Venice hardly counts among the most-polluted places in the world. There are no cars traveling its narrow streets, and all traffic is either by foot or by boat. So despite the crowded walkways and canals, the air in Venice is far cleaner than that of, say, Milan, Italy's economic capital, which recent figures indicate has some of the worst air quality in Europe.
Even so, visitors to the Italian Pavilion of the architecture exhibition in the Venice Biennale, which will remain open until Nov. 19, will get a breath of fresh air. That's because parts of the concrete walls and grounds have been built with cement containing an active agent that, in presence of light, breaks air pollutants such as carbon monoxide, nitrogen oxide, benzene, and others through a natural chemical process called photocatalysis.
The demonstration is a reminder that smart innovation applies also to mundane products and can offer unexpected solutions even for complex problems such as air pollution. The technology, called TX Active, has been under development for almost 10 years in the labs of Italcementi, the world's fifth-biggest cement producer, and is starting to be applied commercially to buildings and streets in Italy, France, Belgium, and elsewhere.
Painting the Town
The results so far are astonishing: A street in the town of Segrate, near Milan, with an average traffic of 1,000 cars per hour, has been repaved with the compound, "and we have measured a reduction in nitric oxides of around 60%," says Italcementi's spokesperson Alberto Ghisalberti. In a test over an 8,000 square meter (or approximately 2 acres) industrial area paved with active blocks near Bergamo, Italcementi's hometown, the reduction was measured at 45%.
In large cities such as Milan, with persistent pollution problems caused by car emissions, smoke from heating systems, and industrial activities, both the company and outside experts estimate that covering 15% of all visible urban surfaces (painting the walls, repaving the roads) with products containing TX Active could abate pollution by up to 50%, depending on the specific atmospheric conditions.
Of course, this approach isn't meant to replace efforts to curb pollution, but it can significantly magnify their effects. Here's how it works: The active principle—basically a blend of titanium dioxide that acts as photocatalyzer—can be incorporated in cement, mortar, paints, and plaster.
The Big Bite
In the presence of natural or artificial light (this applies also indoors) the photocatalyzer significantly speeds up the natural oxidation processes that cause the decomposition of pollutants, transforming them into less harmful compounds such as water, nitrates, or carbon dioxide.
"These aren't necessarily 'clean', but from an environmental standpoint they're much more tolerable," says Rossano Amadelli of the Italian National Research Council (CNR), the scientists who led the laboratory testing of the TX Active materials.
The patented pollution-reduction technology—which in Italy is becoming known as "cemento mangiasmog" or "smog-eating cement"—comes at a premium, of course, but the extra cost is limited by the fact that the active principle only needs to be used on the surface.
Keeping It Clean
"To transform the facade of a five-story building into a photocatalytic surface would add only 100 or so euros ($120) to the cost of a traditional paint or plaster," Ghisalberti estimates. Paving a street or a sidewalk is a different story, but still not extreme: Photocatalytic blocks cost about one-third more than usual paving, which is still far less than the long-term cost of doing nothing about air pollution.
It turns out that the photocatalyzing cement has another advantage, one that has great appeal to star architects such as Richard Meier. TX Active not only hastens the decomposition of organic and inorganic pollutants, it also prevents their build-up on surfaces, helping to preserve a building's pristine appearance over time.
The spectacular design of Meier's Dives in Misericordia Church in Rome, includes three concrete self-bearing white sails, topping out at 26 meters. One of Meier's material requirements was that the whiteness of the sails be durable. That has been achieved through the application of the active principle, which basically "self-cleans" the surfaces.
The same system has been applied to the new Air France headquarters inside the Charles de Gaulle airport in Paris, a place with high concentrations of hydrocarbons and where, needless to say, a standard white facade would not remain white for long.
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