can facilitate the actual development of products for real commercial applications.
One such kind of interesting study has been reported by Wiktor and Jonkers
[174]. This on-site application study of microbial-based crack-fixing was done
using two solutions, A and B. Solution A contains alkaliphilic bacteria, sodiumsilicate (alkaline buffer), and sodium-gluconate (carbon source for bacteria growth),
and solution B contains alkaliphilic bacteria and calcium nitrate. The use of these
two solutions is believed to make the preparation work both in the presence and
absence of oxygen. That means the crack surface can possibly be filled by the
aerobic denitrification, while the anaerobic denitrification process seals the deep
part of the crack with little or no oxygen. Sodium silicate maintains an alkaline
condition in the system and forms a gel when it is injected or sprayed to the crack.
The formation of the gel allows a rapid sealing of the crack (within a few hours) and
creates conducive environment for the microbe to accumulate calcite. The formation
of the gel gives enough time for the precipitation of a substantial amount of CaCO 3
to seal the crack. Considering that one of the limitations of the microbial-based repair
systems is its slow performance, the gel formation can offer a rapid plugging effect
even though it is temporary. The authors successfully used their preparation to treat
damaged ramp of parking garages by spraying the repair solution directly to the
cracked concrete, which is an attractive method of application from technical as well
as economic point of view. The water permeability and freeze-thaw resistance tests
were used to assess the crack-sealing efficiency and improvement of frost salt
scaling, respectively. The use of this system successfully sealed the cracks and
stopped the leaking. In addition, the treatment of the concrete with the repair system
significantly improved the freeze/thaw resistance of concrete.
An additional field trial worth to mention is the study made on 16 m
2 wall which
is divided into two [175]. Part of the concrete cover was removed, and the reinforcement bars were exposed. One part of this wall was treated with concrete
containing bioagent, while the other half was repaired without bioagent. The main
interest in this study was to observe the effect of adding the bioagent on application
(spraying), consistency, and appearance of the concrete. The outcome of this study
shows there is no major difference in the application and consistency of the microbe
containing and the microbe free concrete preparation. Brownish spots on bacterialbased preparation were observed which the authors claim that it faded with time.
Results generated from numerous studies undeniably indicated that the use of
microbial-based CaCO 3 precipitation system with suitable filling materials has a
promising potential to be used for manual repair of already existing cracks. However, there is a need for optimization of the repairing agent composition (bacterial
load, calcium source concentration, the bacterial nutrient concentration, the ratio
between filling materials and the bioactive agents, etc.) to get an effective calcite
precipitation throughout the filling material and greatly enhance the repairing efficiency. Moreover, it is necessary to consider during screening if the repair agent
bonds to the crack walls. If the bonding between the cracked surface and the repair
agent is good, the cracks not only seal but also heal, and that is the grand objective of
repairing concrete cracks. It is also necessary to consider that the whiteness of the
calcite may not redeem aesthetically, and hence it will be rewarding to develop a
coloring means to adjust the color to the desired appearance.
310
G. Mamo and B. Mattiasson
One such kind of interesting study has been reported by Wiktor and Jonkers
[174]. This on-site application study of microbial-based crack-fixing was done
using two solutions, A and B. Solution A contains alkaliphilic bacteria, sodiumsilicate (alkaline buffer), and sodium-gluconate (carbon source for bacteria growth),
and solution B contains alkaliphilic bacteria and calcium nitrate. The use of these
two solutions is believed to make the preparation work both in the presence and
absence of oxygen. That means the crack surface can possibly be filled by the
aerobic denitrification, while the anaerobic denitrification process seals the deep
part of the crack with little or no oxygen. Sodium silicate maintains an alkaline
condition in the system and forms a gel when it is injected or sprayed to the crack.
The formation of the gel allows a rapid sealing of the crack (within a few hours) and
creates conducive environment for the microbe to accumulate calcite. The formation
of the gel gives enough time for the precipitation of a substantial amount of CaCO 3
to seal the crack. Considering that one of the limitations of the microbial-based repair
systems is its slow performance, the gel formation can offer a rapid plugging effect
even though it is temporary. The authors successfully used their preparation to treat
damaged ramp of parking garages by spraying the repair solution directly to the
cracked concrete, which is an attractive method of application from technical as well
as economic point of view. The water permeability and freeze-thaw resistance tests
were used to assess the crack-sealing efficiency and improvement of frost salt
scaling, respectively. The use of this system successfully sealed the cracks and
stopped the leaking. In addition, the treatment of the concrete with the repair system
significantly improved the freeze/thaw resistance of concrete.
An additional field trial worth to mention is the study made on 16 m
2 wall which
is divided into two [175]. Part of the concrete cover was removed, and the reinforcement bars were exposed. One part of this wall was treated with concrete
containing bioagent, while the other half was repaired without bioagent. The main
interest in this study was to observe the effect of adding the bioagent on application
(spraying), consistency, and appearance of the concrete. The outcome of this study
shows there is no major difference in the application and consistency of the microbe
containing and the microbe free concrete preparation. Brownish spots on bacterialbased preparation were observed which the authors claim that it faded with time.
Results generated from numerous studies undeniably indicated that the use of
microbial-based CaCO 3 precipitation system with suitable filling materials has a
promising potential to be used for manual repair of already existing cracks. However, there is a need for optimization of the repairing agent composition (bacterial
load, calcium source concentration, the bacterial nutrient concentration, the ratio
between filling materials and the bioactive agents, etc.) to get an effective calcite
precipitation throughout the filling material and greatly enhance the repairing efficiency. Moreover, it is necessary to consider during screening if the repair agent
bonds to the crack walls. If the bonding between the cracked surface and the repair
agent is good, the cracks not only seal but also heal, and that is the grand objective of
repairing concrete cracks. It is also necessary to consider that the whiteness of the
calcite may not redeem aesthetically, and hence it will be rewarding to develop a
coloring means to adjust the color to the desired appearance.
310
G. Mamo and B. Mattiasson