Bituminous Stabilization

There are two types of Bituminous Stabilization that exist, namely Emulsion Stabilization and Expanded Asphalt Stabilization.

Emulsion Stabilization

The materials to be stabilized are first extracted from the roadway to perform a mix design which indicates the optimum fluids content, verifies the compatibility of the intended materials, and indicates the optimum amount of emulsion to be added to the mixture.

Determining the optimum fluids content is essential for a good quality mix as it enables the emulsion to coat the reclaimed material. If sufficient coating isn’t maintained, the results can be very detrimental to the roadway.

The compatibility is verified by mixing the proposed emulsion with the reclaimed material and assessing the degree of coating achieved.  If substantial coating doesn’t exist, other emulsions are used with the reclaimed material until adequate coating is achieved.

The percentage of emulsion is then determined and can vary between 4.0% and 5.0% depending upon the quality and residual asphalt content of the virgin in-place materials.

The final portion of the mix design is to assess the strength of the stabilized mix to ensure that it will meet the OPSS specifications.

Emulsion Stabilization is performed by injecting emulsion through a spray bar into a predetermined specified depth of reclaimed material typically within the range of 100-200 mm. The spray bar is located within the mixing drum housing enabling the emulsion to mix thoroughly with the reclaimed material.

This process requires a curing time dependant upon the emulsion system used before a surface course may be applied. Significant research and development has been dedicated to manufacture quick setting emulsions to reduce the curing time for this and other processes but are not yet available on the market.

Expanded Asphalt Stabilization

Expanded Asphalt Stabilization is a proven technique that provides the owner with a solid base capable of withstanding some of the most enduring weather cycles.

The materials to be stabilized are first extracted from the roadway to perform a mix design which indicates the optimum moisture content, evaluates material compatibility, determines the foaming characteristics of the asphalt cement, and provides the percentage of asphalt cement required for the mixture. In essence, the mix design proves that the treated material will conform to the Physical Requirements and Gradation Requirements published in OPSS 331.

Measures that determine the foaming characteristics of the asphalt cement include the Expansion Ratio and the Half-Life. The expansion ratio is the ratio between the maximum volume achieved in the foamed state and original volume of the asphalt binder prior to the addition of water. The half-life is the time, measured in seconds, for the foamed asphalt to subside to half of the maximum volume attained. The best quality of foamed asphalt is one that optimizes both parameters. The expansion ratio and half-life values both range between 10 and 15.

The optimum moisture content is then established to ensure that the bulk relative density established in the mix design may be obtained in the field.

The percentage of asphalt cement is then determined by testing the mixture at various asphalt cement percentages. The required injection percentage of asphalt cement can vary between 2.0% to 3.5% depending upon the quality and residual asphalt content of the virgin in-place materials.

The final portion of the mix design is to assess the strength of the stabilized mix to ensure that it will meet the OPSS specifications.

Comprehensive construction practices are then followed to provide the client with a road base capable of outlasting other pavement rehabilitation techniques. The process revolves around a pulverizer fitted with a spray bar capable of injecting the reclaimed material with expanded asphalt.

The expansion of the asphalt occurs within designated chambers located on a spray bar mounted within the mixing drum housing. The 180 °C asphalt and water are combined within the expansion chamber causing the water to evaporate thereby generating steam, resulting in explosive expansion. This causes the asphalt bitumen to form bubbles which encapsulate the steam and adhere to the finer particles passing the 2.36 mm sieve. The bitumen laden particles then form a mortar for the coarser aggregate enabling the treated material to provide significant strength and stability.

Expanded Asphalt Stabilization is very attractive to asset owners due to its low life cycle cost, low environmental impact, and ease of construction.