journal - TSP2

can have very cool temperatures, even
in the summer, and they are limited
as to what they can use for their
pavements by the conditions. They
feel that warm mix will give them the
opportunity to use rubber mixes and
open-graded mixes along the coast.”
They feel that way with good
reason: the average nighttime low
along the Mendocino coast in June is
48 deg F, and in July, when this work
was undertaken, is 49 deg F, according
to U.S. Climate Data. The weather
often is drizzly and rainy, even
in summer.
“The plant is a long ways away, and
it’s such a long haul to get here,” said
Dave Chang, pavement coordinator
for Caltrans District 1. “But when the
mix gets here, it still can be rolled
and worked at 240 to 250 deg F, while
conventional mix has to be at least
280 deg.”
In addition to the 53-mile, 2- to
3-hour-long haul, there are many
variables that can pull the mix
Evotherm DAT warm mix additive from MWV
Asphalt Innovations maintains workability
of asphalt mix despite 2 1/2 hour haul from
plant, and chilly ambient temperatures along
California coast
temperature down, Chang said.
“When you dump it in the shuttle
buggy — which is a requirement for
our thin blanket overlays — it heats
up that big chunk of iron, and that
sucks some of the heat out of it. The
paver will pull more heat out of it, as
will the existing pavement surface.
And the coast is cooler, but WMA
allows us to put the mix down at
cooler temperatures, as last night
we got down to 45 deg F and with
conventional asphalt we don’t like to
place it below 60 deg F.”
In addition to its functional
attributes, Caltrans looks at WMA in
terms of ‘green’ technology, as not as
much energy is required to make the
mix, Chang said, adding rubberized
mix also is a green technology. “It
utilizes tires that would have gone
into a landfill,” Chang said. “But there
are functional reasons to use rubber.
Rubber ‘gives’, and as a result should
last longer than a conventional opengraded
mix. In our district we have
severe winters, and an OGFC might
last five years along the coast. But we
are hoping to get at least seven years
out of this thin blanket overlay, which
is an inch and a quarter deep.”
GAP-GRADED MIX
The RHMA-G was gap-graded, but
not open-graded, and was produced by
prime contractor Granite Construction
Inc., at its Ukiah North plant. Evotherm
DAT warm mix additive and metering
equipment was supplied by Telfer Oil
Co., Martinez, Calif.
424523_Martin.indd 18 View past 1 issues of the Pavement Preservation Journal online at www.naylornetwork.com/fpp-nxt
4/8/09 8:46:10 PM