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Asphalt & Transportation
You know transportation is all about things that go — but what do they go on? Cars, trucks, trains and airplanes — they all depend on asphalt! Asphalt has been a big player in the story of transportation, from the earliest recorded history. The Babylonians were the first to use asphalt to build roads in 625 B.C. under King Naboppolassar. You don't hear his name much anymore, but asphalt is everywhere, helping you get where you need to go.
Who were Telford and McAdam?
In the early 1800s, Scotsmen Thomas Telford and John Loudon McAdam both had the bright idea of building roads with broken stones, or aggregates. Later, road builders discovered hot tar made a perfect glue to hold the stones together. Asphalt pavement is born.
The new pavement arrived in America in 1870, and inventors kept coming up with new mixes for asphalt that were smoother, stronger and longer lasting. In 1908 Henry Ford started selling the "horseless carriage" and changed the way Americans traveled. The more people drove automobiles, the more asphalt roads were needed. In 1956 Congress passed the State Highway Act, giving states $51 billion for road construction. Today asphalt is the top choice for roads in America. In fact, 94 percent of our roads are paved with asphalt.
Asphalt's impact on history
What's so great about asphalt? It can stand up to lots of traffic, bad weather and heavy loads. It lasts for years and years. It's economical, saving money for builders, the government and taxpayers (like your parents). And all that makes it good for more than roads. During World War II, military aircraft needed landing surfaces that could withstand heavier planes — and asphalt was the answer. Since then, airports have counted on the strength and endurance of asphalt pavement for runways and hangars. You'll find asphalt is part of the infrastructure for towns and cities around the country — from racetracks to parking lots, from driveways to railbeds for railroad trains and subways.
Most of America's roads are constructed from a material called hot mix asphalt. Hot mix asphalt paving material is composed of about 5 percent asphalt cement (the dark, sticky stuff that acts as a glue) and 95 percent aggregates (a mixture of various types of stone, sand, and gravel). These ingredients are heated until the aggregates are dry and the asphalt cement turns into a liquid, then mixed together in a giant metal drum. The hot paving material is loaded onto trucks and taken to the paving site.
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