ORIGINAL ARTICLE
Accelerated testing of biological stain growth on external
concrete walls. Part 2: Quantification of growths
Gilles Escadeillas Æ Alexandra Bertron Æ
Erick Ringot Æ Philippe J. Blanc Æ Arnaud Dubosc
Received: 20 April 2007 / Accepted: 30 September 2008 / Published online: 8 October 2008
Ó RILEM 2008
Abstract Aesthetics of external concrete walls can
be altered in various constructions by fast developing
algae and it is useful to propose technical solutions to
prevent this problem. Laboratory tests are thus neces-
sary, on the one hand to accelerate the growth of algae
on concrete and, on the other, to quantify such
growths. The first part of this article was dedicated to
the description of two growth tests. This second part
presents the advantages and drawbacks of three
complementary techniques used to analyze the colo-
nized areas. Two methods are non-destructive and
estimate either the area covered, using image analysis,
or the density of algae, which directly influences the
stain intensity, by spectrophotometry. The third
method is destructive and is based on the measurement
of chlorophyll a. It is used to obtain information on the
state of vitality of the algae on the colonized surface.
Keywords Concrete Á Algae Á Biological stain Á
Laboratory tests
1 Introduction
The fast development of visible biological stains
corresponding to the growth of micro-organisms (and
first algae) affects buildings all over the world, in
both polluted and unpolluted zones. Unfortunately,
concrete is not exempt from this organic prolifera-
tion. Although its high initial pH prevents any
colonization by algae during the first few months,
the reduction linked with its natural carbonation
allows it to be colonized after some time.
The consequences are essentially of an esthetic
nature but more or less serious damage of the
material support can be also observed [1–4]. From
the aesthetics point of view, stains are of various
colors (typically black, green, red) and can extend all
over the building surface [5]. It generally takes them
at least 1 year to appear on walls but, when
conditions are favorable to growth, the development
can be spectacular [6].
To guarantee the esthetic quality of buildings, it is
necessary to identify the most important parameters
of concrete (composition, porosity, roughness…)
which influence the growth of stains and, more
particularly, the growth of algae. The first step was to
develop laboratory accelerated growth tests [7]. The
second step was to propose technical methods to
characterize colonized areas. These techniques,
intended to quantify algal growth on specimens in
the laboratory (area covered, intensity of growth and
state of vitality of the algae) are complementary to
G. Escadeillas Á A. Bertron (&) Á E. Ringot Á A. Dubosc
Laboratoire Mate
´
riaux et Durabilite
´
des Constructions
(LMDC), UPS, INSA, Universite
´
de Toulouse, 135,
Avenue de Rangueil, 31 077 Toulouse Cedex 04, France
e-mail: bertron@insa-toulouse.fr
P. J. Blanc
Laboratoire d’Inge
´
nierie des Syste
`
mes Biologiques et des
Proce
´
de
´
s (LISBP), INSA, CNRS, UMR 5504, Universite
´
de Toulouse, 135, Avenue de Rangueil,
31 077 Toulouse Cedex 04, France
Materials and Structures (2009) 42:937–945
DOI 10.1617/s11527-008-9433-3