AbstractThe present study investigates the use of bacteria (namely, Sporosarcina pasteurii) to enhance the durability of structural concrete members with lightweight weight aggregates (LWAs) or normal weight aggregates (NWAs). As an innovative development, bacterially-induced calcium carbonate crystals have been widely used for improving the properties of concrete materials. In this research, seawater is used as a source of calcium and chloride for calcium carbonate formation by bacteria, whereby seawater serves as a curing environment with beneficial effects on both concrete matrix and durability. For this study, concrete specimens are cured in the two seawater and tap water environments up to the test time. Experimental results indicate that the inclusion of bacteria in the concrete mix water leads to acceptable results in seawater medium and both types of concrete tested. This is evidenced by a decrease of 4% in water absorption and an increase of almost 26% in compressive strength observed in normal-weight aggregate concrete after 91 days of curing. Moreover, both types of concrete made with bacterially-impregnated mix water exhibit reductions in their chloride penetration. In this regard, compared with the control specimens cured in plain water, the bacterially-treated LWA concrete specimens exhibited a reduction of almost 1% in their water absorption and a rise of about 16% in their compressive strength. It is, therefore, expected that exposure to seawater as a threat to concrete structures can be turned into an opportunity for improving their properties if the concrete is properly treated with bacteria.