These pages contain the latest developments in our ongoing foamed asphalt research.

A brief introduction to foamed asphalt:

Who would have dreamed that anything good could result from mixing water and bitumen? In 1956 Prof. Ladis Csanyi did and today, more than 40 years later, his invention promises to revolutionize the way roads are constructed. Foamed asphalt is a mixture of aggregates (stone and soil) and foamed bitumen. The bitumen is foamed by an innovative process, harnessing the usually undesirable reaction which occurs when hot bitumen is contaminated with water.

Here's how it works:

In order to mix bitumen with road-building aggregates, you first need to considerably reduce the viscosity of the cold hard binder. Traditionally, this was done by heating the bitumen and mixing it with heated aggregates to produce hotmix asphalt. Other methods of reducing the bitumen viscosity include dissolving the bitumen in solvents and emulsification. Prof. Csanyi came up with the idea of introducing moisture into a stream of hot bitumen, which effects a spontaneous foaming of the bitumen (similar to spilling water into hot oil). In the foam state the bitumen has a very large surface area and extremely low viscosity making it ideal for mixing with aggregates.

Why is foamed asphalt only now gaining popularity?

Part of the answer lies in the fact that the original bitumen foaming process was a proprietary product, patented by Mobil Oil, with the associated restrictions on the general use of the technology. Furthermore, the lack of standardised mix design procedures meant that foamed asphalt was overlooked in preference for more well documented and familiar products.

What's so special about foamed asphalt?

Foamed asphalt epitomises the asphalt industry drive towards energy efficient, environmentally friendly and cost effective solutions for road-building.

These are the most striking advantages of foamed asphalt (from the mix design guide):

• The foamed bitumen increases the shear strength and reduces the moisture susceptibility of granular materials. The strength characteristics of foamed asphalt approaches that of cemented materials, but foamed asphalt is flexible and fatigue resistant.

• Foam treatment can be used with a wider range of aggregate types than other of cold mix processes.

• Lower binder and transportation costs because foamed asphalt requires less binder and water than other types of cold mixing.

• Saving in time because foamed asphalt can be compacted immediately and can carry traffic almost immediately after compaction is completed.

• Energy conservation because only the bitumen needs to be heated while the aggregates are mixed in cold and damp (no need for drying).

• Environmental side-effects of the evaporation of volatiles from the mix is avoided since curing does not result in the release of volatiles.

• Foamed asphalt can be stockpiled with no binder runoff or leeching. Since foamed asphalt remains workable for very extended periods the usual time constraints for achieving compaction, shaping and finishing the layer are avoided.

• Foamed asphalt layers can be constructed even in adverse weather conditions, such as cold or light rain, without affecting the workability or the quality of the finished layer.