ASPHALTopics | Fall 2015 | VOL 28 | NO 3

a pavement contains a higher percentage of VTAE, and
poor performance can be the result of many other factors.
“For years, asphalt plants have used recycled motor oil,
or RFO, for their burners,” Palmer says. “Studies have shown
that the dissolved metals in the burner fuel are captured
in the HMA plant baghouse and then returned to the mix,
as opposed to being evacuated in the plant’s air emissions
system. When those pavements are recycled as RAP, these
metals start to accumulate, particularly if the plant again
uses recycled oil as its burner fuel. There are trace metals
“VTAE is not a waste product;
we produce it purposefully
to meet the needs of asphalt
blenders.”–Al Palmer
in other materials, including RAP, aggregates and virgin
asphalt which also end up in the mix. Thus, it can be seen
that determining the VTAE content of a new binder from
binder that is extracted from a pavement core is difficult
based on a metals analysis alone.”
When used properly and in an appropriate amount,
VTAE reduces viscosity and improves the cold temperature
properties of binders. The extender helps to reduce the
cracking potential of pavement and improves resistance to
aging. Engineered softer binders are necessary for HMA
mixes that contain RAP and RAS and, as the use of these
recycled materials increases, so too will be the need to
design softer base asphalt.
“We recommend that binders contain from two to
eight per cent VTAE, depending on the properties of
the base asphalt,” Palmer says. “Once you get past ten
per cent of VTAE, then the quality of your base asphalt
may be questionable, unless it is being used in conjunction
with RAP or RAS. The asphalt portion that comes out of
shingles, for example, is very hard. You would have to add
more VTAE to compensate for the stiff recycled asphalt.
In this case, the concentration of VTAE in the virgin asphalt
may need to be greater so that the overall blend of asphalt
in the mix meets specifications. Research indicates that
if you blend 90 per cent or more of reasonably graded
asphalt and 10 per cent or less VTAE, there should not be
enough VTAE to affect the blend and make it susceptible
to stresses. Again, this is dependent on the properties
of the base asphalt used. As with any asphalt blend, it
is important to do the necessary lab work to determine
if performance characteristics of the mix are acceptable.” ››
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