Publication

Abstract : The improvement of strength and durability properties of concrete has been of great interest to researchers in the last two decades. Even though concrete is well known for its strength, there is always the possibility of cracks occurring due to various environmental conditions and loading. Sometimes these cracks may lead to corrosion of embedded reinforcement of structures if left unidentified. Even though there have been several solutions to rectify this problem, the addition of calcite precipitating microbes attracted the attention of researchers around the globe. The current research addressed this specific problem of healing cracks by encapsulating calcite precipitating bacteria into lightweight aggregate and replacing it with certain percentages of fine aggregate. The bacterial cells were encapsulated into expanded perlite, and a two-layer coating was done for better sealing performance to protect bacteria. The encapsulation capacity of the bacteria into the expanded perlite was found to be 6x108 cells/g. The cement mortar specimens were prepared by replacing fine aggregate with bacteria-encapsulated pellets in 10%, 15%, 20%, and 25%. To address the reduction in strength due to aggregate replacement was countered by adding nano silica into the mortar mixture in 5%, 8%, and 10%. The selected bacteria successfully healed a maximum crack width of 0.62 mm on the 28th day was confirmed visually by ImageJ analysis. The 20% aggregate replacement and 5% nano-silica blend was found to be optimum in terms of healing microcracks and compressive strength, respectively, in the prepared specimen. The efficiency of self-healing of bacteria and improving strength due to adding nano-silica was determined through the water permeability rate and compressive strength tests, respectively. The bacteria-precipitated calcite crystals at the crack region were also confirmed by observing under a field emission scanning electron microscope.