Comparative study of heterotrophic and photoautotrophic bacteria on strength and permeability properties of concrete

Abstract

The incorporation of bacterial biomass to cementitious materials improves the strength and permeability properties by altering the pore structure. Previous studies report significant improvement in the strength properties of concrete by using ureolytic bacteria. However, several challenges limit its application in the field, and one such limitation is the release of ammonia gas, a harmful foul-smelling pollutant. In some studies, cyanobacteria are being used as an alternative to heterotrophic bacteria. The present study compares the effect of the addition of heterotrophic bacteria, Bacillus paramycoides, and phototrophic bacteria, Synechocystis pevalekii BDHKU 35101, on the strength and permeability properties of concrete. The specimens treated with S. pevalekii (SPC) and B. paramycoides (BPC) improved the compressive strength significantly compared to the control, however, a marginal difference (1.8 %) was observed between the SPC and BPC specimens. The charge passed through SPC and BPC specimens during the rapid chloride permeability test was 1901 and 1440 coulombs, respectively after 28 days of curing. The water absorption reduced after 28 days with 0.007 and 0.005 sorptivity coefficients of SPC and BPC specimens, respectively. The CaCO3 crystallization in SPC and BPC specimens was confirmed using a field emission scanning electron microscope (FESEM) and energy dispersive X-ray spectroscopy (EDS). The peaks of calcite and vaterite were observed in X-ray diffraction (XRD). This study affirms that both B. paramycoides and S. pevalekii significantly improved the strength and permeability properties of concrete. However, photoautotrophic cyanobacteria do not release harmful pollutants and also sequester atmospheric CO2 during calcification and can serve as potential substitute/alternative for ureolytic bacteria.