POTENTIAL OF UREOLYTIC AND CALCITE FORMING BACILLUS CEREUS SSS1 IN BIO-CEMENTATION

Abstract

Bio-cementation results into formation of deposits of CaCO3
that is essential for the healing of cracks and strengthening
the concrete building materials. In this view, 56 ureolytic bacteria were isolated from rhizospheric soil of sugarcane,
maize, onion and chickpea on Christensen’s agar and screened for calcite formation by growing them on precipitation
agar. The culture was inoculated in calcium chloride-urea broth and incubated at 30˚C for 7 to 8 days. The calcite
crystals were detected by light microscopy, XRD, SEM and EDS. One of the potent isolates, SSS1 was identified by 16S
rDNA sequencing as Bacillus cereus. XRD analysis revealed the formation of rhombohedral structure of calcite crystals by
SSS1. The average size of crystals was 53.75 µm as determined by SEM and EDS. The ability of SSS1 in strengthening of
cement sand mortar and healing of cracks was evaluated. The compressive strength of cement sand mortar was 23, 36.2
and 40.6 N/mm2 on 3rd, 7th and 14th day, respectively and these values were significantly (p8lt higher than 43 grade
cement mortar. Remediation of cracks was experimented by injecting a cementation solution containing urea-CaCl2
and SSS1 cells in the cracks of mortar cubes. Post 14 days incubation, the cracks were found to be sealed indicating filling of
void spaces. This potential of SSS1 is advantageous in the making of cement sand mortars with better compressive
strength and self-healing property. This study is important towards promoting the use of bacterial concrete in practical
engineering applications as compared to conventional ordinary concrete.