The Ductility Test of Bitumen is one of the important tests of bitumen which is essential before using it in road construction. The Ductility Test of Bitumen used to measure the adhesive and elastic properties of any bitumen sample.
Significance of Ductility Test of Bitumen:
- The ductility test of bitumen sample is one of the important tests of bitumen to be conducted before road construction.
- Ductility measures the adhesive property of the bitumen too along with its elasticity.
The bituminous binder used in the pavement should be ductile enough to take up the deformations acting upon it without exceeding the deflection limit. Ductile bitumen can form a thin ductile film around the aggregate particles. Thus, it does not crack at low temperatures. However, the films of brittle bitumen are not ductile and crack may easily develop in lower temperatures.
The ductility test on bitumen is use to measure following:
- The ductility of a given sample of bitumen is measured
- The suitability of bitumen for its use in road construction is measured.
Ductility of bitumen is the distance by which it elongates in cm before it breaks when kept in standard briquettes at standard conditions. The standard temperature of 25oC has to be maintained. Cross-section of 100 mm X 100 mm in a mould is prepared at a specified temperature, excess bitumen is removed and the chips are hooked after setting a pointer to zero.
The specimen is pulled @ 50 mm per minute until rupture. The distance up-to breaking point in cm is the ductility value which depends on temperature, briquette dimension, pulling rate. Ductility values may range from 5 to 100 cms. A minimum of 5 cm value is required for a bitumen of grade 45 and above.
Equipment for ductility test of bitumen
Essentially the following equipment is required
- Briquette of standard dimensions.
- Pulling device with distance measuring dial.
- Water bath arrangement.
Fig: Ductility test apparatus
Apparatus Required:
- Mold - The mold shall be similar in design to that shown in ASTM manual.
- Water Bath - The water bath shall be maintained at the specified test temperature.
- 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 immersed in water.
- Thermometer - A thermometer having a range of -8 to 32 C.
Procedure Molding Test Specimen
The bituminous material to be tested shall be completely melted until thoroughly fluid by heating it in an oil bath maintained at the minimum temperature needed to properly liquefy the sample. It shall then be thoroughly stirred. The mold shall be assembled on a brass plate, to prevent the material under test from sticking the surface of the plate and interior surfaces of the sides of the mold shall be thoroughly amalgamated. In filling the mold, care should be taken not to damage the parts and thus distort the briquette. In filling, the material shall be poured in another stream back and forth from end to end of the mold to make sure it is more than level full. It shall be left to cool to room temperature for a period of 30 - 40 minutes. Then place it in the water bath maintained at the specified temperature of test for 30 minutes. Then the excess bitumen shall be cut off by means of a hot straight-edged putty knife or spatula so that the mold shall be just level full.
The brass place and mold, with briquette specimen, shall then be placed in the water bath and kept at the specified temperature for a period of from 85 - 95 minutes. When the briquette shall be removed from the plate, the side pieces detached, and the briquette immediately tested.
Testing:
The rings at each end of the clips shall be attached at a pine or hooks in the testing machine. Then the two molds shall be pulled apart at a uniform speed and specified until the briquette ruptures. A variation of ± 5% from the speed specified will be permissible. The distance through which the clips have been pulled to produce rupture shall then be measured in centimeters. While the test is being made, the water in the tank of the testing machine shall cover the specimen both above and below it by at least 2.5 cm. It shall be kept continuously covered at the temperature specified within ± 0.5 ±C.
Experimental Data and Results:
Tabulate the data in the given Test Data Sheet. A normal test is one in which the material between the two clips pull out to a point or thread until rupture occurs at the point where the thread has practically no cross-sectional area. The average of three normal tests shall be taken and reported as the ductility of the sample. Adjust the specific gravity of the water by addition of either methyl alcohol or sodium chloride so that the bituminous material comes to the surface of neither water nor touches the bottom of the bath at any time during test. If the bituminous material comes in contact with the surface of water or the bottom of the bath, the test shall not be considered normal.