Cement Chemistry
– Cement materials can be classified into hydraulic cements and non-hydraulic cements.
– Hydraulic cements require water for setting and hardening, while non-hydraulic cements can directly set under air.
– Hydraulic cements, such as Portland cement, contain silicates and oxides.
– The main mineral phases in hydraulic cement are alite, belite, tricalcium aluminate, and brownmillerite.
– The chemistry of these reactions is still under research.
– Hydraulic cement hardens through hydration reactions when water is added.
– The clinker minerals in hydraulic cement undergo hydration to form mineral phases.
– Silicates are responsible for the mechanical properties of hydraulic cement.
– Tricalcium aluminate and brownmillerite are essential for the formation of the liquid phase during the sintering process.
– The chemistry of these reactions is still not completely clear.
– Non-hydraulic cement sets as it dries and reacts with carbon dioxide in the air.
– It does not require water for setting and hardening.
– Non-hydraulic cement is resistant to chemical attack after setting.
– Calcium oxide is obtained through thermal decomposition of calcium carbonate.
– Non-hydraulic cement has been used since ancient times.
Ancient Cement Alternatives
– Bitumen was used by the Babylonians and Assyrians to bind burnt brick or alabaster slabs.
– Ancient Egyptians used a mortar made of sand, burnt gypsum, and calcium carbonate to cement stone blocks.
– Ancient Greeks used crushed potsherds as an artificial pozzolan for hydraulic cement.
– The Greeks used volcanic tuff as their pozzolan, while the Romans used crushed volcanic ash with lime.
– The Romans also used powdered brick or pottery as a substitute for pozzolanic ash.
Ancient Greece and Rome
– Lime was used by the Ancient Greeks and Minoans for cementation.
– The Greeks and Romans discovered the use of pozzolanic materials for hydraulic cement.
– The Romans used pozzolana from Pozzuoli and crushed volcanic ash for their concrete.
– Roman concrete could set under water, increasing its resistance to corrosion.
– Roman structures, such as the Pantheon and Baths of Caracalla, were made from these concretes.
Cement in Mesoamerica and Middle Ages
– Lightweight concrete used by pre-Columbian builders in El Tajin, Mexico.
– Composition of the aggregate and binder: pumice and pozzolanic cement made with volcanic ash and lime.
– Use of hydraulic cement by medieval masons and military engineers.
– Application in structures such as canals, fortresses, harbors, and shipbuilding facilities.
– Lime mortar and aggregate with brick or stone facing material used in the Eastern Roman Empire and Gothic period.
– Hydraulic mortar used in the German Rhineland throughout the Middle Ages.
– Local pozzolana deposits called trass in the German Rhineland.
Cement in the 16th and 18th centuries
– Introduction of tabby, a building material made from oyster shell lime, sand, and whole oyster shells, to the Americas by the Spanish.
– Formalization of technical knowledge for making hydraulic cement by French and British engineers.
– John Smeaton’s contribution to cement development during the construction of the third Eddystone Lighthouse.
– Use of tabby in house construction in the South Atlantic seaboard of the United States.
– Use of hydraulic limes and stucco to imitate stone in Britain.
– Development of Parkers Roman cement by James Parker, made from burnt septaria and sand.
– Popularity of Roman cement due to its success and quick setting time.
– Rival products developed by burning artificial hydraulic lime cements of clay and chalk. Source: https://en.wikipedia.org/wiki/Cement
A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (aggregate) together. Cement mixed with fine aggregate produces mortar for masonry, or with sand and gravel, produces concrete. Concrete is the most widely used material in existence and is behind only water as the planet's most-consumed resource.
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Cements used in construction are usually inorganic, often lime or calcium silicate based, which can be characterized as hydraulic or the less common non-hydraulic, depending on the ability of the cement to set in the presence of water (see hydraulic and non-hydraulic lime plaster).
Hydraulic cements (e.g., Portland cement) set and become adhesive through a chemical reaction between the dry ingredients and water. The chemical reaction results in mineral hydrates that are not very water-soluble and so are quite durable in water and safe from chemical attack. This allows setting in wet conditions or under water and further protects the hardened material from chemical attack. The chemical process for hydraulic cement was found by ancient Romans who used volcanic ash (pozzolana) with added lime (calcium oxide).
Non-hydraulic cement (less common) does not set in wet conditions or under water. Rather, it sets as it dries and reacts with carbon dioxide in the air. It is resistant to attack by chemicals after setting.
The word "cement" can be traced back to the Ancient Roman term opus caementicium, used to describe masonry resembling modern concrete that was made from crushed rock with burnt lime as binder. The volcanic ash and pulverized brick supplements that were added to the burnt lime, to obtain a hydraulic binder, were later referred to as cementum, cimentum, cäment, and cement. In modern times, organic polymers are sometimes used as cements in concrete.
World production of cement is about 4.4 billion tonnes per year (2021, estimation), of which about half is made in China, followed by India and Vietnam.
The cement production process is responsible for nearly 8% (2018) of global CO2 emissions, which includes heating raw materials in a cement kiln by fuel combustion and resulting release of CO2 stored in the calcium carbonate (calcination process). Its hydrated products, such as concrete, gradually reabsorb substantial amounts of atmospheric CO2 (carbonation process) compensating near 30% of initial CO2 emissions, as estimations suggest.
