Environmental Engineering Reference
In-Depth Information
micrographic studies were conducted to analyze the shapes and distribution of the
calcium carbonate crystals. The amounts of capillary water absorption of the
concrete specimens were measured to evaluate the effects of the bacterial pre-
cipitation of calcium carbonate on the moisture transport properties, which may
affect the durability of the concrete.
The size of the calcium carbonate crystals precipitated by the medium with
bacteria was larger than that precipitated by the medium without bacteria.
Moreover, the medium with B. sphaericus formed calcium carbonate crystals with
nano-sized pockmark shapes, and the crystals covered the concrete surface den-
sely. Thus, both the normal and lightweight concrete specimens treated with the
medium containing B. sphaericus showed lower capillary water absorption levels
per unit area than that of the concrete specimens treated with the cell-free medium.
In addition, the respiration characteristics of the bacteria may hinder the devel-
opment of the dome-shaped calcium carbonate structures noted on the lightweight
concrete specimens.
Considering the water absorption rates from the surfaces of the concrete sam-
ples, the efficiency of bacterial treatments is still lower than that of conventional
water-repellent materials, including epoxy or silicone resins (De Muynck et al.
2008b
; Qian et al.
2009
). Moreover, investigations of the long-term performance
of a bacterial surface treatment and life-cycle assessments based on these results
have not been reported, both of which are important for practical applications of
this method. Therefore, further studies will be carried out along this line.
Acknowledgments This research was sponsored by a grant from the National Research Foun-
dation of Korea (NRF) funded by the Korean government (2013028443).
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