Use of Calcium Metal and Compounds

Calcium carbonate is used on a large scale for many purposes. Pure Hmestone, with a content of 98-99% CaCOj, 0.5% MgCOj and less than 0.3% other oxides, ground to very fine particles is used as a filler for paper and makes it dazzHng white. Ground limestone is also used as a filler in plastics, especially PVC. It improves stiffness, impact strength and dimensional stability. 

Large quantities of lime are used in the steel industry to hne furnaces and as a component of molten slags, which take an active part in the refining of steel. For production of this type of lime, rocks can be used that contain at least 80% of the car- 

Cement is a lime-consuming product Portland cement was developed and patented in 1824 by its British inventor Joseph Aspdin (1799-1855). Aspdin heated a mixture of finely ground Hmestone and clay in his kitchen stove and ground the mixture into a powder that hardened after the addition of water [14.4]. The term portland cement was used because concrete made from cement resembled the stone on the Isle of Portland on the British coast. 

A properly designed concrete mixture contains about 10 to 15% cement, 60 to 75% aggregate and 15 to 20% water. Aggregates are inert granular materials such as sand, gravel or crushed stone, which, along with water and portland cement, are essential ingredients in concrete. 

AH Portland cements are hydrauHc cements, which means that they harden through a chemical reaction with water. The initial hardening is caused by the hydration of tricalcium siHcate Ca SiO, which forms jelly-Hke hydrated siHca and calcium hydroxide. These substances crystalHze and bind together the particles of sand or stone that are always included. The calcium hydroxide formed increases the pH, which protects the steel reinforcing bars against corrosion. 

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