Self-healing of Early Cracks in Cement-based Materials by Carbonic Anhydrase Microbiologically Precipitation Calcium Carbonate

ID No: 65 ABSTRACT This research studies the self-healing potential of early cracks in cement-based materials incorporating carbonic anhydrase (CA) bacteria. CA bacteria can accelerate the CO2 hydrated reaction then transfer CO2 to HCO3 which can react with soluble Ca(OH)2 on the surface of specimens. Calcium carbonate deposits because of the reaction of HCO3 with Ca.This research studies the self-healing potential of early cracks in cement-based materials incorporating carbonic anhydrase (CA) bacteria. CA bacteria can accelerate the CO2 hydrated reaction then transfer CO2 to HCO3 which can react with soluble Ca(OH)2 on the surface of specimens. Calcium carbonate deposits because of the reaction of HCO3 with Ca. Cement specimens were used throughout the study. Specimens were pre-cracked at the age of 7, 14, 28, 60 days, the width of cracks were between 100 and 1000 μm. Thereafter, the specimens were submerged in water exposed to atmosphere. The experimental results indicated that the CA bacteria showed excellent cracks closing ability to small cracks formed at early age of 7 days, cracks below 400 μm was almost completely closed. Cracks width influenced self-healing effectiveness significantly. Repair ability was restricted when the cracks width were between 500800 μm and is invalid when the cracks width up to 900 μm. The transportation of CO2 and Ca 2+ controlled the self-healing process. It was hypothesized that the diffusion of CO2 conformed to Fick law in this study. The computer simulation analyses revealed the self-healing process and mechanism of microbiologically precipitation induced by CA bacteria. The depth of precipitated CaCO3 could be predicted base on valid Ca . Moreover, it also explained why cracks closing only occurred on the surface of specimen.