Tuesday, June 25, 2019

What is Cement? and chemical bond

Cement is the most important building materials it is a binding agent that sets and hardens to adhere to building units like stones, bricks, tiles and many more. Cement generally refer as a very fine powder substance very chiefly made up of limestone (calcium), sand or clay (silicon), aluminum and iron ore and may include shells, chalk, marl, shale, clay, blast furnace slag, slate.
Raw materials are processed in cement manufacturing plants and heated to form a rock-hard substance that is then ground into a fine powder to be sold. The cement mixed with water causes a chemical reaction and forms a paste that hardens and hardens to join individual structures of building materials.
Cement is an integral part of urban infrastructure. It is used to make concrete and mortar, and to secure the infrastructure by joining the building blocks. The concrete is made of cement, water, sand and gravel mixed in defined proportions, while the mortar consists of cement, water and lime aggregate. 
These are used to join rocks, stones, bricks and other construction units, fill or seal the holes and make decorative patterns. Cement mixed with water silicates and aluminates, which form a hardened and water-repellent mass that is used for waterproofing.

Cement chemical bond

Cement is mainly of two types according to the way in which it is fixed and hardened: hydraulic cement, which hardens due to the addition of water, and non-hydraulic cement, which hardens by carbonation with carbon present in the air , so it can not be used underwater.
Non-hydraulic cement is produced through the following steps like lime cycle:
  1. Calcination: Lime is produced from the limestone at more than 825°C in 10 hours. (CaCO3 → CaO + CO2)
  2. Slaking: Calcium oxide is mixed with water to make slaked lime. (CaO + H2O → Ca(OH)2)
  3. Setting: Water is completely evaporated.
  4. The cement is exposed to dry air and it hardens after time-consuming reactions. (Ca(OH)2 + CO2 → CaCO3 + H2O)
On the other hand, hydraulic cement is mainly made up of silicates and oxides:
  1. Belite (2CaO·SiO2);
  2. Alite (3CaO·SiO2);
  3. Tricalcium aluminate/ Celite (3CaO·Al2O3)
  4. Brownmillerite (4CaO·Al2O3·Fe2O3)
The ingredients are processed in the kiln in cement plants. 

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