Asphalt emulsions consist of intimate mixtures of asphalt, water and an emulsifying agent or surfactant.  The physical and chemical properties of the emulsion depend on the emulsifying agent's chemical type and molecular structure.  When the surfactant is mixed with asphalt and water, its molecules align with those of the asphalt and water forming an emulsion with a negative (anionic) or positive (cationic) surface charge.  The presence of charged oil droplets in emulsions improves the adhesion of asphalt to aggregates compared to what occurs in asphalt concrete.  The surfaces of aggregate particles carry a charge and if this charge is opposite to that of the droplets in the emulsion, a strong bond can take place.

An important objective is to make an emulsion stable enough for pumping, prolonged storage, transportation and mixing.  During mixing with the contaminated soil, the emulsion coalesces and encapsulates the soil particles.  Any hydrocarbons in the soil preferentially adsorb onto the asphalt surface and diffuse into the asphalt.  The result is a blending of contaminant with the asphalt into an integral, stable part of the mixture that is chemically bonded.  Upon curing, the emplaced product should retain the adhesive, durability and water-resistant properties of the asphalt cement from which it was produced. 

Encapco’s organic-based asphalt emulsion is used to immobilize lead in contaminated soil.  Unlike other fixation or stabilization technologies, which physically bind contaminants in the soil matrix, Encapco’s emulsion is capable of chemically fixating lead.  Encapco’s patented process employs a chemical binding reaction in addition to encapsulation to meet regulatory leaching tests.  The Encapco process has been evaluated on a number of contaminated materials ranging from silty sand from a quarry site, contaminated sand from a steel mill and foundry sand with Marshall stability tests and leaching tests.

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