A Case Study: Bacterial Surface Treatment of Normal and Lightweight Concrete - Biotechnologies and Biomimetics for Civil Engineering - page 363

Fig. 16.10 SEM images of top surface of lightweight concrete treated by the medium with B.
sphaericus measured in 50 lm(a), 2 lm(b), and EDS spectra at point 1 (c). Reprinted from Kim
et al. ( 2013 ), Copyright (2013), with permission from Elsevier
was precipitated in the medium and thus formed spherical particle shapes and was
deposited on the surface of the concrete (Parks 2009 ). On the other hand, for B.
sphaericus, the calcium carbonate crystals were precipitated from the interface
between the medium and the concrete specimen due to the formation of a biofilm
(Kolari et al. 2001 ; Parks 2009 ). These crystals were precipitated with radial
shapes and were developed between other crystals without a gap, covering the top
surface densely (Fig. 16.10 ). The different shapes of the calcium carbonate crystals
shown in the SEM images (Figs. 16.4 , 16.5 , 16.6 , 16.7 , 16.8 , 16.9 and 16.10 ) may
be affected by the different morphologies of the calcite and vaterite phases (de
Leeuw and Parker 1998 ).
16.3.3 Effect of Precipitated Calcium Carbonate
on Capillary Water Absorption of Concrete
Figure 16.11 presents the relative values of the capillary water absorption per unit
area of concrete. It should be noted that the relative values of both the normal and
lightweight concrete were similar, while the absolute value of lightweight concrete
(1.4-2.6 kg/m 2 ) was higher than that of the normal concrete (4.7-9.3 kg/m 2 ).
As shown in Fig. 16.11 , the capillary water absorption per unit area of concrete
was decreased in both the medium with and the medium without bacteria. How-
ever, in the medium without bacteria, the relative values of water absorption of the
concrete specimens were not stable in comparison with the concrete specimens
treated with the medium with bacteria. The relative value of the normal concrete
treated with the cell-free medium was higher at 6 h than that of the concrete
treated with the medium with bacteria, whereas it was lower at 128 h. Moreover,
the relative value of water absorption of the lightweight concrete at 6 h was very