Specialty Emulsions

History

The use of asphalt emulsions for road construction and maintenance is not new. Emulsions were first developed in the early 1900s. It was not until the 1920s, however, that emulsions, as we know them today, came into being. Their early use was confined largely to spray applications and use as a dust palliative. The growth in the use of asphalt emulsions was relatively slow. It was limited by the types available and a lack of knowledge as to how they should be used. Continuing development of new types and grades, coupled with improved construction equipment and practices, now gives a broad range of choices, with which virtually any roadway requirement can be met. Judicious selection and use can yield significant economic benefits.

Use records reveal a slow but steady increase in the amount of emulsions used between 1930 and the mid 1950s. Following World War II, traffic loads and volumes increased so much that roadway designers began to curtail the use of these materials. Instead, they specified high-type hot plant mixes requiring the use of asphalt cement. While the volume of asphalt cement used has shown a rapid increase since 1953, the combined use of other asphalt products has remained almost constant. But one interesting trend is worthy of note-there has been a steady rise in the volume of asphalt emulsions used.

The major uses of asphalt emulsion in the United States are:

• Surface treatments
• Patching and thin overlays
• Stabilization
• Slurry sealing

Asphalt emulsions also are used in base, surface course mixes and in recycling. In the past several factors contributed to a nationwide interest in the use of asphalt emulsions, namely:

• The energy crisis of the early 1970s that prompted conservation measures by the Federal Energy Administration. Asphalt emulsion does not require a petroleum solvent to make it liquid. (However, some medium-setting grades contain limited amounts of solvent to enhance mixing qualities.) Also, asphalt emulsion can be used (in most cases) without additional heat. Both of these contribute to energy savings.
• Reduced atmospheric pollution. There are little or no hydrocarbon emissions from asphalt emulsions .
• The ability of certain types of asphalt emulsion to coat damp aggregate surfaces, which is another energy saving feature.
• Availability of a variety of emulsion types, coupled with improved laboratory procedures, to satisfy design and construction requirements.
• Potential cost savings by the use of less fuel.

Two major environmental factors-energy conservation and atmospheric pollution-caused grave concern and a realization that some type of Federal action was needed. Our nation suddenly became aware that energy needs soon could exceed supply unless conservation laws were enactly promptly. In one of the early actions, the Federal Highway Administration (FHWA) issued notices that directed attention to fuel savings that could be realized by using asphalt emulsions instead cutback asphalts. It estimated that a huge amount of petroleum solvents could be saved annually by such substitution. While the substitution was not mandatory, it was strongly suggested that it be considered. Since that time, all states are substituting, or allowing the substitution of asphalt emulsions for cutback asphalts.

Looking Ahead

The demand for a well maintained, efficient highway network continues and consequently asphalt is essential to meet these requirements.

The Federal Highway Administration annual survey shows that the United States has about 6.3 million kilometres (3.9 million miles) in the roadway network. The survey also shows that of the 3.2 million kilometres (2.0 million miles) of paved highways, about 93 percent have asphalt paved surfaces. A 1983 FHWA survey of the nation's major road system, about 1.9 million kilometres (1.2 million miles), estimated that over 161,000 kilometres (100,000 miles) were in poor condition and needed immediate repair while another 97,000 kilometres (60,000 miles) were only in fair condition.

Other significant findings contained in the report included:

• The cost of maintaining these roads, even at the current level of performance, will exceed $300 billion over the next 15 years and this does not include money that will be required on the 4.3 million kilometres (2.7 million miles) of local roads.
• Between 1983 and the year 2000, approximately 66,000 kilometres (41,000 miles) of Interstate, 538,000 kilometres (334,000 miles) of arterials and 1,024,000 kilometres (636,000 miles) of collector roads will require capital improvements to maintain serviceability.
• Total travel between 1984 and the year 2000 is expected to grow at an annual rate of 2.0 to 2.7 percent. Thus, by the end of the century, America's highways must accommodate 40 to 60 percent more travel than in 1984.

Thus, the demands for a well maintained roadway will be high, and the demand for asphalt will continue. Because of these of these tremendous needs, every attempt should be made to utilize road materials in an efficient, conservative manner.