Modern uses
Asphalt concrete
The largest use of asphalt/bitumen is for making asphalt
concrete for road surfaces and accounts for approximately 85% of the asphalt
consumed in the United States. Asphalt concrete pavement material is commonly
composed of 5% asphalt/bitumen cement and 95% aggregates (stone, sand, and
gravel). Due to its highly viscous nature, asphalt/bitumen cement must be
heated so it can be mixed with the aggregates at the asphalt mixing plant.
There are about 4,000 asphalt concrete mixing plants in the U.S., and a similar
number in Europe.
Asphalt concrete road surface is the most widely recycled
material in the U.S., both by gross tonnage and by percentage. According to an
industry survey conducted by the Federal Highway Administration and the
National Asphalt Pavement Association and released in 2011, more than 99% of
the asphalt removed each year from road surfaces during widening and
resurfacing projects is reused as part of new pavements, roadbeds, shoulders
and embankments.
Roofing shingles account for most of the remaining
asphalt/bitumen consumption. Other uses include cattle sprays, fence-post
treatments, and waterproofing for fabrics.
Asphalt concrete paving is widely used in airports around
the world. Due to the sturdiness and ability to be repaired quickly, it is
widely used for runways dedicated to aircraft landing and taking off.
Mastic asphalt
Mastic asphalt is a type of petroleum products (asphalt)
which differs from dense graded asphalt (asphalt concrete) in that it has a
higher asphalt/bitumen (binder) content, usually around 7–10% of the whole
aggregate mix, as opposed to rolled asphalt concrete, which has only around 5%
added asphalt/bitumen. This thermoplastic substance is widely used in the
building industry for waterproofing flat roofs and tanking underground. Mastic
asphalt is heated to a temperature of 210 °C (410 °F) and is spread in layers
to form an impervious barrier about 20 millimeters (0.8 in) thick.
Asphalt emulsion
A number of technologies allow asphalt/bitumen to be mixed
at much lower temperatures. These involve mixing with petroleum solvents to
form "cutbacks" with reduced melting point, or mixtures with water to
turn the asphalt/bitumen into an emulsion. Asphalt emulsions contain up to 70%
asphalt/bitumen and typically less than 1.5% chemical additives. There are two
main types of emulsions with different affinity for aggregates, cationic and
anionic. Asphalt emulsions are used in a wide variety of applications. Chipseal
involves spraying the road surface with asphalt emulsion followed by a layer of
crushed rock, gravel or crushed slag. Slurry seal involves the creation of a
mixture of asphalt emulsion and fine crushed aggregate that is spread on the
surface of a road. Cold-mixed asphalt can also be made from asphalt emulsion to
create pavements similar to hot-mixed asphalt, several inches in depth and
asphalt emulsions are also blended into recycled hot-mix asphalt to create
low-cost pavements.
Other uses
Asphalt/bitumen is used to make Japan black, a lacquer known
especially for its use on iron and steel. Asphalt/bitumen also is used in paint
and marker inks by some graffiti supply companies to
increase the weather resistance and permanence of the paint and/or ink, and to
make the color much darker. Asphalt/bitumen is also used to seal some alkaline
batteries during the manufacturing process.
It seems like a contradiction, but the flexibility of asphalt is what makes it more durable. Having bitumen mixed with the aggregate gives it a measure of plasticity. Other forms of pavement are stronger, but that can make them crack instead of bending. dawcon.com
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