Self-Cleaning Concrete
Concrete Technology
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Building a Better (Cleaner) World in the
21st Century
 Self-cleaning
buildings and pollution-reducing roadways: These may sound like
futuristic ideas, but they are realities of some of today’s
concrete. Recently introduced formulations of cement are able to
neutralize pollution. Harmful smog can be turned into harmless compounds
and washed away. Anything made out of concrete is a potential application,
because these cements are used in the same manner as regular portland
cements. These products provide value through unique architectural
and environmental performance capabilities.
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.
Presumably, applications for mortar might be beneficial, too., although
the mortar has a smaller surface area. 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 products 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
chemical applications that are potentially harmful to the environment.
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, a white concrete building that 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—where
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 NOx and SOx, that can lead
to acid rain, smog, and respiratory issues. According
to the EPA, 34% 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
0.5 m (19.5 in.) to 1.5 m (58.5 in.) 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.
The Missouri Department of Transportation, with consultation from
the CP Tech Center and the FHWA, is currently preparing for a trial
section of photocatalytic pavement in the St. Louis area. The St.
Louis area is designated a non-attainment area with regards to particulate
matter with a moderate concern for ground-level ozone, both being
primary components of photochemical smog. The use of photocatalytic
pavements or pavement-related structures is being discussed to bring
the region down to attainment levels. The photocatalytic cement
is being evaluated in comparison to typical local Type I cement
for strength, permeability, deicer scaling resistance, air void
system, and compatibility with admixtures and curing compounds.
So far, the differences between the control mixture and photocatalytic
mixture have been statistically negligible.
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 2-inch bonded overlay on-top
of an 8-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.
Click
here to buy our recently updated bibliography of photocatalytic
concrete articles, reports, conference papers, and patents,
identified through searches of online scientific databases as well
as the Library’s collection.
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