Bacteria for Concrete Surface Treatment - Biotechnologies and Biomimetics for Civil Engineering - page 329

phenomenon in concrete structures due to various natural or human activities,
execrably affects concrete structural properties, increases permeability, and sub-
stantially reduces the durability of concrete structures ingress of detrimental
components in moist environments. Once microcracks form a continuous network,
they may provide an easy path for the transport of potentially contain detrimental
substances and substantially contribute to the permeability of cementitious mate-
rials, thereby reducing the resistance against attack of detrimental substances. If
microcracks grow further and reach the reinforcement, not only the concrete itself
may be attacked, but also the reinforcement will be corroded when it is exposed to
water and oxygen, and possibly carbon dioxide and chlorides. Microcracks may
reduce or impair the durability of concrete structures and are therefore precursors
to structural failure. Some important measures were taken to diminish the per-
meability of detrimental components or to slow down or even to eliminate con-
crete degradation. Many of techniques are available but traditional repair systems
have a number of disadvantageous aspects such as different thermal expansion
coefficient compared to concrete and environmental and health hazards and so on.
Biodeposition plays an important role in limiting the infiltration of detrimental
components into concrete and lead to the exploration of remediation technique in
the field of cementitious materials (Peihao et al. 2012). Cracks were plugged and
healed with a mixture of bacteria, nutrients, and a filler material. Among the
different materials that were mixed with S. pasteurii, the silica fume and sand
mixture lead to the highest compressive strength and lowest permeability. Dif-
ferent bacteria have been used to increase the compressive strength of cement
mortar and for the remediation of cracks in concrete. Ghosh et al. ( 2005 ) dem-
onstrated the positive effect of the addition of Shewanella on the compressive
strength of mortar specimens. An increase of 25 % of the 28 days compressive
strength was obtained for a cell concentration of about 105 cellsmL -1 . Microbial
cells also prevent ingress of water effectively in different concentrations of fly ash-
amended concrete. It is therefore more advisable and economical to restrict the
development of early age small cracks the moment they appear, than to repair
them after they have developed to large cracks.
The use of a microbial mineral plugging system based on the deposition of
carbonates was suggested (Ferris and Stehmeier 1992 ; Zhong and Islam 1995 ).
While initial research on biodeposition in sand columns was mainly focused on the
decrease in porosity and permeability as a result of the physical presence of the
newly formed carbonates (Ferris and Stehmeier 1992 ), subsequently investigations
focus on the improvement of strength as a result of the cementation of sand
particles due to the particle binding properties of the bacterially deposition car-
bonates (Kucharski et al. 2006 ). The hydrolysis of urea was selected as a very
suitable pathway for the production of carbonate ions due to its ability to alkalinize
the environment. Furthermore, urea is an important organic nitrogen carrier in
natural environments and is commonly used as an agricultural fertilizer (Nielsen
et al. 1998 ). Furthermore, the ability to hydrolyze urea is widely distributed among
indigenous bacteria in soils and groundwater systems (Fujita et al. 2000 ). Urea-
utilizing bacteria such as Sporosarcina pasteurii and Sporosarcina ureae are