Properties of Bitumen
- Adhesion: Bitumen has the ability to adhere to a solid surface in a fluid state depending on the nature of the surface. The presence of water on the surface will prevent adhesion.
- Resistance to Water: Bitumen is water resistant. Under some conditions water may be absorbed by minute quantities of inorganic salts in the bitumen or filler in it.
- Hardness: To measure the hardness of bitumen, the penetration test is conducted,which measures the depth of penetration in tenths of mm. of a weighted needle in bitumen after a given time, at a known temperature. Commonly a weight of 100gm is applied for 5 sec at a temperature of 77 °F. The penetration is a measure of hardness. Typical results are 10 for hard coating asphalt, 15 to 40 for roofing asphalt and up to 100 or more for water proofing bitumen.
- Viscosity and Flow: The viscous or flow properties of bitumen are of importance both at high temperature during processing and application and at low temperature to which bitumen is subjected during service.
- Ductility: Ductility test is conducted to determine the amount of bitumen will stretch at temperature below its softening point.
- Softening point: The temperature at which a steel ball falls a known distance through the bitumen, when the test assembly is heated at known rate.Usually the test consist of (3/8) inches diameter steel ball, weight 3.5 gram,which is allowed to sink through out (5/8) inches diameter (1/4) inch the disc of the bitumen in a brass ring. When the whole assembly is heated at a rate of 9 F/min.Typical values would be 240F for coating the grade asphalts, 140-220F for roofing asphalts and 115F for bituminous water to fill material.