Asphalt Pavement Magazine - May/June 2018 - 33

E

however, this mandate was later
repealed and interest in using
rubber in asphalt mixtures subsided
in many states. While some states
ignored the use of rubber, other
states such as California, Arizona,
and Florida began developing rubber
programs and specifications for its
inclusion in asphalt mixtures.
In 2008, a polymer shortage
caused the price of polymermodified asphalt binders to rise
and left many agencies wanting
another tool to use in place of
polymer or as an extender to use
with lesser quantities of polymer.
The solution that many agencies
turned to was RTR. In August of
2010, the Alabama Department of
Transportation (ALDOT) placed its
first RTR-modified asphalt mixture
in over a decade outside of Dothan,
Ala., on US-231 South. Blacklidge
Emulsions terminally blended
the RTR-modified binder, which
contained approximately 11 percent
RTR and a crosslinking agent before
it was delivered to APAC Midsouth
in Dothan. This produced a binder
that would pass the PG 76-22
requirement for the DOT.

While laboratory
testing can be used to
evaluate and predict
mixture performance
in the field, the ultimate
proof of a technology's
appropriateness is field
performance.
An experiment developed by
the National Center for Asphalt
Technology (NCAT) and ALDOT
would compare the performance of
the RTR-modified asphalt mixture to
that of a polymer-modified asphalt
mixture in both the laboratory and
the field. Both 19.0 mm maximum
aggregate size mixtures contained
the similar aggregate structures
of granite, limestone, screenings,
shot gravel, sand and 20 percent
RAP. Due to the differences in the
RTR and SBS modified binders, the
asphalt contents of the mixtures and
continued on page 35

© PHOTO COURTESY TOMMY JAMES AND DAVID FARRIS

ach year the United States
generates approximately
290 million scrap tires.
Of these 290 million
tires, approximately
80.4 percent are recycled or
reused in fuel, agricultural or
civil engineering markets, leaving
27 million tires to be placed in
landfills or stockpiles. Currently,
about 12 million scrap tires each
year are being converted into
recycled tire rubber (RTR) for
modifying asphalt binders.
The utilization of scrap tire
rubber in asphalt started in the mid1960s, when ground rubber was
placed in asphalt surface treatments
such as chip seals. Later in the
1970s, RTR-modified asphalt chip
seals were used as a stress absorbing
membrane interlayer. Its use
extended to asphalt mixtures and
has continued to evolve due to the
rubber's enhancement of mixture
performance, including improved
rutting and cracking resistance.
In the early 1990s, the use of
rubber was mandated for agencies,
and contractors were required to use
rubber in their asphalt mixtures;

The rubber-modified mixture had equivalent or better performance than the polymer-modified mixture.
Asphalt Pavement Magazine - May/June 2018 * 33



Asphalt Pavement Magazine - May/June 2018

Table of Contents for the Digital Edition of Asphalt Pavement Magazine - May/June 2018

Chairman’s Commentary
Industry News
Tools for the Trade
A Green Answer for Higher Recycling
Reducing Rolling Resistance to Reduce Emissions
Recycled Tire Rubber Mixture Yields High-Performing Road
The Pavement Economics Committee: A Powerful Partnership
Focus on the Field: Job Spotlight
Industry Events
Index of Advertisers/Advertisers.com
Perspectives
Asphalt Pavement Magazine - May/June 2018 - intro
Asphalt Pavement Magazine - May/June 2018 - cover1
Asphalt Pavement Magazine - May/June 2018 - cover2
Asphalt Pavement Magazine - May/June 2018 - 3
Asphalt Pavement Magazine - May/June 2018 - 4
Asphalt Pavement Magazine - May/June 2018 - 5
Asphalt Pavement Magazine - May/June 2018 - 6
Asphalt Pavement Magazine - May/June 2018 - 7
Asphalt Pavement Magazine - May/June 2018 - 8
Asphalt Pavement Magazine - May/June 2018 - Chairman’s Commentary
Asphalt Pavement Magazine - May/June 2018 - 10
Asphalt Pavement Magazine - May/June 2018 - Industry News
Asphalt Pavement Magazine - May/June 2018 - 12
Asphalt Pavement Magazine - May/June 2018 - 13
Asphalt Pavement Magazine - May/June 2018 - 14
Asphalt Pavement Magazine - May/June 2018 - 15
Asphalt Pavement Magazine - May/June 2018 - 16
Asphalt Pavement Magazine - May/June 2018 - 17
Asphalt Pavement Magazine - May/June 2018 - Tools for the Trade
Asphalt Pavement Magazine - May/June 2018 - 19
Asphalt Pavement Magazine - May/June 2018 - 20
Asphalt Pavement Magazine - May/June 2018 - 21
Asphalt Pavement Magazine - May/June 2018 - A Green Answer for Higher Recycling
Asphalt Pavement Magazine - May/June 2018 - 23
Asphalt Pavement Magazine - May/June 2018 - 24
Asphalt Pavement Magazine - May/June 2018 - 25
Asphalt Pavement Magazine - May/June 2018 - 26
Asphalt Pavement Magazine - May/June 2018 - 27
Asphalt Pavement Magazine - May/June 2018 - Reducing Rolling Resistance to Reduce Emissions
Asphalt Pavement Magazine - May/June 2018 - 29
Asphalt Pavement Magazine - May/June 2018 - 30
Asphalt Pavement Magazine - May/June 2018 - 31
Asphalt Pavement Magazine - May/June 2018 - Recycled Tire Rubber Mixture Yields High-Performing Road
Asphalt Pavement Magazine - May/June 2018 - 33
Asphalt Pavement Magazine - May/June 2018 - 34
Asphalt Pavement Magazine - May/June 2018 - 35
Asphalt Pavement Magazine - May/June 2018 - 36
Asphalt Pavement Magazine - May/June 2018 - 37
Asphalt Pavement Magazine - May/June 2018 - 38
Asphalt Pavement Magazine - May/June 2018 - 39
Asphalt Pavement Magazine - May/June 2018 - The Pavement Economics Committee: A Powerful Partnership
Asphalt Pavement Magazine - May/June 2018 - 41
Asphalt Pavement Magazine - May/June 2018 - 42
Asphalt Pavement Magazine - May/June 2018 - 43
Asphalt Pavement Magazine - May/June 2018 - 44
Asphalt Pavement Magazine - May/June 2018 - 45
Asphalt Pavement Magazine - May/June 2018 - 46
Asphalt Pavement Magazine - May/June 2018 - 47
Asphalt Pavement Magazine - May/June 2018 - Focus on the Field: Job Spotlight
Asphalt Pavement Magazine - May/June 2018 - 49
Asphalt Pavement Magazine - May/June 2018 - 50
Asphalt Pavement Magazine - May/June 2018 - 51
Asphalt Pavement Magazine - May/June 2018 - Industry Events
Asphalt Pavement Magazine - May/June 2018 - 53
Asphalt Pavement Magazine - May/June 2018 - 54
Asphalt Pavement Magazine - May/June 2018 - Index of Advertisers/Advertisers.com
Asphalt Pavement Magazine - May/June 2018 - 56
Asphalt Pavement Magazine - May/June 2018 - 57
Asphalt Pavement Magazine - May/June 2018 - Perspectives
Asphalt Pavement Magazine - May/June 2018 - cover3
Asphalt Pavement Magazine - May/June 2018 - cover4
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