Evaluation of encapsulated Bacillus subtilis bio-mortars for use under acidic conditions

Abstract This research aimed to examine the effects of an acidic environment on the mechanical properties and durability of bio-mortar (BM) encapsulated with Bacillus subtilis bacteria, in comparison to normal mortar (NM). The results at 28 days indicated that both 3% and 6% HCl significantly increased the compressive strength of the BM by 25% and 50%, respectively, compared with that of the NM. However, when 11% HCl was introduced, the compressive strength of the BM decreased to 50% lower than that of the NM. Furthermore, the water absorption rate of the BM was 33% lower than that of the NM. The mass loss for both 3% and 6% HCl was comparable, whereas at 11% HCl, BM experienced a mass loss that was 68% greater than that of NM. These findings suggest that with 3% and 6% HCl, the microbially induced calcium carbonate precipitation (MICP) process effectively generated CaCO3, which filled the pores and enhanced the structural integrity of the BM, leading to improved compressive strength and durability. Conversely, at 11% HCl, the MICP benefits in BM were diminished due to adverse environmental conditions that negatively affected the bacterial cells, highlighting the limitations of the HCl concentration for optimizing MICP efficiency in mortar.