## 11 Self-Healing Cemertitious Materials Obtained Using Encapsulation Technology
The production costs of the cultures, such as the axenic spores of bacteria, are substantial, which is the major limitation of this approach, despite its promising results regarding the effective self-healing. The microbial community named cyclic enriched ureolytic powder (CERUP) was aimed to address this issue by offering a cheaper bioagent alternative [141]. Reduced production costs were achieved by making the specimen in non-sterile conditions while using a sub-stream of a vegetable plant as the microbial source. During a period of 4 weeks, the capacity to plug-in the cracks and autonomous healing was assessed via the incorporation of non-autoclaved and autoclaved CERUP. The width of the largest crack that was repaired by the autoclaved CERUP was below 0.37 mm, while the width of the largest crack healed by the non-autoclaved CERUP was 0.45 mm. A more accurate representation of the autonomous healing capacity of the non-sterile agent is essential, wherein additional evaluations regarding the durability and strength are necessary to ascertain its proficiencies besides significantly lower costs and deficiencies. Autonomous healing that occurs during the entire lifespan of a concrete structure indicates the substantial effectiveness of the self-healing technique in filling the cracks indefinitely. Thus, a critical aspect is the survivability of the bacteria wherein multiple obstacles hindering the survivability of bacteria can appear upon the direct addition of bio-agents to the concrete. Relatively young specimens were found to be the only kind that achieved efficient autonomous healing, as the unprotected spores had a lifespan of two months [142]. The hydration of cement, mixing of concrete and alkalinity of the cement matrix were the main factors that contributed to the lifespan shortening. Residing in a highly alkaline environment for a prolonged period of time could significantly reduce the activity of spores. Additionally, the impact of aggregates, along with the mixing force, could lead to spores being damaged in the mixing stage. Despite the average size of bacteria cells being above 0.5 mm, a reduction in the pore size of the matrix and porosity was triggered by the hydration of cement up to 0.5 mm [25]. It was concluded that, at an advanced stage, a concrete structure can experience a significant or even absolute decrease in the germination of cells due to the shrinkage of pores. The bacteria-induced carbonate precipitation and concrete properties were not impacted when the bacteria were encapsulated, thereby working around the mentioned limitation. The developed techniques to safeguard the bacterial strains include the hydrogels encapsulation, diatomaceous earth, melamine-based microcapsules, polyurethane and silica gel in glass tubes, and expanded clay aggregate encapsulation [138; 143]. Bacillus Sphaericus spores were encapsulated via the melamine-based microcapsules [25]. The nutrients, such as urea and yeast extract, were mixed along with the mineral precursor calcium nitrate in the concrete to obtain efficient autonomous healing of cracks. The ratio of the initial and healed crack area was used to evaluate the healing efficacy of the bacteria. The healing ratio could not surpass 50% in the specimens with no spores, while those with the spores' encapsulation achieved a proportion in the range of 48 to 80%. When water functioned as a medium during the wet and dry cycle of the samples, the highest decrease in crack area occurred. It was argued that the manual intervention may be the main drawback under typical circumstances when performing the wet cycle, as the procedure takes around 16 h. A crack of maximum width of 1000 \(\upmu\)m was repaired using this procedure. While a capsule dosage of 5% led to less deviation, the most effective dosage for the crack healing and restoration of water permeability, was 3%. A dosage of 5% was not considered superior, as a greater decrease in the concrete strength was observed for said dosage compared to the former.