The Effect on Using Cells versus Spores of Bacillus Sphaericus on the Healing Performance of Self-Healing Mortar

Abstract

Bacteria-based self-healing concrete has become an effective approach to mitigate microcracks in the concrete structure. However, there are still doubts about when to use vegetative cells or spores of Bacillus sphaericus as a healing agent. Thus, this research aims to give recommendations regarding this choice. Spores and cells were encapsulated into expanded clay aggregate to protect them from the harsh environment of fresh mortar. The viability of cells and spores after encapsulation was investigated. The 28- and 90-day mortar compressive strength was analysed. The healing performance of the resulting mortar samples that were cracked at the age of 28 and 90 days has also been observed. The results show that both cells and spores were still active after encapsulation. The yeast extract added to mortar containing spores decreased the compressive strength of the mortar compared to the reference sample. From the healing performance result, it seems that the spores are more suitable for mitigating microcracks in aged mortar, while cells are more suitable for mitigating early-age cracks in the mortar.