Bitumen Tests Explained: Softening, Ductility & Flash Point

Bitumen Tests Explained: Softening, Ductility & Flash Point, Bitumen Tests in Highway Engineering: Softening Point, Ductility, Flash & Fire Point Explained

BITUMEN

obtained by fractional distillation of crude oil.
soluble in carbon tetra chloride & carbon disulphide.
less resistance to temp.
more resistance to weathering.
less resistance to temp.
used for damp proof course.

TAR

obtained by destructive distillation of coal & wood.
soluble in toluene.
more resistance to temperature.
less resistance to weathering.
more resistance to temp.
used for coating a wooden frame.
- RT-1 – lowest viscosity → for surface painting
- RT-4 – premix in macadam.
- RT-5 – grouting (highest viscosity)

Form of Bitumen

1) Cutback bitumen

obtained by reducing the viscosity of bitumen wit/’;h diluents (volatile).
It is used in colder regions.
Cutbacks are designated by numerals representing viscous cutback.
e.g. RC-2 is more thick than RC-1 but RC-1, MC-2, SC-2 have same viscosity.

(1) Slow curing cutback (SC)

obtained by blending with high-boiling-point gas oil. (naphtha or gasoline oil).

(2) Medium curing cutback

They have good wetting properties.
Bitumen is flux with kerosene, light diesel oil.

(3) Rapid curing cutback

They have penetration value of 80 to 120.
flux with naphtha or gasoline oil.

2) Emulsion bitumen

It is two-phase system consisting of two immiscible liquids.
It is used rainy season.
Emulsion can be used for soil stabilization in desserts.
Bitumen/tar content in emulsion range for 40% to 60%, and remaining portion is water.

• Emulsion bitumen

Slow setting bitumen – used for surface dressing work.
Medium setting bitumen – used for patch up work.
Rapid setting bitumen –

TEST ON BITUMEN

1) Penetration test

Determines the hardness indirectly.

bitumen penetration test diagram Bitumen Tests Explained: Softening, Ductility & Flash Point

Unit of penetration is 1/10 mm
Load = 100g
Penetration value ↑ → Hardness ↓
Example: 80/100 means penetration of 8–10 mm.
Common grades are 80/40, 60/10 & 80/100.
Tars are soft, so a penetration test is not used.

2) Solubility

It is used to measure the quantity of impurity in bitumen with the help of CS₂ and CCl₄.
Solubility of bitumen in trichloroethylene is a measure of its purity.
As per IRC, insoluble material should not be greater than 1%.

3) Ductility test

It is a measure of the elasticity of the material.
It should be capable of being stretched without breaking.
Stretching standard briquette having c/s area 1 sq. cm at 27°C at a rate of pull being 5 cm/min → 50 mm/min.

As per ISI, the minimum value of ductility is 75 cm.

4) Spot test

This test is used to determine overheated or cracked bitumen.
More sensitivity than the solubility test for the detection of cracking.
2 gm of bitumen is mixed with 10 ml of naphthalene, and the solution is prepared & placed in a filter paper.
- Stain spot → uniform colour → uncracked bitumen
- Stain → annular ring thick, brown or black at centre & fair at periphery → overheated or cracked bitumen

5) Viscosity of bitumen (cup viscometer)

The property of bitumen which resists the flow due to internal friction.
Viscosity of liquid bitumen measured by efflux viscometer.
Methods used are STV (Standard Tar Viscometer), Saybolt, Furol, Redwood & Engler.
Furol viscosity is a standardised test.
In this test, the time taken is in seconds at the given temperature. 60°C.
When the time taken is more, the viscosity of bitumen is higher.
- More viscosity → less compaction

6) Softening point

Measured by the ring & ball apparatus.
Softening point is the temperature at which bitumen attains a particular degree of softness.

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More softening point = the material is more harder.
Softening point ⇒ 35°C to 70°C

7) Flash & Fire point

Flash point – Flash point of a material is the lowest temperature at which vapours take fire in the form of a flash.
Fire point – Temperature at which the material gets burnt (burns for 5 sec at least).
In this test, the apparatus used is Pensky–Marten’s close cup apparatus.
Flash point ⇒ 175°C (specified by IRC).
Safe limit for heating bitumen is normally 50°C below the flash point.

8) Specific Gravity

Determined by the pycnometer method.
Measurements are taken at 27°C. The specific gravity is generally 1.0.
- Bitumen ⇒ 0.97 – 1.02
- Tar ⇒ 1.10 – 1.25

9) Water Content Method