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Hydrated lime is made by adding water to quicklime, and is used to make mortar and plaster. It can be produced from limestone through a three-step process. Different processes produce different percentages of water, calcium, and magnesium. Hydrated lime is classified according to the amount of water it holds and its maximum air content. It is strongly alkaline and can be used to neutralize acid, but can cause skin and eye irritation and health problems if inhaled.
Hydrated lime is a type of dry powder made from limestone. It is created by adding water to quicklime to transform oxides into hydroxides. Combined with water and sand or cement, hydrated lime is often used to make mortar and plaster. Its chemical name is calcium hydroxide or Ca(OH)2.
When producing hydrated lime, a producer must first produce quicklime. Quicklime is obtained directly from calcination in raw limestone by the calcination process and consists of calcium oxide and magnesium oxide. In this process, the limestone is first crushed to reduce its size. Then it is washed and taken to the kilns to be heated through a three-step process: preheating, calcining and cooling. Once cooled, the quicklime is crushed and then water is added.
Depending on the method of production, high-calcium hydrated lime or dolomite can be created. Dolomite hydrated lime can be created at normal atmospheric pressure or at high pressure. The different processes produce different percentages of water, calcium and magnesium in the finished lime. In high pressure procedures all of the magnesium and calcium are hydrated, whereas in normal pressure processes only a portion of the magnesium and calcium is hydrated.
There are several classes of hydrated lime. Type S and type SA denote special limes of high purity and are most often used in mortars. Types N and NA denote normal limes and are not approved for use in building materials, but may be used in asphalt and paper production. Types SA and NA are aerated stocks, so their structure is more porous than their non-aerated counterparts.
Hydrated limes are classified according to the amount of water they hold and their maximum air content. Types S retain 85% of water, types N 75%. Types NA and SA are classified as having a maximum air content of 14% and types N and S have an air content of 14%.
Also called slaked lime, hydrated lime is a good binder and is watertight. It is also strongly alkaline, with a pH of 12.4. For this reason it can be used to neutralize acid, in water and wastewater treatment and to stabilize soil. This also means that it will cause skin and eye irritation if it comes into contact with the body, and inhaling the dust can cause health problems. Gloves, eye protection and masks should be worn at all times when working with these substances.
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