Objective
(i) To compute the ductility of a specific specimen of bitumen
(ii) To assess the suitability of bitumen for its application in road construction.
Apparatus
The apparatus as per IS: 1208-1978 comprises of
- Briquette mould: It is created out of brass. Circular holes are made at ends known as clips to grasp the stationary and mobile ends of the testing machine. The mould when correctly amassed produce a briquette sample of the given dimensions.
Total length 75.0 ± 0.5 mm
Distance between clips 30.0 ± 0.3mm
Breadth at mount of slip 20.0 ± 0.2mm
Width at minimum cross-section
(half way between clips) 10.0 ± 0.1mm
Thickness throughout 10.0 ± 0.1mm
2. Water bath: A bath preserved within the temperature of 27.0° ±0.1 °C of the specified experimentation temperature comprising minimum of 10 litres of water, the sample which is being immersed to a deepness at least minimum of 10 cms and reinforced on a punctured shell and additionally minimum 5 cms from the foot of the bath.
3. Testing Machine: For the process of pulling the briquette of bituminous substances separately, any apparatus could be utilized which is so built that the sample would be constantly partially immersed in the water while the two clips are being drawn separately parallel at a constant speed of 50 ± 2.5 mm per minute.
4. Thermometer: Range 0-44°C and decipherable up to 0.2°C
Theory
The ductility provides the extent of adhesive nature or the properties possessed of bitumen and its capacity to stretch. In elastic pavement design, it is important that binder has to create a shrill ductile film round aggregates so that physical interconnecting of the aggregates is amended. Binder material having inadequate ductility gets broken when exposed to recurrent traffic loads and it delivers penetrable pavement surface. Ductility of a bituminous substances is computed by the distance in centimeters to which it will lengthen prior to breaking when two ends of ordinary briquette sample of the material are pulled separately at a stated speed and stated temperature.
Process
- Melt down the bituminous test substance totally at the maximum temperature of 75°C to 100° C overhead the estimated moderating point until and unless it transform thoroughly into fluid.
- Strain the fluid with the help of IS sieve 30.
- After the process of stirring the fluid, we will now pour it into the cast assembly and position it on a brass plate. For preventing the substance exposed to test from sticking, double coat the exterior of the plate and internal sides of the mould with utilization of mercury or by a blend of identical portions of glycerine and dextrine.
- After letting in still for approximately 40 minutes, put the plate assembly alongside the specimen in a water bath. Preserve the temperature of the water bath at 27° C for another 30 minutes.
- Detach the sample and the cast assembly from the water bath and trim the sample by levelling the surface with help of a hot knife.
- Substitute the mould assembly in water bath for 80 to 90 minutes.
- Detach the sides of the mould.
- Hook the clips cautiously on the device without leading to any kind of initial strain.
- Regulate the pointer to read nil.
- Initiate the machine and pull clips parallel at a speed of 50 mm per minute
- Mark down the distance at which the bitumen thread of specimen breaks.
- The mean of the two observations rounded to the closest whole number is ductility value.
- Note: Machine might have provision to attach two or more moulds so as to test three samples concurrently.
Precautions
(i) The plate assembly on top of which the mould is positioned should be effortlessly flat and horizontal so that the base surface of the mould tads it throughout the process.
(ii) During the process of filling the mould, we should be very careful not to change the briquette and to comprehend that no air pocket is inside the moulded specimen.
Observations
(i) Bitumen Grade =
(ii) Pouring Temperature =
(iii) Test Temperature =
(iv) Period of cooling in minutes
(a) In air =
(b) In water bath before trimming =
(c) In water bath after trimming =
| 1 | 2 | 3 | |
| (a) Initial Reading | |||
| (b) Final Reading |
Result:
Ductility Value=
Recommended value:
The extend of suitability of bitumen is assessed based on its kind and suggested application. Bitumen with low ductility value may get cracked especially in cold weather. Minimum values of ductility stated by ISI for numerous grades are as follows.
| Source of paving bitumen and penetration grade | Min ductility value (cms) |
| Assam Petroleum A25 | 5 |
| A35 | 10 |
| A45 | 12 |
| A65, A90 & A200 | 15 |
| Bitumen from sources other than Assam Petroleum S35 | 50 |
| S45, S65 & S90 | 75 |
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