Asphalt in Road Construction

By: Bob Jent

Though a vast majority of today's roads are constructed using asphalt, its use has been traced back hundreds and even thousands of years. This naturally occurring substance is sought after for a number of applications due to its adhesive and waterproofing properties. Though the substance is so common today that it is not usually given a thought, asphalt is all around us in the form of roads, airport runways, roofs, tennis courts, parking lots, batteries, adhesives and more. Over ninety percent of the roads in the United States are constructed using this valuable, binding substance, but how did this come to be?

Asphalt is a dark brown or black substance composed primarily of bitumen. Bitumen is a broad term referring to a natural or manufactured viscous substance comprised of a mixture of hydrocarbons. Asphalt, also referred to as Hot Mix Asphalt, blacktop, asphalt concrete, tarmac, bituminous concrete or macadam, can be naturally occurring but today is more commonly produced as a byproduct of the refining process in the petroleum industry. Seepage at the surface of the earth in certain areas gave people throughout history access to bitumen many years before contemporary methods made extracting crude oil from within the earth possible. Around the year 1595, Sir Walter Raleigh discovered a naturally occurring lake of asphalt on the Island of Trinidad, and quickly found use for the substance in caulking his ship.

Years after Raleigh's discovery, President Ulysses S. Grant had Pennsylvania Avenue paved using asphalt from the bitumen lake in Trinidad. For several years, Lake Trinidad as well as Venezuela's Bermudez Lake produced almost all of the asphalt imported and used in the United States. By the early 1900s, asphalt production as a byproduct of petroleum refining had become the primary source of the substance. Oil companies developed the ability to produce asphalt superior to that imported from the naturally occurring lakes. Today, crude oil is refined through the process of fractional distillation, which yields bitumen separated from other petroleum components such as gasoline, kerosene, petroleum gas and other products.

In the United States, an increasing need for quality roadways aligned with the proliferation of the thousands of automobiles produced after World War I. Additionally, World War II brought about a need to improve upon runway technology as planes became heavier and more abundant. Continually improving road building technology has led to the over two million miles of bituminous roadways that are central to the lifestyles of Americans today.

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