Application of Lysinibacillus sphaericus for concrete crack healing using different calcium sources

Abstract

Micro-cracks, which develop during the service life of reinforced concrete structures, reduce the durability of concrete through the penetration of fluids. Microbially-induced calcium carbonate precipitation occurs naturally in the presence of ureolytic bacteria which precipitate calcium carbonate (CaCO3) through urea hydrolysis. This deposition leads to the filling of micro-cracks and sealing of pores, reducing ingress of fluids into the concrete. The research aim was to assess the potential of Lysinibacillus sphaericus to precipitate CaCO3 on concrete through urea hydrolysis. Lysinibacillus sphaericus was cultivated in vitro and induction of MICP through urea hydrolysis was tested on cement paste with two different calcium sources. The calcium precipitates where characterised by light microscopy, Scanning Electron Microscopy, Energy Dispersive Spectroscopy and Fourier Transform Infrared Spectroscopy. The study confirmed that MICP is induced successfully on concrete using Lysinibacillus sphaericus. Samples exposed to repeated treatment cycles of Lysinibacillus sphaericus in the presence of a calcium source exhibited a more extensive and even coating of CaCO3 crystals on the surface confirming that repeated cycles of treatment are more effective in increasing the amount of CaCO3 deposition and therefore increasing crack healing capacity.