Calcite Precipitation & Its Effect on the Stability of Earthen Bricks

The calcite-precipitating Streptomyces sp. KRA01 was isolated from the gut of termites inhabiting red loamy soil in Kannur District, Kerala, India. The isolate was confirmed through biochemical tests and molecular sequencing and was designated Streptomyces sp. KRA01; the nucleotide sequence was submitted to GenBank under accession no. MW186183. The application of microbiological methods to improve the mechanical properties of soil is known as microbial geotechnology. In this research, microbes were isolated from the termite gut, analysed and identified as Streptomyces sp. KRA01. The objective of this study was to demonstrate the soil stabilization capacity of Streptomyces sp. KRA01 through microbial geotechnology. The microbes grew well in nutrient broth supplemented with carbon, nitrogen and inorganic sources acting as their nutrient sources. Microbially stabilized mud blocks (MSMB) were prepared using red loamy soil and microbial culture and cured by spraying an optimized nutrient medium for 28 days. The compressive strength of a microbially treated mud block was found to be higher than that of the conventional brick. It was discovered that biomineralized calcium carbonate in bacterial cells contributed to the improvement in strength. The results showed that the rate of water absorption was significantly reduced in the brick stabilized with microbes, suggesting that microbial activities can significantly improve the mechanical properties of MSMB. Calcite precipitation by Streptomyces sp. KRA01 significantly reduced water absorption by the earthen brick. Hence, microbial isolates can be used as additives to stabilize soil. If the technology is tested and found to be successful, it might lead to longer maintenance-free periods, reduced material demand, an increased level of service and the preservation of nature.