Asphalt ... What is this stuff we drive on everyday?? How did our road system become what it is today?
Called at various times... asphalt pavement, blacktop, tarmac, macadam, plant mix, asphalt concrete, or bituminous concrete. No matter the term used asphalt pavements have played an important role in changing the landscape and the history of the U.S. since the late 19th century.
Asphalt as a paving material dates back to 1815, when Scottish road engineer John McAdam (or MacAdam) developed a road surface consisting of a compacted layer of small stones and sand sprayed with water. The water dissolved the natural salts on the stones and helped cement the materials together. This type of road surface was named water macadam in his honor. Later, coal tar was used as a binding material instead of water, and the new pavement became known as tar macadam, from which we get the shortened term "tarmac" that is sometimes used to describe asphalt pavement.
Until about 1900, almost all asphalt used in the U.S came from the natural sources of Lake Trinidad and Bermudez Lake in Venezuela. Refined petroleum asphalts, used initially as an additive to soften the natural asphalt for handling and placing, made an appearance in the mid-1870s and slowly gained acceptance. By 1907, production of refined asphalt had outstripped the use of natural asphalt.
President Ulysses S. Grant first directed that Pennsylvania Avenue be paved with Trinidad bitumen Asphalt in 1876.
Thirty-one years later, In 1907 asphalt derived from petroleum distillation was used to repave the famed pathway to the Capitol. (Shown in the image)
Meanwhile, as the automobile grew in popularity, local and state governments were besieged by requests for more and better roads.
Modern mixed asphalt pavement, which provides a more durable road surface, was introduced in the 1920s. Unlike macadam, in which the stone and sand aggregates are laid on the road surface before being sprayed with the binding material, the aggregates in mixed asphalt are coated with the binding material before they are laid.
At first, mixed asphalt was simply dumped on the roadway and raked or graded level before being rolled smooth. In 1931 Harry Barber, of Barber-Greene Company, developed the first mechanical asphalt paver in the United States. It traveled on a set of steel rails and included a combination loader and mixer to proportion and blend the components before spreading the asphalt evenly over the road surface. The rails were soon replaced by crawler tracks, and the first production paver came off the Barber-Greene line in 1934. This new machine quickly became popular with road builders because it allowed them to place asphalt more rapidly and with greater uniformity. Hydraulic drives replaced mechanical drives in pavers during the late 1950s to give the operator even smoother control.
It wasn't till World War II, asphalt technology improved at a great pace, spurred in part by the need of military aircraft for ground surfaces that could stand up to heavier loads. After the war ended, and families moved to the suburbs, road building became a huge industry.
In 1956 Congress passed the Interstate Highways Act, allotting $51 billion to the states for road construction.
Contractors needed bigger and better equipment. Innovations since then include vibratory steel-wheel rollers, electronic leveling controls and Extra-wide finishers, capable of paving two lanes at once. These Extra-wide finishers made their debut in 1968.
In 1970s The national energy crisis underscored the need for conservation of natural resources. Since that time, both base and surface courses have incorporated an increasing amount of recycled asphalt in their mixes. Today, Asphalt pavement is America's most recycled material. Over 95 million metric tons of asphalt paving material is recycled each year!
In 1986 NAPA established the National Center for Asphalt Technology (NCAT) at Auburn University, Alabama, providing a centralized, systematic approach to asphalt research. NCAT recently opened a new research center and test track and is now the world's leading institution for asphalt pavement research.
In 2002 The EPA announced that asphalt plants are no longer on its list of industries considered major sources of hazardous air pollutants. Asphalt has been approved by the Environmental Protection Agency and used successfully as a primary liner for both sanitary and hazardous-waste landfills. It is also used to line drinking water reservoirs and fish hatcheries in California and Washington.
Today, almost all asphalt roads are placed using paving machines. When you consider that 94% of the roads in the United States are asphalt, you can understand the value of the asphalt paver. Also, Pavements being built today can be engineered to meet a variety of needs – for less noise, greater durability, enhanced skid resistance, reduced splash and spray in rainy weather, and a smoother ride than ever before. ________________________________________________________________________________________________________
One compelling principle: Pavement smoothness is a significant determinant of vehicle fuel economy. The smoother the pavement, the lower a vehicle’s fuel consumption. Experts say that vehicles consume less fuel when traveling on smoother pavements. This makes sense intuitively, smooth asphalt pavements save fuel – potentially billions of gallons every year. And, lower consumption of fuel conserves natural resources for a healthier environment.
Our country has 2.5 million miles of paved roads. Since Americans drive many miles per year, just a slight change in fuel economy per vehicle would result in dramatic fuel savings conserving our natural resources and benefiting the traveling public.
Asphalt pavement, which has been used extensively throughout the United States and Europe for over a hundred years, is a tried and true road pavement material. But in this day of increased environmental attention, the green benefits of 100 percent recyclable asphalt pavement might be surprising to some. For improved storm water management, clean drinking water, and reduced roadside pollution, asphalt pavements are clean and environmentally beneficial.