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Measure Ductility test of Bitumen and its Suitability for Road Construction

Ductility of Bitumen:- Ductility test of Bitumen is a measure of elasticity or adhesiveness of bitumen.

Ductility of Bitumen is expressed as the distance in centimeters to which a standard briquette of bitumen can be stretched before the thread breaks as shown in fig.1. , that test should be conducted at 27 oC and the pull should be applied at the rate of 50 mm per minute. The minimum width of the cross-section of mold should be 10 mm x 10 mm.

Ductility test of bitumen (at beginning) sample in the Briquette
Fig1.Ductility test of bitumen (at beginning) sample in the Briquette

Ductility Test on Bitumen

The ductility test on bitumen is  use to measure following:

  1.  The ductility of a given sample of bitumen is measured
  2. 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. Standard temperature of 25oC has to be maintained. Cross section of 100 mm X 100 mm in mould is prepared at specified temperature, excess bitumen is removed and the chips are hooked after setting 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. Minimum 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

  1. Briquette of standard dimensions.
  2. Pulling device with distance measuring dial.
  3. Water bath arrangement.
 Ductility test ( At the yield point)
Fig2. Ductility test ( At the yield point)

Ductility test of Bitumen (on the stage of failure)
Fig.3.Ductility test of Bitumen (on the stage of failure)

Procedure for ductility test of bitumen

  1. The bitumen sample is heated to bring it in fluid state and poured in the briquette assembly and placed on a brass plate.
  2. The whole equipment including bitumen briquette along with brass plate is allowed to cool in air.
  3. A hot knife is used to cut the excess bitumen and also surface is leveled with the help of a hot knife.
  4. The whole assembly now is kept in a bath maintained at 27 oC for about 85 to 95 minutes.
  5. The side of the mould removed, the clips hooked on the machine and pointer adjusted to zero value or initial reading noted.
  6. Now the clips are pulled apart horizontally at the rate of 50 mm per minute and the distance upto the point of breaking of thread is noted. This distance in cms gives the value of ductility of bitumen.
  7. The ductility of bitumen may vary from 5 to over 100 for different bitumen grades, but for satisfactory performance it should not be less than 50.
  8. Ductility of bitumen is depends upon pouring temperature, dimensions of briquette, test temperature, the rate of pulling etc.

Ductility of Bitumen Suitability for Road Construction

For the purpose of flexible pavement design, it is necessary that binder should form a thin ductile film around aggregates so that physical interlocking of the aggregates is improved.

It is important to consider that the Binder material having insufficient ductility gets cracked when subjected to repeated traffic loads and it provides pervious pavement surface.

 In cold weather Bitumen with low ductility value may get cracked . 

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