User:Paytonmoore17/sandbox

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History
Asphalt or bitumen has had many uses throughout history beyond being used as a material in making roads. The Greeks and Romans used asphalt to seal things like aqua ducts, baths, and reservoirs. Another use in history was using asphalt to waterproof boats. Bitumen is the very sticky black substance that bonds together the aggregate in roads today and sealed these things in the past. Asphalt roads as we know them had their start in Scotland. From The National Pavement Association ”John Loudon McAdam was a trustee of a Scottish turnpike. McAdam observed that it was the “native soil” that supports the weight of traffic, and that “while it is preserved in a dry state, it will carry any weight without sinking.”  To construct his roads, McAdam used broken stone “which shall unite by its own angles as to form a hard surface.” These roads were then covered in tar to make them more durable and less dusty. The first real use of these roads in America began in the 1860s and 1870s where asphalt was used for both roads and sidewalks. From the 1860s until the 1900s natural asphalt was the most commonly used followed by refined asphalt. After the 1900s oil refining was more prominent and yielded more abundant sources of asphalt.

Composition:
There are two forms of asphalt, one being refined and the other natural. Natural asphalt comes from natural deposits of bitumen in from places like the Le Brea Tar pits. This method is no longer used today as refined asphalt comes as a byproduct of refining oil (Pavement Interactive). The material derived from the refining of oil is the same as the naturally found bitumen deposits. It is much more commonly used today because of how much oil is refined for use as gasoline and other products like kerosene. Hot mix asphalt pavement is made from 95% stone, sand or gravel and the rest is the actual asphalt tar material that binds it all together. If larger size stones are used in the mix it gives the road more strength for bearing higher weight loads but can cause the road to be less smooth. For this reason, more than one layer of asphalt pavement is usually used in the construction of a road. The first layer is less smooth and stronger and is followed by a layer using smaller rock for the road surface.

Current Use
Today asphalt is used in roofing as a sealant, but the most common use for it is in asphalt pavement. In America today there are 2.7 million miles of paved roads and highways, and 94% are paved using asphalt (Engineering Overview). Asphalt is cheaper to use than concrete and can. Asphalt is also become more self-sustainable by recycling old asphalt roads that have been milled up. The old road is used as the aggregate material instead of rocks which keeps costs down and is as effective as using rock.

Equipment Usage
In paving asphalt roads there are quite a few pieces of equipment required to make the road come together. To start grading machines are used to level the ground if it is a new construction. If there is a road being replaced a milling machine is used to mill up the old pavement so that the new material can go in its place. After a road is milled a sweeper comes through to clean off any debris that may still be on the road. The sweeper is also used after a layer of pavement has been put down. After that is done the paving machine is used in tandem with a dump truck that is carrying the asphalt and rock mix in the back. These dump trucks are backed into the paver and raise the bed to allow the asphalt mix to fall into the paver. The paver then pushes the dump truck ahead of it while laying the pavement behind it. After this is done a roller is used to smooth out and compact the freshly laid asphalt.