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10thInternationalConferenceonConcretePavements‐QuébecCity,Québec,Canada‐July8‐12,2012
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Environmental benefits of innovative photocatalytic
cementitious road materials
G.L. Guerrini, A. Beeldens, M. Crispino, G. D’Ambrosio and S. Vismara1
Abstract
Air pollution is a prominent critical issue of vehicles. The toxic pollutants are harmful
to the environment, hazardous to human health and difficult to degrade by natural
means. Therefore a significant amount of efforts have been done on road pavements
that directly interact with vehicles. Basing on the synergetic effect of cement and
titanium dioxide discovered in recent years new road pavements were developed. In
particular, photocatalytic cementitious road materials can represent a key element to
improve air quality, thanks to their ability to accelerate the natural reaction of
oxidation.
This paper deals with the development of several types of photocatalytic cementitious
road pavements, such as paving blocks, asphalt concrete filled up with a
photocatalytic slurry and concrete roads.
Large laboratory and field-testing programs have been conducted measuring the
environmental effectiveness by means of a specific set-up and in-situ sources,
respectively. Functional and mechanical tests have also been performed on the
materials studied to investigate their behavior under traffic loadings. Indeed, road
pavements have to guarantee both de-polluting effects and performances usually
required to a road pavement wearing course, according to the current Standards. The
large research activity conducted till now clearly showed the significant contribution
of such innovative materials to the improvement of air quality, reducing the nitrogen
oxides concentration up to 60% in some local weather conditions. They can represent
a new frontier of the research aimed at reducing air pollutants, for environmental
friendly solutions.
The findings underline the benefits of the inclusion of titanium dioxide in concrete
pavements.
Gian Luca Guerrini; Italcementi Group, Innovation Department; Chemical engineer;
Italcementi Group; g.guerrini@itcgr.net, Phone +39 (35)396946, Fax +39 (35) 5095716
Giovanni D’Ambrosio, Researcher, Italcementi Group, Innovation Department;
g.dambrosio@itcgr.net, Phone +39035396741, Fax +390355095716
Anne Beeldens, Researcher, BRRC, Belgian Road Research Centre, a.beeldens@brrc.be
Phone +32 (2)766346, Fax +32 (2)7671780
Maurizio Crispino; Full Professor; Politecnico di Milano; maurizio.crispino@polimi.it;
Phone +39 0223996606; Fax +39 0223996602
Stefania Vismara; PhD; Politecnico di Milano; Phone +39 0223996605; Fax +39
0223996602.
10thInternationalConferenceonConcretePavements‐QuébecCity,Québec,Canada‐July8‐12,2012
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Introduction
The constant increase of traffic and, consequently, air pollutants concentration
represent one of the main problems in urban areas. Many attempts have been made
indoor and outdoor to improve air quality, exploiting the synergetic effect of cement
materials and photocatalysts, in particular, titanium dioxide (TiO2). Its stability,
strong photo-oxidation power, together with its safety for human body, makes the
titanium dioxide in its anatase form the most suitable photocatalyst.
The photocatalysis mechanism involves electro-generated electrons and holes that act
as oxidizing and reducing agents in presence of sunlight, leading to a degradation of
pollutants into non-noxious compounds (Fujishima et al. 1999). TiO2 has been proved
to be very effective in the reduction of pollutants such as nitrogen oxides (NOx),
aromatics, ammonia, and aldehydes. Further, the use of TiO2 in combination with
cementitious materials has shown a favorable synergistic effect in the reduction of
pollutants (Cassar et al. 2007) (Guerrini, 2010). 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), Figure 1. These substances can be
easily removed from the surface by means of the rain (lixiviation) or of washing
actions. A similar degradation can be observed for other pollutants (Strini et al. 2005),
with different mechanism. Finally, in the particular case of NOx reduction, as an
indirect consequence, it is possible to demonstrate that the production of ozone is
strongly inhibited in the atmosphere and a further environmental advantage is evident.
