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 (Vancouver) 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.