Road Science: One More Time
by Tom Kuennen, Contributing Editor
aggregates prone to alkali-silica reactivity (ASR) or is
of Road Building
Recycled materials need
here is no stopping the growth of recycled and
reclaimed materials in pavements.
The use of reclaimed asphalt pavement (RAP),
reclaimed asphalt shingles (RAS), recycled concrete aggregate (RCA), and recycled granulated tire rubber (GTR) in
pavement mixes and structures is growing dramatically as
states accept them more and more in their specs.
But because RAP, RCA, RAS and GTR come from a variety of sources, they must be physio-chemically characterized prior to use in mixes.
remains after years of exposure to the elements and oxida-
16 September 2012 Better Roads
be used as aggregate in fresh asphalt or portland cement
mixes, or is it going to be destined for road base, a much
shingle feed will come from a supplier that certiﬁes the
material meets state specs. The supplier will have sorted,
ground and tested the RAS to make sure it does not contain asbestos, wood scraps or metal and is kept separate
from pre-consumer (manufacturer waste) shingles (more
on this below). Likewise, GTR will come from a supplier
that maintains consistency.
Thus, physio-chemical analysis of beneﬁciated RAP,
RCA, RAS and GTR by in-plant or supplier labs is essential
for their continued usage. Because their source composition varies tremendously, these reclaimed materials must
be chemically characterized and cataloged; then, blended
stockpiles may be managed over time with more or less
material added to maintain consistency.
Use of RAP and RCA as road base or ﬁll is a less-critical
application so a detailed analysis is not essential; here the
research emphasis is on the possibility of leached pollutants ﬁnding their way into ground water, and long-term
Processing Adds Value to RAP
costs the mix producer or contractor additional money,
it adds value to the raw materials as they now are consistently sized.
raw RAP into at least two sizes, typically a coarse fraction
(plus-1/2 or plus-3/8 inch) and a ﬁne fraction (mi-
Reclaimed Asphalt Pavement in Asphalt Mixtures: State-of-the-Practice,
by Audrey Copeland, formerly materials research engineer
technology at the National Asphalt Pavement Association.