Better Roads May 2014 19
HighwayContractor
M
any contractors look to temperature when con-
templating compaction needs. Yet, some off-site
specifi cations also have a signifi cant impact on
the jobsite. These include mix design and aggregate shape.
Dense-graded mixes are produced with continuously
graded aggregate. In other words, there are a variety of sizes
of aggregates in the design. The design formula includes
asphalt cement and fi nes. Typically, the larger aggregates
are surrounded by a matrix of mastic composed of asphalt
cement and fi nes. The asphalt cement may be modifi ed by
materials such as polymer or latex rubber to develop ad-
ditional stiffness.
Because the larger aggregates are surrounded by the
mixture of asphalt cement and fi nes, there is less danger
of damaging aggregates through the use of high-compaction
force. Depending on the layer thickness, medium to high
amplitude is often selected when compacting dense-
graded mixes.
Whether it's dense-graded, open-graded or gap-graded mix or stone-matrix asphalt,
don't forget their impact on compaction.
Size Matters
in Mix Grades and
Aggregate Shapes