Performance Enhancement and Remediation of Microcracks in Cement Mortar by Doping Calcite-Precipitating Microorganisms

Abstract

Concrete is prone to microcracks owing to its brittle nature and durability-related issues when subjected to loading and various environmental conditions. This necessitates the need for an effective crack-healing method combined with reliable techniques to monitor the healing. This paper reports experiments conducted on endospore-forming alkaliphilic calcite-precipitating bacterium Bacillus megaterium MTCC 8510 and its efficacy at enhancing the performance and crack remediation in cement mortar. The capacity and the presence of calcite precipitation were confirmed using X-ray diffraction and field emission scanning electron microscopy. The effects of the direct addition of bacteria to cement mortar on its compressive strength, chloride diffusivity, and water permeability were observed. Apart from the direct addition of bacteria, the crack-healing capacity was also observed by spraying the bacterial solution directly on the cracks every day on a coir-reinforced cement mortar specimen. The results of the compressive strength test, rapid chloride penetration test (RCPT), and water permeability tests showed improved strength, reduced chloride diffusivity, and diminished water permeability with bacteria directly added cement mortar specimens. The healing of cracks inside the mortar specimens was confirmed by ultrasonic pulse velocity testing. The crack area was found using ImageJ software, which showed 94.73% healing in the surface crack area by direct spraying on the surface. It was found that the bacterial strain selected was efficient in terms of improving the performance characteristics and healing of microcracks.