Guidelines to find out the penetration value of bitumen for road construction
Penetration value test on bitumen is conducted to determine the rigidity or uniformity of bituminous material. A 80/100 grade bitumen signifies that its penetration value remains among 80 & 100.
Penetration value refers to the vertical distance traversed or infiltrated by the point of a standard needle into the bituminous material under particular conditions of load, time and temperature. This distance is calculated in one tenths of a millimeter.
The purpose of penetration test is to assess the conformity of bitumen. It is not recommended to be applied in connection with the testing of road tar due to the high surface tension exposed by these materials.
Penetration test on bitumen is undertaken for the following purposes:
1. Reliability of bituminous material
2. Applicability of bitumen for being utilized under various atmospheric conditions and types of construction.
Equipments for Penetration Test for defining the penetration value of bitumen
Container: It is a flat bottomed cylindrical metallic dish having necessary diameter 55 mm and depth 35 mm. If the penetration is of the order of 225 or more, dish of 70mm diameter and 45mm depth is essential.
Needle: It belongs to a straight, extremely polished, cylindrical and hard steel rod.
Water bath: Water bath remains at 25° ± 0.1 °C that comprises of not less than 10 litres of water, the sample is submerged to a depth not below 100mm from top and rested on perforated shelf not under 50mm from bottom of the bath.
Transfer dish or tray: It provides support to the container & should not rock it. It should contain the ability to submerge container entirely throughout test.
Penetration apparatus: It facilitates needle to infiltrate devoid of much friction & is perfectly calibrated to produce results in one tenth of a millimeter.
Thermometer: Range 0- 44 °C and in readable upto 0.20 C.
Time measuring device: It brings exactness of l second.
Safeguards recommended throughout Penetration Test
No movement of the container is allowed when needle enters into sample.
There should be no extraneous matter in the sample.
The needle should be cleansed with benzene and dehydrated prior to penetration.