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Concrete changes in sustainability

May, 16 2007


Sustainability has become something of a catchword in the construction industry. Things that were once done without a second thought are not done now until someone asks: Is this sustainable? That concern has led to renewed interest in pervious concrete pavements. A recent article in the Portland Cement Association's Concrete Technology newsletter notes that when these pavements first appeared 40-plus years ago, they didn't really catch on. Now, though, there is a more obvious need for free-draining pavements. An important one, of course, is the role they can play in stormwater management. If rain runs through the pavement, instead of into a storm sewer, the groundwater is recharged, and there is a reduced load at sewage treatment plants. Their use can lead to design differences. In Sultan, a small city in Washington state, the streets in a new subdivision were built without curbs and gutters since rainwater will simply run through the pervious concrete. Colours were added to the mix used for the sidewalks to differentiate them from the adjacent roadway. Pervious concrete is typically made with fine aggregate — sometimes even 100 per cent fines. These mixes require special admixtures that stabilize the air voids in order to maintain water infiltration rates, even where high percentages of fines are used. Some of the new mixes allow water to flow through them fairly freely. Others act like sponges, allowing some water to percolate through into the ground, but holding some water to evaporate back into the atmosphere. Some use admixtures to strengthen the concrete and improve its self-consolidating properties. We're not at all sure about the potential effects of climate change, but it seems likely that some parts of the world are likely to get more rain, much of it falling as a result of fewer but more severe storms. Patterns are shifting, and that is causing some engineers to scratch their heads over sizing storm sewers or deciding on sizes and depths for stormwater management ponds. Municipal politicians are also scratching their heads over their budgets, which seem to get tighter every year. Engineers often seem to be caught in the middle, between the need to treat or otherwise manage more stormwater, and political masters representing voters who don't want to pay more taxes — no matter what they might be for. Urban financing is another subject, though, and I'll be coming back to if often. In the meantime, if you work with concrete and don't see the PCA's newsletters, you might want to subscribe. The two I like best deal with concrete technology and sustainability. Both are published six times a year, both are informative, and both are free. The PCA has others that I haven't explored, but depending on the type of concrete work you do, you may find one or more pertinent for you. The association's website has a lot of interesting stuff to read, even if you're not interested in the newsletters. You'll find it at www.cement.org/tech

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