Abstract
In this paper, we studied the crack-repair by spraying bacteria-based liquid around the cracks in concrete. To enhance the repair efficiency and speed up the repair process, the transposon mutagenesis method was employed to modify the genes of Bacillus halodurans and create a mutant bacterial strain with higher efficiency of calcium carbonate productivity by catalyzing the combination of carbonate and calcium ion. The efficiency of crack-repairing in concrete by spraying two kinds of bacterial liquid was evaluated via image analysis, X-ray computed tomography (X-CT) scanning technology and the sorptivity test. The results show that the crack-repair efficiency was enhanced very evidently by spraying genetically modified bacterial-liquid as no microbiologically induced calcite precipitation (MICP) was found within the cracks for concrete samples sprayed using wild type bacterial-liquid. In addition, the crack-repair process was also shortened significantly in the case of genetically modified bacteria.
Highlights
Concrete has become the second most consumed material after water on earth nowadays, which contributes greatly to modern buildings due to its high strength, durability, low-cost, and availability worldwide in comparison to other construction materials
Considering the local environmental conditions, Bacillus halodurans was selected for repairing of the cracks in cementitious materials since it is potentially more suitable for growth in the local environment in Singapore with relatively high temperature and humidity
Previous studies have suggested that the transposon mutagenesis method might block related genes, further affecting the metabolism pathway [22,34]
Summary
Concrete has become the second most consumed material after water on earth nowadays, which contributes greatly to modern buildings due to its high strength, durability, low-cost, and availability worldwide in comparison to other construction materials. It is not a trivial task to look for an environmentally friendly and economical repair material that can repair concrete efficiently before it deteriorates from the initial micrometer-sized cracks to millimeter ones In this context, Jonkers et al developed a kind of liquid containing bacteria and sprayed it on the cracked surface of concrete buildings, which was expected to seal the crack by the MICP process [17]. Jonkers et al developed a kind of liquid containing bacteria and sprayed it on the cracked surface of concrete buildings, which was expected to seal the crack by the MICP process [17] The bacterial liquid they developed had been applied in a practical project in the Netherlands to repair cracks (200–300 μm wide) on a parking garage floor. Assessments of repair efficiency via various methods are reported, including image analysis, X-ray computed tomography (X-CT) scans, sorptivity tests, and scanning electron microscopy (SEM) observation
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