Refining Concrete’s micro-structure by enzymatically-induced carbonate precipitation through urease activity of bacteria

Abstract

This paper presents the mechanism of improving the microstructure of concrete by enzymatically-induced carbonate precipitation through urease activity of bacteria Sporosarcina pasteurii. This calcium carbonate or calcite crystal precipitated during the biological activity fills the pores in the concrete imparting the concrete the dense microstructure. The presence of 105 per milliliter of mixing water yields high compressive strength due to precipitation of highest amount of calcium crystals in the concrete pores thereby plugging the micro and macro pores in the concrete refining the micro-structure of the concrete. SEM images, XRD plots and thermo-gravimetric analysis confirmed the presence of calcite mineral in the bacterial mortar specimens. The presence of spores of Sporosarcina pasteurii in the bacterial mortar specimens of 365 days old are found through phase contrast microscopic images. This confirms the sporulation ability of bacteria Sporosarcina pasteurii. Concrete specimens induced with bacteria showed considerably less water absorption capacity compared to normal specimens. This decrease in water absorption capacity of bacteria induced concretes is credited to the reduction of pores in the concrete due to calcite mineral precipitation filling the pores reducing the typical pore radius of concrete. Average pore diameter in bacteria incorporated concrete decreases drastically due to calcite mineral precipitation in the pores because of microbial metabolic activity. The total pore volume also decreased in case of bacteria incorporated concrete samples.