Production of Self-Healing Concrete by <i>Bacillus subtilis</i> Spores Immobilized on Sand Using Gum Arabic as an Adhesion Material: Proof of Concept

Abstract

Production of self-healing concrete involves the immobilization of a bacterium and calcium-based bacterial nutrient on a carrier material before being added to the concrete mixture. The objective of this paper was to test the potential of using gum arabic of Acacia senegal (Hashab) to immobilize Bacillus subtilis on coarse sand for production of self-healing concrete. Dried bacterial spores, gum arabic powder, and calcium lactate were mixed thoroughly in a 1-L flask. The mixture was wetted by adding tap water gradually until spore-coated sand pellets were formed and then left to dry. Three mortar mixtures with different concentrations (2.5%, 5%, and 10%) of spore-coated sand pellets were then prepared and left for 24&nbsp;h at room temperature. Of these, 12 mortar prisms were cast. Prisms were subjected to three-point load testing under a controlled and careful rate of loading until visible cracks appeared on the surface of the prism. Crack healing was then monitored for 14&nbsp;days using stereoscopy and a digital image camera under three curing regimes, namely wet, wet–dry cycles, and polyethylene sheets. Results showed that the efficiency of healing increased with an increase in the percentage of spore-coated sand pellets in the mix without causing a significant impact on prisms strength for mixes with 2.5% and 5% of pellets. The results give an evidence to use gum arabic as a novel, abundant, and sustainable material for immobilization of bacteria on sand surface to produce self-healing concrete.