A Case Study: Bacterial Surface Treatment of Normal and Lightweight Concrete - Biotechnologies and Biomimetics for Civil Engineering - page 355

polymer coating. For suitable hardening of an epoxy resin, the curing temperature
should exceed 15 C and the curing time can require anywhere from two to seven
days (Issa and Debs 2007 ; Ha et al. 2010 ; Lee et al. 2011 ). Similarly, for a
bacterial surface treatment, a sufficient temperature is one that exceeds 20 C, and
the curing time is again about 4-7 days (De Muynck et al. 2008a , b ; Qian et al.
2009 ).
In the present chapter, a previous work of the authors, a case study involving
the bacterial surface treatment of normal and lightweight concrete (Kim et al.
2013 ) is reviewed and summarized. In this work, both normal and lightweight
concrete were subjected to bacterial surface treatment. It is well known that the
durability of lightweight concrete is lower than that of normal concrete (Haque
et al. 2004 ). For lightweight concrete, water, gas, and harmful chemicals can easily
penetrate through the pore networks of the lightweight aggregates in the concrete
(Vaysburd 1996 ; Haque et al. 2004 ). This leads to lower resistance of the concrete
against the chloride penetration, carbonation, and freeze-thaw damage (Vaysburd
1996 ; Haque et al. 2004 ). As environmental attacks on concrete structures start on
the surface, a surface protective layer is the first line of defense for both the
concrete itself and the reinforcements embedded in it (Vaysburd 1996 ). Therefore,
a surface treatment, especially for lightweight concrete, is very important to ensure
its durability.
In the present work, the surfaces of normal and lightweight concrete specimens
were treated with a liquid medium containing bacteria. Macro- and micrographic
assessments were carried out to analyze the shapes and distribution of the calcium
carbonate crystals. The capillary water absorption of the concrete specimens was
measured to evaluate the effects of the bacterial precipitation of calcium carbonate
on the moisture transport properties, which can affect the durability of the concrete.
16.2 Experimental Program
In this work, two types of ureolytic bacteria, S. pasteurii (ATCC 11859) and B.
sphaericus (ATCC 13805), which can precipitate calcium carbonate crystals, were
selected. The details of the preparation of the liquid media are available in Kim
et al. ( 2013 ). As a reference, a cell-free medium was also prepared. The XRD
patterns for the calcium carbonate crystals precipitated in media with and without
bacteria are presented in Fig. 16.1 . Both calcite and vaterite phases were found in
all types of the media, but the intensity ratio between the calcite and vaterite
phases differed in each case. The ratios between the peak intensities of 29.3
(calcite phase) and 27.0 (vaterite phase) were 1:0.72, 1:2.66, and 1:1.05,
respectively, for the calcium carbonate crystals formed in a cell-free medium, the
medium with S. pasteurii, and the medium with B. sphaericus. This indicates that
both types of bacteria tended to form vaterite crystals compared to the medium
without bacteria, where calcium carbonate crystals were precipitated by the natural
reaction between the urea and the calcium acetate in that sample medium.