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Home > Portland cement

Manufacture of portland cement requires the burning of large quantities of fuel, typically coal, which along with impurities contained in the limestone can result in significant emissions of pollutants regulated in many countries, including greenhouse gases such as nitrogen oxides ( NOx) and sulfur dioxide, as well as particulates (PM 10, PM 2.5), volatile organic compounds (VOCs), and carbon monoxide. Cement plants are known to emit substantial quantites of arsenic, lead and mercury.

Portland cement was first manufactured in Britain in the early part of the 19th century, and its name is derived from its similarity to Portland Stone, a type of building stone that was quarried near Portland, England. The patentA patent is a set of exclusive rights granted by a government to an inventor or applicant for a limited amount of time (normally 20 years from the filing date). The term "patent" originates from the term patere which means to lay open (to public inspectio for Portland cement was issued to Joseph AspdinJoseph Aspdin ( 1788 20 March 1855) was an English mason, bricklayer and inventor who patented Portland cement on 21 October 1824. The eldest son of a Leeds bricklayer, he began using artificial cements made by burning ground limestone and clay together., a British bricklayer, in 1824.

1 Production

There are three fundamental stages in the production of Portland cement:

1. Preparation of the raw mixture
2. Production of the clinkerIn metallurgy, clinker is the term for the material remaining after the process of smelting a metal ore. It may contain ash from the smelting fire, and also the impurities, rock, and unreduced metal oxides. Clinker is used in the manufacture of Portland c
3. Preparation of the cement

The chemistry of cement is very complex, so cement chemist notationCement chemist notation (CCN) was deleloped to simplify the formulas cement chemists use on a daily basis. It is a sort of "short hand" way of writing the chemical formula of oxides of calcium, silicon, and various metals. Below is a list of all of the ab was invented to simplify the formula of common molecules found in cement.

The raw materials for Portland cement production are a slurryA slurry is a liquid mixture (especially involving water) composed of a mixture of various insoluble matter, such as mud or plaster of paris. Slurry pipelines are a specialized method of material transport that use a watery slurry to move particulates fro of calcium oxideProperties General Name Calcium oxide Chemical formula Ca O Appearance White solid Physical Formula weight 56. 1 amu Melting point 3200 K (2927 °C) Boiling point 3773 K (3500 °C) Density 3. 3 ×103 kg/ m3 Crystal structure NaCl Solubility hydrolysed Thermo (44%), silicon oxide (14.5%), aluminum oxide (3.5%), ferric oxide (3%), and magnesium oxide (1.6%). The raw materials are usually quarried from local rock, which in some places is already practically the desired composition and in other places requires the addition of clay and limestone, as well as iron ore, bauxite or recycled materials.

The raw mixture is heated in a kiln, a gigantic slowly rotating and sloped cylinder, with temperatures increasing over the length of the cyclinder up to ~1480 °C. The temperature is regulated so that the product contains sintered but not fused lumps; too low a temperature causes insufficient sintering, but too high a temperature results in a molten mass or glass. In the lower temperature part of the kiln, calcium carbonate (limestone) turns into calcium oxide (lime) and carbon dioxide. In the high temperature part, calcium oxides and silicates react to form dicalcium and tricalcium silicates (C₂S C₃S). Small amounts of tricalcium aluminate (C₃A) and tetracalcium aluminoferrite (C₄AF)are also formed. The resulting material is clinker, and can be stored for a number of years before use, prolonged exposure to water decreases the reactivity of cement produced from weathered clinker.

The energy required to produce clinker is ~1700 J/g, however because of heat loss during production actual values can be much higher. The high energy requirements and the release of significant amounts of carbon dioxide makes cement production a concern for global warming.

In order to achieve the desired setting qualities in the finished product, about 2% gypsum is added to the clinker and the mixture is pulverized very finely. This powder is now ready for use, and will react with the addition of water.

The finished cement has approximately the following composition: calcium oxide 64%, aluminum oxide 5.5%, silicon oxide 21%, ferric oxide 4.5%, magnesium oxide 2.4%, sulfate 1.6%, with a loss of ignition about 1% (mostly water).

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Topics: Portland Cement Oxide Water Calcium Production Clinker...

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