This study focuses on the nitrogen oxides reduction, the most critical harmful
substances with their high concentration in urban air, due to the increasing traffic
volumes. In particular, nitrogen dioxide (NO2) is the gas considered as a reference in
the urban limit emissions, as well as PM 10 (particulate matters lower than 10 m).
For several years, the photocatalytic cementitious products have been widely used for
building applications all over the world in order to obtain depolluting actions.
Figure 1: Mechanism of photocatalytic degradation
10thInternationalConferenceonConcretePavements‐QuébecCity,Québec,Canada‐July8‐12,2012
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Materials applied for this purpose were previously developed and validated at
laboratory scale. However, for the first field applications the attempt to demonstrate
the in-situ performances was necessary by adopting dedicated experimental test
protocols and using specific analysis equipment. One of the first significant examples
represented by the European project PICADA (Photocatalytic Innovative Coverings
Applications for De-pollution Assessment), where an experimental activity for the
validation of the photocatalytic process by means of a street canyon was carried out
to evaluate the effects of wall surface-coated with a photocatalytic coating
(www.picada-project.com, 2011). In this project, the effect of photocatalytic
materials on air quality was demonstrated thanks to the correlation between in situ
results and the developed model (Plassais et al. 2007). After the PICADA project,
other in-situ monitoring campaigns were carried out in some experimental projects,
with positive results, such as:
‐ Borgo Palazzo street in Bergamo, Italy (a city road built with paving blocks)
(Guerrini 2009)
‐ Rue Jean Bleuzen in Vanves (Paris), France (concrete city road) (Gignoux, 2010)
‐ Umberto I city road tunnel in Rome, Italy (vault coated with a photocatalytic
paint) (Guerrini 2012)
A reliable estimation of photocatalytic surfaces produced with cement-based
materials, within the 2010 year is around 2.000.000 m2 (2,400,000 sq. yards).
Horizontal surface applications (paving blocks, industrial pavements, whitetopping,
etc.) comprise approximately 50% of the total. Most of projects were developed in
Europe, especially Italy, France, Belgium and Germany.
In this paper, the available applications of TiO2-based photocatalysis in the field of
road construction are briefly presented. Indeed, several kinds of photocatalytic
pavements have been developed in recent years for different performance and
architectural needs. Both laboratory and full-scale field experiments have been
conducted using materials with the proper amount of photocatalyst to guarantee the
best response in terms of environmental, mechanical, functional and economical
features. Some examples of photocatalytic solutions will be presented.
Further, some on-going research projects are presented hereafter.
Laboratory tests
The depollution effectiveness of photocatalytic materials is measured by means of a
NOx test equipment, able to reproduce plausible in-service conditions in terms of gas
concentration, gas flow rate in controlled conditions of UV light, temperature and air
humidity. Most tests are carried out in NOx flow-through conditions, conducted with
a fixed concentration of NOx (the NOx content is set to 0.55 ppm, of which 0.15 ppm
of NO2 and 0.4 ppm of nitrogen oxide - NO) in nitrogen, corresponding to a possible
atmospheric pollution (Italian standard UNI 11247-2010 “Determination of the
10thInternationalConferenceonConcretePavements‐QuébecCity,Québec,Canada‐July8‐12,2012
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degradation of nitrogen oxides in the air by inorganic photocatalytic materials:
continuous flow test method”). The result of the test can be expressed as the NOx
photocatalytic decomposition percentage of a sample under UV radiation. The
intrinsic photocatalytic activity and the degradation rate are also derived. The set-up
is showed in Figure 2.
Typical values of NOx abatement ranges between 10 and 30 gNOx/year/m2, so that
we can calculate a NOx removal of 10-30 kg/NOx/year for 1000 m2 of cement-based
pavement.
Another test can be used for the determination of the air-purification performance of
photocatalytic materials, according to the ISO 22197-1 standard.
It is also possible to carry out such tests on using manufacts (e.g. paving blocks) or
cores extracted from the pavements, in order to evaluate the in-service performances
of the structure (Guerrini 2009, Gignoux 2010). This approach is very useful for
determining the possible effect of dirt particles deposited on the surface, which can
influence the depolluting effect of the active surface (Guerrini 2009).
