Self-cleaning buildings and pollution-reducing roadways: These may sound like futuristic ideas, but they are the realities of some of today’s concrete. Recently introduced formulations of cement are able to neutralize pollution, turning harmful smog into harmless compounds that can be washed away. Anything made out of concrete is a potential application as these cements are used in the same manner as regular portland cements.
Proprietary technology (based on particles of titanium dioxide) is what makes this cement special. The technology can be applied to white or gray cement and it works like any other portland cement: it can be used in all varieties of concrete, including plaster. The only difference is that it is capable of breaking down smog or other pollution that has attached itself to the concrete substrate, in a process known as photocatalysis. As sunlight hits the surface, most organic and some inorganic pollutants are neutralized. They would otherwise lead to discolored concrete surfaces.
The titanium-based catalyst is not spent as it breaks down pollution, but continues to work. Typical byproducts are oxygen, water, carbon dioxide, nitrate, and sulfate. Because rain washes away the pollution from the concrete surface, buildings stay cleaner and do not require potentially harmful chemical applications. Maintenance costs are reduced. This is true even for buildings in highly polluted locations—one noted application is the Air France headquarters at Roissy-Charles de Gaulle International Airport near Paris where a white concrete building has remained white. Another is the Church of the Year 2000 in Rome.
Clean buildings are great: A perhaps even more astounding environmental benefit is the potential for cleaner air. Concrete products that are exposed to sunlight throughout their life, like precast building panels, pavers, and roof tiles, are especially suited to manufacture with photocatalytic cement. For instance, city streets made with special pavers are capable of reducing the pollution at its source—when it comes out of the tailpipe.
Photocatalytic Pavements Reduce Air Pollution
The need for pavements is ubiquitous. As our population increases, more roads are needed to get people and goods from place to place. Unfortunately, with this added traffic comes a higher concentration of air pollution. To reduce our current and future levels of air pollution, more attention is being given to the use of photocatalytic concrete in pavements.
The internal combustion engine is used everywhere in the United States, from cars to trains to jets. These engines produce the power required to travel, but also emit pollution. The primary pollution from fossil fuel combustion is carbon dioxide (CO2), but other gasses are formed, such as nitric oxide (NOx) and sulfur oxide (Sox) that can lead to acid rain, smog, and respiratory issues.
According to EPA reports, 34 percent of the national NOx emissions come from vehicles on roads.
Photocatalytic concrete contains titanium dioxide particles that act as the catalyst for the natural breakdown of NOx into nitrates in sunlight. This occurs at the surface of the concrete, where the nitrates can be easily washed away. Without the catalyst, the NOx will breakdown in the atmosphere, creating photochemical smog and ground level ozone. With an abundant surface area and proximity to a major source of air pollution, the use of photocatalytic concrete for pavements is a logical concept.
A study conducted in the Netherlands used photocatalytic concrete pavers on a section of a busy roadway and monitored the air quality 19.5 to 58.5 inches above the pavement in both a control area with normal pavers and the test section. It was found that the NOx levels were reduced by 25 to 45 percent.
Ultimately, the photocatalytic concrete will be tested on a roadway. The current concept for the design is a two-lift pavement, with the photocatalytic portion being a two-inch bonded overlay on top of an eight-inch non-photocatalytic concrete base. The air quality and, possibly, the run-off water quality will be monitored. The ultimate goal is to assess the effectiveness of photocatalytic concrete for use in pavements, barrier walls, sound walls, or other pavement-related structures.