chemically active state like the calcium in calcined
limestone.
When this lime-ash mixture is slaked, a whole new substance viz. calcium
silicate hydrate ( i.e C-S-H : approximately SiCa2O4
· xH2O) is formed. C-S-H is an amorphous gel
without any set crystalline structure. It hardens fast, even in water.
And it is more durable than lime cement.
The ancient Greeks used this
cement in a variety of ways. Some concrete cisterns built in that period
survive to this day.
Later Greeks & Romans used volcanic ash &
tuff mixed with lime & sand. Roman engineers mastered the technology and
constructed seaports, aqueducts and temples of concrete as well. Some of
these structures are as good as ever today, two thousand years later. The
formula for Roman cement was not improved upon until the development of
Portland cement in the early 1800s.
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Some old Roman Structures
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Foundations and
columns of aqueducts
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Arches of the
Colosseum
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Dome of the
Pantheon
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3. Earliest manmade
cement (called Hydraulic Cement)
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There
was a general decline in the quality & use of cement in Middle
ages. Advancement in the knowledge of cements could really take place
only in 18th century. In mid-eighteenth century, an English
engineer named John Smeaton needed a strong material to rebuild the Eddystone
lighthouse (shown in the picture on your right ) off the coast of Devon. He needed a hydraulic
mortar that would set and develop some strength in the twelve hour period
between successive high tides.
Smeaton concluded after investigations that lime-stone which
contained considerable proportion of clayey matter yielded better lime
possessing superior hydraulic properties. Thus was born, in 1756, the earliest manmade cement,
called hydraulic cement. This was made by calcining nodules of
argillaceous lime-stones.
However, it can not be
called as an entirely new discovery. In fact, it was well known to builders in the earliest historic times that certain
limes would, when set, resist the action of water, i.e. were hydraulic. It was also known that this property
could be conferred on ordinary lime by admixture of siliceous materials such
as pozzolana.
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4. Roman Cement?
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"Roman cement"
was developed by James Parker in the 1780s, and finally
patented in 1796.
It was, in fact, nothing
like any material used by the Romans, but was a “Natural cement"
made by burning septaria - nodules that are found in certain clay deposits,
and that contain both clay minerals and calcium carbonate. The burnt nodules
were ground to a fine powder. This product, made into a mortar with sand, set
in 5-15 minutes.
The success of "Roman Cement" led other manufacturers to develop
rival products by burning artificial mixtures of clay and chalk.
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5. Artificial cement
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Smeaton had noted that the "hydraulicity" of the lime was
directly related to the clay content of the limestone from which it was made.
Apparently unaware of
Smeaton's work, the same principle was identified by Louis Vicat in
the first decade of the nineteenth century. Vicat went on to devise a
method of combining chalk and clay into an intimate mixture, and, burning
this, produced an "Artificial Cement" in 1817.
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6. British cement
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Artificial cement was produced
in 1817 by Louis Vicat by burning an intimate mixture of Chalk &
Clay.
Around the same time,
James Frost, working in Britain,
produced what he called "British Cement" in a manner similar
to that for Artificial Cement, but did not obtain a patent until 1822.
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7. Portland Cement
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Joseph Aspdin is credited
with invention of “Portland Cement” which he got patented in 1824.
It
was manufactured by mixing & grinding hard lime stones and finely divided
clay into form of slurry & then calcining it in a furnace.
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8. Modern Portland
Cement
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Hydraulic limes, "Natural"
cements and "Artificial" cements all relied upon their
Belite content for strength development. Belite develops strength slowly.
They contained no Alite (which is responsible for early strength in
modern cements) because they were burned at temperatures below
1250 °C.
Thus these suffered
from two major disadvantages:
1. Fast-setting : this gave
insufficient time for placement
2. Low
early strengths: this required a delay of many weeks before formwork
could be removed.
The first cement to
consistently contain Alite was that made by Joseph Aspdin's son William Aspdin
in the early 1840s. This was what we call today "Modern
Portland Cement".
Because of the air of
mystery with which William Aspdin surrounded his product, others (e.g. Vicat
and
I C Johnson) have claimed precedence in this invention, but recent
analysis of both his concrete and raw cement have shown that William Aspdin's
product made at Northfleet, Kent was a true Alite-based cement.
However, Aspdin's
methods were "rule-of-thumb": Vicat is responsible for establishing
the chemical basis of these cements, and Johnson established the importance
of sintering the mix in the kiln.
However manufacturing
cost of William Aspdin's product was considerably high & as such, his
product was not received very well by the cement manufacturers of that time.
But the product set reasonably slowly and developed strength quickly.
Slowly a market opened
up for its use in concrete. The use of concrete in construction grew rapidly
from 1850 onwards, and was soon the dominant use for cements. Thus Portland
cement began its predominant role.
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