Portland Cement

Portland cement is the common type of cement used around the world due to its basic ingredients of concrete, mortar, stucco and non specialty grout. It is fine powdered by grinding Portland cement clinker. The Portland cement clinker is the hydraulic material; consist of two - thirds by mass of calcium silicates (3 CaO.SiO₂ and 2Cao.SiO₂) and the remainder consists of aluminium and iron containing clinker phase and other compounds. The ratio of CaO to SiO₂ should not be less than 2.0, and the magnesium content should not exceed 5.0% by mass.

Portland clinkers are made by heating, in a kiln, which is about 1450⁰C for modern cements. The aluminium oxide and iron oxide are used as a flux and contribute little to strength. For special cements, such as Low Heat and sulfate Resistant types, it is essential to limit the amount of tricalcium aluminate (3 CaO.Al₂O₃) formed. Limestone is the major raw material for clinker making, and is mixed with a second material containing clay as source of alumino- silicate.

History

In the early part of nineteenth century, Portland cement was developed from natural cements made in Britain, and name is derived from its Portland stone, that was a type of building stone, which was quarried on the isle of Portland in Dorset, England.

Production of Portland cement

Portland cement consists of three basic stages. They are; preparation of raw mixture, production of clinker, and preparation of the cement. Cement chemist notation was invented, to simplify the complex chemical formulae which describe the compounds present in the cement. This cement chemist notion shows that, most of the elements are present in their higher oxidation state, and chemical analyses of cement are expressed as mass percent.

Setting and hardening

Cement sets when its mixed with water. The different constituents will slowly crystallize and their interlocking of cements will provide strength to cement. To convert portlandite into insoluble calcium carbonate, carbon dioxide is slowly absorbed. After all, immersion in the warm water will speed up the settings. In Portland cement, gypsum is added to prevent cement flash settings.

Use of Portland cement

Portland cement is widely used in production of concrete. As a construction material, concrete can be available in any desired shape, and once hardened it becomes structural strong (load bearing) element. It is involved in factory production pre cast units such as panels, beams, road furniture and may make cast-in-situ concrete such as building superstructures, dams, roads.

Questions:

• Explain the use of Portland cement?
• Briefly explain Portland cement?