Environmental Engineering Reference
In-Depth Information
culture medium consisting of beef extract, peptone, and urea was used for culti-
vation of bacteria. Whey, ecologically dangerous byproduct from dairy industry,
was found to be effective as a culture medium. The presence of calcium carbonate
crystals covering aggregate grains was confirmed by observations under scanning
electron microscope. Chahal and Siddique (
2013
) discussed that biodeposition had
influence on permeation properties of fly ash and silica fume concrete. The bacteria
(S. pasteurii) present in the concrete rapidly sealed freshly formed cracks through
calcite production. The bacterial concentrations were optimized to 10
3
,10
5
, and
10
7
cells/ml. In concrete mix, cement was replaced with fly ash and silica fume.
The percentage replacement of fly ash and silica fume was by weight of cement.
The percentage use of fly ash was 0, 10, 20, and 30 %, and that silica fume was 0, 5,
and 10 %. The experiments were carried out to evaluate the effect of S. pasteurii on
the compressive strength, water absorption, water porosity, and rapid chloride
permeability of concrete made with fly ash and silica fume up to the age 91 days.
The test results indicated that inclusion of S. pasteurii enhanced the compressive
strength, reduced the porosity and permeability of the concrete with fly ash and
silica fume. The improvement in compressive strength was due to deposition on the
bacteria cell surfaces within the pores which was scanned by electron microscopy
and confirmed by XRD which revealed calcium carbonate precipitation. This
precipitation reduced the chloride permeability in concrete with fly ash and silica
fume. The bacteria improve the permeability of concrete by improving its pore
structure and thereby enhancing the life of concrete structures.
15.3.3 Influence on Strength of Concrete by Biodeposition
The compressive strength of the concrete is considered as an index to assess the
overall quality of concrete, generally an improvement in the compressive strength
results in improvement of all other properties. Bacterial induced carbonates as a
binder material, i.e., biocementation, have been added to concrete for the
improvement of compressive strength. Several studies have shown that biodepo-
sition can be used to improve the compressive strength of mortar (Bang et al.
2001
;
Ghosh et al.
2005
; Achal et al.
2009
,
2011a
,
b
,
c
; Park et al.
2010
) where bacteria,
salinity, and composition of the synthetic medium have also been applied in the
concrete mixture. According to Ramachandran et al. (
2001
), the use of bacteria in
concrete remediation was considered unorthodox. Biodeposition is highly desir-
able because the biodeposition carbonate crystal is pollution-free, natural, and eco-
friendly. Ramachandran et al. (
2001
) investigated the use of microbiologically
induced mineral deposition for the improvement of the compressive strength of
Portland cement mortar cubes at the age of 7 and 28 days. They used live and
killed cells of different concentrations of Bacillus pasteurii and found that the live
cells, at lower concentrations, increase the compressive strength of cement mortar
with a longer incubation period. The overall increase of strength, therefore,
resulted from the presence of an adequate amount of organic substances in the
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