Evaluating the Potential of Alkalophilic Bacteria to Enhance Concrete Durability

Nowadays, concrete has been widely used as one of the best and most practical building materials in various types of structures. Concrete permeability is a factor that reduces its stability and decreases the service life of concrete structures. This study has been conducted with the aim of finding bacteria able to repair concrete surface in order to reduce its permeability. Isolated bacteria from alkaline soils of north and center of Iran were subjected to primary and secondary screening for producing urease enzyme and calcium carbonate precipitation. Selected isolates were cultured in specific broth medium for calcium carbonate precipitation. Then, the rate of their growth and calcium carbonate production were compared. Produced calcium carbonate, by the premier isolate, was verified using XRD. The ability of this isolate was evaluated in the repair of the concrete surface porosity and the reduction of its permeability by Scanning Electron Microscopy (SEM). The results of primary and secondary screening showed that Bacillus sp. UTMC 2623 produces the highest amount of calcium carbonate precipitation (8.8 g/L) in three days. Its XRD analysis confirmed the presence of crystalline calcium carbonate in dried bacterial precipitate. SEM analysis showed that this bacterium creates the best coating on the concrete surface along with the calcium source.
Discussion and The present study is a report on the repairing activity of Bacillus sp. UTMC 2623 which can be used to find other native and promising microorganisms in concrete surface repair.