Determination of Softening point of bitumen

Softening point of bitumen (IS 1205:1978)

Softening point of bitumen is that temperature at which it attains some degree of softness.The test is conducted by using Ring and Ball apparatus. A brass ring containing test sample of bitumen is suspended in liquid like water or glycerin at a given temperature. A steel ball is placed.upon the bitumen sample and the liquid medium is heated at a rate of 5⁰C per minute. Temperature is noted when the softened bitumen touches the metal plate which is at a specified distance below. Generally, higher softening point indicates lower temperature susceptibility and is preferred in hot climates.

 Apparatus

Ring and ball apparatus with all components, Thermometer, heating apparatus, Bath and stirrer.

Softening point apparatus

 

 

 

Procedure

1. Sample of bitumen is heated to a temperature between 75° and 100°C above the approximate softening point until it is completely fluid and is poured in heated rings placed on the metal plate.
2. To avoid sticking of the bitumen to metal plate, coating is done to this with a solution of glycerin.
3. After cooling the rings in air for 30 minutes, the excess bitumen is trimmed and rings are placed in the support.
4. At this time the temperature of distilled water is kept at 5°C. This temperature is maintained for 15 minutes after which the balls are placed in position.
5. Then the temperature of water is raised at uniform rate of 5°C per minute with a controlled heating unit, until the bitumen softens and touches the bottom plate by sinking of balls. At least two observations are made. For material whose softening point is above 80°C, glycerin is used for heating medium and the starting temperature is 35°C instead of 5°C.

Observations

Softening point of bitumen varying from 35 degree Celsius to 70 degree Celsius are used for various paving zones.Bitumen with higher temperature susceptibility or lower softening points are used in colder regions and vice versa.

 

Penetration test on bitumen

Penetration test on bitumen

Penetration on bitumen is conducted to classify the bitumen in different grades.This tests determine the consistency of bitumen for the purpose of grading by measuring the depth of standard needle penetrating the bitumen sample vertically under specific conditions of load, temperature time.

Apparatus

A flat bottomed cylindrical metallic dish 55mm in diameter and 35 mm in depth is required. If the penetration is of the order of 225 or more, dish of 70mm diameter and 45mm depth is required, Water bath maintained at 25 degree Celsius, Penetration apparatus: Should be such that it allows needle to penetrate without much friction & is accurately calibrated to give results in one tenth of a millimeter, Time measuring device with an accuracy of a second.

Penetrometer

Procedure

1. Soften the material to a pouring consistency at a temperature not more than 60 degree Celsius for tars and 90 degree Celsius for bitumen above the approximate softening point and stir it thoroughly until it is homogeneous and is free from air bubbles and water.
2. Pour the melt into the container to a depth at least 10 mm in excess of the expected penetration. Protect the sample from dust and allow it to cool in an atmosphere at a temperature between 15degree Celsius to 30 degree Celsius for one hour. Then place it along with the transfer dish in the water bath at 25 degree Celsius.
3. Fill the transfer dish with water from the water bath to depth sufficient to cover the container completely, place the sample in it and put it upon the stand of the penetration apparatus.Clean the needle with benzene, dry it and load with the weight. The total moving load required is 100 grams, including the weight of the needle, carrier and super-imposed weights. 
4. Adjust the needle to make contact with the surface of the sample. This may be done by placing the needlepoint in contact with its image reflected by the surface of the bituminous material.
5. Make the pointer of the dial to read zero or note the initial dial reading.Release the needle for exactly five seconds.Adjust the penetration machine to measure the distance penetrated
6. Make at least 3 readings at points on the surface of the sample not less than 10 mm apart and not less than l0mm from the side of the dish. After each test return the sample and transfer dish to the water bath and wash the needle clean with benzene and dry it. In case of material of penetration greater than 225, three determinations on each of the two identical test specimens using a separate needle for each determination should be made, leaving the needle in the sample on completion of each determination to avoid disturbance of the specimen.

Observations

Penetration test is generally used to determine the hardness of bitumen because of its simplicity.Softer the bitumen more will be its penetration value.For example 80/100 bitumen grade denotes the bitumen sample having penetration value between 8 mm to 10 mm.