Foamed Bitumen Stabilisation

The Principle

Foamed bitumen stabilisation (FBS) is a unique pavement treatment option for treating new materials or rehabilitating pavements that have exceeded their serviceable life. The foamed bitumen process creates a visco-elastic material which once compacted is strong, durable, non-temperature sensitive, moisture resistant and flexible yet rut resistant.  The performance of a foamed bitumen stabilised pavement is similar to that of structural or deep lift asphalt however, foamed bitumen stabilisation represents significant advantages over structural asphalt in productivity, resistance to high in service temperatures, bitumen content and therefore cost.

The introduction of FBS into WA now allows specifiers and designers a high performance pavement treatment option that fills the gap between conventional stabilisation and structural or deep lift asphalt. This allows better allocation of funding and more economical pavement construction projects state wide.

In the last two decades the use of foamed bitumen has increased rapidly and is being used extensively on both new construction projects and pavement rehabilitation projects around the world.  Foamed Bitumen Stabilisation has been successfully implemented when the use of cement or lime modification no longer meet the pavement design criteria to support the heavier trafficked sections of freeways, urban arterials, quarry / mine access roads, industrial roads and yards, container storage facilities and aircraft pavements.

WA Stabilising has successfully completed over a quarter of a million square meters of foamed bitumen stabilisation between 2013 and 2019 for various MRWA ISA regions, mining companies and on metropolitan projects.

The Main Benefits

The benefits specifically of the Foamed Bitumen Stabilisation Process include:

  • Results in a strong durable and flexible pavement layer
  • Foamed Bitumen has an affinity to most natural gravels and crushed rock aggregates
  • More cost effective than other forms of bitumen stabilising agents
  • Reduction in basecourse thickness resulting in reduction in premium basecourse aggregates
  • Can achieve the desired engineering properties without requiring basecourse specified aggregates
  • The foamed bitumen stabilised material results in a significant reduction in moisture susceptibility
  • A successful method of rehabilitation on historically troublesome sections of pavement
  • Significantly reduces or eliminates excavation volumes and the requirement to import pavement materials
  • Conserves aggregate resources
  • The compacted and finished layer can be trafficked almost immediately
  • Minimises inconvenience to the road user by speed and efficiency of the process

What is Foamed Bitumen?

Foamed bitumen is produced when small amounts of water (approx. 2 to 3 % of the bitumen amount) are added to hot bitumen between 170 and 180 °C. The bitumen used for this process is standard bitumen grade C170.  When injecting water into hot bitumen the water evaporates instantaneously, forming a gaseous “bubble” surrounded by the oil, which causes in the bitumen to foam and expand by 10 to 30 times its original volume.  This increased volume results in a reduction of the viscosity, which allows the mixing of the bitumen with cold, damp materials.  The tiny bitumen shards only have enough energy to encapsulate the fines fraction (< 75 microns) of the aggregates thereby creating a bitumen rich mortar within the granular material.  The foaming process takes place in a controlled environment, called an expansion chamber, where the water and air are injected into the hot bitumen at high pressure.

The Process

The foamed bitumen escapes from the expansion chamber through a nozzle and is immediately mixed with the aggregate in the milling and mixing chamber of the stabilisation machine.  Thereafter, similar to conventional basecourse construction the rollers, water tankers and graders are used to compact, moisten and finish the Foamed Bitumen Stabilised layer.  WA Stabilising has the expertise to prepare the surface of the Foamed Bitumen Stabilised layer to allow high volume trafficking soon after final compaction, thereby reducing traffic delays that would be caused from deterioration of the finished stabilised surface.  Depending on the weather conditions the stabilised layer is cured for 24 to 36 hours before the application of the sprayed seal.  Where required by higher traffic volumes, the asphalt surfacing can be applied onto the sprayed seal after the diluents have evaporated.