When you consider that residential structures contribute 21% of all the CO2 produced in the U.S. and commercial structures add another 18%, it stands to reason the construction industry and its products play a critical role in sustainability. If they can be designed and constructed to reduce energy consumption and greenhouse gas emissions, building concrete homes can have such a large impact, in addition to offering many advantages over wood-frame and steel counterparts. Energy savings is a well-documented aspect of concrete homes, but there are other ways the structures contribute to sustainability.
Concrete and cement have been misunderstood in the green movement and the concrete industry has done a poor job of explaining the benefits of its products. As a fragmented industry, the resources, primarily financial, to sway public opinion and educate those who develop rules for LEED conformance and other standards are not available. Hopefully, this will change with the Joint Sustainability Initiative (JSI)—a cooperative effort of the cement-based trade associations. But what are some of the benefits of concrete construction?
Cement manufacturing. Concrete is the most widely used material in the world. Nearly twice as much concrete is used annually than steel, aluminum, wood, and plastic combined. Portland cement produces less equivalent CO2 greenhouse gas (including methane) than either forest products or steel. Concrete accounts for less than 1.5% of U.S. CO2 production.
Although cement itself is high in embodied energy, the U.S. cement industry has improved production efficiency and in turn its carbon footprint. This has occurred through the use of industrial byproducts for alternative fuel and raw material substitution for portland cement. In 2008 more than 58 million tires were consumed in the cement kiln firing process, diverting them from landfills.
Industrial byproduct use. Many modern concrete mix designs use cement substitutes that are industrial byproducts from other manufacturing processes. These include fly ash from the power generating industry and slag from steel manufacturing. More than 19 million tons of fly ash and other coal combustion byproducts were used in 2007, and more than 3.4 million tons of slag from steel and iron industries were consumed.
Concrete uses local materials. Concrete is manufactured from local materials. Sand, gravel, and water—which comprise 75% of concrete—are available locally with minimal impact on the environment for both extraction and transportation. There is a ready-mix concrete plant in almost every community in the country.
Less waste. Because concrete is mixed specifically for each project and comes in relatively small batches, there is little waste at the jobsite. Many enterprising contractors have molds onsite to precast splash blocks or other elements that can be used, eliminating nearly all concrete waste.
Longevity/reuse. Concrete structures will be usable, and reusable, long after wood structures. Concrete buildings constructed more than 2000 years ago are still performing their original functions today. The longer a structure is viable, the less negative impact it has on the environment.
Recyclability. What becomes of a structure when it outlives its useful existence? If it is made of concrete, it is recyclable. More than 140 million tons of concrete are recycled annually, including into concrete highways. Machinery for separating reinforcing steel from concrete and grinding the concrete into base material and aggregate is common and available.
Concrete is a green material—it always has been and it's getting better. With these, and many other advantages, it's time that concrete is seen as a significant and permanent option when considering a building system. It's now up to the industry to educate the public and the design community that a sustainable solution is at their fingertips.