EFFECT OF BACILLUS MEGATERIUM AND BACILLUS STEAROTHERMOPHILUS ON THE CHLORIDE PENETRATION RESISTANCE OF CALCINED CLAY CEMENT MORTAR

The durability of concrete structures, particularly their resistance to chloride penetration, is crucial for ensuring long-term performance, especially in marine and other chloride-rich environments. Calcined clay, recognized for its pozzolanic properties, is increasingly utilized as a sustainable supplementary cementitious material (SCM) due to its availability and beneficial effects on mechanical properties and durability. However, the potential for further enhancement with the incorporation of bacteria remains underexplored. This research investigated the impact of microbial-induced calcite precipitation (MICP) facilitated by Bacillus Megaterium and Bacillus Stearothermophilus on the chloride penetration resistance of calcined clay cement mortars. Mortar specimens were infused with varying concentrations (10-5, 10-7, 10-9) of Bacillus Megaterium and Bacillus Stearothermophilus were prepared under different pH conditions (pH 4 and pH 9). These specimens were coated with epoxy in all but one face to allow for unidirectional ingress of chloride and then cured for periods of 7, 28, and 90 days. Chloride penetration tests were conducted to assess the depth of chloride ingress, and the results were compared with those of control specimens. The findings reveal that the inclusion of Bacillus Megaterium and Bacillus Stearothermophilus significantly reduces chloride penetration in calcined clay cement mortar. The effectiveness of these bacteria varied with concentration and pH levels, with higher bacterial concentrations generally resulting in better performance. Bacillus Megaterium showed superior efficacy at lower pH levels, while Bacillus Stearothermophilus exhibited enhanced performance at higher pH levels. In conclusion, the incorporation of Bacillus Megaterium and Bacillus Stearothermophilusinto calcined clay cement mortar presents a promising approach to improving chloride penetration resistance. This microbial intervention has the potential to extend the service life of concrete structures, offering a sustainable and effective solution for enhancing durability in chloride-rich environments.