How is cement used

From there the raw meal extracted from the silo, now called kiln feed, is fed to the top of the preheater kiln for sintering. The preheater kiln system consists of a multi-stage cyclone preheater, combustion chamber, riser duct, rotary kiln, and grate cooler. In the preheater, the kiln feed is preheated by hot gas coming from the combustion chamber and rotary kiln. It is then partially calcined in a combustion chamber and riser duct.

The feed then moves into the rotary kiln where it is superheated to approximately C to form clinker components through a process called sintering. The heat is produced from the burning of fuel in the main burner rotary kiln and in the combustion chamber with the help of preheater exhaust Fans or Kiln ID Fans.

Coal, natural gas, fuel oil, and petroleum coke are often used for firings. Sintering is when the chemical bonds of the raw meal are broken down through heat, recombining into new compounds that form a substance called clinker. Clinker comes out of the kiln as extremely hot, small, dark gray nodules 1mm to 25mm in size. It drops onto the grate cooler for cooling from approximately C to approximately C through the use of different cooling fans. Part of the hot air extracted from the cooler is utilised as a secondary and tertiary air for combustion in rotary kiln and combustion chamber, respectively.

The cooled clinker discharges from the cooler into the pan conveyor and it is transported to the clinker storage ready to be transported to the cement mills via cement mill ID fans. At the cement mills the clinker is mixed with other additives required for producing the specific type of cement.

Gypsum for OPC, limestone for limestone cement, and slag for slag cement. The ball mill then grinds the feed to a fine powder. The fine powder is then sent to a separator which separates fine and coarse product.

The latter is sent to the mill inlet for regrinding. At the lower end is a roaring blast of flame, produced by precisely controlled burning of powdered coal, oil, alternative fuels, or gas under forced draft. As the material moves through the kiln, certain elements are driven off in the form of gases. The remaining elements unite to form a new substance called clinker. Clinker comes out of the kiln as grey balls, about the size of marbles.

Clinker is discharged red-hot from the lower end of the kiln and generally is brought down to handling temperature in various types of coolers. The heated air from the coolers is returned to the kilns, a process that saves fuel and increases burning efficiency. After the clinker is cooled, cement plants grind it and mix it with small amounts of gypsum and limestone. Cement is so fine that 1 pound of cement contains billion grains. The cement is now ready for transport to ready-mix concrete companies to be used in a variety of construction projects.

Although the dry process is the most modern and popular way to manufacture cement, some kilns in the United States use a wet process. The two processes are essentially alike except in the wet process, the raw materials are ground with water before being fed into the kiln. A cement is any substance which binds together other materials by a combination of chemical processes known collectively as setting.

Mortar is a mixture of cement and sand whereas concrete also includes rough aggregates Figure 1. Because it is a major component of both of these building materials, cement is an extremely important construction material. It is used in the production of the many structures that make up the modern world including buildings, bridges, harbours, runways and roads.

It is also used for facades and other decorative features on buildings. The constant demand for all of these structures, increasingly from the developing world, means that cement is the second most consumed commodity in the world after water. Modern cement has come a very long way from its origins. Archeological evidence has been found that a form of crude concrete was used in hut construction in the areas now covered by Serbia, dating from around BC and Israel BC.

The ancient Greeks also had access to lime plaster, 8 which was often used for decorative purposes and crude cements derived from calcined lime were also used by the Roman empire, 9 notably in the construction of the Pantheon in Rome. The progress of cement development was slowed in the Middle Ages, with significant information being lost, but by the industrial revolution, cements and the concretes that they could be used to make were increasingly being researched as an alternative to wood and stone.

In the late s and early s a great number of novel cement patents and formulations were devised by those keen to exploit the need for new building materials. Among the first to realise the great potential of cement and concrete for modern engineering was James Smeaton, who was charged with the task of rebuilding the Eddystone Lighthouse on the English Channel in following a devastating fire.

Smeaton researched the properties of lime from many regions of the UK and tested them systematically for their resistance to water. After much research he determined that lime obtained from Aberthaw in Wales was the most suitable and remarked that he had found a cement that could, "equal the best merchantable Portland stone in solidity and durability.

A string of others were awarded patents for novel cementitious materials in the coming years, including James Parker , Edgar Dobbs , Louis Vicat , Maurice St. Leger , James Frost and Joseph Aspdin The most successful of these were Parker, who termed his invention 'Parkers Cement' then 'Roman Cement', Frost who coined the term 'British Cement' and Aspdin, who possibly inspired by the earlier work of Smeaton termed his invention 'Portland Cement.

For much of the s, Roman cement dominated, but in the latter part of the century developments into the use of rotary kilns for cement production in the US led to Portland cement becoming the dominant cement type. By , Atlas Cement Company, based in the Lehigh Valley, had 29 rotary cement kilns producing cement 10 times more rapidly than earlier kilns.

By this point Portland cement had undergone a large number of incremental improvements, but its place at the top of the global cement pile was far from assured. Writing in , British construction consultant Henry Faija wrote, "I do not wish to frighten manufacturers, but my own impression is that in a few years Portland cement will be superceded by another material. Portland cement, as at present made, is a chemical combination carried out in the crudest way. Continued heating and reaction causes calcination in which varying calcium silicates are produced.

By adjusting the proportion of gypsum it is possible to give rise to cements with different setting times.