North / South America
New “green” concrete prevents runoff
May, 27 2009
(Shoreview, Minnesota) -- Shoreview is taking a gamble on a new form of pervious concrete that is designed to let rainwater go through it rather than it running off into storm sewers and lakes. The pervious concrete is made of gravel and cement, but does not include sand, the component which provides the impervious nature of typical concrete. Under the pervious concrete layer is a layer of aggregate, which will store the water so that it can filter gradually into the ground.
For about five years, several cities in Minnesota have experimented with this concrete in some limited areas such as parking lots. Shoreview is the first Minnesota city to fully commit to using it on residential streets in place of traditional storm drainage systems, which include catch basins, pipes, and settling ponds. Settling ponds need maintenance and generally result in buildup of potentially toxic materials that have to be removed and disposed of. It is hoped that the reduced runoff will help to protect a nearby lake, which has been becoming increasingly polluted from runoff.
There are some concerns and caveats. One question is whether it will hold up in frigid Minnesota winters. It is crucial that snow and ice does not build up and result in freeze-thaw cycles that will break apart the concrete. However, the history of the product where it has been used so far, and the very nature of the product allowing drainage of the water, has been promising.
It does require some special maintenance to keep the pores open. Shoreview has included in the budget a special street sweeper machine to do the job. It also requires those who install it to be familiar with the product, and as one may expect, it is more expensive than traditional concrete. The Ramsey Conservation District will be monitoring the groundwater to determine any impact on either the level or the quality of the groundwater in the area.
This exciting project holds great promise, and should be carefully watched by other cities as a model for the future.
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