Incubation temperature effect on bacterial self-healing capabilities of cementitious mortar cracks: Deep learning based crack sealing rates evaluations.

Successful implementation of microbial self-healing cementitious materials requires the provision of a suitable incubation environment, which activates the bacteria to produce calcium carbonate sealing the cracks. Affecting microbial mineralization, incubation temperature determines the self-healing efficiency of microbial cement which limits its widespread application. To investigate the effect of incubation temperature on the self-healing abilities, laboratory experiments were conducted on polyvinyl alcohol (PVA) fiber reinforced cement mortar impregnated with Sporosarcina pasteurii. The mortar specimens were initially cracked by three point bending to generate 0.4 mm width cracks at the bottom and then sprayed the calcium chloride and urea solution periodically for 2 days and immersed in the water for 28 days at ambient temperatures of 20 ∘ C, 25 ∘ C, 30 ∘ C, and 35 ∘ C. The cracks were inspected regularly which were further analyzed via deep learning to evaluate the crack healing ratio and sealing rate. The cracks failed to completely repair at 20 ∘ C, while cracks at 30 ∘ C requires only 4 days to seal. The crack healing rate accelerated with increasing temperature from 20 ∘ C to 30 ∘ C, exhibiting a trend of initial increase followed by decrease across all temperatures. The bacterial-repaired mortar specimens exhibited a recovery in flexural strength, with a regained strength ratio of approximately 7.184 % at 30 ∘ C. Supported by Scanning Electron Microscope (SEM) and X-ray diffractometer (XRD), the results revealed that the higher temperature actives larger particle CaCO 3 with mainly vaterite and some calcite morphology. The interaction mechanism of temperature effect on bacterial self-healing capabilities was revealed by the comprehensive assessment between the microbial activity, crack width evolution and mechanical performance. This paper may shed some light on the engineering application of microbial cementitious material resilient infrastructures with desirable healing efficiency under real ambient temperatures during service. • The optimal incubation temperature is 30 °C taking 3 days for complete healing. • Crack width sealing rates displayed an initial increase followed by a decrease. • Wider cracks exhibited faster sealing rates due to more friendly ecological niches. [ABSTRACT FROM AUTHOR]