Influence of bacteria on the compressive strength, water absorption and rapid chloride permeability of concrete incorporating silica fume

This paper presents the effect of the ureolytic bacteria (Sporosarcina pasteurii) on the compressive strength, water absorption and rapid chloride permeability of concrete made with silica fume. Three bacterial concentrations were optimized (103, 105, 107 cells/ml) and further designing of concrete mixes was done. In making concrete, cement was replaced with 5% and 10% of silica fume by weight. Tests were performed for compressive strength, water absorption and rapid chloride permeability at the age of 28 and 91 days. Test results indicated that inclusion of S. pasteurii in concrete enhanced the compressive strength, reduced the porosity and permeability of the concrete. Maximum increase of 38.2 MPa and 44 MPa in compressive strength at 28 and 91 days was observed. Moreover, reduction in water absorption was observed with 105 cells/ml of bacteria. This improvement in compressive strength was possibly due to deposition on the bacteria cell surfaces within the pores. Scanning electron microscopy revealed the direct involvement of S. pasteurii in calcium carbonate precipitation which was further confirmed by XRD. Due to calcite deposition in concrete it was observed that reduction in chloride permeability of concrete occurred.