And for those living in the San Francisco Bay Area… there are patents in
the New Bay Bridge’s sparkling white appearance!
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Self-cleaning cement is an
Italian invention based on the principles of photocatalysis, discovered in the
1970s. Photocatalysis is a light driven chemical reaction that decomposes and
transforms a wide range of pollutants and contaminants into harmless or
potentially beneficial matter, in particular via the chemical reaction of the
sun and titanium dioxide (TiO2).
Other uses of the principles of photocatalysis using TiO2 are
invoked in a wide variety of applications such as solar water purification (Salih,
F, 2004); asphalt pavements for the mitigation of vehicle emissions (Hassan et.
al, 2013), or micro particles in various applications intended for the
oxidation of organic contaminants (Venugopal, Tezier and Tezier, 2009).
In this EPO nominated invention concerning “self-cleaning cement”, the principle of photocatalysis using TiO2 was transferred to cement (in the right proportions and after extensive
experimentation in the 1990s, involving 85 patents). The cleansing and brightening effects of the
reaction are mixed in with the cement which is then used for
construction.
One of the first
constructions using this titanium dioxide-enriched cement was the Dives in Misericordia Church in Rome,
designed by American architect Richard Meier [Dives, Italicimenti]. After
construction of the church, scientists discovered that the air next to the
church was also cleaner, and that harmful substances in the air surrounding the
church also oxidized faster. It follows then, that a photocatalytic city, that
is, one where all the buildings are
covered with photocatalytic titanium dioxide-enriched cement, paint or plaster,
could potentially reduce the levels of harmful substances by means of the
sunlight.
Adding a titanium-enriched surface to a building increases construction
costs 15%, but it is also estimated that it decreases pollution by 20% in the
immediate vicinity. The cement, plaint or plaster repels dirt and cleanses the
air, using sunlight! This is also the reason why the New San Francisco-Oakland
Bay Bridge might retain its sparkling white color, while creating a better work
environment for maintenance crews, and perhaps for the Toll Plaza workers also
(Hassan, 2009; Lence et. al, 2014).
The following three patents awarded to Luigi Cassar et. al and the
Italian firm Italicimenti, are cited as part of the nomination of this
invention:
- EP0946450 titled Hydraulic binder and cement
compositions containing photocatalyst particles
- EP2242806 titled Titanium
dioxide photocatalytic composites and derived products on a metakoalin
support
- EP2282203 titled Method
of measuring the photocatalytic activity of cementitious material
An mage of the Dives in Misericordia
Church (Rome, Italy) built with titanium-dioxide-enriched and photocatalytic
materials is included above, and to the right a detail of the sparkling San
Francisco – Oakland Bay Bridge….
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Now… stop dreaming… and start building a photocatalytic city!
References
Dives in
Misericordia Church – Italicimenti http://www.italcementigroup.com/ENG/Architecture/Dives+in+Misericordia+Church/
Lence,
A., Hassan, M. Zaylor, A and R. Rupnow (2014) Best practices for maintenance of
concrete bridge elements against mold and mildew growth. Proceedings of the
Construction Research Congress - Construction in a Global Network, Atlanta, GA,
May 19-21, 2014. pp. 1556-1565.
Nader,
M., and B. Mahoney (2013) The New San Francisco-Oakland Bay Bridge. Proceedings
of the Structures Congress 2013- Bridging your passion with your profession,
in Pittsburgh, PA, May 2-4, 2013.
Salih,
F. (2004) Water purification by a combination of sunlight, titanium dioxide and
alum. Proceedings of the World Water and Environmental Congress,
2004, Salt Lake City, UT, June 27- July 1, 2004, pp. 1-9. http://ascelibrary.org/doi/abs/10.1061/40737%282004%29341
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