Asphalt Technologies
Asphalt Technologies
Asphalt Technologies
Asphalt is also known as bitumen. It is a sticky, black and highly viscous liquid or semi-solid
form of petroleum. It may be found in natural deposits or may be a refined product; it is a
substance classed as a pitch. The primary use (70%) of asphalt/bitumen is in road construction,
where it is used as the glue or binder mixed with aggregate particles to create asphalt
concrete. Its other main uses are for bituminous waterproofing products, including production
of roofing felt and for sealing flat roofs.
The terms asphalt and bitumen are often used interchangeably to mean both
natural and manufactured forms of the substance.
The naphthene aromatics and polar aromatics are typically the majority
components. Additionally, most natural bitumen contains organosulfur compounds,
resulting in an overall sulfur content of up to 4%. Nickel and vanadium are found in
the <10 ppm level, as is typical of some petroleum.
The substance is soluble in carbon disulfide. It is commonly modelled as a colloid,
with asphaltenes as the dispersed phase and maltenes as the continuous phase and
"it is almost impossible to separate and identify all the different molecules of
asphalt, because the number of molecules with different chemical structure is
extremely large"
Hot mix asphalt concrete (commonly abbreviated as HMAC or HMA) is produced by heating
the asphalt binder to decrease its viscosity, and drying the aggregate to remove moisture from
it prior to mixing. Mixing is generally performed with the aggregate at about 300 °F (roughly
150 °C) for virgin asphalt and 330 °F (166 °C) for polymer modified asphalt, and the asphalt
cement at 200 °F (95 °C). Paving and compaction must be performed while the asphalt is
sufficiently hot. In many countries paving is restricted to summer months because in winter
the
compacted base will cool the asphalt too much before it is able to be packed to the required
density. HMAC is the form of asphalt concrete most commonly used on high
traffic pavements such as those on major highways, racetracks and airfields. It is also used as
an environmental liner for landfills, reservoirs, and fish hatchery ponds.
Superpave, short for "superior performing asphalt pavement," is a pavement system
designed to provide longer lasting roadways. Key components of the system are careful
selection of binders and aggregates, volumetric proportioning of ingredients, and evaluation
of the finished product.
HMAC is most commonly used for high-traffic areas, such as busy highways and airports.
Cold mix asphalt concrete is produced by emulsifying the asphalt in water with
(essentially) soap prior to mixing with the aggregate. While in its emulsified state the asphalt
is less viscous and the mixture is easy to work and compact. The emulsion will break after
enough water evaporates and the cold mix will, ideally, take on the properties of cold HMAC.
Cold mix is commonly used as a patching material and on lesser trafficked service roads.
Cut-back asphalt concrete is produced by dissolving the binder in kerosene or another lighter
fraction of petroleum prior to mixing with the aggregate. While in its dissolved state the
asphalt is less viscous and the mix is easy to work and compact. After the mix is laid down
the lighter fraction evaporates. Because of concerns with pollution from the volatile organic
compounds in the lighter fraction, cut-back asphalt has been largely replaced by asphalt
emulsion.
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Ali Almuajel
IBMK7T