Bacterially-promoted carbonation of lime-based building materials

Abstract

Lime-based binders, while historically significant, exhibit low strength and slow hardening, which has led to its replacement by cement. Hardening in lime-based materials occurs primarily through carbonation, whereby Ca(OH)2 reacts with atmospheric CO2 and produces CaCO3 cement. This study explores using bacterial additives to accelerate lime hardening by producing extra CO2. Three bacterial species were isolated and grown in liquid media. In a closed container, lime-mortar specimens were indirectly exposed to a cotton soaked in either bacterial suspension or water. Thermogravimetric analysis after 7 and 14 days indicated increased carbonation in cubes incubated with bacterial suspension, but not significantly. Subsequently, one bacterial suspension was mixed directly with lime. Progression of carbonation was tested with phenolphthalein and after 7, 14 and 21 days faster carbonation was seen in bacteria-containing pastes than those with only culture media. Overall, bacteria can carbonate lime materials but further optimization is needed for practical application.