Algae on building materials
Building façades, designed by an architect to be yellow, red, white or any
other colour often become green due to algal growth. Such bio-colonisation
does not only cause esthetic damage, but may also result in deterioration
of building materials in the long term, damaging the façade, with evident
economical losses. An apparent increase of algal growth on building
façades is currently observed in the Netherlands, even within a short period
of time after construction. Rain, temperature, air pollution, materials, and
the design, construction and maintenance of buildings are key factors
controlling bio-colonisation. On the other hand, cleaning of façades may
also cause unexpected green coloration of the surface. Therefore, understanding of algal growth on building materials is an important issue to
extend the durability of buildings and constructions.
Algal growth: a green
TNO provides profound
growth and offers innov
Algae
Algae are simple plant-like organisms. They are usually green, but
their colour may vary from orange or red to black. As for every form
of life, water is an essential component for the growth of algae, even
though they can survive long dry periods. Algae can grow on any
kind of material – from stones, bricks and plasters to rubbers, metals
and glass – providing that there is enough light, nutrients and carbon
dioxide. The optimal growth temperature for most species is in the
range of 15 to 30°C. Algae prefer a rather alkaline environment and,
in practice, only a very high alkalinity, such as that of fresh concrete,
precludes their development.
Algal resistance of building materials
To resolve the problems related to esthetic damage and material
degradation due to algae and other micro-organisms, i.e. bio-deterioration, understanding of the processes causing this damage is crucial.
TNO has elaborate experience in studies on the effect of material
properties, material interaction, prevention and potential side effects
of surface treatments (e.g. acid cleaning) on algal growth.
To asses the different parameters affecting
algal growth, TNO has dedicated laboratory
facilities. To test bio-receptivity of building
materials with respect to algae, TNO uses the
following standardised procedures:
challenge asking for a "green" answer.
knowledge of the physical and chemical conditions affecting algal
vative technology solutions.
ganic material that can absorb water up to 400% of its own volume.
Regular and systematic observations of the samples under treatment
provide indications on the algal growth.
Vermiculite bed method
In this method, samples are kept at constant
moisture conditions in a water-saturated vermiculite bed, as recommended by the
International Bio-deterioration Research
Group (IBRG). Samples are inoculated with
five algae species, which are considered characteristic for developing green coloration of
materials. Subsequently, they are incubated
in glass containers. Vermiculite is an inor-
TNO standard method
TNO has developed a test method to determine the material
susceptibility for algae under varying environmental conditions. In
this method, natural weathering of a material is accelerated. The
algal growth on test samples which were exposed to both algae and
acid-rain, is monitored. For this purpose, test samples are stored
under controlled ambient conditions in a specially designed
experimental set-up, which periodically sprays the test material with
acid rain. The periodicity of the rain simulates real ambient conditions,
whilst the acidity accelerates the natural neutralisation process of
the material’s alkalinity (which normally would take place over a
period of several years). Any preliminary results obtained in the laboratory can be verified in practice. By means of systematic observations of the test samples and statistical treatment of the collected
data, it is possible to simulate and evaluate the durability of the
material. The major advantage of this method compared to the
vermiculite method is that it resembles reality much better, because
of the wet and dry cycles and the use of artificial acid rain.
Building and Construction
Towards product innovation
Reduced resource consumption together with an improved product
performance is increasingly critical for industrial competitiveness and
sustainable development. Stricter environmental legislation is pushing materials innovation to decrease environmental impact even
more. Research and development should focus on smart materials
that release active components (such as biocides) on demand, in order
to prevent biological growth. The experience and knowledge within
TNO of the interaction of algae and building materials, and experience with respect to smart materials is crucial for further product
innovation.
What we can do for you
Our group focuses on building materials and is situated within TNO
Built Environment and Geosciences. We actively work on improving
the durability and sustainability of materials for construction. To
achieve this, we closely cooperate with universities, other research
institutes and industry, generating knowledge and providing solutions to industry and society.
The innovative partner of authorities and the
business community for the sustainable
organisation, use and management of the
built environment, infrastructure and subsoil.
Van Mourik Broekmanweg 6
P.O. Box 49
2600 AA Delft
The Netherlands
T +31 15 276 32 00
F +31 15 276 30 18
tno.nl
[email protected]
Contact person:
Dr. S.J.F. (Bart) Erich MSc
T 31 15 276 32 91
E [email protected]