Concrete crack-healing materials using biocalcification by ureolytic bacteria isolated in marine environment: An overview

H.Y. Kim, H.M. Son, H.K. Lee
Korea Advanced Institute of Science and Technology,
Korea

Keywords: biocalcification, ureolytic bacteria, crack-healing in concrete, marine environment

Summary:

Micro-cracks on the surface of concrete structures frequently occur due to external force and shrinkage [1]. The deterioration of concrete durability is accelerated by the penetration of moisture and chemicals into microcracks and pores [2]. However, unlike concrete in a soil environment, the degree of concrete deterioration in seawater is significantly influenced by the water depth and location since salinity, temperature, and dissolved oxygen vary with depth [3]. Even though the marine environment accelerates the infiltration rate of Cl-, it is more difficult to repair concrete microcracks in a marine than in a soil environment [3]. Conventional crack healing materials, such as chemical synthetic repair agents have a relatively fast repair time, but they are expensive, harmful to the environment, and do not provide a persistent healing effect [4]. Furthermore, the determination of the exact location of the crack is challenging in a marine environment [4]. Therefore, biocalcification by microorganisms is one feasible method for concrete microcrack repair, by acting as a filler for cracks and pores in concrete. Alkaliphilic bacteria that can alkalize their surrounding environment after metabolism in vivo are mainly used for concrete crack healing [5]. The alkalized culture medium and bicarbonate is produced from the urease expressed by ureolytic bacteria [6]. The urease that is expressed by ureolytic bacteria can alkalize the culture medium and produce bicarbonate [6]. CO32- combines with Ca2+ around the cell wall of the bacteria resulting in the precipitation of calcium carbonate [6]. Bacillus species that are found in soil have been used as a self-healing concrete material and were applied to microcracks of the mortar to confirm that the cracks had healed [7,8]. The self-healing technology using microbial-induced calcium carbonate precipitation (MICCP) is an economic and innovative way to satisfy both maintainability and environmental needs. A number of studies on self-healing concrete using MICCP isolated from soil have been actively carried out, but research on self-healing concrete in a marine environment is sparse. This study reviews previous works done on self-healing concrete based on the biocalcification metabolism of bacteria. A feasibility study on identifying bacteria capable of calcium carbonate precipitation in seawater to be used in self-healing concrete materials will be also presented [9].