SAMSON WALELIGN AREGAWI, ABIY SHIMELES GOSHU, BISRAT ESHETU ALEMU, DAGMAY GEBEYEHU WOLDAREGAY, NATNAEL DERES ABDULKADIR, YONATAN BIRHANE MESFIN
The concept of microbial concrete is one of the recent advances in concrete technology, in the past two decades, concrete technologies are working towards developing high performance concrete. Researches over the globe are being carried out in the wake of promising results found on the improvement of cementitious mix performances due to the application of live microorganisms. In this research live microorganism named sporosarcina pasteurii, a common soil bacterium which can induce the precipitation of calcite has been used. This research has tried to show the effect of introducing sporosarcina pasteurii into concrete as well as mortar with a particular focus on the compressive strength. Different set of experiments were carried out to investigate the effect of bacterial medium for different water-cement ratio, the effect of bacterial concentration as well as the effect of the bacterial nutrient. The experiment tried to show the effect of introducing these components on the compressive strength of concrete which was conducted at 7th, 28 th and 90 th day, to indirectly prove the possibility of calcite precipitation due to the inclusion of the bacteria. From the test result it was found out that the bacterial medium had little effect, while the bacterial nutrient, whose main constituent is yeast extract, significantly reduced the compressive strength and increased the flow table as well as the slump in both mortar and concrete. Those samples with aforementioned bacteria together with the bacterial nutrient showed an improved compressive strength compared with samples with only the nutrient. The micro behaviors observed in terms of compressive strength indicate that this gain of strength was due to the calcite precipitation induced by the bacteria. The paper concludes by stating the need of further investigation, especially with regards to finding better substitute for yeast extract of the bacterial nutrient so that only calcite precipitation, one will be able to achieve a higher performance for mortar and concrete.