Cement concrete is only next to water in terms of the amount
of material used on our planet. Over hundreds of years, concrete has
become the material of choice for constructing residential and commercial
buildings, infrastructural facilities such as highways, dams and bridges,
canals, ports and other important facilities. The popularity of concrete
owes to its economy, ability to be cast into any shape, ability to be
fabricated practically anywhere and last but not the least, its inherent
durability. Innumerable historical landmarks in concrete speak volumes
about its durability and versatility.
The principal component that makes concrete possible is cement,
which has developed into a well-engineered and processed material from
its relatively humble beginnings early in history. The word ‘cement’
means to join something. Cementing materials have an interesting history.
The oldest structures relied on the sheer mass of the stone blocks for
stability – an example is the set of pyramids in Egypt. With the
progress of time, Egyptians switched over to smaller blocks and bricks
which needed some cementing material. There is evidence of the use of
bitumen as a cementing material by the Babylonians and Assyrians, as
well as of burnt gypsum in Egypt. The first uses of lime mortar for
binding are attributed to Egpytians, Greeks and Cretans, and some of
the structures built by them are still standing today. The use of pozzolanic
additives is also an age old practice – this is evident by the
use of burnt powdered brick (surkhi) in Bengal and Santorin Earth (volcanic
tuff) in Greece. In fact, the use of volcanic ash that spewed from Mt.
Vesuvius near Pozzuoli in Italy, by the Romans, led to the coining of
the word ‘pozzolana’.
It was in 1756 that John Smeaton, a British engineer, while
planning the building of Eddystone lighthouse tower, discovered that
the best limes for mortar contained a high degree of clayey matter.
Ultimately, such a lime was used along with pozzolana in equal quantities.
This was one of the first documented examples of application of a binding
material that was similar in composition to modern Portland cement.
In the early 19th century, Vicat prepared artificial hydraulic lime
by calcining an intimate mixture of limestone (chalk) and clay –
this is the principal forerunner to Portland cement. The development
of ‘Portland’ cement is actually attributed to Joseph Aspdin.
In 1824, Aspdin, while obtaining a patent for his hydraulic cement,
termed it as Portland cement, upon Portland stone (limestone from Dorset,
UK), which had a high quality and durability and a similar appearance.
The patent has long since run out, but the name ‘Portland’
has stayed on ever since.
In the last fifty years, there has been significant progress
in concrete technology, mainly owing to the revival of the interest
in supplementary cementing materials, as well as because of the advent
of new generation chemical additives for concrete. With the selection
of materials available today, it is possible to design tailor-made concretes
for any type of construction. The progress in concrete technology also
owes partly to the change in research outlook – modern researchers
try to learn about concrete from an interdisciplinary viewpoint, combining
chemistry and materials science with civil engineering. The emphasis
on fundamentals has paved the way for many an important breakthrough.
These advances have ensured that concrete will be a material of choice
for many decades into the future.