عنوان مقاله [English]
Concrete is one of the most widely used constructional materials which is disposed to cracking for various reasons. Cracking is one of the unavoidable defects in concrete. When micro-cracks develop and join together, a continuous network of cracks is formed inside the concrete. Cracks increase the permeability and reduce the impermeability against moisture and aggressive substances such as sulfate ions, chloride ions, and acids. These factors affect the structure durability and reinforcement corrosion and destroy the concrete matrix. The concrete self-healing approaches appear to be an appropriate idea to remove this damage. Among the different self-healing ways which are basically chemical, the Calcium Carbonate precipitation, resulting from the micro-organisms metabolic activities, is a new environmentally friendly strategy. Their ecological variety is high and can be found in different natural settings. In this way, to treat damaged structures, a microbial process is applied wherein the combination of bacteria, urea, and a calcium source forms calcium carbonate crystal that results in crack reduction, impermeability, and improved concrete mechanical properties. Biologically, the calcium carbonate precipitation helps heal the small cracks, fill pores, and bind other materials such as sand and gravel in concrete. These precipitations are the byproducts of the usual metabolic processes such as photosynthesis, urea hydrolysis, and sulfate reduction. To obtain a useful insight in this important researching area and to protect the environment, this article investigates different approaches of using bacteria in concrete, the bacteria potential to heal the cracks. Improving the properties of concrete was examined, and the laboratory results were interpreted. Investigation of the concrete micro-structure indicated the formation of the calcite crystals in the samples and confirmed the promising performance of bacteria in healing micro-cracks, improving the mechanical properties, and the concrete durability in the destructive environments. By reducing structural pores, bacterial participation at a concentration of 105-107 cells/ml led to an increase in compressive strength by and a decrease in the penetration of chloride ions and water absorption to and , respectively. Moreover, the maximum crack healing width at a concentration of 107-109 cells/ml about was mm.