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Photocatalytic cement-based materials - Situation, challenges and perspectives

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This paper briefly reviews the situation with the photocatalytic cement-based materials and their current applications in the building sector. Starting from the pioneer application of the Church “Dives in Misericordia” in Rome, where a new type of cement was used with the aim of providing an innovative property (maintenance of white colour along time), it can be said that these materials are now a valid solution which is frequently chosen by architects, designers and stakeholders for the achievement of structures, buildings and large works which are environmentally friendly and distinctive in terms of quality and durability. Considerable costs have been sustained in “pilot” projects, in order to validate the solutions which were certified by means of laboratory tests specifically developed for the assessment of photocatalytic properties. However, photocatalytic cement-based applications are by now widely recognized as effective and environmentally friendly. The research activity on this field is still remarkable, aiming to develop further functional properties which can be added to the classic ones ( maintenance of color sometimes called “self cleaning” and depolluting).
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A short history of photocatalytic
cement-based materials
An innovative approach to the material science has demonstrated
that photocatalytic activity may be conferred to cement-based
construction materials, such as concrete, mortars, paints, etc.1-2.
Among the various semiconductor materials, TiO2 (Titanium
dioxide) in the form of anatase has attracted wide interest,
due to its strong oxidising power under near-UV radiation, its
chemical stability when exposed to acidic and basic compounds,
its chemical inertness in the absence of UV light, and its relatively
low cost (in comparison with other photocatalysts). TiO2 has
proved to be very effective in the reduction of pollutants such as
NOx, aromatics, ammonia, and aldehydes. The use of TiO2 in
combination with cementitious materials has shown a favourable
synergistic effect in the reduction of pollutants. Indeed, in
comparison with other photocatalytic building materials, these
special binders (and their corresponding products) are able
to absorb the NOx on the surface, to transform them in non-
noxious ions and to block them in form of salts (nitrates). These
substances can be easily removed from the surface by means
of rain (lixiviation) or by washing. A similar mechanism can be
observed for other pollutants (e.g. SOx). In the particular case
of NOx reduction, as an indirect consequence, it is possible to
demonstrate that the production of ozone is inhibited in the
atmosphere and a further environmental advantage is evident.
Photocatalysis of cement-based materials is a recent matter
(mid-1990s): first developments were made by Italcementi3 and
Mitsubishi4, and several patents have been filed to date (16 of
them by Italcementi), with a progressive development of new
products that are commercially available.
Gian Luca Guerrini – CTG Italcementi Group, Italy
Photocatalytic
Cementitious Materials:
Situation, Challenges and
Perspectives
This paper briefly reviews the situation with photocatalytic cementitious materials and their
current applications in the building sector.
Starting from the pioneer application of the Church “Dives in Misericordia” in Rome, where a
new type of cement – developed by the Technical Centre of Italcementi – was used with the aim
of providing an innovative property (maintenance of white colour over a long period of time), it
can be said that these materials are now a valid solution that is frequently chosen by architects,
designers and stakeholders for the achievement of structures, buildings and large works that are
environmentally friendly and distinctive in terms of quality and durability.
Considerable costs have been sustained in “pilot” projects, in order to validate the solutions
that were certified by means of laboratory tests specifically developed for the assessment of
photocatalytic properties. However, photocatalytic cement-based applications are by now widely
recognised as effective and environmentally friendly.
The research activity on this field is still remarkable, aiming to develop further functional
properties that can be added to the classic ones (i.e. maintenance of colour sometimes called “self
cleaning” and depolluting).
1
Photocatalysis was firstly applied to building materials
(ceramics and glasses), to obtain self-cleaning and anti-
bacterial surfaces and had its best moment in Japan in the
1990s. Just in Japan, numerous scientific conferences and
national expositions were organised on this innovative topic,
considering titanium dioxide as the most common (and
cheapest) catalyst.
The first official publication on such products was presented
by L. Cassar et al. in 19975. Since then, the development of
photocatalytic cements has been carried out with increasing
innovative solutions, passing from the self-cleaning performance
to depolluting effect.
The first meaningful application of the photocatalytic
cement-based materials has certainly been the “Dives in
Misericordia” church in Rome for which, on demand of arch.
Richard Meier, CTG Laboratories developed a white concrete
possessing a prolonged maintenance of colour over time (Figure
1). The first concrete trials were carried out in 1997, well before
the beginning of the construction of the Church, and the first
results were presented in Italian and International congresses
starting from 1998. This church was inaugurated in 2002,
but the colour of its sails has constantly been monitored since
the year 2000, in order to verify the preservation of whiteness
(Figures 2 – 3).
