Bacteria for Concrete Surface Treatment - Biotechnologies and Biomimetics for Civil Engineering - page 334

15.3.2 Influence on CO 2 ,Cl 2 ,H 2 O Penetrativity of Concrete
by Biodeposition
An important measure to protect concrete against damage is diminishing penetr-
ativity. Surface treatments play an important role in limiting the infiltration of
water and consequently of detrimental components into concrete. In the market,
lots of organic and inorganic products are available for surface protection of
concrete, such as a variety of coatings, water repellents, and pores blockers.
Penetrativity controls the ingress of moisture, ionic and gaseous species into
concrete; accordingly, the durability of concrete depends on the permeation
properties of concrete surface. As the permeation of concrete decreases, its
durability performance resisting physicochemical corrosion increases. Nowadays a
broad range of organic and inorganic products is applied to the protection of
concrete surfaces, such as a variety of coatings, water repellents, and pore
blockers. These conventional surface treatments show, however, beside their pro
influences also a number of disadvantageous aspects, e.g., different thermal
expansion coefficient of the treated layers, degradation over time and the need for
constant maintenance, and environmental pollution. There are some conventional
techniques available to improve impermeability to enhance the durability of
building materials. Chemical admixtures such as plasticizers, superplasticisers, and
water reducing agents help to improve the workability by reducing the inter-
granular friction ultimately affecting the porosity and distribution of pores.
However, these conventional methods of protection have a number of disadvan-
tages, such as (1) an incompatibility of the protective layer and the underlying
layer due to differences in their thermal expansion coefficient; (2) disintegration of
the protective layer over time; and (3) a need for constant maintenance by a
treatment that is reversible and repeatable. Such chemical treatments commonly
result in the formation of incompatible and often harmful surface films. Addi-
tionally, because large quantities of chemical solvents are used, they contribute to
pollution (Camaiti et al. 1988 ; Rodriguez-Navarro et al. 2003 ) and also such
techniques are not long lasting.
Shortcomings have drawn the attention to alternative techniques to reduce
permeation properties for the improvement of the durability of concrete. Tiano
( 1995 ) proposed the use of organic matrix macromolecules extracted from Mytilus
californianus shells to induce the deposition of calcium carbonate within the pores
of the stone. The organic matrix was shown to produce a more relevant and
durable carbonate deposition compared to the single use of calcium chloride or
hydroxide. This deposition resulted in a slight decrease in porosity and water
absorption by capillarity. Tiano et al. ( 1999 ) also observed a reduction of about
60 % from the limestone samples treated with biodeposition. Le Metayer-Levrel
et al. ( 1999 ) studied the bacterial carbonatogenesis for the protection and regen-
eration of limestone in buildings, monuments, and statues. The biodeposition of
protective surface on the stone was confirmed to reduce its permeability for gas
without affecting its esthetic appearance. They further state that biodeposition