Cement is a binder, a substance that sets and hardens independently, and can bind other materials together. It is used in construction for binding materials like bricks, stones and tiles, and is also used for flooring and plastering purposes.
Cements used in construction can be either hydraulic or non-hydraulic. Hydraulic cements (e.g., Portland cement) set and harden because of hydration and hydrolysis reactions between the anhydrous cement powder and water.
Non-hydraulic cement such as slaked limes (calcium hydroxide mixed with water) harden due to the carbonation reaction by carbon dioxide present naturally in the air.
Cement alone cannot be used for construction work. It is used as a mixture with sand and crushed stones. It may be used as mortar or concrete. Mortar It is a mixture of cement, sand and water which is used for binding bricks together and for plastering.
Concrete It is a mixture of cement, gravel (crushed stones), sand and water. It is used in flooring works, columns, beams, foundations, etc. If instead of cement, lime is used, then the concrete is known as lime concrete.
Reinforced concrete construction (RCC) It is concrete reinforced with steel rods or heavy wire mesh. Reinforced concrete is used in floors, beams, girders, columns, slabs, bridges, etc. It imparts high tensile strength to structures.
Portland cement was discovered by Joseph Aspdin in 1824. The name Portland cement comes from the fact that the colour and quality of the resulting concrete are similar to Portland stone, a kind of limestone found in England.
Types of cements
The different types of cements based on Indian Standards are as follows:Ordinary Portland cement It is the most important type of cement and is commonly called OPC. It is made by grinding and mixing clay and lime bearing minerals in proper proportions and then heating the mixture to nearly 1400 °C. It is not in much use these days, having been replaced by Portland pozzolana cement (PPC).Portland pozzolana cement It can be fly ash-based or calcined clay-based. PPC is obtained by mixing OPC with suitable pozzolans at a certain temperature. Pozzolans are deposits of volcanic ash produced by rapid cooling. When mixed with slaked lime, pozzolans show properties similar to cement when it comes in contact with water. PPC is commonly used for various construction activities.