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Foamed asphalt is not an invention. Any hot asphalt that comes into contact with water will foam and its volume increases rapidly. For many, this situation is not wanted and in such cases, anti-foaming agent (silicones) are used to prevent this from happening. However, in 1956, Dr. Ladis H. Csanyi, professor at the Engineering Experiment Station in Iowa State University, saw the possibility of using the foamed asphalt as a binder for soil stabilization. Foaming the asphalt reduces its viscosity considerably and has shown to increase adhering properties making it well suited for mixing with cold and moist aggregates.
No chemical reaction is involved, only the physical properties of the asphalt are temporarily altered. When the cold water comes into contact with the hot asphalt, it is turned into steam which is trapped in thousands of tiny asphalt bubbles. However this is not a permanent state, after a few minutes, the asphalt will resume its original properties. Foamed asphalt is generally characterized in terms of expansion ratio and half-life. The expansion ratio of the foam is defined as the ratio between the maximum achieved volume of the foam, versus its original volume. The half-life is the time elapsed from the moment the foam was at his maximum volume to the time it reached half of this volume
The first reported use of foamed asphalt dates back to 1957 on an Iowa County Road. Several other field applications were also reported including projects in Arizona (1960) and in Nipawin, Canada (1960-1962). However, the original process consisted of injecting high pressure steam, at controlled pressure and temperature, into a heated penetration grade asphalt cement. This required special equipment on the job site such as a boiler and was not very practical.
In 1968, Mobil Oil Australia modified the original process by adding cold water rather than steam, into a stream of hot asphalt in a low pressure system. This made the process much more practical and economical. The foam was created within an expansion chamber after which it was dispersed through a series of nozzles, onto the aggregate mass. However, the nozzles were prone to blockage and the manufacturer could not control the foam characteristics.
Today, and since 1989, Soter is using foamed asphalt with a new refined system. Air and cold atomized water (1% to 2% by weight of asphalt cement) are injected into hot asphalt cement (165°C) in 16 individual expansion chambers with nozzle.
Foamed asphalt can be used with a variety of materials, whether new, recycled or even marginal material such as those having a high plasticity index. The foamed asphalt can be applied by two means, in-situ or in a central mobile plant.