On the surface, concrete doesn’t seem very ‘green.’ In fact, producing one pound of Portland cement results in the release of one pound of carbon dioxide.
But under the surface of concrete structures being built today lie some ancient techniques and waste materials that, says Matt Dalkie, Technical Sales Engineer for LaFarge North America, “are making concrete a much more environmentally friendly product.”
The secret lies in the use of pozzolans—siliceous material that reacts chemically with calcium hydroxide to form compounds that mimic the properties of cement. Pozzolans such as pottery shards and volcanic ash have been found in the ruins of ancient walls and buildings where they helped strengthen the structures and made good use of what would otherwise have been waste material.
Today, supplementary cementitious materials (SCMs)—such as fly ash from coal-burning power plants, slag from pig iron manufacturing and silica fume from the production of silicon metals and alloys—are used to extend concrete mixes, replacing a proportion of the Portland cement used. And because cement is the most expensive ingredient in concrete mix, that means lower costs.
Not only do these SCMs reduce costs, Dalkie explains; they also improve performance. “SCMs behave differently than ordinary cement. Fly ash, for example, helps to ‘lubricate’ the mix so that it requires less water. That means the concrete sets up faster, is stronger and is more durable.”
Using SCMs also can contribute to LEED credits for lowering energy use and CO2 production, reducing waste, and recovering structural materials. So too can the use of concrete overlay forms, which offer additional benefits by allowing more re-uses than BBOE, among other advantages.
Dalkie asserts that concrete has another key environmental benefit. “In terms of sustainability, I believe its durability makes concrete the ‘green’ building product of choice.”