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.
Assemble the mold on a brass plate. Thoroughly coat the surface of the plate and interior surfaces of the sides of the mold 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 mold is placed shall be perfectly flat and level so that the bottom surface of the mold 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 mold. In filling the mold, 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 mold until the mold is more than level full.
Let the mold 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 mold just level full.
Place the brass plate and mold, 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
Attach the rings at each end of the clips to the pin or hooks in the testing machine and pull the two clips apart at a uniform speed specified until the briquet ruptures.
Measure the distance in centimeters through which the clips have been pulled to produce rupture. 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 and shall be kept continuously at the temperature specified.
If the bituminous material comes in contact with the surface of the water or the bottom of the bath, the test shall not be considered normal. Adjust the specific gravity of the bath by the addition of either methyl alcohol or sodium chloride so that the bituminous material neither comes to the surface of the water, nor touches the bottom of the bath at any time during the test.
Observations & Results:-
Grade of Bitumen = 60/70
Test Temperature = 18o C
Ductility Value = ……..cm
Recommended Values of Bitumen Ductility:-
Suitability of bitumen is judged depending on its type and proposed use. Bitumen with low ductility value may get cracked especially in cold weather. Minimum values of ductility specified by IS for various grades are as follows.
The Ductility test has been performed and the ductility value has been calculated as 116 cm. The ASTM D-113 for 60/70 grade the value of Ductility = 100 min. Temperature was not maintained in the lab so the value may differ at 25o C as we performed at the Lab temperature
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