Flash and Fire Test of Bitumen

Flash and Fire Point Test of Bitumen | Procedure & Result

Flash and Fire Point Test of Bitumen is used to determine the safe temperature up to which bitumen sample can be exposed. The Procedure, Result, Significance, Conclusion of are described in this test.

Aim:

To determine the flash point and fire point of asphaltic bitumen, fluxed native asphalt, blown type bitumen, or cutback bitumen.

Here, the flash and fire point determination by Pensky-Martin’s Closed Cup tester is described.

[Sometimes, the Cleveland Open Cup Apparatus is also used for conducting the flash and fire point test of a bituminous specimen.]

Read More: Viscosity Test of Bitumen- Absolute, Kinematic, Industrial Viscosity

Significance of the Flash and Fire Point Test of Bitumen:

Flash and fire point test of bitumen sample is one of the important tests of bitumen to be conducted before road construction.

Flash and fire point measures the temperature at which the material is at risk of catching fire.

The temperature at which the vapour of the bituminous material catches an instant fire or the material burns for some seconds is different for different types and grades of bitumen binders.

Bituminous materials are primarily hydrocarbons and hence at high temperatures, they release various volatile materials. These liberated volatile compounds catch fire with a flash. And this can prove hazardous.

Bitumen is heated for its application as bitumen binder for road pavements.

While dealing with hot bitumen during the processes like heating, mixing, or application, the temperature should be kept well below the critical temperatures determined by flash and fire point. 

Important Terms related to Flash and Fire point Test of Bitumen:

Flash point: It is the lowest temperature whose application causes the vapour of the bituminous material to catch an instant fire in a flash form in specified conditions.

Fire point: It is the lowest temperature whose application causes the binder material to ignite for at least 5 seconds in specified conditions.

Apparatus:

The apparatus required for performing the flash and fire point test of bitumen are described below:

1. Pensky Martens Tester: It is the testing machine for flash and fire point test of bitumen. The various parts of this apparatus are described below:

Pensky MArtens- Flash and Fire Point Test Apparatus
Pensky MArtens- Flash and Fire Point Test Apparatus

2. Closed Cup Tester: It is made up of brass and its inside diameter is slightly larger above the filling mark. The outside surface of the cup is tapered above the flange. The flange also has devices for receiving the lid of the cup and the cup too when kept in the stove. A handle is also fixed to the cup flange permanently.

The wall thickness at the upper edge is not less than 1 mm.

Flange width = 12 mm approx

Flange thickness = 3mm

3. Open Cup Tester: In this tester, the cover of the cup is replaced by a clip that encircles the upper rim of the cup. It also has provision for test flame and thermometer.

A lid includes the following-

1. Stirring device: It is in the form of vertical shaft mounted centrally on the cup. It has brass propellers- 2 in number. Propeller blades are mounted on a collar. The stirrer is operated mechanically in a close cup test. For testing cutback bitumen in a close cup, a hand-operated stirrer is needed.

The dimension details of various parts of the stirring device are as follows-

Diameter of Vertical steel shaft = 2.5-3 mm

Width of the propeller blade =  8 mm at approximately 45 ° angle

Overall diameter of smaller propeller = 20 mm

Overall diameter of larger propeller = 32-44 mm

Thickness of propeller blades = 1.2-2 mm

Horizontal and vertical dimensions of collar ≯ 10 mm

Distance between the plane of the centre of propeller and rim of the cup = 10 mm

2. Cover proper: It is made up of brass. Its rim projects almost to the flange of the cup and closely fits the outside of the cup. A proper locating device is present on the cover that engages with the corresponding locating device on the flange of the cup.

Thickness of cover measured from just inside the rim is in-between 0.8-2 mm.

[In open cup test, instead of cover, a clip that encircles the upper rim of the cup and has a provision for carrying thermometer and test flame is used.]

There are four openings in the cover as follows:

Opening A: It is the area formed by the arcs of two concentric circles and intersected lengths of the two radii.

Radius of the outer circle = 22.4-24.6 mm

Radius of inner circle = 13.5-14.2 mm

Chord of the arc of the outer circle = 12.7-13.7 mm

Openings B and C: Both have equal areas. Their general form is similar to the opening A but these openings have approximately half the angular width.

