Study on Mechanical Properties of Cement Mortar by the Addition of Ureolytic Bacteria

Abstract

In the present scenario where the constructions are increasing, the need to find a supplementary cementing material for the improvement of strength and which has less environmental effects is of great significance. Ureolytic bacteria are the ones which can improve the strength of cement mortar by the precipitation of calcium carbonate in the presence of urea and a calcium source. In the present study Bacillus sphaericus is used to check its applicability in this regard. Various tests like consistency and initial setting time are done to find out the effect of bacterial solution on cement. Tests such as compression strength and sorptivity test are used in the present study to identify the variation in the mechanical properties of cement mortar. To know the mineralogy and morphology of the calcium carbonate precipitated by the bacteria XRD and FESEM analysis are carried out. Compressive strength (at 7-day and at 28-day) of mortar cube found to be increasing with the increase of bacteria concentration up to 107 cells/ml The optimum doses of bacteria found to increase the average compressive strength by 58% (at 7-day) and 23% (at 28-day) over the control specimen. The more increase in strength after 7 day curing may be due to the presence of nutrient medium and it getting depleted as it reaches 28 days and causing death of bacteria The minimum cumulative water absorption is obtained for a cell concentration of 109 cells/ml The mineralogy and morphology of the calcium carbonate precipitated by the bacteria test was able to confirm that the bacterially precipitated calcium carbonate is calcite and is having lamellar rhombohedra or hexagon shape