The fascination of bitumen emulsion – a binder with many facets

The history of bitumen emulsion goes back more than 100 years and is based on the endeavour to bind the then ever-present road dust and thereby prevent its harmful health effects. Initially, environmentally harmful low-viscosity creosotes from gas works and liquid distillation residues from petroleum processing (“road oil”) were used to bind dust. Eventually, it was discovered that viscous to solid distillation residues (bitumen) can also be cold-processed to a large extent if emulsified with water. Emulsification refers to the distribution of fatty substances (like bitumen) in water in the form of microscopically small droplets. For example, a bitumen emulsion containing 70 % bitumen and 30 % water at 40 °C is about 1000 times thinner than the bitumen it contains – a major advance for road construction applications at the time!

Today, bitumen emulsions are among the most frequently used construction materials in road construction and maintenance. Their advantages are undisputed:

• No risk of burning or fire
• No toxic solvents
• No risk of explosion due to solvent vapours
• Only release water when setting
• Are processed in a cold state and therefore save energy
• Do not penetrate the soil
• Highly variable properties and therefore versatile in use

Due to the water content, construction methods using bitumen emulsions rely on a minimum outdoor temperature during and after processing. The required evaporation of the “diluent” water during the setting process is brought about by free and environmentally friendly solar energy! In our latitudes, construction work with bitumen emulsions is limited to the three warmer seasons. They are mainly used for surface treatment and the production of cold-applied slurry surfacing – classic construction methods for road maintenance that are widespread all over the world. But they are also of great importance for the production of bonding bridges prior to the application of hot asphalt layers.

Bitumen emulsion – a jack-of-all-trades in road construction and maintenance

Depending on the application, the bitumen content of modern bitumen emulsions ranges from 40 % to 70 %. One litre of emulsion contains up to one quadrillion microscopic droplets with an average particle diameter of about 0.1 to 10 µm.

Bitumen emulsions are a standardised group of construction materials (requirements according to ÖNORM EN 13808, ÖNORM B 3508, ÖNORM B 3509, tests according to a large number of other ÖNORM EN regulations). Their importance for economical road maintenance is generally acknowledged, which is why they have also been quality-protected in Austria for a good 30 years now (externally monitored and tested in field trials).