RSP f
2w 2g2Foaming occurs when
water is in excess of the specified amount.
In this test water-free petroleum distillate
is added to the sample and heated. Then
the distillate is condensed and the quantity
of water collected at the bottom is expressed
as percentage by weight of the sample. It
should not exceed 1 per cent. 2
This test indicates the purity of bituminous
binders by finding the quantity of bitumen
in binder. Insoluble impurities like free
carbon, mineral salts, dusts, etc. are found
by this test. The sample consists of 2 to 5 g
of bitumen in 100 g of carbon-disulphide or
carbon tetrachloride.
2s
2
This test is performed to find the presence
of paraffin, naphthalene, benzene, etc. which produce greasy effect and fail to hold the
aggregate. Moreover, binder does not set in the presence of these impurities.
The tar sample is treated with sulphuric acid and the volume of unsulphonated residue is
expressed in millimeter per 100 g to tar. The number denotes the index value of the sample.
h 2
All bituminous materials must have some specified
ductility so that when placed in the pavement,
they will distort rather than crack. The test consists
of stretching the bitumen binder (in the form of
a standard briquette shown in Fig. 18.7) at a
standard temperature of 27°C and at a standard
rate of 5 cm per minute till the thread breaks. The
ductility is expressed as the distance stretched in
centimeters.
X2The binder is heated slowly to a pouring consistency between 75°C to 100°C above
the approximate softening point. The mould is placed on a brass plate and coated with a
mixture of equal parts of glycerin and dextrine. The fluid bitumen is poured into the mould
more than level full and is allowed to cool. The whole assembly is placed for 30 minutes in a
water bath maintained at 27°C. The moulds are taken out and the excess bitumen removed
by means of a hot sharp knife. The assembly is placed again in bath and kept their for 85 to
95 minutes at 27°C. The sides of the mould are removed and the clips are hooked on to the
ductility machine. The pointer is set to read zero. Load is applied and the reading on the scale
recorded when the bitumen thread just breaks (Fig. 18.8).
p# 2IV T ,-Ew 2 p# 2IV U f 2w