Chord of outer arc =4.8-5.6 mm

Sum of areas of these openings = 75-100 % of the area of Opening A

Radii drawn through their centre is at an angle = 135-140° 

Opening D: It is in the form of a split tube that helps to grip the thermometer. Its height should be such that when a standard thermometer is kept in position the bottom of the bulb lies below the rim of the cup by 35.6-40.6 mm.

Distance between the centre of the opening and the centre of lid = 20 mm

Angle of the opening to the perpendicular = 10-15°

3. Shutter: It is made up of brass and it is attached to the lid. It operates on the plane of the upper surface of the lid. Its shape and mounting are so decided that it rotates on the horizontal axis of the centre of the lid. When it is placed in an extreme position, openings A, B, and C of the lid are closed completely. When it is placed in the other extreme position, openings A, B, and C of the lid are opened completely.

4. Flame exposure device: It has a tip with 0.7-.8 mm diameter opening. It also has an operating mechanism which depresses the tip when the shutter is open. A pilot frame is also provided that helps in relighting of the exposure flame automatically. A  4 mm diameter bead is also placed on the lid to regulate the size of the test flame. The shutter operating mechanism is of spring-type and constructed in such a way that openings A, B, and C are closed when it is at rest.

4. Heating device with temperature regulator:

5. Thermometer: Its range should be from -7 – +110 °C with a least count of 0.5 °C.

6. Other accessory apparatus used in flash and fire point test include:

  • Ignition source device
  • Air bath

Materials:

  • Bituminous material
  • Solvent for cleaning

Precaution:

Following precautions should be taken while performing the flash and fire point test of bitumen to obtain accurate results:

  • Size of the test flame and the frequency of the application of test flame should be adhered to, else the surface layer may be superheated.
  • The bluish flame surrounding the test flame should not be confused with the true flame.
  • The traces of solvent used for cleaning the apparatus should be removed completely
  • The locating devices of the cup and the lid should be engaged properly

Procedure for Flash and Fire Point Test of Bitumen:

There are two types of tester for determining the flash point of bitumen- closed cup tester and open cup tester. However, fire point of bitumen is determined by an open cup tester only.

Determination of Flash Point by Closed Cup Tester:

The procedure for finding out the flash point in closed cup tester varies for cutback bitumen. Both the procedure are described below-

For Bituminous material EXCEPT for Cutback Bitumen:

  1. Clean all the parts of the cup and its accessories thoroughly and allow them to dry.
  2. Take the bitumen sample in a beaker and heat it to a temperature of 75-100°C- above its approximate softening point. Allow the bitumen to melt until it is converted completely into a liquid state.
  3. Fill the melted bitumen in the cup up to the filling mark indicated on the cup.
  4. Close the cup with the help of the lid. Ensure that the locating devices of the cup and lid are properly engaged.
  5. Place the cup on the stove.
  6. Insert a thermometer and adjust the test flame to a size of a bead of about 4 mm diameter. Control the rate of the application of heat such that the temperature increases by 5-6 °C  per minute as recorded from the thermometer.
  7. Turn the stirrer at the rate of 60 rev/min.
  8. Apply the first test flame when the temperature reaches approximately 17 °C  before the actual flash point. When test flame is applied, discontinue the stirring.
  9. Apply test flame at every reading of the temperature up to 104 °C in the multiples of 1 °C. When the temperature exceeds 104 °C, carry out the test at an interval of 2 °C.
  10. Operate the device to apply the test flame by controlling shutter and test flame burner in such a way that the flame is lowered in 0.5 seconds for. It remains in the lowered position for a second and is raised quickly to the higher position.
  11. Note down the temperature at which a distinct flash is observed in the interior of the cup.

For Cutback Bitumen:

  1. Heat the material to a temperature 17 lower than the expected flash point. Bring the tester to the same temperature too.
  2. Fill the space between the cup and the interior of the air bath with the same temperature to remove the air.
  3. The same procedure as above is followed then after. Except for the rate of the application of heat. Control the rate of the application of heat such that the temperature increases by 1-1.5 °C  per minute as recorded from the thermometer.
  4. Turn the stirrer at the rate of 70-80 rev/min.
  5. Then the test flame is applied and the other steps are followed as described previously except for the interval at which test flame is applied. Instead of applying test flame at intervals of 1 °C, the test flame is applied at every 0.5 °C rise in temperature.

