Performance of Ordinary Grade Bacterial Concrete with Fly Ash as Partial Replacement for Cement

Cracks in the concrete are common no matter how carefully it is designed and casted. These micro cracks are undesirable because they provide an open pathway for the ingress of water and other deleterious substances and corrode the steel reinforcement. So it is necessary to prevent cracks or limit crack width to enhance the durability of the structure. The most common crack treatments include using acrylics, epoxy injections, polyurethanes or latex treatment and grouting. Major problem is that the chemicals used in these treatments are harmful to the environment, expensive, and sometimes cannot reach the deeper portions of the cracks in the structural member. If an effective method and material is found that can repairs cracks in concrete automatically (self healing) with sustainable approach, then the performance of the structure would enormously increase. On the other hand it would also save money, time and material. One effective method for repairing cracks is self healing mechanism and material used is bacteria. The bacteria used in concrete works by the phenomenon called Microbiologically Induced Calcite Precipitation (MICP) or Bio mineralization and the concrete is called Bacterial Concrete or Selfhealing Concrete. Bio mineralization is process where common soil bacterium like Sporosarcina Pasteurii, Bacillus subtilis produce calcite. This calcite fills the cracks and eventually compressive strength and durability of concrete is improved. Suitable addition of mineral admixtures such as fly ash, silica fume, ground granulated blast furnace slag, rice husk ash, and metakaolin in concrete and induction of suitable bacteria in concrete improve the strength and durability of concrete due to considerable improvement in the microstructure of the concrete. Also, utilizing the environmental friendly sustainable construction materials like fly ash which can improve the strength and durability of concrete structures has developed interest in self healing Bacterial Concrete with Fly Ash. In the present study an attempt is made to understand the effect of bacteria and fly ash on performance of M20 grade concrete. Fly ash content has been varied by 0%, 10%, 20%, and 30% as replacement for cement and bacteria (Sporosarcina Pasteurii) is kept constant at 106 cells/ml concentration. Cubes and cylinders were cast and strength is monitored for 7, 28, 56 & 90 days. Based on the results, mix with combination of 106 cells/ml bacteria and 20% Fly Ash (MB20620) has given optimum performance in terms of compressive strength, split tensile strength, strength loss, weight loss and water absorption.