Investigating the effects of bacterial activity on compressive strength and durability of natural lightweight aggregate concrete reinforced with steel fibers

Abstract

The present study investigated the effects of a specific strain of Bacillus subtilis introduced into natural lightweight aggregate concrete (LWAC) as a new approach on its water absorption, electrical resistance, compressive strength, chloride ion penetration, carbonation depth, water penetration depth, and compressive strength in a sulfate environment. For this purpose, specimens of two general groups were made: with and without bacteria. Two mix designs were also used to cast specimens with and without reinforcing steel fibers. The bacterial concentration in the concrete mix water was 107 cells.ml−1. Finally, the specimens were cured in the three different environments of plain water, urea-calcium lactate solution, and nutrient solution. Overall, 252 specimens were cast each with 2 replicates. Test results revealed that, compared to normal specimens, those containing bacteria in their mix water and cured in the calcium lactate environment, recorded decreases of about 13.1%, 20.5%, 27.2%, and 44.3%, respectively, in their water absorption, chloride penetration, carbonation depth, and water penetration depth while their electrical resistance increased by about 103.6%. Moreover, in this study additional specimens containing bacterial spores, due to their dormant state and sustainability in the alkaline environment of concrete, were also cast to compare the two types of specimens in terms of their water absorption, electrical resistance, and compressive strength. The results of this study showed that incorporating the bacterial treatment method in natural LWAC mixture reinforced with steel fibers reduces not only the high dead load and cracking potential of concrete elements but also their water absorption and chloride ion penetration due to the occlusion of fine cracks.