Application of bacillus subtilis as a self-healing agent for alkali-activated slag (AAS)

Recently, new techniques of smart innovative technology have been introduced to overcome one of the most critical challenges, the shrinkage-cracking behavior of the alkali-activated slag (AAS) systems. This new technology, named “self-healing” in specific bacterial mechanisms, was introduced as an alternative solution rather than other additives such as fibers, chemical additives, etc. Despite the abundant research on the bacteria-based self-healing of Ordinary Portland concrete (OPC), limited studies were devoted to its application in the AAS composite. This study examined three cell concentrations (10 3 , 10 5 , and 10 7 cells/ml) of Bacillus subtilis in AAS and their influence on mechanical characteristics, durability, and cracking behavior. Four mixes of AAS were poured to attain the three-cell concentrations of Bacillus subtilis, including the control mix (no Bacteria). Compressive and flexural strengths, water absorption, and chloride permeability were examined. Further X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray, was explored. The findings revealed remarkable crack healing development when applying the bacteria-based technique to AAS composites. The viability of Bacillus Subtilis to decompose urea in the AAS harsh alkaline conditions was significantly proven. Further, an enhancement in the strength of the AAS composites reaching up to 50 % was reported. The observed healing crack widths reached 350 µm. • The critical challenge in Alkali-activated slag (AAS) systems is the shrinkage-cracking behavior. • Three cell concentrations of 10 3 , 10 5 , and 10 7 cells/ml concentration of Bacillus subtilis in AAS were explored. • The results revealed remarkable crack healing development when applying the bacteria-based technique. • The Bacillus Subtilis proved to decompose urea relevantly in the AAS harsh alkaline conditions. • The AAS composites enhanced the strength reaching up to 50 % and healing crack widths up to 350 µm.