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d. Contaminated soil has been used in ASB construction in several states (Ellison 1991).
Typical ASB mixtures normally consist of approximately 95 percent aggregate and 5 percent
asphalt cement binder (by weight of total mixture), where the aggregate provides the load-
bearing properties and the asphalt binds the aggregates together (Friend 1996). For use in ASB,
the soils are normally screened and used without thermal pretreatment (EPA 1992). When
contaminated soil is used in the ASB, the soil replaces part of the clean aggregate, and the asphalt
cement immobilizes the petroleum contaminates in the soil (Friend 1996). The effectiveness of
ASB in immobilizing contaminates has not been well documented. Consequently, many
regulatory agencies have not readily supported this technology (Friend 1996).
3. Soil Types and Requirements.
a. Almost any type of soil including clay/silt, sand, gravel, and boulders can be incorporated
into ASB in certain applications. However, when the contaminated soil is predominately a sand, it
is normally not a candidate for ASB because of other insitu remediation technologies that can be
more applicable including isolation/containment and passive remediation (Ellison 1991).
Contaminated soils that contain large amounts of clay, especially expansive clays, will not perform
well in ASB or in any application of road construction (Dineen 1991).
b. The amount or level of liquid petroleum or hydrocarbon material that can be held in soil
above the water table (unsaturated) varies with the particle size of the soil. The larger the particle
size, the smaller the amount of liquid petroleum that can be held without draining out of the soil.
Fine sand/silt combinations will be able to hold 2 to 3 times the amount of liquid that a coarse
sand can hold, and the coarse sand will hold a similar amount more than a coarse gravel (API
1989). This is generally true for all petroleum materials ranging from lighter (gasoline) to heavier
materials (fuel oils).
c. To perform as an effective base or stabilized material, a given range of aggregate gradation
and particle shape must be developed. Generally, small amounts of contaminated material could
be blended with other aggregates, prior to the addition of asphalt cement, to obtain satisfactory
material for almost any use. The higher the quality of the aggregate in the contaminated soil, the
more that can be used in relation to additional aggregate, provided levels of contamination are
acceptable. The Corps of Engineers has Guide Specifications (CEGSs) that have been developed
for bituminous base courses (CEGS-02242), bituminous binder and wearing courses (CEGS-
02742), bituminous road-mix surface courses (CEGS-02744), or cold-mix recycling (CEGS-
02965). The appropriate CEGS can be selected based upon existing conditions in regards to the
type and degree of contamination and the intended use of the contaminated soil mixture. The
corresponding requirements for aggregate gradation and particle shape given for the various types
of mixtures will have an effect in deciding the applicability of a particular type of asphalt mixture.
Generally, the closer to the surface the material is placed the greater the quality required.