Various tests are performed to assess the stability, gradation, viscosity, temperature sensitivity and safety of bitumen.
There are several tests to assess the properties of bituminous materials. The following tests are generally performed to evaluate the various properties of bituminous materials.
- entrance examinations
- resilience test
- softening point test
- specific gravity test
- viscosity test
- flash and fire point test
- float test
- water content test
- loss on heat test
It measures the hardness or softness of bitumen by measuring the depth to one tenth of a millimeter, which a standard loaded needle would enter vertically in 5 seconds. BIS had standardized the equipment and testing procedure.
The penetrometer consists of a needle assembly with a total weight of 100 g and a device to release and lock in any position. The bitumen is softened to the consistency of an insert, shaken well and poured into containers at a depth of at least 15 mm above the expected penetration. test 25. must be held at the specified temperature of0C.
It may be noted that the penetration value is largely affected by any inaccuracy with respect to insert temperature, needle size, weight placed on the needle and test temperature.
In hot climates, low penetration grades are preferred. Fig-1 shows a schematic penetration test setup.
Also read: Bitumen Penetration Testing Process
Tensile is the property of bitumen that allows it to undergo a great deal of deformation or elongation. Ductility is defined as the distance, in cm, from which a standard sample or briquette of material will elongate without breaking. The dimensions of the briquette so made are exactly 1 cm square. The bitumen sample is heated and poured into a mold assembly placed on a plate. These samples along with the mold are cooled in air and then in a water bath. is cooled on0C temperature. Excess bitumen is cut off and the surface is leveled with a hot knife. The sample mold containing the assembly is then placed in the water bath of the ductility machine for approximately 90 minutes. The sides of the mold are removed, the clip is mounted on the machine and the machine is operated. The distance to the breaking point of the thread is the ductility value which is reported in cm.
The ductility value is affected by factors such as pouring temperature, test temperature, stretching rate, etc.
The minimum tensile value specified by BIS is 75 cm. Fig-2 shows the ductility test procedure.
Read also: The ductility test procedure of bitumen
3.softening point test
The softening point refers to the temperature at which bitumen attains a particular degree of softening under the specified test conditions.
The test is conducted using ring and ball equipment. A brass ring containing a test sample of bitumen is suspended in a liquid such as water or glycerin at a given temperature. A steel ball is placed on a sample of bitumen and the liquid medium is kept at 5. is heated at the rate of0c per minute. The temperature is noted when the soft bitumen touches the metal plate at a specified distance below.
Typically, a higher softening point indicates sensitivity to lower temperatures and is preferred in warmer climates. Figure-3 shows the softening point test setup.
Read also: Softening test procedure of bitumen
4.specific gravity test
The specific gravity of bitumen is defined as the ratio of the mass of a given volume of bitumen of a known material to the mass of the same volume of water at 27.0c. Specific gravity can be measured using a pycnometer or by preparing a cubic sample of bitumen in a semi-solid or solid state.
In paving work, the density property is of great use to classify a binder. In most cases bitumen is weighed, but when used with aggregates, bitumen is converted to volume using density values.
The density of bitumen is greatly influenced by its chemical composition. An increase in the aromatic type of mineral impurities leads to an increase in specific gravity.
The specific gravity of bitumen varies from 0.97 to 1.02.
Read also: Specific gravity test procedure of bitumen
Viscosity refers to the fluid property of bituminous material and is a measure of its resistance to flow. At application temperature, this characteristic greatly affects the strength of the resulting paving mixes.
Low or high viscosity has been observed to result in low stability values during compaction or mixing. At high viscosity, it opposes the compaction effort and consequently the mixture is heterogeneous, hence the low stability value. And at low viscosity, instead of providing a uniform film over the aggregate, it will lubricate the aggregate particles.
The orifice type viscometer is used to indirectly find the viscosity of liquid binders such as cutbacks and emulsions.
Viscosity expressed in seconds is the time taken by 50 ml of bitumen material to pass through the orifice of one cup under standard test conditions and specified temperature. The viscosity of the cutback is measured with a 4.0 mm aperture as 25 . can be measured on0c or 10 mm orifice 25 or 40 . Feather0C.
Read also: Viscosity test of bitumen emulsion By Saybolt Furol Viscometer
6.flash and fire point test
At higher temperatures, bitumen releases volatile depending on the grade of the material. And these volatiles catch fire which is very dangerous and hence it is necessary to qualify this temperature for each bitumen grade. The BIS defined the ash point as the temperature at which bitumen vapor momentarily ignites as ash under specific test conditions. Fire point is defined as the minimum temperature under specified test conditions at which bituminous material ignites and burns.
Generally the stability of bituminous material can be measured by penetration test or viscosity test. But for certain range, these tests are not applicable and float test is used.
The instrument consists of an aluminum oat and a brass collar filled with bitumen for testing. Put the sample in the mold 5 . is cooled to a temperature of0C and spoiled in oats. Total Test Assembly 50 . but swims in the water bath0The time required for C and water to pass its way through the sample plug is noted in seconds and is expressed as the ot value.
8.water content test
It is desirable that there be a minimum amount of water to prevent froth of bitumen when the bitumen is heated above the boiling point of water.
Water in bitumen is determined by adding a known weight of the sample to a water-free pure petroleum distillate, heating and distilling the water. The weight of the condensed and collected water is expressed as a percentage of the weight of the original sample.
The allowable maximum water content should not exceed 0.2% by weight.
9.loss on heat test
When bitumen is heated it loses its volatility and hardens. About 50 grams of the sample is weighed and 163. is heated to a temperature of0c for 5 hours in the specified oven designed for this test. The sample is weighed again after a heating period and the weight loss is expressed as a percentage of the original sample’s weight.
Bitumen used in pavement mixes should not imply a loss of more than 1% in weight, but bitumen with a weight loss of 150-200 to 2% is permitted.
List of IS Codes for Bitumen Testing
Testing for Bitumen with IS Code
|Test Name||IS code number|
|entrance examinations||IS: 1203-1978|
|resilience test||IS: 1208-1978|
|softening point test||IS: 1205-1978|
|specific gravity test||IS: 1202-1978|
|viscosity test||IS: 1206-1978|
|flash and fire point test||IS: 1209-1978|
|float test||IS: 1210-1978|
|determination of water content||IS: 1211-1978|
|Determination of Loss on Heating||IS:1212-1978|
Dr. Tom V Matthews (IIT Bombay)