# Bio-Influenced Self-Healing Mechanism in Concrete and Its Testing: A Review
## 3 Results and Discussion
### Type of Test: Destructive and Non-Destructive
[65] discovered that self-healing can be attained by coating expanded perlite, as a partial replacement to fine aggregates, by 20% and calcium acetate was given to obtain a suitable ratio of the spores. [PERSON] et al. [59], used the Bacillus subtilis and immobilized the bacteria in the limestone powder (LSP) before mixing it with other concrete components, and found that the compressive strength was improved by 5.75% at 14 days. It was concluded that limestone powder (LSP) can be considered as a protective material for Bacillus subtilis which can ensure the long term viability of the bacteria in an alkaline environment. [PERSON] et al. [66] used a porous ceramics particles as microbial carrier and found out that the regain ratio of compressive strength increased over 20% with a healing ratio of cracks by 86%. [PERSON] and [PERSON] [67] showed that low-alkali cementitious material made by calcium sulphoaluminate cement with 20% silica fume can be used as a protective carrier for ureolysis-based bacteria and the regain ratio of compressive strength and water tightness increased by 130% and 50% compared with the plain mortar. [PERSON] et al. [68] examined the effect of the two bacteria, such as Sporosarcina ureae and Sporosarcina pasteurii to the compressive strength of cementitious composites. They found that the long term performance of the cementitious composites with Sporosarcina pasteurii was 8% higher than the Sporosarcina ureae. [PERSON] (2018) showed that the specimens incorporated with expanded perlite-immobilized bacteria exhibited the most efficient crack-healing after each healing time. It can be concluded that protective carrier has a specific role for the growth and survivability of bacteria inside the concrete matrix. Additionally, it can be observed that different protective materials have varying efficiencies in healing the cracks in concrete. The protective carrier can be used only for a short-term period but others can also be used for almost a year, as long as there is a nutrient needed by the bacteria to survive. Moreover, the results of the researchers pave the way to develop a self-healing and self-curing concrete with an extended service life, because of the nutrients present within the protective material. Encapsulation is another way of delivering the healing material into the cementitious composites. For this method, the primary requirement is to have enough strength and resistance as the mixing process takes place and against the internal forces present in the cementitious composites. The healing agent within the capsule should have a low viscosity in order to be released efficiently inside the crack ([PERSON], 2018). The healing performance of the encapsulation method is also a function of the following: surface texture, thickness of the shell and capsule diameter ([PERSON] et al., 2018). [PERSON] et al. (2018) studied the potential of use of encapsulated bacteria in a bead for marine application. They found that the bead showed a crack healing potential because of its capability to swell and induce bacterial precipitation. [PERSON] et al. (2018) showed that, compared with unbroken microcapsules, higher calcium precipitation activity (CPA) was achieved by breaking the microcapsule to release the bacterium, suggesting good protection for the encapsulated spores. [PERSON] et al. (2018) investigated the self-healing efficiency of encapsulate bacterial with different curing environments. They found that wet/dry cycles was the best curing method in mortar specimens with encapsulated bacteria and the presence of water was an important component for the self-healing process in cementitious composites. [PERSON] et al. (2018) presented that those samples containing alginate beads with bacteria had superior self-healing efficiencies than the control samples without alginate beads. [PERSON] et al. (2018) evaluated the self-healing potential of encapsulated bacteria in hydrogels which are used as bacterial carriers and water reservoirs for the uninterrupted healing process in cracks.