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What Does Asphalt Come From? |
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The chances are you’ve walked, driven, bicycled on asphalt pavements, and seen them all your life. But did you know that asphalt was also known and used in ancient times? Asphalt has a waterproofing quality and it was known to the early Babylonians who called it “pitche” and “slime.” It was known much later to the Romans who called it “bitumen.” They lined reservoirs and swimming pools with asphalt to keep them from leaking.
Asphalt is a dark brown to black mineral substance found in the earth in liquid, solid, and partly solid forms. It is also a natural part of most crude oils. Asphalt softens when warmed. It becomes liquid when heated, and then hardens when cooled. Chemically, asphalt is a combination of hydrogen and carbon.
There are two kinds of asphalt—natural asphalt and petroleum asphalt. Natural asphalt comes from deposits found on or near the surface of the earth. |
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Petroleum asphalt is separated from crude oil by modern refining methods.
Natural asphalt was formed in the early ages by oil being forced to the surface through sand beds and rock formations. The purest asphalt was trapped in the rocks where it was protected. It oozed out as almost pure liquid asphalt.
One of the largest known lakes of natural asphalt is on the island of Trinidad in the West Indies. It covers about 40 hectares and is more than 30
meters deep. When the streets of Washington, D.C., were paved in 1876,
most of the asphalt came from this source in Trinidad.
Asphalt cement is the name for modern paving asphalt. Asphalt cement is used in paving to hold sand and stone tightly together, and to prevent water from entering the pavement. It has rubberlike qualities which cause it to bend under extra heavy blow rather than break like a rock. The heavy-duty asphalt pavements are built for airfields where planes may weigh 140,000 kilograms and for roads with trucks of 45,000 kilograms. |
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