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.