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The softening point is defined as the mean of the temperatures at which the bituminous material is softened and sagged downward at a distance of 25 mm under the weight of steel ball. In general, with materials of these types, softening does not take place at the definite temperature. As the temperature rises, the bituminous material gradually and imperceptibly changes from brittle or exceedingly slow flowing material to softer and less viscous. For this reason, the determination of the softening point must be made by a fixed, arbitrary and closely defined method if the results are to be comparable (MS 687: 1995).
This method is useful in determining the consistency of bituminous material assign element in establishing the uniformity of shipments or sources of supply. (The engineering term consistency is an empirical measure of the resistance offered by a fluid to continue deformation when it is subjected to shearing stress). The consistency is a function of the chemical constituents of bituminous material viz. the relative proportions of asphaltenes, resins and oils. The type and amount of these constituents are determined by the source of crude petroleum and the method of processing at the refinery plant (ASTM Designation D36).
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The OBJECTIVES lives of this experiment are:
i.
To determine the temperature at which a given bituminous material specimen reaches a certain degree of softness.
ii.
To deduce the penetration index (Pl) value of the specimens directly from PI Nomograph in Figure 2.2.
Two steel balls of diameters 9.5 mm and each weighing 3.50 ± 0.05 g, tapered ring made of brass, ball-centering guides, ring moulds and suspended ring holder, thermometers, ice cubes, stop watches, spatula, forceps, magnetic stirrers, beakers and heaters.
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i.
Some water was poured in a beaker to prepare a water bath. A magnetic stirrer was put in the water bath. Some ice cubes was also put into the beaker.
ii.
The temperature of the water bath was measured by a thermometer. A suspended ring holder was then put in the water bath, followed by placing the thermometer in the centre part of the suspended ring holder.
iii.
The temperature of the water bath was maintained at 5° ± 2°C for 15 minutes. The specimens in the ring holders were placed once stabilizing the temperature.
iv.
A few minutes before a-fifteen minute conditioning period was set, the steel balls was placed in the ball-centering guides using a forceps.
v.
After 15 minutes, an electric heater was positioned just next to the suspended ring holder and switches it on.
vi.
The water bath which should be heated up at 5° ± 2°C per minutes were monitored and make sure it is increasing uniformly, that is, the increment of 4° - 5°C per minute and no more than 7°C.
vii.
Temperature and the corresponding time was noted and recorded at instant the bituminous material was sagged downward, dropping at the base plate of the suspended ring holder.
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Timer
Temperature
Timer
Temperature
Reading
(°C)
Reading
(°C)
(Minutes)
(Minutes)
0
5
11
27
1
7
12
30
2
8
13
32
3
10
14
34
4
11
15
36
5
13
16
38
6
15
17
40
7
19
18
42
8
20
19
44
9
23
20
45
10
25
21
46
NOTE: The test is recommended to be done all over again if the difference between the two temperature of the water bath for two steel balls exceeds 1OC (MS 687: 1995).
Softening point, R = (R1 + R2) / 2 = (45 + 46) / 2 = 45.5
Where, R= average temperature of the water bath for two steel balls.
The temperature and the corresponding time at which a tested bituminous material specimen reaches a certain degree of softness:
Softening point: 45.5 °C and 20.5 minutes
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` ` Table 1.0 Characteristic of bitumen according to PI value
PI values can be used to determine the stiffness (modulus) of a bitumen at any temperature and loading time. It can also, to a limited extent, be used to identify a particular type of bituminous material. One drawback of the PI system is that it uses the change in bitumen properties over a relatively small range of temperatures to characteristic as bitumen; extrapolations to extremes of the behaviour can sometimes be misleading. PI range between -1 < PI < +1 is suitable for road construction.
1. From the data above, the temperature of the first specimen to drop is 45°C while for the second specimen is 46°C. From these last two data, we can determine the softening point by taking the average, and the value that we get is 45.5°C.
2. It is observed that the softening point increases by the addition of polymer to the bitumen. The influence over the softening point is depended on the chemical nature of the polymer added. This will differ in the classification of bitumen.
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3. Bitumen can be classified into several grades and each grade has different softening point and physical characteristics. For this experiment, the grade used is 80/100. As the temperature rises, the bitumen gradually becomes softer and less viscous. Based from the result, the maximum temperature for this specimen to sagged downward is at 46°C. Compared to the other group that used a grade of 60/70, the temperature for the specimen to soften is a bit higher. Thus the higher the grade, the softer the bitumen.
4. After relate to the depth of penetration, we can determine that the penetration index or PI for grade 80/100 is -3.4. According to the table of characteristic, since the value is less than -2, the type of bitumen is Temperature Susceptible Bitumen (Tars).
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` 1. This test method covers the determination of the softening point of bitumen in the range from 30 to 157°C (86 to 315°F) using the ring-and-ball apparatus immersed in distilled water (30 to 80°C).
2. The softening point is useful in the classification of bitumen, as one element in establishing the uniformity of shipments or sources of supply, and is indicative of the tendency of the material to flow at elevated temperatures encountered in service.
3. Rigid adherence to the prescribed preparation of specimens and heating is absolutely essential for reproducibility of the results. The mean temperature of the two specimens (which shall not differ by more than 1oC) is recorded as the softening point. This temperature is to be used in conjunction with the penetration value to obtain the Penetration Index (PI). The temperature of the two specimens is 45 oC and 46 oC, which the difference is 1 ºC.
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` Recommended value of Softening point indicates the temperature at which binders possess the same viscosity. Bitumens are viscoelastic materials without sharply defined melting points. Rather, the change of state from solid to liquid is gradual over a wide range of temperature. Softening point has particular significance for materials to be used as joint and crack fillers. Higher softening point ensures that they will not flow during service. Higher the softening point, lesser the temperature susceptibility. Bitumen with higher softening point is preferred in warmer places.
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[1] AB. Karim, S. N., Tey, L.S., Ishak, S.Z., Abd Rahman, M.Y., and Adnan, M.A., (2010). , 2nd .Edition, University Publication Centre (UPENA) : UiTM, 5
8.
[2] ASTM D0036 - 06: 2008
! ! " #$#$ ASTM International, PA, USA.
[3] Historical Standard: ASTM D36-95: 2000 el.
! ! " #$#$ ASTM International, PA, USA.
[4] Malaysia. Standards and Industrial Research Institute of Malaysia (SIRIM), 1995. MS 687: 1995. %
& ' Shah Alam: SIRIM Board.
[5] Website
Google
search
:
http://theconstructor.org/practical-guide/softening-point-of-
biuminous-material/2571/
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Sample of hot bituminous
Beaker and heater
Ring mould Magnetic stirrer Steel Ball Thermometer
Suspended ring holder
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i) Before the experiment starts
ii) Ice cubes were put into beaker
to reduce the temperature
iii) The bituminous material is sagged downward
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Group members (from left) : Siti Sarah, Nurul Hidayah, Nur Insyirahnadia, Siti Aishah and Nur Asyikin.