Determination of Flash Point and Fire Point by Open  Cup Tester in Flash and Fire Point Test:

  1. Clean all the parts of the cup and its accessories thoroughly and allow them to dry. Ensure all the traces of solvent used for cleaning are removed.
  2. Take the bitumen sample in a beaker and heat it to a temperature of 75-100°C- above its approximate softening point. Allow the bitumen to melt until it is converted completely into a liquid state.
  3. Fill the melted bitumen in the cup up to the filling mark indicated on the cup.
  4. Fix the clip in position on the cup. Ensure that the locating devices of the cup and lid are properly engaged.
  5. Insert a thermometer and adjust the test flame to a size of a bead of about 4 mm diameter. Control the rate of the application of heat such that the temperature increases by 5-6 °C  per minute as recorded from the thermometer.
  6. Observe the surface of the material carefully during heating.
  7. Then after the same steps are followed as mentioned in closed cup tester except that the stirrer is rotated manually instead of mechanically.
  8. Note down the temperature when the first distinct flash appears at any point on the surface of the material. Record this temperature as the flash point.
  9. Continue the heating beyond the flash point and applying the test flame at intervals of 1 °C.
  10. Note down the temperature when the material ignites and continues to burn for at least 5 seconds. Record this temperature as fire point.

The entire practical is repeated for 2 more times. The corresponding average value of the three tests is the flash point and fire point of the given bitumen specimen.

Observation:

As the test flame is applied, at a certain temperature, a flash can be observed. This temperature is noted down as flash point.

Again, the test flame is continued to be applied. At a certain temperature, the fire occurs for at least 5 seconds. This temperature is noted down as fire point.

Observation Table:

(A sample observation table for flash and fire point test is drawn below)

  Readings
  Trial 1 Trial 2 Trial 3

Flash Point 

in °C

     

Fire point (b)

in °C

     

Flash point of the sample = Average value of flash point of 1, 2, 3.

Fire point of the sample = Average value of fire point of 1, 2, 3.

Result:

The average of the flash point and fire point values to the obtained from the three tests are the flash point and fire point values of the given bitumen specimen respectively.

For close cup tester, the value of flash point carried out for three times should not differ by more than ± 2 °C for temperature below or equal to 104 °C. And for temperature beyond 104 °C,  the tolerance value is increased to ± 5.5°C.  

For open cup tester, the values of both the flash and fire point carried out for three times should not differ by more than ± 8 °C. 

Flash and fire point of the bitumen specimen is dependent on the grade of the bitumen.

Conclusion:

By performing the flash and fire point test of bitumen, we can determine the flash point and fire point of the bitumen sample.

Flash point and fire point gives a measure of the critical temperatures beyond which the bitumen should not be exposed to. Thus, these critical temperatures help in preventing a hazardous situation.

Summary:

Test Procedure for Flash and Fire Point Test of Bitumen

Flash Point in Close Cup Tester for Bituminous Products Except for Cutback Bitumen
Flash Point Test Procedure and Result All the parts of the cup and its accessories are cleaned thoroughly with the help of a solvent and allowed to dry
Flash and Fire Point Test of Bitumen | Procedure & Result
The bitumen sample is heated in a beaker at 75-100 °C- above the softening point of bitumen till it is completely melted into a fluid
Flash and Fire Point Test of Bitumen | Procedure & Result

Melted bitumen is poured into the mould

Flash and Fire Point Test of Bitumen | Procedure & Result
The cup is filled with the molten bitumen till the filling mark
Flash and Fire Point Test of Bitumen | Procedure & Result

The lid is placed on the cup to close it

The locking device of cup and lid should be engaged

Flash and Fire Point Test of Bitumen | Procedure & Result
The cup along with the lid is placed on the stove
Flash and Fire Point Test of Bitumen | Procedure & Result

Thermometer is inserted and the test flame is so adjusted that its size is similar to a bead of about 4 mm

Flash and Fire Point Test of Bitumen | Procedure & Result
The rate of application of heat is controlled to 5-6 °C  per minute
Flash and Fire Point Test of Bitumen | Procedure & Result The stirrer is rotated at the rate of 60 rev/min
Flash and Fire Point Test of Bitumen | Procedure & Result

As the temperature reaches 17 below the expected flash point, the test flame is applied

At the time of application of test flame, stirring is discontinued

Flash and Fire Point Test of Bitumen | Procedure & Result

The test flame is applied at every reading of the temperature up to 104 °C in the multiples of 1 °C.

