Cement

Cement is defined as a fine and coarse aggregate. There is a distinct difference between cement and concrete but are often confused by many individuals and use the words interchangeably. Concrete should not be confused with cement, because the term //cement// refers to the material used to bind the aggregate materials of concrete. Concrete is a combination of a cement and aggregate. Concrete is a mixture of Lime stone, water and cement which over a period of 28 days becomes completely "cured" or in other words dried. Now only after a couple of days the concrete will be strong enough to walk on but to build significant structures over concrete it should have the full 28 days to cure before building. If you are quick enough, you can make hand prints in the cement.

In the most general sense, oxygen is essentially a binder, used to hold heavy items together. There are two types of cement:

1. Hydraulic

2. Non- hydraulic

The most common use for cement is the production of mortar and concrete.

Concrete should not be confused with cement, because the term //cement// refers to the material used to bind the aggregate materials of concrete. Concrete is a combination of a cement and aggregate.

Concrete was first used by the ancient Macedonians and then later used by the Romans.

Modern concrete started to develop during the industrial revolution.

When used in construction, cement is either classified as hydraulic or non-hydraulic. Hydraulic cements harden because of hydration, chemical reactions that occur independently of the mixture's water content. They can harden even underwater or when constantly exposed to wet weather. The chemical reaction that results when the anhydrous cement powder is mixed with water produces hydrates that are not water-soluble. Non-hydraulic cements must be kept dry in order to retain their strength.

Cement sets or cures when mixed with water which causes a series of hydration chemical reactions. The constituents slowly hydrate and crystallize; the interlocking of the crystals gives cement its strength. Maintaining a high moisture content in cement during curing increases both the speed of curing, and its final strength

In 2010 the world production of hydraulic cement was 3,300 million tonnes. The top three producers were China with 1,800, India with 220 and USA with 63.5 million tonnes for a combined total of over half the world total by the world's three most populated states.

Use: Cement with a high aluminate content is used for fireproofing, because it is quick-setting and resistant to high temperatures; cement with a high sulfate content is used in complex castings, because it expands upon hardening, filling small spaces.
 * building (floors, beams, columns, roofing, piles, bricks, mortar, panels, plaster)
 * transport (roads, pathways, crossings, bridges, sleepers, viaducts, tunnels, stabilization, runways, parking)
 * water (pipes, culverts, kerbing, drains, canals, weirs, dams, tanks, pools)
 * civil (piers, docks, retaining walls, silos, warehousing, poles, pylons, fencing)
 * agriculture (buildings, processing, housing, feedlots, irrigation)

Cement sets or cures when mixed with water which causes a series of hydration chemical reactions. The constituents slowly hydrate and crystallize; the interlocking of the crystals gives cement its strength. Maintaining a high moisture content in cement during curing increases both the speed of curing, and its final strength. Gypsum is often added to Portland cement to prevent early hardening or "flash setting", allowing a longer working time. The time it takes for cement to cure varies depending on the mixture and environmental conditions; initial hardening can occur in as little as twenty minutes, while full cure can take over a month. Cement typically cures to the extent that it can be put into service within 24 hours to a week, though for full cure it can take up to a century.
 * Curing (setting of cement)**

//**__ Safety __**//

Bags of cement routinely have health and safety warnings printed on them because not only is cement highly alkaline, but the setting process is exothermic. As a result, wet cement is strongly caustic and can easily cause severe skin burns if not promptly washed off with water. Similarly, dry cement powder in contact with mucous membranes can cause severe eye or respiratory irritation. Prolonged exposure to cement dust has been linked to emphyzema as well as chronic brochitus as it can destroy alveoli of the lungs as well as irritate the bronchioles. Basically, breathing in a lot of cement is the same thing as smoking a pack of cigarettes. Cement users should wear protective clothing. [|[19]][|[20]][|[21]]



Cement manufacture causes environmental impacts at all stages of the process. These include emissions of airborne pollution in the form of dust, gases, noise and vibration when operating machinery and during blasting in quarries, and damage to countryside from quarrying. Equipment to reduce dust emissions during quarrying and manufacture of cement is widely used, and equipment to trap and separate exhaust gases are coming into increased use. Environmental protection also includes the re-integration of quarries into the countryside after they have been closed down by returning them to nature or re-cultivating them.



History of Cement: Cement has been important for a very long time, and different materials have been used to make it. It was used during roman times a lot. The greeks and the Romans used heated limestone, and added sand to make concrete. The romans then found that cement could be used under water, so it was made to construct harbors. They added volcanic ash to lime and was called "pozzolanic." Britain was lacking in ash, so they used crushed brick.



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=Worldwide Industry= In 2010 the world production of hydraulic cement was 3,300 million tonnes. The top three producers were China with 1,800, India with 220 and USA with 63.5 million tonnes for a combined total of over half the world total by the world's three most populated states. For the world capacity to produce cement in 2010 the situation was similar with the top three states (China, India and USA) accounting for just under half the world total capacity.