Synergistic self-healing effect of fiber and bio-capsule on mortar cracks

Self-healing is an effective technique to prolong the service life of cement-based materials. In this study, the porous volcanic rock was used as the carrier to prepare the bio-capsules, and the waterproofness and storage stability of the bio-capsules were studied by weighing method. The influence of different dosage of bio-capsules on mortar strength was studied by three-point bending and uniaxial compression. Then, PVA and sisal fibers containing a large amount of –OH and bio-capsules were placed in cement mortar, and the self-healing effect of mortar cracks, as well as the synergistic heal mechanisms of both fibers and bio-capsules on the formation of cracks were studied by using water permeability, gas permeability, crack healing width and healing area. The results show that the bio-capsules have good waterproofness and storage stability. When the content of bio-capsules was 12%, the compressive and flexural strengths of the mortar could be increased by 32.01% and 14.39%, respectively. The water permeability of the mortar was reduced by two orders of magnitude (from 1.63 × 10⁻⁴to 7.55 × 10⁻⁶cm s⁻¹) after crack healing. At the end of testing (28 days), most cracks with widths of 0–600 μm were completely healed, leading to an area healing rate of 100% for sample C–BH. The presence of large amounts of –OH in the fiber could keep the crack area in the water environment, as well as accelerate the rate of bacterial mineralization and the fiber as the nucleation site can make the mineralization product form three-dimensional networking structures in the cracked areas.