Viability determination of Bacillus sphaericus after encapsulation in hydrogel for self-healing concrete via microcalorimetry and in situ oxygen concentration measurements

Techniques for bacteria based self-healing concrete are currently limited to indirect bacterial activity measurements and visual crack closing effects after self-healing has occurred. In the present study, direct and reliable bacteria survival measurements after encapsulation in protective carriers were carried out by utilizing microcalorimetry analysis. After further incorporation in mortar oxygen consumption was determined by use of an optical oxygen sensing system. The microscope analysis showed that a 90% sporulation of Bacillus sphaericus was achieved after 24 h incubation. Microcalorimeter measurements detected the heat generation from microbial activity on the third day of incubation which provides direct evidence that bacteria can be activated after encapsulation inside the hydrogel. The application of the O-2 sensing film on cracked mortar showed a high oxygen concentration reduction (66%) near the crack opening. This confirmed the activation of B. sphaericus and use of oxygen as an electron acceptor for their metabolism after incorporation inside mortar specimens.