Another breakthrough for this innovation consists in the
funded European research project PICADA (“Photocatalytic
Innovative Coverings Applications for Depollution Assessment”,
2002 – 2005), through which a pilot scale experience (street
canyon) was carried out for the evaluation of depolluting
performances of coating materials in real conditions6.
Afterwards, the research was aimed to develop products
capable to obtain a surface degradation of gaseous polluting
agents (NOx, SOx, etc.), so that several commercial solutions
(pavements, roofing and coatings) are now available on the
market.
Figure 4 summarises the Italian consumptions of TX Active®
cements by Italcementi by end product (2006 – 2009). The
trend in volume consumptions show a shift from paving blocks
plus paints, to ready mix and precast concrete manufacts. This
means that there has been a breakthrough in consumptions
that does not correspond to a proportional increase in the
surfaces covered. Indeed, the photocatalytic surface in paving
blocks is only the upper layer. Paints and coatings represent
a small amount of the product (cement) used, but in terms of
photocatalytic surfaces they represent more than 50% of the
total. Currently, about 60 Companies are TX partners in Italy,
and more than 100 in the world (France, USA, Spain, Belgium,
Morocco).
Besides, in 2008 Italcementi and Heidelberg Cement signed
a licensing agreement for joint use of photocatalytic binders
based on TX Active® technology, expanding the offer in other 12
Countries.
According to a reliable estimation, the photocatalytic surfaces
produced in Europe with cement-based materials until 2009
result to be over 1.5 million m2.
Further than Italy, the most relevant applications of
photocatalytic cement-based materials have been carried out in
France, Belgium, United States, Spain, Germany, UK, Czech
Republic and Morocco.
Another breakthrough is now expected, due to an
optimisation of compositions and performances and due to a
reduction in the price of TX Active® products.
Figure 1. Church “Dives in Misericordia”.
Figure 2. Trend of luminance values (L*) for the three sails of the
Church “Dives in Misericordia”.
Figure 3. Trend of yellowness values (b*) for the three sails of the
Church “Dives in Misericordia”.
Figure 4. Segmentation of the Italian market (volumes), for
photocatalytic cement-based products.
2
Challenges and perspectives
Sustainable architecture
These innovative products have been developed in order to
provide an environmentally friendly solution in the building
market and are becoming more and more widely recognised for
green building constructions. By virtue of its aesthetic qualities
and environmental benefits, TX Active® has become the best
choice for all the architects wishing to meet a variety of objectives,
the first of which is sustainability.
These materials can be adopted to promote a whole-
building approach to sustainable development by recognizing
performance in areas of human and environmental health,
such as in the case of the LEED (Leadership in Energy and
Environmental Design) worldwide certification. Indeed, in
LEED, points are awarded for environmentally friendly actions
taken during design, construction, and use phases and the use
of photocatalytic cements will obtain a variety of credit points in
the “New Construction and Major Renovation” categories LEED
rating system, promoted by the U.S. Green Building Council
(USGBC). In particular, TX Active® photocatalytic cements can
help earn from 9 to 15 points, with reference to 69 points of
total: heat island effect (sustainable sites category), optimisation of
energy performance (energy and atmosphere), recycled content
and regional materials (materials and resources), and innovation
are the outstanding characteristics (Table 1)7.
Using these materials, the new ITCLab (Innovation and
Technology Center Laboratories) of Italcementi Group designed
by Richard Meier (Figure 5), will be completed in Bergamo (Italy)
aiming to the highest levels of LEED certification (gold/platinum)
(Table 2)7.
Urban heat island mitigation
Photocatalytic cement-based materials could represent one of the
most efficient solutions for the mitigation of urban heat island
effect, a phenomenon that causes urban areas to be 2 to 4 °C
warmer than their surrounding areas8, 9. Indeed, the increase of
temperature in cities is dramatically influenced by the presence
of large percentages of black or dark surfaces, and this condition
could be limited by the use of lighter roofs and pavements. The
photocatalytic properties of this “cool” materials are a further
added value, from the environmental point of view. For example,
paved surfaces (such as highways, roads, runways, parking
areas, sidewalks, and driveways) typically represent from 30 to
60% of developed urban areas10, and could be transformed – on
the occasion of periodical maintenance or renovation works
– into more environmental surfaces. In pavement structures,
the topmost surface is the only layer which affects the solar
reflectance (commonly known as “albedo”). Therefore, pavement
type selection should also include a consideration of albedo,
where heat generation is a concern.
