We mentioned in passing the other day that concrete, while a sustainable and renewable building material, does have some drawbacks that make is less than totally "green."
Concrete is composed mainly of sand and aggregate and the mining of these components can be environmentally disruptive. The machinery used to dig up and transport them use energy and cause pollution. Many of the sealers and finishes used for concrete products such as countertops contain petroleum and/or give off volatile gasses. But the primary problem with concrete is in the use of Portland cement. That product makes up about 12 percent of most concrete and is not environmentally friendly, a problem that is just beginning to be addressed by manufacturers in this country.
The first drawback to using concrete can be partially addressed by incorporating waste materials such as glass fragments into the concrete, reducing the amount of sand and aggregate needed. More and more water based sealers are being used in the industry, thus ameliorating the second problem. Portland cement poses a more complicated issue - the production of large amounts of CO2 in its manufacture.
It is estimated that 1.1 to 0.9 tons of CO2 is spread into the atmosphere during the production of 1 ton of Portland cement. By 2010 concrete production throughout the world is expected to contribute 2 billion tons of CO2.
However, the incorporation of fly ash into Portland cement during its manufacture significantly reduces CO2 emissions. Fly ash is produced in large quantities during the burning of coal in coal-powered electric plants. Once the combustible parts of the coal are consumed what remains are extremely small molten particles of silica, alumina, and calcium. This material is known chemically as a pozzolan and when combined with lime it forms a cementitious compound. When used as a component of concrete it provides greater strength, durability, and resistance to chemicals. These benefits, in fact, are actually quite stunning but beyond the scope of our discussion.
Not all fly ash is suitable for use in concrete, it largely depends on the type of furnace used to generate the electricity, but currently about 12 million tons of fly ash consumed by the industry.
This is an environmental no-brainer. The concrete is better, its manufacture is more eco-friendly, and it uses up a waste product which is a major storage and disposal problem for utilities. Check with your concrete contractor and insist that your new countertops or any other concrete project are made with fly ash.