Traditional Material - Lime
Stones, bricks, cement, lime and timber are the traditional
materials used for civil engineering constructions for several centuries. In
this chapter types, properties, tests and uses of these materials is explained.
1.3 LIME
It is an important binding material used in building construction.
Lime has been used as the material of construction from ancient time. When it
is mixed with sand it provides lime mortar and when mixed with sand and coarse
aggregate, it forms lime concrete.
1.3.1 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
percentage of calcium oxide. When water is added, it slakes
vigorously and its volume increases to 2 to 2,5 times. It is white
in 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 contains
clay and ferrous oxide. Depending upon the percentage of clay present, the
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 colour is muddy. It has poor binding property. The mortar made
with such lime is used for inferior works.
Class A Lime: It is
predominently hydraulic lime. It is normally supplied as hydrated lime and is commonly
used for structural works.
Class B Lime: It contains
both hydraulic lime and fat lime. It is supplied as hydrated lime or as quick
lime. It is used for making mortar for masonry works.
Class C Lime: It is
predominently fat lime, supplied both as quick lime and fat lime. It is used
for finishing coat in plastering and for white washing.
Class D Lime: This lime
contains large quantity of magnesium oxide and is similar to fat lime. This is
also commonly used for white washing and for finishing coat in plastering.
Class E Lime: It is an
impure lime stone, known as kankar. It is available in modular and block form.
It is supplied as hydrated lime. It is commonly used for masonry mortar.
1.3.2 Tests on Limestones
The following practical tests are made on limestones to determine
their suitability:
(i) Physical
tests
(ii) Heat test
(iii) Chemical
test
(iv) Ball
test.
(i) Physical Test: Pure limestone is white
in colour. Hydraulic limestones are bluish grey, brown or are having dark
colours. The hydraulic lime gives out earthy smell. They are having clayey
taste. The presence of lumps give indication of quick lime and unburnt lime
stones.
(ii) Heat Test: A piece of dry stone
weighing W1 is heated in an open fire for few hours. If weight of sample after
cooling is W2, the loss of weight is W2 – W1. The loss of weight indicates the amount of carbon
dioxide. From this the amount of calcium carbonate in limestone can be worked
out.
(iii) Chemical Test: A teaspoon full of lime
is placed in a test tube and dilute hydrochloric acid is poured in it. The
content is stirred and the test tube is kept in the stand for 24 hours.
Vigourous effervescence and less residue indicates pure limestone. If
effervescence is less and residue is more it indicates impure limestone. If
thick gel is formed and after test tube is held upside down it is possible to
identify class of lime as indicated below:
- Class A lime, if gel do not flow.
- Class B lime, if gel tends to flow down.
- Class C lime, if there is no gel formation.
(iv) Ball Test: This test is conducted
to identify whether the lime belongs to class C or to class B. By adding
sufficient water about 40 mm size lime balls are made and they are left
undisturbed for six hours. Then the balls are placed in a basin of water. If
within minutes slow expansion and slow disintegration starts it indicates class
C lime. If there is little or no expansion, but only cracks appear it belongs
to class B lime.
1.3.3
Uses of Lime
The following are the uses of lime in civil works:
(i) For white
washing.
(ii) For
making mortar for masonry works and plastering.
(iii) To
produce lime sand bricks.
(iv) For soil
stabilization.
(v) As a
refractory material for lining open hearth furnaces.
(vi)
For making cement.