Environmental Engineering Reference
In-Depth Information
this substance in construction to lower the environmental hazard caused by
cement. Again question rises, what about the quality of such structure? We need
to find a novel way to do this without compromising the quality of building
structures. Finding such a sustainable material means, we could reduce the envi-
ronmental impact of cement.
Concrete is the most widely used building material and most of the building
structures are made up of it. However, natural processes including earthquake or
weathering or land subsidence and human activities play enough roles to degrade
or reduce the durability of concrete structures. Durability of concrete is the ability
of a concrete to resist deterioration, particularly deterioration due to weather
exposure, chemical exposure or surface abrasion (Reddy et al.
2012
).
Though ignored for centuries with respect to their role in construction industry,
bacteria have enormous potential in carbonate formation leading to increment in
compressive strength, a key parameter while designing buildings structures.
Moreover, bacteria are omnipresent, especially in soil, regardless of normal to
harsh environmental conditions. It can be used perfectly in construction as live
building materials, rather than inert one, as it can precipitate carbonate when
required, even once construction is over. Together with building components,
nutrient solutions; bacteria in cementitious materials will form ''concrete eco-
system.'' Concrete ecosystem (perhaps a term coined first time here) looks simpler
as will contain only microbes as living component in conjunction with cement,
sand, aggregates and some other building materials; however, the ecosystem
process under it is highly complex due to harsh environment. It provides favorable
condition for Microbially induced Calcium Carbonate Precipitation (MICP).
The importance of MICP has been reported in several applications including
remediation of heavy metals (Achal et al.
2011a
,
2012a
), soil strengthening/
improvement (Whiffin et al.
2007
), restoration of calcareous stone materials (Tiano
1995
; Castanier et al.
1999
; Stocks-Fisher et al.
1999
; Rodriguez-Navarro et al.
2003
), wastewater treatment (Hammes et al.
2003
), sand consolidation (Achal
et al.
2009a
), strengthening of concrete (Ramchandran et al.
2001
), and durability
of building materials (Achal et al.
2010a
). The present chapter outlines, based on
the reports from researchers worldwide, the mechanism driving MICP, concrete
construction using bacteria (thus known as microbial concrete, a term coined by
Achal et al. (
2011b
)) and how microbial concrete is effective to enhance the
durability of building structures.
14.2 Microbially Induced Carbonate Precipitation
Microbially induced calcite precipitation is resultant of complex biochemical
reaction often governed by an enzyme urease (urea amidohydrolase; EC 3.5.1.5)
produced by microbes. This reaction/precipitation requires urea as substrate while
calcium source as chief agent for calcite production. During microbial urease
activity, 1 mol of urea is hydrolyzed intracellularly to 1 mol of ammonia and
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