D2f
2
2e RSQThe average distance (of two normal tests) in
centimeters through which the pointer has travelled
to produce rupture is reported. In a normal test the
material between two clips pulls to a thread and
rupture occurs where the cross section is minimum.
The water cover, both below and above the speci-
men, must remain at least 10 mm throughout the
test.
This test indicates the cohesive
property of the bitumen and its ability to form a
thin, continuous film around the aggregate. It is also
an indication of the binding strength and ability to
withstand shocks. In the flexible pavement
construction bitumen binders should form thin ductile film around the aggregate. The binder
material which does not possess sufficient ductility would crack resulting in damping effect.
The ductility values of bitumen vary from 5 to over 100 cm. Often minimum value of 50 cm
is specified for bituminous pavement construction.
2q 2 Specific gravity is defined as the ratio of the mass of a given volume of the substance to the
mass of an equal volume of water at 27° ± 0.1°C. It can be determined by Pycnometer method
or Balance method.
In the Pycnometer method the specific gravity bottle is cleaned, dried and
weighed along with the stopper. It is then filled with fresh distilled water and kept in water
container for half an hour at temperature 27° ± 0.1°C. The bottle is removed and cleaned from
outside. The bottle containing distilled water is now weighed. The bitumen is heated to a
pouring temperature and is poured in the empty bottle. The material is filled up to half and
inclusion of air is prevented. To permit an escape of air bubbles, the sample bottle is allowed
to stand for half an hour at a suitable temperature, then cooled to 27°C before weighing.
In the Balance method the test specimen is 12 mm cube prepared by pouring the liquefied
sample in brass mould. The sample is weighed in air and is then weighed in distilled water,
maintained at 27° ± 0.1°C, to the nearest 0.1mg.
The specific gravity of the bitumen material is calculated as follows
2w!
Specific gravity =(c – a)
(b – a) – (d – c)where a = weight of specific gravity bottle
b = weight of the specific gravity bottle filled with distilled water
c = weight of the specific gravity bottle about half filled with material
d = weight of the specific gravity bottle about half filled with the material and the
rest distilled water
p# 2IV V h-2 2