Investigation Into
Marine Concrete
Anti-Fouling Coatings
Peter Hughes, Contributing Writer
Our civil engineers involved in the construction or maintenance of marine concrete structures are faced with the problem of preventing unwelcome microbial
growth in an environmentally friendly way. A long term ecologically sound answer to organic growth remains unsolved,
however the use of titanium dioxide (TiO2) particles within
coatings for concrete pavements have received considerable attention in recent years as these particles can trap and decompose organic and inorganic air pollutants by a photocatalytic
process (1). In spite of these promising benefits, the durability
and resistance to wear of TiO2 surface coatings upon fibre reinforced marine concrete has not been evaluated. In this article,
the development of fundamental research on the application of
TiO2-based photocatalysis in a marine environment will be introduced. The problems encountered at a UK study site restricting a larger scale application of the technology are discussed.
Photocatalytic coatings are successfully used with many
other building materials and have been shown to retard algal
growth on concrete (2). In spite of these promising benefits,
applications of this technology are currently limited. The du-
rability of this technology in a marine application needs to be
established before large-scale practical implementation is under-
taken. Titanium dioxide (TiO2) is a white inorganic substance
that is thermally stable, non-flammable and insoluble. TiO2, the
oxide of the metal titanium, which is the ninth most abundant
element in the earth’s crust, occurs in many rocks and mineral
sands, the most economically important being ilmenite and ru-
tile deposits. Ultra-fine (nano-scale) titanium dioxide (Anatase)
was used in this research for surface treatments. The potential
of titanium dioxide as a photocatalyst was discovered by ( 3).
This process, which is similar to plant photosynthesis, allows
the decomposition of water into oxygen and hydrogen in the
presence of light, by means of a TiO2-anode (1). Based on this
heterogeneous photocatalytic oxidation process, nitrogen ox-
ides are oxidized into water-soluble nitrates while sulfur dioxide
is oxidized into water-soluble sulfates; these substances can be
washed away by moisture in the form of rainfall or seawater.
The overall aim of this research, is to advance the understanding
of how a photocatalytic (TiO2) coatings responds in a marine
environment. This phase of work, carried out in the northwest
of England, has recorded anti-fouling performance and intends
to progress towards a non-toxic, environmentally-benign strat-
egy for future industrial applications.
The ‘Development’ Tio2 Coating Used In This Research
Primary particles of ultrafine TiO2 within the development coating used was typically in the range of size from 10 to 60 nm,
not only as existing discreet primary particles but as aggregates,
with secondary particle sizes typically >100 nm. The coating
was a stable aqueous dispersion (sol) of ultrafine TiO2 particles.
Key features included an anatase crystal form with a 10 wt% of
TiO2 content. The coating had a neutral pH of 8. 5, with a high
surface area (dry) of 300 m²/g, it dried clear, and was UV light
activated with limited fluorescent light activity. It is marketed
for architectural applications.
Tio2 Coating Application In This Study
The coating procedure consisted of three independently applied
layers brushed (concrete tiles) or roller applied (static site) onto
the surface of concrete specimens, as per the manufacturer’s recommendation. The primer layer was applied to lower the viscosity of the material. This assisted in generating a good seal in the
priming process through the filling of cracks and blowholes in
the concrete surface. The primer formed a coating layer with
a dry film thickness of 10µm. On top of the dried primer, an
40 | Coatings World
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April 2013
