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Martin Laplante

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Thu, 07 Dec 2006

The Environmental Cost of Concrete and Aggregates

The Ontario government has decided to approve last year's joint decision of the Ontario Municipal Board and the Environmental Review Tribunal to allow expansion of the Dufferin Aggregates Milton quarry, located in the Niagara Escarpment and the Greenbelt (map), with strong conditions. This decision had been appealed to the Provincial Cabinet by two environmental groups and three members of the public.

This is the off note in the recent set of Ontario governement initiatives that include stronger rules to protect the greenbelt, the Escarpment, and to put stronger environmental controls on the aggregates industry.

The environmental groups argue that we should use less aggregates. Is building with rocks harder on the environment than using wood or other materials? Ontarians are among the world's biggest users of stone, gravel, and sand, at 15-20 tons per person per year, double the U.S. per capita consumption, and triple Europe's. Half of it is for roads and bridges.

The biggest environmental problem with concrete, a major use of aggregates, is the greenhouse gases emitted in producing cement and other components of concrete. For every ton of cement produced, more than a ton of greenhouse gases are released into the air. Half of it from the energy required to make it and half because the limestone itself releases CO2 into the air during the process. You are taking two sources of trapped CO2 laboriously extracted from the air by creatures millions of years ago, and releasing them again. And because concrete structures are not suited to adaptive re-use, you have disposable buildings with a disposal problem that will have environmental costs of their own in the relatively near future.

Building with wood, on the other hand, is a carbon sink. A natural forest, contrary to popular belief, is not a very good carbon sink. Yes, the trees take carbon out of the air, but eventually it all falls to the ground where natural processes release it all into the air again, some of it as methane which is even worse. But if you put that tree into some 2 by 4s or even fibreboard, the wood runs a fair chance of staying out of the atmosphere for a century or two.

The environmental scorecard of aggregates is considerably more complex than that. For a variety of reasons the quarries are likely to be on environmentally sensitive land, they consume and pollute water, emit fine particulates and sulfur and nitrogen oxides, and are a natural source of radioactivity near us. Their use in road building is certainly excessive. We could definitely do with less of it.



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