Abstract
Karst regions in Indonesia have the uniqueness of the landscape and biodiversity. The karst is formed by the dissolution of rocks and the precipitation of mineral. In the cave, there are ornaments of stalactite and stalagmite which are formed by the process of mineral precipitation. We have isolated, screened, and identified the soil bacterium from the cave environment (Lysinibacillus macroides). These bacteria are able to precipitate calcium carbonate and can be developed as a self-healing agent concrete. We investigated the proportions and the properties of mixtures concrete containing lightweight aggregate and volcanic ash impregnated with bacteria. A comparison study was made by concrete cylinders subjected to compressive strength tests with and without the bacteria. It found that the strength of concrete with bacteria decreased by less than 10.56% for 28 days of cured specimens. This study showed that the effects of bacteria on the strength of concrete are not considerable. However, these bacteria are effective to repair in the microcrack less than 0.3 mm
Highlights
Calcium carbonate is a mineral that represents a large portion of carbon reservoir in the earth
Calcium carbonate precipitation has produced from urease activity by microbes
The discoloration of the media was from yellow to bright pink. This color indicated there was a urease activity in the media. 25 of 40 isolates of bacteria result in the bright pink
Summary
Calcium carbonate is a mineral that represents a large portion of carbon reservoir in the earth. Microorganisms are important active and passive promoters of redox reactions that can influence the precipitation of minerals, including calcium carbonate [1]. Calcium carbonate precipitation has produced from urease activity by microbes. It could be found in the sediments and the cave walls. Considerable research on calcite precipitation by bacteria has been investigated by using ureolytic bacteria [3][4]. The ureolytic bacteria hydrolyzed urea into ammonium and carbonate ion. The result of the hydrolysis increased the pH and calcium carbonate precipitation. Biotic urease activity is a widespread phenomenon and includes the actions of bacteria. Bio-mineralization phenomenon is observed in cave isolates, showing their abilities to precipitate and dissolve calcium carbonate [5]
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