(AASHTO DESIGNATION: T-49)
In this test we examine the consistency of a sample of bitumen by determining the distance
in tenths of a millimetre that a standard needle vertically penetrates the bitumen
specimen under known conditions of loading, time and temperature.
This is the most widely used method of measuring the consistency of a
bituminous material at a given temperature. It is a means of classification rather
than a measure of quality.
- Penetration Apparatus
- Water Bath
- Thermometer for Water Bath
- Stop watch
It measures the hardness or softness of bitumen by measuring the depth in tenths of a millimeter to which a
standard loaded needle will penetrate vertically in 5 seconds.
- Heat the sample until it becomes fluid.
- Pour it in a container to a depth such that when cooled, the depth of sample is at least 10mm greater than the expected penetration.
- Allow it to cool in an atmospheric temperature.
- Clean the needle and place a weight above the needle.
- Use the water bath to maintain the temperature of specimen.
- Mount the needle on bitumen, such that it should just touch the surface of bitumen.
- Then start the stop watch and allow the penetration needle to penetrate freely at same time for 5 seconds. After 5 seconds stop the penetration.
- Result will be the grade of bitumen.
- Take at least three reading.
USES AND SIGNIFICANCE:
Penetration test is used to measure the consistency of bitumen, so that they can be classified into standard grades. Greater value of penetration indicates softer consistency. Generally higher penetration bitumen is preferred for use in cold climate and smaller penetration bitumen is used in hot climate areas.
- 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 of the material will be elongated without breaking”.
- Dimension of the briquette thus formed is exactly 1 cm square. The bitumen sample is heated and poured in the mould assembly placed on a plate. These samples with moulds are cooled in the air and then in water bath at 27 °C temperature.
- The excess bitumen is cut and the surface is leveled using a hot knife.
- Then the mould with assembly containing sample is kept in water bath of the ductility machine for about 90 minutes.
- The sides of the moulds are removed, the clips are hooked on the machine and the machine is operated.
- The distance up to the point of breaking of thread is the ductility value which is reported in cm.
- The ductility value gets affected by factors such as pouring temperature, test temperature, rate of pulling etc. A minimum ductility value of 75 cm has been specified by the IS.