Lime
It is an important binding material used in building construction. Lime has been used as a building material since ancient times. When it is mixed with sand it provides lime mortar and when it is mixed with sand and coarse aggregates, it forms lime concrete.
Types of Limes and their Properties
The limes are classified as fat lime, hydraulic lime and poor lime:
(i) Fat Lime: It is composed of 95 percent calcium oxide. When water is added, it sags strongly and its volume increases by 2 to 2*1/2 times. It is of white colour. Its properties are:
(a) hardens slowly
(b) has high degree of plasticity
(c) sets slowly in the presence of air
(d) white in colour
(e) slakes vigorously.
(ii) Hydraulic Lime: It consists of clay and ferrous oxide. Depending on the percentage of clay present, hydraulic lime is divided into the following three types:
(a) Feebly hydraulic lime (5 to 10% clay content)
(b) Moderately hydraulic lime (11 to 20% clay content)
(c) Eminently hydraulic lime (21 to 30% clay content)
The properties of hydraulic limes are:
• Sets under water
• Colour is not perfectly white
• Forms a thin paste with water and do not dissolve in water.
• Its binding property improves if its fine powder is mixed with sand and kept in the form of heap for a week, before using.
(iii) Poor Lime: It contains more than 30% clay. Its color is muddy. It has bad binding property. The mortar made from such lime is used in substandard works.
IS 712-1973 classifies lime as class A, B, C, D and E.
Class A Lime: This is primarily a hydraulic lime. It is usually supplied in the form of hydrated lime and is commonly used for structural works.
Class B Lime: Contains both hydraulic lime and fat lime. It is supplied as hydrated lime or quick lime. It is used to make mortar for masonry works.
Class C Lime: This is primarily a rough lime, supplied as both quick lime and fat lime. It is used in plastering for coat finish and whitewashing.
Class D Lime: This lime contains large amounts of magnesium oxide and is similar to fat lime. It is also commonly used for whitening and for finishing coats in plastering.
Class E Lime: This is an impure limestone, known as Kankar. It is available in modular and block form. It is supplied in the form of hydrated lime. It is commonly used for masonry mortar.