POWER October 2016 - 35

COAL
3. Rare earth. The rare earth elements are lanthanum (La), cerium (Ce), praseodymium (Pr),
neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium
(Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu),
scandium (Sc), and yttrium (Y). Source: National Energy Technology Laboratory
As part of the proving process, We Energies
conducted a side-by-side field test to
compare standard asphalt and ASHphalt.
It paved about a mile-long heavy-haul road
near its power plant in Oak Creek, Wisc.,
in 2012 (Figure 4). The paving was done in
control sections both with and without ASHphalt.
Both sections were constructed using
the same crew and equipment. The workers
who performed the work reported that they
didn't notice any differences between the two
mixes. There were no changes in the paving
operation, compaction operation, or the number
of passes for compaction.
In follow-up testing conducted using a
4. Take the high road. This road was constructed using ASHphalt, which is nearly identical
to standard asphalt, except that 10% of the bitumen binder is replaced with fly ash, making
the pavement stronger and more durable. Courtesy: We Energies
falling weight deflectometer, which is a common
way to evaluate asphalt, the ASHphalt
section outperformed the standard asphalt
section. Greater strength readings were observed
in the ASHphalt as early as six months
into the test. The product performed similarly
well during further laboratory testing.
The savings can be substantial for highway
departments. Not only is the ASHphalt
cheaper than standard asphalt, but the improved
performance means road maintenance
costs are also reduced. The fly ash helps the
pavement resist aging and reduces cracking.
" About 93% of the roadways in the U.S.
are paved with asphalt, " said Ramme, " so
it's a big potential market, even though only
a small amount of fly ash is used per ton of
ASHphalt. "
cial viability there. "
When questioned about recovering REEs
from ash, Ramme admitted that We Energies
is interested in the possibilities, but he said he
couldn't discuss the company's progress due
to a confidentiality agreement.
ASHphalt
One product that Ramme was happy to talk
about, however, was a relatively new high-performance
asphalt paving mixture that We Energies
calls ASHphalt. The product is different
from standard asphalt in that fly ash is substituted
for some of the binder that would othOctober
2016 | POWER
erwise be used. The effect is similar to what
is seen when fly ash is added to concrete-
greater strength and improved durability.
The ASHphalt mixture is made just like
any other asphalt mixture at a standard batch
mixing plant for hot-mix asphalt. Aggregate
is first introduced to a large rotating drum
and heated to elevated temperatures to ensure
it is dry. Then the aggregate is mixed with a
bitumen binder (liquid asphalt cement) in a
mixer to uniformly coat all of the aggregate
particles. In the case of ASHphalt, the only
change is that 10% of the binder is replaced
with fly ash.
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Shrinking Supplies
It may seem odd to worry about a decrease in
the production of CCPs-after all, less than
50% of CCPs are beneficially used nationwide-but
the truth is, there are fly ash and
gypsum supply shortages in some areas. As
federal air emissions standards have become
more stringent, many companies have retired
older, less-efficient coal plants, rather than
investing in major air quality control system
retrofits. These plants are rarely replaced by
new coal-fired facilities, which means ash
production has decreased.
At the same time, hydraulic fracturing and
horizontal drilling have increased the supply
of natural gas, causing a significant decrease
in its price. That has made natural gas-fired
generation cheaper in many cases than coalfired
generation, which means gas plants are
often dispatched before coal facilities. This
has also resulted in less ash being produced,
compounding the CCP supply problem.
Seasonal fluctuations in demand also cause
challenges. Fly ash sees strong demand during
the summer, when construction work is in full
swing. However, when demand slows during
winter months, many power plants have no alternative
but to send ash to landfill.
Delivery can present another difficulty.
35

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POWER October 2016

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