As widely explained in literature8-9, urban heat islands are
not inevitable, however an effective use of white or light-colored
pavements (roads, sidewalks, roofs and paints) could significantly
contribute to temperature mitigation during sunny periods.
Some examples of typical reflectance values of pavements are
summarised in Table 311.
A broad utilisation of white photocatalytic materials in
the cities could give a relevant support in the reduction of
temperature, thereby saving energy for cooling buildings,
keeping parking lots and roads cool and improving air quality.
Further, if we consider that the formation of smog is highly
sensitive to temperatures, a reduction of ozone formation during
the summer period is also possible (ozone is a highly oxidising
and irritating gas and is the main ingredient of urban smog).
Besides, the kinetics rate for photochemical pollution reactions
could be decreased, with a subsequently lower production of
noxious substances.
For example, a study has been already completed in
cooperation with the Polytechnic of Milan12, regarding the
modelisation of the combined “urban heat island”/photocatalysis
phenomenon, with the intention to test the developed system on
a specific area of Milan (Figure 6).
Standardisation
It is well known that innovative materials can have some
limitations in their commercial success, if there are not adequate
standards for both qualitative and quantitative evaluation of
their performances. Reference standards and photocatalytic
Table 1.
Credit category Total points
available
Potential points
with TX Active®
cement products
Sustainable sites 14 2
Water efficiency 5 -
Energy and atmosphere 17 1 to 4
Materials & resources 13 2 to 4
Indoor environmental
quality
15 -
Innovation & design process 5 4 to 5
Total 69 9 to 15
Table 2.
LEED Certification Levels Points required
Certified 26-32
Silver 33-38
Gold 39-51
Platinum 52-69
Figure 5. ITCLab Center in Bergamo.
3
parameters are absolutely necessary to define the performances
required in specifications and projects and to compare different
building materials.
This is also the situation of photocatalytic products, so an
intense standardisation activity is in progress (ISO and CEN).
Current ISO test methods and standards are mainly dedicated to
ceramics and coatings, as they were developed in Japan (JIS) and
then extended to the international level.
As to the cement-based materials, standardisation activity
started in Italy with the first publication of three standards,
dealing with the determination of photocatalytic activity of
cementitious products (NOx test, UNI 11247-2009) (Volatile
Organic Compounds test, UNI 11238-1-2007) and of hydraulic
binders (Rhodamine B test method, UNI 11259-2008).
In 2008, the activity of the European Technical Committee
on Photocatalysis (TC386) was officially established and currently,
there are six Working Groups (WGs) which have started to develop
test methods on photocatalytic materials, including cement-based
products. “Air purification” (WG2), “Self-cleaning” (WG4) and
“Light sources” (WG6) are the most relevant topics considered.
Trends in research and innovation
Research activities carried out until now have focused on the
optimization of both depolluting and self-cleaning performances
for general applications. Due to marketing efforts and to the
creation of a strong link with architects, designers and main
contractors, the use of photocatalytic cement-based materials is
steadily growing with a clear, ecological footprint.
The research in progress is carried out in collaboration
with several academic groups and research centres, with a
multi-disciplinary approach (engineering, architecture, chemistry,
physics, medicine, etc.), in order to develop new solutions for
next generation products and applications.
The most advanced studies are dealing with the development
of photocatalytic products for indoor applications,
in combination with the design of lighting system.
Reasonable solutions seem to be suggested with
the use of doped TiO2 (e.g. C-doped, N-doped).
However, some doubts on long-term efficiency in
cement environment are still limiting the use of
these modified products. Taking the opportunity to
participate in a European funded project (Clear-
up), Italcementi is working on this topic for the
improvement of indoor air quality (IAQ)13.
Another field of research is concerned with
the antibacterial properties that can be obtained by
modifying traditional photocatalytic system with the
possible addition of other chemicals.
Finally, the development of innovative but
cheap photocatalysts seem to be the most exciting
result, which could lead to a further commercial
breakthrough in this sector.
Conclusion
Photocatalysis has perhaps represented one of the most innovative
solutions in the cement industry over the last 20 years, thanks to
the active research carried out by the Italcementi Group.
After the first encouraging experiences aimed to assess both
architectural and environmental performances of photocatalytic
cement-based products in pilot projects, this class of building
materials is by now a certainty, with increasing quantities of
TX Active® cements being consumed for structural, architectural
and environmental purposes.
