SOFTENING POINT TEST
OBJECTIVE
TO DETERMINE TEMPRATURE AT WHICH THE GIVEN GRADE OF
BITUMEN ATTAINS PARTICULAR DEGREE OF SOFTENING UNDER THE
SPECIFIED CONDITION OF TEST.
APPARATUS REQUIRED
(i) The ring and ball apparatus consisting of
(a) Steel balls-two numbers each of 9.5 mm diameter weighing 3.5 ± 0.05 g.
(b) Brass rings-two numbers each having depth of 6.4 mm. The inside
diameter at bottom and top is 15.9mm and 17.5 mm respectively.
(c) Ball guides: to guide the movement of steel balls centrally.
(d) Support -that can hold rings in position and also allows for suspension
of a thermometer. The distance between the bottom of the rings and the top
surface of the bottom plate of the support is 25mm.
(ii) Thermometer: that can read up to 100° C with an accuracy of 0.2° C.
(iii) Bath-heat resistant glass beaker not less than 85 mm in diameter &1220mm
deep.
(iv) Stirrer: Used for fixing ensuring uniform heat distribution at all time
throughout the bath.
THEORY
The Softening Point of bitumen or tar is the temperature at which the substance
attains particular degree of softening. As per IS: 334-1982, it is the temperature in
ºC at which a standard ball passes through a sample of bitumen in a mould and
falls through a height of 2.5 cm, when heated under water or glycerin at specified
conditions of test. The binder should have sufficient fluidity before its applications
in road uses. The determination of softening point helps to know the temperature
up to which a bituminous binder should be heated for various road use
applications. Softening point is determined by ring and ball apparatus.
PROCEDURE
(i) Preparation of test sample: Heat the material to a temperature between 75-100°
C above its softening point; stir until, it is completely fluid and free from air
bubbles and water. If necessary, filter it through IS sieve 30. Place the rings
previously heated to a temperature approximating to that of the molten material, on
a metal plate which has been coated with a mixture of equal parts of glycerin and
dextrin. After cooling for 30 minutes in air, level the material in the ring by
removing the excess material with a warmed, sharp knife.
(ii) Assemble the apparatus with the rings; thermometer and ball guides in position
(iii) Fill the bath with distilled water to a height of 50mm above the upper surface
of the rings. The starting temperature should be 5° C.
Note: Use glycerine in place of water if the softening point is expected to be above
80° C; the starting temperature may be kept 35° C.
(iv) Apply heat to the bath and stir the liquid so that the temperature rises at a
uniform rate of 5 ± 0.5 °C per minute.
(v) As the temperature increases the bituminous material softens and the balls sink
through the rings carrying a portion of the material with it.
(vi) Note the temperature when any of the steel balls with bituminous coating
touches the bottom plate.
(i) Record the temperature when the second ball touches the bottom plate.
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