Bitumen

Bitumen has been used in construction since ancient times, thanks to its key waterproofing properties. Unmodified bitumen is a highly viscous liquid, and its tendency to become brittle at low temperatures and soft at high temperatures has limited its use.

For many decades, bitumen has been successfully used in asphalt concrete to pave roads. Despite continuous improvements to bitumen production processes, mix design and pavement design, there are limits to the extent that bitumen can surmount the challenge. Accelerating wear and tear caused by heavy traffic and harsh climates are taking a toll. In addition there are increasing demands for quieter and safer roads.

Polymer modification of bitumen is helping to overcome the challenges. Today, millions of tons of polymer modified bitumen is used by the global roads industry

Photo: Use of soft unmodified bitumen on a dyke to bind the stones and provide waterproofing. The flow patterns result from the non-elastic viscous characteristics of bitumen.

Composition

Bitumen is an complex mixture of hydrocarbons. It can be derived from a straight distillation of a single crude oil. However, it is usually a combination of the heavier products from different processes in a refinery, blended to obtain the right specification. Because of its complexity, the composition is expressed by determining the relative amounts of classes of molecules, asphaltenes and maltenes. 

Asphaltenes – these are polar aromatics which associate in large structures to give solidity at ambient temperatures.

Maltenes consist of:

• Saturates – segregated into paraffins and naphthenes. Regarded as carrier or solvent for the asphaltenes.
• Aromatics – also regarded as carrier or solvent for the asphaltenes.
• Resins – act as dispersion agents