| EcoSmart concrete:
historical use
Although
it wasn't called "EcoSmart" in past centuries, concrete made with
high volumes of ash and other pozzolans has been used in construction
for almost 1,000 years.
The Roman Empire
The Romans
knew that certain volcanic materials (now called pozzolans) when
finely ground and mixed with lime and sand, yielded a mortar that
was not only cementitious, but water resistant and very strong.
Both the Pantheon temple and the Roman Coliseum were built with
high volumes of volcanic ash in the cement mixture.
The
Pantheon, built in Rome in 128 A.D., is a circular concrete temple
with walls 6.1 metres thick and a dome measuring 43.3 metres in
diameter. The building still stands in its original form due to
the excellent quality of the mortar mixture and careful selection
of aggregate material. In the event of an earthquake, the building
distorts rather than collapsing and moves with the shifts of the
earth instead of cracking.
Ancient
concrete mixtures were characterized by low cementitious material
content, low water content, a very slow rate of development and
little shrinking or cracking from drying. Today's ashes from coal-fired
power plants have similar properties to the volcanic ash used by
the Romans.
Early
use in the U.S.
The first
major documented use of high-volume fly ash concrete in the U.S.
was by the Bureau of Reclamation to repair a tunnel spillway at
the Hoover Dam in 1942. The second was the Hungry Horse Dam, near
Glacier National Park in Montana. Constructed between 1948-52, this
massive structure required 2,453,600 square metres of concrete.
Approximately 35% of the portland cement was replaced by coal fly
ash. At the time of its completion, Hungry Horse was the third largest
and second highest concrete dam in the world, and it remains one
of the most impressive concrete structures in the U.S.
1980s
- 1990s
In 1983,
the U.S. Environmental Protection Agency issued "Cement
and Concrete Containing Fly Ash: Guidelines for Federal Procurement,"
which encouraged increased use of concrete containing coal fly ash
in federally-funded projects. The Washington, D.C. area Metro subway
system, built during the 1980s, used more than 200,000 cubic yards
of concrete containing coal fly ash. The massive 85,000-seat stadium
built in 1996 for the Summer Olympics in Atlanta is another example
of high-volume fly ash construction.
EcoSmart
History in Greater Vancouver, BC
Fly ash
was introduced commercially in the Lower Mainland during the 1970s
and was typically used to replace about 10% of the portland cement
in a concrete mix. There was some initial resistance in the construction
industry, but by the early 1980s the benefits were better understood.
Typical volumes of fly ash increased to 15-20%. Larger percentages
were used occasionally, mainly for mass concrete - first 30% and
then up to 40% fly ash. In the 1990s, 20% fly ash replacement became
common for structural concrete, and up to 40% for mass concrete.
In the 2000s, more and more engineers are looking to use 40-60%
fly ash in structural concrete.
To review some examples of high-volume fly ash
usage in Greater Vancouver, browse the case studies in our Knowledge
Base. The EcoSmart concrete Project, a government-industry partnership
founded in March 2000, is working hard to encourage awareness and
understanding of EcoSmart concrete.
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