A series of new projects is currently developed, by which
photocatalytic cement-based materials will be widely used,
maintaining their properties for the expected service life. By
contrast, the other products that are currently proposed on the
market for surface coating of concrete products (sol-gels and TiO2
solutions) are capable to guarantee a photocatalytic performance
only for a limited period of time.
References
CASSAR, L., “Photocatalysis of cementitious materials: Clean buildings and
clear air”, MRS Bulletin, May 2004. pp 4.
CASSAR, L., BEELDENS, A., Pimpinelli, N. and Guerrini, G.L., “Photocatalysis
of cementitious materials, RILEM Int. Symposium on Photocatalysis
‘Environment and Construction Materials’, (Florence/Italy, 8-9 October
2007), TDP 2007, (Florence/ltaly, 8-9 October 2007) Rilem Proc. PRO55 (eds. P.
Baglioni and L Cassar), pp. 131 -146.
Italcementi SpA, EP Patent Nr. 946,450, US 6,409,821.
Mitsubishi Mat. Corp., EP 786,283.
CASSAR, L., PEPE, C., PIMPINELLI, N., AMADELLI, R. and BONATO, T.,
‘Materiali cementizi e fotocatalisi’, Seminario FAST: Materiali: Ricerca e
ProspettiveTecnologiche alle Soglie del 2000, (Milano, 10-14 Novembre 1997)
(in Italian).
website: http://www.picada-project.com
Essroc Italcementi Group, LEED-NC®2.2 Guide: Using TX Arca® and TX Aria®
Photocatalytic Cements for New Construction and Major Renovations,
technical report, 2008.
website: http://heatisland.lbl.gov
AKBARI, H., ROSENFELD, A. H., and TAHA, H., Cool Construction Materials
Offer Energy Savings and Help Reduce Smog”, ASTM Standardization News,
November 1995, pp. 32-37.
Cambridge Systematics, Cool Pavement Report EPA Cool Pavements Study,
June 2005, pp. 72.
American Concrete Pavement Association, Albedo: a measure of pavement
surface reflectance, Number 3.05, June 2002, pp. 2.
MANGIAROTTI A. PAOLETTI I., “The effects of volume of buildings
and surface coatings on air temperatures in urban areas”, Final report,
Polytechnic of Milan, 2007 (in Italian)
website: http://www.clear-up.eu
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
Table 3. Albedos (reflectance) of pavement surfaces
Pavement Type Albedo
Asphalt 0.05 – 0.10 (new)
0.10 – 0.15 (weathered)
Grey Portland cement concrete 0.35 – 0.40 (new)
0.20 – 0.30 (weathered)
White Portland cement concrete 0.70 – 0.80 (new)
0.40 – 0.60 (weathered)
Figure 6. Simulation of the mitigation of heat island effect, using photocatalytic
light-coloured materials (Campus Leonardo – Polytechnic of Milan) – left: real
situation during summer period; right: possible results applying the materials on the
roads, sidewalks, parking lots and building roofs. Dark red color zones: critical points
(highest temperatures)12.
4
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Nitrogen oxide (NOx) is a significant precursor of particulate matter (PM), particularly in high-traffic areas. Accordingly, this study aimed to reduce the presence of nitrogen oxide (NOx) along roadsides. Titanium dioxide (TiO2) is used as a photocatalyst to remove NOx through a chemical reaction. Typically, concrete and TiO2 are mixed to create TiO2 concrete. However, air pollutants or UV rays cannot be allowed to come into contact with a significant amount of TiO2. Thus, the TiO2 surface penetration method was used to fix TiO2 to the surface of the concrete. In this method, surface penetrants and TiO2 are combined and sprayed onto the concrete surface, enabling the possibility of NOx reduction using relatively less TiO2. When the fixation method is applied to vertical concrete structures, however, a peeling issue arises. To address this, a pressurized TiO2 fixation method was applied to vertical concrete structures. This method uses external force to penetrate and fix TiO2 to a specific depth. In the instance of the pressurized TiO2 fixation method, which was tried for the first time, penetration depth was used to ensure long-term durability as well as NOx removal efficiency. To investigate TiO2 distribution characteristics, the penetration depth and mass ratio of TiO2 particles in TiO2 concrete were measured using a scanning electron microscope (SEM/EDX). In addition, NOx removal efficiencies were evaluated using the NOx analyzing system (ISO 22197-1 standard). The experimental results showed that NOx removal efficiency increased with an increasing TiO2 mass ratio. When the TiO2 fixation method was used, the NOX removal efficiency was 32% when the TiO2 mass ratio at the surface was 50%, and the efficiency was 61% when the TiO2 mass ratio was 70%. This is attributed to the increase in NOx removal efficiency as TiO2 content at the concrete surface increases. This study analyzed and forecasted the NOx removal efficiency of TiO2 concrete based on the mass ratio of TiO2 on the surface. As the TiO2 mass ratio increased, the NOx removal efficiency improved, and it was determined that the surface TiO2 mass ratio significantly influences the NOx removal efficiency. Consequently, this study developed an equation to estimate NOx removal efficiency, making it possible to determine a suitable maintenance interval for TiO2 concrete.
