Specialty Emulsions

Emulsion Ingredients

Asphalt

Asphalt cement is the basic ingredient of asphalt emulsion and, in most cases, it makes up from 55 to 70 percent of the emulsion. Tables II-1 and II-2 show the asphalt content specified for various types of emulsions.

Because asphalt cement is such a complex material, only those properties that significantly affect emulsion are discussed. There is not an exact correlation, however, between the properties and the ease with which the asphalt can be emulsified. Although hardness of base asphalt cements may be varied as desired, most emulsions are made with asphalts in the 100-250 penetration range. On occasion, climatic conditions may dictate the a harder or softer base asphalt be used. In any case, compatibility of the emulsifying agent with the asphalt cement is essential for production of a stable emulsion.

Asphalt is a colloid composed of several fractions, the major ones being asphaltenes and maltenes. The colloidal make-up of the asphalt depends on the chemical nature and percentage of these fractions and their relationship to each other.

The asphaltenes are the dispersed phase in the asphalt whereas the maltenes are the continuous phase. The asphaltenes are thought to furnish hardness while the maltenes are believed to provide the adhesive and ductile properties of the asphalt. The maltenes present have an influence on the viscosity, or flow properties, of the asphalt. The complex interaction of the different fractions makes it almost impossible to predict accurately the behavior of an asphalt to be emulsified. For this reason, constant quality control is maintained on emulsion production.

Several analytical methods of asphalt analysis are in use today to separate and evaluate the asphalt fractions. There is no agreement among technologists as to how each fraction affects field performance.

Each emulsion manufacturer has his own formulations and production techniques. They have been developed to achieve optimum results with the asphalt cement and emulsifying chemicals that are used.

Water

The second largest ingredient in an asphalt emulsion is water. Its contribution to the desired properties of the finished product cannot be minimized. Water wets and dissolves; it adheres to other substances; and, it moderates chemical reactions. These are all important factors to the production of a satisfactory emulsion. On the other hand, water may contain minerals or other matter that affect the production of stable asphalt emulsions.

Water found in nature may be unfit because of impurities, either in solution or colloidal suspension. Of particular concern is the presence of positive and negative ions, which can affect the properties of the emulsion.

Water containing impurities should not be used in emulsion production. It may result in an imbalance of the emulsion components that can adversely affect performance or cause premature breaking.

Emulsifying Agents

Properties of an asphalt emulsion depend greatly upon the chemical used as the emulsifier. That chemical is a surface-active agent, commonly called a surfactant, that determines whether the emulsion will be classified as anionic, cationic, or nonionic. The emulsifier keeps the asphalt droplets in stable suspension and controls the breaking time. The surfactant changes the surface tension at the interface, i.e., the area of contact between the asphalt droplets and the water. A great many chemical emulsifiers are available. Each must be appraised for compatibility with the asphalt cement being used.

In the early days of asphalt emulsion productions, such materials as ox-blood, clays, and soaps were used as emulsifying agents. As the demand for emulsion increased, new and more efficient emulsifying agents were found. Several chemical emulsifiers now are commercially available.

The most often used anionic emulsifiers are fatty acids, which are wood-product derivates such as tall oil, rosin, and lignins. Anionic emulsifiers are saponified (turned into soap) by reacting with sodium hydroxide or potassium hydroxide.

Most cationic emulsifiers are fatty amines (diamines, imidazolines, amidoamines, to name three). The amines are converted into soap by reacting with acid, usually hydrochloric. Another type of emulsifying agent, fatty quarternary ammonium salts, is used to produce cationic emulsions. They are water-soluble salts as produced and do not require the addition of acid to make them water-soluble. They are stable, effective cationic (positively charged) emulsifiers.

Each manufacturer has his own procedure for using his agent in asphalt emulsion production. In most cases, the agent is combined with the water before introduction into the colloid mill. In other cases, however, it may be combined with the asphalt cement just before it goes into the colloid mill.