OBJECTIVES
i.
To
measure the ductility of a given sample of bitumen.
ii.
To
determine the suitability of bitumen for its use in road construction.
APPARATUS REQUIRED
The apparatus for the standard ductility test
as per IS 1208-1978 consists of followings:
i.
Briquette
mould: It is made up of
brass. Circular holes are provided at ends called clips to grip the fixed and
movable ends of the testing machine. The mould when properly assembled form a
briquette specimen of following dimensions: -
Total length =75.5 ± 0.5 mm
Distance between clips = 30.0 ± 0.3 mm
Width at mount of slip = 20.0 ± 0.2 mm
Width at minimum cross-section
(Half way between clips) =10.0 ± 0.1 mm
Thickness throughout = 10.0± 0.1 mm
ii.
Water
bath: - A bath maintained within 27.0° ± 0.1°C of
the specified test temperature containing not less than 10 liters of water, the
specimen being submerged to a depth of not less than 10cms and supported on a
perforated shell and less than 5 cm from the bottom of the bath.
iii.
Testing
machine: - For pulling the
briquette of bituminous material apart, any apparatus may be used which is so
constructed that the specimen will be continuously submerged in water while the
two clips are being pulled apart horizontally at a uniform speed of 50± 2.5 mm
per minute.
iv.
Thermometer: Range 0-44°C and readable up to 0.2°C
THEORY
Ductility is the property of bitumen that
permits it to undergo great deformation or elongation. Ductility is defined as
the distance in cm to which a standard sample or briquette of material will be
elongated without breaking. The
ductility test gives a measure of adhesive property of bitumen and its ability
to stretch. In flexible pavement design, it is necessary that binder should
form a thin ductile film around aggregates so that physical interlocking of the
aggregates is improved. Binder material having insufficient ductility gets
cracked when subjected to repeated traffic loads and it provides pervious
pavement surface. Ductility of a bituminous material is measured by the distance
in cm to which it will elongate before breaking when two ends of standard
briquette specimen of material are pulled apart at a specified speed and
specified temperature. The distance up to the point of breaking of thread is
the ductility value which is reported in cm.
PROCEDURE
i.
The bituminous material was melted
completely at a temperature of about 75° to 100°C above the approximate
softening point until it becomes thoroughly fluid.
ii.
The surface of the plate an
interior part of mould is coated with mercury or glycerine and dextrine in
order to prevent from sticking of material.
iii.
The fluid was then poured in the
mould after stirring.
iv.
After about 30-40 minutes the
plate assembly was placed along with sample in water bath.
v.
The sample and mould assembly was
removed and levelled the surface using hot knife.
vi.
The clips were hooked carefully on
the machine without causing any initial strain.
vii.
The machine was turned on and
clips was pulled horizontally at speed of 50mm per minute.
viii.
The distance at which bitumen
threads broken was noted.
OBSERVATIONS
Bitumen
grade = 80/100
Pouring
temperature =120℃
Test
temperature = 25℃
Sample
no.
|
Initial
reading (a)
|
Final
reading(b)
|
Ductility(b-a)
|
1.
|
0
|
>100
|
>100 cm
|
2.
|
0
|
>100
|
>100 cm
|
3.
|
0
|
>100
|
>100 cm
|
RESULTS
Ductility value=>100cm
CONCLUSIONS AND DISCUSSIONS
Suitability of bitumen is
judged depending on its type and proposed use. Bitumen with low ductility value
may get cracked especially in cold weather. The ductility values of bitumen
vary from 5 to over 100 for different grades. A minimum ductility value of 75cm
has been specified by the ISI for bitumen of grade 45 and above. From the
experiment, the ductility value is over 100 which suggests that the bitumen can
be generally used and doesn’t crack on cold weather. The ductility
value may be affected by pouring temperature, test temperature as well as rate
of pulling. Besides these errors, the experiment was completed.
PRECAUTIONS
i.
The plate assembly upon which mould is placed
should be completely flat and level.
ii.
Briquette mould should not be disturbed and touch.
iii.
Plates as well as interior part of mould should be
properly coated with mercury or glycerin.
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