Bitumen (Grade 60/70)
In early years of nineteenth century, the Penetration Rating System used to be applied for specifying the quality consistency of semi-solid bitumen.
This rating system was originally adapted for those kind of bitumen products which were manufactured through the refining process and in fact it was the residual substances left at the last stage of crude oil refining.
The type of bitumen which are used in road construction works, are classified on the basis of the results of the penetration tests. Such classification is made purely for the bitumen penetration degree.
For instance, in the laboratory tests, the penetration resistance of the grade 60/70 bitumen falls in the range of 6-7 millimeter and its softness point reaches between 49-56 centigrade.
For better and clear understanding of the grade 60/70 bitumen, due consideration should be given to the testing mechanism and method which is normally carried out after the production phase.
The said laboratory test is so called “Bitumen Penetration Test”. According to current laboratory definition, the bitumen penetration resistance degree is called in the situation when a laboratory standard needle (one-tenth of millimeter length) is put under 100 grams pressure and at 25 centigrade temperature and the penetration into the bitumen can be visible in five seconds.
In other words, if the needle in five seconds has penetrated into the product, then we come to know that the grade of our bitumen is 60/70.
The quality of 60/70 bitumen in mostly dependent on the physical and properties of the bitumen such as viscosity, softness, shaping and loss of temperature at flash point. It is notable that in the countries with moderate temperature, the type of 60/70 grade bitumen is widely used in road construction projects.
Those grades of bitumen which have high degree of penetration (such as 85/100 bitumen) are known as soft bitumen and are utilized in cold climate regions. On contrary, the bitumen with low penetration degree (i.e. 40/50) is named relatively solid bitumen and are mainly used in the areas with high temperature climate.