|Ductility of bitumen|
What is ductility test ?
Ductility of Bitumen -Definition
Distance of Elongation(Length of elongation) In centimetres to which the bituminous material gives before breaking when the briquette specimen of that bituminous material is pulled at specified temperature and at a specified speed.
Test of Ductility of Bitumen
The purpose of Ductility test of bitumen is as following :-
➱To know and to measure of the Ductility of any Bituminous sample or specimen.
➱To know the suitability of the material Where ever(Road or other Construction) Works it is going to be used.
Which factors may affect the value of ductility of bitumen ?
Apparatus For Ductility Test
1- Testing Machine➱
The testing Machine for Ductility is Designed such way for pulling the Briquette of bituminous material apart,In This machine The Specimen is Submerged in water continuously While The Both sides clips are being pulled apart Horizontally at an uniform speed of 50 + or – 2.5 mm per minute.
|Ductility Testing machine|
What is the maximum value of ductility test ?
2- Briquette Mould➱
A Mould Made of Brass is used, At The both Ends of the mould Circular holes Are Made To grip The Fixed and Movable Ends Of the machine These Circular holes are called Clips, The Dimensions of Briquette specimen After the mould is Properly assembled are as following.
➱The Total Length 75.0 ±0.5 mm.
➱Distance Between the Clips 30.0 ±0.3 mm.
➱ Width at Mouth at clip 20.0 ±0.2 mm.
➱Width of Briquette at minimum cross section 10.0 ±0.1 mm.
➱Throughout Thickness 10.0 ±0.1 mm.
|Ductility testing machine with briquette mould|
3- Water Bath➱
A Water bath Preferably with a thermostat and minimum capacity of 10 liter is used.It Maintain the The Specified Testing temperature 27.0 ±0.1 ℃.
Thermometer of Capacity of 250 ℃ is used.Which can Read The temperature up to 0.01℃.
Principles of Ductility Test ➱
While Designing The flexible pavements in road works, The Most essential and important factor is that the binder or the bituminous material should create a thin and ductile film all around the aggregate so that the physical interlocking of the aggregate get improved, the ductility test of bituminous material gives the adhesive properties of bitumen and it’s ability to get stretched.
The Distance in centimetres between two ends of standard briquette specimen After elongation before breaking in Bituminous material due to being pulled apart at specified temperature and speed is called the Ductility of That particular bituminous material.
If The binder material used in road construction have less ductility than specified,it will get cracked when it is subjected to a repeated traffic loads.and will give a pervious pavement surface.
|Laying of flexible pavement|
Procedure of Ductility Test➱
➱The Ductility test shall be conducted at a temperature of 27 ±0.5 ℃ and at rate of pulling of 50 ± 2.5 mm/minute ( This Temperature and rate pull is taken in normal testing unless otherwise specified)
➱Melt the bitumen to be tested to a temperature of 75 to 100 ℃ above its approximate softening point till it become fluids.
➱Assemble the mould on a brass plate and coated on all the sides with a mixture glycerin and dextrin of equal parts to avoid sticking of the material.
➱Fill the mould until it is more than level full.
➱In filling the mould, pour the material in a thin stream back and forth from end to end of the mould.
➱Leave it to cool room temperature for 30 to 40 minutes and then place it in water bath maintained at a specific temperature for 30 minutes.
➱Cut off excess bitumen by means of hot straight edged putty knife level full.
➱The Brass Plate and mould with briquette specimen will be placed in water after cutting the excess bitumen and it will be kept at a specified temperature for about 85 to 90 minutes.
➱Remove the briquette from the plate, detach sidepieces and test the briquette immediately.
➱While the test is being conducted, make sure that the water in the tank of the testing machine covers the specimen above by at least 25 mm and is maintained continuously within ±0.5 ℃ of specified temperature.
➱Attach rings at each end of the clips to the hooks in the testing machine and pull the two clips apart horizontally at a uniform speed as specified until the briquette raptures.
➱Measure the distance in centimetres through which the clips have been pulled to produce rapture.
➱At least Three determinations shall be made for each test.
➱Report the average of three normal test as ductility of the sample, provide that, the three determinations be within ± 5 % of their mean value.
➱If the Value of three determinations do not lie within ± 5 % of their mean value but the two higher are within ± 5 % of their mean value, then record the mean of the two higher values as the test results.
➱The Duplicate test results should not differ by more than the values Given Below (For Road work).
Precautions In Ductility test➱
➱In the Filling of mould care shall be taken to see that no air bubbles shall be formed, and not to disarrange the parts and thus distorting the briquette.