Exp 11 Ductility Test on Asphalt

EXPERIMENT NO. 11

TO PERFORM DUCTILITY TEST ON ASPHALT. [ASTM DESIGNATION: D 113-86]

RELATED THEORY Ductility test on asphalt, 

DUCTILITY

The ductility of a bituminous material is defined as the distance in centimeters, to which it will elongate before breaking when two ends of a briquet specimen of the material, are pulled apart at a specified speed and a specified temperature. Unless otherwise specified, the test shall be made at a temperature of 25 ± 0.5 °C and with a speed of 5 cm/min ± 5.0 %. At other temperatures the speed should be specified. Ductility of asphalt depends upon the grade of asphalt, pouring temperature, dimensions of briquet, test temperature, rate of pull and levellin

g of mold.

IMPORTANCE OF DUCTILITY:

The ductility of a bitumen specimen tells us about

i)-      Tensile strength of bitumen
ii)-      Grade of sample (ductility grade)

SCOPE & SIGNIFICANCE

1. This test method provides measure of tensile properties of bituminous materials and may be used to measure ductility for specification requirements.
2. 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.
3. The ductility value varies from 5 to over 100 cm’s.
4. 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.
5. Roads expand at daytime while they contract at night. So, if the bitumen is not adequately ductile cracking will occur.
6. 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

Mold — the mold is made of brass, the ends being known as clips, and the middle parts asides of the mold.
Water Bath — the water bath shall be maintained at the specified test temperature, varying not more than 0.1 °C from this temperature. The volume of water shall be not less than 10 liters, and the specimen shall be immersed to a depth of not less than 10 cm and shall be supported on a perforated shelf not less than 5 cm from the bottom of the bath.
Testing Machine — For pulling the briquet of bituminous material apart, any apparatus may be used which is so constructed that the specimen will continuously immersed in water, while the two clips are pulled apart at a uniform speed, as specified, without undue vibration.
Thermometer — A thermometer having a range -8 to 32 °C (18 – 89 °F)

PROCEDURE

• 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.

TESTING:

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 = 18^o C
Ductility Value = 116cm

COMMENTS

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 25^o C as we performed at the Lab temperature

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