A Case Study: Bacterial Surface Treatment of Normal and Lightweight Concrete - Biotechnologies and Biomimetics for Civil Engineering - page 360

Fig. 16.4 SEM images of top surface of normal concrete treated by the cell-free medium
measured in 300 lm(a) and 50 lm(b), and EDS spectra at point 1 (c). Reprinted from Kim et al.
( 2013 ), Copyright (2013), with permission from Elsevier
round-shaped calcium carbonate crystals were formed and were stacked upon each
other on the normal and lightweight concrete specimens (Figs. 16.4 and 16.5 ).
The diameters of these crystals were in the range of 10-80 lm. There were no
significant differences between the normal concrete and lightweight concrete
samples. It was noted that, when bacteria were not used, a single pure bulk crystal
consisting of many plate-shaped, small crystals formed (Fig. 16.5 b). Moreover, as
shown in Fig. 16.6 , the calcium carbonate crystals filled the pores of the light-
weight aggregates.
Compared to the cell-free medium, the sizes of the calcium carbonate crystals
were smaller and their distribution was denser in the medium with bacteria
(Figs. 16.7 , 16.8 , 16.9 and 16.10 ). Moreover, the distribution of calcium carbonate
on the lightweight concrete was slightly different from that on the normal concrete.
As shown in Fig. 16.7 , in the normal concrete, small calcium carbonate crystals
with a size of approximately 500 nm were stacked like gravel on the surface of the
Fig. 16.5 SEM images of top surface of lightweight concrete treated by cell-free medium
measured in 100 lm(a), 10 lm(b), and EDS spectra at point 1 (c). Reprinted from Kim et al.
( 2013 ), Copyright (2013), with permission from Elsevier