Potential of bacteria-based repair solution as healing agent for porous network concrete

Bacterially induced calcium carbonate precipitation has received considerable attention for its potential application in enforcing or repairing construction material. The mechanism of bacterially mediated calcite precipitation in those studies is primarily based on the enzymatic hydrolysis of urea. Besides calcite precipitation, this reaction mechanism leads also to the production of ammonium ions which may result in excessive environmental pressure. More recently, bacterially mediated calcite precipitation thanks to metabolic conversion of calcium lactate has been successfully applied in self-healing concrete. This concept is also now considered for the development of bio-based repair system for concrete structures. The bio-based repair system as presented in this paper is a liquid-based system which transports the bio-based agent into concrete. This paper presents the recent advances on the development of the bacteria-based repair system and especially its possible application as healing agent in porous network concrete. To assess the repair capacity of the system the bacteria-based solution is injected into porous cores, and the production of the biomineral in time is monitored by X-ray micro-tomography. In parallel, water permeability testing is conducted before and after the injection of the bacteria-based solution to determine the sealing efficiency of the system. The precipitate is analyzed with FTIR and thermal analysis for identification and quantification. Finally, at the end of the healing period, polished sections of injected specimens are observed with ESEM/EDS to analyze and locate precipitated biominerals. FTIR results coupled with thermal analysis and ESEM observations showed that CaCO3 has been formed in pores after 21 days, with increased amount after 28 days. Moreover, the evidence that CaCO3 precipitation was indeed mediated by bacteria has been found with observations of bacteria imprints on Ca based minerals. It can be concluded that the bacteria-based repair system can successfully be injected as healing agent into porous network concrete