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The
following is a list of some commonly used terms in the HMA industry.
Asphalt Binder
This is the black, sticky stuff produced by petroleum refineries. It is the
"glue" that holds the pavement together. Generally, it makes up about
less than 8 percent, by weight, of the total pavement mixture.
Aggregates
These make up the remaining 92 percent, by weight, of the pavement mixture. They are
usually various sized stones, dust, and sand. They are "any hard, inert
mineral materials used for mixing in graduated fragments." (That's
engineering talk for crushed stone, gravel, sand, etc.)
Hot Mix Asphalt (HMA)
This is the final product produced at an HMA facility which is a mixture of
asphalt cement and aggregates, up to the maximum proportions listed above.
HMA Pavement
This is the final form and use Hot Mix Asphalt generally takes. Briefly, what happens in an HMA facility is that paving
aggregates are dried and heated, then mixed and coated with asphalt cement. As HMA, it is
transferred to holding bins (called silos) for short-term storage, then to
trucks for transportation to the paving site. It is a mixing or combining process rather than
a manufacturing process.
Material Transfer
Device (MTV)
A device which transfers mix from the truck to the laydown machine or paver.
Proper use of a material transfer device can result in a smoother pavement and
less segregation with increased production.
Recylced Asphalt
Pavement (RAP)
RAP is old HMA pavements which have been milled or planed. A portion
of the RAP material can then be added to a new mix to reduce the overall mix
cost.
Rubblization
Rubblization is the process of breaking an existing concrete pavement into very
small pieces or fragments (approximately 8 to 10 inches top size) prior to
overlaying with HMA. This is the Alabama Department of Transportation's
method of choice for
rehabilitating its remaining distressed concrete pavements. To date, there
have been approximately 170 miles of concrete interstate rubblized in Alabama.
Stone Matrix
Asphalt (SMA)
SMA is a mix with a high percentage of coarse aggregate, high filler content, a
high asphalt cement content, a stabilizing additive, and generally a polymer
modified asphalt cement. First developed in Europe, it has been used in
the U.S. since 1991 with great performance. SMA is a very rut and crack
resistant mix and is widely referred to as the premium hot mix asphalt mix.
Superpave (Superior
Performing Asphalt Pavements)
Superpave is the product of the Strategic Highway Research Program (SHRP).
Superpave is not just a new mix type, but rather a new mix design system
utilizing the gyratory compactor and a new method of specifying aggregate
and asphalt binder. The fine-graded Superpave mixes resemble the old 416
mixes used by the Alabama DOT.
Open Graded
Friction Course (OGFC)
OGFC is very similar to SMA, with the exception of having a low filler content
and being slightly coarser. OGFC is used as the wearing or surface layer and allows for surface water to
be removed very quickly from the roadway surface, resulting in improved
safety. SMA used in conjunction with OGFC is becoming the mix combination
of choice for Alabama's interstate highways with great success.
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