Asphalt is everywhere. It is used to pave roadways, parking lots, airport runways, race tracks and anything else that needs a smooth, durable surface.
According to the National Asphalt Pavement Association, the United States has approximately 3,500 production sites which produce more than 350 million metric tons of asphalt per year. Asphalt is used to surface 94 percent of the 2.6 million miles of U.S. roadways.
Most of us drive on it every single day, but where did asphalt come from?
In the Beginning
The history of asphalt as paving material starts more than 2,700 years ago.
Road builder John Metcalf pioneered asphalt paving in England. Source:Wikimedia Commons.
Asphalt is actually a naturally occurring substance found in asphalt lakes and in rock asphalt. Asphalt lakes are tar pits that form when a type of petroleum called bitumen is forced from underground up to the Earth’s surface. These lakes usually are found along fault lines. The bitumen pools at the surface and the lighter elements vaporize, leaving a pool of natural asphalt. Rock that contains asphalt is known as asphalt rock. Asphalt rock is generally found in porous sandstone or limestone.
The first recorded use of asphalt as a road building material was in 615 BCE in Babylon. The Romans used asphalt to seal their baths, reservoirs and aqueducts.
Asphalt did not officially take off until after Englishman John Metcalf developed an efficient and professional road building method. Metcalf, born in 1717, had discovered the importance of good drainage and used a foundation of large stones covered with excavated road material, which were then covered with a layer of gravel,
In the early 1800s, a Scottish man named John McAdam was able to find ways to improve Metcalf’s method. McAdam argued that roads should be raised above the surrounding ground. His roads also were slightly raised in the middle to ensure that rainwater could rapidly drain off of the roadway.
According to engineering publication Interesting Engineering, McAdam’s drainage solution has been called one of the greatest advancements in road building since the Romans.
McAdams said that the native soil under the roadway was strong enough to support the weight of the road and that the massive foundations of rock on rock were unnecessary. McAdam’s method vastly simplified the process and improved the longevity of the infrastructure.
His smaller surface of large rocks was covered with a mixture of gravel and broken stone, which came to be known as “Telford pitching.”
Making its way to the United States
The first true asphalt pavement in the United States was laid in 1870 by Belgian chemist named Edmund J. DeSmedt. He went on to pave Pennsylvania Avenue in Washington D.C. with sheet asphalt from Lake Trinidad. This proved that the quality of asphalt found in the United States was just as good as what was being imported from Europe.
The Cummer Company opened the first central asphalt pavement production facility in the United States in 1870, and by 1907 production of refined asphalt easily outpaced the use of natural asphalt. As the popularity of automobiles grew, there was an outcry for better roads.
Laying asphalt in Toronto Canada in 1902. Source:Wikimedia Commons.
Along with innovations in the manufacturing of asphalt, there were also significant innovations in how asphalt was transported to work sites and in the equipment used to pour and lay asphalt. In the 1920s, in an effort to make asphalt more readily available, innovations in cold feed systems for portable and semi-portable systems were introduced. Cold feed systems accurately measure and mix the materials used to make asphalt. Vibrating screens and pressure injection systems arrived on the scene in the 1930s. The 1930s also saw the incorporation of a tractor unit (instead of horse-drawn equipment) and a vertical tamping bar.
Inspired by military needs during World War II, asphalt technology improved at a fast pace in the middle of the 20th century. This improvement was used post war as families began moving to suburbs and road building boomed. To assist with the boom, Congress passed the State Highway Act of 1956, allotting $51 billion to the states for road construction.
Hot-Mix Asphalt
To keep up with demand, paving equipment needed to be bigger and more efficient. According to the National Asphalt Pavement Association, by the 1960s, automated controls were added to paving equipment and extra-wide finishers could pave two lanes at once.
The wide acceptance of hot mix asphalt also rapidly increased the pace at which asphalt jobs could be completed.
Until the 20th century, asphalt was found in natural sources like lakes and rivers. As demand increased, asphalt refineries produced virtually all paving asphalt.
Mixing equipment supplier Mixer Direct says that today’s asphalt is actually the byproduct of the oil-refining process. When crude oil is heated, the crude is transferred into a distillation container which is then separated into products like gasoline, diesel fuel, kerosene and other petroleum products. One heavy deposit of the distillation process is asphalt.
Hot-mix asphalt, sometimes referred to as HMA, is used for high traffic areas like roadways. Asphalt and aggregate are mixed and heated at a facility to remove moisture and to make sure the material is the best consistency for spreading.
Mobile hot-mix facilities make it possible to move from job site to job site faster. Drum mixing heats and blends the asphalt and then proper amounts are placed into trucks or storage containers.
Asphalt Innovations
The energy crisis of the 1970s led to one of the most significant changes in the history of asphalt. The crisis introduced the use of recycled asphalt. Today, more than 95 million metric tons of asphalt paving material is recycled every year, making it America’s most recycled material.
In 1986, the National Asphalt Pavement Association established the National Center for Asphalt Technology at Auburn University in Alabama. This center was established to drive innovation and quality and to conduct asphalt research. Today, NCAT leads the world in asphalt pavement research.
The asphalt industry continues to innovate today, creating materials that are more durable, improve vehicle gas mileage, reduce noise, create a smoother ride and improve safety on the roads.
Contact us today to learn how we innovate with asphalt every day.
Featured image depicts workers paving road in Missouri with asphalt circa 1910. Source: Wikimedia Commons.