Janet Reid, age 11, of Victoria, B.C., Canada, for her question:
How do they manufacture asphalt?
Young students born into the Age of Science are used to man made materials. Newer and still newer synthetic substances do not surprise them. But this was not always so. In the past, all our useful materials were created by nature. Many still are, and one of them is asphalt.
Most of our supplies of tacky asphalt are created in the ground by Mother Nature. As usual, she takes her time and the recipe is slow. The basic ingredients are hydrocarbons, thought to be the remains of long gone, tiny sea dwellers who lived and died millions of years ago. These hydrocarbon chemicals are very varied and very complicated, much more so than the non living chemicals in the rocks and the atmosphere. And since life began, hydrocarbons have been produced by plants and animals on land and in the sea.
The basic ingredients in hydrocarbons are hydrogen and carbon and these atoms are packaged in durable molecules. They endure long after the living things that created them have departed. They are present in fossils and decaying remains. The hydrocarbon ingredients in the asphalt recipe were buried and sealed below ground, eventually becoming oily petroleum, the complex fossil material from which we extract gasoline.
In some cases, petroleum deposits were formed near the surface or earth movements shifted deeper reservoirs closer to ground level. These deposits were no longer sealed from the air and the atmosphere worked changes on their assorted hydrocarbons. Some of the molecules were small and light, lighter than the gaseous molecules of the air. When the petroleum was uncapped, methane and butane, ethane and propane and other light hydrocarbons freed themselves molecule by molecule and went off to mingle with the air.
This left behind the oily, tacky substances present in the petroleum. These heavier materials clogged together in gummy pools and puddles of asphalt. At first they were shiny dark pools and puddles of sticky liquid. In time they dried out and formed surface layers of fairly firm asphalt that can be mined. Some of the world's asphalt deposits are immense and new upwellings of underground petroleum are adding more asphalt for the future. In the meantime, our clever chemists have learned a way to speed up the making of asphalt.
The asphalt we manufacture cannot be called a true man made substance. The basic ingredients are exactly the same as those used to make natural asphalt. The recipe is exactly the same, except that it is performed faster. Natural petroleum is a mixture of many substances and we must refine it to separate them. This is done by heat and each ingredient turns to its gaseous state at its own boiling point. The light ingredients evaporate, leaving gobs of heavy solids. The tacky residue resembles natural asphalt. The road repairmen claim that nature's slow recipe is the best. It produces firmer and more durable paving, material than the kind produced by man's speedy recipe.