Field tests
On the laboratory promising findings, the effectiveness of the photocatalytic surface
layers has been evaluated on large scale, proving the ability of the photocatalytic
concrete to reduce NO and NO2 content in the air.
Measuring the effectiveness of photocatalytic surface in real conditions has been
carried out in several pilot projects. Data from these projects in Italy, beginning in
2002, yielded NOx reduction of approximately 60% compared to an asphalt surface
air NOx
control box
reactor
lamp
mixing
chamber NOx analyserpump
flowmeter
V1
V2 V3
mass flow
meters
air NOx
control box
reactor
lamp
mixing
chamber NOx analyserpump
flowmeter
V1
V2 V3
mass flow
meters
Figure 2: A schematic view of the “continuous flow” method (UNI 11247-2010)
10thInternationalConferenceonConcretePavements‐QuébecCity,Québec,Canada‐July8‐12,2012
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control (Plassais et al. 2007, Guerrini and Peccati 2007). After a series of positive
results, further in-field testing was discouraged by the complexity of the
measurements (due to the influence of local atmospheric conditions) and the costs for
monitoring.
Innovative photocatalytic cementitious road materials
Several types of cementitious road materials with photocatalytic properties were
developed and large laboratory and in-field campaigns were conducted to get a better
understanding of their effect on environment and surface and mechanical features.
Currently, there are several, possible solution for the construction of photocatalytic
roads and pavements, using cement-based materials (Figure 3):
1. Interlocking paving blocks for roads, parking areas, shopping areas, sidewalks,
crossroads, traffic calming zones and bike routes;
2. pre-cast or ready-mix concrete pavements.
Photocatalytic paving blocks. Concrete blocks found large applications, Figure 4.
They were demonstrated to give contribution to the air quality improvement in Japan,
Italy, France, Belgium and North America (Beeldens and Redant 2007, Poon and
Cheung 2007).
In this category of pavements can be also included other concrete manufacts, which
can be produced using photocatalytic cements: slabs, plates and curbs. They can be
white, grey, or colored.
Figure 3: Possible photocatalytic solutions for roads and pavements
10thInternationalConferenceonConcretePavements‐QuébecCity,Québec,Canada‐July8‐12,2012
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Figure 4: Two examples of paving blocks (left) and slabs (rights) applications.
These manufacts requires an adequate design approach in order to be applied for
roads, squares and parking lots where the service loads are relevant. If some problems
of deterioration can arise with a consequent production of dirt, the photocatalytic
performances are reduced (see below).
In a recent study, in order to perform a photocatalytic evaluation of some paving
blocks in a city street (Guerrini 2009), an original, experimental set-up for NOx
depollution tests was used, including a special reactor which could contain an entire
block, instead of a small specimen), Figure 5. This test can reproduce a typical
situation of a polluted street, in urban environment.
In these conditions, results – expressed as a NOx% abatement, after 60 min of light
irradiation – are absolutely relative and referred to the geometry of the blocks. The
values cannot be compared with those of standard tests.
- installed: blocks extracted and tested “as is” (dusty blocks)
- cleaned/washed: test repeated on the same blocks, cleaned, washed and dried
- warehouse: test on paving blocks available for substitution (stock)
Figure 5: A view of the developed testing equipment (NOx gas recirculation method)
10thInternationalConferenceonConcretePavements‐QuébecCity,Québec,Canada‐July8‐12,2012
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Figure 6: Test results for paving blocks (Guerrini 2009)
Dusty blocks were firstly tested in their “as-is condition” and showed a lower
depolluting activity, with respect to the “in-stock (warehouse) blocks” (15-16%),
Figure 6. They recovered the initial performances (corresponding to the reference
warehouse values) after a brushing, washing and drying treatment and a further NOx
test.
Small differences among some blocks performances can also be due to the presence
of other substances, which are hard to be removed (oil, grease, sticky materials…).
This presence could slightly reduce the active surface of the blocks (not observed on
the surface of the tested elements). So, the photocatalytic action is more evident,
when the street is clean.
