Old Concrete Can Have Second Life Protecting Nature

Usually we think of demolished concrete walls and floors as environmental contaminants, but in fact this material may turn out to be a valuable resource in nature protection work. This is the conclusion from researchers from University of Southern Denmark after studying the ability of crushed concrete to bind phosphorus.

"We have shown that crushed concrete can bind up to 90 per cent of phosphorus, "says PhD student and environmental engineer, Melanie Sønderup, Department of Biology at the University of Southern Denmark. Since March 2013 researchers have tested the technique in a full-scale experiment, which will run until March 2014. But already now they find that the technique is very effective.

Large amounts of phosphorus can be washed out into lakes and streams when it rains. Rainwater that runs off from catchments, especially those fertilized with phosphorus, carries the phosphor with it. This phosphorus rich rainwater is then often collected in rainwater ponds, which discharges into lakes and streams. "The water in these rainwater ponds can be very rich in phosphorus, and if it is discharged into a lake, it can lead to an increase in algae growth. This can lead to oxygen depletion and a reduction in the number of species that can live in the water," explains Melanie Sønderup and continues:

"By letting the pond water pass through a filter of crushed concrete, we can remove up to 90 per cent of the phosphorus". Phosphorus binds so well to the concrete because it contains cement. Cement is rich in calcium and also contains aluminum and iron. All three can bind phosphorus. Preliminary results show that the size of concrete grains is of importance. The smaller the grains the better they bind phosphorous. Fine concrete powder is thus more effective than millimeter sized concrete bits.

"It is also important that we do not use concrete that has been exposed to wind and rain for a long time, as this washes out the cement, which holds the essential calcium," explains Melanie Sønderup. As the experiments have only run for six months, the scientists do not yet know the durability of crushed concrete, but they believe that a filter of crushed concrete can last for a long time, probably several years. "Only when the concrete cannot bind more phosphorous, it will be time to switch to a new layer of crushed concrete - and then the disposed layer can be recycled as road fill", says Melanie Sønderup.

http://www.enn.com/wildlife/article/46346

Chicago’s ‘Greenest Street’ Uses Smog-Eating Cement

A solar- and wind-powered energy station and a bioswale are seen on West Cermak Street in Chicago. Image via Phys.org.

by Randy Woods 

In a city better known for turning its rivers bright green every March 17, a new title has been bestowed upon an unassuming little stretch of pavement in the industrial Pilsen section of Chicago. Two miles of West Cermak Road have been ceremoniously dubbed by the city as “the greenest street in America” for the long list of sustainable features lurking under and around the pavement.

While this is obviously just a little more wind from the Windy City (a million dirt roads anywhere in the world are far greener), the technology embedded in the $14 million stretch of pavement in front of Chicago’s Benito Juarez Community Academy looks promising enough to make a difference if it’s scaled up to an entire neighborhood.

First of all, the permeable pavement itself contains concrete created by Italcementi, the Italian manufacturer of “smog-eating cement,” which has been used on some buildings to resist discoloration. The cement contains titanium dioxide, which reacts with sunlight to speed up decomposition of any organic materials that build up on the surface. Tests have shown that the material actually helps clean the air as far away as eight feet from its surface.

The areas surrounding the pavement are equally impressive. On both sides of the street, bioswales have been added to absorb as much as 80 percent of storm water before it has a chance to overwhelm the sewer system. The drought-resistant trees, shrubs and grass in these bioswale belts are expected to withstand Chicago’s hot summers. They also consume CO2 and reduce the heat-island effect of paved surfaces.

Streetlamps are also lit by stored energy generated from a combination of solar panels and small windmills that are cleverly contained with slender energy kiosks sticking up from the sidewalks. Dedicated bicycle lanes have also been added to encourage non-polluting commuting. About 60 percent of the project’s construction waste was recycled and 23 percent of the new materials used contained recycled content.

According to the Chicago’s Office of Environment and Sustainability, the $14 million project cost 21 percent less than a traditional road resurfacing project and is expected to have fewer maintenance costs. The city said it is currently working on guidelines that may require many of these affordable green features to be included in all future road projects.