Cement

Cement is a kind of binder, which is a substance that is used in building and is characterised by the ability to set, become hard, and stick to other materials in order to bind those elements together. Sand, gravel, and other forms of aggregate are often combined with cement before usage so that the aggregate may be compacted. Mortar for masonry is produced by combining cement with fine aggregate; when combined with sand and gravel, cement makes concrete. Concrete is the substance that is used the most in existence and comes in second place, after water, as the most utilised resource on the world.

The majority of construction uses inorganic cement, which is often based on lime or calcium silicate. Cements are classified as either non-hydraulic or hydraulic, respectively, based on their capacity to harden in the presence of water (see hydraulic and non-hydraulic lime plaster).

The non-hydraulic kind of cement does not harden when it is damp or when it is submerged in water. Instead, it solidifies as it dries due to a reaction with the carbon dioxide in the air. After it has been set, it is not susceptible to damage by chemical agents.

Hydraulic cements, such as Portland cement, become set and sticky as a result of a chemical reaction that takes place between the dry materials and the water. The chemical reaction produces mineral hydrates as a byproduct, and these hydrates are not particularly water-soluble; as a consequence, they are extremely stable in water and resistant to chemical assault. This not only permits the material to be set in damp settings or under water, but it also protects the substance against additional chemical assault. The ancient Romans discovered the chemical procedure for making hydraulic cement by combining pozzolana (ash from volcanic eruptions) with lime (calcium oxide).

The Ancient Roman phrase opus caementicium is whence we get the word "cement." This term was used to describe masonry that was similar to contemporary concrete and was produced from crushed rock with burned lime serving as the binder. In order to create a hydraulic binder, volcanic ash and powdered brick supplements were first added to burned lime. In later times, this substance was referred to as cementum, cimentum, cament, and cement. In today's world, organic polymers are occasionally utilised in place of cement in the making of concrete.

The annual global output is around four billion tonnes, almost half of which is produced in China. If the cement manufacturing business were a nation, it would be the third highest emitter of carbon dioxide in the world, producing up to 2.8 billion tonnes of the gas annually, behind only China and the United States. About four percent of the world's total CO2 emissions may be attributed to the calcination reaction that occurs at the beginning of the cement manufacturing process. The cement kiln, in which the reaction takes place, is commonly fueled by coal or petroleum coke owing to the brilliant flame that is necessary to heat the kiln through radiant heat transfer. As a result, the complete process is responsible for around 8 percent of the world's total CO2 emissions. Because of this, the manufacturing of cement is one of the primary activities that drives climate change.