Paving blocks and slabs have been the first, relevant application in terms of installed
surfaces (especially in Italy), due to their peculiarity (two layers of concrete, only the
top layer is photocatalytic, 6-10 mm). The cost of photocatalytic cement is not more
than 20% higher than conventional cement and the cost of installed photocatalytic
concrete is only 3-4% higher than conventional concrete (Data by Italcementi).
Durability of photocatalytic performances is the same of the manufact in itself, as the
photocatalyst is the whole top layer (Cassar 2004).
Slurry infiltrated in an asphalt pavement. Combining an open grade asphalt concrete
with a photocatalytic cementitious slurry, high performances road pavements can be
obtained (Guerrini and Grelaud 2009), Figure 7.
10thInternationalConferenceonConcretePavements‐QuébecCity,Québec,Canada‐July8‐12,2012
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Some experimental studies were conducted in the past, to evaluate the advantages of
both peculiar technology of bituminous asphalt combined with cement mortar or
slurry and photocatalytic technology (Crispino and Lambrugo 2007, Crispino and
Lambrugo 2008, Crispino et al. 2008).
Adopting this hybrid solution, it is possible to construct a concrete pavement without
joints, whose structural performances can be varied from high punching strength (for
industrial pavements) to semi-flexible performances (for roads). Void percentage can
be chosen in order to obtain the best performance in terms of elastic modulus and
tensile strength.
A surface post-treatment (rutting) is sometimes recommended in order to obtain
desired skid values.
This type of pavement is available in different colors, by adding inorganic pigment
into the slurry. Further architectural improvements can be obtained by using colored
aggregates.
Two experimental fields were completed in Italy in 2010 (Ancona and Carpiano-
Milan), for the performances evaluation of this solution for highways and roads,
Figure 8. Some projects have been already approved, in Italy.
Other Countries where this technology is widely adopted are France and Spain.
Ready-mix concrete. Ready mix concrete pavements have also been studied, with the
intent to optimize structural performance, architectural needs and photocatalytic
properties for the ideal cost/performances ratio.
Figure 7: Open-grade asphalt (left) and an example
of the pavement obtained (right).
10thInternationalConferenceonConcretePavements‐QuébecCity,Québec,Canada‐July8‐12,2012
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Figure 8: Field tests for highways (left) and roads (right).
In other words, it is absolutely not difficult to complete a photocatalytic concrete
pavement (by substituting the traditional Portland cement with the photocatalytic
cement) but the solution must be economically acceptable, without very high extra
prices per surface area.
In this sense, two-layers (thin whitetopping) or low thickness solutions seem to be
reasonable, considering their long-term durability.
A specific example of ultra-thin solution is represented by the industrial concrete
pavements that are completed with a thin layer (10-30 mm) of a abrasion-resistance
photocatalytic mortar, grey or colored, with a “fresh on fresh” method.
One-lift paving. The one-lift paving technology was successfully applied in the Rue
Jean Bleuzen – Porte de Vanves (Paris - France):
• Traffic: 13.000 cars/day.
• Geometry: length: 300 m (photocatalytic)
• Thickness of photocatalytic concrete: 120 mm
• Total photocatalytic surface: about 6000 m2 (64583 square feet)
• Upper surface: exposed aggregate concrete overlay (retarding admixture)
• Sidewalks: Photocatalytic precast paving flags and curbs
A periodical sampling of cores from the pavement was also done, for laboratory
testing. The core surfaces were contaminated with tires residue and consequently,
their photocatalytic activity was lower than that of the original material. The initial
values were obtained again after washing.
A NOx monitoring campaign was carried out by LROP (Western Paris Regional
Transport Research Laboratory), for one year (Gignoux L., 2010).
Two-lift paving. As part of the reconstruction of Route 141 in St. Louis between
Ladue Road and Olive Boulevard, the Missouri Department of Transportation
(MoDOT), in collaboration with the Federal Highway Administration, the National
10thInternationalConferenceonConcretePavements‐QuébecCity,Québec,Canada‐July8‐12,2012
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Concrete Pavement Technology Center at Iowa State University’s Institute for
Transportation, the Essroc Italcementi Group, and Lehigh Hanson, Inc., has started an
extensive research on the environmental benefits of using concrete made with an
innovative new cement product in the construction of highways.
