Sustainability was a focus of a four-year renovation and construction project in downtown Nashville, TN, that wrapped up in April 2022. As a result, the 339,000-square-foot Fred D. Thompson US Courthouse and Federal Building features a special concrete façade.
The concrete used for the building’s exterior walls was made using photocatalytic cement. As of 2022, the building is the largest project in the US that has used photocatalytic concrete elements.
The photocatalytic cement in the concrete contains a catalyst that reacts with sunlight and humidity, a process that already occurs in nature. The photocatalytic reaction heightens and accelerates that natural process, taking advantage of the benefits of sunlight, in this case on the building’s exterior surfaces. The components work together to make the façade on the Thompson Courthouse self-cleaning. The concrete sheds soil from itself and consumes smog without affecting the amount of catalyst or eroding the concrete.
As explained by GATE Precast, the concrete contractor on the courthouse job, an additional sustainable benefit of the photocatalytic façade is that the building’s exterior needs little to no maintenance over its entire lifetime. Used in concrete on projects since 1996, photocatalysts utilize ultraviolet light energy from the sun plus atmospheric humidity to form strong oxidizing reagents. These substances cause the chemical reaction that decomposes organic and inorganic pollutants in the surrounding environment. Most pollutants are reduced to salts, which occur naturally.
OnGreening describes air pollution in urban areas as one of the key problems for protection of the environment and the well-being of the community. Common air pollutants include nitrogen dioxide, volatile organic compounds and fine airborne particles (combustion byproducts, nitrates, sulphates, heavy metals).
Over decades, the photocatalysts have gradually been refined and enhanced so they can now also absorb organic and inorganic pollutants from the air and neutralize toxic and unpleasant odors.
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The photocatalytic process has also been applied to materials like glass and ceramics for self-cleaning. One type of tile has a special glaze that reacts with sunlight to break down polluting nitrogen oxides into harmless nitrates and nitrites. According to SCI at soci.org, the built industry is making use of photocatalytic paving blocks and materials that can control mildew and bacteria levels.
In addition, there is an environmental application for glass-ceramic combinations that contain photocatalysts. Because they have physical, chemical and thermal stability, they can be useful for hydrogen generation, bacterial disinfection and water purification, a challenge around the world, with an estimated 800 million people not having access to clean water.
Being able to put solar light, humidity and rainwater to beneficial use with photocatalytic construction components is helping the industry make a positive contribution to a built environment that promotes sustainability.