microbially driven CaCO 3 crystallization processes [133, 223, 241, 257]. However,
formation of other crystal forms has also been noted. For instance, Rivadeneyra et al.
[110] reported that Deleya halophila predominantly produce aragonite. In the case of
Proteus mirabilis, the CaCO 3 produced is complex and has even an unusual
morphology, vaterite hollow spheres [89]. This type of strain-based variation
could be due to the difference in the nature of the extracellular polymeric substances
(EPS) which dictates the formation of specific CaCO 3 crystal [105, 258] through
peculiar Ca
2+ -binding pattern that promotes the crystal formation [239]. Medium
composition, calcium source, and the crystallizing conditions have also a profound
impact on CaCO 3 crystal morphology [71, 239, 259, 260]. For instance, the type of
crystal biodeposited by a Myxococcus strain can be vaterite or calcite depending on
the composition of the medium [67, 261] , which can possibly affect the nature of the
EPS among other things. Calcium chloride characteristically induces formation of
calcite [236, 262, 263]. On the other hand, calcium acetate induces a lettuce/lamellar
shape crystal of vaterite, while calcium lactate and calcium gluconate result in a
more complex form, a spherical-shape vaterite [264]. This possibly indicates that the
microbes do not genetically or directly determine which crystal form to precipitate.
5 Conclusion
Construction is one of the biggest pillars of the world economy, and in the year 2020,
the value of the global construction output is forecasted to reach about $10 trillion
and projected to grow to $15.5 trillion by 2030. Concrete, being one of the most vital
construction materials, has been in use for nearly two millennia and probably will
remain as the dominant construction material in the foreseeable future. Thus, its role
in the world economy is very prestigious. However, this remarkable construction
material is prone to crack formation, which if not repaired will lead to deterioration
and collapse of the structure. The world spends billions of dollars to protect and
repair existing concrete structures. A variety of chemicals such as concrete admixtures, concrete adhesives, concrete sealants, and protective coatings are available in
the market. Although these chemicals are used to repair and enhance the durability of
concrete structures, it suffers from limitations. On the other hand, the use of
biological means to improve the durability of concrete seems to have some advantages over the chemical-based approach. It is safe; the healing quality is remarkable,
sustainable, and greener. Since the concrete industry has a negative image due to its
high CO 2 footprint, consumption of resources, and generation of waste, the use of
greener biological processes to improve concrete properties may also contribute to
change the public opinion.
The last decade witnessed a tremendously growing interest in developing biologically based concrete: crack repair, self-healing, and protective coatings. Almost
all the studies made in this regard focused on microbially induced calcite precipitation. The results of the laboratory scale studies made so far show promising results.
The general trend indicates that the microbial-based system, as measured by the
strength gain, reinforcement corrosion resistance, reduced water permeability, and
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G. Mamo and B. Mattiasson
formation of other crystal forms has also been noted. For instance, Rivadeneyra et al.
[110] reported that Deleya halophila predominantly produce aragonite. In the case of
Proteus mirabilis, the CaCO 3 produced is complex and has even an unusual
morphology, vaterite hollow spheres [89]. This type of strain-based variation
could be due to the difference in the nature of the extracellular polymeric substances
(EPS) which dictates the formation of specific CaCO 3 crystal [105, 258] through
peculiar Ca
2+ -binding pattern that promotes the crystal formation [239]. Medium
composition, calcium source, and the crystallizing conditions have also a profound
impact on CaCO 3 crystal morphology [71, 239, 259, 260]. For instance, the type of
crystal biodeposited by a Myxococcus strain can be vaterite or calcite depending on
the composition of the medium [67, 261] , which can possibly affect the nature of the
EPS among other things. Calcium chloride characteristically induces formation of
calcite [236, 262, 263]. On the other hand, calcium acetate induces a lettuce/lamellar
shape crystal of vaterite, while calcium lactate and calcium gluconate result in a
more complex form, a spherical-shape vaterite [264]. This possibly indicates that the
microbes do not genetically or directly determine which crystal form to precipitate.
5 Conclusion
Construction is one of the biggest pillars of the world economy, and in the year 2020,
the value of the global construction output is forecasted to reach about $10 trillion
and projected to grow to $15.5 trillion by 2030. Concrete, being one of the most vital
construction materials, has been in use for nearly two millennia and probably will
remain as the dominant construction material in the foreseeable future. Thus, its role
in the world economy is very prestigious. However, this remarkable construction
material is prone to crack formation, which if not repaired will lead to deterioration
and collapse of the structure. The world spends billions of dollars to protect and
repair existing concrete structures. A variety of chemicals such as concrete admixtures, concrete adhesives, concrete sealants, and protective coatings are available in
the market. Although these chemicals are used to repair and enhance the durability of
concrete structures, it suffers from limitations. On the other hand, the use of
biological means to improve the durability of concrete seems to have some advantages over the chemical-based approach. It is safe; the healing quality is remarkable,
sustainable, and greener. Since the concrete industry has a negative image due to its
high CO 2 footprint, consumption of resources, and generation of waste, the use of
greener biological processes to improve concrete properties may also contribute to
change the public opinion.
The last decade witnessed a tremendously growing interest in developing biologically based concrete: crack repair, self-healing, and protective coatings. Almost
all the studies made in this regard focused on microbially induced calcite precipitation. The results of the laboratory scale studies made so far show promising results.
The general trend indicates that the microbial-based system, as measured by the
strength gain, reinforcement corrosion resistance, reduced water permeability, and
328
G. Mamo and B. Mattiasson