Expanded Clay as Bacteria Cells Protector in Manufacturing Self-healing Mortar: The Possibility of Adding Less Nutrient to Maintain the Mechanical Properties of Mortar

Bacteria-based self-healing is a promising method due to its effectiveness to completely heal the crack. Expanded clay was chosen as a bacteria protector as it can retain a high amount of bacteria liquid in its pores and it is compatible with the mortar matrix. Most researchers employed bacteria in the form of spores to produce self-healing concrete due to its survivability in a harsh environment. However, to activate the spores, yeast extract, which has a negative effect on mortar strength, needs to be added. In this research, Bacillus sphaericus (BS) vegetative cells were used as a healing agent to determine whether these cells survive in the mortar and could precipitate CaCO₃. The variation in the amount of yeast extract as a bacteria nutrition was also investigated. The mechanical properties of fresh and hardened mortar, such as flow, compressive strength, and bulk density, were determined. The healing efficiency was observed through crack closure observation. In the end, the morphology of CaCO₃ precipitation was observed under a scanning electron microscope (SEM). The result shows that it is possible to remove yeast from the mixture when producing self-healing concrete with vegetative cells as a healing agent. The resulting mortar’s mechanical properties are similar to the reference, and the healing efficiency was still acceptable.