Ductility of Bitumen
Aim:
To determine the ductility property of the Bitumen
Apparatus:
Ductility machine, Briquette ,mould, putty knife ,water bath square and towel.
Theory:
In the flexible pavement construction where bitumen binders are used , it is of
significant importance that the binders form ductile thin films around the
aggregates .This serves as a satisfactory binder in improving the physical
interlocking of the Aggreates. The binder material which does not posses
sufficient ductility would crack and thus provide pervious pavement surface.
The ductility is express distance in centimeters to which a standard briquette of
bitumen can be stretched before the thread breaks.
Application :
1. The temperature changes in the bituminous mixes & repeated
deformation that occur in
Flexible pavement +due to the traffic load.
2. If bitumen pavement has low ductility value, the bituminous pavement
may crack, especially in cold weather.
3. The ductility values vary from 5 to over 100.
4. Often a minimum ductility value of 50 cm is specified for bituminous
construction.
Procedure :
1. The bitumen is softened to a pouring Consistency between 75 and
100 C above the approximate temperature at which bitumen softens.
2. It is poured in the mould assembly and placed on a brass plate, after
a solution of glycerine is applied at all the surfaces of the mould
exposed to bitumen.
3. After 30 to 40 minutes, the Plate assembly along with the sample is
placed in the water bath maintained at 27 C for 30 minutes.
4. After trimming the specimen, the mould assembly containing sample
is replaced in water bath maintained at 27 C for 85 to 95 minutes.
5. The sides of the mould are now removed and the clips are carefully
booked on the machine without causing any initial strain.
6. The pointer is set to read zero. The machine is started and the two
clips are thus pulled apart horizontally and the sample should be
immersed in water at depth of at least 10mm.
The distance at which the bitumen thread breaks is recorded in cm.
Results:
The distance stretched by the moving end of the specimen up to the point
of breaking of thread measured in centimeters is recoded as ductility value.
References:
Indian standard Methods for Tar and Bitumen. Determination of ductility
IS:1203. Indian standard Institution.
Indian standard Specification for paving Bitumen.IS:73-1961.Indian Standard
Institution.
IRC Recommended for Ductility of Bitumen:
A certain minimum ductility is necessary for a bitumen binder. This is
because of the temperature changes in the bituminous mixes and the repeated
deformations that occur in flexible pavements due to the traffic loads. If the
bitumen has low ductility value. the bituminous pavement may crack.
especially in cold whether. The ductility value of bitumen vary from 5 to over
100. Several agencies have specified the minimum ductility values for various
types of bituminous pavements. Often a minimum ductility value of 50cm is
specified for bituminous construction.
The minimum ductility values specified by the Indian standards Institution
for various grades of bitumen available in India are given below:
Sources of paving bitumen and penetration Minimum ductility value, cm
Grade
Assam petroleum A25 5
A35 10
A45 12
A65,A90 & A 200 15
Bituminous from sources other than Assam 50
Petroleum S 35
S 45, S 65 & S 90 75
Conclusion:
Softening Point of Bitumen
Aim:
To determine the softening point(the temperature at which the bitumen
attains particular degree of softening)of the bitumen
Apparatus:
Ring &ball apparatus , thermometer , bath & stirrer
Theory:
Bitumen does not suddenly change from solid to liquid state , but as the
temperature increases. It gradually softer until it flows readily. The common
Procedure however is so liquefy the bitumen by heating. For bitumen it is
determined by ring & ball test.
Application:
Softening point is essentially the temperature at which the bituminous
binder has an equal viscosity. The softening point of is therefore
related to equiviscous temperature. The softening point found by the
ring & ball apparatus is approximately 20 degree lower than the e.v.t.
Softening point thus gives an idea of the temperature at which the
bituminous material attains a certain viscosity. Bitumen with higher
softening point may be preferred in warmer place. Softening is also
sometimes use to specify hard bitumen & pitches.
Procedure:
The bitumen is softened to a pouring consistency between 75 and 100
degree above the approximate softening point until it is completely and
is poured in heated rings placed on metal plate.
After cooling the rings in the air for 30 minutes, the excess bitumen is
trimmed
