A study on the performance of the bacterial concrete embedded with Bacillus Subtilis

Abstract

Concrete, a strong, durable material composed of cement, aggregate and water, is the most used building material in the world. Concrete has an ultimate load bearing capacity under compression but the material is weak in tension. That is why steel bars are embedded in the concrete for the structures to carry tensile loads. The steel reinforced bars take the load when the concrete cracks in tension. On other hand the concrete protects the steel reinforced bars from the environment and prevents corrosion. However, the cracks in the concrete form a major problem which affects the durability of the structures. Here the ingress of water and chloride ions takes place and deterioration of the structure starts with the corrosion of the steel. To increase the strength and durability of the structure either the cracks that are formed should be repaired conventionally using epoxy injection or latex treatment or by providing extra reinforcement in the structure during the design phase to ensure that the crack width stays within a permissible limit. This extra reinforcement is only needed for durability reasons (to keep the crack width small) and not for structural capacity. Especially with current steel prices on rise providing extra steel is not economically viable. Main reason to prevent cracks or limit crack width is to enhance the durability of the structure. If in some way a reliable method could be developed that repairs cracks in concrete automatically (self healing), this would increase and ensure durability of the structure enormously. On the other hand it would also save a lot of money, time and energy. A reliable self healing biological approach is first proposed by V.Ramakrishnan to make use of bacterial concrete to heal cracks in concrete structures. Bacillus subtilis strain no.JC3 could be one of the answers to the long quest for crack free concrete.