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
- 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.