Self-healing efficiency of cement-based materials containing extruded cementitious hollow tubes filled with bacterial healing agent

In this work, the use of the ureolytic bacterial strain Bacillus sphaericus for developing a self-healing cementitious material was investigated. These bacteria are able to precipitate CaCO3, thus the precipitated crystals can fill the cracks that can reduce the service life of concrete as a function of their size and distribution. These crystals are compatible with the concrete matrix and are environmentally-friendly. However, bacterial activity decreases in the high-pH environment inside concrete and bacterial cells might be destroyed during the hydration process if they are not adequately protected. To provide protection against the alkaline environment and preserve the bacterial vitality, extruded cementitious hollow tubes were used in this study as containing/releasing devices. Self-healing mortar specimens were produced by incorporating one tube filled with the bacterial suspension and silica sol coupled to another filled with the deposition medium. The self-healing efficiency was assessed in terms of capability to autonomously seal some intentionally-introduced cracks. It was quantified though the reduction in water flow/uptake during permeability/absorption tests. Encouraging results were achieved, suggesting that the proposed self-healing system can be effective in prolonging the material functionality, since the permeability reduction leads to an increased protection against the ingress of water-based deleterious substances.