Building with Concrete

Is building with concrete good for the environment? I know it lasts a long time, but concrete is also heavy to transport.

J. Galliano, Philadelphia, PA

Concrete has two components, “cement” and an “aggregate” of round or crushed stone. Concrete is essentially loose stones glued together by cement. (Brick mortar is cement and sand mixed together.)

The cement part of concrete, called “Portland cement” (no relation to the city) is made though an energy-intensive process of baking lime and other minerals at very high temperatures. The resulting cement powder, usually gray in color, hardens (crystalizes) when mixed with water.

By itself, crystalized or cured cement is not particularly strong — sidewalks made with pure cement would easily crack from people walking on them. But the stone aggregate adds a great deal of compressive strength to the finished product.

So building with concrete embodies a great deal of energy, because the cement is energy-intensive to create and shipping the heavy cement and the heavy aggregate uses a lot of fuel. On the other hand, properly mixed and “placed” (installed) concrete is extremely durable — a lot of it has survived since Roman times. Once you’ve made the initial investment in time and materials, building with concrete should easily yield a return on your investment of the seven-generations of service that is usually considered the standard for sustainable construction.

Ideally, we should build with products from our own bioregion — timber in the Pacific Northwest, adobe in the desert. Building with concrete is especially useful in wet climates, where wood tends to rot, or where a lot of durability is needed, such as for sidewalks and steps. So building with concrete is best done where the Portland cement that is made, and the aggregate is quarried close to your building site.


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