Environmental Engineering Reference
In-Depth Information
results in accelerated deterioration of the structure (Neville
1995
). The solution
to prevent corrosion of such structure can be achieved by sealing the paths of ingress
to improve the life of the reinforced concrete (RC) structures.
As MICP promises to alleviate permeability and transport of pollutants inside
concrete, it can be effective in reducing corrosion in RC by making protective layer
or carbonate followed by calcite precipitation. However, there is scarce research on
the role of MICP in corrosion prevention of RC structure. Such research was mainly
reported by Achal et al. (
2012b
) where they performed detailed investigation
leading to positive impact of MICP in the RC corrosion prevention.
To determine the effect of MICP, Achal et al. (
2012b
) prepared the RC spec-
imens with bacterial cells (Bacillus sp. CT-5) and induced corrosion by applying a
constant anodic potential of 40 V for 7 days. There was visible calcite precipita-
tion on bacterially treated RC specimens. After 7 days of accelerated corrosion,
numerous (at least seven) cracks with widths nearly 0.2 mm (0.008 in.) were
observed on control specimens with one longitudinal localized crack of width
0.3 mm within 36 h, whereas in bacterially treated samples, a crack of that width
appeared not before 168 h. The control specimens had significantly higher Icorr
(60.83 mA/m
2
[39.25 mA/in.
2
]) compared to MICP samples (14.78 mA/m
2
[9.53 mA/in.
2
]) in nutrient and 20.03 mA/m
2
(12.92 mA/in.
2
) in CSL media. An
approximate four-fold reduction in Icorr by Bacillus sp. CT-5 suggests that the
calcite precipitation has the effect of greatly reducing corrosion. Achal et al.
(
2012b
) concluded that the formation of calcite might facilitate the protective
passive film around the steel and act as a corrosion inhibitor by interrupting the
transport process in such samples. Further, they also found that pullout strength
was enhanced and mass loss of the reinforcing bar was reduced due to MICP.
Based on calcium carbonate induced by B. pasteurii, Qian et al. (
2010a
) showed
improvement in the surface impermeability of cement mortars, resulted in resis-
tance to the acid (pH [ 1.5). They concluded MICP ability in the prevention of
corrosion of building materials and structures. The results of various researchers
on microbial concrete with their target materials have been summarized in
Table
14.1
.
14.5 Cost Analysis of Microbial Concrete?
As microbial concrete is novel product, which can be used to enhance the dura-
bility of building structures, many researchers or engineers doubt on its production
cost. The costs of microbial concrete depend very much on the price of bacteria
and nutrients. Further, the price of bacteria varies country to country; however, one
standard bacterial strain, if bought from ATCC, costs US $500, and from MTCC,
costs US $10, while CGMCC sells at US $200. De Muynck et al. (
2010
) reported
the cost analysis of microbial concrete based on personal communication by an
employee of the Belgian company FTB remmers 2008;
http://www.ftbremmers.
com/
). The price of 1 kg lyophilized bacteria is about US $1,500 (1,100 €) and
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