Introduction:-
Ductility of bitumen is its property to elongate under traffic load without getting cracked in road construction works. Ductility test on bitumen measures the distance in centimeters to which it elongates before breaking.
Apparatus required, theory, procedure, precautions, observations, reporting and recommended values of bitumen ductility is discussed in this article.
Importance of Ductility Test:-
The ductility of a bitumen specimen tells us about
- Tensile strength of bitumen
- Grade of sample (ductility grade)
Scope & Significance:-
- This test method provides measure of tensile properties of bituminous materials and may be used to measure ductility for specification requirements.
- Bituminous materials used in pavement construction should possess sufficient ductility otherwise the pavement would crack due to temperature or traffic stresses and may render the pavement pervious and damage the pavement structure.
- The ductility value varies from 5 to over 100 cm’s.
- Several agencies have specified minimum ductility values for various types of bitumen pavements. However a ductility of 100 cm’s is specified generally for bituminous construction.
- Roads expand at daytime while they contract at night. So, if the bitumen is not adequately ductile cracking will occur.
- More than one grade may be used in the same project. For example; we may use grade 80/100 on the main traffic lane and lower grades on the arteries.
Apparatus Required:-
- Mold
- Water Bath
- Testing Machine
- Thermometer
Procedure:-
- Assemble the mould on a brass plate. Thoroughly coat the surface of the plate and interior surfaces of the sides of the mould with a thin layer of a mixture of glycerin and china clay to prevent the material under test from sticking.
- The plate upon which the mould is placed shall be perfectly flat and level so that the bottom surface of the mould will be in contact throughout.
- Carefully heat the sample to prevent local overheating until it has become sufficiently fluid to pour.
- Strain the molten sample through a # 50 sieve. After a thorough stirring, pour it into the mould. In filling the mould, take care not to disarrange the parts and thus distort the briquet.
- Infilling, pour the material in a thin stream hack and forth from end to end of the mould until the mould is more than level full.
- Let the mould containing the material cool to room temperature for a period of from 30 to 40 minutes and then place it in the water bath maintained at the specified temperature of test for 30 minutes; then cut off the excess bitumen with a hot straight-edged knife or spatula to make the mould just level full.
- Place the brass plate and mould, with briquet specimen, in water bath and keep at the specified temperature for a period of from 85 to 95 minutes. Then remove the briquet from the plate, detach the sidepieces, and immediately test the briquet
