7 Important questions on Bituminous Materials
Q1. What are the Bituminous Materials?
A1. Bituminous materials are mainly of two types-
- Bitumen
- Tar
Bitumen may be petroleum asphalt (bitumen) or native asphalt.
Do you know?
Native asphalts that are associated with a large proportion of mineral matter are called rock asphalts. The viscosity of bitumen is reduced sometimes by a volatile diluent, this material is called cutback. When bitumen is suspended in a finely divided condition in an aqueous medium and stabilized with an emulsifier, the material is known as an emulsion.
Q2. What are the general requirements for the Bitumen?
A2. General requirements for Bitumen-
- Adequate viscosity at the time of mixing
- Low susceptibility to temperature
- It should not strip off from aggregate
Q3. What are the tests on bitumen?
A3. Tests of Bitumen-
- Penetration test
- Ductility test
- Viscosity test
- Float test
- Specific Gravity Test
- Softening Point Test
- Flash and Fire test
- Solubility Test
- Spot Test
- Loss on heating test
- Water content test
Q4. Define the Penetration Test.
A4. Penetration Test-
- Penetration test determines the hardness or softness (consistency) of bitumen by measuring depth in tenths of a millimetre to which a standard loaded needle will penetrate vertically in 5 seconds. The sample is maintained at 250C.
- The penetrometer consists of a needle assembly of 100gm.
- 80/100 reading means needle penetrates 8 to 10mm at 250C.
Note- The penetration values of various types of bitumen used in pavement construction in this country range between 20 and 225, 30/40, and 80/100 grade bitumen are more commonly used.
Tars are soft and a penetration test is not used.
Q5. Define Ductility Test.
A5. Ductility test-
- The ductility is expressed as the distance in centimeters to which a standard briquette of bitumen can be stretched before the thread breaks. The cross-section of the specimen is 10mm * 10mm.
- The test is conducted at 370C and at a rate of the pull of 50mm per minute.
- ISI has recommended a minimum ductility value of 75 cm of grades of 45 and above.
- The minimum ductility value specified is 15cm for the bitumen grades A-65 to 200 for use in certain regions.
- The minimum ductility value may be 50cm for grades S35.
Q6. Define Viscosity Test.
A6. Viscosity Test-
- Viscosity test is the measure of resistance to flow.
- Orifice type viscometer is commonly used.
- Viscosity is measured by determining the time taken by 50ml of the material to flow from a cup through a specified orifice under standard test conditions.
- Furol viscosity is standardized test which is used only to measure the viscosity of liquid bituminous materials.
Q7. What is Cutback bitumen? Define.
A7. Cutback Bitumen is defined as the bitumen, the viscosity of which has been reduced by a volatile diluent. These are of three types:
- Rapid Curing (RC)
- Medium Curing (MC)
- Slow Curing (SC)
The cutbacks are designated by numerals representing progressively thicker or viscous cutback. For Example- RC-2 is thicker than RC-1 but RC-2, MC-2 and SC-2 have same viscosity.
RC-0 and SC-0 may have 45% solvent and 55% bitumen whereas RC-5 and MC-5 may contain 15% solvent and 85% bitumen.
Various tests carried out of cut-back bitumen are:
- Viscosity tests at specified temperature using specified size of orifice.
- Distillation test to find distillation fractions, up to specified temperature and to find the residue from distillation up to 3600C.
- Penetration test, ductility test and test for matter soluble in carbon disulphide on residue from distillation up to 3600C.
- Flash point test on cutback using Pensky Martens closed type apparatus.
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