(Today, two of my friends will help you informing about cement which is quite familiar as widely used in construction. Usually while conversation they often meet-up a battle ground yet they follow rules of friendliness quite well.)
Chiru: Hey what happened to your shirt?
Piu: Don’t ask, a grey powder fall on shirt while roaming in my under-construction house.
Chiru: Idiot, it’s called cement, substance used widely for construction that sets, hardens, and adheres to other materials to bind them together. It is mostly formed in concrete form i.e. a mixture of cement, sand (fine aggregates), gravel (coarse aggregates) and bind with water.
Piu: How great our scientists invented this material for construction! I think they must be inspired from me.
Chiru: So unfortunate to tell that the occurrence of cement was from twelve million years ago. A deposit of cement was formed after an occurrence of oil shale located near to a bed of limestone burned due to natural causes. These were investigated in the 1960s and 1970s. They made from volcanic ash, pulverized bricks later added to lime for hydraulic binder, people referred as cementum, cimentum, cäment, and then cement.
Piu: But I know that the structures without cement built since ancient period are remarkable for their longevity!
Chiru: Yes, I’ll tell you some facts since antiquity. The Babylonians and Assyrians used bitumen to bind together burnt brick or alabaster slabs whereas in Egypt stone blocks were cemented together with a sand mortar and roughly burnt gypsum, which often contained calcium carbonate. Greeks and Crete used lime (calcium oxide). Later, the combination of hydrated non-hydraulic lime and a pozzolan produced a hydraulic mixture used by Ancient Macedonians and after three centuries by Romans on a large scale. The huge dome of the Pantheon in Rome and the massive Baths of Caracalla are examples made from these concretes, many of which still stand. The technical knowledge of hydraulic cement production was formalized by French and British engineers in the 18th century.
Piu: Well well, I’m too now excited to tell something that was once spelled from my 8th grade history teacher. The Spanish introduced tabby to Americas in 16th century. It was peculiar in content due to oyster-shell lime, sand, and whole oyster shells to form a concrete. In the South Atlantic seaboard of the United States, tabby relying on the oyster-shell middens was used in house construction from the 1730s to 1860s.
Chiru: Your efforts are appreciated to prove me wrong in assuming you brutish.
Piu: Taking this partly as a compliment, I would like to know further about cement used now.
Chiru: Surely, the modern development began along with the industrial revolution (1800s). We have definite proportion of chemical quantities defining the type and other characteristics of the cement. Most often preferred are Portland cement or Portland cement blends, but industry also uses other cements.
This cement is made by heating limestone with other materials like clay to 1450 °C in a kiln, that liberates a molecule of carbon dioxide (calcination) from the calcium carbonate to form calcium oxide, which then chemically combines with the other materials in the mix to form calcium silicates and other cementitious compounds. The resulting called ‘clinker’, is then ground with a small amount of gypsum into a powder to make Ordinary Portland cement (OPC).
Piu: Cement is used everywhere in the world, that means so much of lime and chemicals?
Chiru: The raw materials used in cement manufactures are extracted in large quarries, typically over 2.5 million tonnes per year! Nevertheless, such sedimentary rocks may vary considerably in their chemistry and properties, thus in their suitability. It is essential that chemical variation within the deposit is known so that development can be planned, and proper blending of stockpiles can consistently achieve the desired chemistry. Alternative materials include marble, chalk, marl, shell deposits, blastfurnace slag and alkali waste, which are endorsed by special features strengthening the quality of the cement.
Piu: I’ve heard about ample of construction projects in India, wondering how much India produces the cement!!!
Chiru: Only 7%
Chiru: Yes, and still being the second largest cement producer in the world. India produces around 500 million tonnes and goals to achieve 550 MT. China remains first (around 2500 MT) past 18 years consistently producing the largest cement quantity and exporting to other countries.
Piu: I think I should also contribute some tonnes to the society.
Chiru: But I think going back home would help you now the most.