In this project – which represents the first application of a photocatalytic concrete for
a road in U.S.A. – a monitoring campaign will be carried out to verify the efficiency
of two different solutions:
1) A photocatalytic concrete mainline pavement
2) A photocatalytic pervious concrete (see below) shoulder pavement
The mainline pavement material will be applied using a two-lift paving strategy,
which involves the placement of two wet-on-wet layers of concrete instead of a single,
homogeneous layer. The lower, base level layer is expected to be constructed with
less expensive materials (e.g., a low cementitious-material content base lift) which
will then be overlaid with a thinner top wearing-course of concrete containing
photocatalytic cement.
The shoulder pavement element of this research effort involves photocatalytic cement,
which will be used in a pervious (rather than conventional) concrete application.
Together, this set of innovative mainline and shoulder paving materials, including
both a two-lift photocatalytic mainline pavement and a photocatalytic pervious
shoulder pavement, are believed to represent one of the most technically advanced
and environmentally-friendly concrete pavement systems ever employed.
This project was officially presented in occasion of the national two-lift concrete
paving open house, hosted by the National Concrete Pavement Technology Center
(NCPTC) in Chesterfield, MO - USA (September 2010). This experimental road was
constructed in October 2011 (Figure 9) and the monitoring campaign will last for one
year, at least. Pervious shoulders will be constructed in May 2012.
Pervious concrete. Pervious concrete is a promising ‘green’ solution. Its mix design
must incorporate the correct blend of aggregate that allows adequate drainage of
recyclable rainwater.
From the photocatalytic point of view, this solution really offers high specific
surfaces and corresponding high depolluting performances. However, pervious
concrete does provide a lower compressive strength than that of conventional
concrete, so that its use can be limited for specific road and pavement applications.
Other sustainable projects for road applications.
A photocatalytic wooden concrete was applied to a section of noise barriers along
Highway 401, near the Highway 404 Interchange in Toronto, starting in the summer
of 2011. For this study (which includes an air quality monitoring campaign over the
course of one year), the Ontario Ministry of Transportation (MTO) is partnering with
the Ministry of Environment, the University of Toronto, Armtec (a noise barrier
manufacturer), and Essroc Italcementi Group, Figure 10 (http://
www.dcnonl.com/article/id48919).
10thInternationalConferenceonConcretePavements‐QuébecCity,Québec,Canada‐July8‐12,2012
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In the framework of Life+ European project “Photopaq”, an experimental campaign
was carried out in the “Leopold II” tunnel in Brussels (Belgium). For this test, a
photocatalytic skim coat was applied on a partial section of the tunnel (about 100m)
as well as a dedicated UV lighting system for activating the photocatalytic effect
(photopaq.ircelyon.univ-lyon1.fr 2011).
Figure 9: Two-lift photocatalytic concrete paving, in Chesterfield, MO (October
2011)
Figure 10: Photocatalytic concrete walls in Toronto (October 2011)
A wide utilization of coatings and paints possessing depolluting properties seems to
be particularly interesting for urban contexts, especially in case of their utilization
close to busy roads and highways.
Conclusions
The experimental analysis carried out demonstrated that photocatalytic road materials
could affect significantly air quality, reducing pollutant concentrations, through the
10thInternationalConferenceonConcretePavements‐QuébecCity,Québec,Canada‐July8‐12,2012
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beneficial presence of adequate photocatalysts. The large amount of measurements of
nitrogen oxides abatements in laboratory as well as in situ, reported in this paper,
have widely proved the enhancement of these kind of innovative materials and have
created a linkage between results obtained in the two different contexts.
Concrete solutions here described seem to be very promising for the implementation
of photocatalytic solutions. Paving blocks are already widely utilized; slurry-
infiltrated open-grade asphalts, ultra-thin whitetopping and pervious concrete have a
reliable quality but further experimental trials are needed to confirm their cost
effectiveness.
