- Education and Science
Cement and Concrete - History and Facts
How Cement is Made
Cement is made from a mixture of calcium, aluminium, silica and iron. A high-temperature kiln, often fuelled by coal, heats the raw materials, transforming them physically and chemically into a substance known as clinker (grey pebble-like material). The material is then mixed with gypsum before being grounded to a fine powder to make cement. Being one of the key construction materials, cement is considered as the most consumed material on earth – second only to water.
Difference Between Cement and Concrete
Cement is what holds concrete (which is made of cement mixed with rocks) together. The rocks form most of the mass, and this cement holds them in place. Indeed, cement is the key ingredient of concrete. Varying the mix of sand, aggregate and cement enables concrete to be used in a range of applications. Concrete is made up of three basic components – cement, aggregate (sand, rock, or gravel), and water.
Some concete suppliers use limestone as aggregate and many other also use river rock, pea gravel or other type of aggregate so that the concrete can react well in different situations. As concrete hardens, the mixture becomes stronger but the hardening process can take years. After a chemical process known as "hydration" concrete solidifies and hardens thus becomes a stone-like material and can be used to make foundations, architectural structures, pavements, overpasses, motorways/roads, patios, parking structures, driveways, patios, brick/block walls and footings for gates, poles and fences.
The more cement (the most expensive ingredient in concrete) the stronger the concrete, and if you found much more cheaper one, it is probably concrete that contains a lot of fly ash (or slag) instead of cement. Concrete can withstand the pressure of heavy loads because of its high compression strength. It can also be made porous or watertight, can be molded into any shape and is an affordable material for use in construction projects. Good concrete gets stronger with age. Concrete is also the world’s most widely used building material.
Coal is used as an energy source in cement production. In order to produce cement, large amount of energy is required. Kilns usually burn coal in the form of powder, it consumes about 450g of coal for 900g of cement produced.
Clay was used by the Assyrians and Babylonians as the bonding substance or cement. Lime and gypsum cement was used by the Egyptians. In 1756, John Smeaton (British engineer) made the first modern concrete (hydraulic cement) by adding pebbles and mixing powered brick into the cement. In 1824, Joseph Aspdin (English inventor) invented Portland cement (type of cement used in almost all concrete), and it remained as the dominant cement used in concrete production today. By burning ground limestone and clay together, he also created the first artificial cement. The chemical properties of the materials was changed by the burning process and he created a cement that is stronger than what using plain crushed limestone would produce. Modern cement is made of limestone, calcium, silicon, and often iron and aluminum.
Types of Cement
There are three types of cement – blended, Portland, and hydraulic. All blended and Portland cements are hydraulic cement. Hydraulic cement refers to all cement that set and harden when combined with water. Most construction cements today are hydraulic. If you mix hydraulic cement with water, certain chemical reactions will take place and these reactions will form chemical compounds which contain water. The formation of these compounds will then cause the mixture to harden. Hardened cements are insoluble in water, and they will retain its hardness and strength even if they are immersed in water.
- Concrete can last for thousands of years
- Concrete is considered as the most natural-disaster proof building material.
- Average concrete strength is around 3000 psi, and some concrete can actually reach strength over 20,000 psi.
- The largest concrete structure is the Three Gorges Dam in China, consuming 35 million cubic yards of concrete.
- Concrete will last longer than any other building material.
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