Asphalt
Often, asphalt is used as an abbreviation for asphalt concrete.
The History Says
In the ancient middle-east, natural asphalt deposits were used for
mortar between the bricks and stones, ship caulk, and waterproofing.
In Persian, asphalt is known as "mumiya." Some say that this
may be the source for the English word "mummy."
The Present Scenario
Asphalt is hard to transport. It hardens unless kept very hot. For
this reason, it is sometimes mixed with diesel oil or kerosene before
shipping. At delivery point, these lighter materials are separated.
This mixture is often called as bitumen feedstock, or BFS.
ASPHALT,
also known as Asphaltum, is the most common variety of bitumen (also
called mineral pitch). It is a compact, glassy, brittle, black or
brown mineral. It is highly viscous liquid or semi-solid which is
present in most crude petroleums and in some of the natural deposits.
It breaks with a polished fracture, melts very easily giving a strong
pitchy odor when heated, and leaves no ashes when pure asphalt is
burnt.
Asphalt is sometimes confused with tar, coal tar, or pitch because
the appearance is similar and the substances may be used
interchangeably in many industrial processes. Tar and pitch are
obtained from the coal products that are chemically and physically
different.
Some other names of asphalt are road tar, road binder, petroleum
pitch, petroleum asphalt, mineral pitch, and seal-coating material.
Types of Asphalt
There are two main types of asphalt. They are as follows:
-
Straight-run asphalt or asphalt cement - These are used for paving
roads, airport runways, and packing lots. Since its nature is solid
to semi-solid, it must first be cut with a solvent in order to bring
it to a more liquid state. This process is known as Cut Back
Asphalt. Highway workers mostly use straight run asphalt.
- Air-blown
or oxidized asphalt - It has a high softening point and is primarily
used in roofing, pipe covering, and in other similar situations.
Specifications
Asphalt is separated from other components in crude oil like naptha,
gasoline and diesel by the process called fractional distillation,
generally under vacuum conditions. A better separation is achieved by
further processing of the heavier fractions of the oil in
de-asphalting unit. Either propane or butane is used in a
supercritical phase to dissolve the lighter molecules and then
separate it. Any further processing is possible only by "blowing"
the product, namely reacting it with oxygen. This process make the
product more hard and more viscous.
Uses of Asphalt
Asphalt is used for road paving, roofing tar, roofing felt,
roll-roofing, shingles, pipe covering, waterproofing, floor tile, and
many other products and processes.
Occurrences of Asphalt
The natural deposits of asphalt include the Lake Asphalts, Gilsonite,
the Dead Sea in Israel, and Tar Sands. The Lake Asphalts was primarily
from the Pitch Lake in Trinidad and Tobago and Bermudez Lake in
Venezuela.
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