Performance Grade Bitumen

What is PG Bitumen?

PG Bitumen stands for Performance Grade Bitumen, which is classified according to its behavior under different temperature conditions. This type of bitumen is produced following standards such as AASHTO M 320-10 and ASTM D6373-1.

Introduction to Performance Grade Bitumen

Traditionally, bitumen was categorized based on penetration, indicating its hardness, and viscosity, showing its consistency. Penetration is measured at 25°C, while viscosity is determined at both 60°C and 135°C.

Over time, engineers realized that temperature is one of the most critical factors affecting bitumen performance. Previous classification systems did not fully consider temperature, even though the durability and functionality of bitumen are highly temperature-dependent.

PG Bitumen Grading System

The PG grading system evaluates bitumen based on its performance at low, medium, and high temperatures.

For instance, a PG 58-28 grade indicates that the bitumen is suitable for areas where the maximum pavement temperature reaches 58°C and the minimum temperature drops to -28°C.

• The positive number (58) represents the average of the highest pavement temperatures over seven consecutive summer days.
• The negative number (-28) shows the lowest pavement temperature over seven consecutive winter days.

This means that the bitumen will not perform adequately above 58°C or below -28°C.

PG grades are divided into Modified and Unmodified types. A simple way to distinguish them is by adding the high and low temperature numbers:

• If the sum exceeds 92, the bitumen is polymer-modified. For example, PG 76-22 is polymer-modified since 76 + 22 = 98.
• If the sum is less than 92, the bitumen is unmodified. For example, PG 64-10 is unmodified, as 64 + 10 = 74.

Generally, grades with high-temperature ranges in the upper part of the table are considered modified. When the difference between high and low temperatures exceeds 92°C, the use of modifiers becomes necessary, which also increases the cost of the bitumen.

PG Bitumen Testing

PG bitumen is evaluated according to AASHTO testing standards. The main focus is on rutting, fatigue, and thermal cracking, along with standard tests such as solubility, flash point, specific gravity, and softening point.

Additional performance tests include:

• Viscosity Determination using Rotational Viscometer (RV) – AASHTO T 316
• Rheological Properties using Dynamic Shear Rheometer (DSR) – AASHTO T 315
• Fracture Properties in Direct Tension (DT) – AASHTO T 314
• Flexural Creep Stiffness using Bending Beam Rheometer (BBR) – AASHTO T 313
• Rolling Thin-Film Oven Test (RTFOT) – AASHTO T 240
• Accelerated Aging using Pressurized Aging Vessel (PAV) – AASHTO R 28
• Elastic Recovery Test – AASHTO T 301
• Separation Tendency of Polymer from Polymer-Modified Bitumen – ASTM D7173

These tests ensure that PG bitumen meets the required standards for durability, flexibility, and performance across a wide range of temperatures.