References
Beldeens, A., Redant, K. (2006). “Air purification and self-cleaning materials:
photocatalytic pavement blocks on the “Leien” of Antwerp”. Proc. 10th International
Symposium on Concrete Roads, Brussels, 2006
Cassar, L., Beeldens, A., Pimpinelli, N., Guerrini, G.L. (2007). “Photocatalysis of
cementitious materials”, RILEM Int. Symposium on “Photocatalysis, Environment
and Construction Materials, (Florence/Italy, 8-9 October 2007), RILEM PRO 55,
pp.131-145 .
Crispino, M., Lambrugo, S. (2007a). An experimental characterization of a
photocatalytic mortar for road bituminous pavements. Proc. International RILEM
Symposium on Photocatalysis, Environment and Construction materials.
Crispino, M., Lambrugo, S. (2007b). “Surface characteristics and environmental
performance of a photocatalytic innovative pavement”. Proc. RSS Road and Safety
Simulation.
Crispino, M., Lambrugo, S. (2008). Effectiveness of a photocatalytic wearing course
through experimental analysis. Proc. ISAP.
Crispino, M., Lambrugo, S., Bacchi, M. (2008). Photocatalytic road pavements: an
analysis of structural and functional performances. Proc. 4th International Gulf
Conference on Roads.
Fujishima, A., Hashimoto, K., Watanabe, T. (1999). TiO2 Photocatalysts:
Fundamentals and its Applications. BKC Inc.
Gignoux L. (2010), “Concrete roadways and air quality - Assesment of trials in
Vanves in the heart of the Paris region”, 11th International Symposium on Concrete
Roads, 13 - 15 October 2010, Seville (Spain)
10thInternationalConferenceonConcretePavements‐QuébecCity,Québec,Canada‐July8‐12,2012
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Guerrini, G.L. and Peccati, E. (2007), “Photocatalytic cementitious roads for de-
pollution”, RILEM Int. Symposium on “Photocatalysis, Environment and
Construction Materials, (Florence/Italy, 8-9 October 2007), RILEM PRO 55, pp.179-
186 .
Guerrini G.L. (2009), “Some observations regarding in-service performances.
Photocatalytic paving block surfaces”, BFT 05/2009, pp. 16-25
Guerrini, G.L., (2010), “Photocatalytic cement-based materials - Situation, challenges
and perspectives”, World Cement (www.worldcement.com), April 2010, 4 pages.
Guerrini, G. L. (2012), “Photocatalytic performances in a city tunnel in Rome”. J.
Construction and Building Materials, vol. 27 issue 1 February, 2012. pp. 165-175
Guerrini G.L., Grelaud J.P. (2009), “Paving with a pollution-abating activity and a
photocatalytic mixture for its preparation”, Patent application, WO/2009/133094.
ISO 22197-1:2007 - Fine ceramics (advanced ceramics, advanced technical ceramics)
-- Test method for air-purification performance of semiconducting photocatalytic
materials -- Part 1: Removal of nitric oxide
Photopaq.ircelyon.univ-lyon1.fr, (May 2, 2012)
Plassais, A., Rosseau, F., Eriksson, E., Guillot, L. (2007). “Photocatalytic coverings
assessment: from canyon street measurements to 3-D modelling”. International
RILEM Symposium on Photocatalysis, Environment and Construction materials,
Florence, ITALY, October 8-9, 2007.
Poon, C.S., Cheung, E. (2007). NO removal efficiency of photocatalytic paving
blocks prepared with recycled materials. J. Construction & Building Materials.
Strini, A., Cassese, S. and Schiavi, L. (2005), 'Measurement of benzene, toluene,
ethylbenzene, and o-xylene gas phase photodegradation by titanium dioxide dispersed
in cementitious materials using a mixed flow reactor', Applied Catalysis b 61 (2005)
90-97.
UNI 11247-2010 “Determination of the degradation of nitrogen oxides in the air by
inorganic photocatalytic materials: continuous flow test method” (in Italian)
www.dcnonl.com/article/id48919, February 23, 2012 (May 2, 2012)
www.picada-project.com (May 2, 2012).
