Bitumen is a by-product of crude oil which has strong adhesive and waterproofing properties. It is involved in many tests to determine its grade and durability. 

The penetration test is performed to determine the penetrate value of the bitumen and a softening point test is conducted to determine the viscosity point of the bitumen.

The flash and fire point test is performed on a particular bitumen grade to identify the safe temperature of bitumen for reliable work.

What is a flash and fire point test?

Flash point – The lowest temperature of bitumen that induces the material to vapour and momentarily catch fire in the form of flash is known as a flashpoint.

Fire Point – The lowest temperature of bitumen that induces the material to ignite and burn at least for 5 seconds is known as fire point.

Why do we check flash point and fire point?

Since bitumen is a by-product of crude oil, it contains highly flammable particles.

  • The flash and fire point test is conducted to check the safe work temperature.
  • The fire point test is performed to determine the combustible particles which exist in the bitumen.
  • The flashpoint value indicates material storage and transportation temperature.
  • The analysis also helps us to find the contamination of bitumen binder.

How do you determine the flash and fire point?

The Pensky-Martens can find the flash and fire point value using a closed cup and open cup test apparatus.

Apparatus Required

Flash and Fire Point Test Apparatus

  • Pensky-Martens Open/Closed tester – It consists of a cup on a top surface and heat exposure device. The heating device fixed at the bottom with a connection temperature regulator to control heat production.
  • Thermometer – 0 to 370 °C
  • Stirring

Procedure for Closed cup Test – Bitumen

  • All closed cup apparatus relevant to this experiment should be free from dust and dried in a hot air oven.
  • The bitumen specimen should be heated above its softening point.
  • Fill the bitumen into the cup up to the filling mark. 
  • Now place the cup on the tester and close the cup. 
  • The thermometer & stirrer should be placed in their position to start the test.
  • Now heat the bitumen at the range of 5 °C to 6 °C per minute with help of the heat regulator.
  • At the same time stir the specimen by the stirrer at the rate of rotation 60 per minute.
  • Look carefully on the thermometer reading when the temperature reaches at 17 °C below the expected flashpoint the test flame should be applied.
  • The bead of the test flame should be in 4mm and stirring should be stopped while applying the test flame.
  • The test flame should be applied at 1 °C rising from that point. 
  • A unique flash will appear when applying the test flame with respect to the gradual increase of temperature. 
  • Take the reading as the Flashpoint of the bitumen.
  • Now continue applying heat and test flame at a temperature rising for every 2 °C.
  • Note the temperature reading as the Fire point of the bitumen from the thermometer when the bitumen catches fire and burns at least for 5 seconds.
  • Repeat the test at least 3 times and the average value is the Flash and Fire point of the bitumen.

Lab Report

Type – Closed/Open Sample1 Sample2 Sample3
Flashpoint
Fire point

The difference of duplicate test results should be in the limit as mentioned in the below table as per IS code 1209.

Flash Point Repeatability Reproducibility
104°C and below 2°C 3.5°C
Above 104°C 5.5°C 8.5°C

Procedure for Open cup Test – Cut back Bitumen

The apparatus required for the Open cup test is similar to the Pensky-Martens closed cup tester with the only modification is the cover of the cup is replaced by a clip that is placed on the upper rim of the cup.

  • All open cup apparatus relevant to this experiment should be free from dust and dried in a hot air oven.
  • The bitumen specimen should be heated above its softening point.
  • Fill the bitumen into the cup up to the filling mark. 
  • Now place the cup on the tester.  The clip carries the thermometer and flame tester.
  • Now heat the bitumen at the range of 5 °C to 6 °C per minute with the help of the regulator.
  • Look carefully on the thermometer reading when the temperature reaches at 17 °C below the expected flashpoint the test flame should be applied.
  • The test flame bead should be 4mm, and it can be adjusted.
  • The test flame should be applied at every 1 °C rising from that point on the bitumen surface.
  • A unique flash will occur when applying the test flame with respect to the gradual increase of temperature. 
  • Take the reading as the flashpoint of the bitumen.
  • Now continue the applying heat and use the test flame at a temperature rising for every 1 °C to 3 °C.
  • At a specific temperature, the bitumen will catch fire and burn at least for 5 seconds. 
  • Note the temperature reading from the thermometer when the bitumen catches fire and burns at least for 5 seconds as the Fire point of the bitumen.
  • Repeat the test at least three times, and the average value is the Flash and Fire point of the bitumen.

Lab Report

Type – Closed/Open Sample1 Sample2 Sample3
Flashpoint
Fire point

The difference of duplicate test results should be in the limit as mentioned in the below table, as per IS code 1209.

Conditions Repeatability Reproducibility
Flashpoint 8°C 11°C
Fire point 8°C 14°C

The flash and fire point value will differ based on the bitumen grade. The recommended minimum Values of flash & fire point is given below. 

Usually, the fire point value is 8 to 10% greater than the flash point value.

Condition Minimum Temp Value
Flashpoint 175 °C
Fire point 175 °C +5 °C

Video Illustration

Factors affecting the flash point and fire point

  • The high density of bitumen will show the higher value of fire & flashpoint.
  • When the bitumen sample is mixed with other particles, then it shows different values while testing the sample.
  • Improper specimen heating will affect the result of the test.

Happy Learning 🙂

Author

Bala is a Civil Engineer who has more than 9+ Years of experience in planning & costing in Infrastructure. He is the author, editor of Civil Planets.

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