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https://en.wikipedia.org/wiki/Cement


00:02:09 1 Chemistry
00:02:42 1.1 Non-hydraulic cement
00:04:13 1.2 Hydraulic cement
00:05:24 2 History
00:05:55 2.1 Alternatives to cement used in antiquity
00:06:36 2.2 Macedonians and Romans
00:08:51 2.3 Middle Ages
00:09:35 2.4 16th century
00:09:58 2.5 18th century
00:12:32 2.6 19th century
00:17:44 2.7 20th century
00:19:44 3 Modern cements
00:20:25 3.1 Portland cement
00:21:54 3.2 Portland cement blends
00:26:09 3.3 Other cements
00:30:08 4 Setting, hardening and curing
00:31:15 5 Safety issues
00:31:39 6 Cement industry in the world
00:32:26 6.1 China
00:36:26 7 Environmental impacts
00:38:02 7.1 COsub2/sub emissions
00:38:53 7.2 Heavy metal emissions in the air
00:41:33 7.3 Heavy metals present in the clinker
00:42:39 7.4 Use of alternative fuels and by-products materials
00:42:58 8 Green cement
00:46:26 9 See also



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SUMMARY
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A cement is a binder, a substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (aggregate) together. Cement mixed with fine aggregate produces mortar for masonry, or with sand and gravel, produces concrete. Cement is the most widely used material in existence and is only behind water as the planet's most-consumed resource.Cements used in construction are usually inorganic, often lime or calcium silicate based, and can be characterized as either hydraulic or non-hydraulic, depending on the ability of the cement to set in the presence of water (see hydraulic and non-hydraulic lime plaster).
Non-hydraulic cement does not set in wet conditions or under water. Rather, it sets as it dries and reacts with carbon dioxide in the air. It is resistant to attack by chemicals after setting.
Hydraulic cements (e.g., Portland cement) set and become adhesive due to a chemical reaction between the dry ingredients and water. The chemical reaction results in mineral hydrates that are not very water-soluble and so are quite durable in water and safe from chemical attack. This allows setting in wet conditions or under water and further protects the hardened material from chemical attack. The chemical process for hydraulic cement found by ancient Romans used volcanic ash (pozzolana) with added lime (calcium oxide).
The word "cement" can be traced back to the Roman term opus caementicium, used to describe masonry resembling modern concrete that was made from crushed rock with burnt lime as binder. The volcanic ash and pulverized brick supplements that were added to the burnt lime, to obtain a hydraulic binder, were later referred to as cementum, cimentum, cäment, and cement. In modern times, organic polymers are sometimes used as cements in concrete.