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Among the different photocatalytic solutions available on the market, i.active® cements by Italcementi Group are the most common raw materials currently utilized for the manufacturing of building products possessing an added value in terms of sustainability and durability. One of the main purposes for their use is to reduce pollution, in order to improve the air quality in urban environments. Another environmental advantage in their use is in terms of mitigation of urban heat island effects. Currently, photocatalyctic cements are commercially available in Europe, North America, North Africa and India. Several million square meters of photocatalytic cement-based surfaces, have already been applied, and this number is expected to grow substantially in the coming years. In this framework, photocatalytic cementitious roads and pavements represent the widest application for the improvement of air quality in urban environment. This paper gives an overview of the product performances to help engineers to choose and design sustainable and durable paved surfaces that typically represent from 30% to 60% of developed urban areas.
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A new and innovative approach to the material science has demonstrated that photocatalytic activity may be conferred to cementitious construction materials such as paints, mortars, concrete manufacts, pavements, etc. This has been confirmed by the results obtained in the generalised use of self-cleaning surfaces which allows buildings to maintain their aesthetic appearance unaltered over time. In parallel, the capability of photocatalysis in cementitious materials to reduce the levels of urban pollution has been demonstrated in laboratory, at pilot scale and, more recently, with some specific in-field monitoring programs carried in occasion of relevant realizations. In this paper, after a description of the most relevant aspects concerning the photocatalysis applied to the cement-based materials, some test methods for the evaluation of the photocatalytic activity will be described. Furthermore, some pilot projects will be cited and finally, some examples of relevant applications will be reported.
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While the primary function of concrete is structural, its pervasiveness in our society lends it to other functions and creates the need for it to maintain its integrity and aesthetic quality. Therefore, concrete with added functionality–for example, self-cleaning characteristics and the ability to remove pollutants–is desirable. Heterogeneous photocatalysis (e.g., gas–solid or liquid–solid catalytic processes caused by light irradiation) by semiconductor particles or coatings has now reached a high level of development and is a promising technology for the reduction of global environmental pollutants. Among the various semiconductor materials, TiO2 in the form of anatase has attracted wide interest, due to its strong oxidizing power under near-UV radiation, its chemical stability when exposed to acidic and basic compounds, its chemical inertness in the absence of UV light, and the absence of toxicity. TiO2 has proved very effective in the reduction of pollutants such as NOx, aromatics, ammonia, and aldehydes. Surprisingly, the use of TiO2 in combination with cementitious materials has shown a favorable synergistic effect in the reduction of pollutants. These new materials have already found relevant applications in self-cleaning building walls and in the reduction of urban pollutants.
american Concrete Pavement association, Albedo: a measure of pavement surface reflectance
Cambridge Systematics, Cool Pavement Report EPA Cool Pavements Study, June 2005, pp. 72. american Concrete Pavement association, Albedo: a measure of pavement surface reflectance, number 3.05, June 2002, pp. 2.
The effects of volume of buildings and surface coatings on air temperatures in urban areas
  • Mangiarotti A Paoletti
ManGIarOTTI a. PaOLETTI I., "The effects of volume of buildings and surface coatings on air temperatures in urban areas", Final report, Polytechnic of Milan, 2007 (in Italian) website: http://
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CaSSar, L., PEPE, C., PIMPInELLI, n., aMaDELLI, r. and BOnaTO, T., 'Materiali cementizi e fotocatalisi', Seminario FAST: Materiali: Ricerca e ProspettiveTecnologiche alle Soglie del 2000, (Milano, 10-14 novembre 1997) (in Italian).
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Essroc Italcementi Group, LEED-NC®2.2 Guide: Using TX Arca® and TX Aria® Photocatalytic Cements for New Construction and Major Renovations, technical report, 2008. website: http://heatisland.lbl.gov