ASPHALT BINDERS AND ASPHALT MIXTURES - Materials for Civil and Construction Engineers - page 319

ASPHALT BINDERS AND
ASPHALT MIXTURES
Asphalt is one of the oldest materials used in construction. Asphalt binders
were used in 3000 B . C ., preceding the use of the wheel by 1000 years. Before
the mid-1850s, asphalt came from natural pools found in various locations
throughout the world, such as the Trinidad Lake asphalt, which is still
mined. However, with the discovery and refining of petroleum in Pennsyl-
vania, use of asphalt cement became widespread. By 1907, more asphalt
cement came from refineries than came from natural deposits. Today, practi-
cally all asphalt cement is from refined petroleum.
Bituminous materials are classified as asphalts and tars, as shown in
Figure 9.1. Several asphalt products are used; asphalt is used mostly in
pavement construction, but is also used as sealing and waterproofing agents.
Tars are produced by the destructive distillation of bituminous coal or by
cracking petroleum vapors. In the United States, tar is used primarily for wa-
terproofing membranes, such as roofs. Tar may also be used for pavement
treatments, particularly where fuel spills may dissolve asphalt cement, such
as on parking lots and airport aprons.
The fractional distillation process of crude petroleum is illustrated in
Figure 9.2. Different products are separated at different temperatures.
Figure 9.2 shows the main products, such as gasoline, kerosene, diesel oil,
and asphalt residue (asphalt cement). Since asphalt is a lower-valued prod-
uct than other components of crude oil, refineries are set up to produce the
more valuable fuels at the expense of asphalt production. The quantity and
quality of the asphalt depends on the crude petroleum source and the re-
fining method. Some crude sources, such as the Nigerian oils, produce lit-
tle asphalt, while others, such as many of the Middle Eastern oils, have a
high asphalt content.