When the temperature exceeds 104 °C, the test is carried out at an interval of 2 °C

Flash and Fire Point Test of Bitumen | Procedure & Result The temperature at which a distinct flash is observed at the interior of the cup is noted down as flash point
Flash Point in Close Cup Tester for Cutback Bitumen
Flash and Fire Point Test of Bitumen | Procedure & Result All the parts of the cup and its accessories are cleaned thoroughly with the help of a solvent and allowed to dry
Flash and Fire Point Test of Bitumen | Procedure & Result Melted bitumen is poured into the mould
Flash and Fire Point Test of Bitumen | Procedure & Result The cup is filled with the molten bitumen till the filling mark
Flash and Fire Point Test of Bitumen | Procedure & Result

The cup is placed on the stove

Thermometer is inserted and the test flame is so adjusted that its size is similar to a bead of about 4 mm

Flash and Fire Point Test of Bitumen | Procedure & Result

The rate of application of heat is controlled to 1-1.5 °C  per minute

The stirrer is rotated at the rate of 70-80 rev/min

Flash and Fire Point Test of Bitumen | Procedure & Result

As the temperature reaches 17 °C below the expected flash point, the test flame is applied

At the time of application of test flame, stirring is discontinued

Flash and Fire Point Test of Bitumen | Procedure & Result The test flame is applied at every reading of the temperature up to 104 °C in the multiples of 0.5 °C
Flash and Fire Point Test of Bitumen | Procedure & Result The temperature at which a distinct flash is observed at the interior of the cup is noted down as flash point
Fire Point in Open Cup Tester for Bituminous Products
Flash and Fire Point Test of Bitumen | Procedure & Result All the parts of the cup and its accessories are cleaned thoroughly with the help of a solvent and allowed to dry
Flash and Fire Point Test of Bitumen | Procedure & Result The bitumen sample is heated in a beaker at 75-100 °C- above the softening point of bitumen till it is completely melted into a fluid
Flash and Fire Point Test of Bitumen | Procedure & Result

Melted bitumen is poured into the mould

Flash and Fire Point Test of Bitumen | Procedure & Result The cup is filled with the molten bitumen till the filling mark
Flash and Fire Point Test of Bitumen | Procedure & Result

The open cup has a clip in place of cover as the lid

The rim encircles the upper rim of the cup completely

The locking device of the clip and cup are to be engaged properly

Flash and Fire Point Test of Bitumen | Procedure & Result

A thermometer is inserted

The test flame is adjusted to a size of a bead of about 4 mm diameter

Flash and Fire Point Test of Bitumen | Procedure & Result Control the rate of the application of heat such that the temperature increases by 5-6 °C  per minute as recorded from the thermometer
Flash and Fire Point Test of Bitumen | Procedure & Result The same steps as closed cup tester are followed and the stirrer is rotated manually
Flash and Fire Point Test of Bitumen | Procedure & Result The temperature at which the first distinct flash is observed at the interior of the cup is noted down as flash point
Flash and Fire Point Test of Bitumen | Procedure & Result The heating is continued further and the test flame is continued to be applied at an interval of 1 °C
Flash and Fire Point Test of Bitumen | Procedure & Result The temperature at which the flame is observed to be ignited for at least 5 seconds at the interior of the cup is noted down as fire point

Result for Flash and Fire Point Test of Bitumen

Flash point The temperature at which the first distinct flash is observed
Fire point The temperature at which the material is ignited for at least 5 seconds
Flash point of the sample

The average flash point value of the 3 samples

(The three values should not differ by ± 2 °C  for the flash point below 104 °C

The three values should not differ by ± 5.5 °C  for the flash point beyond 104 °C)

Fire point of the sample

The average of the fire point value of the 3 samples

(The three values should not differ by ± 8 °C)

Image Courtesy: Image1

 

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