Effects of bacterial consortium enhanced recycled coarse aggregates on self-healing concrete immobilized with Bacillus megaterium MTCC 1684 and Bacillus subtilis NCIM 2193

The strength and durability properties of the recycled aggregate concrete (RAC) have been affected by the cracks and the weak interfacial transition zone (ITZ) of the recycled coarse aggregates (RCA). However, the mechanical and physical features of RCA can be improved by microbially induced calcite precipitation (MICP). Therefore, immobilization techniques were used to protect and maintain the high efficiency of Bacillus bacteria for the formation and precipitation of calcium carbonates in self-healing concrete over a period of time. The objective of the present study was to show the viability of the immobilized bacterial consortium-enhanced RCA to form self-healing cracks. Further, the self-healing capability of enhanced RCA was investigated along with two other immobilization methods, that is, RCA and hydrated lime and brick powder (HBr)-immobilized bacteria. The experimental results show that the increase in the bio-deposition time improved the physical and mechanical properties of the RCA. Further, subsequently 56 days of the healing incubation period, the immobilized consortium-enhanced RCA concrete specimens completely healed the cracks of width 0.58 mm. However, the equivalent cracks of width 0.56 mm were also recovered by the HBr immobilized bacterial cultures. Furthermore, the field emission scanning electron microscope (FESEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis revealed that the existence of precipitation at the crack surface was calcium carbonate with a regular cubic-shaped and lamellar layer morphology. The outcomes of the current study show that consortium-enhanced RCA has promising potential to develop self-healing concrete with self-repaired and improved durability properties in the concrete construction field.