Bitumen: Grades and Method of Grading

In this post, we will discuss 5 types of bitumen grades and the method of grading bitumen.

Grades of Bitumen.

Bitumen is graded in 5 types.

1. Penetration grade bitumen – Bitumen 60/70 is commonly used as the major Penetration Grade Bitumen.
2. Oxidised bitumen grade – These types of bitumen are custom made for projects and they are highly water resistant and durable. They are available in many grades like 95/25, 85/25, 75/25, 90/40 and 115/15.
3. Cutback bitumen – These types of bitumen are produced by diluting in petroleum hydrocarbon (Kerosene).Commonly available cutback bitumen are MC-30 and MC-70.
4. Bitumen Emulsion – There are three types of grades, Rapid setting (RS), Medium setting (MS), and Slow setting (SC).
5. Polymer Modified bitumen – PMB polymer modified bitumen grades are PG 64–16, PG 64–22, PG 70–10, PG 70–16, PG 76–10, PG 76–16.

Methods of Grading Bitumen

There are mainly four methods used for grading of bitumen.

1. Grading by chewing – Before scientific testing methodologies were invented bitumen was tested by chewing to determine the hardness of the material. It was done by experts and their word was taken at face value.
2. Penetration grading – The American Society for Testing Materials (ASTM) tested bitumen quality using penetration of a needle which has 100g of bitumen at a temperature of 25-degree Celsius in a water bath for a period of 5 seconds.
3. Viscosity grading – This method was used to grade bitumen based on the viscosity of the material.
4. Superpave performance grade – Superpave system was invented to avoid ravelling, fatigue cracking and thermal cracking of bitumen during the testing process. The higher grades are PG 52, PG 58, PG 64, PG 70, PG 76 and PG 82. The lower grades are -4, -10, -16, -22, -28 and -34.